Due to low cost and wide applicability, global plastics production has increased rapidly, reaching 367 million tonnes in 2020, not including fiber plastics (Plastics Europe 2021). Due to its intense use worldwide and lack of proper management system, plastic has become a pollution problem of global proportions (Geyer et al. 2017; Horton and Dixon 2017). The investigation of microplastics (MP) as contaminants of environmental matrices can be considered a relatively new area of study, although knowledge about the presence of plastic particles in aquatic environments was initially reported since the early 1970s (Carpenter and Smith 1972). As a rule, MP are particles up to 5 mm in diameter (Courtney et al. 2009), and can also be divided into small (< 1 mm) and large (1 to 5 mm) MP (Eriksen et al. 2014; Hanvey et al. 2017).
Although MP has been widely reported in aquatic ecosystems around the world, demonstrating its occurrence in water bodies (Cincinelli et al. 2017; Luo et al. 2019) and its toxic potential for certain groups of organisms, such as annelids, crustaceans and fish (Doyle et al. 2022; Qiao et al. 2022), there is a great lack of knowledge regarding other classes. So far, Diptera species have been superficially studied as having neglected toxic effects due to exposure to MP. Diptera is an order of insects that have at least one of their life cycle stages in aquatic environments. This group of organisms is considered extremely rich, comprising approximately 158 families and more than 159,000 recognized species (Ibáñez-Bernal et al. 2020), of which 46,000 are aquatic species. In addition, they are the only aquatic insects that colonize all continents, including Antarctica (Adler and Courtney 2019).
Chironomid larvae are considered models in toxicity tests due to their wide distribution in aquatic environments, ease of cultivation in the laboratory, short life cycle and their biological characteristics, which confer the ability to adapt to adverse environments (OECD/ OECD, 2010 Rosa et al. 2014; Serra et al. 2017). The species Chironomus sancticaroli has been widely used in the literature as a bioindicator of environmental quality with several pollutants and chemical compounds, including MP (Pinto et al. 2021; Rebechi et al. 2021; Palacio-Cortés et al. 2022). The life cycle of C. sancticaroli is characterized by four stages: egg, larva, pupa and adult (aerial). Of these, the first three are aquatic stages with benthic habits (Strixino and Strixino 1982). Due to their ecological role, Chironomidae larvae are an important biological representative of the benthic macrofauna and it is essential to understand their behavior and interaction with the various pollutants present in aquatic ecosystems.
MP are subject to several environmental factors that lead to chain breakage and plastic degradation. Among the environmental conditions that can act in this process, it is possible to mention temperature, weathering, intensity of ultraviolet radiation (UV), winds, physical friction, salinity and pH (Antunes et al. 2013, Liu et al. 2016, Wagner and Lambert 2017, Torres et al. 2020). Aged MP present increased toxicity due to the release of monomers, additives and compounds generated by the reactions of these degradative processes (Hermabessiere et al. 2017, Zhang et al. 2019), and the increase in the porosity of the particles, which will facilitate the sorption of chemical compounds present in the environment. In toxicity tests, the most studied particles refer to primary or artificially aged MP, due to experimental practicality. However, even though the environmental distribution and toxicity of MP have already been investigated, only limited information is available for the environmental transformation of this pollutant in the laboratory. Therefore, it is necessary to investigate the phototransformation of MP under natural radiation to understand how the aging process can influence the potential risks of MP to biota.
Considering the scenario presented, the present study aimed to study the effects of exposure of C. sancticaroli larvae to naturally aged polypropylene MP (PP; PP-MP) through diet. In order to establish a pattern of response at the cellular and/or individual level, the organisms were evaluated for PP-MP intake, changes in oxidative stress markers and mortality after 6 days of exposure.