Mercury bioaccumulation in aquatic ecosystems of forested streams in Pennsylvania

Mercury (Hg) is a persistent element in the environment that has the ability to accumulate in organisms (e.g., plants, fish) and to biomagnify across trophic levels of food chains, with potentially harmful effects for human health and ecosystems. In this study, Hg was characterized in aquatic ecosystems of 36 streams across Pennsylvania. The streams are located in predominantly forested watersheds, within varying climatic and physiographic settings. The status of Hg in streams was characterized by sampling several different types of media: stream water, stream bed sediments, and submerged aquatic mosses (Fontinalis spp.) (in all 36 streams), and tissues of brook trout (Salvelinus fontinalis) (in seven of the streams).;Detectable levels of Hg were found in all media sampled, and concentrations of mercury increased among compartments (stream water<< stream sediments < brook trout < aquatic mosses). Concentrations of Hg in media were generally low and did not exceed guidelines for human consumption . Stream water samples from all 36 streams were lower than the safe drinking water maximum contaminant level for Hg of 0.002 mg/L Hg as set by the US Environmental Protection Agency (USEPA). Further, fish tissues from the 7 streams where brook trout were sampled did not exceed the fish consumption advisory limit of 0.3 mug/g Hg as set by USEPA. However, samples from six streams exceeded wildlife consumption advisory guidelines for Hg concentrations, in varying media. In particular, three streams had Hg concentration levels in brook trout above the US Fish and Wildlife Service fish-eating bird and wildlife advisory of 0.10 mug/g wet weight, one stream had Hg levels in sediment above a Threshold Effect Concentration (TEC) level of 180ng/g, and two streams had Hg in stream water above US Environmental Protection Agency's fish-eating wildlife level of 1.3ng/L.;Using exploratory statistical analyses, wet atmospheric deposition of Hg, watershed elevation, watershed size, percent of watershed forested, quantity and quality of dissolved organic carbon, and percent organic matter in sediments were found to be significantly correlated with Hg concentration in at least one media (p<0.01). Additionally, mercury concentrations in aquatic mosses were found to be highly correlated (Sr = 0.84, p < 0.01) with mercury in biopsies of brook trout muscle tissues, suggesting that aquatic mosses could be used as a proxy for Hg concentration in brook trout. The use of aquatic mosses as indicators of Hg levels in brook trout is a novel finding of great utility because mosses are relatively easy and inexpensive to sample, and no fish need to be sampled, which is particularly important for small populations of brook trout.;A large range of Hg concentrations were observed in all media among streams across the state, reflecting heterogeneity of environmental conditions and regional differences. Importantly, variations of Hg concentrations were also observed within streams, in the multiple samples of sediments and brook trout that were collected in each reach. A statistical analysis of these field replicate samples showed that as sample size increases, variability in the prediction of mean Hg concentration decreases. This finding has implications for policy and management, and recommendations are made about adequate sample sizes with regard to assessing Hg accumulation in aquatic ecosystems.