Chironomus riparius molecular response to polystyrene primary microplastics

Microplastics are emerging as a central concern for the environment. They can be found worldwide, produced for the industry and because of plastic debris degradation. The microplastics are smaller than 5 mm, but they can also range in micro and nanometer scales, present in soil and aquatic ecosystems. Furthermore, they can have different chemical compositions, including additives with putative toxicity. Chironomus riparius is a dipteran with aquatic larvae used in toxicology tests. As a benthic organism, it can be exposed to microplastics in the water and the sediments, being able to ingest some of them depending on the size and shape. However, it is still poor knowledge of the effects that microplastics have on invertebrates, especially at the molecular level. We have analyzed the impact that 5-5.9 mu m spheres of polystyrene have on the metabolism of C. riparius, studying the transcriptional activity of eighty genes, twenty-eight described here for the first time. The genes covered the endocrine response, the detoxification mechanisms, the stress response, the DNA repairing mechanisms, hypoxia, oxidative stress, apoptosis, immunity, cholesterol metabolism, energy metabolism, the circadian rhythm, signaling, and regulation of piRNAs. The results showed that at 24 h, the stress response was the most affected, while at 48 h, the endocrine response and detoxification were slightly affected. Finally, at 72 h, endocrine response, detoxification mechanisms, and lipid metabolism genes were altered. Overall, the data suggest an acute response involving stress genes downregulation, while the later response seems to move to metabolic alterations, with changes in hormonal regulation and metabolism. It could be because micrometer microplastics are confounded with food, decreasing the availability of resources for larval development. The present work shows a dynamic impact of polystyrene microspheres and provides new putative biomarkers to analyze several mechanisms involved in the cellular and physiological response to toxicants.