The use of acid insoluble residue to correct for the presence of soil-derived metals in the gut of earthworms used as bio-indicator organisms

The use of acid insoluble residue (AIR) as a marker fraction in the soil is proposed for correcting measurements of the heavy metals: Zn, Cu, Cd and Pb in earthworm samples to eliminate the contribution from soil in the earthworm gut. Five species of earthworm were kept for 15 days on four experimental soils which contained different levels of Zn, Cu, Cd and Pb. Results of heavy metal concentrations in earthworm tissue obtained after calculation using the correction based on AIR content were compared statistically with results obtained by other methods. In the majority of soil/earthworm combinations no significant difference emerged between the calculated results and those obtained after dissection of earthworm samples, suggesting that the correction using AIR content provides a suitable method for estimating levels of heavy metals present in earthworm tissue.