India, too, suffers from a high burden, with Bihar showing an upsurge in cases affected by arsenic poisoning
Sea-level rise driven by climate change could significantly release arsenic — a cancer-causing agent — into Bangladesh’s drinking well water, according to a new study.
Climate change could accelerate chemical reactions in the aquifer, leading to the release of arsenic from alluvial sediments deposited by the Ganga, Brahmaputra, and Meghna rivers.
“As change progresses, sea levels will continue to rise, and the area and duration of these annual floods will increase,” the researchers wrote in their paper published in the journal PLOS One.
This could affect roughly 97 per cent of Bangladesh’s population consuming well water. Approximately 49 per cent of the area’s drinking well water is contaminated with arsenic concentrations exceeding 10 micrograms per litre limit by the World Health Organization. Exposure to arsenic is already increasing the rates of death and disease from skin, bladder, liver, and lung cancers and vascular disease in the country.
Arsenic poisoning is a global health issue. Some 300 million people worldwide are affected by the consumption of arsenic-contaminated groundwater. India, too, suffers from a high burden, with Bihar showing an upsurge in cases affected by arsenic poisoning, according to a 2021 Scientific Reports study.
The researchers evaluated how chemical changes in the coastal aquifer due to sea level rise is related to the release of arsenic from sediments into Bangladesh’s drinking well water.
So they collected groundwater samples from 83 random drinking water wells from July 22 to August 14, 1997.
These samples were then analysed for the levels of dissolved oxygen, oxidation-reduction potential, specific conductance (measures the ability of water to conduct an electrical current), pH, and temperature.
The oxidation-reduction reaction refers to the transfer of electrons between atoms or molecules.
As sea levels continue to rise and floods and cyclones in Bangladesh increase in area and duration, floodwaters prevent atmospheric oxygen, a very strong oxidising agent, from diffusing into the aquifer. This favours a reducing environment in the aquifers.
As a result, the insoluble arsenate from minerals is reduced to soluble arsenite, causing arsenic to dissolve in drinking well water.
The researchers estimated dissolved oxygen levels to be in the range of 0.16 milligrams per litre (mg/L) to 12.70 mg/L. “As predicted, relatively low concentrations of dissolved oxygen are associated with relatively high concentrations of arsenic,” reads the paper.
Further, rising sea levels can increase the salt concentration in the aquifer. This, according to the paper, should increase the release of arsenic from sediments into the drinking well water.
The researchers also highlighted that with increasing specific conductance, the concentration of arsenic increases. This study found the specific conductance of drinking well water to range from 40 microsiemen per centimeter (μS/cm) to 5,360 μS/cm.
“Bangladesh’s drinking well water has a higher specific conductance in the south near the Bay of Bengal and a lower specific conductance in the north near the Himalayan mountains. This is consistent with floods and storm surges causing relatively higher specific conductance saltwater to intrude from the south to the north,” the researchers wrote in the paper.
Also, as the pH (which measures the concentration of aqueous hydroxide ion) increases, the concentration of arsenic increases. The pH of Bangladesh’s drinking well water in this study ranged from 3.90 to 7.96. For comparison, the pH of ocean water is 8.1.
Like specific conductance, the pH values are higher in the south near the Bay of Bengal and lower in the north near the Himalayan mountains.
This increased exposure to arsenic, the researchers explained, is expected to increase the rates of death and disease from chronic arsenic poisoning.
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