Team:IISER-Kolkata/Problem
Description
"The chronic arsenic poisoning in West Bengal represents the single largest environmental health problem the world has ever seen, other than that associated with the Chernobyl disaster" - D. Chakraborti et. al., Elsevier, May 2002
Introduction
Arsenic has been called “The king of poisons” and “The poison of the kings” owing to its use by the ruling class to murder one another. A Group-A carcinogen on WHO list, arsenic in all forms is also ranked at the top of the list of hazardous substances by U.S. Agency for Toxic Substances and Diseases Registry. Now imagine if your food and drinking water had been contaminated with arsenic enough to kill you but slowly by gradual accumulation in your body over years, what a miserable living that would be! This is the plight of the millions of inhabitants in West Bengal, India and Bangladesh.
Origin of Arsenic in Bengal Alluvial Plains and Underground aquifers
The sedimentation of Arsenic on the plains of Bengal started 15,000 to 12,000 years ago with the melting of glaciers at the end of the Pleistocene epoch. The water on the Himalayan slopes eroded the exposed arsenic laden rocks from the Indus ophiolite belt and the high grade gneisses solvating the arsenic minerals and carrying them downstream along the Ganga and Brahmaputra rivers. Upon reaching the flat lands of Bengal, the river waters start deloading their carries depositing heavy alluvial sediments along with high concentration of eroded arsenic salts on these plains. When rain and accumulated water seeps into the ground through such arsenic contaminated soil layers, it solvates the inorganic salts on its way down to the aquifers. This in turn leads to arsenic pollution of groundwater aquifers with contamination increasing steadily over years as more deposits are laid upon by the rivers and more water seeps through the soil reaching the underground stores.
Problem severity in West Bengal
WHO allowed levels of Arsenic in drinking water for it to be deemed safe is 10μg/L, while the government national standards for India and Bangladesh are 50μg/L. In comparison to these recommended figures, let us compare the average arsenic concentrations in groundwater in the six most badly affected districts of West Bengal.
| District in West Bengal | Average Arsenic conc. In groundwater (in μg/L) | Range of Arsenic concentrations in samples (in μg/L) |
|---|---|---|
| North 24 Parganas | 737 | 50 to 1250 |
| South 24 Parganas | 278 | 50 to 3700 |
| Murshidabad | 257 | 50 to 950 |
| Nadia | 241 | 50 to 1180 |
| Malda | 210 | 50 to 930 |
| Bardhaman | 193 | 50 to 640 |
The above chart is sufficient to paint a realistic and drastic picture of the severity of the arsenic contamination problem in West Bengal. It is also worth noting that our Institute IISER Kolkata is situated in the district Nadia, one of the most severely impacted regions in West Bengal.
Problem severity across the globe
Though of particular importance in India and Bangladesh, contamination of ground water by arsenic is a global issue with its presence being felt in over 66 countries of the world spanning all continents. Argentina, Chile, Mexico, USA and China are among the other major sufferers of the crisis along with India and Bangladesh. Our collaboration with iGEM TecCEM Mexico team has helped us get a hold on the arsenic contamination data in Mexico and Latin America improving our insights regarding the problem.
| Country | Range of Arsenic concentrations in groundwater aquifers |
|---|---|
| Mexico | 8 to 620 μg/L |
| China | 50 to 4440 μg/L |
| USA | Upto 2600 μg/L |
| Brazil | 0.4 to 350 μg/L |
| Vietnam, Thailand | 1 to 5000 μg/L |
| Greece | Upto 10,000 μg/L |
Data obtained from collaborator team TecCEM Mexico:
- Alluvial aquifers in northern and central mexico show highest levels of contamination.
- These regions are also amongst the most populated regions of Mexico leaving a large population vulnerable to water extracted from these polluted groundwater stores.
- The Arsenic concentration in these Mexican aquifers varies from 3 to 443 μg/L while more than 50% samples had arsenic levels above the national standard of 50μg/L.
Fixating on the Problem
Therefore, team IISER Kolkata chose to work on the problem of “Arsenic contamination of groundwater and resulting health crisis due to poisoning” due to its high relevance and importance especially in the region where our institute is located as well as in other parts of the world. In this problem we could see the exciting challenge of putting our knowledge and skills to use in solving something really pressing for the common people around us while by large, still staying committed to the needs of a global community facing the same issue.
Existing solutions and their shortcomings
Although arsenic contamination is still a pertinent problem, people have been trying to address it in the ways listed below. Also described are the shortcomings of each of the previously existing solutions to counter this issue:
| Arsenic Removal Technique | Description | Shortcomings |
|---|---|---|
| Chemical Oxidation | Process is complex and produces difficult to dispose As rich residue. | Oxidise highly toxic and difficult to separate As(III) form to docile and easily separable As(V) form followed by further treatment, filtration or flocculation. |
| Coagulation and Flocculation | Leads to secondary pollution of the environment due to problems involved in disposal of Arsenic laden sludge whose management is difficult and expensive. | Addition of coagulants like FeCl3 agglutinates colloidal suspension of Arsenic ions in water and further flocculation by adding substances like alum produces an easily separable sludge. |
| Selective Filtration | Membrane filters need constant pH maintenance and reagent refilling. Also they are slow due to long time needed for conditioning. | Several filtration techniques make use of sieves and membranes that filter out arsenic based on size and/or charge. Diatomaceous Earth matrix is also used as a filter. |
| Adsorption on Surfaces | Specificity in action of these units is low and have problems with regeneration of the adsorbent material after repeated uses. | Certain material surfaces such as that of Coconut Shell Carbon etc. can be activated to bind and adsorb Arsenic ions due to their chemical affinity. |
Apart from the above mentioned drawbacks of each of the existing techniques there are certain shortcomings common to all:
- Expensive Kits not affordable to the majority of suffering households in West Bengal and Bangladesh.
- Kits and Technologies are mostly developed in U.S. or abroad and therefore do not suit the specific requirements of India and Bangladesh. Indigenously researched technologies for Arsenic removal are mostly in the process of development and scaling up to be released as products.
Ref: Technologies for Arsenic Removal from Water, Nicomel N. R., et. al., Int. Journal of Environmental Research and Public Health, 2016
Arsenicosis
Consumption of arsenic contaminated food and water over long term of 5 to 20 years leads to accumulation of the heavy metal in body tissues starting from hair to skin epidermis causing several dreadful symptoms such as:
- Hair loss
- Hyperpigmentation (darkening of the skin)
- Bowen’s lesions
- Peripheral neuropathy
- Diabetes
- Cardiovascular diseases
- Still-births to affected pregnant women
- Expensive Kits not affordable to the majority of suffering households in West Bengal and Bangladesh.
- Cancers of skin, bladder, kidney and lung
Now one can filter groundwater before drinking. However, substantially high amount of As is also ingested through food. When contaminated groundwater is used to irrigate fields of crop plants such as rice or to fill ponds to rear fishes, the heavy metal enters their living tissues and starts getting accumulated therein. Later, when these cereals or fishes enter the human food chain they lead start being absorbed into the human body and getting accumulated in human tissues which later manifest into the symptoms of arsenicosis.
Based on the study conducted in high As contamination Nadia district of West Bengal, India:
| Food Item | Mean Arsenic Content (in μg/Kg) |
|---|---|
| Raw rice grains | 315 |
| Cooked Rice | 97 |
| Cooked Fish | 96 |
| Cooked Egg | 191 |
| Chapati (Wheat Tortilla) | 171 |
| Fruit | 20 |
| Milk | 60 |
| Cooked Meat | 29 |
| Arsenic Intake | Mean Value |
|---|---|
| Daily intake through diet | 164 μg/day |
| Daily intake through water and diet | 349 μg/day |
| Total As dose through diet | 3.37 μg/Kg/day |
| Total As through water and diet | 6.93 μg/Kg/day |
From the above tabular representation of the data, it is clear that food is a major contributor of As ingestion along with contaminated water. Currently, no techniques exist to combat this pathway of As entry into human body due to lack of feasibility of filtering out As from large amounts of water used to raise food crops and livestock. Also, it is very alarming that Rice and Fish both of which form the staple food of a large population in Bengal, have the highest levels of Arsenic accumulation among all food items and hence pose a great risk to the health of these people.
Assuming on average 450g of cooked rice and 4L of water is consumed daily by an adult in West Bengal, 550 ppb and 110 ppb of As gets ingested daily through these respective sources.
Ref: What are Safe Levels of Arsenic in Food and Soils?, Duxbury and Zavala, Cornell Univ
The median excess internal cancer risk parameter is a measure of the likelihood of cancer in a population. This value is 0.7 per 10,000 Italians as compared to 22 per 10,000 for residents of Bangladesh.
Ref: Arsenic and Food Chain
Therefore, Team IISER Kolkata wanted to develop a novel and prevention based approach to battle Arsenicosis by targeting its intake from diet as well as water by engineering a probiotic bacterial system to compete with gut epithelium to uptake ingested Arsenic.
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