The teratogenicity and embryotoxicity of the herbicide monosodium methanearsonate (MSMA) to early embryos of Xenopus laevis has been studied. The 96-hour LC50 (concentration that causes 50% lethality) and EC50 (concentration that causes 50% survivors to be abnormal) values for embryos are 225 and 46 mg/liter, respectively. This is in contrast to adult 96-h LC50, which is 1,132 mg/liter. Sublethal effects on early embryos include stunted development and malformations. The severity of these effects is directly dependent upon concentration, length of exposure, and time of initial exposure. Major malformations include optic and musculature defects.
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