Arsenic in Water

By Michael Edmonds 04/12/2011 4

Last week I attended an excellent talk by Professor Neil Ward from the University of Surrey where he spoke about detection of arsenic in various water supplies around the world. The World Health Organisation has set a guideline maximum of 10 parts per billion (10 ppb) for drinking water. This guideline is based on a precautionary approach to arsenic levels in water – in many countries (and in the USA until it was reduced) the standard for water quality is set at 50 ppb.

Professor Ward has developed a number of techniques for not only determining the amount of arsenic in water supplies at such low levels, but also for determining the levels of each type of arsenic.

Arsenic can exist in a variety of forms in the environment. Arsenic (III) is the most toxic, while arsenic (V) and organic forms of arsenic (dimethylarsinic acid and monomethylarsonic acid) are progressively less toxic. Hence to fully understand the safety of water which contains arsenic it is important where possible to determine the levels of each type of arsenic, rather than look at the total arsenic content. The type of arsenic compounds present in water is dependent of several factor include the water pH.

The problem of high levels of arsenic in drinking water is experienced in a number of countries in South America and Asia, as well as in parts of New Zealand and the USA. The most common cause is the exposure of the water to volcanic material which has high levels of arsenic. Consequently water obtained from geothermal sources or wells sunk deep enough to penetrate volcanic ash layers can prove to be high in arsenic. High arsenic levels can also be found in agricultural areas which were treated with arsenic-based herbicides.

For many years Professor Ward has worked with the people of Argentina to monitor the levels of arsenic in their water supplies and has found that arsenic can be present in very high levels. In some areas the levels of total arsenic can exceed 4500 ppb (i.e. 4.5 ppm) a staggering 450 times the WHO guidelines. However, in many areas much of the arsenic is at least in the form of the less toxic As(V).

High levels of arsenic can result in a number of diseases including skin and bladder cancer. However, because of the different toxicities of the different forms arsenic can take in water, it is difficult to determine what an appropriate safe level should be.

Professor Ward’s work with the people of Argentina has inspired them to take a greater interest in their environment and to look after. Various methods have been employed to remove arsenic from their water supplies and his work has recently attracted the interest of the president of Argentina. Professor Ward has also used this interest in their environment to engage local students in learning science – teaching them how to analyse local water supplies. (What better way to engage students than to show them that science can help examine and solve problems of local importance).

4 Responses to “Arsenic in Water”

  • I take it there is no Arsenic “Toxic Equivalents” calculation?
    For Benzo[a]pyrene there is a calculation that you can use to total up a number of PAH compounds and multiply them by a factor depending on how toxic they are compared to BaP. The final result gives an amount that is equivalent to how much BaP you would need to achieve the same toxicity.

    Sounds like something similar should be done for Arsenic.

  • Not that I’m aware of. Up until now it has been quite difficult to determine the amount of each individual species of arsenic as the moment a sample is stored there is the possibly that the species will change. Prof Ward has developed a system whereby the different species are separated at the moment of collection thereby avoiding this problem.
    Now that this can be done, I would not be surprised if soon some toxic equivalents are calculated.

  • Here’s an interesting paper to chase up, Michael:
    Bundschuh et al. 2010 Emergeing mitigation needs and sustainable options for solving the arsenic problems of rural and isolated urban areas in Latin America – a critical analysis. Water Research 44, 5828-5845.
    They consider arsenic removal methods right down to the household scale.