Events & Issues

New Delhi, 21 May 2012

Arsenic Contamination

WATCH WHAT YOU EAT, DRINK

By Dhurjati Mukherjee

Recent reports indicate that arsenic contamination of groundwater from the Yamuna floodplains in the country’s Capital, Delhi is several times higher than the permissible limit. Shockingly, the prime culprit for this poisoning is fly ash and other residues from the State’s thermal power stations. A study ‘Anthropogenic Arsenic Menace in Delhi Yamuna Floodplains’, carried out by the Dept of Geology, Delhi University states the highest arsenic content, 180 parts per billion (ppb), were present in the pre-monsoon groundwater samples collected near the Badarpur plant.  Moreover, coal used in Badarpur and Rajghat power plants was found to contain over 2000 ppb of arsenic while arsenic contamination in fly ash was as high as 3200 ppb.

Arsenic (As), which is a metalloid element found ubiquitously in nature, has exposed human beings to it primarily from air, water, food and some manufactured chemicals.  It has become synonymous with toxicity and is playing havoc not only in India but in other nations too because of its grave consequences to human health.

The presence of arsenic in amounts exceeding the prescribed level can be detrimental to plants, animals and human beings. Natural processes such as weathering of rocks and volcanism contribute to arsenic input to the environment. Relatively high concentrations of arsenic have been reported in ground water, adjoining arsenic-bearing minerals, fly ash disposal ponds and sea waters. Arsenic may also be an anthropogenic pollutant of groundwater, derived from chemical wastes and wastewater. The arsenic levels found in water resources are from the parts per billion (ppb) to parts per million (ppm) range.

Shockingly, groundwater arsenic contamination exists in around 30 countries at least of which four major occurrences have occurred in Asia, which includes Bangladesh, India, China (Inner Mongolia) and Taiwan. Severe arsenic contamination has also been reported from Vietnam where several million people are said to be at considerable risk of chronic arsenic poisoning (Berg et. al. 2001). This apart, arsenic groundwater contamination was reported from Lao People’s Democratic Republic, Cambodia, Myanmar, Pakistan Nepal and Argentina, Mexico and Chile. Although arsenic problems have now been recognized in many regions, there are other areas, principally aquifers, where issues need to be identified. 

Arsenic in groundwater in India is most acute in West Bengal, with Assam, Bihar, Uttar Pradesh, Jharkhand and Chhattisgarh too affected. Of the 60-million people at risk of arsenic exposure in Asia, over 1.5 lakh people alone belong to West Bengal spread over 12 districts. While one lakh people exhibited the effects of arsenic poisoning, including skin lesions, the remaining are at risk because of consumption of arsenic contaminated water. Even in Kolkata, 78 wards have tube wells with arsenic contaminated water, as per the School of Environmental Studies, Jadavpur University.

A World Bank study ‘Arsenic in Food Chain: Effects & Mitigation’ undertaken by West Bengal University of Animal & Fishery Sciences and Indian Veterinary Research Institute among others found that the level of arsenic in faeces and milk from cattle, various types of milk products etc was considerably higher, 10 to 20 times more than the permissible level laid down by the Bank (national permissible standard is .05 ppm (microgram per ml), the WHO standard is .01 ppm). Apparently, white milk contains 77 per cent arsenite, 14 per cent arsenate and 8 per cent organic arsenic. Arsenic contamination in cattle occurs through ingestion of drinking water, paddy straw, mustard oil cake, crops, vegetables reared in the endangered zone.      

Additionally, foodgrains such as rice and even vegetables have been found to contain high traces of arsenic in affected areas. West Bengal University of Animal & Fishery Sciences has noted that “paddy plants have been found to show a greater affinity towards arsenic than other crops.”

The problem is acute in adjoining Bangladesh too. A study ‘Arsenic in Groundwater: Contamination in the Food Chain’ by Department of Soil, Water & Environment, Dhaka University and Commonwealth Scientific & Industrial Research (CSIRO) found that samples collected from various districts contained dangerous levels of arsenic in rice and water.

The health effects of arsenic contamination vary between individuals but the most severe is related to skin diseases. With farmers and villagers filling ponds with groundwater, its use in irrigation is suspect to the toxic effects which range from gangrene of the peripheral organs to skin cancer of the internal organs such as liver, kidney and bladder. Other health risks include nervous system disorders, stomach pain, nausea and diarrhea, vascular lesions and liver or kidney damage. Estimates suggest that 50-odd of every 1000 Indians can be affected with cancer if they consume four litres of water with arsenic content of 0.05 mg/litre daily. Also 13 out of 1000 people can be affected by cancer if a person daily consumes one litre of drinking water with the same arsenic content.

On the flip side, the Bengal Government has identified arsenic-resistant varieties of rice that can absorb much of the poisonous element and such arsenic-resistant seed varieties would be distributed in affected areas. Besides, it was found that cattle when fed with sodium thiosulphate, a chemical compound, the arsenic level in milk came down considerably.  

A path-breaking achievement has been the invention of a soil-based filter by IIT Kharagpur that could solve arsenic contamination in the backdrop that similar filters tried so far have been extremely expensive and beyond the reach of Third World countries. Now, for just Rs 1 a day, a family can get 30 litres of water filtered without having to use electricity. Experiments with the filter in some households in critical areas have given readings as low as 0.2 micrograms per litre.

Additionally, research at the chemical engineering department adopted a unique approach to the problem – it started investigating why some areas in Bengal were spared arsenic contamination. It was found that commonplace laterite – a reddish claylike substance that forms the topsoil in districts such as Birbhum and Bankura – traps arsenic through a unique adsorption process. The laterite soil abounds in ferrous and aluminum oxide which are natural filters for arsenic. 

Another solution was found by Dr. Mohan Mishra, former Professor of Medicine of Darbhanga Medical College through the use of alum as a purifier. This could remove arsenic content and certain other impurities from groundwater almost completely and make it fit for drinking. “Treating a litre of water should cost 02 to 03 paise”, according to him as only 0.5 gm food grade alum is needed to clean one litre of contaminated water. The research is significant as he had followed international parameters on the permissible limit of arsenic presence (0.01mg/litre or 10 ppb) to establish purity of water.

In sum, given the harmful effects of arsenic contamination and the fact that low-cost solutions are available, all State Governments need to embark on a coordinated action, either by making available low-cost filters through panchayats or NGOs or making alum available to the masses. At the same time, there is need to initiate an awareness campaign regarding consumption of contaminated water on a war-footing. No more precious time be wasted. -INFA

(Copyright, India News and Feature Alliance)