The Global Arsenic Timebomb

About 140 million people, mainly in developing countries, are being poisoned by arsenic in their drinking water, researchers believe. Speaking at the Royal Geographical Society (RGS) annual meeting in London, scientists said this will lead to higher rates of cancer in the future, and South and East Asia account for more than half of the known cases globally. Eating large amounts of rice grown in affected areas could also be a health risk, scientists said.

“It’s a global problem, present in 70 countries, probably more,” said Peter Ravenscroft, a research associate in geography with Cambridge University.

The first signs that arsenic-contaminated water might be a major health issue emerged in the 1980s, with the documentation of poisoned communities in Bangladesh and the Indian state of West Bengal. In order to avoid drinking surface water, which can be contaminated with bacteria causing diarrhoea and other diseases, aid agencies had been promoting the digging of wells, not suspecting that well water would emerge with elevated levels of arsenic.

The metal is present naturally in soil, and leaches into groundwater, with bacteria thought to play a role. Since then, large-scale contamination has been found in other Asian countries such as China, Cambodia and Vietnam, in South America and Africa.

Asian countries use water for agriculture as well as drinking, and this too can be a source of arsenic poisoning. Rice is usually grown in paddy fields, often flooded with water from the same wells. Arsenic is drawn up into the grains which are used for food.

Andrew Meharg from Aberdeen University has shown that arsenic transfers from soil to rice about 10 times more efficiently than to other grain crops. This is clearly a problem in countries such as Bangladesh where rice is the staple food, and Professor Meharg believes it could be an issue even in the UK among communities which eat rice frequently.

“The average (British) person eats about 10g to 16g of rice per day, but members of the UK Bangladeshi community for example might eat 300g per day,” he said.

The Science Bit:

The LD₅₀ (median lethal dose) for pure arsenic is 763 mg/kg (by ingestion) and 13 mg/kg (by intraperitoneal injection). For a 70 kg (~155 lb) human, this works out to about 53 grams (less than 2 ounces).

The “safe” limit for arsenic in water in the EU is 10 parts per billion (ppb), while levels in Bangladesh well can be in excess of 1 part per thousand (100 times greater). 10 parts per billion equates to 10 micrograms per litre, so you would need 53,000 litres of water (that’s 53 grams diluted in approx 1.5 petrol tankers in size) to contain the lethal dose at EU levels.

The inorganic arsenic exposure from ingesting 2 ounces (56 grams) of uncooked rice ranges from 1 – 5.4 µg (micrograms) assuming a 2 litre/day intake (source: US EPA). A daily dose of arsenic for a British person is approx anything from 0.26 µg to 1.45 µg (if you eat rice every day), but Bangladeshi’s eat more and this level rises to between 5.4 µg and 29 µg. Of course, the source of the rice alters the level of arsenic in it and so this level goes up or down accordingly, but in high toxicity areas such as Asia, the life expectancy could become very low indeed.

And what happens if we export such toxic rice worldwide? The UK’s Food Standards Agency is currently assessing whether the level of UK consumption carries any risk for all ethnic groups.

Full Story: BBC NEWS | Science/Nature | World facing ‘arsenic timebomb’

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