UVB radiation enhances the toxic effects of three organophosphorus insecticides on tadpoles from tropical anurans.

Amphibians are declining around the world as they are particularly sensitive to multiple environmental stressors, among them the increase of UVB radiation and the environmental contaminations of body waters caused by agrochemicals. Because of the limited research on the interaction between agrochemicals and UVB radiation on tropical amphibians, we performed this study to test the hypothesis that the exposure to UVB radiation will enhance the toxic effects of the organophosphorus (OPs) insecticides chlorpyrifos, diazinon and monocrotophos, which are widely used in Colombia, on tadpoles from three tropical anuran species. Under laboratory conditions, we exposed independently tadpoles of Boana xerophylla, Engystomops pustulosus and Rhinella horribilis to each of the three insecticides with the presence of UVB radiation and without UVB, during 96 h toxicity tests. We then examined their effects on tadpole mortality, capacity to swim and total length. We found that UVB enhanced the mortality of insecticides (these treatments had a lower LC₅₀ than those without UVB radiation), increased the tadpole immobility (they were unable to swim), and decreased the total length. Therefore, we validated the prediction that UVB radiation enhances the toxicity of the OPs insecticides studied on our anuran species and consequently may be one of the causal factors of amphibian population declines in the tropical countries. However, we suggest to perform more realistic field studies in areas with agrochemical presence to a better understanding of the effect of these stressors on anurans as there are environmental factors that attenuate underwater UVB radiation and toxicity in aquatic organisms, although it is also known that under field conditions some OPs insecticides become more toxic in the presence of UVB. [ABSTRACT FROM AUTHOR]