Environmental Protection

Agricultural Use of Malathion Contributes to Frog Decline

Environmental Toxicology and Chemistry has published a study showing that malathion used as an agricultural insecticide and pesticide is responsible for interfering with the normal development of pickerel frog embryos, thus leaving them more susceptible to parasite invasion, according to a Jan. 6 press release.

Malathion is present in natural water sources that have been exposed to urban and agricultural runoff. It is the only organophosphate insecticide that may be applied by planes to control mosquito populations, and so it also enters water from the air.

Although direct lethal and sublethal effects of chemical contaminants have been documented, latent and long-term effects have been less well documented. Therefore, researchers sought to fill this knowledge gap and found, as suspected, that tadpole survival rates decreased and malformations and susceptibility to parasite encystment rates increased as a result of exposure to malathion concentrations mimicking those found in actual water sources.

Tadpoles are being exposed to increasing numbers of parasites in waters that are warming as a result of global climate change, and the researchers who performed this study speculate that, as a consequence, those exposed to malathion will have weakened immune systems that render them less able to defend themselves from invasion. Indeed, trematode infection was observed in tadpoles seven weeks after embryonic exposure to low concentrations of malathion.

This study shows that declines in amphibian populations are related to the agricultural application of malathion, which causes various kinds of damage to frog embryos and tadpoles that are, as a consequence, increasingly susceptible to parasite invasion.

To read the entire review, "Effects of Malathion on Embryonic Development and Latent Susceptibility to Trematode Parasites in Ranid Tadpoles" (Vol. 27(12):2496–2500), visit http://www.allenpress.com/pdf/entc_27.12_2496.pdf.

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