Ecotoxicological analysis and health risk assessment of heavy metal-contaminated urban soils in the City of Manila, Philippines

Abstract

The City of Manila, Philippines has undergone rapid urbanization and industrialization in recent years. This has resulted in the unabated accumulation of heavy metals in urban soils that could pose health risks to the general population. To determine the current levels of heavy metal and the associated health risks and ecotoxicological relevance, forty-five (45) soil samples were collected in different areas within the city of Manila including a park, hospital zone, commercial district, poor urban settlement, and former dumpsite. The levels of Cu, Cr, Pb, Zn, Cd, Ni, Hg, and As were determined using X-Ray fluorescence spectrometry (XRF), while organic matter and pH levels were determined using standard methods. The degree of pollution across sites was determined using pollution indices while health risk was assessed by calculating the hazard quotient and carcinogenic health risk values for each heavy metal. Ecotoxicological relevance was determined using the Caenorhabditis elegans nematode assay. The results indicated that the soils in the former Smokey mountain contained statistically higher levels of heavy metals compared to the other areas. Moreover, correlations were observed between pH and Ni, As, and Pb, and between organic matter and Ni, Cr, Cu, Zn, Hg, and Pb. The overall pollution as revealed by the Nemerow Integrated Pollution Index (NIPI), showed that all areas have high levels of pollution. Significant Hazard Index values, through the dermal pathway, were found in all areas for both children and adults. The total carcinogenic Risk value of all areas were much higher than the acceptable values set by the US Environmental Protection Agency. For Caenorhabditis elegans test, all the nematodes died after 72 hours except those in the control and exposed in the soil collected from Baseco, which unexpectedly exhibited a positive population growth. Overall, the study showed that currently, there are high levels of heavy metals in the sampled urban soils from selected sites in the City of Manila and such levels pose significant ecotoxicological and health hazards to the tested organism and the general public.