Feeding responses of cladocerans (Cladocera) exposed to microplastics, imiprothrin and their combinations

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