Distribution, prevalence and health risk assessment of fluoride and arsenic in groundwater from lower Gangetic plain in West Bengal, India

Distribution pattern of fluoride and arsenic in groundwater (n = 984) from 35 wards of Rajpur-Sonarpur Municipality and its associated health risk have been evaluated. Presence of fluoride >1.5 mg/L (mean = 1.9 mg/L, range: 1.51-2.9 mg/L) and <1.5 mg/L (mean = 0.6 mg/L, range: 0.01-1.49 mg/L), whereas, for arsenic >= 10 mu g/L (mean = 56.2 mu g/L, range: 10.1-213 mu g/L) and <10 mu g/L (mean = 3.3 mu g/L, range: <3-9.7 mu g/L) have been observed in the studied groundwater samples. Simultaneous occurrence of fluoride and arsenic above their permissible limit in drinking water were found from two wards (ward number 6 and 7). About 13% and 16% of the collected groundwater samples (n = 984) have been found beyond the permissible limit of fluoride and arsenic, respectively. Mean concentrations of calcium and iron in groundwater were 31 mg/L (range: 7.3-184 mg/L) and 3.79 mg/L (range: <0.05-50.4 mg/L), respectively. The distribution of both fluoride and arsenic was established with a moderate positive correlation value (r = 0.30) and their relationship is dependent on the interrelationship between Ca and Fe. While the negative correlation between F- and Ca (r = -0.33) designates the increasing F-/Ca ratio in solution. Cluster analysis showed that calcium, iron and the two above contaminants are likely to be highly concentrated in the depth ranges 30.5-60.9 m, 60.9-152 m and 152-305 m. The highest concentration of both the toxicants has been observed in the depth range of 24.4-30.5 m. Weak (fluoride) to strong (arsenic) correlation between water & urine showed exposure of two toxic contaminants. Modelled Average Daily Dose (ADD) and Targeted Hazard Quotient (THQ) of fluoride and arsenic were found maximum for adults followed by teenagers and children. Cancer risk of arsenic was estimated higher than the threshold value among all the age groups.