Spatio-temporal variation and health risk associated with trace element concentrations in groundwater of Mathura city using modified indexing approach

The aim of this study is to ascertain the human risk linked with trace element contaminants in groundwater in the urbanizing region of Mathura city, known for its touristic value. A systematic sampling consisting of 152 groundwater samples from 3 different depth zones and 2 different seasons was collected. The samples were analyzed for physico-chemical, major, and trace elements concentration using standard techniques. From all three representative depths, the average TDS for shallow, intermediate, and deep aquifer (2182 mg/l, 2080 mg/l, and 1683 mg/l, respectively) corroborate vertical differentiation in salinity distribution. The vertical salinity distribution is likely due to presence of thick clay and lake water precipitates giving rise to inland salinity. The majority of the groundwater samples show brackish water characteristics and is hard to very hard type. The dominant chemical facies is Na+K-Cl+SO4 type in premonsoon season which transform partially into Ca+Mg-Cl+SO4 type during post monsoon season. Slightly elevated concentrations of Al, As, Mn, Mo, Zn, and U were recorded in both the seasons. Seventy of 359 total trace element tests failed the drinking criteria in premonsoon season. This was slightly improved with 51 out of 334 tests failing the drinking criteria in post monsoon season. The order of failed test parameters in premonsoon follows Sr>Mo>U>Al>Mn which alters to Sr>>U>Al>Mn in post monsoon season. Trace element pollution index (TPI) indicates higher contamination in shallow wells which decreases with depths in premonsoon season. This is rather a conspicuous trend which is likely due to several factors like restricted groundwater circulation due to excessive clay, inland salinity, alkalinity, pH dependency and over abstraction. Hazard index (HI) values indicate that the study area is at non-carcinogenic risk. Non-carcinogenic risk in humans is comparatively higher for children, followed by adults and infants for all 3 sample types. The high concentrations of trace elements such as As, Mo, Sr, and Zn add to the health hazard. The investigation demonstrates comparatively high health hazard in shallow depths. This manifests the depositional environment; small scale industries, urban waste disposal, oil refinery, fertilizers application, and groundwater used in agriculture activities are polluting the shallow groundwater environment.