Heavy Metal Concentration in Neotropical Aquatic Snakes (Helicops Pastazae) and Its Potential as a Bioindicator of Water Pollution

Abstract

The purpose of the present study was to test the potential role of the aquatic snake Helicops pastazae as indicators of water pollution caused by heavy metals. In particular, we tested whether the total heavy metal concentration is related to (1) the position (upstream vs downstream) of the sampling point and its distance from the point where wastewater is discharged; (2) the taxonomic group studied and its place in the trophic chain: piscivorous snakes vs characid fish that co-occur with them; and (3) the organ or tissue examined: snake liver versus muscle. We quantified cadmium (Cd), chromium (Cr) and lead (Pb) by using atomic absorption spectrophotometry with electrothermal atomization. Significant differences were found between some of the sampling points, particularly high metal concentrations were detected upstream at point 1, but no clear spatial pattern was found. There were no significant differences in the concentration of any of the metals between fish and snake muscle, suggesting potential mechanisms of metal excretion in snakes. With regard to interactions, the snake liver had the highest concentrations of cadmium and the muscle of lead and chromium, which may indicate tissue affinity differences for certain metals. Altogether, our results indicate that H. pastazae accumulates contaminants differentially, depending on the tissue and location, which render them useful bioindicators of water contamination.