Nephrotoxic contaminants in drinking water and urine, and chronic kidney disease in rural Sri Lanka

Chronic kidney disease of unknown ("u") cause (CKDu) is a growing public health concern in Sri Lanka. Prior research has hypothesized a link with drinking water quality, but rigorous studies are lacking. This study assesses the relationship between nephrotoxic elements (namely arsenic (As), cadmium (Cd), lead (Pb), and uranium (U)) in drinking water, and urine samples collected from individuals with and/or without CKDu in endemic areas, and from individuals without CKDu in nonendemic areas. All water samples - from a variety of source types (i.e. shallow and deep wells, springs, piped and surface water) - contained extremely low concentrations of nephrotoxic elements, and all were well below drinking water guideline values. Concentrations in individual urine samples were higher than, and uncorrelated with, those measured in drinking water, suggesting potential exposure from other sources. Mean urinary concentrations of these elements for individuals with clinically diagnosed CKDu were consistently lower than individuals without CKDu both in endemic and nonendemic areas. This likely stems from the inability of the kidney to excrete these toxic elements via urine in CKDu patients. Urinary concentrations of individuals were also found to be within the range of reference values measured in urine of healthy unexposed individuals from international biomonitoring studies, though these reference levels may not be safe for the Sri Lankan population. The results suggest that CKDu cannot be clearly linked with the presence of these contaminants in drinking water. There remains a need to investigate potential interactions of low doses of these elements (particularly Cd and As) with other risk factors that appear linked to CKDu, prior to developing public health strategies to address this illness.

Fluoride exposure from groundwater as reflected by urinary fluoride and children's dental fluorosis in the Main Ethiopian Rift Valley

This cross-sectional study explores the relationships between children's F(-) exposure from drinking groundwater and urinary F(-) concentrations, combined with dental fluorosis (DF) in the Main Ethiopian Rift (MER) Valley. We examined the DF prevalence and severity among 491 children (10 to 15 years old) who are life-long residents of 33 rural communities in which groundwater concentrations of F(-) cover a wide range. A subset of 156 children was selected for urinary F(-) measurements. Our results showed that the mean F(-) concentrations in groundwater were 8.5 ± 4.1 mg/L (range: 1.1-18 mg/L), while those in urine were 12.1±7.3 mg/L (range: 1.1-39.8 mg/L). The prevalence of mild, moderate, and severe DF in children's teeth was 17%, 29%, and 45%, respectively, and the majority (90%; n=140) of the children had urinary F(-) concentrations above 3 mg/L. Below this level most of the teeth showed mild forms of DF. The exposure-response relationship between F(-) and DF was positive and non-linear, with DF severity tending to level off above a F(-) threshold of ~6 mg/L, most likely due to the fact that at ~6 mg/L the enamel is damaged as much as it can be clinically observed in most children. We also observed differential prevalence (and severity) of DF and urinary concentration, across children exposed to similar F(-) concentrations in water, which highlights the importance of individual-specific factors in addition to the F(-) levels in drinking water. Finally, we investigated urinary F(-) in children from communities where defluoridation remediation was taking place. The lower F(-) concentration measured in urine of this population demonstrates the capacity of the urinary F(-) method as an effective monitoring and evaluation tool for assessing the outcome of successful F(-) mitigation strategy in relatively short time (months) in areas affected with severe fluorosis.