The Nile monitor (Varanus niloticus), an indicator species for pollution in sub-Saharan wetlands
In Africa, metal and pesticide contamination of wetlands is supposed to continue on a permanent basis. However, the ecotoxicological status of these ecosystems remains poorly documented. The aim of the present work is to assess the value of the Nile monitor (Varanus niloticus) as a sentinel species for the environmental contamination of continental wetlands in sub-Saharan Africa. Lead and cadmium on the one hand, and organochlorine and organophosphate pesticides on the other, have been quantified in several tissues by atomic absorption spectrophotometry and gas chromatography, respectively. Samples come from 71 specimens originating from four sites considered unequally contaminated (in Mali and Niger). Although clear differences appear between sites, the environmental contamination turns out to be moderate at the four sites, and does not seem to represent a significant risk neither for the monitors themselves, nor for occasional human consumers. However, the interindividual variability is important. The organotropisms relative to the detected pollutants are consistent with those described in previous studies. Concerning the pesticides, no gender effect has been found, whereas females were more contaminated by metals. The relation between other factors (size, proportion of fat) and tissue concentrations has been considered too. Nile monitors can reveal subtle differences in local pollution and the spatial resolution of this tool seems to be very sharp. Its practical relevance is thus validated. Additionally, an experimental work has been carried out on captive monitors to go into the subject in greater depth