Cotton and polyester microfibers cause chronic toxicity in the freshwater invertebrate Chironomus dilutus

Concern over microplastic pollution has intensified in recent years as mounting evidence reveals its persistence, ubiquity, and potential biological impacts, with particular attention now turning to microfibers-one of the most abundant microplastic forms in the environment. Microfibers include more than just plastic textiles, as microfibers shed from non-plastic textiles are also ubiquitous in nature. To increase our understanding about how microfibers and associated chemicals affect aquatic ecosystems, we investigated the effects of clean microfibers and microfibers soaked in wastewater treatment plant final effluent (a common pathway for microfibers to reach aquatic ecosystems) on the benthic invertebrate Chironomus dilutus in a full-lifecycle test. We tested different microfiber types (polyester, cotton), and exposed animals to 50 and 500 microfibers L-1. No effects on percent emergence, fecundity, or hatchability were observed. There was a significant increase in time to emergence across all microfiber treatments at the higher concentration. Some effects were observed for growth and survival, although results were inconsistent among treatments. Overall, our results suggest that synthetic and natural microfibers can have developmental effects on C. dilutus and future work would benefit from assessing all environmentally-relevant microfibers, including different microfiber types and chemical mixtures.