Identifying fluoride endemic areas and exposure pathways for assessment of non-carcinogenic human health risk associated with groundwater fluoride for Gujarat state, India.

Analytical data of fluoride concentration in groundwater collected from various geological formations in Gujarat, India, have been studied to assess their spatial distribution characteristics and related potential chronic health risks. Decadal analysis of groundwater was attempted for precise quantification and a realistic ground representation of fluoride concentration in the entire state. This exercise involved collection of 6407 samples over a period of 10 years (2009-2018), from 641 representative locations, distributed evenly throughout the state (6407 = 641 locations × 10 years). The analytical results indicate that 19% of the sample locations have fluoride concentration higher than the permissible limit and 42% of the locations have fluoride concentration much below the desirable limit, thereby exposing children to a higher risk of associated dental morbidities. Monte Carlo simulation integrated with sensitivity and uncertainty analysis was applied for an accurate and realistic assessment of the non-carcinogenic health risk. Model results indicated that groundwater fluoride exposure through consumption is way higher than the exposure due to dermal absorption pathway. It is inferred that 94 locations (15%) have total hazard index greater than the unity value for all population groups, thereby increasing the vulnerability of the local populace to dental and skeletal fluorosis. Total hazard index in 210 locations (36%) and 188 locations (29%) are beyond the permissible limit for the population comprising infants and children. Populaces living in these locations are susceptible to health hazards that stems from high fluoride concentration. Children and infants are at greater risk due to groundwater fluoride toxicity when compared to the adult populace. The order of the geographic stratification of vulnerability is Mainland regions > Saurashtra region > Kachchh region. Ingestion rate and fluoride concentration are the sensitive parameters with high impact and residents of these vulnerable locations should be advised to abstain from direct intake of groundwater and resort to defluoridised groundwater.