Occurrences of nitrate-contaminated groundwater in the piedmont aquifers: hydrogeochemical characteristics and health risks.

ABSTRACT

Groundwater nitrate (NO3-) contamination is a global concern. The distribution patterns, enrichment mechanisms, and human health risks of NO3- contaminated groundwater were investigated using 144 groundwater samples collected from domestic and irrigation wells in the piedmonts of the North China Plain (Beijing and Shijiazhuang areas). The results showed that the groundwater was neutral to weakly alkaline, and 47% of the groundwater samples had NO3- concentrations exceeding 50 mg/L, a threshold proposed by world health organization to threaten infants up to 3 months. Groundwater NO3- concentrations were generally higher in the Beijing piedmont than in the Shijiazhuang piedmont and decreased with depth in both piedmonts. High-NO3- (> 50 mg/L) groundwater was distributed sporadically spatially and mainly was of Ca-Mg-HCO3 hydrochemical facies. Stable isotopes (D and 18O) compositions and NO3-/Cl- ratios indicated that NO3- accumulation in groundwater was primarily due to use of N-fertilizers under agricultural practices, and was associated with groundwater recharge sources such as septic tank leakage and re-infiltration of reclaimed irrigation water. Water quality evaluation showed that groundwater quality was highly dependent on NO3- concentration, with entropy-weighted water quality index values increasing linearly with increasing NO3- concentrations. The potential health risk of high-NO3- groundwater was the most serious for infants in both the piedmonts. Therefore, reducing NO3- input from sources and drinking water intake is recommended to minimize the human health risk.