Arsenic speciation in field-collected and laboratory-exposed earthworms Lumbricus terrestris

Mature Lumbricus terrestris were host soils and leaf litter were collected from a former arsenic mine in Devon, UK (Devon Great Consols), a former gold mine in Ontario, Canada (Deloro), and an uncontaminated residential garden in Nottingham, UK. Arsenic concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) in soils were 16–348 mg kg−1, 6.0–239 mg kg−1 in the earthworms and 8.6 mg kg−1 in leaf litter sampled at Deloro (all dry weight). High performance liquid chromatography (HPLC–ICP-MS) analysis revealed arsenite (AsIII), arsenate (AsV) and five organoarsenic species; arsenobetaine (AB), methylarsonate (MAV), dimethylarsinate (DMAV), arsenosugar 1 (glycerol sugar), arsenosugar 2 (phosphate sugar), and trimethylarsineoxide (TMAO) in field-collected L. terrestris. Differences were observed in the variety of organoarsenic species present between field sites. Several organoarsenic species were observed in the leaf litter (DMAV, arsenosugar 2 and TMAO) but not AB. Depuration resulted in higher concentrations of inorganic As being detected in the earthworm whereas the concentration or variety of organoarsenic species was unchanged. Commercially sourced L. terrestris were exposed to As contaminated soil in laboratory mesocosms (1.0, 98, 183, 236, 324 and 436 mg kg−1) without leaf litter and were additionally analyzed using X-ray absorption near edge structure (XANES). Only inorganic AsIII and AsV was observed. It is proposed that ingestion of leaf litter and symbiotic processes in the natural soil environment are likely sources of organoarsenic compounds in field-collected L. terrestris.

► Occurrence and source of organoarsenicals in L. terrestris were investigated.
► L. terrestris from contaminated and uncontaminated soils contain complex organoarsenicals.
► L. terrestris exposed in laboratory without leaf litter contain only inorganic arsenic.
► Leaf litter at soil surface may be a dietary source may be organoarsenic compounds.