Influence of a chlor-alkali superfund site on mercury bioaccumulation in periphyton and low-trophic level fauna.

In Berlin, New Hampshire, USA, the Androscoggin River flows adjacent to a former chlor-alkali facility that is a US Environmental Protection Agency Superfund site and source of mercury (Hg) to the river. The present study was conducted to determine the fate and bioaccumulation of methylmercury (MeHg) to lower trophic-level taxa in the river. Surface sediment directly adjacent to the source showed significantly elevated MeHg (10-40× increase, mean ± standard deviation [SD]: 20.1 ± 24.8 ng g(-1) dry wt) and total mercury (THg; 10-30× increase, mean ± SD: 2045 ± 2669 ng g(-1) dry wt) compared with all other reaches, with sediment THg and MeHg from downstream reaches elevated (3-7× on average) relative to the reference (THg mean ± SD: 33.5 ± 9.33 ng g(-1) dry wt; MeHg mean ± SD: 0.52 ± 0.21 ng g(-1) dry wt). Water column THg concentrations adjacent to the point source for both particulate (0.23 ng L(-1)) and dissolved (0.76 ng L(-1)) fractions were 5-fold higher than at the reference sites, and 2-fold to 5-fold higher than downstream. Methylmercury production potential of periphyton material was highest (2-9 ng g(-1) d(-1) dry wt) adjacent to the Superfund site; other reaches were close to or below reporting limits (0. 1 ng g(-1) d(-1) dry wt). Total Hg and MeHg bioaccumulation in fauna was variable across sites and taxa, with no clear spatial patterns downstream of the contamination source. Crayfish, mayflies, and shiners showed a weak positive relationship with porewater MeHg concentration.