Which country has natural arsenic water contamination ?

Question

UnlockIAS · Accepted Answer

Correct — A, Bangladesh. Bangladesh is the archetypal case of natural arsenic contamination of groundwater, and the one the World Health Organization has described as the largest mass poisoning of a population in history. The mechanism is geological, not industrial: from the 1970s millions of shallow tube wells were sunk across the country, on excellent public-health advice, to get people off microbially contaminated surface water that was killing children with diarrhoeal disease. Those wells tapped young alluvial sediments of the Ganges-Brahmaputra delta in which arsenic is bound to iron oxyhydroxides, and in the oxygen-poor conditions of the aquifer that iron is reduced and the arsenic released into solution. Routine water testing at the time simply did not include arsenic, so the problem went unnoticed until it was identified in 1993 and drew international attention from 1995. One honest qualification the question does not make: Bangladesh is the best-known and worst-documented case, not the only affected country in this list's region — the Indus plain of Pakistan is also seriously arsenic-affected, and so are West Bengal, parts of Bihar and stretches of the Ganga plain in Uttar Pradesh. What makes (a) the answer is that Bangladesh is the case defined by natural arsenic contamination in the literature and in every textbook treatment of the subject.

Why the other options are wrong — (b) The one distractor a careful student can argue with, and it deserves an honest answer rather than a flat denial: arsenic above WHO limits has in fact been documented widely in Pakistan's Indus plain aquifers. But the question is reaching for the country whose arsenic crisis defines the subject, and that is unambiguously Bangladesh — identified in 1993, quantified across the whole country, and the case on which the WHO guidance and the global literature are built.  (c) Sri Lanka is not among the countries recorded for natural arsenic contamination of groundwater. Its widely reported drinking-water health problem is of a different kind — chronic kidney disease of unknown aetiology in the dry-zone farming districts — and it is not attributed to naturally occurring arsenic in aquifers.  (d) Bhutan is a Himalayan country of hard rock and steep gradients, supplied largely from surface streams and springs rather than from deep alluvial aquifers. It has no equivalent of the delta sediments that release arsenic, and it does not appear in the record of arsenic-affected countries.

Concept: Geogenic contamination means a pollutant that comes out of the rock and sediment itself rather than from a factory or a farm. Arsenic in the Ganges-Brahmaputra-Meghna delta is the standard example: arsenic-bearing minerals eroded from the Himalaya were deposited with the delta sediments and adsorbed onto iron oxyhydroxide coatings on the sand grains. Where the aquifer is reducing — starved of oxygen because buried organic matter is being consumed by bacteria — those iron coatings dissolve and the arsenic they held goes into the water. This is why the contamination is patchy well by well, why deeper and older aquifers are often safer than shallow Holocene ones, and why the problem cannot be solved by stopping any discharge. Fluoride in Rajasthan and Andhra Pradesh and uranium in parts of Punjab are the other Indian examples of the same geogenic class.

State PCS 2022 Q84 — Environment & Ecology PYQ with Answer

State PCS 2022 Q84 — Environment & Ecology PYQ with Answer