Arsenic Speciation of Terrestrial Invertebrates

The distribution and chemical form (speciation) of arsenic in terrestrial food chains determines both the amount of arsenic available to higher organisms, and the toxicity of this metalloid in affected ecosystems. Invertebrates are part of complex terrestrial food webs. This paper provides arsenic concentrations and arsenic speciation profiles for eight orders of terrestrial invertebrates collected at three historical gold mine sites and one background site in Nova Scotia, Canada. Total arsenic concentrations, determined by inductively coupled plasma mass spectrometry (ICP-MS), were dependent upon the classification of invertebrate. Arsenic species were determined by high-performance liquid chromatography (HPLC) ICP-MS and X-ray absorption spectroscopy (XAS). Invertebrates were found by HPLC ICP-MS to contain predominantly arsenite and arsenate in methanol/water extracts, while XAS revealed that most arsenic is bound to sulfur in vivo. Examination of the spatial distribution of arsenic within an ant tissue highlighted the differences between exogenous and endogenous arsenic, as well as the extent to which arsenic is transformed upon ingestion. Similar arsenic speciation patterns for invertebrate groups were observed across sites. Trace amounts of arsenobetaine and arsenocholine were identified in slugs, ants, and spiders.