Arsenic contamination in Ballia and phytoremediation

Abstract

Over thousands of years, Arsenic (As) has been washing down from the Himalayas with the Ganga water as sediment, sinking in and mixing with groundwater. In the plains, this As has been leaching into the ground. Some As occurs naturally in groundwater, within limits not harmful. It remained within permissible limits and did no harm till around the 1970s when, concerned over deaths in the Gangetic belt caused mainly by the unhygienic pattern of water consumption and poor sanitary conditions, the Indian government and UNICEF sank millions of tubewells. After 1970, indiscriminate drawing of groundwater resulted in water table sinking and increasing As content. In India, seven states namely, West-Bengal, Jharkhand, Bihar, Uttar Pradesh in the flood plain of Ganga River; Assam and Manipur in the flood plain of Brahamaputra and Imphal rivers and Rajnandgaon village in Chhattisgarh state have so far been reported affected by As contamination in groundwater above the permissible limit of 50 μg/L. People in these affected states have chronically been exposed to As drinking arsenic contaminated hand tube-wells water. With every new survey, more As affected villages and people suffering from arsenic related diseases are being reported, and the problem resolving issues are getting complicated by a number of unknown factors. It is now generally accepted that the source is of geological origin and percolation of fertilizer residues may have played a modifying role in its further exaggeration. Identification of parental rocks or outcrops is yet to be recognized, including their sources, routes, transport, speciation and occurrence in Holocene aquifers along fluvial tracks of the Ganga-Brahmaputra-Barrak valley. It is reported that the contaminated waters are enriched in Fe, Mn, Ca, Mg, bicarbonates, and depleted in sulphate, fluoride, chloride; pH ranged from 6.5 to 8.0; redox condition usually in reducing; high an organic matter content; lodged mostly in sand coatings, or sorbed on clays and organic matters. It has been proved that As has affinity with iron in groundwater both positively and negatively, depending upon the condition. This gives a positive hope of devising in situ remediation of the problem of As contamination by removal of Fe from groundwater before withdrawal. Varieties of As removal devices have been developed, based on different working principles, and have been extended to fields. Many of those could not produce satisfactory performance due to sludge disposal problems. Among the various removal technologies, lime softening and iron co-precipitation have been reported to be the most effective removal technologies, and observed running satisfactorily, where operation and maintenance problems were taken care of by public-private partnership. The available As removal technologies require refinement to make them suitable and sustainable for their large scale effective uses. Alternative removal technology i.e. phytoremediation is ecofriendly and cost effective.