Bioaccumulation of organochlorine pesticides in the parasite Cosmocerca sp. (Nematoda: Cosmocercidae) and the amphibian host Amietophrynus regularis (Reuss, 1833) within Lagos metropolis, Nigeria

BACKGROUND: Amphibian species are being threatened worldwide and chemical pollution is one of the leading causes of this decline. The use of agrochemicals such as organochlorine pesticides (OCPs) among the several health and ecological challenges it causes, the sharp amphibian population decline is most pressing. Toad specimens Amietophrynus regularis were sampled from three (3) selected areas; each comprising of natural habitat and dumpsites within Lagos metropolis. METHODS: The congeners of organochlorine pesticides were tested in the liver, intestine, and parasite (Cosmocerca sp.) of the toads and soil samples from the respective locations using gas chromatography-mass spectrometer (GC–MS). Histopathological analyses were conducted on the intestines and liver of the toads using hematoxylin and eosin (H&E) stain and then examined under the binocular dissecting microscope. RESULTS: The concentration of aldrin in the intestine of A. regularis sampled at the dumpsites was higher than the concentrations in the intestines of A. regularis in the natural habitat. The concentrations of dieldrin in the uninfected A. regularis at both dumpsite and natural habitat were higher than the concentrations in the infected A. regularis at both environments. This indicated that the parasite Cosmocerca sp. may have played a depurative role in sequestering the concentration of dieldrin in the toads irrespective of the location. The parasites exhibited marked sequestration capacity characterized by the notably high total bioaccumulation rate both in the liver and the intestine at the dumpsite. The stunted villi being the common histological alteration in the infected and uninfected toads at the dumpsite but missing in the uninfected counterparts at the natural habitat may be attributed to the differences in the background concentration of the OCP congeners. CONCLUSIONS: The parasite- Cosmocerca sp. has been shown to be a potential tool in the biomonitoring of these OCP congeners which persists in the environment. Continuous research on these congeners is a searchlight to checkmate the environment to see how compliant industries and the consumers are in terms of regulation of these chemicals.