Monitoring of bacterial and potentially toxic elements contamination in the Rawal Lake tributaries and filtration plant

Abstract

This study examines bacterial and potentially toxic elements pollution in Jinnah Stream, Nurpur Stream, and Rawal Lake filtration plant during dry and wet seasons; Rawal Lake serves as a key source of water supply for the twin cities of Rawalpindi and Islamabad. Three growth media (Salmonella-Shigella agar, Brilliant Green agar, and Chromo-select agar) were used for microbial plating targeting Escherichia coli, Shigella spp., Salmonella spp., Citrobacter freundii spp., and Klebsiella pneumoniae spp. qPCR Taqman Probe-based assay was used for detection of E. coli (uidA), Salmonella (invA), Campylobacter (glyA), and Shigella (ipaH). Potentially toxic elements concentration was determined by atomic absorption spectrophotometry, Zn and Pb were not detected in any of the sites for either season whereas concentrations of Cd and Cr exceeded the WHO drinking water guidelines (Cd: 0.003 mg/L; Cr: 0.05 mg/L), posing chronic health risk. Shapiro-Wilk test was employed to assess the distribution of data. Kruskal-Wallis H test and Mann-Whitney U test predicted the significance between seasons. Bacterial analysis revealed significant seasonal variability, with higher concentrations of Salmonella spp. and E. coli in the Nurpur Stream during the wet season, while others exhibited spatial variations. No statistically significant differences were observed in concentrations of potentially toxic elements across seasons. qPCR confirmed E. coli detection in both seasons except filtration plant. Interpolation techniques were employed to highlight their spatial distribution. Pollution risk classification maps showed various levels of toxicity at all sampling sites. This study stressed the significance of monitoring and highlighting quality of water for ensuring public health.

Keywords: Microbial analysis; Pollution risk maps; Potentially toxic elements; Rawal Dam tributaries; Water quality; qPCR.