Hydrogeochemical factors controlling the occurrence of chronic kidney disease of unknown etiology (CKDu)

Geochemical characterization of groundwater and source apportionment of potential pollutants in a tribal stretch infected with chronic kidney disease of unknown etiology

This paper draws world attention toward a tribal stretch in central India exposed to chronic kidney disease of unknown etiology (CKDu). To date, about 100 people have died and more than 300 hospitalized from a single village, Supebeda, of 1200 inhabitants. The occurrence of CKDu in this part of the world is a recent discovery and its potential pollutants are still eluding human understanding. Since groundwater is being accused as the culprit, this contribution attempts to characterize the area geochemically, study major rock-water interactions, identify potential pollutants, and apportion their sources. Analytical results of 27 groundwater samples reveal that the area suffers from NO3- (0-128.3 mg/L) and F- (0-1.9 mg/L) contamination with total hardness, Ca2+, Mg2+, and Cl- as other violator parameters. Comprehensive Water Quality Index classifies ∼52% of the samples as potable; ∼37% could be suitable for drinking pending certain treatment. While elevated F- concentrations are due to the weathering of fluoride-bearing minerals (fluorite, amphiboles, biotite, hornblende, granite gneiss, etc.), the excess Ca2+ and Mg2+ ions are attributed to 63% of the samples exhibiting cation exchange processes (Ca2+, Mg2+, Cl- < Na+ + K+) resulting from the weathering of carbonate (calcite, dolomite), anhydrite, gypsum, calc-silicate (anorthite, plagioclase, amphiboles) and ferromagnesian (hornblende, biotite) minerals in the metamorphic rocks. About 22% of the samples depict reverse ion exchange processes (Ca2+, Mg2+, Cl- > Na+ + K+) due to silicate weathering including dissolution of Cl- salts (albite and halite minerals) and anthropogenic inputs that also contribute to elevated concentrations of NO3-.

Hydrogeochemical forecasting in a tribal stretch infected with chronic kidney disease of unknown etiology

A tribal stretch in central India has been silently suffering from the enigmatic chronic kidney disease of unknown etiology (CKDu) for the past many years. It drew national attention in 2018 when over a quarter of the population from a single village of 1200 people got hospitalized with at least 100 deaths in a few years' span. This contribution tries to understand the geochemical genesis of the problem and its evolution process through a study of major rock-water interactions. The future hydrogeochemical environment of the area has been forecasted based on saturation indices of several key minerals. Finally, a probabilistic estimation of the population's exposure to the Hofmeister ion series has been made to understand the role of the specific ion effect on the onset of CKDu. Three distinct chemical facies have been identified based on the analytical results of 27 groundwater samples: Ca2+-Mg2+-HCO3- (55.56 %), Ca2+-Mg2+-Cl--SO42- (29.63 %), and Na+-K+-HCO3- (14.81 %). The positive loadings (r) of EC and TDS with Ca2+ (0.89; 0.98), Mg2+ (0.79; 0.89), Na+ (0.78; 0.48), Cl- (0.99; 0.93), and NO3- (0.72; 0.85) have led to groundwater hardness and salinity. Ion exchange processes and saturation indices of the geogenic minerals, such as anhydrite, gypsum, fluorite, halite, and sylvite, play crucial roles in the mineralization process. As these minerals progress toward full saturation, their dissolution with the host aquifers releases more of Ca2+, Na+, K+, SO42-, Cl- and F- ions continually. This exacerbates the fluorosis problem besides increasing salinity and water hardness in the study area. The combined effects of Ca2++Mg2+ ions with a control on the total hardness, increased Na+/Ca2+ ratio, and excess F- ions in groundwater are suspected to be the inducing factors for CKDu. This hypothesis is strongly supported by the occurrence of Hofmeister phenomena in the tubular areas of human kidneys through ingested groundwater.

Quality and sources of food and water consumed by people with chronic kidney disease of unknown etiology in Sri Lanka: a systematic review

BACKGROUND

Prevalence data indicates that chronic kidney disease (CKD) affects approximately 15% of people worldwide, and chronic kidney disease of unknown etiology (CKDu) is highly prevalent in Sri Lanka. Food and water contamination are factors that were suggested as associated with CKDu. This systematic review aimed to summarize evidence on the patterns in quality and sources of food and water consumed by people with CKDu in Sri Lanka.

METHODS

MEDLINE, EMBASE, PsycINFO, and SLJOL databases were searched from inception to August 2024 for studies investigating the quality and sources of food and water consumed by the people with CKDu in Sri Lanka. Studies assessing children below 18 years, pregnant women and dialysis patients were excluded. Studies not specifically investigating CKDu were likewise excluded from the review. Two independent reviewers completed the screening, and the conflicts were resolved by consensus. Extracted data were presented as a narrative summary.

RESULTS

Of 1067 studies, 57 were eligible for the final analysis. Commonly investigated food sources were contaminated with heavy metals, while water sources were contaminated with heavy metals, toxic anions and cations, agrochemicals, fertilizers, herbicides, glyphosate, and aminomethylphosphonic acid (AMPA).

CONCLUSION

Nephrotoxic heavy metals and fluoride contamination alter the quality of food and water, and pose high risks with regard to the kidney function of the people in Sri Lanka. Appropriate strategies to reduce the contamination of heavy metals, agrochemicals, and major ions that afftect the quality of water and food, should be implemented to lower the burden of CKDu in Sri Lanka.

A critical review of a hidden epidemic: examining the occupational and environmental risk factors of chronic kidney disease of unknown etiology (CKDu)

A form of chronic kidney disease has been described in people without any known risk factors. These cases are referred to as chronic kidney disease of an unknown etiology (CKDu).

Geoenvironmental determinants influencing chronic kidney disease of unknown etiology in the dry zone of Sri Lanka: a study based on a cohort of at-risk communities

Chronic kidney disease of unknown origin (CKDu) has emerged as a serious health risk for farming communities in remote semi-arid lowland regions of Sri Lanka, with geoenvironmental factors widely believed to be associated with the etiology. Although numerous case-control studies have been carried out to determine the causes of CKDu, none have been conducted in at-risk communities. The main objective of this study is to identify the potential geo-environmental risk factors associated with the at-risk community in the Wilgamuwa region, a CKDu endemic area in Sri Lanka. The study collected and analyzed 92 water sources currently or previously used in the study area for major cations, anions, and trace elements, mainly As, Cd, Pd, Mn, Zn, Ba and Sr. The major cations and anions in CKDu-susceptible groundwater varied Si4+ > Ca2+ > Na+ > Mg2+ > K+ and HCO3- > Cl- > SO42- > NO3- > F- > PO43- > Br-. The higher average values of Si4+, F- and total hardness (TH) were reported in groundwater consumed by communities at risk of CKDu, with average values (in mg/L) of Si4+-46, F--0.62, and TH-178. Considering the Water Quality Index (WQI) values, 73% of groundwater sources are classified as poor water quality, and the groundwater quality mainly depends on the fluoride distribution in the region. According to the Hazard Quotient (HQ), the risk of adverse health effects from exposure to F- and SiO2 increased in magnitude in the order of male < female < children. Health hazards due to As, Cd and Pb exposure fell between the 'no-risk' and 'low-risk' categories. As outlined in this study, continuous monitoring of vulnerable communities for environmental exposures to key groundwater constituents is important in the dry zone of Sri Lanka.

Intranasal Administration of Sugarcane Ash Causes Chronic Kidney Disease in Rats

Background. Silica nanoparticles found in sugarcane ash have been postulated to be a toxicant contributing to chronic kidney disease of unknown etiology (CKDu). However, while the administration of manufactured silica nanoparticles is known to cause chronic tubulointerstitial disease in rats, the effect of administering sugarcane ash on kidney pathology remains unknown. Here we investigate whether sugarcane ash can induce CKD in rats. Methods. Sugarcane ash was administered for 13 weeks into the nares of rats (5 mg/day for 5d/week), and blood, urine and kidney tissues were collected at 13 weeks (at the end of ash administration) and in a separate group of rats at 24 weeks (11 weeks after stopping ash administration). Kidney histology was evaluated, and inflammation and fibrosis (collagen deposition) measured. Results. Sugarcane ash exposure led to the accumulation of silica in the kidneys, lungs, liver and spleen of rats. Mild proteinuria developed although renal function was largely maintained. However, biopsies showed focal glomeruli with segmental glomerulosclerosis, and tubulointerstitial inflammation and fibrosis that tended to worsen even after the ash administration had been stopped. Staining for the lysosomal marker, LAMP-1, showed decreased staining in ash administered rats consistent with lysosomal activation. Conclusion. Sugarcane ash containing silica nanoparticles can cause CKD in rats.

Food-mediated exposure of Hofmeister ions in Oryza sativa (Rice) from selected CKDu endemic regions in Sri Lanka

The objectives of this study were to determine selected Hofmeister anions and cations that are important for kidney health, in raw rice samples from selected Chronic Kidney Disease of unknown etiology (CKDu) endemic and non-endemic areas in Sri Lanka and their intake. The anions and cations were analyzed by Ion Chromatography and Microwave Plasma Atomic Emission Spectrometry (MP-AES), respectively, after alkaline and acid digestion in thirty raw rice samples each from CKDu endemic and non-endemic areas, and the dietary intake was estimated. The mean concentrations of fluoride (F-), chloride (Cl-), phosphate (PO43-), sulfate (SO42-), sodium (Na+), magnesium (Mg2+), potassium (K+), and calcium (Ca2+) in raw rice in CKDu endemic areas were 53.317, 1515.3, 2799.6, 2704.9, 30.603, 300.76, 1001.3, and 90.075 mg/kg, respectively. The mean concentration of the anions and cations in raw rice from CKDu non-endemic areas were 22.850, 947.52, 4418.7, 6080.2, 23.862, 364.45, 955.78, and 96.780 mg/kg, respectively. Significantly higher differences (p < 0.05) were reported in the mean concentration of F-, Cl-, and Na+ in raw rice from CKDu endemic areas in comparison with the samples from non-endemic areas. The aggregated estimated daily intake (EDI) and cumulative EDI of F- via consumption of cooked non-traditional samba rice from CKDu endemic areas for adults were the highest (0.155 and 0.172 mg/kg bw/d, respectively), which were higher than the recommended tolerable upper intake value (0.15-0.2 mg/kg bw/d). In contrast, the traditional rice from CKDu non-endemic areas for adolescents, reported the lowest values (0.0210 and 0.0470 mg/kg bw/d, respectively). Adults who consume non-traditional samba rice from CKDu endemic areas were at health risk, while children were the most vulnerable group due to their low body weight. These results indicate that the consumption of rice rich in Hofmeister ions may contribute to the total intake and act as risk factors to negatively affect weak kidneys in CKDu endemic areas. Further research to analyze Hofmeister ions in cooked rice and rice from different countries is recommended.

Chronic kidney disease with unknown cause across the global spectrum

PURPOSE OF REVIEW

In the 1990s, a type of chronic kidney disease with unknown cause (CKDu) was identified in Central America and Sri Lanka. Patients lacked hypertension, diabetes, glomerulonephritis, or other usual causes of kidney failure. Affected patients are predominantly male agricultural workers aged 20-60 years, living in economically disadvantaged areas with poor access to medical care. Patients typically present late and progress to end-stage kidney disease within 5 years, resulting in social and economic hardship for families, regions, and countries. This review covers the current state of knowledge for this disease.

RECENT FINDINGS

The prevalence of CKDu is increasing in known endemic regions and across the globe, reaching epidemic proportions. There is primary tubulointerstitial injury with secondary glomerular and vascular sclerosis. No definitive etiologic factors have been identified, and these may vary or overlap in different geographic locations. The leading hypotheses include exposure to agrochemicals, heavy metals and trace elements, and kidney injury from dehydration/heat stress. Infections and lifestyle factors may play a role, but are likely not key. Genetic and epigenetic factors are beginning to be explored.

SUMMARY

CKDu is a leading cause of premature death in young-to-middle-aged adults in endemic regions and has become a public health crisis. Studies are underway to investigate clinical, exposome, and omics factors, and hopefully will provide insights into pathogenetic mechanisms resulting in biomarker discovery, preventive measures, and therapeutics.