Geospatial Profiling and Environmental Risk Analysis of Cadmium and Lead Dispersion in Dry Zone Soils and Sediments of Sri Lanka.

Abstract

This study delves into the contamination, spatial dispersion, and geoaccumulation of Cadmium (Cd) and Lead (Pb) in soils and reservoir sediments within Sri Lanka’s dry zone, emphasizing their environmental and public health ramifications, particularly in CKDu-endemic areas. Elevated concentrations of Cd and Pb in soils from Girandurukotte (GK), Kusumpokuna (KP), and Horowpathana (HP) originate from anthropogenic inputs, including intensive agriculture. The spatial distribution coupled with spatial autocorrelation (Moran’s Index values) of Cd (GK = -0.044, KP = -0.074, HP = -0.035) and Pb (GK = 0.197, KP = .181, HP = .314) in soils and sediments reflects mainly diffuse and clustered contamination patterns driven by agricultural runoff, irrigation practices, and geogenic sources. Cd showed considerable to very high contamination across sites, with Cf values ranging from 4.22 to 6.46, while Pb remained low to moderate (Cf: 0.23–2.01). The ecological risk was driven primarily by Cd, with Er values up to 193.8, resulting in PERI scores of 203.85 (HP), 169.50 (KP), and 132.75 (GK). These results highlight Cd as the dominant ecological concern in the study area. Irrigation networks facilitating the transport of Cd and Pb into reservoirs like Ulhitiya, Diwulankadawala, and Wahalkada, where sediment Igeo values indicate significant anthropogenic enrichment and demonstrated Cd concentrations exceeding sediment quality guidelines, such as LEL, CB-TEC, ERL, and SEPA. Cd, existing primarily as Cd2 +, demonstrates high mobility under slightly acidic conditions, forming soluble complexes and precipitating in reducing environments. Conversely, Pb exhibits reduced bioavailability due to its strong affinity for adsorption onto clay minerals, Fe-Mn oxides, and its precipitation as pyromorphite. Reservoir sediments, enriched with fine silts and clays, act as sinks for metal-laden runoff, while arid environmental conditions and cyclic irrigation-induced redox fluctuations further modulate metal speciation, mobility, and ecological risks, necessitating integrated soil and water management interventions.