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Arsenic in Drinking Water: a Global Problem – CPS talk 11/11/14

By Penny Carmichael, on 14 November 2014

– Article by Stephen Leach

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This week the CPS was fortunate enough to be visited by Professor Neil Ward; an analytical chemist from the University of Surrey, newly invited Fellow of the Royal Society and recipient of the Queen’s Anniversary Prize for Higher Education. All round great guy, (who’s definitely not Australian). So what has warranted this sort of decoration? His work spans scrupulous analytical methodology and the advancement of education and policy in developing countries, a pretty healthy combination.

Prof. Ward has been actively investigating the extent and speciation of arsenic in drinking water in Argentina, which the World Health Organisation has ranked in the top ten chemicals of public health concern. He placed a great emphasis not only on the severity of the problem but the necessity of knowing the speciation of the arsenic. That is, beyond the identification and quantification of arsenic, the precise chemical species is also discovered. This is important since the toxicity of arsenic depends on the nature of the chemical species present.

The origin of arsenic in the soil is completely natural; it results from the volcanic activity responsible for shaping the continents. Large volcanic eruptions coat vast areas in ash containing amongst other things, arsenic. When Mount St. Helens in the US state of Washington erupted in 1980, 110 kg of arsenic was distributed over a 230 square mile area. As a direct result of that eruption the total arsenic per litre in drinking water went over the 10 microgram safe limit defined by the World Health Organisation.

Numerous eruptions have occurred throughout the geological history of the planet, resulting in the presence of arsenic on all continents. In Argentina, Prof. Ward found ~ 6000 μg/L levels of total arsenic in drinking water, which was often the only water source for people living in certain regions. As a result arsenic has been causing serious health problems and threatening human life in poor rural communities.

A major point made in his lecture was that much of the current literature had wrongly categorised the predominant species of arsenic and that this was a of result poor field work practises. It was thought that the predominant species was As(V), when in many cases it was actually the more toxic As(III). This arose due to the oversight of redox reactions occurring in arsenic between the time of sample collection and time of analysis. A slightly disengaged assumption that a sample being stored and transported across the world, will be unchanged and fit for meaningful analysis at the other end.

Arsenic analysis has also been thwarted in mass spectroscopy techniques by the formation of ArCl+ in-situ during examination of the arsenic species. Arsenic is mono-isotopic with an atomic mass of 75 Da, which is the same as the contaminant noble gas halide species. Prof. Ward made significant discoveries by carrying out solid phase extraction of the arsenic species at the point of collection, allowing for all arsenic species to be separated and prevented from undergoing chemical changes prior to analysis. This methodology has allowed for much more accurate results to be obtained. Unfortunately the discovery showed that the predominant species is in many cases is the more toxic As(III). Beyond that discovery, Prof. Ward and his team have begun to investigate the nature of the geological chemical systems. One profound suggestion was a relationship between arsenic and vanadium. Data shows that vanadium concentration is proportional to As(III) concentration and that vanadium may in some way be protecting people from the ill-effects of As.

Prof. Ward’s passion rang out throughout his lecture. He has not been limited to a life in the lab, recently he has been visiting schools in Argentina showing pupils how to carry out rigorous analytical work and become more active in shaping their communities and making demands of their local councils. All round great guy indeed; he’s from New Zealand, but you’ll find him here.

 

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