Distribution of five toxic heavy metals in biotic and abiotic constituents of the Negombo Lagoon, Sri Lanka

The presence of toxic metals in water has become a matter of national concern. This situation is potentially more dangerous when it occurs in lagoons and estuaries which are both highly productive and sensitive in comparison to other natural habitats. In this study, the levels of five toxic heavy metals, As, Cd, Cr, Pb and Hg, present in several abiotic and biotic constituents of the Negombo lagoon, Sri Lanka, were investigated with the objective of assessing the potential risks of accumulation. Sampling, in five locations, was conducted from December 2014 to April 2015. Water, sediment, soil, bark and leaves of the mangrove Bruguiera gymnorhiza, and fauna of selected taxa were collected and heavy metals were analyzed using ICP – OES following microwave digestion. Apart from Cr which was detected at low levels, none of the other metals were detected in the water. Nevertheless, the five heavy metals were present in relatively large amounts in one or more of the other tested constituents, indicating lagoon pollution, depicting an overall trend water < leaves < bark < snails < fish < crab < sediment < soil. Our investigation suggests that As and Cd, due to their high levels of accumulation in soil and sediment, impose the highest potential risks. Trends in accumulation suggest non-point sources for Cd, Cr and Pb. Findings reported here call for continual monitoring and for controlling discharge of contaminated effluents into productive lagoon ecosystems.