title: Activated carbon mitigates mercury and methylmercury bioavailability in contaminated sediments.
abstract: There are few available in situ remediation options for Hg contaminated sediments, short of capping. Here we present the first tests of activated carbon and other sorbents as potential in situ amendments for remediation of mercury and methylmercury (MeHg), using a study design that combined 2 L sediment/water microcosms with 14 day bioaccumulation assays. Our key end points were pore water concentrations, and bioaccumulation of total Hg and MeHg by a deposit-feeding oligochaete Lumbriculus variegatus. Four amendments were tested: an activated carbon (AC); CETCO Organoclay MRM (MRM); Thiol-SAMMS (TS), a thiol-functionalized mesoporous silica; and AMBERSEP GT74, an ion-exchange resin. Amendments were tested in four separate microcosm assays using Hg-contaminated sediments from two freshwater and two estuarine sites. AC and TS amendments, added at 2-7% of the dry weight of sediments significantly reduced both MeHg concentrations in pore waters, relative to unamended controls (by 45-95%) and bioaccumulation of MeHg by Lumbriculus (by between 30 and 90%). Both amendments had only small impacts on microcosm surface water, sediment and pore water chemistry, with the exception of significant reductions in pore water dissolved organic matter. The effectiveness of amendments in reducing bioaccumulation was well-correlated with their effectiveness in increasing sediment:water partitioning, especially of MeHg. Sediments with low native sediment:water MeHg partition coefficients were most effectively treated. Thus, in situ sediment sorbent amendments may be able to reduce the risk of biotic Hg and MeHg uptake in contaminated sediments, and subsequent contamination of food webs.
authors.affiliation: Smithsonian Environmental Research Center 647 Contees Wharf Rd., Edgewater, Maryland 21037, United States.
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Gilmour
authors.forename: Georgia S
authors.initials: GS
authors.lastname: Riedel
authors.forename: Gerhardt
authors.initials: G
authors.lastname: Riedel
authors.forename: Seokjoon
authors.initials: S
authors.lastname: Kwon
authors.forename: Richard
authors.initials: R
authors.lastname: Landis
authors.forename: Steven S
authors.initials: SS
authors.lastname: Brown
authors.forename: Charles A
authors.initials: CA
authors.lastname: Menzie
authors.forename: Upal
authors.initials: U
authors.lastname: Ghosh
mesh_terms: D000818:Animals; D001673:Biodegradation, Environmental; D001682:Biological Availability; D002606:Charcoal / Q000737:chemistry*; D063366:Estuaries; D005618:Fresh Water / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D009835:Oligochaeta / Q000378:metabolism; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D008767:Methylmercury Compounds; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D002606:Charcoal; D008628:Mercury