Browsing by Author "Gilmour, Cynthia C."
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Item Development of a Novel Equilibrium Passive Sampling Devicefor Methylmercury in Sediment and Soil Porewaters(Society of Environmental Toxicology and Chemistry, 2019-11-06) Sanders, James P.; McBurney, Alyssa; Gilmour, Cynthia C.; Schwartz, Grace E.; Washburn, Spencer; Driscoll, Susan B. Kane; Brown, Steven S.; Ghosh, UpalWe explored the concept of equilibrium passive sampling for methylmercury (MeHg) using the strategy developedfor hydrophobic organic chemicals. Passive sampling should allow prediction of the concentration of the chemically labilefraction of MeHg in sediment porewaters based on equilibrium partitioning into the sampler, without modeling diffusionrates through the sampler material. Our goals were to identify sampler materials with the potential to mimic MeHg parti-tioning into animals and sediments and provide reversible sorption in a time frame appropriate for in situ samplers. Can-didate materials tested included a range of polymers embedded with suitable sorbents for MeHg. The most promising wereactivated carbon (AC) embedded in agarose, thiol–self‐assembled monolayers on mesoporous supports embedded inagarose, and cysteine‐functionalized polyethylene terephthalate, which yielded log sampler–water partition coefficients of2.8 to 5 for MeHgOH and MeHg complexed with dissolved organic matter (Suwannee River humic acid). Sampler equili-bration time in sediments was approximately 1 to 2 wk. Investigation of the MeHg accumulation mechanism by AC em-bedded in agarose suggested that sampling was kinetically influenced by MeHg interactions with AC particles and notlimited by diffusion through the gel for this material. Also, AC exhibited relatively rapid desorption of Hg and MeHg,indicating that this sorbent is capable of reversible, equilibrium measurements. In sediment:water microcosms, porewaterconcentrations made with isotherm‐calibrated passive samplers agreed within a factor of 2 (unamended sediment) or 4(AC‐amended sediment) with directly measured concentrations. The present study demonstrates a potential new approachto passive sampling of MeHg.Environ Toxicol Chem2020;39:323–334. © 2019 SETACItem Persistent Reductions in the Bioavailability of PCBs at a Tidally Inundated Phragmites australis Marsh Amended with Activated Carbon(Wiley, June 5, 2018) Sanders, James P.; Andrade, Natasha A.; Menzie, Charles A.; Amos, C. Bennett; Gilmour, Cynthia C.; Henry, Elizabeth A.; Brown, Steven S.; Ghosh, UpalIn situ amendment of sediments with highly sorbent materials like activated carbon (AC) is an increasingly viable strategy to reduce the bioavailability of persistent, sediment‐associated contaminants to benthic communities. Because in situ sediment remediation is an emerging strategy, much remains to be learned about the field conditions under which amendments can be effective, the resilience of amendment materials toward extreme weather conditions, and the optimal design of engineered applications. Here we report the results of a multi‐year, pilot‐scale field investigation designed to measure the persistence and efficacy of AC amendments to reduce the bioavailability of polychlorinated biphenyls (PCBs) in an intertidal Phragmites marsh. The amendments tested were granular AC (GAC), GAC with a layer of sand, and a pelletized fine AC. Key metrics presented include vertically‐resolved black carbon concentrations in sediment and PCB concentrations in sediment, porewater, and several invertebrate species. The results demonstrate that all three amendments withstood Hurricane Sandy and remained in place for the duration of the study, successfully reducing porewater PCB concentrations by 34–97%. Reductions in invertebrate bioaccumulation were observed in all amendment scenarios, with pelletized fine AC producing the most pronounced effect. Our findings support the use of engineered AC amendments in intertidal marshes, and can be used to inform amendment design, delivery, and monitoring at other contaminated sediment sites.Item Uptake Mechanisms of a Novel, Activated Carbon-Based Equilibrium Passive Sampler for Estimating Porewater Methylmercury(Wiley, 2022-06-14) Washburn, Spencer J.; Damond, Jada; Sanders, James P.; Gilmour, Cynthia C.; Ghosh, UpalHere we describe the validation of a novel polymeric equilibrium passive sampler comprised of agarose gel with embedded activated carbon particles (ag+AC), to estimate aqueous monomethylmercury (MeHg) concentrations. Sampler behavior was tested using a combination of idealized media and realistic sediment microcosms. Isotherm bottle experiments with ag+AC polymers were conducted to constrain partitioning to these materials by various environmentally relevant species of MeHg bound to dissolved organic matter (MeHgDOM) across a range of sizes and character. Partitioning coefficients ranged from log(Kps) = 1.98±0.09 for MeHg bound to Suwannee River Humic Acid to log(Kps) = 3.15±0.0.52 for MeHg complexed with Upper Mississippi River Natural Organic Matter. Reversible equilibrium exchange of environmentally relevant MeHg species was demonstrated through a series of dual isotope labeled exchange experiments. Isotopically labeled MeHgDOM species approached equilibrium in the samplers over 14 d while mass balance was maintained, providing strong evidence the ag+AC polymer material is capable of equilibrium measurements of environmentally relevant MeHg species within a reasonable deployment time frame. Samplers deployed across the sediment-water interface of sediment microcosms estimated both overlying water and porewater MeHg concentrations within a factor of 2 to 4 of measured values, based on the average measured Kps values for species of MeHg bound to natural organic matter (MeHgNOM) in the isotherm experiments. Taken together, our results indicate that ag+AC polymers, used as equilibrium samplers, can provide accurate MeHg estimations across many site chemistries, with a simple back calculation based on a standardized Kps.