The effects of mercuric chloride and methylmercuric chloride on the developmental biology of the estuarine teleost Fundulus heteroclitus (Walbaum)

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1979

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Embryos of the estuarine teleost, Fundulus heteroclitus, were exposed to Hg^(++) as mercuric chloride (MC) and methylmercuric chloride (MMC) under seven different exposure conditions. Four-to-eight cell stage embryos (0-day old) were exposed to four distinct treatment regimes (continuous, 5, 2, and 1 day of exposure) while mid-blastula (1-day old), midneurula (2-day old) and well-pigmented, beating heart (5-day old) stage embryos were exposed continuously to Hg^(++) concentrations derived from two test compounds. Several different embryonic responses were measured to assess and compare the embryotoxic nature of the two mercury compounds. Significant increases in adverse developmental features were typically effected at concentrations ranging from 60 - 100 ppb Hg^(++) and 40 - 100 ppb Hg^(++) as MC and MMC, respectively. As determined for mortality during the first 4 days of exposure, 4-8 cell stage embryos proved to be the most vulnerable life history stage examined. The 96-hour LC50 for 4-8 cell stage embryos exposed acutely to MC showed that this stage is 3 - 30x more sensitive than adults Delaying the initiation of continuous exposure for 1, 2 and 5 days showed that embryonic tolerance, as measured by 4-day mortality, increases with developmental advancement. Four-to-eight cell stage embryos exposed for only 1 day and 5-day old embryos exposed continuously to mercury exhibited a decrease in the adverse long-term effects of mercury on the developmental success of this species. In general, increases in adverse morphological responses (anomalous development, hatching success, viability of hatch and embryonic growth) resulted flowing exposure to increasing Hg^(++) concentrations, increasing exposure duration and by initiating continuous exposure to earlier developmental stage. In most instances, methylmercuric chloride resulted in more adverse effects than mercuric chloride. By decreasing the severity of the exposure conditions to both compounds, embryos exposed to MC responded more positively (increased survival potential) than embryos exposed to MMC...

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