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==PFAS Transport and Fate==
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==Sediment Porewater Dialysis Passive Samplers for Inorganics (Peepers)==  
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The transport and fate of Per- and Polyfluoroalkyl Substances (PFAS) in the environment is controlled by the nature of the PFAS source, characteristics of the individual PFAS, and environmental conditions where the PFAS are present.  Transport, partitioning, and transformation are the primary processes controlling PFAS fate in the environment. PFAS compounds can also be taken up by both plants and animals, and in some cases, bioaccumulate through the food chain.
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Sediment porewater dialysis passive samplers, also known as “peepers,” are sampling devices that allow the measurement of dissolved inorganic ions in the porewater of a saturated sediment. Peepers function by allowing freely-dissolved ions in sediment porewater to diffuse across a micro-porous membrane towards water contained in an isolated compartment that has been inserted into sediment. Once retrieved after a deployment period, the resulting sample obtained can provide concentrations of freely-dissolved inorganic constituents in sediment, which provides measurements that can be used for understanding contaminant fate and risk. Peepers can also be used in the same manner in surface water, although this article is focused on the use of peepers in sediment.  
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Understanding PFAS transport and fate is necessary for evaluating the potential risk from a PFAS release and for predictions about PFAS occurrence, migration, and persistence, and about the potential vectors for exposure. This knowledge is important for site characterization, identification of potential sources of PFAS to the site, development of an appropriate conceptual site model (CSM), and selection and predicted performance of remediation strategies.  
 
  
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
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'''Related Article(s): '''
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'''Related Article(s):'''
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
 
  
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'''Contributor(s): '''
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*[[Contaminated Sediments - Introduction]]
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Dr. Hunter Anderson and Dr. Mark L. Brusseau
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*[[Contaminated Sediment Risk Assessment]]
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
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*[[Passive Sampling of Munitions Constituents]]
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*[[Sediment Capping]]
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*[[Mercury in Sediments]]
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*[[Passive Sampling of Sediments]]
  
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'''Key Resource(s): '''
 
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*[https://pfas-1.itrcweb.org/wp-content/uploads/2020/04/ITRC_PFAS_TechReg_April2020.pdf  Per- and Polyfluoroalkyl Substances (PFAS), PFAS-1. ITRC 2020.]<ref name="ITRC2020">Interstate Technology and Regulatory Council (ITRC), 2020. Technical/Regulatory Guidance: Per- and Polyfluoroalkyl Substances (PFAS), PFAS-1. ITRC, PFAS Team, Washington DC. [https://pfas-1.itrcweb.org/wp-content/uploads/2020/04/ITRC_PFAS_TechReg_April2020.pdf  Free Download from ITRC].&nbsp;&nbsp; [[Media: ITRC_PFAS-1.pdf | Report.pdf]]</ref>
 
  
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*[[Media: Brusseau2018manuscript.pdf | Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Brusseau 2018 (manuscript).]]<ref name="Brusseau2018">Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of the Total Environment, 613-614, pp. 176-185. [https://doi.org/10.1016/j.scitotenv.2017.09.065 DOI: 10.1016/j.scitotenv.2017.09.065]&nbsp;&nbsp; [[Media: Brusseau2018manuscript.pdf | Author’s Manuscript]]</ref>
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'''Contributor(s):'''
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*Florent Risacher, M.Sc.
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*Jason Conder, Ph.D.
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'''Key Resource(s):'''
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*A review of peeper passive sampling approaches to measure the availability of inorganics in sediment porewater<ref>Risacher, F.F., Schneider, H., Drygiannaki, I., Conder, J., Pautler, B.G., and Jackson, A.W., 2023. A Review of Peeper Passive Sampling Approaches to Measure the Availability of Inorganics in Sediment Porewater. Environmental Pollution, 328, Article 121581. [https://doi.org/10.1016/j.envpol.2023.121581 doi: 10.1016/j.envpol.2023.121581]&nbsp;&nbsp;[[Media: RisacherEtAl2023a.pdf | Open Access Manuscript]]</ref>
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*Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern<ref name="RisacherEtAl2023">Risacher, F.F., Nichols, E., Schneider, H., Lawrence, M., Conder, J., Sweett, A., Pautler, B.G., Jackson, W.A., Rosen, G., 2023b. Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern, ESTCP ER20-5261. [https://serdp-estcp.mil/projects/details/db871313-fbc0-4432-b536-40c64af3627f Project Website]&nbsp;&nbsp;[[Media: ER20-5261BPUG.pdf | Report.pdf]]</ref>
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*[https://serdp-estcp.mil/projects/details/db871313-fbc0-4432-b536-40c64af3627f/er20-5261-project-overview Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern, ESTCP Project ER20-5261]
  
 
==Introduction==
 
==Introduction==
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The transport and fate of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] is a rapidly evolving field of science, with many questions that are not yet resolved.  Much of the currently available information is based on a few well-studied PFAS compounds. However, there is a large number and variety of PFAS with a wide range of physical and chemical characteristics that affect their behavior in the environment. The transport and fate of some PFAS could differ significantly from the compounds studied to date. Nevertheless, information about the behavior of some PFAS in the environment can be ascertained from the results of currently available research.  
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Biologically available inorganic constituents associated with sediment toxicity can be quantified by measuring the freely-dissolved fraction of contaminants in the porewater<ref>Conder, J.M., Fuchsman, P.C., Grover, M.M., Magar, V.S., Henning, M.H., 2015. Critical review of mercury SQVs for the protection of benthic invertebrates. Environmental Toxicology and Chemistry, 34(1), pp. 6-21. [https://doi.org/10.1002/etc.2769 doi: 10.1002/etc.2769]&nbsp;&nbsp; [[Media: ConderEtAl2015.pdf | Open Access Article]]</ref><ref name="ClevelandEtAl2017">Cleveland, D., Brumbaugh, W.G., MacDonald, D.D., 2017. A comparison of four porewater sampling methods for metal mixtures and dissolved organic carbon and the implications for sediment toxicity evaluations. Environmental Toxicology and Chemistry, 36(11), pp. 2906-2915. [https://doi.org/10.1002/etc.3884 doi: 10.1002/etc.3884]</ref>. Classical sediment porewater analysis usually consists of collecting large volumes of bulk sediments which are then mechanically squeezed or centrifuged to produce a supernatant, or suction of porewater from intact sediment, followed by filtration and collection<ref name="GruzalskiEtAl2016">Gruzalski, J.G., Markwiese, J.T., Carriker, N.E., Rogers, W.J., Vitale, R.J., Thal, D.I., 2016. Pore Water Collection, Analysis and Evolution: The Need for Standardization. In: Reviews of Environmental Contamination and Toxicology, Vol. 237, pp. 37–51. Springer. [https://doi.org/10.1007/978-3-319-23573-8_2 doi: 10.1007/978-3-319-23573-8_2]</ref>. The extraction and measurement processes present challenges due to the heterogeneity of sediments, physical disturbance, high reactivity of some complexes, and interaction between the solid and dissolved phases, which can impact the measured concentration of dissolved inorganics<ref>Peijnenburg, W.J.G.M., Teasdale, P.R., Reible, D., Mondon, J., Bennett, W.W., Campbell, P.G.C., 2014. Passive Sampling Methods for Contaminated Sediments: State of the Science for Metals. Integrated Environmental Assessment and Management, 10(2), pp. 179–196. [https://doi.org/10.1002/ieam.1502 doi: 10.1002/ieam.1502]&nbsp;&nbsp; [[Media: PeijnenburgEtAl2014.pdf | Open Access Article]]</ref>. For example, sampling disturbance can affect redox conditions<ref name="TeasdaleEtAl1995">Teasdale, P.R., Batley, G.E., Apte, S.C., Webster, I.T., 1995. Pore water sampling with sediment peepers. Trends in Analytical Chemistry, 14(6), pp. 250–256. [https://doi.org/10.1016/0165-9936(95)91617-2 doi: 10.1016/0165-9936(95)91617-2]</ref><ref>Schroeder, H., Duester, L., Fabricius, A.L., Ecker, D., Breitung, V., Ternes, T.A., 2020. Sediment water (interface) mobility of metal(loid)s and nutrients under undisturbed conditions and during resuspension. Journal of Hazardous Materials, 394, Article 122543. [https://doi.org/10.1016/j.jhazmat.2020.122543 doi: 10.1016/j.jhazmat.2020.122543]&nbsp;&nbsp; [[Media: SchroederEtAl2020.pdf | Open Access Article]]</ref>, which can lead to under or over representation of inorganic chemical concentrations relative to the true dissolved phase concentration in the sediment porewater<ref>Wise, D.E., 2009. Sampling techniques for sediment pore water in evaluation of reactive capping efficacy. Master of Science Thesis. University of New Hampshire Scholars’ Repository. 178 pages. [https://scholars.unh.edu/thesis/502 Website]&nbsp;&nbsp; [[Media: Wise2009.pdf | Report.pdf]]</ref><ref name="GruzalskiEtAl2016"/>.
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To address the complications with mechanical porewater sampling, passive sampling approaches for inorganics have been developed to provide a method that has a low impact on the surrounding geochemistry of sediments and sediment porewater, thus enabling more precise measurements of inorganics<ref name="ClevelandEtAl2017"/>. Sediment porewater dialysis passive samplers, also known as “peepers,” were developed more than 45 years ago<ref name="Hesslein1976">Hesslein, R.H., 1976. An in situ sampler for close interval pore water studies. Limnology and Oceanography, 21(6), pp. 912-914. [https://doi.org/10.4319/lo.1976.21.6.0912 doi: 10.4319/lo.1976.21.6.0912]&nbsp;&nbsp; [[Media: Hesslein1976.pdf | Open Access Article]]</ref> and refinements to the method such as the use of reverse tracers have been made, improving the acceptance of the technology as decision making tool.
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==Peeper Designs==
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[[File:RisacherFig1.png|thumb|300px|Figure 1. Conceptual illustration of peeper construction showing (top, left to right) the peeper cap (optional), peeper membrane and peeper chamber, and (bottom) an assembled peeper containing peeper water]]
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[[File:RisacherFig2.png | thumb |400px| Figure 2. Example of Hesslein<ref name="Hesslein1976"/> general peeper design (42 peeper chambers), from [https://www.usgs.gov/media/images/peeper-samplers USGS]]]
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[[File:RisacherFig3.png | thumb |400px| Figure 3. Peeper deployment structure to allow the measurement of metal availability in different sediment layers using five single-chamber peepers (Photo: Geosyntec Consultants)]]
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Peepers (Figure 1) are inert containers with a small volume (typically 1-100 mL) of purified water (“peeper water”) capped with a semi-permeable membrane. Peepers can be manufactured in a wide variety of formats (Figure 2, Figure 3) and deployed in in various ways.
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Two designs are commonly used for peepers. Frequently, the designs are close adaptations of the original multi-chamber Hesslein design<ref name="Hesslein1976"/> (Figure 2), which consists of an acrylic sampler body with multiple sample chambers machined into it. Peeper water inside the chambers is separated from the outside environment by a semi-permeable membrane, which is held in place by a top plate fixed to the sampler body using bolts or screws. An alternative design consists of single-chamber peepers constructed using a single sample vial with a membrane secured over the mouth of the vial, as shown in Figure 3, and applied in Teasdale ''et al.''<ref name="TeasdaleEtAl1995"/>, Serbst ''et al.''<ref>Serbst, J.R., Burgess, R.M., Kuhn, A., Edwards, P.A., Cantwell, M.G., Pelletier, M.C.,  Berry, W.J., 2003. Precision of dialysis (peeper) sampling of cadmium in marine sediment interstitial water. Archives of Environmental Contamination and Toxicology, 45(3), pp. 297–305. [https://doi.org/10.1007/s00244-003-0114-5 doi: 10.1007/s00244-003-0114-5]</ref>, Thomas and Arthur<ref name="ThomasArthur2010">Thomas, B., Arthur, M.A., 2010. Correcting porewater concentration measurements from peepers: Application of a reverse tracer. Limnology and Oceanography: Methods, 8(8), pp. 403–413. [https://doi.org/10.4319/lom.2010.8.403 doi: 10.4319/lom.2010.8.403]&nbsp;&nbsp; [[Media: ThomasArthur2010.pdf | Open Access Article]]</ref>, Passeport ''et al.''<ref>Passeport, E., Landis, R., Lacrampe-Couloume, G., Lutz, E.J., Erin Mack, E., West, K., Morgan, S., Lollar, B.S., 2016. Sediment Monitored Natural Recovery Evidenced by Compound Specific Isotope Analysis and High-Resolution Pore Water Sampling. Environmental Science and Technology, 50(22), pp. 12197–12204. [https://doi.org/10.1021/acs.est.6b02961 doi: 10.1021/acs.est.6b02961]</ref>, and Risacher ''et al.''<ref name="RisacherEtAl2023"/>. The vial is filled with deionized water, and the membrane is held in place using the vial cap or an o-ring. Individual vials are either directly inserted into sediment or are incorporated into a support structure to allow multiple single-chamber peepers to be deployed at once over a given depth profile (Figure 3).
  
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PFAS transport and fate in the environment is controlled by the nature of the PFAS source, characteristics of the individual PFAS, and environmental conditions where the PFAS are present.  Perfluoroalkyl acids (PFAAs) (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] for nomenclature) are strong acids and are anionic in the environmentally-relevant pH range.  They are extremely persistent in the environment and do not degrade or transform under typical environmental conditions. Polyfluoroalkyl substances (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] for nomenclature) include compounds that have the potential to degrade to PFAAs. These compounds are commonly referred to as PFAA precursors or just ‘precursors’.  Because some polyfluoroalkyl substances can degrade into PFAA via biotic or abiotic degradation pathways, PFAAs are sometimes referred to as “terminal PFAS” or “terminal degradation products”.
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==Peepers Preparation, Deployment and Retrieval==
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The most important molecular properties controlling PFAA transport are the carbon chain length and functional moieties of the headgroups (e.g., sulfonate, carboxylate). The molecular properties of PFAA precursors are more varied, with different carbon chain lengths, headgroups and ionic states<ref name="Buck2011">Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., de Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A., and van Leeuwen, S.P.J., 2011. Perfluoroalkyl and Polyfluoroalkyl Substances in the Environment: Terminology, Classification, and Origins. Integrated Environmental Assessment and Management, 7(4): pp. 513-541. [ https://doi.org/10.1002/ieam.258  DOI: 10.1002/ieam.258]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.258 Open Access Article]</ref><ref name="Wang2017">Wang, Z., DeWitt, J.C., Higgins, C.P., and Cousins, I.T., 2017. A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)? Environmental Science and Technology, 51(5), pp. 2508-2518. American Chemical Society.  [https://doi.org/10.1021/acs.est.6b04806 DOI: 10.1021/acs.est.6b04806]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/acs.est.6b04806 Free Download from ACS]</ref> (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]]). All of these properties can influence transport and fate of PFAA precursors in the environment.  
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[[File:RisacherFig4.png | thumb |300px| Figure 4: Conceptual illustration of peeper passive sampling in a sediment matrix, showing peeper immediately after deployment (top) and after equilibration between the porewater and peeper chamber water (bottom)]]
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Peepers are often prepared in laboratories but are also commercially available in a variety of designs from several suppliers. Peepers are prepared by first cleaning all materials to remove even trace levels of metals before assembly. The water contained inside the peeper is sometimes deoxygenated, and in some cases the peeper is maintained in a deoxygenated atmosphere until deployment<ref>Carignan, R., St‐Pierre, S., Gachter, R., 1994. Use of diffusion samplers in oligotrophic lake sediments: Effects of free oxygen in sampler material. Limnology and Oceanography, 39(2), pp. 468-474. [https://doi.org/10.4319/lo.1994.39.2.0468 doi: 10.4319/lo.1994.39.2.0468]&nbsp;&nbsp; [[Media: CarignanEtAl1994.pdf | Open Access Article]]</ref>. However, recent studies<ref name="RisacherEtAl2023"/> have shown that deoxygenation prior to deployment does not significantly impact sampling results due to oxygen rapidly diffusing out of the peeper during deployment. Once assembled, peepers are usually shipped in a protective bag inside a hard-case cooler for protection.
  
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Important environmental characteristics include the nature of the source (mode of input into the environment), the length of time that the source was active, and the magnitude of the input, as well as precipitation and infiltration rates, depth to groundwater, surface water and groundwater flow rates and interactions, prevailing atmospheric conditions, the properties of the porous-media (e.g., soil and sediment) and aqueous solution, microbiological factors, and the presence of additional fluid phases such as air and non-aqueous phase liquids [[Wikipedia: Non-aqueous phase liquid | (NAPLs)]] in the vadose zone and water-saturated source.  In the subsurface, soil characteristics (texture, organic carbon content, clay mineralogy, metal-oxide content, solid surface area, surface charge, and exchange capacity) and solution characteristics (pH, redox potential, major ion chemistry, and co-contaminants) can influence PFAS transport and fate.  
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Peepers are deployed by insertion into sediment for a period of a few days to a few weeks. Insertion into the sediment can be achieved by wading to the location when the water depth is shallow, by using push poles for deeper deployments<ref name="RisacherEtAl2023"/>, or by professional divers for the deepest sites. If divers are used, an appropriate boat or ship will be required to accommodate the diver and their equipment. Whichever method is used, peepers should be attached to an anchor or a small buoy to facilitate retrieval at the end of the deployment period.
  
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==PFAS Transport and Fate Processes==
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During deployment, passive sampling is achieved via diffusion of inorganics through the peeper’s semi-permeable membrane, as the enclosed volume of peeper water equilibrates with the surrounding sediment porewater (Figure 4). It is assumed that the peeper insertion does not greatly alter geochemical conditions that affect freely-dissolved inorganics. Additionally, it is assumed that the peeper water equilibrates with freely-dissolved inorganics in sediment in such a way that the concentration of inorganics in the peeper water would be equal to that of the concentration of inorganics in the sediment porewater.  
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[[File:AndersonBrusseau1w2Fig1.png | thumb | 600px | Figure 1. Illustration of PFAS partitioning and transformation processes. Source: D. Adamson, GSI, used with permission.]]
 
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Transport, partitioning, and transformation are the primary processes controlling PFAS fate in the environment (Figure 1). PFAS compounds can also be taken up by both plants and animals, and in some cases, bioaccumulate through the food chain. However, PFAS uptake and bioaccumulation is not discussed in this article (see “Environmental Concern” section of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]).
 
  
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* '''Transport:''' PFAS can be transported substantial distances in the atmosphere<ref name="Ahrens2012">Ahrens, L., Harner, T., Shoeib, M., Lane, D.A. and Murphy, J.G., 2012. Improved Characterization of Gas–Particle Partitioning for Per- and Polyfluoroalkyl Substances in the Atmosphere Using Annular Diffusion Denuder Samplers. Environmental Science and Technology, 46(13), pp. 7199-7206. [https://doi.org/10.1021/es300898s DOI: 10.1021/es300898s]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Tom_Harner/publication/225046057_Improved_Characterization_of_Gas-Particle_Partitioning_for_Per-_and_Polyfluoroalkyl_Substances_in_the_Atmosphere_Using_Annular_Diffusion_Denuder_Samplers/links/5cc730c4299bf12097893fdc/Improved-Characterization-of-Gas-Particle-Partitioning-for-Per-and-Polyfluoroalkyl-Substances-in-the-Atmosphere-Using-Annular-Diffusion-Denuder-Samplers.pdf ResearchGate].</ref>, surface water<ref name="Taniyasu2013">Taniyasu, S., Yamashita, N., Moon, H.B., Kwok, K.Y., Lam, P.K., Horii, Y., Petrick, G. and Kannan, K., 2013.  Does wet precipitation represent local and regional atmospheric transportation by perfluorinated alkyl substances? Environment International, 55, pp. 25-32. [https://doi.org/10.1016/j.envint.2013.02.005 DOI: 10.1016/j.envint.2013.02.005]</ref>, soil<ref name="Braunig2017">Bräunig, J., Baduel, C., Heffernan, A., Rotander, A., Donaldson, E. and Mueller, J.F., 2017. Fate and redistribution of perfluoroalkyl acids through AFFF-impacted groundwater. Science of the Total Environment, 596, pp. 360-368. [https://doi.org/10.1016/j.scitotenv.2017.04.095 DOI: 10.1016/j.scitotenv.2017.04.095]</ref>, and groundwater<ref name="Weber2017">Weber, A.K., Barber, L.B., LeBlanc, D.R., Sunderland, E.M. and Vecitis, C.D., 2017. Geochemical and Hydrologic Factors Controlling Subsurface Transport of Poly- and Perfluoroalkyl Substances, Cape Cod, Massachusetts. Environmental Science and Technology, 51(8), pp. 4269-4279. [https://doi.org/10.1021/acs.est.6b05573 DOI: 10.1021/acs.est.6b05573]&nbsp;&nbsp; [https://bgc.seas.harvard.edu/assets/weber2017_final.pdf Free Download]</ref>. The primary mechanisms controlling PFAS transport are [[Wikipedia:Advection | advection]] and [[Wikipedia:Dispersive_mass_transfer | dispersion]], similar to other dissolved compounds. For additional information on transport in groundwater, see [[Advection and Groundwater Flow]] and [[Dispersion and Diffusion]].
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After retrieval, the peepers are brought to the surface and usually preserved until they can be processed. This can be achieved by storing the peepers inside a sealable, airtight bag with either inert gas or oxygen absorbing packets<ref name="RisacherEtAl2023"/>. The peeper water can then be processed by quickly pipetting it into an appropriate sample bottle which usually contains a preservative (e.g., nitric acid for metals). This step is generally conducted in the field. Samples are stored on ice to maintain a temperature of less than 4°C and shipped to an analytical laboratory. The samples are then analyzed for inorganics by standard methods (i.e., USEPA SW-846). The results obtained from the analytical laboratory are then used directly or assessed using the equations below if a reverse tracer is used because deployment time is insufficient for all analytes to reach equilibrium.
  
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* '''Partitioning:''' Partitioning of PFAS between the mobile and immobile phases is one of the most important processes controlling the rate of migration in the environment. The primary mobile phases are typically air and water. Relatively immobile phases include stream sediments, soils, aquifer material, NAPLs, and interfaces between different phases (air-water, NAPL-water).  Partitioning of a significant portion of the PFAS mass into an immobile phase increases the amount of material stored in the system and slows the apparent rate of migration in the mobile phase – a phenomenon that has been observed in field metadata<ref name="Anderson2019">Anderson, R.H., Adamson, D.T. and Stroo, H.F., 2019. Partitioning of poly-and perfluoroalkyl substances from soil to groundwater within aqueous film-forming foam source zones. Journal of Contaminant Hydrology, 220, pp. 59-65. [https://doi.org/10.1016/j.jconhyd.2018.11.011 DOI: 10.1016/j.jconhyd.2018.11.011]&nbsp;&nbsp; Manuscript available from [https://www.researchgate.net/profile/Hans_Stroo3/publication/329227107_Partitioning_of_poly-_and_perfluoroalkyl_substances_from_soil_to_groundwater_WITHIN_aqueous_film-forming_foam_source_zones/links/5e56996b299bf1bdb83e2f69/Partitioning-of-poly-and-perfluoroalkyl-substances-from-soil-to-groundwater-WITHIN-aqueous-film-forming-foam-source-zones.pdf ResearchGate]</ref>.
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==Equilibrium Determination (Tracers)==
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The equilibration period of peepers can last several weeks and depends on deployment conditions, analyte of interest, and peeper design. In many cases, it is advantageous to use pre-equilibrium methods that can use measurements in peepers deployed for shorter periods to predict concentrations at equilibrium<ref name="USEPA2017">USEPA, 2017. Laboratory, Field, and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual. EPA/600/R-16/357.&nbsp;&nbsp; [[Media: EPA_600_R-16_357.pdf | Report.pdf]]</ref>.  
  
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* '''Transformation:''' Transformation of PFAS is controlled by the molecular structure of the individual compounds. Perfluorinated compounds, including PFAAs, are resistant to abiotic and biotic transformation reactions under typical conditions and highly persistent in the environment. In contrast, precursors can be transformed by both abiotic and biotic processes, often resulting in the production of so-called “terminal” PFAA daughter products.
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Although the equilibrium concentration of an analyte in sediment can be evaluated by examining analyte results for peepers deployed for several different amounts of time (i.e., a time series), this is impractical for typical field investigations because it would require several mobilizations to the site to retrieve samplers. Alternately, reverse tracers (referred to as a performance reference compound when used with organic compound passive sampling) can be used to evaluate the percentage of equilibrium reached by a passive sampler.
  
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==Transport and Partitioning in the Atmosphere==
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Thomas and Arthur<ref name="ThomasArthur2010"/> studied the use of a reverse tracer to estimate percent equilibrium in lab experiments and a field application. They concluded that bromide can be used to estimate concentrations in porewater using measurements obtained before equilibrium is reached. Further studies were also conducted by Risacher ''et al.''<ref name="RisacherEtAl2023"/> showed that lithium can also be used as a tracer for brackish and saline environments. Both studies included a mathematical model for estimating concentrations of ions in external media (''C<small><sub>0</sub></small>'') based on measured concentrations in the peeper chamber (''C<small><sub>p,t</sub></small>''), the elimination rate of the target analyte (''K'') and the deployment time (''t''):
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Air serves as a transport media for PFAS, particularly for uncharged polyfluorinated PFAS.  Airborne PFAS transport contributes to global distribution and can lead to localized deposition to soils and surface water in the vicinity of emission sources<ref name="Simcik2005">Simcik, M.F. and Dorweiler, K.J., 2005. Ratio of Perfluorochemical Concentrations as a Tracer of Atmospheric Deposition to Surface Waters. Environmental Science and Technology, 39(22), pp.  8678-8683. [https://doi.org/10.1021/es0511218 DOI: 10.1021/es0511218]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Matt_Simcik/publication/7444956_Ratio_of_Perfluorochemical_Concentrations_as_a_Tracer_of_Atmospheric_Deposition_to_Surface_Waters/links/5f035861299bf1881603c3be/Ratio-of-Perfluorochemical-Concentrations-as-a-Tracer-of-Atmospheric-Deposition-to-Surface-Waters.pdf ResearchGate]</ref><ref name="Prevedouros2006">Prevedouros, K., Cousins, I.T., Buck, R.C. and Korzeniowski, S.H., 2006. Sources, Fate and Transport of Perfluorocarboxylates. Environmental Science and Technology, 40(1), pp. 32-44. [https://doi.org/10.1021/es0512475 DOI: 10.1021/es0512475]&nbsp;&nbsp; Free download available from [https://d1wqtxts1xzle7.cloudfront.net/39945519/Sources_Fate_and_Transport_of_Perfluoroc20151112-1647-19vcvbf.pdf?1447365456=&response-content-disposition=inline%3B+filename%3DSources_Fate_and_Transport_of_Perfluoroc.pdf&Expires=1605023809&Signature=Z6KqgaDN6lKdAazoe6qoASoCtVystG5i~5EnrTcb~qMg3xZPz4O49Kghh62WmMzqEKE788~6EwrnlBVo9o6cM0hjf2vymFYxg4mx-eSIOEonfFjk6RonSaWp5gRbA6m~SNjwsjaKXID3OQyWIlLVpUd2LzAdI5rLGFA~gIXXtNPyCArLuGn-kbPYUIcBUg5TIkTZ6TDLXF~ujmzK9tNv~55UYabsJL4pmwIGC2sNGkEyJrYMfU577fbactdrmQXTJH7XbgpfDSfd4-xWkDZTdvVf~TypDDqUCZdtCkY8wINdpqtfe1KEzLrAj7rxxALAHUYxlVbPB45XTkLAGe5qww__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA  Academia]</ref><ref name="Ahrens2011">Ahrens, L., Shoeib, M., Harner, T., Lane, D.A., Guo, R. and Reiner, E.J., 2011. Comparison of Annular Diffusion Denuder and High Volume Air Samplers for Measuring Per- and Polyfluoroalkyl Substances in the Atmosphere." Analytical Chemistry, 83(24), pp. 9622-9628. [https://doi.org/10.1021/ac202414w DOI: 10.1021/ac202414w]&nbsp;&nbsp; Free download available from [https://www.informea.org/sites/default/files/imported-documents/UNEP-POPS-POPRC11FU-SUBM-PFOA-Canada-2-20151211.En.pdf Informea].</ref><ref name="Rauert2018">Rauert, C., Shoieb, M., Schuster, J.K., Eng, A. and Harner, T., 2018. Atmospheric concentrations and trends of poly-and perfluoroalkyl substances (PFAS) and volatile methyl siloxanes (VMS) over 7 years of sampling in the Global Atmospheric Passive Sampling (GAPS) network. Environmental Pollution, 238, pp. 94-102. [https://doi.org/10.1016/j.envpol.2018.03.017 DOI: 10.1016/j.envpol.2018.03.017]&nbsp;&nbsp; Open access article available from [https://reader.elsevier.com/reader/sd/pii/S0269749117352521?token=4C770E6E8AEDB0B3BA6A1D5B2C20ED5385F81823612551FA3380AAA1DA7A978F9CB36834AF6B7F91F35FF57E32013252 ScienceDirect]&nbsp;&nbsp; [[Media:Rauert2018.pdf | Report.pdf]]</ref>.
+
</br>
 +
{|
 +
| || '''Equation&nbsp;1:'''
 +
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation1r.png]]
 +
|-
 +
| Where: || ||
 +
|-
 +
| || ''C<small><sub>0</sub></small>''|| is the freely dissolved concentration of the analyte in the sediment (mg/L or &mu;g/L), sometimes referred to as ''C<small><sub>free</sub></small>
 +
|-
 +
| || ''C<small><sub>p,t</sub></small>'' || is the measured concentration of the analyte in the peeper at time of retrieval (mg/L or &mu;g/L)
 +
|-
 +
| || ''K'' || is the elimination rate of the target analyte
 +
|-
 +
| || ''t'' || is the deployment time (days)
 +
|}
  
−
PFAAs, which are ionic and possess a negative charge under ambient environmental conditions, are far less volatile than many other groundwater contaminants.  An online database of vapor pressures and Henry’s Law constants for different PFAS, including PFAAs, is maintained by the Interstate Technology Regulatory Council<ref name="ITRC2020"/>.  In general, vapor pressures of PFAS are low and water solubilities are high, limiting partitioning from water to air<ref name="ITRC2020"/>.  However, under certain conditions, particularly within industrial stack emissions, PFAS can be transported through the atmosphere in both the gas phase and associated with fugitive particulates.  In particular, volatile compounds including fluorotelomer alcohols (FTOHs) may be present in the gas phase, whereas, PFAAs can aerosolize and be transported as particulates<ref name="Ahrens2012"/>. In addition, precursors can be transformed to PFAAs in the atmosphere, which can result in PFAA deposition.
+
The elimination rate of the target analyte (''K'') is calculated using Equation 2:
−
Short-range atmospheric transport and deposition can result in PFAS contamination in terrestrial and aquatic systems near points of significant emissions, impacting soil, groundwater, and other media of concern<ref name="Fang2018">Fang, X., Wang, Q., Zhao, Z., Tang, J., Tian, C., Yao, Y., Yu, J. and Sun, H., 2018. Distribution and dry deposition of alternative and legacy perfluoroalkyl and polyfluoroalkyl substances in the air above the Bohai and Yellow Seas, China. Atmospheric Environment, 192, pp. 128-135. [https://doi.org/10.1016/j.atmosenv.2018.08.052 DOI: 10.1016/j.atmosenv.2018.08.052]</ref><ref name="Brandsma2019">Brandsma, S.H., Koekkoek, J.C., van Velzen, M.J.M. and de Boer, J., 2019.  The PFOA substitute GenX detected in the environment near a fluoropolymer manufacturing plant in the Netherlands. Chemosphere, 220, pp. 493-500. [https://doi.org/10.1016/j.chemosphere.2018.12.135 DOI: 10.1016/j.chemosphere.2018.12.135]&nbsp;&nbsp; Open access article available from [https://reader.elsevier.com/reader/sd/pii/S0045653518324706?token=E541D5C4B200C8626A86F41049FE9DCA92652BC9A8BA7D9E47832C08070AB5AF256F4872474C50B5C4908F5CA4C24947 ScienceDirect].&nbsp;&nbsp; [[Media: Brandsma2019.pdf | Report.pdf]]</ref>.  Releases of ionic PFAS from factories are likely tied to particulate matter, which settle to the ground in dry weather and are also wet-scavenged by precipitation<ref name="Barton2006">Barton, C.A., Butler, L.E., Zarzecki, C.J., Flaherty, J. and Kaiser, M., 2006. Characterizing Perfluorooctanoate in Ambient Air near the Fence Line of a Manufacturing Facility: Comparing Modeled and Monitored Values. Journal of the Air and Waste Management Association, 56(1), pp.  48-55. [https://doi.org/10.1080/10473289.2006.10464429 DOI: 10.1080/10473289.2006.10464429]&nbsp;&nbsp; Free access article available from [https://www.tandfonline.com/doi/pdf/10.1080/10473289.2006.10464429?needAccess=true Taylor and Francis Online]&nbsp;&nbsp; [[Media: Barton2006.pdf | Report.pdf]]</ref>.  The impact of other potential sources, such as combustion emissions or wind-blown fire-fighting foam from fire training and fire response sites, on the fate and transport of PFAS in air may need to be assessed.
+
</br>
 +
{|
 +
| || '''Equation&nbsp;2:'''
 +
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation2r.png]]
 +
|-
 +
| Where: || ||
 +
|-
 +
| || ''K''|| is the elimination rate of the target analyte
 +
|-
 +
| || ''K<small><sub>tracer</sub></small>'' || is the elimination rate of the tracer
 +
|-
 +
| || ''D'' || is the free water diffusivity of the analyte (cm<sup>2</sup>/s)
 +
|-
 +
| || ''D<small><sub>tracer</sub></small>'' || is the free water diffusivity of the tracer (cm<sup>2</sup>/s)
 +
|}
  
−
Long-range transport processes are responsible for the wide distribution of neutral and ionic PFAS across the Earth as evidenced by their occurrence in biota, surface snow, ice cores, seawater, and other environmental media in regions as remote as the Arctic and Antarctic<ref name="Bossi2016">Bossi, R., Vorkamp, K. and Skov, H., 2016. Concentrations of organochlorine pesticides, polybrominated diphenyl ethers and perfluorinated compounds in the atmosphere of North Greenland. Environmental Pollution, 217, pp. 4-10. [https://doi.org/10.1016/j.envpol.2015.12.026 DOI: 10.1016/j.envpol.2015.12.026]</ref><ref name="Ahrens2010">Ahrens, L., Gerwinski, W., Theobald, N. and Ebinghaus, R., 2010. Sources of polyfluoroalkyl compounds in the North Sea, Baltic Sea and Norwegian Sea: Evidence from their spatial distribution in surface water. Marine Pollution Bulletin, 60(2), pp. 255-260. [https://doi.org/10.1016/j.marpolbul.2009.09.013 DOI: 10.1016/j.marpolbul.2009.09.013]</ref>. 
+
The elimination rate of the tracer (''K<small><sub>tracer</sub></small>'') is calculated using Equation 3:
−
Distribution of PFAS to remote regions far removed from direct industrial input is believed to occur from both: a) long-range atmospheric transport and subsequent degradation of volatile precursors; and b) transport via ocean currents and release into the air as marine aerosols (sea spray)<ref name="DeSilva2009">De Silva, A.O., Muir, D.C. and Mabury, S.A., 2009. Distribution of perfluorocarboxylate isomers in select samples from the North American environment. Environmental Toxicology and Chemistry: An International Journal 28(9), pp. 1801-1814. [https://doi.org/10.1897/08-500.1 DOI: 10.1897/08-500.1]</ref><ref name="Armitage2009">Armitage, J.M., 2009. Modeling the global fate and transport of perfluoroalkylated substances (PFAS). Doctoral Dissertation, Institutionen för tillämpad miljövetenskap (ITM), Stockholm University. [[Media: Armitage2009.pdf | Report.pdf]]</ref>.
+
</br>
 +
{|
 +
| || '''Equation&nbsp;3:'''
 +
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation3r2.png]]
 +
|-
 +
| Where: || ||
 +
|-
 +
| || ''K<small><sub>tracer</sub></small>'' || is the elimination rate of the tracer
 +
|-
 +
| || ''C<small><sub>tracer,i</sub></small>''|| is the measured initial concentration of the tracer in the peeper prior to deployment (mg/L or &mu;g/L)
 +
|-
 +
| || ''C<small><sub>tracer,t</sub></small>'' || is the measured final concentration of the tracer in the peeper at time of retrieval (mg/L or &mu;g/L)
 +
|-
 +
| || ''t'' || is the deployment time (days)
 +
|}
  
−
==Transport and Partitioning in Aqueous Systems==
+
Using this set of equations allows the calculation of the porewater concentration of the analyte prior to its equilibrium with the peeper water. A template for these calculations can be found in the appendix of Risacher ''et al.''<ref name="RisacherEtAl2023"/>.
−
PFAS adsorb from water to a variety of solid materials including organic materials, clay minerals, metal oxides, and granular activated carbon<ref name="Du2014">Du, Z., Deng, S., Bei, Y., Huang, Q., Wang, B., Huang, J. and Yu, G., 2014. Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents – A review. Journal of Hazardous Materials, 274, pp. 443-454. [https://doi.org/10.1016/j.jhazmat.2014.04.038 DOI: 10.1016/j.jhazmat.2014.04.038]</ref>.  This process is thought to occur through two primary mechanisms: 1) sorption to organic-carbon components of the solids; and 2) electrostatic (and other) interactions with inorganic constituents of the solids, including clay minerals and metal-oxides<ref name="Guelfo2013">Guelfo, J.L. and Higgins, C.P., 2013. Subsurface Transport Potential of Perfluoroalkyl Acids at Aqueous Film-Forming Foam (AFFF)-Impacted Sites. Environmental Science and Technology, 47(9), pp. 4164-4171. [https://doi.org/10.1021/es3048043 DOI: 10.1021/es3048043]&nbsp;&nbsp; [https://mountainscholar.org/bitstream/handle/11124/80055/Guelfo_mines_0052E_10298.pdf?sequence=1#page=64 Doctoral Dissertation]</ref><ref name="Zhao2014">Zhao, L., Bian, J., Zhang, Y., Zhu, L. and Liu, Z., 2014. Comparison of the sorption behaviors and mechanisms of perfluorosulfonates and perfluorocarboxylic acids on three kinds of clay minerals. Chemosphere, 114, pp. 51-58. [https://doi.org/10.1016/j.chemosphere.2014.03.098 DOI: 10.1016/j.chemosphere.2014.03.098]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Lixia_Zhao8/publication/262148355_Comparison_of_the_sorption_behaviors_and_mechanisms_of_perfluorosulfonates_and_perfluorocarboxylic_acids_on_three_kinds_of_clay_minerals/links/5b1be5dca6fdcca67b681a4f/Comparison-of-the-sorption-behaviors-and-mechanisms-of-perfluorosulfonates-and-perfluorocarboxylic-acids-on-three-kinds-of-clay-minerals.pdf ResearchGate].</ref>. The relative contribution of each mechanism varies depending on surface chemistry and other geochemical factors, as well as the molecular properties of the PFAS.  In general, the impact of electrostatic interactions with charged soil constituents is more important for PFAS than non-polar, hydrophobic organic contaminants (e.g. hydrocarbons, chlorinated solvents).  Adsorption of PFAS by solids is often nonlinear, with greater sorption at lower solute concentrations.  The impacts of adsorption kinetics and their potential reversibility on PFAS transport have not yet been examined for most PFAS compounds. 
 
  
−
Sorption of hydrocarbons, chlorinated solvents and other hydrophobic organics is often controlled the by organic-carbon components of the solid phase (see [[Sorption of Organic Contaminants]]).  However, studies of PFAS sorption to solid phase organic carbon have reported conflicting results.  In a study of field sites with aqueous film-forming foam (AFFF, a type of fire-fighting foam) releases, solid phase organic carbon content was found to significantly influence PFAS soil-to-groundwater concentration ratios.  Statistical modeling was then used to derive apparent organic carbon partition coefficients for 18 different PFAS<ref name="Anderson2019"/>.  A recent compilation of published organic carbon partition coefficients found a good correspondence to PFAS molecular structure<ref name="Brusseau2019a">Brusseau, M.L., 2019. Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per-and poly-fluoroalkyl substances. Environmental Pollution, 254B, p. 113102. [https://doi.org/10.1016/j.envpol.2019.113102 DOI: 10.1016/j.envpol.2019.113102]</ref>. However, other studies have shown a general lack of correlation between solid phase partition coefficients and organic carbon<ref name="Li2018">Li, Y., Oliver, D.P. and Kookana, R.S., 2018. A critical analysis of published data to discern the role of soil and sediment properties in determining sorption of per and polyfluoroalkyl substances (PFASs). Science of the Total Environment, 628, pp. 110-120. [https://doi.org/10.1016/j.scitotenv.2018.01.167 DOI: 10.1016/j.scitotenv.2018.01.167]</ref>. It is possible that greater variability may be observed for broader data sets that incorporate different ranges of PFAS concentrations, different solution conditions, different measurement methods, and field-based data which often have less well-defined conditions and may also be influenced by other retention processes<ref name="Anderson2019"/><ref name="Brusseau2019a"/>.
+
==Using Peeper Data at a Sediment Site==
 +
Peeper data can be used to enable site specific decision making in a variety of ways. Some of the most common uses for peepers and peeper data are discussed below.
  
−
[[File:AndersonBrusseau1w2Fig2.png | thumb | 500px | Figure 2. Example of expected orientation and accumulation of PFAS at air-water interface. Source: D. Adamson, GSI, used with permission.]]
+
'''Nature and Extent:''' Multiple peepers deployed in sediment can help delineate areas of increased metal availability. Peepers are especially helpful for sites that are comprised of coarse, relatively inert materials that may not be conducive to traditional bulk sediment sampling. Because much of the inorganics present in these types of sediments may be associated with the porewater phase rather than the solid phase, peepers can provide a more representative measurement of C<small><sub>0</sub></small>. Additionally, at sites where tidal pumping or groundwater flux may be influencing the nature and extent of inorganics, peepers can provide a distinct advantage to bulk sediment sampling or other point-in-time measurements, as peepers can provide an average measurement that integrates the variability in the hydrodynamic and chemical conditions over time.
−
Most solids present in the environment contain both fixed-charged (negative) and variably charged surfaces. At neutral to high pH, variably charged clay minerals have a net-negative charge.  As a result, negatively charged PFAAs do not strongly interact electrostatically in most soils, although as the soil pH decreases electrostatic sorption would be expected to increase in soils with variably charged clay minerals.  Cationic and zwitterionic precursors are expected to be more strongly sorbed than anionic PFAAs in most environments due to well-established cation exchange reactions. Other factors, including ionic strength, composition, and the presence of co-solutes, can affect adsorption of PFAS<ref name="Higgins2006">Higgins, C.P. and Luthy, R.G., 2006. Sorption of Perfluorinated Surfactants on Sediments. Environmental Science and Technology, 40(23), pp. 7251-7256. [https://doi.org/10.1021/es061000n DOI: 10.1021/es061000n]</ref><ref name="Chen2009">Chen, H., Chen, S., Quan, X., Zhao, Y. and Zhao, H., 2009. Sorption of perfluorooctane sulfonate (PFOS) on oil and oil-derived black carbon: Influence of solution pH and [Ca2+]. Chemosphere, 77(10), pp. 1406-1411. [https://doi.org/10.1016/j.chemosphere.2009.09.008 DOI: 10.1016/j.chemosphere.2009.09.008]</ref><ref name="Pan2009">Pan, G., Jia, C., Zhao, D., You, C., Chen, H. and Jiang, G., 2009. Effect of cationic and anionic surfactants on the sorption and desorption of perfluorooctane sulfonate (PFOS) on natural sediments. Environmental Pollution, 157(1), pp.325-330. [https://doi.org/10.1016/j.envpol.2008.06.035 DOI: 10.1016/j.envpol.2008.06.035]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Gang_Pan2/publication/23189567_Effect_of_cationic_and_anionic_surfactants_on_the_sorption_and_desorption_of_perfluorooctane_sulfonate_PFOS_on_natural_sediments/links/5be19d23a6fdcc3a8dc2550d/Effect-of-cationic-and-anionic-surfactants-on-the-sorption-and-desorption-of-perfluorooctane-sulfonate-PFOS-on-natural-sediments.pdf ResearchGate]</ref><ref name="Guelfo2013"/><ref name="Zhao2014"/>.
 
  
−
Most PFAS compounds act as surface-active agents (or [[Wikipedia:Surfactant | surfactants]]) due to the presence of a hydrophilic headgroup and a hydrophobic tail.  The hydrophilic headgroup will preferentially partition to the aqueous phase and the hydrophobic tail will preferentially partition to the non-aqueous phase (air or organic material).  As a result, PFAS tend to accumulate at interfaces (air-water, water-NAPL, water-solid) (Figure 2).  This tendency to accumulate at interfaces can influence transport in the atmosphere (on water droplets and hydrated aerosols), in the vadose or unsaturated zone at air-water interfaces, in the presence of NAPLs, and in wastewater treatment systems<ref name="Brusseau2018"/><ref name="Brusseau2019b">Brusseau, M.L., 2019. The Influence of Molecular Structure on the Adsorption of PFAS to Fluid-Fluid Interfaces: Using QSPR to Predict Interfacial Adsorption Coefficients. Water Research, 152, pp. 148-158.  [https://doi.org/10.1016/j.watres.2018.12.057 DOI: 10.1016/j.watres.2018.12.057]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374777/ Author’s Manuscript]</ref>.
+
'''Sources and Fate:''' A considerable advantage to using peepers is that C<small><sub>0</sub></small> results are expressed as concentration in units of mass per volume (e.g., mg/L), providing a common unit of measurement to compare across multiple media. For example, synchronous measurements of C<small><sub>0</sub></small> using peepers deployed in both surface water and sediment can elucidate the potential flux of inorganics from sediment to surface water. Paired measurements of both C<small><sub>0</sub></small> and bulk metals in sediment can also allow site specific sediment-porewater partition coefficients to be calculated. These values can be useful in understanding and predicting contaminant fate, especially in situations where the potential dissolution of metals from sediment are critical to predict, such as when sediment is dredged.
−
 
 
−
In theoretical and experimental studies of transport in unsaturated porous media, adsorption at the air-water interface increased PFOS and PFOA retention<ref name="Brusseau2018"/><ref name="Lyu2018">Lyu, Y., Brusseau, M.L., Chen, W., Yan, N., Fu, X., and Lin, X., 2018.  Adsorption of PFOA at the Air-Water Interface during Transport in Unsaturated Porous Media. Environmental Science and Technology, 52(14), pp. 7745-7753.  [https://doi.org/10.1021/acs.est.8b02348 DOI: 10.1021/acs.est.8b02348]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6312111/ Author’s Manuscript]</ref><ref name="BrusseauEtAl2019">Brusseau, M.L., Yan, N., Van Glubt, S., Wang, Y., Chen, W., Lyu, Y., Dungan, B., Carroll, K.C., and Holguin, F.O., 2019. Comprehensive Retention Model for PFAS Transport in Subsurface Systems. Water Research, 148, pp. 41-50.  [https://doi.org/10.1016/j.watres.2018.10.035 DOI: 10.1016/j.watres.2018.10.035]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6294326/ Author’s Manuscript]</ref>, contributing approximately 20% to 80% of total retention in sands and soil. The impact of oil-water interfacial adsorption on PFAS transport was also quantitatively characterized in recent studies and shown to contribute to total retention on a similar scale as air-water interfacial adsorption<ref name="Brusseau2018"/><ref name="BrusseauEtAl2019"/>. These processes may result in increased PFAS mass retained in NAPL source zones, increased PFAS sorption with the resulting retardation of transport, and greater persistence of dissolved PFAS in the environment.  
 
  
−
==Transformation==
+
'''Direct Toxicity to Aquatic Life:''' Peepers are frequently used to understand the potential direct toxicity to aquatic life, such as benthic invertebrates and fish. A C<small><sub>0</sub></small> measurement obtained from a peeper deployed in sediment (''in situ'') or surface water (''ex situ''), can be compared to toxicological benchmarks for aquatic life to understand the potential toxicity to aquatic life and to set remediation goals<ref name="USEPA2017"/>. C<small><sub>0</sub></small> measurements can also be incorporated in more sophisticated approaches, such as the Biotic Ligand Model<ref>Santore, C.R., Toll, E.J., DeForest, K.D., Croteau, K., Baldwin, A., Bergquist, B., McPeek, K., Tobiason, K., and Judd, L.N., 2022. Refining our understanding of metal bioavailability in sediments using information from porewater: Application of a multi-metal BLM as an extension of the Equilibrium Partitioning Sediment Benchmarks. Integrated Environmental Assessment and Management, 18(5), pp. 1335–1347. [https://doi.org/10.1002/ieam.4572 doi: 10.1002/ieam.4572]</ref> to understand the potential for toxicity or the need to conduct toxicological testing or ecological evaluations.
−
[[File:AndersonBrusseau1w2Fig3.png | thumb | 600px | Figure 3. Conceptual model of precursor transformation resulting in the formation of PFAAs. Source L. Trozzolo, TRC and C. Higgins, Colorado School of Mines, used with permission.]]
 
−
Certain polyfluorinated substances have the potential to transform to other PFAS, with PFAAs as the typical terminal daughter products. These polyfluorinated substances are often referred to as “precursors”. The transformation potential of polyfluorinated precursors is influenced by the presence, location, and number of carbon-hydrogen (C-H) bonds and potentially carbon-oxygen (C-O) bonds throughout the carbon chain. Specifically, PFAS with C-H bonds are subject to a variety of biotic and abiotic reactions that ultimately result in the formation of PFAAs with perfluorinated carbon chains of the same length or shorter than the initial polyfluorinated precursor<ref name="Houtz2013">Houtz, E.F., Higgins, C.P., Field, J.A. and Sedlak, D.L., 2013. Persistence of perfluoroalkyl acid precursors in AFFF-impacted groundwater and soil. Environmental Science and Technology, 47(15), pp.  8187-8195.  [https://doi.org/10.1021/es4018877 DOI: 10.1021/es4018877]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Erika_Houtz/publication/252323955_Persistence_of_Perfluoroalkyl_Acid_Precursors_in_AFFF-Impacted_Groundwater_and_Soil/links/59dbddeeaca2728e2018336d/Persistence-of-Perfluoroalkyl-Acid-Precursors-in-AFFF-Impacted-Groundwater-and-Soil.pdf ReseqarchGate]</ref><ref name="McGuire2014">McGuire, M.E., Schaefer, C., Richards, T., Backe, W.J., Field, J.A., Houtz, E., Sedlak, D.L., Guelfo, J.L., Wunsch, A., and Higgins, C.P., 2014. Evidence of Remediation-Induced Alteration of Subsurface Poly- and Perfluoroalkyl Substance Distribution at a Former Firefighter Training Area. Environmental Science and Technology, 48(12) pp. 6644-6652.  [https://doi.org/10.1021/es5006187 DOI: 10.1021/es5006187]&nbsp;&nbsp; Manuscript available from [https://ir.library.oregonstate.edu/downloads/td96k706f Oregon State University]</ref><ref name="Anderson2016">Anderson, R.H., Long, G.C., Porter, R.C. and Anderson, J.K., 2016. Occurrence of select perfluoroalkyl substances at US Air Force aqueous film-forming foam release sites other than fire-training areas: Field-validation of critical fate and transport properties. Chemosphere, 150, pp. 678-685. [https://doi.org/10.1016/j.chemosphere.2016.01.014 DOI: 10.1016/j.chemosphere.2016.01.014]</ref><ref name="Weber2017"/>.
 
  
−
Transformation studies published to date have tested only a small subsample of possible precursors and, therefore, much uncertainty exists regarding 1) the extent to which precursor transformation occurs on a global scale, 2) which environmental compartments represent the majority of transformation, 3) relevant environmental conditions that affect transformation processes, and 4) transformation rates and pathways. Nevertheless, a portion of the precursors are expected to transform to PFAAs over time as shown in Figure 3.
+
'''Bioaccumulation of Inorganics by Aquatic Life:''' Peepers can also be used to understand site specific relationship between C<small><sub>0</sub></small> and concentrations of inorganics in aquatic life. For example, measuring C<small><sub>0</sub></small> in sediment from which organisms are collected and analyzed can enable the estimation of a site-specific uptake factor. This C<small><sub>0</sub></small>-to-organism uptake factor (or model) can then be applied for a variety of uses, including predicting the concentration of inorganics in other organisms, or estimating a sediment C<small><sub>0</sub></small> value that would be safe for consumption by wildlife or humans. Because several decades of research have found that the correlation between C<small><sub>0</sub></small> measurements and bioavailability is usually better than the correlation between measurements of chemicals in bulk sediment and bioavailability, C<small><sub>0</sub></small>-to-organism uptake factors are likely to be more accurate than uptake factors based on bulk sediment testing.
  
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Precursors can be transformed by a variety of abiotic processes including hydrolysis, photolysis, and oxidation. Hydrolysis of some precursors, followed by subsequent biotransformation, can produce perfluoroalkyl sulfonates (PFSAs).  An important example is the production of PFOS from perfluorooctane sulfonyl fluoride (POSF)<ref name="Martin2010">Martin, J.W., Asher, B.J., Beesoon, S., Benskin, J.P. and Ross, M.S., 2010. PFOS or PreFOS? Are perfluorooctane sulfonate precursors (PreFOS) important determinants of human and environmental perfluorooctane sulfonate (PFOS) exposure? Journal of Environmental Monitoring, 12(11), pp.1979-2004.  [https://doi.org/10.1039/C0EM00295J DOI: 10.1039/C0EM00295J]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Matthew_Ross3/publication/47415684_PFOS_or_PreFOS_Are_perfluorooctane_sulfonate_precursors_PreFOS_important_determinants_of_human_and_environmental_perfluorooctane_sulfonate_PFOS_exposure/links/00b7d520a6132da945000000.pdf ResearchGate]</ref>.  Other hydrolysis reactions produce perfluoroalkyl carboxylates (PFCAs). At neutral pH, the hydrolysis of fluorotelomer-derived polymeric precursors results in the formation of monomeric precursors of PFOA and other PFAAs with half-lives of 50 to 90 years)<ref name="Washington2010">Washington, J.W., Ellington, J.J., Jenkins, T.M. and Yoo, H., 2010. Response to Comments on “Degradability of an Acrylate-Linked, Fluorotelomer Polymer in Soil”. Environmental Science and Technology, 44(2), pp. 849-850.  [https://doi.org/10.1021/es902672q DOI: 10.1021/es902672q]&nbsp;&nbsp;  [https://pubs.acs.org/doi/pdf/10.1021/es902672q Free Download from ACS].</ref>.  Oxidation of precursors by hydroxyl radicals can occur in natural waters, with the fluorotelomer-derived precursors being oxidized relatively rapidly<ref name="Gauthier2005">Gauthier, S.A. and Mabury, S.A., 2005. Aqueous photolysis of 8: 2 fluorotelomer alcohol. Environmental Toxicology and Chemistry, 24(8), pp.1837-1846.  [https://doi.org/10.1897/04-591R.1 DOI: 10.1897/04-591R.1]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Suzanne_Gauthier/publication/7609648_Aqueous_photolysis_of_8_2_fluorotelomer_alcohol/links/5ec16c4792851c11a86d9438/Aqueous-photolysis-of-8-2-fluorotelomer-alcohol.pdf ResearchGate].</ref><ref name="Plumlee2009">Plumlee, M.H., McNeill, K. and Reinhard, M., 2009. Indirect Photolysis of Perfluorochemicals: Hydroxyl Radical-Initiated Oxidation of N-Ethyl Perfluorooctane Sulfonamido Acetate (N-EtFOSAA) and Other Perfluoroalkanesulfonamides. Environmental Science and Technology, 43(10), pp.3662-3668.  [https://doi.org/10.1021/es803411w DOI: 10.1021/es803411w]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Megan_Plumlee/publication/26309488_Indirect_Photolysis_of_Perfluorochemicals_Hydroxyl_Radical-Initiated_Oxidation_of_N-Ethyl_Perfluorooctane_Sulfonamido_Acetate_N-EtFOSAA_and_Other_Perfluoroalkanesulfonamides/links/5aac0437a6fdcc1bc0b8d002/Indirect-Photolysis-of-Perfluorochemicals-Hydroxyl-Radical-Initiated-Oxidation-of-N-Ethyl-Perfluorooctane-Sulfonamido-Acetate-N-EtFOSAA-and-Other-Perfluoroalkanesulfonamides.pdf ResearchGate].</ref>.
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'''Evaluating Sediment Remediation Efficacy:''' Passive sampling has been used widely to evaluate the efficacy of remedial actions such as active amendments, thin layer placements, and capping to reduce the availability of contaminants at sediment sites. A particularly powerful approach is to compare baseline (pre-remedy) C<small><sub>0</sub></small> in sediment to C<small><sub>0</sub></small> in sediment after the sediment remedy has been applied. Peepers can be used in this context for inorganics, allowing the sediment remedy’s success to be evaluated and monitored in laboratory benchtop remedy evaluations, pilot scale remedy evaluations, and full-scale remediation monitoring.
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Evidence of aerobic biotransformation is provided from studies of PFAS composition throughout the continuum of wastewater treatments<ref name="Arvaniti2015">Arvaniti, O.S. and Stasinakis, A.S., 2015. Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment. Science of the Total Environment, 524, pp. 81-92.  [https://doi.org/10.1016/j.scitotenv.2015.04.023 DOI: 10.1016/j.scitotenv.2015.04.023]</ref>, from field studies at AFFF-impacted sites<ref name="Houtz2013"/><ref name="McGuire2014"/><ref name="Anderson2016"/><ref name="Weber2017"/>, and from microcosm experiments. In general, the literature on aerobic biotransformation collectively demonstrates or indirectly supports the following conclusions as summarized in ITRC 2020<ref name="ITRC2020"/>:
 
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* Numerous aerobic biotransformation pathways exist with relatively rapid kinetics
 
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* All polyfluorinated precursors studied to date have the potential to aerobically biotransform to PFAAs
 
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* Aerobic biotransformation of various fluorotelomer-derived precursors exclusively results in the formation of PFCAs, including PFOA, without necessarily the conservation of chain-length
 
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* Aerobic biotransformation of various electrochemical fluorination-derived precursors primarily results in the formation of PFAAs, including PFOS, with the conservation of chain-length
 
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Precursor transformation can complicate CSMs (and risk assessments) and should be considered during comprehensive site investigations.  For example, atmospheric emissions of volatile precursors can result in long-range transport where subsequent transformation and deposition can result in detectable levels of PFAAs in environmental media independent of obvious point-sources<ref name="Vedagiri2018">Vedagiri, U.K., Anderson, R.H., Loso, H.M. and Schwach, C.M., 2018. Ambient levels of PFOS and PFOA in multiple environmental media. Remediation Journal, 28(2), pp. 9-51.  [https://doi.org/10.1002/rem.21548 DOI: 10.1002/rem.21548]</ref>.  With respect to site-related precursors, transformation of otherwise unmeasured PFAS into detectable PFAAs is obviously relevant to site investigations to the extent transformation occurs after initial site characterization efforts or if past remedial efforts have accelerated ''in situ'' transformation rates<ref name="McGuire2014"/>.  Additionally, differential transport rates between precursor PFAS and the corresponding terminal PFAA could also confound CSMs if transformation rates are slower than transport rates as has been suggested<ref name="Weber2017"/>. 
 
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To account for otherwise unmeasurable precursors, several surrogate analytical methods have been developed. See [[PFAS Sampling and Analytical Methods]] for additional detail.
 
  
 
==References==
 
==References==
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==See Also:==
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==See Also==
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*[https://vimeo.com/809180171/c276c1873a Peeper Deployment Video]
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*[https://vimeo.com/811073634/303edf2693 Peeper Retrieval Video]
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*[https://vimeo.com/811328715/aea3073540 Peeper Processing Video]
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*[https://sepub-prod-0001-124733793621-us-gov-west-1.s3.us-gov-west-1.amazonaws.com/s3fs-public/2024-09/ER20-5261%20Fact%20Sheet.pdf?VersionId=malAixSQQM3mWCRiaVaxY8wLdI0jE1PX Fact Sheet]

Latest revision as of 21:47, 14 October 2024

Sediment Porewater Dialysis Passive Samplers for Inorganics (Peepers)

Sediment porewater dialysis passive samplers, also known as “peepers,” are sampling devices that allow the measurement of dissolved inorganic ions in the porewater of a saturated sediment. Peepers function by allowing freely-dissolved ions in sediment porewater to diffuse across a micro-porous membrane towards water contained in an isolated compartment that has been inserted into sediment. Once retrieved after a deployment period, the resulting sample obtained can provide concentrations of freely-dissolved inorganic constituents in sediment, which provides measurements that can be used for understanding contaminant fate and risk. Peepers can also be used in the same manner in surface water, although this article is focused on the use of peepers in sediment.

Related Article(s):


Contributor(s):

  • Florent Risacher, M.Sc.
  • Jason Conder, Ph.D.

Key Resource(s):

  • A review of peeper passive sampling approaches to measure the availability of inorganics in sediment porewater[1]
  • Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern[2]

Introduction

Biologically available inorganic constituents associated with sediment toxicity can be quantified by measuring the freely-dissolved fraction of contaminants in the porewater[3][4]. Classical sediment porewater analysis usually consists of collecting large volumes of bulk sediments which are then mechanically squeezed or centrifuged to produce a supernatant, or suction of porewater from intact sediment, followed by filtration and collection[5]. The extraction and measurement processes present challenges due to the heterogeneity of sediments, physical disturbance, high reactivity of some complexes, and interaction between the solid and dissolved phases, which can impact the measured concentration of dissolved inorganics[6]. For example, sampling disturbance can affect redox conditions[7][8], which can lead to under or over representation of inorganic chemical concentrations relative to the true dissolved phase concentration in the sediment porewater[9][5].

To address the complications with mechanical porewater sampling, passive sampling approaches for inorganics have been developed to provide a method that has a low impact on the surrounding geochemistry of sediments and sediment porewater, thus enabling more precise measurements of inorganics[4]. Sediment porewater dialysis passive samplers, also known as “peepers,” were developed more than 45 years ago[10] and refinements to the method such as the use of reverse tracers have been made, improving the acceptance of the technology as decision making tool.

Peeper Designs

Figure 1. Conceptual illustration of peeper construction showing (top, left to right) the peeper cap (optional), peeper membrane and peeper chamber, and (bottom) an assembled peeper containing peeper water
Figure 2. Example of Hesslein[10] general peeper design (42 peeper chambers), from USGS
Figure 3. Peeper deployment structure to allow the measurement of metal availability in different sediment layers using five single-chamber peepers (Photo: Geosyntec Consultants)

Peepers (Figure 1) are inert containers with a small volume (typically 1-100 mL) of purified water (“peeper water”) capped with a semi-permeable membrane. Peepers can be manufactured in a wide variety of formats (Figure 2, Figure 3) and deployed in in various ways.

Two designs are commonly used for peepers. Frequently, the designs are close adaptations of the original multi-chamber Hesslein design[10] (Figure 2), which consists of an acrylic sampler body with multiple sample chambers machined into it. Peeper water inside the chambers is separated from the outside environment by a semi-permeable membrane, which is held in place by a top plate fixed to the sampler body using bolts or screws. An alternative design consists of single-chamber peepers constructed using a single sample vial with a membrane secured over the mouth of the vial, as shown in Figure 3, and applied in Teasdale et al.[7], Serbst et al.[11], Thomas and Arthur[12], Passeport et al.[13], and Risacher et al.[2]. The vial is filled with deionized water, and the membrane is held in place using the vial cap or an o-ring. Individual vials are either directly inserted into sediment or are incorporated into a support structure to allow multiple single-chamber peepers to be deployed at once over a given depth profile (Figure 3).

Peepers Preparation, Deployment and Retrieval

Figure 4: Conceptual illustration of peeper passive sampling in a sediment matrix, showing peeper immediately after deployment (top) and after equilibration between the porewater and peeper chamber water (bottom)

Peepers are often prepared in laboratories but are also commercially available in a variety of designs from several suppliers. Peepers are prepared by first cleaning all materials to remove even trace levels of metals before assembly. The water contained inside the peeper is sometimes deoxygenated, and in some cases the peeper is maintained in a deoxygenated atmosphere until deployment[14]. However, recent studies[2] have shown that deoxygenation prior to deployment does not significantly impact sampling results due to oxygen rapidly diffusing out of the peeper during deployment. Once assembled, peepers are usually shipped in a protective bag inside a hard-case cooler for protection.

Peepers are deployed by insertion into sediment for a period of a few days to a few weeks. Insertion into the sediment can be achieved by wading to the location when the water depth is shallow, by using push poles for deeper deployments[2], or by professional divers for the deepest sites. If divers are used, an appropriate boat or ship will be required to accommodate the diver and their equipment. Whichever method is used, peepers should be attached to an anchor or a small buoy to facilitate retrieval at the end of the deployment period.

During deployment, passive sampling is achieved via diffusion of inorganics through the peeper’s semi-permeable membrane, as the enclosed volume of peeper water equilibrates with the surrounding sediment porewater (Figure 4). It is assumed that the peeper insertion does not greatly alter geochemical conditions that affect freely-dissolved inorganics. Additionally, it is assumed that the peeper water equilibrates with freely-dissolved inorganics in sediment in such a way that the concentration of inorganics in the peeper water would be equal to that of the concentration of inorganics in the sediment porewater.

After retrieval, the peepers are brought to the surface and usually preserved until they can be processed. This can be achieved by storing the peepers inside a sealable, airtight bag with either inert gas or oxygen absorbing packets[2]. The peeper water can then be processed by quickly pipetting it into an appropriate sample bottle which usually contains a preservative (e.g., nitric acid for metals). This step is generally conducted in the field. Samples are stored on ice to maintain a temperature of less than 4°C and shipped to an analytical laboratory. The samples are then analyzed for inorganics by standard methods (i.e., USEPA SW-846). The results obtained from the analytical laboratory are then used directly or assessed using the equations below if a reverse tracer is used because deployment time is insufficient for all analytes to reach equilibrium.

Equilibrium Determination (Tracers)

The equilibration period of peepers can last several weeks and depends on deployment conditions, analyte of interest, and peeper design. In many cases, it is advantageous to use pre-equilibrium methods that can use measurements in peepers deployed for shorter periods to predict concentrations at equilibrium[15].

Although the equilibrium concentration of an analyte in sediment can be evaluated by examining analyte results for peepers deployed for several different amounts of time (i.e., a time series), this is impractical for typical field investigations because it would require several mobilizations to the site to retrieve samplers. Alternately, reverse tracers (referred to as a performance reference compound when used with organic compound passive sampling) can be used to evaluate the percentage of equilibrium reached by a passive sampler.

Thomas and Arthur[12] studied the use of a reverse tracer to estimate percent equilibrium in lab experiments and a field application. They concluded that bromide can be used to estimate concentrations in porewater using measurements obtained before equilibrium is reached. Further studies were also conducted by Risacher et al.[2] showed that lithium can also be used as a tracer for brackish and saline environments. Both studies included a mathematical model for estimating concentrations of ions in external media (C0) based on measured concentrations in the peeper chamber (Cp,t), the elimination rate of the target analyte (K) and the deployment time (t):

Equation 1:      Equation1r.png
Where:
C0 is the freely dissolved concentration of the analyte in the sediment (mg/L or μg/L), sometimes referred to as Cfree
Cp,t is the measured concentration of the analyte in the peeper at time of retrieval (mg/L or μg/L)
K is the elimination rate of the target analyte
t is the deployment time (days)

The elimination rate of the target analyte (K) is calculated using Equation 2:

Equation 2:      Equation2r.png
Where:
K is the elimination rate of the target analyte
Ktracer is the elimination rate of the tracer
D is the free water diffusivity of the analyte (cm2/s)
Dtracer is the free water diffusivity of the tracer (cm2/s)

The elimination rate of the tracer (Ktracer) is calculated using Equation 3:

Equation 3:          Equation3r2.png
Where:
Ktracer is the elimination rate of the tracer
Ctracer,i is the measured initial concentration of the tracer in the peeper prior to deployment (mg/L or μg/L)
Ctracer,t is the measured final concentration of the tracer in the peeper at time of retrieval (mg/L or μg/L)
t is the deployment time (days)

Using this set of equations allows the calculation of the porewater concentration of the analyte prior to its equilibrium with the peeper water. A template for these calculations can be found in the appendix of Risacher et al.[2].

Using Peeper Data at a Sediment Site

Peeper data can be used to enable site specific decision making in a variety of ways. Some of the most common uses for peepers and peeper data are discussed below.

Nature and Extent: Multiple peepers deployed in sediment can help delineate areas of increased metal availability. Peepers are especially helpful for sites that are comprised of coarse, relatively inert materials that may not be conducive to traditional bulk sediment sampling. Because much of the inorganics present in these types of sediments may be associated with the porewater phase rather than the solid phase, peepers can provide a more representative measurement of C0. Additionally, at sites where tidal pumping or groundwater flux may be influencing the nature and extent of inorganics, peepers can provide a distinct advantage to bulk sediment sampling or other point-in-time measurements, as peepers can provide an average measurement that integrates the variability in the hydrodynamic and chemical conditions over time.

Sources and Fate: A considerable advantage to using peepers is that C0 results are expressed as concentration in units of mass per volume (e.g., mg/L), providing a common unit of measurement to compare across multiple media. For example, synchronous measurements of C0 using peepers deployed in both surface water and sediment can elucidate the potential flux of inorganics from sediment to surface water. Paired measurements of both C0 and bulk metals in sediment can also allow site specific sediment-porewater partition coefficients to be calculated. These values can be useful in understanding and predicting contaminant fate, especially in situations where the potential dissolution of metals from sediment are critical to predict, such as when sediment is dredged.

Direct Toxicity to Aquatic Life: Peepers are frequently used to understand the potential direct toxicity to aquatic life, such as benthic invertebrates and fish. A C0 measurement obtained from a peeper deployed in sediment (in situ) or surface water (ex situ), can be compared to toxicological benchmarks for aquatic life to understand the potential toxicity to aquatic life and to set remediation goals[15]. C0 measurements can also be incorporated in more sophisticated approaches, such as the Biotic Ligand Model[16] to understand the potential for toxicity or the need to conduct toxicological testing or ecological evaluations.

Bioaccumulation of Inorganics by Aquatic Life: Peepers can also be used to understand site specific relationship between C0 and concentrations of inorganics in aquatic life. For example, measuring C0 in sediment from which organisms are collected and analyzed can enable the estimation of a site-specific uptake factor. This C0-to-organism uptake factor (or model) can then be applied for a variety of uses, including predicting the concentration of inorganics in other organisms, or estimating a sediment C0 value that would be safe for consumption by wildlife or humans. Because several decades of research have found that the correlation between C0 measurements and bioavailability is usually better than the correlation between measurements of chemicals in bulk sediment and bioavailability, C0-to-organism uptake factors are likely to be more accurate than uptake factors based on bulk sediment testing.

Evaluating Sediment Remediation Efficacy: Passive sampling has been used widely to evaluate the efficacy of remedial actions such as active amendments, thin layer placements, and capping to reduce the availability of contaminants at sediment sites. A particularly powerful approach is to compare baseline (pre-remedy) C0 in sediment to C0 in sediment after the sediment remedy has been applied. Peepers can be used in this context for inorganics, allowing the sediment remedy’s success to be evaluated and monitored in laboratory benchtop remedy evaluations, pilot scale remedy evaluations, and full-scale remediation monitoring.

References

  1. ^ Risacher, F.F., Schneider, H., Drygiannaki, I., Conder, J., Pautler, B.G., and Jackson, A.W., 2023. A Review of Peeper Passive Sampling Approaches to Measure the Availability of Inorganics in Sediment Porewater. Environmental Pollution, 328, Article 121581. doi: 10.1016/j.envpol.2023.121581   Open Access Manuscript
  2. ^ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Risacher, F.F., Nichols, E., Schneider, H., Lawrence, M., Conder, J., Sweett, A., Pautler, B.G., Jackson, W.A., Rosen, G., 2023b. Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern, ESTCP ER20-5261. Project Website   Report.pdf
  3. ^ Conder, J.M., Fuchsman, P.C., Grover, M.M., Magar, V.S., Henning, M.H., 2015. Critical review of mercury SQVs for the protection of benthic invertebrates. Environmental Toxicology and Chemistry, 34(1), pp. 6-21. doi: 10.1002/etc.2769   Open Access Article
  4. ^ 4.0 4.1 Cleveland, D., Brumbaugh, W.G., MacDonald, D.D., 2017. A comparison of four porewater sampling methods for metal mixtures and dissolved organic carbon and the implications for sediment toxicity evaluations. Environmental Toxicology and Chemistry, 36(11), pp. 2906-2915. doi: 10.1002/etc.3884
  5. ^ 5.0 5.1 Gruzalski, J.G., Markwiese, J.T., Carriker, N.E., Rogers, W.J., Vitale, R.J., Thal, D.I., 2016. Pore Water Collection, Analysis and Evolution: The Need for Standardization. In: Reviews of Environmental Contamination and Toxicology, Vol. 237, pp. 37–51. Springer. doi: 10.1007/978-3-319-23573-8_2
  6. ^ Peijnenburg, W.J.G.M., Teasdale, P.R., Reible, D., Mondon, J., Bennett, W.W., Campbell, P.G.C., 2014. Passive Sampling Methods for Contaminated Sediments: State of the Science for Metals. Integrated Environmental Assessment and Management, 10(2), pp. 179–196. doi: 10.1002/ieam.1502   Open Access Article
  7. ^ 7.0 7.1 Teasdale, P.R., Batley, G.E., Apte, S.C., Webster, I.T., 1995. Pore water sampling with sediment peepers. Trends in Analytical Chemistry, 14(6), pp. 250–256. doi: 10.1016/0165-9936(95)91617-2
  8. ^ Schroeder, H., Duester, L., Fabricius, A.L., Ecker, D., Breitung, V., Ternes, T.A., 2020. Sediment water (interface) mobility of metal(loid)s and nutrients under undisturbed conditions and during resuspension. Journal of Hazardous Materials, 394, Article 122543. doi: 10.1016/j.jhazmat.2020.122543   Open Access Article
  9. ^ Wise, D.E., 2009. Sampling techniques for sediment pore water in evaluation of reactive capping efficacy. Master of Science Thesis. University of New Hampshire Scholars’ Repository. 178 pages. Website   Report.pdf
  10. ^ 10.0 10.1 10.2 Hesslein, R.H., 1976. An in situ sampler for close interval pore water studies. Limnology and Oceanography, 21(6), pp. 912-914. doi: 10.4319/lo.1976.21.6.0912   Open Access Article
  11. ^ Serbst, J.R., Burgess, R.M., Kuhn, A., Edwards, P.A., Cantwell, M.G., Pelletier, M.C., Berry, W.J., 2003. Precision of dialysis (peeper) sampling of cadmium in marine sediment interstitial water. Archives of Environmental Contamination and Toxicology, 45(3), pp. 297–305. doi: 10.1007/s00244-003-0114-5
  12. ^ 12.0 12.1 Thomas, B., Arthur, M.A., 2010. Correcting porewater concentration measurements from peepers: Application of a reverse tracer. Limnology and Oceanography: Methods, 8(8), pp. 403–413. doi: 10.4319/lom.2010.8.403   Open Access Article
  13. ^ Passeport, E., Landis, R., Lacrampe-Couloume, G., Lutz, E.J., Erin Mack, E., West, K., Morgan, S., Lollar, B.S., 2016. Sediment Monitored Natural Recovery Evidenced by Compound Specific Isotope Analysis and High-Resolution Pore Water Sampling. Environmental Science and Technology, 50(22), pp. 12197–12204. doi: 10.1021/acs.est.6b02961
  14. ^ Carignan, R., St‐Pierre, S., Gachter, R., 1994. Use of diffusion samplers in oligotrophic lake sediments: Effects of free oxygen in sampler material. Limnology and Oceanography, 39(2), pp. 468-474. doi: 10.4319/lo.1994.39.2.0468   Open Access Article
  15. ^ 15.0 15.1 USEPA, 2017. Laboratory, Field, and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual. EPA/600/R-16/357.   Report.pdf
  16. ^ Santore, C.R., Toll, E.J., DeForest, K.D., Croteau, K., Baldwin, A., Bergquist, B., McPeek, K., Tobiason, K., and Judd, L.N., 2022. Refining our understanding of metal bioavailability in sediments using information from porewater: Application of a multi-metal BLM as an extension of the Equilibrium Partitioning Sediment Benchmarks. Integrated Environmental Assessment and Management, 18(5), pp. 1335–1347. doi: 10.1002/ieam.4572

See Also

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