Arsenic; Natural but Nasty
Arsenic; Natural but Nasty
by Lisa Saffron
In 1900, beer drinkers in northern England died of arsenic poisoning when sulphuric acid contaminated with arsenic was used in the processing of the beer. Murderers prefer arsenic as it has no taste or odour. But arsenic is not just a cause of accidental deaths or a convenient means of eliminating enemies. It is an environmental pollutant of global proportions. An international conference in February highlighted the serious problem of arsenic-contaminated well water in Bangladesh. The scale of the problem is probably greater in Bangladesh than anywhere else in the world but people in other countries have also suffered from arsenic pollution.
In countries such as Bangladesh and Taiwan, arsenic is a natural contaminant of ground water. Arsenic is an element found in geological formations, particularly in granites also containing copper and tin. As long as the arsenic remains bound in the granite, it causes no problems to people. But in certain conditions, natural weathering of the granite occurs and the arsenic is released into the ground water. Hydrogeologist say that in Bangladesh, the weathering occurs deep in the ground where no oxygen is present and where the sediments contain high concentrations of arsenic-rich iron hydroxides.
Well Water in Bangladesh
Although well endowed with rainfall, Bangladesh does not have the resources to provide clean water to all its residents. Without proper sanitation, surface water becomes contaminated with faecal microorganisms, causing cholera, diarrhoea, hepatitis and other water-borne diseases. To avoid this, more than 3 million tubewells wells have been sunk, providing microbiologically safe drinking water to 97% of the population.
But the tubewells have generated a new health problem. Health workers began noticing symptoms of arsenic poisoning -- increased pigmentation (melanosis), painful wart-like skin lesions which start on the palms and soles and spread all over the body (keratosis), lesions on the mucous membranes, and disorders of the nervous and respiratory systems. They connected these symptoms of arsenic poisoning to high arsenic levels in water from tubewells. No one knows the extent of the problem. One tubewell may contain high levels of arsenic while a nearby tubewell in the same village may be free of arsenic. Large scale testing supported by Unicef is being carried out and other sources of clean water are being found for those whose tubewells are contaminated. But little can be done to treat people already suffering the effects of arsenic poisoning. If the experience of Taiwan is anything to go on, people in Bangladesh are at higher risk of cancers of the skin and internal organs.
Well Water in Taiwan
Residents of southern Taiwan have been drinking arsenic-contaminated well water since the Second World War. Blackfoot disease, a unique vascular disease, is common in this area. Residents also have a significantly higher rate of cancers of the liver, lung, skin, bladder, kidney, and prostate. In addition to cancer, there is a higher rate of diabetes and hypertension.
Natural weathering is to blame for polluting the wells in Bangladesh and Taiwan. But in other countries, the arsenic pollution has a human source. Mining, smelting, pesticide spraying and coal burning all pollute the environment with arsenic.
Long before organochlorine and organophosphate pesticides, arsenic-based pesticides were the most common type of pesticide used in agriculture. The evidence linking arsenic-based pesticides with skin and lung cancer is strong and persuasive. The increased cancer risk has not been associated with eating food containing residues but with occupational exposure, particularly among professional pesticide sprayers and among workers in pesticide manufacturing plants.
Mining and Smelting
Arsenic pollution is a consequence of arsenic, tin and copper mining and smelting. Mine spoils have been dumped on the land and near or into streams. Smelting of the ore scatters the arsenic through the air in a plume of soot, contaminating soil and streams in a wide area. Poisoning can occur when people are exposed to contaminated water, dust and soil.
A thousand year history of mining and smelting has left a legacy of arsenic pollution in Devon and Cornwall. During the last half of the nineteenth century, Cornwall was the world's largest producer of arsenic. Soil in some parts of Cornwall has the world's highest concentration of arsenic, up to 2500 ppm. Elsewhere in the UK and the rest of the world, arsenic levels are usually below 40 ppm. Although arsenic levels in Cornish streams and rivers occasionally exceed WHO drinking water guidelines, the main concern about human exposure is through ingesting or inhaling dust and soil. Fortunately, locally grown vegetables do not accumulate arsenic from the soil to a dangerous level.
Last year the Environmental Geochemistry Group of Imperial College tested the urine of people living in Cornwall and found higher concentrations of various forms of arsenic in people living in former mining areas than in the control group. But the research group did not find a significant increase in bladder cancer as a result of arsenic exposure in Cornwall. As yet, there have not been any proven associations between high arsenic levels and health problems in the south west of England. The Department of Health is funding ongoing research in this area.
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