engleski

Suitable bioassays for screening of toxic neonicotinoid effects in aquatic ecosystems

Knowledge about the toxicity of hazardous substances is important to ensure the integrity of the ecosystems we live in. Spreading of pesticides via spray drift, runoff, accidental spillage and leaching from agricultural fields can affect non-target organisms in adjacent aquatic ecosystems. To assess the risk of pesticides for the aquatic environment, the performance of ecotoxicological tests in accordance to standard guidelines with aquatic model organisms is prescribed by legislation. Used standard organisms represent different levels in an ecosystem, going from bacteria up to unicellular algae, invertebrate and vertebrate organisms. Neonicotinoids are widely applied pesticides due to their higher affinity for insect nicotinic acetylcholine receptors. These compounds are extensively applied to control pest insects in different agricultural crops ; however they can also affect non–target organisms. In addition, little is known about the toxicity effects of their transformation products and applied commercial formulations. In this study, we wanted to test the toxic effect of imidacloprid (IMI) and its four transformation products (i.e. 6-chloronicotinic acid (6CNA), desnitro-IMI, olefin-IMI and hydroxy-IMI) applying a battery of acute and mechanism specific bioassays. Oxidative stress responses in the crustacean amhipod Gammarus fossarum were investigated as well as the growth rate in freshwater algae Scenedesmus subspicatus after 24 and 96 h exposure to IMI, its commercial formulation Confidor 200SL and its transformation 6CNA. Furthermore, toxicity testing of aqueous solutions for three IMI products (hydroxy-IMI, desnitro-IMI and olefin-IMI) was performed with the luminescent aquatic bacteria Vibrio fischeri. Algal growth has shown significant sensitivity to Confidor 200SL and 6CNA when compared to pure compound. Alterations induced in the evaluated biochemical responses underlined different mechanism of IMI and 6CNA-induced oxidative stress in amphipods. Different levels of luminescent inhibition were demonstrated also for the IMI products tested on V. fisheri. Toxicity testing of pesticides in aquatic environment should be performed on whole organism models at different levels of biological organization allowing a better comparison of the data. In addition, this battery of bioassays reflects different species susceptibility to xenobiotics and also the complexity of entire ecosystems.

neonicotinoids; transformation products; bioassays; biomarkers; organism models

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