Plastics and Microplastics: Environmental Impacts, Health Implications and Prospects for the Circular Economy

Plastics are synthetic materials based on organic polymers, widely used in all sectors of the global economy. World production reached 431 million metric tons in 2024, having grown at a compound annual rate of 4.8% since the beginning of the 21st century. However, only 9% of the total plastic produced up to 2015 had been recycled, while 79% was discarded in landfills or in the natural environment. The progressive fragmentation of these materials gives rise to microplastics (MPs) — particles with a diameter of less than 5 mm — emerging contaminants detected in all terrestrial and aquatic ecosystems, including human tissues. The objective was to conduct a scoping review of the literature (2000–2025) on the definition, classification, and uses of plastics; the origin and environmental dynamics of microplastics; the repercussions on ecosystems and human health; statistics on associated diseases; and biotechnological strategies for biodegradation and circular economy. The methodology adopted was a scoping review using the PubMed/MEDLINE, Web of Science, Scopus, SciELO, and Google Scholar databases, with Boolean operators and MeSH/DeCS controlled descriptors. Coverage period: 2000–2025. Criteria: original articles, systematic reviews, and meta-analyses in English, Portuguese, and Spanish, indexed in peer-reviewed journals. The results identified 7 classes of plastics using the international coding system, distinguishing between thermoplastics and thermosets. Microplastics (MPs) have primary origins (cosmetic microspheres, industrial pellets) or secondary origins (photodegradation, mechanical abrasion, tire wear, synthetic fiber washing). Studies associate exposure to MPs with cardiovascular diseases (accelerated atherosclerosis, myocardial infarction, and stroke), diabetes mellitus, systemic arterial hypertension, endocrine disruption, neurotoxicity, and alterations in the intestinal microbiota. Research by the American College of Cardiology (ACC, 2025) with 555 census tracts in the US confirmed a positive correlation between the concentration of microplastics (MPs) in water bodies and the prevalence of hypertension, diabetes, and stroke. Enzymes such as PETase, MHETase, laccases, and FAST-PETase, produced by bacteria such as Ideonella sakaiensis, Pseudomonas, and Bacillus, demonstrate potential for polymer biodegradation. PHA and PLA-based bioplastics represent viable alternatives in the circular economy. Conclusion: the microplastic crisis constitutes a global public health and environmental emergency. Although causal relationships with chronic diseases still lack confirmation through longitudinal studies, the associative evidence is growing and robust. Biodegradation biotechnologies and circular economy models represent the most promising strategies for mitigation, requiring convergence between science, regulation, and public policies.