Arsenic poisoning from drinking water

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A study published in The Lancet this month calculated mortality rates associated with arsenic exposure from drinking water in a Bangladeshi population. Individual-level data was used to determine that 21.4% of all deaths and 23.5% of deaths associated with chronic disease in this population could be attributed to arsenic exposure.

Millions of people worldwide are chronically exposed to arsenic through drinking water, including 35-77 million people in Bangladesh. WHO described the arsenic crisis in Bangladesh as 'the largest mass poisoning of a population in history'. An estimated 35-77 million people in Bangladesh have been chronically exposed to increased concentrations of arsenic through drinking water, beginning in the 1970s when about 10 million hand-pumped wells were installed to provide pathogen-free groundwater for the prevention of waterborne diseases. However, the natural contamination of the groundwater with arsenic in these wells was not realised until the 1990s.

Exposure to arsenic in drinking water has been associated with several cancers; toxic effects on the liver, skin, kidney, cardiovascular system and lung; and fatal poisoning. Dose-dependent associations have been shown between arsenic levels in well water and cancers of the bladder, kidney, skin and lung. Dose-response associations between arsenic exposure and peripheral vascular disease have also been reported.

In the prospective cohort Health Effects of Arsenic Longitudinal Study (HEALS), trained physicians unaware of arsenic exposure interviewed and clinically assessed 11,746 population-based participants (aged 18-75 years) from Araihazar, Bangladesh. Participants were recruited from October 2000 to May 2002, and followed-up biennially. Data for mortality rates were available throughout February 2009. The authors used Cox proportional hazards model to estimate hazard ratios (HRs) of mortality, with adjustment for potential confounders, at different evels of arsenic exposure.

Results indicated that the mortality rate increased at all concentrations of arsenic in well water, indicating an increasing risk rather than a threshold effect. A one-quartile increase in arsenic concentration in well water was associated with a 15% increase in all-cause mortality, with corresponding increases of 14% for arsenic dose per day and 13% for total arsenic concentration in urine. Similar results were noted for the associations between arsenic exposure and mortality associated with chronic disease. Based on the risk estimates, an estimated 21.4% f all deaths and 23.5% of deaths associated with chronic disease in this population could be attributed to arsenic exposure (>10 μg/L) in drinking water.

The authors conclude that chronic arsenic exposure through drinking water was associated with an increase in the mortality rate. Follow-up data from this cohort will be used to assess the long-term effects of arsenic exposure and how they might be affected by changes in exposure. Although initiatives to reduce exposure to arsenic in drinking water are in progress, investigations of solutions to mitigate the resulting health effects of this catastrophe require urgent attention and resources.

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