Comparative toxicity of conventional and biodegradable microplastics to the marine algae Chlorella vulgaris: a critical review

Microplastics (MPs), both conventional and biodegradable, are emerging contaminants of significant concern in marine ecosystems. While biodegradable plastics such as polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT) are marketed as eco-friendly alternatives, growing evidence suggests that their degradation products may exhibit comparable toxicity to conventional polymers like polyethylene (PE) and polystyrene (PS). This review critically examines the physicochemical properties, degradation behavior, and ecotoxicological impacts of both biodegradable and conventional MPs on the marine microalga Chlorella vulgaris. The analysis highlights that both MP types inhibit algal growth, disrupt photosynthesis, and induce oxidative stress through reactive oxygen species (ROS) generation, enzymatic imbalance, and cellular membrane damage. Mechanistic pathways involve particle aggregation, surface adsorption, and the release of toxic leachates and nano-sized derivatives, amplifying their ecological risks. Furthermore, biodegradable MPs often fragment faster, increasing MP particle counts and pollutant adsorption potential. The findings challenge the perceived environmental safety of “biodegradable” plastics and underscore the need for realistic field-based assessments. Understanding MP-algae interactions is crucial, as disruptions at this trophic level may cascade through marine food webs, affecting productivity and biogeochemical cycling. The review calls for comprehensive ecotoxicological frameworks to guide sustainable polymer design and effective marine pollution management.