SOURCE OF ARSENIC
A single Rural Water Supply Scheme (RWSS) from Malda, one of the arsenic-affected districts of West BengalIndia, is withdrawing 147 kg of arsenic with groundwater in a year and 6.4 t of arsenic is being withdrawn
in a year from 3000 shallow, large-diameter tubewells in use for agricultural irrigation in Deganga police station of North 24-Parganas district, West Bengal.[4] It indicates that the source of arsenic is not antropogenic and is geologic. Although the source of arsenic is believed to be aquifer sediments, the chemistry and mineralogy of the sediments of GangesBrahmaputraMeghna (GBM) delta and arsenic leaching from the aquifer are not well understood.
Reports[5,6] show existence of arsenic-rich pyrite in sediments of the delta region of Gangetic West Bengal.
A probable explanation of arsenic contamination to the aquifer was predicted due to breakdown of arsenic-rich pyrite that occurred due to heavy groundwater withdrawal (i.e., underground aquifer is aerated and oxygen causes degradation of pyrite, the arsenic rich source). The cause of groundwater arsenic contamination in West Bengal and Bangladesh was also predicted due to reduction of arsenic-rich iron oxy-hydroxide in anoxic groundwater.[7,8,9]
Whatever may be the mechanism of arsenic leaching to the aquifer, in West BengalIndia 38,865km2 and
in Bangladesh 118,849km2 are arsenic affected areas, and population in West BengalIndia living in arsenic
affected areas is 42.7 million and 104.9 million in Bangladesh. This does not mean that the total population
(147.6 million) is drinking arsenic-contaminated water in West Bengal and Bangladesh and will suffer rom arsenic toxicity, but it does indicate the risk levels. Our knowledge about long-term effects on those who have stopped drinking arsenic-contaminated water, those drinking contaminated water, and those suffering from arsenical skin lesions is not complete. A limited follow-up study for the last 10 yr indicates that a percentage of those suffering from severe skin lesions are getting internal/external cancers. A future danger to those living in West BengalIndia and Bangladesh is that arsenic is entering the food chain. Of great concern is the huge amount of arsenic applied
to agricultural land from contaminated water from hand tube-wells used for irrigation.
