The presence of biodegradable microplastics (BMPs) alongside toxic metals in soil significantly threatens plant health. Current research mainly focuses on the effects of original BMPs. In contrast, the specific impacts of ultraviolet (UV)-aged BMPs and their interaction with Cadmium (Cd) on seed germination and growth are unclear. Therefore, this study incubated aged polylactic acid (PLA) MPs through a UV irradiation aging process and used an indoor hydroponic experiment to systematically investigate the single and combined effects of Cd and BMPs (virgin and aged) on pakchoi (Brassica chinensis L.) germination, photosynthesis, antioxidant systems, and Cd accumulation. The results showed that after 21 days of UV irradiation (UPLA MPs), PLA MPs formed a fractured surface, demonstrating more detrimental effects on pakchoi than virgin ones. UPLA MPs and Cd alone inhibited pakchoi germination, growth, and photosynthesis, while PLA MPs alone promoted these processes. Combined treatment with Cd and UPLA MPs significantly increased oxidative damage and reduced pakchoi root length, chlorophyll, Mg, Mn, and Zn content. Under the combination of Cd and BMPs, PLA MPs could effectively alleviate the toxic effect of Cd on pakchoi. The results unraveled here emphasized that UPLA MPs, especially aged BMPs, could trigger adverse effects on agro-systems with heavy metals. Therefore, the results of this study can provide a new perspective and reference for the ecological risk evaluation of Cd and BMPs pollution in agricultural soils.

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

The fate of black biodegradable mulch film (MF) based on starch and poly(butylene-adipate-co-terephthalate)-co- terephthalate) (PBAT) in agricultural soil is investigated herein. Pristine (BIO-0) and UV-aged film samples (BIO-A192) were buried for 16 months at an experimental field in southern Italy. Visual, physical, chemical, morphological, and mechanical analyses were carried out before and after samples burial. Film residues in the form of macro- and microplastics in soil were analyzed at the end of the trial. Progressive deterioration of both pristine and UV-aged samples, with surface loss and alterations in mechanical properties, occurred from 42 days of burial. After 478 days, the apparent surface of BIO-0 and BIO-A192 films decreased by 57 % and 66 %, respectively. Burial determined a rapid depletion of starch from the polymeric blend, especially for the BIO-A192, while the degradation of the polyester phase was slower. Upon burial, an enrichment of aromatic moieties of PBAT in the film residues was observed, as well as microplastics release to soil. The analysis of the MF degradation products extracted from soil (0.006-0.008 % by mass in the soil samples) revealed the predominant presence of adipate moieties. After 478 days of burial, about 23 % and 17 % of the initial amount of BIO-0 and BIO-A192, respectively, were extracted from the soil. This comprehensive study underscores the complexity of biodegradation phenomena that involve the new generation of mulch films in the field. The different biodegradability of the polymeric components, the climate, and the soil conditions that did not strictly meet the parameters required for the standard test method devised for MFs, have significantly influenced their degradation rate. This finding further emphasizes the importance of implementing field experiments to accurately assess the real effects of biodegradable MFs on soil health and overall agroecosystem sustainability.