Use of Midge Chironomus riparius Larvae in Plastic Ecotoxicity Studies and Peculiarities of Their Responses ^†

Chironomus riparius, a common test organism [1], has been widely used for the assessment of the ecotoxicity of metal and organic contaminants in aquatic systems. Due to having both aquatic and sediment-based developmental stages, midge larvae can be exposed to both waterborne and sediment-bound contaminants, and hence, represent a versatile model for toxicity studies. Recently, C. riparius has also been widely used in the environmental risk assessment of microplastic contamination in water bodies. The responses of chironomid larvae that were experimentally exposed to nano- or microplastic particles were shown to range from the molecular to whole organism level, e.g., [2,3,4]. However, these responses have not been strongly related to the microplastic concentrations used for exposure or load within the organism (the number of ingested particles). Instead, although the presence of microplastic particles in the gut of C. riparius was demonstrated [5,6], the populations of C. riparius that were continuously exposed to microplastic during three generations showed recovery after the first generation [7]. Moreover, despite the greater number of ingested particles at a higher microplastic concentration (1 g kg⁻¹), compared to the 10 times lower concentration (0.1 g kg⁻¹), the emergence of adult midges in both cases was not significantly different [6]. In this work, a review of the responses of C. riparius to plastic exposure based on the published literature and our own data is provided, and the peculiarities of the observed responses are discussed.