Population dynamics and competitive interactions of Plationus patulus (Müller, 1786) and Ovalona glabra (Sars, 1901) under microplastics and imiprothrin exposure

Emerging pollutants, including synthetic pyrethroid imiprothrin, are used indiscriminately in both urban and rural areas. Due to its long half-life (> 50 days) and diverse application in areas, such as agriculture, industries and households, imiprothrin reaches aquatic ecosystems and is adsorbed by microplastics. Microplastics induce different responses in zooplankton interactions, individually and in combination with other contaminants, and can have a synergistic effect. Plationus patulus, a globally distributed freshwater rotifer species, in nature can be exposed to these contaminants and can be adversely affected by competition with other zooplankton such as cladocerans. Ovalona glabra, a common littoral cladoceran often coexists with P. patulus. Therefore, in this study we evaluated the acute toxicity of the pesticide imiprothrin and microplastics, separately and in combination, on the population growth and competitive interactions between P. patulus and O. glabra. The median lethal concentrations (LC50) of P. patulus and O. glabra with only the pesticide were 3.43 and 336 μg 1−1, respectively. The LC50 of both the zooplankton species were much lower, when exposed to microplastics and imiprothrin together compared to one stressor. In chronic toxicity tests, survivorship of P. patulus was adversely affected by imiprothrin and microplastics. This effect was also observed in O. glabra, both alone and when competing with P. patulus.