Arsenic contamination

A RECENT study published in the Science Advances journal, ‘Extensive arsenic contamination in high-pH unconfined aquifers in the Indus Valley’, has led to widespread concern about the health effects of arsenic in Pakistan’s water supply. The study’s findings have been widely discussed in the media, with some commentators suggesting that it is a national emergency possibly affecting about 50 to 60 million Pakistanis.
Unfortunately, this figure, which is also mentioned in the study, is not backed by robust evidence. This is because the study focused solely on water samples and did not conduct a health assessment. The absence of a separate health-focused analysis means that there is no firm evidence of the harmful effects of arsenic exposure.
In order to assess the health risks facing Pakistanis, one has to conduct systematic population-based research. This involves first assessing the presence of arsenic in water sources and then correlating its presence with health risks for the local population.
In neighbouring Bangladesh, there has been a great deal of inquiry into the adverse health effects of arsenic. More than a hundred studies have found very high concentrations of arsenic in groundwater leading to the presence of very specific types of skin lesions.
Such lesions, which can only be caused by arsenic exposure, are distinctive because they are symmetrical in nature. One would notice the hardening of both palms and or both soles of the feet: a clear-cut sign of excessive arsenic exposure. Such changes to the texture of the skin are not seen in any other medical condition and do not mimic any other disease. It can only be caused by arsenic exposure. In 2009, researchers from Aga Khan University, in collaboration with Unicef and local government, conducted a health-focused study similar to the one referred to above. This study examined levels of arsenic in Khairpur, Sindh, a district that has significant arsenic levels in its water, according to national arsenic surveys. In other words, this was an area where rampant health effects like skin lesions should have been found, since there was strong evidence of unusual levels of arsenic in the water.
But researchers only found signs of skin lesions in 13 out of 1,000 cases, and only noted indications of abnormal thickening of the skin (hyperkeratosis) in 3.4 out of 1,000 cases. There should be no doubt that arsenic contamination exists in Pakistan and that its health consequences are an important issue, but the scale and severity is not in line with the figures being published in the media. The international study also developed geographic models to map arsenic exposure that do not consider a key point. Arsenic doesn’t uniformly contaminate underground water or soil. It exists in a scattered pattern; so it’s possible for water in one well to have high amounts of contamination but for another, nearby well to have water that’s safe for use.
This finding, that has been noted in many studies in Bangladesh, means that not all groundwater or river water across the country contains arsenic. This is why one strategy to mitigate arsenic exposure in Bangladesh and Pakistan is called ‘well-switching’, in which villagers work to find safe wells within walking distance of an arsenic-contaminated well. Arsenic’s contamination pattern means that researchers have to be cautious before designating entire areas as dangerous.
Another area for researchers to consider is the nature of arsenic in water. Inorganic arsenic is three times as dangerous as organic arsenic. Therefore, conducting risk assessments based on the total level of arsenic may be misleading, as judging the health risk from arsenic requires a more refined chemical analysis. More research on this aspect can yield promising insights about adverse health effects.

The writer is a professor in the Community Health Sciences department at Aga Khan University, Karachi.

Source : Dawn


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