Mercury speciation and bioaccumulation in lotic primary producers and primary consumers

Mercury speciation and bioaccumulation were strongly affected by trophic position and distance from contamination source in this study of lower trophic levels in two eastern Tennessee streams. Methylmercury and inorganic mercury (Hg(II)) were analyzed in samples of periphyton, grazing fish (stonerollers, Campostoma anomalum), and omnivorous fish (striped shiners, Luxilus chysocephalus) taken from three sites in an industrially contaminated stream and one site in a reference stream. Inorganic mercury predominated in periphyton and fish samples from all sites, always exceeding 50% of total mercury. However, the proportion of methylmercury increased significantly with both trophic level and distance downstream. Bioconcentration factors for methylmercury increased 0.5-1.5 log units per trophic level at all sites, implying significant biomagnification of this species. Bioconcentration factors for Hg(II) declined with increasing trophic level at three of the four sites and were 1-2 log units lower than those for methylmercury, providing little evidence of Hg(II) biomagnification. Primary producers and primary consumers are critical intermediaries in the movement and biomagnification of mercury from water to upper trophic levels.