Combined Toxicity of Microplastics and Antimicrobials on Animals: A Review

Background/Objectives: Microplastics are ubiquitous pollutants that pose physical toxicity and serve as vectors for antimicrobial agents, altering their bioavailability and toxicity. Unlike previous reviews that focus solely on antibiotics and terrestrial or aquatic ecosystems, this review integrates recent findings on the combined impacts of microplastics and antimicrobials on both aquatic and terrestrial animals, highlighting their biological responses. Methods: Recent experimental studies involving aquatic and terrestrial animals published in peer-reviewed journals were reviewed. These studies employed co-exposure designs using microplastics of different sizes, aging conditions, and surface chemistries in combination with antimicrobial compounds. Results: Microplastics combined with antimicrobials cause species-specific and often synergistic toxicity in aquatic organisms, affecting reproduction, immunity, oxidative stress, gene expression, and microbiota, with co-exposure often amplifying adverse physiological and developmental effects. Similarly, co-exposure to microplastics and antimicrobials in rodents, amphibians, birds, and soil invertebrates frequently leads to synergistic toxicity, oxidative stress, disrupted gut microbiota, and enhanced accumulation and bioavailability of pollutants, promoting inflammation, neurotoxicity, metabolic dysfunction, and increased antibiotic resistance gene propagation. Particle size, aging, and antimicrobial type influence toxicity severity. Certain microplastic-antimicrobial combinations can exhibit antagonistic effects, though less frequently reported. Conclusions: The interactions between microplastics and antimicrobials pose heightened risks to the health of organisms and ecological stability. These findings underscore the need to revise current risk assessment protocols to consider pollutant mixtures and microplastics-mediated transport. Future research should focus on environmentally relevant exposures, mechanistic studies using omics tools, and long-term ecological impacts. Integrated regulatory strategies are essential to address the compounded effects of microplastics and chemical contaminants.