Measuring Arsenic Speciation in Environmental Media: Sampling, Preservation, and Analysis

There is an extensive literature relating to As contents of various geological and biological media, driven in large part because of As-related diseases, which include for example, melanosis, leucomelanosis, keratosis, hyper-keratosis, oedema, gangrene, skin cancer and extensive liver damage. As an example, using the keywords “arsenic” and “environmental” in the academic search engine Scopus yields >12,300 references (title, abstract, and keywords). However, there is also increasing recognition that the toxicology of As is controlled by the form (speciation) of As (Scopus “Arsenic” and “speciation” yields >2900 references). It is commonly held that inorganic As(III) is the most toxic form, followed by arsenate (As(V)), with the various methylated forms generally having much less toxicity, although the epidemiology of the methylated forms has not been as well studied (e.g., Bacquart et al. 2010; Kobayashi 2010; Quazi et al. 2011; Whaley-Martin et al. 2013). However, the effect of inorganic speciation on human metabolism is debatable because As(V) is rapidly reduced after ingestion. Recent studies have shown that cellular biomethylation can result in the production of trivalent methylated As species, which can be more toxic than inorganic As forms (e.g., Styblo et al. 2000; Mass et al. 2001; Dopp et al. 2010; Rahman and Hassler 2014). For a recent review of As toxicology, see Mitchell (2014, this volume). Because in most terrestrial waters As(III) occurs as a neutral species (H3AsO3°), arsenite is more difficult to remove from solution in terms of water treatment, without first undergoing an oxidation step (e.g., Hu et al. 2012). There are a large variety of techniques for the measurement of total As and arsenic species, both in the field and in the laboratory. For the former, the main challenges are analytical time, complexity of sample treatment and …