Abstract
Imidacloprid is one of the most used neonicotinoid insecticides all over the world and is considered as a contaminant of concern due to its high toxicity potential to aquatic organisms. However, the majority of the studies that have evaluated the effects of imidacloprid on aquatic organisms were conducted under temperate conditions. In the present study, a mesocosm experiment was conducted under sub-tropical conditions to assess the effects of imidacloprid on the structure (macroinvertebrates, zooplankton and phytoplankton) and functional endpoints of an aquatic ecosystem and to compare the results with similar temperate and (sub-)tropical mesocosm studies. Imidacloprid (0, 0.03, 0.3 and 3 µg/L) was applied to 13 mesocosms weekly over a period of 4 weeks, followed by a one month recovery period. At the community level a lowest NOECcommunity of 0.03 µg/L was calculated for the zooplankton, phytoplankton and macroinvertebrate communities. The highest sensitivity to imidacloprid (NOEC < 0.03 µg/L) were observed for Gerris sp., Diaptomus sp. and Brachionus quadridentatus. Imidacloprid induced population declines of the larger zooplankton species (Diaptomus sp. and Ostracoda) resulted in increased rotifer abundances and shifted the phytoplankton community to a graze resistant gelatinous cyanobacteria dominated ecosystem. These cyanobacteria blooms occurred at all different concentrations and could pose an important public health and environmental concern. Although there are some differences in species and community sensitivity between the present and the other (sub-)topical mesocosm studies, it can be observed that all show a similar general community response to imidacloprid. Under (sub-)tropical conditions, the toxic effects of imidacloprid occur at lower concentrations than found for temperate ecosystems.
Highlights
At present, China is one of the largest producer and consumer of pesticides in the world (Grung et al, 2015)
The dominant factors affecting the dissipation of imidacloprid are photolysis and temperature, and to a lesser extent sorption to the sediment (Bonmatin et al, 2015; Lu et al, 2015)
Sumon et al (2018) observed that after 7 days about 50% of the imidacloprid dissipated from the water phase in an outdoor mesocosm study conducted in Bangladesh
Summary
China is one of the largest producer and consumer of pesticides in the world (Grung et al, 2015). As with many countries in transition, this is partly due to the government’s policy to increase agricultural yields (Grung et al, 2015) This extensive use of pesticides can lead to high levels of pesticide residues in the environ ment. The adverse effects imidacloprid has on terrestrial pollinators such as honey bees and bumble bees are of particular concern since they are essential for providing the pollination ecosystem services in agriculture (Blacquiere et al, 2012). This is one of the main reasons why imidacloprid is banned for outdoor agricultural applications in Europe (European commission, 2018c)
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