Assessment of Heavy Metal Contamination in Surface Water and Associated Health Risks

https://doi.org/10.5281/zenodo.19974131

Abstract

Background: Surface water contamination by heavy metals has become a major environmental and public health concern due to their persistence, toxicity, and bioaccumulative nature.

Objective: To assess the level of heavy metal contamination in surface water and evaluate the associated health risks.

Methodology: This was a cross-sectional analytical study conducted from April 2025 to October 2025. A total of 65 surface water samples were collected using non-probability purposive sampling from rivers, lakes, and reservoirs near industrial, agricultural, and urban areas of Karachi. Samples were analyzed for lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) using atomic absorption spectrophotometry.

Results: The mean concentrations of Pb, Cd, As, Hg, and Cr were 0.048 ± 0.021 mg/L, 0.012 ± 0.006 mg/L, 0.031 ± 0.014 mg/L, 0.006 ± 0.003 mg/L, and 0.057 ± 0.025 mg/L, respectively. Concentrations exceeding permissible limits were observed in 58.5% (n=38) for Pb, 36.9% (n=24) for Cd, 44.6% (n=29) for As, 26.2% (n=17) for Hg, and 61.5% (n=40) for Cr. Pollution index analysis showed that 52.3% (n=34) of samples were moderately polluted and 30.8% (n=20) were highly polluted. Health risk assessment indicated that HQ values exceeded 1 for Pb in 49.2% (n=32) and for Cr in 53.8% (n=35) of samples, while the hazard index exceeded 1 in 46.2% (n=30) of cases.

Conclusion: Surface water in the study area is significantly contaminated with heavy metals, posing considerable health risks.