Spatio-temporal variation of fluoride in groundwater and agricultural soil and crops of Unnao district, UP: Monitoring and assessment

Fluoride (F−) contamination in groundwater of Unnao district, Uttar Pradesh was reported for the first time in 1994, however comprehensive monitoring of F− in different environmental matrices remains to be undertaken. The presented study reports spatio-temporal monitoring of F− content in groundwater, crops and soil from F− affected district Unnao, in pre-monsoon (PRM), monsoon (MO) and post-monsoon (PMO), to establish F− groundwater-soil-plant continuum. More than 80% of groundwater samples were contaminated with F−> 1.0 mg L−1 with highest level (mg L−1), at Patiyara (3.6 ± 0.64), during PRM > Pathakpur (2.73 ± 0.57) during PMO > Sarukheda (2.40 ± 0.43) during PRM. High Cr in groundwater was observed in Jajmau (7.08 ± 1.42). The level of F− (mg Kg−1) in agricultural soils followed 3.4 ± 0.71 at Patiyara (MO) > 2.9 ± 0.14 at Badlikheda (PRM) 1.89 ± 0.28 at Jagatkhera (PRM). Among the different edible parts of crops in selected sites, highest F− content (mg Kg−1), F− level in grains of Oryza sativa ranged between 0.23 ± 0.02 to 2.01 ± 0.24. Whereas in the edible fruit of Trichosanthes diocia contained 1.47 ± 0.32 and Momordica charantia 1.47 ± 0.02. Leaf of spinach (1.03 ± 0.22) and seed of Brassica juncea (0.73 ± 0.08). Overall, comparing across all the three seasons, level of F− was highest in all the plants during MO, as compared to PRM and PMO. The regression analysis of physiochemical properties of groundwater show negative relationship between Na+ and F− whereas soil alkalinity exhibited strong influence in soil F−. The high F− content in soil and groundwater at Patiyara and Shekhpur also coincided with presence of several brick kilns, possibly contributing to the high F−.