Earthworm Depuration: Analysis of Coprophagy and Light Impacts

Abstract

Earthworms are used as biomarkers to determine the bioavailability of contaminants. As such, their uptake of contaminants has been studied extensively. Protocols have been established to ensure that laboratory-obtained data are valid and comparable. However, the method of removing the organism’s gut content (depuration) before assessing the contaminant in the tissue is not standardized. The aim of this research project is to investigate some parameters for earthworm depuration: light conditions and coprophagy prevention. Eisenia fetida were depurated for 48 hours in two separate studies according to guidelines ASTM-E1676 and OECD Test No. 317. In one study, 2 frequencies of egesta removal were employed during depuration to prevent coprophagy and compared to the control (egesta and worms removed after 48 hours). In another study, the subjects and material egested were assessed under conditions of continuous darkness and the control (continuous light). The depuration methods that included egesta removal every 12 and 24 hours resulted in 62% and 10% more egested material per mg of earthworm than the control (filter paper disc change after 48 hours), respectively. The earthworms depurated in continuous darkness egested 94% more material per mg of earthworm than the control. The results indicate that depuration would be more total under continuous darkness and employing a coprophagy prevention method. These findings could lead to more efficient depuration methods.