DNA damage in earthworms from highly contaminated soils: assessing resistance to arsenic toxicity by use of the Comet assay.

Earthworms native to the former mine site of Devon Great Consols (DGC), UK reside in soils highly contaminated with arsenic (As). These earthworms are considered to have developed a resistance to As toxicity. The mechanisms underlying this resistance however, remain unclear. In the present study, non-resistant, commercially sourced Lumbricus terrestris were exposed to a typical DGC soil in laboratory mesocosms. The earthworms bio-accumulated As from the soil and incurred DNA-damage levels significantly above those observed in the control mesocosm (assessed using the Comet assay). A dose response was observed between DNA damage (% tail DNA) and As concentration in soil (control, 98, 183, 236, 324 and 436mgkg(-1)). As-resistant earthworms (Lumbricus rubellus, Dendrodrilus rubidus and L. terrestris) collected from contaminated soils at DGC (203 to 9025mgkg(-1) As) had also bio-accumulated high levels of As from their host soils, yet demonstrated low levels of DNA damage compared with earthworms from uncontaminated sites. The results demonstrate that the As-contaminated soils at DGC are genotoxic to non-native earthworms and much less so to earthworms native to DGC, thus providing further evidence of an acquired resistance to As toxicity in the native earthworms.

Quantitative arsenic speciation in two species of earthworms from a former mine site.

The relationship between the total arsenic concentration and the chemical speciation of arsenic in two species of earthworm (Lumbricus rubellus and Dendrodrilus rubidus) in relation to the host soil, was investigated for 13 sites of varying arsenic content, including a background level garden soil and a former mine site at the Devon Great Consols, UK. Earthworms were collected with the host soil (As soil concentration range 16-12, 466 mg kg(-1) dry weight) and measured for their total arsenic (concentration range 7-595 mg kg(-1) dry weight) using inductively coupled plasma mass spectrometry (ICP-MS). A methanol-water mixture was used to extract arsenic species from the earthworms prior to determination of the individual arsenic species by a combination of anion and cation exchange high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). A gradient elution anion exchange method is presented whereby nine arsenic species could be measured in one sample injection. Arsenic species were identified by comparison of retention times and sample spiking with known standards and a fully characterised seaweed extract. Arsenic was generally present in the earthworm as arsenate (As(V)) or arsenite (As(III)) and arsenobetaine (AB). Methylarsonate (MA), dimethylarsinate (DMA) and three arsenosugars (glycerol, phosphate, sulfate) were present as minor constituents. These results are discussed in relation to the mechanisms for coping with exposure to soil bound arsenic.