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Feeding responses of cladocerans (Cladocera) exposed to microplastics, imiprothrin and their combinations
Summary
Scientists studied how tiny water fleas (a key food source for fish) respond when exposed to microplastics and a common pesticide together, since both pollutants often end up in the same waterways. They found that low doses actually made the water fleas eat more (a stress response), but higher combined doses of pesticide and microplastics disrupted their normal feeding—which matters because these tiny creatures form the base of aquatic food chains that eventually reach our dinner plates. While this study was done in water fleas, not humans, it highlights how combinations of pollutants can have unexpected effects that single-pollutant studies might miss.
Aim: In this work, we determined the ingestion and filtration rates of three cladoceran species (Ceriodaphnia dubia, Simocephalus vetulus and Alona glabra) exposed to microplastics or pesticide imiprothrin separately and together on the green alga Tetradesmus obliquus. Methodology: We tested the acute toxicity (24 hr) of imiprothrin for C. dubia, S. vetulus and A. glabra and the values were 0.248, 0.307, and 0.336 mg l-1, respectively. For feeding studies two concentrations of the pesticide (equivalent to 10% and 20% of LC50 for each species) and one density of microplastics, 20 mg l-1 for C. dubia and 40 mg l-1 for S. vetulus and A. glabra were used. Results: With microplastics alone the mortality rate did not exceed 40% for any cladoceran species. The results showed that, depending on the treatment, the ingestion and filtration rates varied considerably, depending on the test species. For C. dubia, the controls differed significantly from other treatments. C. dubia and S. vetulus, when exposed to pesticide at 10% LC50+MPs, significantly higher ingestion rates compared to controls were observed, but this was not the case for A. glabra. At higher concentrations of pesticide+microplastics, both the ingestion and filtration rates were adversely affected for all the tested cladoceran species. Interpretation: The results further showed that imiprothrin and microplastics interacted to cause significant changes in the feeding responses of the chosen cladoceran species. These changes included stress responses, such as hormesis, which have been discussed in this work. Key words: Cladocerans, Feeding responses, Microplastics, Pesticide, Zooplankton