Potentially Toxic Elements in Sediments of Urban Wetlands of Delhi, India

Wetlands in fast-growing urban spaces are rapidly losing their ecological quality due to incessant pollution and encroachment of catchments. As a primary component of a wetland environment, sediment can be used as a proxy to determine the pollution state of wetlands. In the present study, an attempt has been made to assess the sediment quality of two urban wetlands of Delhi (Sanjay lake and Bhalswa lake) by comparing the observed levels of potentially toxic elements (Cr, Ni, Cu, Zn, Pb, Co and Cd) with recommended quality guidelines and calculating numerous indices such as geo-accumulation index, enrichment factor, modified degree of contamination, pollution load index, potential ecological risk index, etc. Moreover, the surface sediments have been assessed for their potential non-carcinogenic health risk to wetland users. While sediments from both the wetlands generally comply with probable effect levels for all the metals, these show some non-compliance with threshold effect levels for various metals, indicating some occurrence of the harmful effect of metals on aquatic life, though only rarely. Single-metal indices suggest that lead, nickel and cadmium are the most important metals of concern for the sediment environment of the studied wetlands. Sediments from both wetlands show severe anthropogenic metal pollution, medium-low biological toxicity and low to moderate ecological risk. As per the non-carcinogenic health risk assessment, sediments from both lakes show no health risk for adults. However, sediments from BL show significant non-carcinogenic health risks for children. Therefore, immediate steps are required to limit the exposure of children to Bhalswa lake by restricting swimming, fishing and other recreational activities.