DDT exposure of frogs: A case study from Limpopo Province, South Africa.

Amphibians are globally under pressure with environmental contaminants contributing to this. Despite caution aired more than 80 years ago of threats posed to amphibians by DDT spraying for disease vector control, no data have been published on concentrations or effects of DDT contamination in frogs from areas where DDT is actively sprayed to control the insect vectors of malaria. In this study, we sampled fat bodies of Xenopus laevis and Xenopus muelleri naturally occurring in an area where indoor residual spraying of DDT is employed and from adjacent, non-sprayed, areas. ΣDDT concentrations ranged between <LOQ and 280 ng/g ww (wet weight) from the non-sprayed area, and 5.5-910 ng/g ww from the sprayed area, but statistical significance could not be shown. We observed significant asymmetric testicular morphology in frogs from the sprayed area, possibly due to endocrine disruption by compounds such as the DDTs. A previous study from the same area found very high concentrations of DDT in the eggs of the Grey Heron Ardea cinerea. This suggests that the DDT we found in frogs may have contributed to DDT loadings higher in the food web. These findings, combined with other studies from this area, support the need to reduce and eventually move away from DDT in malaria control safely and sustainably.