Using multiple methods to assess heavy metal pollution in an urban city

Heavy metal pollution in urban cities is now an accepted fact. An understanding of the natural and anthropogenic contributions to heavy metal accumulation in these cities is necessary to develop strategies to mitigate their impacts, particularly on human health. Here, we used multiple records using geological and biological pollution indicators to assess the extent of pollution in the Colombo Metropolitan Region (CMR), Sri Lanka. Elemental concentrations of Cu, Zn, Ni and Pb were determined in four depositories: surface soil (90 samples), canal sediments and canal water (45 samples each) and vegetation (62 samples). These were mapped using GIS overlapping the road network to identify hotspots of heavy metals. While the surface soil, canal sediments and leaves of trees had higher and different amounts than background levels of heavy metals, canal water had low levels. Our results suggest that anthropogenic activities are the major source of heavy metals in an urban city, and unique natural factors, such as coastal conditions, terrain morphology and climate, combine and influence the distribution of these metals. We discuss the possible remediation of metal pollution and the necessity of a holistic multi-proxy approach to understand urban heavy metal contamination in a rapidly populating area.