Assessment of land use and monsoon impact on high nitrate groundwater and health risk in the hard rock aquifer, South India.

Groundwater sustainability in hard rock aquifers is compromised largely due to nitrate contamination from anthropogenic sources resulting in diminishing potable resources and attendant health issues. A purpose-driven study through an integrated approach was undertaken in the area of interest (hard rock aquifer) to assess the variations in nitrate concentration and resultant health impacts in response to variations in monsoon and land use patterns. Groundwater samples (n = 284) were collected for a period of three years (2017-2019) and analysed. From the analytical data, it is inferred that 27% and 9% of groundwater samples in the study area have high NO3- values of > 45 mg/l and > 100 mg/l, respectively. NO3- contamination zones mapping illustrates that NO3-contaminated area (> 45 mg/l) varied seasonally 1164 km2 (2017), 1086 km2 (2018) and 1640 km2 (2019)) and high-risk area (NO3- > 100 mg/l) has reduced drastically during 2018 due to dilution by monsoon (277 km2 (2017), 41 km2 (2018), 634 km2 (2019)). The lowest NO3- and Cl-concentrations are recorded during 2018 which coincides with high rainfall (2061 mm). NO3- concentrations in response to land use pattern indicate that the hot spots (NO3- > 45 mg/l and > 100 mg/l) are observed in groundwater samples of residential areas which are vulnerable to contamination from domestic wastewater, septic tanks and other pollutants. Further, wastewater infiltration facilitated the dissolution of certain minerals in the unsaturated zone which enhanced the accumulation of NO3- and other ions in this aquifer. Mineral weathering, denitrification and evaporation processes also affected the groundwater chemistry. The health risk model (HQoral) indicates that groundwater in 1261 km2 (2017), 1232 km2 (2018) and 1669 km2 (2019) is unsuitable for drinking (HQ > 1) and causes adverse health risks to the local inhabitants. The study has identified areas from the central and southeastern regions significantly affected by nitrate pollution underpinning the necessity of using treated groundwater for drinking purposes.

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.