REVIEWS
INORGANIC CHEMISTRY Arsenic – the truth will out
For many of us, one of the delights of science comes down to how it illuminates and explains what we see in the world around us. Examples from real life, demonstrating a scientific concept or property, can spark the interest of the most disengaged student; although sadly the tactic sometimes goes awry when they later display vivid recollection of the anecdotes but have little to impart on the underlying science. For some topics, one might labour
to find suitable examples to enliven the subject. This is certainly not the case when describing the impact of the chemistry of the metalloid element, arsenic, on humankind and the environment. Even the relatively uninitiated will immediately recall examples from the extensive history of arsenic’s use to poison relatives or rivals, particularly when they stand on the path to true love or the acquisition of wealth. Much of this anecdotal material has already been covered in an earlier book by William Cullen, also published by the RSC. In this book, Arsenic is everywhere: cause for concern?, however, with co-author Kenneth Reimer, Cullen covers a broader canvas to demonstrate the ubiquity of arsenic and how its impact is much wider than just some occasional criminal skulduggery in the parlour. In this they succeed wonderfully;
they show how arsenic is everywhere, describe the biological and chemical processes by which it is spread and give an expert appraisal of the threat it poses in different situations. They also show how the burden of arsenic poisoning falls disproportionately on the world’s poor – a case in point being the reliance of people in some parts of Bangladesh on polluted surface drinking water. The unforeseen consequence of this has been described as the largest mass poisoning in history. By 2000, it was estimated that between 33m and 77m people were being chronically exposed to arsenic in their drinking water and a 2012 study concluded that it resulted in an estimated 43,000 deaths/year. There is a plethora of interesting facts about arsenic supplemented with the underlying chemistry. For example, how the strong adsorption of arsenic
to ferric oxides prevents its uptake by crops grown in aerated soils, but is less effective in crops such as rice, grown under less oxygenated, flooded conditions. The book also illustrates how potentially alarming reports of the presence of arsenic in foods need to be moderated by considering the species of arsenic present. These differ considerably in their
toxicity so that arsenobetaine, the major form in which arsenic occurs in seafoods, is non-toxic and excreted unchanged in the urine. The much- repeated canard that Napoleon was poisoned by trimethylarsine released from the pigment Scheele’s Green in wallpaper by mould growth is also laid to rest.
As a counterbalance to the abundant
literature detailing the harmful effects of arsenic, the authors pose the seem- ingly unlikely question of whether arse- nic is essential for human life, pointing to the numerous biological transforma- tions it undergoes and the importance of arsenic salts in the redox metabolism of many microorganisms. The analogy is made with selenium, which is essential in small amounts but toxic in higher doses. As the authors admit, such a contention remains to be established. There is also the salutary tale of
the now discredited claim, made in 2010 by a scientist at NASA, to have isolated a microorganism in which arsenic replaced phosphorus in DNA.
Despite the similar chemistries of arsenate and phosphate, chemists knew that arsenic-containing DNA would be extremely unstable in aqueous systems but regrettably none had been involved in the review process of the original report. Had they been, then a considerable amount of subsequent wasted effort might have been avoided. Medicinal arsenic has been
around for a very long time, although its presence in old remedies is not necessarily any recommendation as to its value. For example, the belief that arsenic increased levels of subcutaneous fat led to its use in ‘bust pills’, the consumption of which resulted in 149 women being admitted to a London hospital in 1906. Its use today is more limited but it famously featured prominently in the early days of scientific chemotherapy. Following reports of the efficacy of atoxyl (arsanilic acid) against sleeping sickness in Africa, Paul Ehrlich tested a range of atoxyl derivatives as chemotherapeutic agents. His labours were rewarded with the 606th compound produced, arsphenamine or Salvarsan – the’ arsenic that saves’. Salvarsan was active against Treponema pallidum, the cause of syphilis, and the basis of treatment until the advent of penicillin. This book is clearly the distillation
of a lifetime’s interest; inevitably somewhat eclectic, it is nonetheless varied, interesting and informative.
Arsenic is everywhere
Authors Wil- liam R. Cullen and Kenneth J. Reimer
Publisher RSC Publishing
Pages 293 Price £66.99
ISBN 978-1- 78262-314-4
Reviewer Martin Adams is emeritus professor of food microbiology at the University of Surrey, UK
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