How do polyethylene microplastics, ibuprofen, and sediment mud levels influence meiobenthic features and their interactions with CeO2-doped ZnO nanoparticles? Answers through nematode taxon/functional traits, allometry of Metoncholaimus pristiurus, and computational analyses

Microplastic pollution and pharmaceutical contaminants represent growing environmental threats, particularly in aquatic ecosystems. This research examines the individual and combined effects of polyethylene microplastics, sediment particles, and ibuprofen on meiobenthic species, specifically free-living nematodes. Abundance changes, species diversity, and functional characteristics were monitored during a 30-day microcosm experiment. The binding affinities and molecular interactions of both contaminants with germ-line development protein 3 (GLD-3) and sex-determining protein (SDP) have been assessed using computational modeling assays. The results indicate that contamination significantly alters nematode communities, with pronounced declines in sensitive species such as Dorylaimopsis timmi and Halalaimus longicaudatus. At the same time, opportunistic taxa like Paramonhystera pellucida and Parodontophora beviseta exhibited increased abundance, resulting in a worldwide reduction of nematofauna (432 individuals in controls compared to 233-322 individuals in treated communities). The experimental results and computational assays supported each other. Furthermore, the strongest negative effects were observed in combined polyethylene-ibuprofen treatments, suggesting a synergistic interaction that enhances toxicity. Polyethylene microplastics appear to modulate the bioavailability and toxicity of ibuprofen, potentially exacerbating its impact on benthic communities. According to regressions linking body dimensions, the combination of polyethylene microplastics and ibuprofen with ZnO-CeO (slopes: 0.53629 and 0.31718, respectively) nanoparticles enhanced the growth rate of the nematode Metoncholaimus pristiurus, compared to the control group (slopes: 0.05775).