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Arsenic speciation: a tool for assessing the environmental toxicology of arsenic using earthworms and toenails as biomarkers

Michael J. Watts,a* Mark Buttona,b and Gawen R.T. Jenkinb

aBritish Geological Survey, Nottingham, NG12 5GG, UK. E-mail: mwatts@bgs.ac.uk
bDepartment of Geology, University of Leicester, Leicester, UK

Introduction

The health implications of chronic exposure to arsenic are well known, with populations exposed on a worldwide scale, the majority of which are in locations such as Bangladesh, South-East Asia and South America. Serious health problems have been associated with drinking water high in arsenic, including various cancers, vascular disease and skin keratoses. In the UK, arsenic concentrations in drinking water are strictly regulated to meet the World Health Organisation recommended upper limit of 10 µg L–1 As for drinking water. Significant exposure can also arise from the consumption of contaminated food, inhalation of dust or ingestion of contaminated soil. The UK region Devon and Cornwall, which are located in the south-west of England, have a historical legacy of past mining activities which has led to locations with elevated levels of arsenic in soils, where soil ingestion is expected to be a significant exposure risk. Increasing evidence of exposure in these areas has resulted in growing concern about the potential health effects in populations exposed to arsenic. The assessment of exposure is inherently complex, in that the total amount of arsenic in soil provides an indication of the extent of the problem, but not the direct risk from exposure. The toxicity of arsenic is largely species dependent, with several inorganic and organic species being highly toxic yet other common species such as arsenobetaine and arsenocholine have been reported to be of minor toxicological significance. The speciation of arsenic is therefore important in understanding the pathways from source to exposure, biotransformation following exposure and associated risk to the health of organisms and humans.

Ecosystem indicator species such as earthworms have been employed as a tool for assessing soil contamination, in particular using bioaccumulation as a guide to a contaminant bioavailability. Whilst not directly indicating potential human health effects, the use of sentinel organisms such as earthworms may provide a useful surrogate to human studies at arsenic contaminated sites and provide a complementary line of evidence in assessing risk.  However, biomonitoring of human populations is needed to provide quantitative estimates of exposure to arsenic. Urine is often used, although the residence time of arsenic is about 24 hours meaning that it will most likely be influenced by dietary intake and is not ideal for assessing exposure from soil where ingestion may be sporadic. Long-term measures of exposure including hair and nails provide a time-integrated sample for assessing the uptake of arsenic in humans.

Analytical methodologies were developed for the speciation of arsenic in a range of materials by coupling high performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) to understand the exposure and uptake of arsenic in bioindicator organisms and humans. This work was part of a British Geological Survey sponsored PhD studentship, in collaboration with the University of Leicester. This article highlights the versatility of the developed methodology for the measurement of arsenic species in a range of materials from Devon Great Consols (DGC), one of many former mining sites in the south- west of England. A summary of results is presented with a focus on the instrumental measurement of arsenic species, whilst greater detail regarding sampling sites, sample preparation for analysis, and detailed interpretation of the findings can be found in the appropriate publications for this work.