The contribution of a pyrethroid insecticide to the massive eel (Anguilla anguilla) devastation, in Lake Balaton, in 1995

In the summer of 1995, 30 tonnes of eel (Anguilla anguilla) died in Lake Ba laton, Hungary. An investigation was carried out to find the causes of this ecocatastrophe. During this investigation, certain biochemical parameters, i.e. the blood sugar level, the acetylcholinesterase (AChE, EC 3.1.1.7), l actate dehydrogenase (LDH, EC 1.1.2.3), glutamic-oxaloacetic transaminase ( GOT, EC 2.6.1.1), and glutamic-pyruvic transaminase (GPT, EC 2.6.1.2) activ ities in the blood serum of the collected surviving and dying eels were exa mined. Deltamethrin, the active ingredient of the insecticide K-OTHRIN 1 UL V, used against mosquitoes was detected in different animal species, i.e. e el, bream (Abramis brama), pike perch (Stizostedion lucioperca), and the co mmon gull (Larus canus) and in sediment samples from the lake. Additionally , laboratory experiments were carried out to study the effects of deltameth rin on eels. During the investigation in the field it appeared that the AChE activity wa s significantly lower in the blood serum of the dying eels as compared to t hat in living animals (P < 0.05, Student's t-test). The blood glucose conte nt exhibited a difference, too: it was 2.5 times higher in the dying eels t han in the surviving ones. A huge increase in the LDH level was measured in the dying eels. The GOT activities of the serum were twice as high in the dying eels as in the living fish, while the GPT was not significantly changed. Deltamethrin was detected in different tissue samples of the dying eels: 2. 70-18.1 mu g/kg in the liver, 9.0-31.1 mu g/kg in the gill and 3.0 mu g/kg wet tissue in the muscle. Deltamethrin residues were found in tissue sample s from other animals, in the following concentrations: 0.44 mu g/kg in brea m, 2.14 mu g/kg in pike perch and 1.06 mu g/kg wet tissue in dead gulls. Th e sediment samples collected from the sites of the devastation contained de ltamethrin in a concentration of 5.50-30.00 mu g/kg wet sediment at the tim e of the eel deaths, and in a concentration 7.00-8.75 mu g/kg wet sediment a month later. Laboratory experiments with the insecticide K-OTHRIN 1 ULV revealed that 1. 00 mu g/l of its active ingredient, deltamethrin, caused the death of 50% o f the eels after an exposure time of 96 h. During this experiments similar trends could be observed in changes of enzyme activities of the treated eel s to those that were detected in filed study during the eel devastation in Lake Balaton. At the end of a one-week treatment with the insecticide at the concentratio n of 0.5 mu g/l of its active ingredient the gills of the treated eels cont ained deltamethrin at 12.6-44.8 mu g/kg wet tissue concentration, while at the 24th hour after the treatment (11.2-42.7 mu g/kg wet tissue) deltamethr in concentration in the liver of treated eels could be detected.