engleski

Acute toxicity of imidacloprid to the aquatic invertebrate Gammarus fossarum in static-exposure condition

Neonicotinoids are used like fast-acting veterinary and crop protection. Their selective target is insect nicotinic acetylcholine receptor. This selectivity is important to guarantee safety and to minimize undesired effects on humans, despite its unwanted action on non-target species. Neonicotinoids present a possible important hazard for the contamination of soil and aquatic ecosystems with cumulative effects on freshwater biota. Although imidacloprid is an insecticide, there is evidence that at higher concentrations it may be harmful to plants and algae. A preliminary testing of pure compound imidacloprid (IMI) and commercial formulation of IMI - Confidor (Bayer Crop Science) was performed on freshwater algae Scenedesmus subspicatus, before proceeding with further testing on aquatic invertebrates. Consequently, we have explored the baseline toxicity of these compounds on biochemical responses of non-target aquatic bioindicator species such as Gammarus fossarum (Amphipoda, Crustacea). The algal cultures were exposed to 5 doses of tested insecticides (30-1000 μM) and a 96-h static growth inhibition test was conducted. The growth of S. subspicatus was inhibited at the highest concentrations of 1000 μM (IMI) and 500 – 1000 μM (Confidor). After 96-h test the inhibition rate ranged from 10% up to 50% for IMI and Confidor, respectively. The algal cultures were more sensitive to the commercial formulation of IMI compared to pure compound. Furthermore, we tested the effect of different doses of IMI (0.4- 2 μM) on animal survival, behavior, changes of total protein content and general biochemical biomarkers (i.e. enzymatic activities). Our data demonstrated an overall low toxicity of IMI after 24 h exposure, with no significant changes in the mortality rate and total protein content with respect to control. The commercial formulation Confidor demonstrated an increase in mortality at higher concentrations. Both compounds showed at the highest doses an increased number of inactive animals with only respiration movements left (~ 90%). We found that low concentrations of IMI (0.4 μM) resulted in increased lipid peroxidation (LP) levels, while no effects were observed on glutathione-S-transferase (GST) and catalase (CAT) activities. Higher concentration of Confidor (1-2μM) induced a moderate increase in CAT and significant one in GST activity, as well as a significant rise in LP. Laboratory toxicity data contrasting responses of aquatic organisms to insecticides are important for focusing also on non-target species exposed to aqueous concentrations of these insecticides in field studies. These data also allow evaluation of expected responses of aquatic species to a range of insecticide concentrations in situ. These results are a part of preliminary approaches based on the usage of biochemical biomarkers and confirm the need to integrate these conventional tools with new methodologies for the risk assessment of acute and chronic exposure of complex pesticides mixtures in the aquatic environment.

neonicotinoids; Gammrus; imidaclprid; biochemical response

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