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DEVELOPMENT TOXICITY OF METHOPRENE AND ITS DEGRADATION PRODUCTS IN XENOPUS LAEVIS
Citation:
Degitz, S J., E J. Durhan, P A. Kosian, G T. Ankley, AND J E. Tietge. DEVELOPMENT TOXICITY OF METHOPRENE AND ITS DEGRADATION PRODUCTS IN XENOPUS LAEVIS. Presented at Society of Toxicology National Meeting, San Francisco, CA, March 25-29, 2001.
Description:
Methoprene is an insect growth regulator which is used for the control of mosquitos and other insects. It acts by mimicking natural juvenile hormone, which inhibits pupae from molting and developing to adult stages. Methoprene and methoprene acid have been shown to be transcriptionally-active in a mammalian retinoic X receptor reported cell line, suggesting that they may be active in vertebrates as well. This has led to speculation that methoprene use may have a negative impact on non target vertebrates, including amphibian. Specifically, it has been suggested that methoprene use in the Midwest may be a contributing factor to the recent increase in malformed amphibians found in that region. However, there is little data on the developmental toxicity of methoprene and its degradation products in amphibia. Our objective was to examine the degradation of methoprene in aqueous solution and to assess the developmental toxicity of methoprene and its degradation products (methoprene acid, methoprene epoxide, methoxycitronellal, and methoxycitronellic acid). Xenopus laevis embryos (stage 8) were exposed to the parent compound and the 4 degradation products for 96 hrs. The exposure solutions were changed every 24 hours and chemical concentrations were measured at 8, 8, and 24 hrs. In these experiments methoprene exposure did not result in developmental toxicity at or below water solubility (1.4 ppm). Methoprene acid, a relatively minor degradation product, produced developmental toxicity only when concentrations exceeded 1.25 ppm. Methoprene epoxide and methoxycitronellal produced developmental toxicity at concentrations >1 ppm. Methoxycitronellic acid was the least toxic of the chemicals tested, with no signs of development toxicity at 10 ppm. These data indicate the methoprene and its degradation products are not potent development toxicants to Xenopus laevis. This, in combination with the fact that field applications of sustained-release formulations of methoprene result in methoprene concentrations which do not typically exceed .01 ppm, suggest that there is little evidence for methoprene-mediated developmental toxicity to amphibians.