title: Net methylmercury production as a basis for improved risk assessment of mercury-contaminated sediments.
abstract: Sediments contaminated by various sources of mercury (Hg) were studied at 8 sites in Sweden covering wide ranges of climate, salinity, and sediment types. At all sites, biota (plankton, sediment living organisms, and fish) showed enhanced concentrations of Hg relative to corresponding organisms at nearby reference sites. The key process determining the risk at these sites is the net transformation of inorganic Hg to the highly toxic and bioavailable methylmercury (MeHg). Accordingly, Hg concentrations in Perca fluviatilis were more strongly correlated to MeHg (p < 0.05) than to inorganic Hg concentrations in the sediments. At all sites, except one, concentrations of inorganic Hg (2-55 microg g(-1)) in sediments were significantly, positively correlated to the concentration of MeHg (4-90 ng g(-1)). The MeHg/Hg ratio (which is assumed to reflect the net production of MeHg normalized to the Hg concentration) varied widely among sites. The highest MeHg/Hg ratios were encountered in loose-fiber sediments situated in southern freshwaters, and the lowest ratios were found in brackish-water sediments and firm, minerogenic sediments at the northernmost freshwater site. This pattern may be explained by an increased MeHg production by methylating bacteria with increasing temperature, availability of energy-rich organic matter (which is correlated with primary production), and availability of neutral Hg sulfides in the sediment pore waters. These factors therefore need to be considered when the risk associated with Hg-contaminated sediments is assessed.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå. ulf.skyllberg@sek.slu.se
authors.forename: Ulf
authors.initials: U
authors.lastname: Skyllberg
authors.forename: Andreas
authors.initials: A
authors.lastname: Drott
authors.forename: Lars
authors.initials: L
authors.lastname: Lambertsson
authors.forename: Erik
authors.initials: E
authors.lastname: Björn
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Karlsson
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Johnson
authors.forename: Sven-Ake
authors.initials: SA
authors.lastname: Heinemo
authors.forename: Henning
authors.initials: H
authors.lastname: Holmström
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000378:metabolism; D002683:Chironomidae / Q000378:metabolism; D002980:Climate; D004784:Environmental Monitoring; D017859:Esocidae / Q000378:metabolism; D019015:Geologic Sediments / Q000032:analysis*; D008628:Mercury / Q000032:analysis* / Q000378:metabolism; D008767:Methylmercury Compounds / Q000032:analysis*; D010471:Perches / Q000378:metabolism; D018570:Risk Assessment; D054712:Salinity; D013548:Sweden; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000378:metabolism; D015048:Zooplankton / Q000378:metabolism
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury