Assessment of the toxicity of ethyl-parathion to earthworms (Aporrectodea caliginosa) using behavioural, physiological and biochemical markers

The aim of this study was to determine the influence of soil properties on ethyl-parathion toxicity to earthworms (Aporrectodea caliginosa) using different markers (mortality, cholinesterase (ChE) activity, body mass change and burrowing behaviour). In a first experiment, the toxicity of five different concentrations of ethyl-parathion was studied in four different soils, three from Mexico and one from France, which were previously seen to have different adsorption partition coefficient (Kd) values for ethyl-parathion. In a second experiment, which focused on the sublethal effects of ethyl-parathion, the markers were compared in the French soil only. In all four soils, high mortality was observed at 70 mg active ingredient kg−1 of dry soil, significant body mass loss at 7 mg kg−1 and significantly decreased ChE activity at 0.7 mg kg−1 (the normal application rate). Mortality was highest in one of the Mexican soils, an Andosol characterised by the lowest pH and highest Kd. Nevertheless, almost no differences were observed between body mass change and cholinesterase activity values among the four soils suggesting that ethyl-parathion toxicity was not greatly affected by Kd values or soil characteristics. The second experiment showed that (i) body mass change was the least sensitive toxicity marker whereas (ii) ChE activity and some characteristics of the burrow systems (burrow length and the number of branches) were sensitive parameters showing responses at very low ethyl-parathion (0.07 mg kg−1) concentrations. Even if the burrowing behaviour of earthworms is not so easy to measure, it appears preferable to ChE activity, which is only a biomarker of exposure and cannot be used to predict environmental effects on the soil ecosystem or functioning.