Distribution of nephrotoxic trace elements (As, Cd and Pd) in rice paddy soils of Sri Lanka and their association with chronic kidney diseases of unknown etiology

Chronic kidney disease of unknown etiology (CKDu) has become a major public health issue in Sri Lanka’s North Central Province, one of five Asian regions with frequent CKDu reports. This study tested two hypotheses: (i) that concentrations of exchangeable toxic trace elements-arsenic (As), cadmium (Cd), and lead (Pb)- are higher in lowland paddy soils of CKDu-affected areas compared to unaffected zones, and (ii) that CKDu prevalence is associated with the distribution of soil orders in Sri Lanka. A total of 9,270 topsoil samples (0–15 cm) were collected from rice fields in all 25 districts using a stratified random sampling method, covering both CKDu-affected and non-affected regions. Classification of these zones was based on CKDu intensity as defined by Ranasinghe et al. (2019). Exchangeable As, Cd, and Pb were extracted using 0.01 M CaCl₂ and quantified via inductively coupled plasma mass spectrometry (ICP-MS). Soil pH and electrical conductivity (EC) were analyzed using a 1:5 soil-to-water ratio. Statistical analyses were conducted to compare exchangeable trace element levels, pH, and EC between areas with different CKDu intensities. Results showed no significant differences (P > 0.05) in exchangeable As and Cd concentrations between affected and unaffected regions, while Pb levels were significantly higher (P < 0.05) in non-CKDu areas. Additionally, CKDu prevalence was higher in Alfisol-dominant regions, and lowest in areas dominated by Inceptisols, Entisols, Histosols, Ultisols, and Vertisols. These findings indicate no direct association between CKDu and exchangeable As, Cd, or Pb, suggesting other environmental or anthropogenic factors may play a role.