The largest mass poisoning in history: arsenic in the water in Bangladesh

The Bangladesh is facing the worst case of collective poisoning of history: the presence of high concentrations of arsenic (chemical symbol As) in groundwater, also called “aquifer”, primary source for human consumption and for irrigation in the country, it involves the population of different regions of the country. Some studies estimate between 35 and 77 million citizens involvedwith consequences ranging from skin lesions and keratosis until the onset of tumorsmainly to the bladder, kidneys or lungs.

Poor infrastructure it's a weak economy they make it difficult to fight the emergency or even just have more precise data on the affected populationdespite the interest of international organizations such as the WHO (World Health Organization)which has been following the case for several years and studying countermeasures in collaboration with local authorities.

The spread of the wells and the first evidence of the presence of arsenic

The poor sanitary conditions in Bangladesh they were already causing concern in 70's: the mortality above all childish remained high, mainly due to intestinal infections caused by microorganisms present in surface waters. The rapidly growing population (in the 1970s there were less than 70 million people, today more than 170) needed clean sources to survive.

For this reason, theUNICEF started a program for the installation of wells small in size, capable of exploiting the biologically “cleaner” groundwater. The program, thanks also to growing private interventions since the 1980s, achieved its objective of providing “safe” water to at least 80% of the population in 1997.

The first evidence of presence of arsenic in groundwater they took place in 1993 in the district of Nawabganj: in the following years, investigations into the search for arsenic in waters spread throughout the entire country.

An extended 1996 studywhich involved Indian universities and Bangladeshi institutions, highlighted how out of 400 wells analyzed, 50% exceeded the expected limit by local authorities for human consumption of 50 µg/l while the8.4% surpassed even values ​​of 300 µg/l. For reference, the value recommended by the WHO and adopted by European and Italian regulations and of 10 µg/l.

Because there is arsenic in the water

The presence of arsenic in surface or groundwater it is, unfortunately, a problem that unites various areas on all continents, fromAsia (China, Taiwan) atAmerica (Chile, Argentina, USA), with areas at risk also in Europe (Belgium, Spain); in someone of these areas theorigin And anthropogenici.e. due to industrial human activities such asextraction mining or the processing and use of fossil fuels, but it is natural origin is very commondue to composition of rocks in contact with aquifers.

Even in the case of Bangladesh the origin is natural: Erosion of the Himalayan mountains caused the deposition of sediments in the enormous Ganges delta for millennia. The sediments are rich in iron and manganese minerals and contain arsenic impurities.

Arsenic is soluble in water mainly in two forms. One is arsenic acid (H₃AsO₄), that yes League (technically, “adsorbs”) more easily to the ground; the other form isarsenious acid (H₃AsO₃one less oxygen), which remains more dissolved in water.

The basic pH (between 7.17 and 8.09) of many Bangladeshi aquifers increases the quantity of dissolved arsenic, because OH ions^– interact with i exchange sites in the ground in place of dissolved arsenic.

The consumption of groundwater excessive (for human use or for irrigation) also leads tolowering of water levels, permitting all'oxygen (OR₂) in the air of to react with i minerals in the sediments first submerged, releasing further arsenic.

The check of concentrations is difficult also for the lack of aqueducts: studies indeed require analysis for each well used, made possible by the use of portable kits.

The health effects and the probable surge in cases

The effects of arsenic poisoning are different: a short term can appear nausea, vomiting or diarrheawith evidence of hyper- or hypo-pigmentation of the skin.

What causes more concern, however, are the long-term effectswhich they often have from 5 to 20 years of latency: the skin lesions and keratosis are among the most evident, found in some regions even in 57% of the population followed by some studies between 1996 and 1997, but never in individuals with less than 10 years of age.

The onset of kidney, bladder and lung cancers are another typical effect of arsenicosis: studies in populations exposed in previous decades, as in the case of citizens of Antofagasta in Chilehighlight how up to 5/10% of deaths for individuals over 30 years of age could be attributed to tumors of this type. The US National Research Council estimates that a exposure to 50 µg/l can bring the combined risk of cancer at 1 in 100and higher concentrations (50o µg/l) also to 13 cases per 100 individuals.

Precisely these numbers raise fears that, unfortunately, i registered cases in Bangladesh they are destined to grow in the coming decades.

Corrective actions

The main corrective actions already implemented focus on closure of the most polluted wells from arsenic, but also on the use of filtration systems of the water of small size, easy maintenance and low cost: it's mostly about cartridge filtersbut also economic systems of filtration at multiple stagesperhaps using water purification kits.

The other front is obviously that of care of people already suffering from arsenicosis.

The first objective is definitely supply to the subjects arsenic-free water: the organism is able to free itself with the urine of the “free” arsenic taken after about a weekbut Not of the part accumulated in the tissues most affected, such as the skin or internal organs. Reducing chronic exposure can however lower the risk of future complicationsand some keratosis patients report improvements over time.

Precisely because of the body's natural ability to get rid of the element, the use of treatments chelators, that is, capable of interacting with free arsenic in the body to facilitate its expulsion, it is not considered effective.

In addition to screening to diagnose any tumors early, the importance of the treatment of skin lesions: keratosis can be a disabling problem for the person, and it is therefore essential to help those affected with hydration and treatment products of the skin, decreasing also the onset of infections.

Arsenic has also been considered a possibility factor in the onset of diabetes mellitus, another reason why screening of the affected population is advisable. Unfortunately, however, even decades after the first studies, the economic and infrastructural situation of the country still yields difficult to act effectively and help Bangladeshi citizens deal with this disaster.