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Arsenic MitigationDepartment of Water Resources, RD & GRMinistry of Jal Shakti
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1. What is Arsenic:
Arsenic is a chemical element with the symbol Asand atomic number 33. It is a natural component of the earth’s crust and is widely distributed throughout the environment in the air, water and land.
It is highly toxic in its inorganic form.Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining due to the toxicity of arsenic and its compounds.
Occurrence of arsenic in high concentration, beyond the acceptable limit of drinking water has been reported from various parts of the century. Long-term exposure to inorganic arsenic, mainly through drinking-water and food, can lead to chronic arsenic poisoning. Skin lesions and skin cancer are the most characteristic effects.
2. Sources of Arsenic in Groundwater:
The sources of arsenic in the environment include both geogenic and anthropogenic.Because Arsenic occurs naturally in the environment and as a by-product of some agricultural and industrial activities, it can enter drinking water through the ground or as runoff into surface water sources.
When agricultural fields are irrigated with arsenic contaminated groundwater, inorganic forms of arsenic get absorbed by the plants and hence arsenic enters the food cycle.The anthropogenic sources of arsenic are agrochemicals, wood preservatives, industrial sources, mineral processing, acid mine drainage, burning of fossil fuels etc.
3. Health impact due to Arsenic consumption
Human system is sensitive to arsenic. Arsenic can get into the human body through drinking water as well as eating food that has been contaminated with arsenic.
Arsenicosis
is the medical word for arsenic poisoning, which occurs due to accumulation of large amounts of arsenic in the body. Arsenicosis leads to adverse health effects through inhibition of essential enzymes, which ultimately leads to death from multi-system organ failure.
As per BIS Standards (IS 10500: 2012) the maximum permissible limit of Arsenic in drinking water is 0.01 mg/l (ppm) or 10 µg/L(ppb). If consumed in greater amount than the permissible limits, Arsenic can cause various health disorders in humans such as:
Respiratory distress, cardiac problems, gastrointestinal effects,anaemia and leucopenia.
Skin disorders leading to hyperkeratosis, warts or corns on the palms and soles and areas of hyperpigmentation interspersed with small areas of hypopigmentation in the face, neck and back.
Ingestion of inorganic arsenic can result in neural injury, skin cancer and lung cancer when exposure occurs through inhalation.
4. Arsenic contamination in groundwater: Distribution
As per the available with Central Ground Water Board, Arsenic >10 µg/L(ppb) is found in ground water samples spreading over 153 Districts in parts of 21 States/UTs of India (Figure 1). However, most affected areas are middle, lower and deltaic parts of Ganga basin.
1: Map showing locations having high Arsenic in Ground water (Source: CGWB)
5. Prevention & Control
Prevention of further exposure to arsenic can be achieved by the provision for supply of arsenic free / sfae water for drinking, food preparation and irrigation of food crops. There are a number of options to reduce levels of arsenic in drinking-water.
Substitute high-arsenic sources, such as groundwater, with low-arsenic safe sources such as rain water and treated surface water. Low-arsenic water can be used for drinking, cooking and irrigation purposes, whereas high-arsenic water can be used for other purposes such as bathing and washing clothes.
Discriminate between high-arsenic and low-arsenic sources. For example, test water for arsenic levels and paint tube wells or hand pumps different colours. This can be an effective and low-cost means to rapidly reduce exposure to arsenic when accompanied by effective education.
Blend low-arsenic water with higher-arsenic water to achieve an acceptable arsenic concentration level.
Install arsenic removal systems – either centralized or domestic – and ensure the appropriate disposal of the removed arsenic.
6. Arsenic Remedial Techniques:
Major source of arsenic in groundwater is due togeogenic origin and is intricately linked to the aquifer geometry and ground water flow regime, its effective remediation warrants understanding of physicochemical processes in ground water and aquifer framework, lithology and groundwater flow regime of the area.
The remedial measures includes variety of options, ranging from removing arsenic from ground water after it is extracted, searching alternative aquifers, reducing the level within the aquifer itself, dilution of the contaminants by artificial recharge, blending with potable water etc. The arsenic remediation techniques involving arsenic removal can be grouped under two broad categories i.eEx –situ and In-situ techniques.
Ex-situ Techniques:
This method primarily targets to lower the concentration of As after the water is extracted from aquifers. A brief outline of the major processes in this group is given below;
Precipitation processes:includes coagulation/filtration, direct filtration, coagulation assisted microfiltration, enhanced coagulation, lime softening, and enhanced lime softening.
Adsorptive processes: Adsorptive processes involve the passage of water through a contact bed where arsenic is removed by surface chemical reactions.
Ion-exchange processes
Membrane processes: This includes nano-filtration, ultrafiltration, reverse osmosis and electro-dialysis which uses synthetic membranes for removal of many contaminants including arsenic.
In-situ (sub-surface) arsenic treatment:
In situ remediation refers to all such techniques that make arsenic immobilization possible within the aquifer itself. As arsenic is mobilized in groundwater under reducing conditions, it is also possible to immobilize the arsenic by creating oxidized conditions in the subsurface such as:
Use of atmospheric O2 for iron and arsenic rich water
Use of atmospheric O2 and ferrous chloride for low Iron and Arsenic rich water
The SAR (Sub-terranean Arsenic Removal)
Permeable Reactive Barriers (PRB) Technology
Electrokinetic treatment Biological arsenic removal
7 Technology for tapping of Arsenic free aquifers:
It has been observed that the deeper aquifers are generally Arsenic free. Central Ground Water Board has come out with technology to construct Arsenic free wells tapping deeper aquifers.
The specially designed wells with cement seal technique provide the solution to handle the situation of the interconnection between the lower and upper aquifers. The cement sealing is applied to a suitably thick intervening clay layer separating the arsenic contaminated aquifer from arsenic free aquifer.This cement seal prevents seeping of contaminated water through the annular space which is filled with gravel material. The schematic diagram of innovative well design, adopted by Central Ground Water Board for constructing Arsenic free wells is given in figure 2. It is suggested that this design be used in arsenic affected areas of the State of Bihar, Uttar Pradesh and West Bengal where deeper aquifers are underlain by thick separating clay layer.
Figure 2: Innovative Design of well for tapping Arsenic free aquifer by CGWB
8. Way Forward:
Through this window, an attempt has been made to create general awareness and to update all concerned about efforts made by various government authorities towards Arsenic Mitigation in drinking water.
General public is also requested to forward their Complaint/Grievance/Suggestions towards Arsenic Mitigation through this window in the submit GRIEVANCE/SUGGESTION TAB.
More and more participation of general public is requested.