Multigenerational Effects of Weathered Polyethylene Microplastics on <i>Drosophila melanogaster</i>

Most plastics are released into the environment once they are discarded, resulting in microplastics (<5 mm) being found in every part of the world. To better understand their toxicity, we exposed four generations of the fruit fly, <i>Drosophila melanogaster</i>, to high-density polyethylene (HDPE) microplastics (<38 μm) and monitored their reproductive performance. We found that the eclosion fraction of pupae was 5.7% higher (<i>p</i> < 0.05) in the stream of flies that were fed 100 mg/kg HDPE across all generations when compared to those fed control food. Several fourth-generation treatment flies expressed malformed salivary glands and scutella. No toxicity was observed in the number of pupae and flies that emerged from the eggs laid in each generation or their mean pupation and eclosion time. Moreover, no toxicity was observed in the development of larvae into adult flies (0.1-10 000 mg/kg HDPE) and various sublethal end points (100 mg/kg HDPE) such as larva and adult fly locomotion and the mass of female and male flies. These results, obtained with realistic weathered microplastics, indicate that HDPE microplastics at the concentrations evaluated are unlikely to be lethal in <i>Drosophila melanogaster</i>; however malformations are still possible despite little-to-no observable internalization of the microplastics.