Revealing the Risks: A Review on the Toxicity and Mechanisms of Biodegradable Microplastics in Terrestrial Mammals

Biodegradable plastics (BPs) have emerged as promising alternatives to conventional plastics, yet their incomplete degradation in natural environments leads to the formation of biodegradable microplastics (BMPs), which raises potential risks to human health. This review synthesizes current knowledge on BMP-induced mammalian toxicity, emphasizing exposure routes, internal fate, toxicities, and related mechanisms. Specifically, BMPs enter organisms through ingestion, inhalation, dermal contact, and medical applications. And their distribution depends on physicochemical properties, particularly particle size, with smaller particles exhibiting greater bioavailability and organ accumulation. Following uptake, BMPs induce adverse effects in the digestive, respiratory, nervous, reproductive, and cardiovascular systems. These effects encompass direct pathological injury to key organs, as well as the induction of inflammatory responses. Mechanistically, BMPs trigger oxidative stress, causing mitochondrial dysfunction, calcium overload, and DNA damage that compromise physiological functions. However, most BMPs used in current research are laboratory-made and differ in properties in real environments. Furthermore, the research objectives are still limited to short-term, high-dose studies of single BMP types, leaving critical gaps regarding chronic effects, mixture interactions, and human health risks. Future studies should develop environmentally realistic exposure models, examine pollutant interactions, and combine longitudinal with epidemiological designs.