Review of groundwater arsenic of the Kolkata Municipal Corporation (KMC)

by Rohan Nath

Introduction 

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). 

Table 1.

Year Incident
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

Study area 

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.

Fig. 1. An arsenic contaminated tube-well (60 µg/l) quenches the thirst of a child inside  Kalighat Kali Temple. Image Source: 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.

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. 

Results 

The concentration of arsenic in the groundwater of KMC 

The arsenic contamination status in all 141 wards of KMC was studied (Fig 2).

Fig. 2. Arsenic contamination in Kolkata. Image Source: 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.

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. 

Conclusion 

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. 

Reference 

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.

Published by LakesOfIndia

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