Radial distribution of arsenic and lead contamination from Kerawalapitiya waste dump: Seasonal and pH-dependent variations in waterways of Muthurajawela wetland, Sri Lanka

Abstract

Muthurajawela is the largest wetland in Western Province of Sri Lanka, is characterised as a complex peat-dominated system influenced by natural processes. Heavy metals, such as arsenic and lead, are described as serious environmental and health threats because of their persistence potential for bioaccumulation and toxicities even at trace levels. Seasonal variations in precipitation, temperature, and biological activity generate the dynamic environment that affects the speciation of metals and mechanisms of metal transport. The seasonal variation of arsenic and lead contamination in relation to pH dynamics in a selected area of the Muthurajawela wetland were analysed through water quality measurements. Accordingly, thirty-six (36) water samples were collected from twelve stations at radial distances of 50 m, 100 m, 250 m, 500 m, and 1000 m from the Kerawalapitiya open waste dump site during the dry, wet, and intermediate seasons, revealing significant spatiotemporal heterogeneity in heavy metal concentrations and pH levels in this vital surface water network. This involves developing standard physical and chemical characteristics of surface waters, comparing them with the parameters of the National Ambient Water Quality Standards of Sri Lanka, and identifying significant pollutants that have affected the ecological integrity of the wetland. Additionally, the research aims to develop an advanced contamination audit using critical inspection of matrices of water quality and identify the extent of surface water pollution from direct waste dumping activities. It was shown that arsenic concentrations were found to range from 0.012 to 1.247 mg/L across the seasons, with the highest values being recorded during the dry seasons (mean: 0.35 mg/L). Similarly, lead concentrations were determined to range from 0.0017 to 5.13 mg/L, showing the highest levels noted during intermediate seasons (mean: 1.48 mg/L). The range of pH levels was observed between 5.16 and 12.4, which exhibited an extreme negative correlation with heavy metal solubility. The findings of this research are summarised in this analysis to explore the complex interaction between arsenic and lead contamination, pH regimes, and seasonal variation in the context of the Muthurajawela wetland. The data and analysis of this study reveal that the major contributor to heavy metal contamination of surface waters in the Muthurajawela wetland is the Kerawalapitiya open waste dump site and its discharges.