Distribution and ecological risks of heavy metals in Lake Hussain Sagar, India

Lake contamination by anthropogenic activities has become a serious threat to the aquatic ecosystem due to the presence of a high concentration of toxic heavy metals. In this study, a contaminated Lake Hussain Sagar in India was assessed for toxic heavy metal pollutants at sites associated with industrial discharges and idol immersion activities. The observed high concentration of As, Cd, Pb, Zn, Cu, and Ni in the surface water was due to industrial effluent discharge. About 1.5 times the high concentration of the same elements were observed in surface sediments (0–10 cm) by both industrial discharges and idol immersion activities, compared to deep sediments (0–40 cm) associated only with industrial discharge. The depth-wise variation of heavy metal concentration in surface sediments is due to sorption and settling behavior of suspended solids; whereas in deep sediment, it is due to constant loading of effluents, over a period of time. The sorption capacity of surface sediments is in increasing order as Pb > Cd ≥ Ni ≥ Cr ≥ Zn ≥ Cu, and the desorption revealed that Pb and Cu were retained to a greater extent due to high clay and organic content. By fractionation study, 20–50% of Zn and 50–80% of Cd were associated with exchangeable and carbonate fraction of sediments. By risk assessment code, Zn and Cd are classified under high risk to a very high-risk category, and Cr, Pb, Ni, and Cu are classified under the medium risk category. The enrichment factor value of sediments for Cd (20.42–119.48), Zn (2.19–4.85), Cu (2.02–3.19), and Pb (2.85–7.72) signifies the significant pollution by anthropogenic activities. Therefore, this study evaluates the intensity and distribution of heavy metals in the lake environment for remediation and restoration of the lake ecosystem.