Bioaccumulation of Total and Monomethylmercury in Earthworms and the Ecological Risk to Birds and Mammals at the Northeast Test Hut, Graces Quarters, Aberdeen Proving Ground, Maryland

Mercury-contaminated soils were found at the Northeast Test Hut, Graces Quarters, Aberdeen Proving Ground, Maryland, which contain concentrations of total mercury (T-Hg) that ranged from approx. 0.1 up to approx. 15 mg/kg dry weight. The current study was initiated to 1) determine the bioaccumulation factors (BAFs) for monomethylmercuy (MMHg) (most toxic form of mercury) in earthworms and 2) use the site-specific derived BAFs to assess the ecological risks to the American robin and short-tailed shrew which feed on earthworms exposed to MMHg. The BAFs for MMHg were 179, 184, 232, and 260 for earthworms exposed to high, intermediate, low, and reference soil containing 0.00735, 0.00256, 0.00148, and 0.00112 mg MMHg/kg dry weight soil, respectively. The environmental effects quotients (EEQs) for robins from the ingestion of MMHg in earthworms and all surface soils were <1 when earthworms comprised 22% of a robin's diet. The EEQs were >1 from the ingestion of MMHg and the high- and intermediate-contaminated soils when earthworms comprised 100% of the robin's diet.