Heavy metals in surface waters of Laguna de Bay, Philippines: current levels and trends

Laguna de Bay is the largest multipurpose lake in the Philippines. Of the primary uses, fish cultivation and potable water production depend mainly on its water quality. Over the years, this tropical lake has been inundated with pollution from agricultural, industrial and domestic wastewaters. While new contaminants have emerged, traditional contaminants including heavy metals continue to threaten the lake’s resources. In this study, the levels and distribution of heavy metals in Laguna de Bay were investigated. Surface water samples from nine sampling sites were analyzed for As, Pb, Cd, Cr, Cu, Co, Ni, and Mn by ICP-MS and Hg by cold-vapor AAS. These heavy metals are variably dispersed across the lake and the mean concentrations were from below detection limits to 110.7 µg/L. Except for As and Mn, the levels are within the national standards for surface waters. In the south side of the lake near hot springs, As was found in relatively high concentrations up to 116.2 µg/L. The findings of this study on the present-day levels of heavy metals in Laguna de Bay are useful in assessing and sustaining the pollution prevention strategies in this valuable aquatic system that provides natural resources and ecosystem services.