Arsenic: Lurking in the shadows across Ganga, Brahmaputra basins

As the geography of arsenic contamination spreads, there is an urgent need for governments to reorient mitigation measures. That’s because the focus till now has only been on drinking water, but new research says arsenic has contaminated our food chain

By Simran Sumbre, Trinayani Sen
Published: Monday 10 February 2020
Arsenic contamination. Illustration: Ritika Bohra

Arseic contamination in groundwater is one of the most crippling issues in the drinking water scenario of India. According to the latest report of the Central Ground Water Board (CGWB), 21 states across the country have pockets with arsenic levels higher than the Bureau of Indian Standards’ (BIS) stipulated permissible limit of 0.01 miligram per litre (mg/l).

The states along the Ganga-Brahmaputra-Meghna (GBM) river basin — Uttar Pradesh, Bihar, Jharkhand, West Bengal and Assam — are the worst affected by this human-amplified geogenic occurrence.

In India, arsenic contamination was first officially confirmed in West Bengal in 1983. Close to four decades after its detection, the scenario has worsened. About 9.6 million people in West Bengal, 1.6 million in Assam, 1.2 million in Bihar, 0.5 million in Uttar Pradesh and 0.013 million in Jharkhand are at immediate risk from arsenic contamination in groundwater, according to latest data published by the National Rural Drinking Water Programme (NRDWP) of the Ministry of Jal Shakti (MoJS).

The presence of arsenic contamination, as specified by diverse sources for each of the affected states in the GBM river basin presents a perplexing riddle. For instance, in Bihar, the state Public Health Engineering Department (PHED) data from 2016 claims that 13 districts have arsenic contamination in groundwater.

The data published by CGWB in 2018 contradicts PHED’s data and says 18 districts in Bihar are at risk. However, data published by NRDWP in the same year claims 11 arsenic affected districts. The level of discrepancy in numbers gets worse.

In West Bengal, data published by the West Bengal PHED in 2014 claims 11 districts were facing arsenic contamination. But CGWB’s 2018 data puts the affected districts at eight, while NRDWP’s (2018) data raises it to nine. In Assam, 18 districts are affected according to the NRDWP’s 2018 data. NRDWP’s 2018 data puts the affected districts at eight. The Assam PHED 2017 data says 17 districts are affected by arsenic contamination.

For Uttar Pradesh, CGWB’s 2018 data claims there are 12 affected districts, while NRDWP’s 2018 report puts the figures at 17. Similarly, for Jharkhand, CGWB’s 2018 data claims two affected districts and NRDWP’s 2018 report raises it to three districts. The state PHED for both Uttar Pradesh and Jharkhand do not have any online published data on the district level presence of arsenic contamination.

Whatever the number, every report only reinforces the fact that arsenic contamination is present in various parts of the country. And these numbers could very well be underestimates. The growing districts with inconsistent data can be termed as “missed districts”. The population in these districts remain oblivious of the arsenic presence in their groundwater.

The gravity of arsenic contamination can be found in NRDWP’s report in 2018, which says that there are 46 districts across these states with arsenic levels between 0.01-0.05 mg/l and 17 districts with levels beyond 0.05 mg/l. This is way above the BIS stipulated permissible limit (between 0.01 mg/l and 0.05 mg/l and beyond 0.05 mg/l). It must be noted here that there are 11 districts (without Bihar districts) in these states that fall in both categories. 

Contamination chain 

Recent research papers say arsenic contamination in groundwater has penetrated the food chain. That should have woken up governments. Yet the focus remained on drinking water, and the affected regions became the primary stake-holder in the mitigation approach.

The government has only been focussed on drinking water in the affected regions with PHED being the primary stakeholder in the mitigation approach. Mitigation measures are targeted in treatment of groundwater or supply of surface water.

Similarly, government testing of water sources for arsenic contamination has also been restricted to drinking water sources; it has not widened the scope of investigation to water sources used for irrigation. What has aided in this contamination is our dependence on groundwater to cater to water needs. Modern groundwater-based irrigation techniques and a gradual shift from a rainfed crop to multiple irrigated crops has increased the crisis.

Regular extraction of groun dwater using “shallow large diameter” tube wells for irrigation is increasing the deposits of arsenic in soil and consequently its uptake by the crops being grown on that soil. In 2005, a paper published in Chemosphere based on a study conducted in Murshidabad district of West Bengal highlights the positive correlation between the level of arsenic in groundwater and in agricultural soil and in various plants grown on them.

Further, the flow-irrigation techniques utilised for crops like paddy is a long-term irrigation process which allows the soil to be flooded with contaminated water.

It eventually causes photo-accumulation of arsenic in the food crops, say AK Ghosh and S Singh in their paper published in World Applied Sciences in 2011. Bioaccumulation of arsenic in plants, especially in the leaves, can emanate from contaminated water sprayed on them, says T Roychowdhury in a paper published in Food and Chemical Toxicology in 2008.

Thus a chain for transfer of arsenic from water to food is facilitated when farmers use contaminated water for irrigation. The ramifications of this transfer of poison are multifold. Coincidentally, the GBM plains are conducive to agriculture which is why field crops such as rice, maize, lentils and wheat and horticultural crops are widely cultivated across these states.

But what is grown in these states is laced with hazardous arsenic. A study published in Food and Chemical Toxicology in 2008 found rice — even in boiled rice — vegetables and pulses contaminated with arsenic. Arsenic content in boiled or cooked rice was approximately 2.1 times that of raw rice grains. The accumulation of arsenic begins from the time the rice is washed in contaminated water. Ghosh and Singh's study also revealed that wheat in Bihar has the highest retention of arsenic. The retention levels reduce from rice husk, rice grains to lentils with minimum retention in maize. 

Diffused contamination 

The entry of arsenic into the food chain, in addition to drinking water, presents an array of consequences, the most alarming of which is the shift of arsenic — from a point source contamination in terms of drinking water — to a more diffused source contamination in the case of food products, with possibilities of biomagnification, says SK Sanyal in a study published in Dialogue — Science, Scientists and Society in 2018.

Juxtaposing the presence of arsenic in food crops into the currently larger problem of arsenic contamination in drinking water show that the spread of arsenic is much wider and beyond the GBM basin. But there are no estimates of diffused arsenic contamination of our food chain through food products.

A deeper look into the food web reveals rice husk — containing high levels of arsenic — is being used as fodder for livestock, exposing them to the hazardous impacts of arsenic contamination. This is also leading to a potential risk for humans when they consume cattle based food products. While research in this domain is nascent, the potential risk of arsenic contamination is unsettling due to its implications.

This implies mitigation measures — that are currently focused on drinking water — must have a more comprehensive approach to ensure arsenic-free water for drinking and agricultural products. That means that the government must check for arsenic in water used for agricultural produce.

Both the Union and state governments must work toward facilitating research that can investigate the accumulation of arsenic in crops and addressing the agricultural concerns of the affected regions. They must watch out for arsenic percolation in the food chain and the possibilities of biomagnification.

The government needs to also conduct a larger study on the arsenic contamination of our food chain and its health impacts to understand its spatial spread through the agricultural supply chain. As the poison is spreading, the clock is ticking too. 

The authors work with Megh Pyne Abhiyan, a Delhi-based non-profit working on water and sanitation issues

This was first published in Down To Earth's print edition (dated 1-15 February, 2020) 

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