Heavy metal accumulation in lizards living near a phosphate treatment plant: possible transfer of contaminants from aquatic to terrestrial food webs

We investigated the accumulation of heavy metals in Bosk’s fringe-toed lizards (Acanthodactylus boskianus) living in Gabès region (southeastern Tunisia), in relation to habitat, diet, and distance from the Gabès-Ghannouche factory complex of phosphate treatment. More specifically, we compared the concentrations of cadmium, lead, and zinc in the stomach contents and samples of the liver, kidney, and tail from lizards living in four sites corresponding to different combinations of habitat (coastal dunes vs backshore) and distance from the factory complex (<500 vs 20 km). Examination of stomach contents showed that lizards living on the coastal dunes mainly feed on littoral amphipods, while those living in the backshore feed exclusively on terrestrial invertebrates. The concentrations of heavy metals in lizard tissues were overall positively correlated with those in the preys they ingested. Moreover, there was a general tendency towards increased concentrations of cadmium, lead, and zinc in the samples from lizards living on coastal dunes compared to those from the other sites, although some differences still lacked statistical significance. These results suggest that the highest contamination of lizards living on coastal dunes was probably related to the ingestion of contaminated amphipods. Thus, amphipods and Bosk’s fringe-toed lizards seem to provide an important link between the marine and terrestrial food webs, with higher concentrations appearing to accumulate from materials released into the sea rather than the terrestrial environment. With regard to metal distribution among tissues, our results were overall in agreement with previous findings in other reptiles. In particular, cadmium was most concentrated in the liver samples, stressing once more the role of the liver as a storage organ of Cd. Moreover, high concentrations of the three assessed metals were found in the kidney samples, showing the role of the kidney as an active site of heavy metal accumulation.