by Rohan Nath
Arsenic contamination of groundwater has been a daunting threat for the public in different regions of the world for the past few decades. More than 200 million populations in 105 countries are exposed to arsenic contamination. Plains of Ganga-Meghna-Brahmaputra (GMB) in India and Bangladesh are heavily polluted with arsenic. More than 100 million inhabitants in the GMB plain are at risk from groundwater arsenic contamination.
The groundwater arsenic contamination has a long history in India, and specifically West Bengal (Table 1).
|1976||Arsenic contamination and its hazardous effect on human life were first reported from Chandigarh in North India.|
|1984||The next arsenic contamination problem was observed in the plains of the Lower Ganges in West Bengal.|
|1988||The School of Environmental Studies (SOES) began analysing the arsenic pollution in the groundwater of West Bengal.|
|1995||An international arsenic conference was held in Kolkata for 5 days with the help of SOES.|
|2002||The groundwater arsenic contamination was reported in West Bengal and several discussions were held regarding the attitude of the government and other organizations towards this critical problem.|
|2009||The condition of groundwater arsenic contamination from 1988 to 2009 in West Bengal was reported which also had an additional report on Kolkata city itself. i. 19 districts of West Bengal were analysed for 140,150 hand tube wells. ii. The groundwater arsenic concentration exceeded the World Health Organization (WHO) guideline value (10 µg/l) in 13 districts. iii. Arsenical skin symptoms are observed in 9 districts that had groundwater arsenic concentration above 300 µg/l. iv. The percentage of hand tube-wells that had arsenic concentrations above the WHO guideline value is 48.1%. v. Nine districts had tube-wells with an arsenic concentration above 300 µg/l: a. Bardhaman b. Hooghly c. Howrah d. Kolkata e. Malda f. Murshidabad g. Nadia h. North 24 Parganas i. South 24 Paraganas|
Three municipal corporations (KMC, Howrah and Chandhannagore) are situated in the Kolkata Metropolitan Area (KMA). The Kolkata Municipal Corporation (KMC) is the major Municipal Corporation in West Bengal covering an area of 185 km2 with a population of 4,496,694 and forms the financial and economical focal point of eastern India.
Kolkata lies 3.5-6 m above mean sea level in the lower deltaic plains of the Ganga-Bhagirathi River system. Deltaic plain, younger levee, paleochannels and inter-distributary marsh constitute the typical geomorphological characteristics. Younger alluvial soil with silt and clayey loams form the dominant soil type.
141 wards of the KMC were investigated for groundwater samples between 1993 and 2015. Acid pre-washed 10 ml polythene bottles were used to collect the water samples without filtration. A preservative such as dilute nitric acid-water (7M) was used in the sample.
During the groundwater samples collection, nail, hair and, urine samples were collected from populations of KMC. The hair and nail samples were secured in zip lock bags whereas the urine samples were refrigerated in an icebox and all of these samples were sent to the lab for analysis. Inorganic arsenic and its metabolites were measured in the urine samples. Total arsenic concentration was analysed in the hair and nail samples.
The concentration of arsenic in the groundwater of KMC
The arsenic contamination status in all 141 wards of KMC was studied (Fig 2).
The southern part of Kolkata Municipal Corporation had a higher concentration of arsenic contamination compared to other parts of the city.
Biological samples arsenic content
All of the collected samples have hair and nail arsenic greater than that population who were unexposed to arsenic-contaminated groundwater. 71.4% of the urine samples have arsenic content above 100 µg/l.
The hazard of arsenic concentration is in the order – Murshidabad > North 24 Parganas > Nadia > KMA > South KMC > the KMC. The low contamination of KMC might be due to a greater average depth of the hand tube wells than other parts of West Bengal.
Until a full-fledged surface water scheme is implemented, groundwater cannot be a sustainable source for drinking water in the KMC due to quantity and quality issues. The activity mapping of groundwater for each ward should be prepared. GIS method must be used for identifying the bore wells and continuous monitoring. Installation of new tube wells in the arsenic-contaminated area should be banned.
The Hooghly River can provide an ample amount of surface water and proper infrastructure must be constructed to make this sector financially and technologically sustainable. Pressure monitoring systems and domestic meters need to be installed at the consumer level.
The average annual rainfall in the KMC area is 1821 mm with annual net rainwater availability of 247 Mm3. Roof-water harvesting method should be implemented to collect this huge rainfall. The government of West Bengal built a rooftop harvesting system for building greater than 60,000 sq. ft. or more than 100 flats which seem to be inadequate for such a huge population.
1. Chakraborti, D., Das, B., Rahman, M. M., Nayak, B., Pal, A., Sengupta, M. K., … & Dutta, R. N. (2017). Arsenic in groundwater of the Kolkata Municipal Corporation (KMC), India: Critical review and modes of mitigation. Chemosphere, 180, 437-447.