Long-Term Effects of Methylmercuric Chloride on Three Generations of Brook Trout (Salvelinus fontinalis): Toxicity, Accumulation, Distribution, and Elimination
During a 144-wk period three generations of brook trout (Salvelinus fontinalis) were continuously exposed to mean water concentrations of methylmercuric chloride (MMC) of 2.93, 0.93, 0.29, 0.09, 0.03, and 3) and a pH of 7.5 fell between 0.93 and 0.29 μg Hg/liter. The mean 96-h LC50 for yearling (200 g) and 20-wk-old (12 g) juvenile brook trout exposed to MMC was 75.0 μg Hg/liter, and the application factor (MATC/96-h LC50) lies between 0.004 and 0.013. The accumulation rate of mercury by eight selected tissues of first-generation trout exposed to MMC was relatively rapid at all MMC concentrations tested. The 2-wk tissue Hg: water Hg concentration factors ranged from 1 × 103 to 12 × 103, depending on the tissue, whereas after 28–38 wk of exposure the maximum tissue Hg: water Hg concentration factors for both first- and second-generation trout ranged from 6.9 × 103 to 6.3 × 104. The blood, spleen, and kidney accumulated mercury most rapidly and contained the highest residues in both first- and second-generation trout followed by liver, gill, brain, gonad, and muscle in order of decreasing mercury residues. There was no significant elimination of mercury from the tissue of first- or second-generation fish, yet a "steady state" (micrograms mercury per gram = constant) was reached in all tissues after 20–28 wk of continuous water exposure. Monomethylmercury made up 90–95% of the total mercury present in muscle, the only tissue analyzed for this compound. Mean muscle residues in first-generation trout, dying after 16–28 wk of exposure to 2.93 μg Hg/liter and in second-generation trout, dying after 64–100 wk of exposure to 0.93 μg Hg/liter, were 23.5 and 9.5 μg Hg/g, respectively.