Dynamics of acetylcholinesterase activity recovery in two earthworm species following exposure to ethyl-parathion Magali Rault a, * , Be ´ atrice Collange a , Christophe Mazzia a , Yvan Capowiez b a Universite´ d’Avignon et des Pays de Vaucluse, UMR 406 Abeilles et Environnement, Site AGROPARC, F-84914 Avignon Cedex 09, France b INRA, Unite´ PSH, Site AGROPARC, F-84914 Avignon Cedex 09, France article info Article history: Received 26 May 2008 Received in revised form 4 September 2008 Accepted 8 September 2008 Available online 12 October 2008 Keywords: Acetylcholinesterase Biomarker Earthworms Organophosphate abstract In order for cholinesterase (ChE) activity to be used as an effective biomarker in earthworms, the time course of enzyme activity inhibition and recovery must be fully characterized. A laboratory experiment was carried out using parathion as a model organophosphorus pesticide at the recommended dose (1 mg kg 1 ) and a 10 fold higher dose (10 mg kg 1 ), on two earthworm species (Allolobophora chlorotica and Aporrectodea caliginosa). ChE activity and weight were measured every week for a 14 day period of exposure to parathion and then for 8 weeks in uncontaminated soil. After 3 days of exposure, the weight of both earthworm species had decreased by 10–15% compared to the control, regardless of the dose used. During the remainder of the exposure period, no differences were observed between the two doses for A. chlorotica; but A. caliginosa showed rapid weight recuperation for the lowest dose applied. After 28 days and over, the control and both exposed species of worms lost similar amounts of weight. ChE inhibition was measured during and after the exposure period. ChE inhibition followed a different time course for the two species investigated. A. chlorotica appeared less sensitive to parathion than A. cal- iginosa. In this latter species, ChE inhibition was rapid at close to 70% of the control after 3 days, for either dose, and reached 80–90% after 7 days exposure. While A. chlorotica exhibited the same pattern of inhibition for 10 mg kg 1 of parathion, the inhibition process was slower for the recommended dose with 50% inhibition after 7 days of exposure and 70% after 14 days. ChE activity recovery, after transfer to uncontaminated soil, also followed a different pattern for the two species. After exposure to 1 mg kg 1 parathion, ChE activity from A. chlorotica underwent a slow but constant recovery process to regain the control value after 8 weeks in unpolluted conditions. On the other hand, the ChE activity from A. cal- iginosa remained strongly inhibited. The differential susceptibility to parathion found in this study could be related to differences in the specificity of the total ChE activities between those two species. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Organophosphorus (OP) pesticides are widely used in agricul- ture worldwide as they are pesticides highly effective and relatively non persistent in the environment (Fulton and Key, 2001). However, these compounds lack specificity and are highly toxic to non-target species. OP pesticides produce acute toxicity by inhib- iting cholinesterase (ChE) enzymes through phosphorylation, in both invertebrate and vertebrate organisms (Habig and Di Giulio, 1991). Further modifications known as ‘‘aging’’ lead to persistence of ChE inhibition in tissues for days to weeks, even when there are no detectable traces of pesticide remaining in the organism (Stenersen, 1979a; Aamodt et al., 2007). After exposure, ChE activity is then only restored by de novo enzyme synthesis (Habig and Di Giulio, 1991). As a result, measurement of ChE activity is now well accepted as a biomarker of exposure to OP pesticides (Fulton and Key, 2001). Mammalian ChEs are divided into two major groups, acetyl- cholinesterase (AChE, EC 3.1.1.7), and pseudocholinesterases such as butyrylcholinesterase (BuChE, EC 3.1.1.8). The main function of AChE is the hydrolysis of acetylcholine, the neurotransmitter in cholinergic synapses of the nervous system, while the physiological role of BuChE remains unclear (Massoulie ´ et al., 1993). In verte- brates, BuChE is more sensitive to anti-cholinesterase compounds than AChE (Wogram et al., 2001). In invertebrate species, ChEs appear to be a group of related enzymes with varying mixed properties from mammalian AChE and BuChE, and little is known about their differential sensitivity towards OP pesticides. Earthworms, as ‘‘ecosystem engineers’’ (Jones et al., 1994), influence many physical (transfer properties), chemical (biogeo- chemical cycles) and biological (interactions with other compo- nents of the soil ecosystem) processes in the soil (McCoy et al., * Corresponding author. Tel.: þ33 4 32 72 26 16; fax: þ33 4 32 72 26 02. E-mail address: rault@avignon.inra.fr (M. Rault). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2008.09.010 Soil Biology & Biochemistry 40 (2008) 3086–3091