Abstract
The purpose of this study was to test the potential role of the aquatic snake Helicops pastazae as an indicator 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: piscivorous snakes vs characid fish that occupy the same habitats; and (3) the organ or tissue examined: snake liver versus muscle. We used atomic absorption spectrophotometry with electrothermal atomization to quantify cadmium (Cd), chromium (Cr) and lead (Pb) and found significant differences between some of the sampling points, with particularly high metal concentrations detected upstream at point 1. However, we found no clear spatial pattern nor any significant differences in the concentration of any of the metals in fish and snake muscle, suggesting that both species accumulate similar amounts of the sampled elements. With regard to interactions, snake liver had the highest concentrations of Cd, while muscle had the highest concentrations of Pb and Cr, 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 highlights their potential as bioindicators of water contamination. Further research is necessary to understand their role as bioindicators based on extensive sampling and environmental contaminant data.
Highlights
The discharge of domestic or industrial wastewater has severe impacts on communities of aquatic organisms, leading to a decrease in water quality, and potentially affecting public health, fauna and flora
We tested whether the total heavy metal concentration is related to (1) the distance and position of the sampling point with the discharge of wastewater; (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
Snake body mass was inversely correlated with chromium concentrations (Z=-2.411, p = 0.0159, n = 83 samples, correlation coefficient=-0.02995) (Fig. 3c), but not with lead or cadmium
Summary
The discharge of domestic or industrial wastewater has severe impacts on communities of aquatic organisms, leading to a decrease in water quality, and potentially affecting public health, fauna and flora. Heavy metals are natural elements of the earth's crust, which in trace quantities play a positive role on the life of organisms; in very high concentrations, they are usually toxic Because of their high toxicity and difficult transformation, they undergo bioaccumulation processes in aquatic organisms, which negatively affects physiological performance and ecological interactions (Zorrilla 2011). They can be assimilated by phytoplankton and filter organisms and subsequently incorporated into the trophic chain, increasing their concentration as they are ingested by higher trophic organisms (Márquez et al 2008). They can be efficiently absorbed through biological membranes due to their high chemical affinity with the sulfhydryl group (SH) present in proteins (Mancera-Rodríguez and Álvarez-León 2006)
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