Japanese Medaka (Oryzias latipes) eggs were treated with 40, 60, and 80 parts per billion (ppb) methylmercuric chloride (MMC) for a period of 10 to 25 days in order to observe gross teratogenic and lethal effects caused by methylmercury during embryogenesis. Over the period tested, 40 ppb-treated embryos were less affected than other treated animals. Embryos treated with 60 ppb MMC showed greater effects in that there was a higher death rate and those which survived ranged considerably in size, degree of gross teratogenic defects, and behavior if development was normal enough for hatching to occur. Most did not hatch during the 25-day test period. Embryos treated with 80 ppb MMC were very abnormal in development, being stunted, poorly pigmented, and they showed various eye defects. None hatched in 25 days. Many did not incorporate the heart into the body. Methylmercuric chloride in trace amounts caused various defects and presents a potential hazard to development of embryos of aquatic vertebrates.
Rana pipiens embryos at the cleavage, blastula, gastrula, and neural-plate stages of development were treated with methylmercuric chloride in concentrations of 0.5-200 parts per billion (ppb) to determine embryocidal and teratogenic effects. Concentrations of 40 ppb and above were lethal to embryos treated during the cleavage stage. Embryos at the blastula, gastrula, and neuralplate stages were treated for 5 days with 5-30 ppb; 5 ppb had only minor effects, 10, 15, and 20 ppb caused various defects (exogastrulae, poor tail development, poor general development) and increased death rates related to exposure time and concentration, and embryos treated with 30 ppb had a high frequency of defects after 24 h and all died by the end of the 3rd day. Individual tolerances to methylmercury of various degrees were observed.
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