Residue loads in amphibians used as biomarkers of pesticide levels entering food chains in sub‐Saharan Africa

Abstract

Residues accumulate rapidly in amphibians to reach lethal levels. During previous years in Zimbabwe, total DDT residues from general agricultural contamination were at 3.90 ppm wet weight in Bufo gutturalis and 1.50 ppm in Ptychadena anchietae. Dieldrin residues in the Tomopterna cryptotis downstream of heavy pesticide spillage in Somaliland were up to 0.135 ppm (geometric mean 0.035 ppm), with ß‐HCH up to 0.43 ppm and total DDT up to 0.08 ppm. Dieldrin was within the 0.02–0.20 ppm range. At these levels, it should present no hazard to vertebrate predators ingesting amphibian prey. After the fifth and final application of the non‐persistent insecticide, endosulfan (14.0–23.8 g ha^‐1 at 11–14‐day intervals), against tsetse flies (vectors of trypanosomiasis in cattle) in Zimbabwe, residues were at 0.14–0.57 ppm in P. anchietae. Over the 51‐day period of treatment, exponential accumulation to 2.05 ppm in the liver of anuran species was significantly correlated with time. Organochlorine residues accumulated to a geometric mean of 30.88 ppm in corpses of frogs that had been placed experimentally in contact with heavily contaminated soil (3728 ppm), and exceeded the baseline control mean (0.18 ppm) 168‐fold. Amphibian residue loads are biomarkers of the levels of pesticides entering faunal food chains, and thus the environment of sub‐Saharan Africa generally.