The report suggests that groundskeepers, landscape maintenance workers and farmers have an even stronger incentive to limit pesticide use and pursue advanced integrated pest management practices. The study by Prof. Tyrone Hayes?EUR??,,????'??? team found that the problem may be the mixture of pesticides?EUR??,,????'??+even though individual levels are far below federal limits.

To provide a vivid example, Hayes said that residual pesticides contained in the urine of one farm worker could effectively castrate 720,000 frogs?EUR??,,????'??+even though the pesticides are extremely diluted.

The Berkeley scientists tested four herbicides, three insecticides and two fungicides in combination. Each was administered to tadpoles at 0.1 part per billion ?EUR??,,????'??+ amounts commonly found in waters near farms but thousands of times lower than the doses in most pesticide experiments.

Frogs exposed to a mix of pesticides at extremely low concentrations like those found around farms suffer deadly infections, suggesting that the chemicals could be a major culprit in the global disappearance of amphibians, the researchers reported.

The frogs developed an array of health problems, including meningitis, because the chemicals suppressed their immune systems. They also took longer to complete the transformation from tadpole to frog, which reduces their chances of survival.

At least one-third of amphibians worldwide, or 1,856 of the known species of frogs, toads, salamanders and caecilians, are in danger of extinction, according to an international group of conservation biologists.