The objective of this study was to evaluate the applicability of adenosine energy charge (AEC) as an indicator of sublethal pollutant contamination for an aquatic invertebrate Asellus aquaticus L. ( Crustacea, Isopoda ). This study was carried out under laboratory conditions.
Asellus collected in natural ponds were acclimated in the laboratory during a minimum period of 15 days. Individuals between 3 and 7 mg in weight were selected and kept at 15°C for 24 hours before contamination with lindane. Contamination was performed in glass containers in 250 ml of water, and 1 ml of lindane acetone solution. Concentrations of 2, 4, 8 and 10 mg/l were tested. The experimental period was 48 hours. After cold-induced anesthesia, Asellus individuals were rapidly dried and then dipped into liquid nitrogen and ground to a powder at - 80°C. Extraction of adenylates was performed with dimethyl sulfoxide (DMSO). ADP and AMP were converted to ATP with pyruvate kinase and phospho-enol-pyruvate for ADP; pyruvate kinase, myokinase and phospho- enol-pyruvate for AMP. The concentrations of ATP, ADP and AMP were measured using a bioluminescence technique with a luminometer (LKB Wallac 1250). AEC, defined as the ratio between (ATP + 1/2 ADP) and (ATP + ADP + AMP) concentration, was then calculated.
AEC values were 0.77, 0.79, 0.69, 0.65 and 0.72 respectively for control animals and for Asellus specimens exposed to 2, 4, 8 and 10 µg/l lindane. According to IANOVICI (1979), AEC values for Asellus contaminated with 4, 8 or 10 µg/l of lindane were representative of the perturbation of environmental conditions. Nevertheless, these values show that recovery is possible if environmental conditions return to normal. However statistically significant differences (ANOVA, p=0.05) were noted only between control and 4 or 8 µg/l lindane contaminated Asellus.
ATP concentrations were 0.1451, 0.1876, 0.1821, 0.2325 and 0.1570 µmol/mg respectively for control, 2, 4, 8 and 10 µg/l of lindane. No significant difference was noted between control and contamination, except for 8 mg/l of lindane ( p=0.01 ). ADP concentrations were 0.0698, 0.0253, 0.1200, 0.2121 and 0.0679 mmol/mg respectively for control, 2, 4, 8 et 10 mg/l of lindane. Only the ADP concentration for 8 mg/l of lindane was significant of ADP accumulation (ANOVA, p=0.05 ). AMP concentrations were 0.0193, 0.0272, 0.0470, 0.1182 and 0.0416 mmol/mg respectively for control, 2, 4, 8 and 10 mg/l of lindane. The increase of AMP concentration for 8 mg/l of lindane was significant ( risk 0.05 ). Variations of the adenylate pool (ATP + ADP + AMP) were 0.2342, 0.2401, 0.3491, 0.5628 and 0.2665 mmol/mg respectively for control, 2, 4, 8 et 10 mg/l of lindane. The increase of the adenylate pool concentration for 4 and 8 mg/l of lindane was significant (p=0.05 ).
It appeared that the decrease of AEC at lindane concentrations of 4 and 8 mg/l was indicative of the increase of the energetic cost and the metabolism, resulting from the hyperexcitability characteristically induced by this category of contaminant. At 10 mg/l of lindane, the AEC value was approximately equal to that of the control exposure. It appeared correlated to the decrease in metabolic activity and accompanying reduction energy expenditure in response to the paralytic phase of intoxication.
Finally under laboratory conditions AEC values appeared to be indicative of sublethal contamination, for this species and this toxicant. However for acute exposures it does not appear that AEC is a very good indicator.
Asellus aquaticus, Adenosine energy charge (AEC), ATP, ADP, AMP, lindane.
S Le Bras, CNRS - URA 1492, Laboratoire d'écologie et de zoologie, bâtiment 442, Université de Paris-Sud, 95405 Orsay Cedex, FRANCE