Agricultural Activities Influence Nitrate and Fluoride Contamination in Drinking Groundwater of an Intensively Cultivated District in India

Abstract

We assessed the potential of nitrate–nitrogen (NO3–N) and fluoride (F) contamination in drinking groundwater of an intensively cultivated district in India as a function of its agricultural activities. Three hundred and forty two groundwater samples were collected from different types of wells with varying depths and analyzed for pH, EC, NO3–N load and F content. Database on predominant cropping system, fertilizer and pesticide uses were also recorded for the district. The NO3–N load in groundwater samples were low ranging from 0.01 to 5.97 mg L−1 with only 6.7% of them contained greater than 3.0 mg L−1. Samples from the habitational areas showed higher NO3–N content over the agricultural fields. But all the samples contained NO3–N below the 10 mg L−1, the threshold limit fixed by WHO for drinking purpose. The content decreased with increasing depth of wells (r = −0.297, P ≤ 0.01) and increased with increasing rate of nitrogenous fertilizer application (r = 0.931, P ≤ 0.01) and was higher in areas where shallow-rather than deep-rooted crops are grown. Fluoride content in groundwater was also low (0.02 to 1.19 mg L−1) with only 2.4% of them exceeding 1.0 mg L−1 posing a potential threat of fluorosis in some locality. On average, its content varied little spatially and along depth of sampling aquifers indicating homogeneity in lithology of the district. The content showed a significant positive correlation (r = 0.237, P ≤ 0.01) with the amount of phosphatic fertilizer (single super phosphate) used for agriculture. Results thus indicated that the groundwater of the study area is presently safe for drinking purpose but some anthropogenic activities associated with intensive cultivation had a positive influence on its loading with NO3–N and F.