Accumulation of Arsenic and Other Heavy Metals in Rice Paddy (water, soil and plant components) Irrigated with Contaminated Groundwater: Implication for Food Security

Shrivastava, Anamika (2016) Accumulation of Arsenic and Other Heavy Metals in Rice Paddy (water, soil and plant components) Irrigated with Contaminated Groundwater: Implication for Food Security. PhD thesis, Indian Institute of Science Education and Research Kolkata.

PDF (PhD thesis of Anamika Shrivastava (12RS012)) ANAMIKA_PhD_THESIS_09_2016.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

This study investigated the levels of arsenic (As) and other elements (Fe, Mn, Cu, Zn) in surface and groundwater, surface soils and rice components (roots, shoots, husks and grains) for traditional continuously flooded (CF) rice paddy cultivation in Chakdaha, West Bengal, India. The study also focused on the development of As-mitigation method (alternative system of irrigation) that could be adapted to reduce the arsenic levels in rice grains. The impact was evaluated using data on the accumulation of arsenic in soils and the subsequent uptake of arsenic by rice plant components, with special attention on rice grains. The results indicated that average level of arsenic in the groundwater (85.84 μg/l As) exceeds the World Health Organisation, WHO guidelines for arsenic in drinking water (10 μg/l As). The results for other heavy metals in groundwater, such as, iron (5100 μg/l) and manganese (273.61 μg/l) were above the permissible limits by the WHO, FAO (Food and Agricultural Organisation) and BIS (Bureau of Indian Standards). Over time this has resulted in arsenic contamination of soil (56.58 mg/kg dry weight of As) and other heavy metals (Fe = 15845.67 mg/kg; Mn = 315. 49 mg/kg; Cu = 76.82 mg/kg; Zn = 47.88 mg/kg). The trend for arsenic in surface soils (top 20 cm) over the study period, despite substantial arsenic losses, has resulted in a significant portion of the arsenic introduced via irrigation that has remained within the soil over the period of three years. Furthermore, the order of arsenic accumulation in plants from the rice paddies of the study area were: root (26.95 – 30.67 mg/kg) > straw (6.88 – 11.73 mg/kg) > grain (1.32 – 1.82 mg/kg) > husk (0.67 – 1.27). The levels of arsenic in grains from plants grown in “Boro”, “Amon” and control, resulted in As-levels of 1.60 – 1.85 mg/kg, 1.35 – 1.52 mg/kg and 0.20 – 0.68 mg/kg, respectively. A comparison of continuously flooded, CF systems with the intermittently flooded, IF system of irrigation showed that in three years, the arsenic accumulation was 6.44 mg/kg (CF) and 3.36 mg/kg (IF), respectively. This decreased the bioavailable arsenic level from up to 20 % to below 15 % for IF system, which resulted in a lower arsenic accumulation by plants when compared to CF fields. The estimates of dietary exposure of arsenic by rice grains by CF (0.87 mg/day) and IF (0.58 mg/day) showed a significant decline (p = 0.002). Although the arsenic levels in grains was reduced by IF system, the values were still above the Maximum Allowable Daily Level (MADL) of arsenic through ingestion, dermal contact and inhalation listed by Office of Environmental Health Hazard Assessment (OEHHA) as 0.22 mg/day. Adopting the alternative system of irrigation (IF) may provide a positive result for food security in the arsenic contaminated rice paddies cultivated areas.

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