Effects of Polyethylene Microplastics on Freshwater Oligochaeta Allonais inaequalis (Stephenson, 1911) Under Conventional and Stressful Exposures Gleyson B. Castro & Aline C. Bernegossi & Fernanda R. Pinheiro & Mayara C. Felipe & Juliano J. Corbi Received: 16 June 2020 /Accepted: 27 August 2020 # Springer Nature Switzerland AG 2020 Abstract The occurrence of microplastics in the aquat- ic environment has been reported around the world; however, their effects on freshwater oligochaetes are unknown. In this research, we investigated the toxic effects of polyethylene microplastics (MP), size be- tween 40 and 48 μm, on the aquatic worm Allonais inaequalis. We applied the bioassays considering 24 °C as standard temperature and thermal stress of 19 °C and 29 °C, associated with the presence and absence of sediment in short-term and chronic expo- sures (96 h and 240 h, respectively). MP did not cause significant mortality in short-term exposures and did not affect the reproduction of worms. In addition, when we analyzed whether thermal stress, as well as substrate availability, would have an additional impact on MP toxicity, there were no significant effects. At 29 °C, the individuals reached the highest reproduction rates, whereas at 19 °C the offspring significantly reduced. Moreover, the lack of sediment substantially reduced survival rates after 96 h under 24 °C (p = 0.018). This paper also records for the first time, the ability of microplastic ingestion by a freshwater naidid. Due to its capacity to respond in a short period, adaptation to laboratory cultivation, and representativeness among freshwater aquatic invertebrates, A. inaequalis is pre- sented as a tropical test organism for toxic effect analysis of microplastics, either in conventional expo- sures or simulated environmental disturbances. Keywords Aquatic worm . Survival . Ingestion . Reproduction . Thermal stress . Sediment perturbance 1 Introduction Microplastics are defined as synthetic polymer particles, less than 5 mm, originated from primary or secondary sources (Eerkes-Medrano et al. 2015; Gong and Xie, 2020). Plastic debris are found in different forms, such as fragments, spherical or fibers, and have multiple chemical constitutions, such as low- and high-density polyethylene, polystyrene, polyvinyl chloride, polypro- pylene, polyamides, polycarbonates, polyester, and polyethylene terephthalate (Andrady 2011; Browne et al. 2015; Costa et al. 2017; Khoironi et al. 2020). The synthetic polymer polyethylene (C 2 H 4 ) n is one of the most produced plastics in the world (Association of Plastics Manufacturer 2018) and its persistence in the environment is related to its chemical structure because it is a compound derived from fossil hydrocarbons (Palmisano and Pettigrew 1992). It can be obtained from reactions of ethylene and benzaldehyde under high tem- perature and pressure conditions (Patel et al. 2008). Although there is more information about occurrence and impact of microplastic in the marine environment than in the freshwater environment, continental aquatic ecosystems can contain and accumulate many micropar- ticles and plastic fibers (Wagner et al. 2014; Wagner and Water Air Soil Pollut (2020) 231:475 https://doi.org/10.1007/s11270-020-04845-y G. B. Castro (*) : A. C. Bernegossi : F. R. Pinheiro : M. C. Felipe : J. J. Corbi Aquatic Ecology Laboratory, Department of Hydraulic and Sanitation, São Carlos School of Engineering, University of São Paulo, São Carlos, SP, Brazil e-mail: gleysonborges@usp.br