DIFFERENT ROUTES OF ARSENIC ACCUMULATION IN RICE GRAIN: ROOT TO GUT

Drinking of contaminated groundwater is a major route of arsenic exposure in arsenic-affected regions of West Bengal, but the problem aggravates when the same water is being used for irrigational purposes. This study based in arsenic affected district North 24 Parganas, deciphers the impact of arsenic contaminated groundwater on paddy and its accumulation and distribution patterns in field soil and plant parts during various phases of pre-monsoonal cultivation (Boro). Decreasing trend of arsenic was observed in plant parts during reproductive phase compared to vegetative phase and a reversal in ripening phase was observed. During growth period, formation of iron plaque on root surface was confirmed at the reproductive phase, which sequestered arsenic and restricted its uptake. Accumulation and uptake pattern of arsenic in field soil and plant parts during monsoonal cultivation depends on groundwater, phase-wise movement of soil arsenic with its enrichment status, and variation of rainfall. The synergistic effect of groundwater and rainwater makes a unique impact on arsenic distribution in plants, since rain water dilutes arsenic available for translocation. This phenomenon produces least arsenic containing grain (one-third of Boro cultivation) irrespective of cultivar variety and cultivation area. Higher accumulation of arsenic was observed in parboiled rice due to domestic scale post harvesting of paddy using arsenic-contaminated groundwater and additional risks were posed to populations through consumption of parboiled rice, especially used for cooked rice preparation. The entry or elimination (movement) of arsenic to/from rice grain and water during cooking is conspicuous. Lower arsenic in cooked rice was observed when contaminated rice grain was cooked with low/moderate arsenic-contaminated water (>3-60 µg/l) and arsenic movement from water to rice grain was inferred with increasing water arsenic (>80 µg/l). Concurrently, similar reduction percentage of arsenite, arsenate and total arsenic was observed in wet cooked rice when cooked with low-arsenic containing water.