Microplastics contamination on spinach (Spinacia oleracea): influence of plastic polymers, growing media, and copper co-exposure

Microplastics (MPs), plastic fragments smaller than 5 mm, are increasingly detected in agricultural soils, where they can interact with other pollutants such as heavy metals (HMs), creating complex contamination scenarios with implications for food safety. This study provides a multi-factorial assessment of how different MP polymers (conventional vs. bio-based), soil types, and copper (Cu) co-contamination affect spinach ( Spinacia oleracea ). A pot experiment tested low-density polyethylene (LDPE), polybutylene adipate terephthalate (PBAT), and starch-based (STARCH) MPs at 0.5 and 1 % w/w , alone or combined with 100 mg kg⁻¹ Cu, in natural and commercial soils. Plant physiology (leaf chlorophyll content, photosystem II efficiency, and leaf spectral reflectance), growth parameters, and nutrient and Cu uptake were measured. The MPs negatively impacted plant physiology and growth, effects were more pronounced in the natural soil. LDPE and PBAT altered photosystem II efficiency in both soils, while bio-based PBAT and STARCH MPs significantly increased Cu accumulation when co-exposed to Cu. These results reveal a previously underestimated pathway for HM entry into edible crops and underscore the importance of considering soil-specific interactions in environmental risk assessments of both conventional and bio-based plastics.