Technical guidance on normal levels of contaminants in Welsh soil : Arsenic (As) : January 2013

Defra. 2013 Technical guidance on normal levels of contaminants in Welsh soil : Arsenic (As) : January 2013. British Geological Survey, 5pp. (Soils R&D Project SP1008)

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Abstract/Summary

Arsenic (As) is a chemical element that is naturally found in trace amounts in our environment so, in addition to being referred to as a metalloid, it is a trace element. It is the 20th most abundant element in rocks (1-2 mg/kg) and, due to its reputation as the Victorian’s poison of choice, awareness of the harmful aspects of this element to human health is high. It occurs in many geological materials with the highest concentrations found in arsenic sulphide minerals such as arsenopyrite (FeAsS), as well as an accessory element in other sulphides such as iron pyrites (FeS2). A significant source of As released into the surface environment is as a result of oxidation of sulphide minerals. Phosphate-rich rocks, ironstones and coal-bearing strata can also contain high levels of As. Overall, As minerals and compounds are generally soluble but the mobility of As can be limited by strong sorption by clays, hydroxides and organic matter. Under normal oxidising conditions the most common form of As in solution is the arsenate oxyanion (containing As5+), under more reducing conditions (e.g. waterlogging) the arsenite oxyanion (containing As3+) is more stable.