Risk assessment of heavy metals in the freshwater lake sediments around Eppawala phosphate deposit, Sri Lanka

The Eppawala area in Sri Lanka has an agricultural-based economy. As a result, the recent agricultural intensification could increase the risk of heavy metal contamination in lakes in the area as the main water canal in the area, i.e., Jaya Ganga, flows across these lakes. Therefore, this study focuses on the risk assessment of heavy metals in the freshwater lake sediments in the Eppawala area and the identification of potential sources for heavy metal contamination in the lakes. Nine heavy metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) were investigated in surface sediments (n = 22) of the upstream and downstream lakes of the Eppawala Phosphate Deposit (EPD). The average heavy metal concentrations in the upstream lake sediments were higher than those downstream. Eppawala lake sediments were heavily polluted by As along with moderate to high Cr pollution. However, only As and Cd indicated considerable to moderate ecological risk levels to the local environment. The downstream lake sediments showed lower heavy metal contents compared to those upstream and had negative correlations between heavy metals and P₂O₅ contents. This reveals that the EPD does not contribute to the heavy metal contamination in the Eppawala lake sediments. However, the statistical analysis showed that heavy metals were mostly derived from similar pollution sources. Agrochemicals used in paddy cultivation in the vicinity might be a potential source of heavy metals. This study highlights the importance of implementing remediation to control the heavy metal pollution prevailing in the Eppawala lakes.