What Is Your Poison?

January 13th, 2013 BY Hilary Feldman | No Comments

You may be getting more than you bargained for in your beverages. Whether at home or abroad, the question could be, “Coffee, tea, or arsenic?” And don’t look for clues – this toxic element is colourless, odourless, and tasteless in water.

Arsenic is a natural component of rocks rich in certain minerals, including iron and sulphur compounds, such as iron pyrite. As part of normal erosion processes, arsenic leaches out of rock into groundwater supplies – and then can move into wells and other drinking water sources. These inorganic forms of arsenic are more toxic than their organic counterparts. Currently, the World Health Organization limit is 10 micrograms of arsenic per litre; many countries such as the US and Canada have adopted this guideline.

Chronic exposure to arsenic may lead to a host of medical conditions, including cardiovascular and pulmonary disease, neurological problems, skin complaints, and a higher risk of certain cancers. Exposure to arsenic is not reversible.

Geology knows no boundaries, and so arsenic toxicity is a global concern. Some of the most affected countries include Bangladesh, India and China. Parts of the US have reported high levels of arsenic in groundwater. In Wisconsin, arsenic levels are extremely high in many regions. About 70% of the population relies on wells – and increasing demand has resulted in a lower water table. As a result, wells must be deeper and arsenic levels are higher. Arsenic levels can change over time, meaning that regular testing is sensible for affected areas.

To complicate the issue, sulphide minerals release arsenic due to oxidation, while iron oxides are broken down by bacteria in low-oxygen conditions. Two different scenarios require completely different solutions. For example, where water is treated with chlorine, this may lead to the reduction of arsenic-producing bacteria. But the chlorine bleach also creates high oxygen conditions that may then erode sulphide minerals in the aquifer. Given the wrong conditions, treating wellwater with bleach may increase arsenic levels.

Recent research reported at the American Geophysical Union meeting found that chlorination was a viable treatment for arsenic-producing bacteria when the water level was high and oxygen low. However, with low water tables, the same treatment is not as successful.

Another approach to arsenic removal is through filtration. For widespread use, filter materials must be quick and cheap. Just this year, one researcher won an engineering prize for his innovative filtration system based on charcoal, brick, and cast iron fragments. Clearly, this has to be the direction to take – since arsenic is an unavoidable fact of life (and supplemented by many industrial sources), particularly in rural areas that rely on wells and groundwater.

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