Century-old mercury pollution: Evaluating the impacts on local fish from the eastern United States

Abstract

Mercury (Hg) bioaccumulates and exerts toxic effects on freshwater fish upon assimilation into tissues. The Still River, USA, was subjected to severe Hg pollution as a result of the 19th century hat-making industry. Our objective was to determine if the legacy Hg pollution from the hat industry continues to manifest as elevated Hg in the environment (sediment, water, and suspended particulates) and in the muscle and liver of fish from the Still River watershed. Rhinichthys atratulus (Eastern Blacknose Dace), a freshwater fish that display high site fidelity, was chosen as an indicator of total (THg) and methyl (MeHg) mercury bioavailability at four legacy polluted sites, and three reference sites. THg in surface sediments ranged from 134.69 ng/g dw - 1990.00 ng/g dw in legacy Still River sites and from 25.45 ng/g dw – 48.39 ng/g dw in reference sites. Surprisingly, the average levels of THg in fish muscle were significantly lower (p ≤ 0.04) for fish from the majority of legacy sites (0.36 μg/g ww – 0.39 μg/g ww) compared to the majority of reference sites (0.47 μg/g ww – 0.52 μg/g ww). There was no significant difference (p ≥ 0.15) among liver THg concentrations for most sites and there was no significant relationship found (p ≥ 0.09) between either tissue type and any environmental parameters. Our results demonstrate that the presence of legacy Hg pollution does not directly translate into enhanced MeHg accumulation in fish.