Major and trace elements in rice paddy soils in Sri Lanka with special emphasis on regions with endemic chronic kidney disease of undetermined origin

Environmental exposure to trace elements has been widely suspected as an etiological factor for the emergence of chronic kidney disease of undetermined origin (CKDu) that prevails in certain districts of the dry zone areas of Sri Lanka. Contaminated rice can be act as a host for potentially toxic trace elements that ultimately led to health hazards; thus, rice soils were investigated in detail, giving particular attentions to identified CKDu hotspots. A total of 102 rice soil samples were collected from main climatic zones viz. wet and dry zones including CKDu hotspots. In addition to pH, electrical conductivity and cation exchange capacity, acid extracted major and trace element contents in rice soils were determined by using ICP-MS. Significant differences were observed for Mn, Ni, Cu, Zn, and Pb contents between climatic zones. Arsenic and Pb contents in soils were lower than the levels reported in soils from other regions of the world, though significantly higher contents were observed in CKDu regions compared to non-endemic wet zone regions. Calculation of enrichment factor revealed that soils in both dry and wet zones were moderately enriched with As, Cd, and Pb, suggesting an influence of anthropogenic processes. Twenty percent of the wet zone samples showed significant enrichment of Ni, Cu, and Zn. Geo-accumulation index assorted that the studied soil samples were uncontaminated to moderately contaminated, implying that rice soils in both climatic zones are not alarmingly contaminated with toxic trace elements. However, regular and continuous monitoring of rice soil quality is extremely important.