Arsenic is widely distributed through the earth’s crust and is present in almost all waters in very small amounts.

However, in certain areas there are dangerous levels of this toxin in drinking water. One of the most serious cases is Bangladesh, where thousands of wells cause mass poisoning of the population.

Arsenic is a known carcinogen, and when constantly consumed it can affect the gastro-intestinal, respiratory and vascular systems, often resulting in cancers of the skin, lung and bladder.

During the 1990s, 900 million people around the world gained access to an improved water supply, yet 1.1 billion people in rural areas and urban slums still rely on unsafe drinking water from rivers, lakes and open wells.

Children, in particular, suffer from water-related illnesses. Each episode of diarrhoea can reduce their appetite and lower their calorie and nutrient uptake. Persistent diarrhoea, and severe diseases such as typhoid and dysentery, jeopardize children’s healthy development. Every year, nearly two million children die as a result.

It is believed that arsenic in Bangladesh originated in the Himalayan headwaters of the Ganges and Brahmaputra rivers, and remained dormant and embedded in the land.

The poisoning began as enormous quantities of water were pumped out from deep underground reservoirs. Water levels dropped and exposed arsenic-bearing pyrite to air, leading to oxidization – a reaction that flushed arsenic into the remaining water.

The combined high probability, moderate probability and low probability contamination zones cover about 60% of the country’s total area.

In the 1970s, international agencies headed by the United Nations Children’s Fund invested millions of dollars of aid money into digging shallow tube wells in Bangladesh. Due to a lack of facilities the water was never tested for arsenic.

With groundwater consumption increasing over the next two decades, the water from more than a million tube wells began to slowly poison Bangladeshi villagers. The World Health Organization says large-scale withdrawal of ground water from an estimated 10 million tube wells may be the main cause of arsenic contamination in Bangladesh.

Control of arsenic is more complex where drinking water is obtained from many sources – such as hand-pumps and wells – as is common in rural areas. Low-arsenic water is needed only for drinking and cooking. Arsenic-rich water can be used safely for laundry and bathing.

Discriminating between low-arsenic and high-arsenic sources by painting hand-pumps green or red can be an effective and low-cost way of rapidly reducing exposure, when accompanied by effective health education.

Several initiatives have been set up in Bangladesh to investigate water quality testing and control with a view to supplying arsenic-free drinking water. One positive outcome has been the testing of new types of treatment technology.

Only a few proven sustainable options are available to provide safe drinking and irrigation water. These include obtaining low-arsenic groundwater from shallow systems or deeper aquifers (more than 200m or 220 yards approx), rainwater harvesting, pond-sand filtration, household chemical treatment and piped water supply from safe or treated sources. But cost is once again the negating factor.

Alternative low-arsenic sources such as rainwater and treated surface water may be a valid solution in some circumstances. However, arsenic removal technology for piped water is costly and requires technical expertise. It is inapplicable in some urban areas of developing countries and in most rural areas worldwide.

New types of treatment technology – including co-precipitation, ion exchange and activated alumina filtration –are being field tested, but there are few proven methods of removing arsenic on a grand scale at high-risk water collection points.