Bioaccumulation of organochlorine pesticides in frogs of the Rana esculenta complex in central Italy

Concentrations of commonly used organochlorine pesticides (OCPs) were determined in tissues of 23 adult and 24 larval water frogs of two coexisting species (Rana lessonae and the hemiclonal hybrid R. esculenta) and in the water of their breeding pond in an agricultural zone in Umbria, central Italy, where increased occurrence of infectious diseases and distinctly oversized tadpoles were recently observed. The concentrations of OCP in tissues of both species were lower than those in the water of their breeding pond, except for DDT, which was more concentrated in adult frogs than in pond water (bioaccumulation factor 7 for R. lessonae, 15 for R. esculenta). Total OCP concentration and adult body weight were positively correlated for both species, which is consistent with bioaccumulation. In accord, adults contained higher OCP concentrations than tadpoles. Oversized tadpoles had higher OCP concentrations than normal tadpoles. Mean OCP concentrations in individual organs were about an order of magnitude higher than those in whole-frog homogenates. They were highest in brain, higher in ventral than in dorsal skin, and moderately high in ovaries; transmission of bioaccumulation loads to the next generation is therefore possible. The observed OCP concentrations appear too low to directly cause mortality in water frogs, but effects of cumulative exposure to low-level pollutants and their synergistic interactions with the effects of other natural and anthropogenic environmental stressors are unknown.