Polystyrene microplastics decrease dibutyl phthalate uptake and metabolism in pumpkins

The environmental impact of polystyrene (PS) and dibutyl phthalate (DBP) has become a research hotspot, but studies on their effects on higher plants remain limited. In this study, different sizes (100 and 300 nm) and concentrations (5 and10 mg L −1 ) of PS were used in combination with DBP (10 and 20 mg L −1 ) to explore their combined toxicity to pumpkins and to assess how PS influences the absorption and metabolism of DBP in plants. The results showed that after 7 days of exposure to 20 mg L −1 DBP, 10 mg L −1 100 nm PS reduced the DBP content in the roots and leaves by 25.5% and 23.4%, respectively, while inhibiting its metabolism. DBP (PS) reduced the biomass of roots and leaves by 18.8% and 18.4% (22.4% and 15.1%) respectively, although co-exposure to PS and DBP decreased pumpkin biomass, the interaction of DBP and PS was antagonistic for 300 nm PS but synergistic for 100 nm PS. The inhibition of DBP uptake and metabolism was associated with increased oxalic acid secretion, decreased root activity, and reduced carboxylate esterase activity. Biomass reduction was associated with declines in dehydrogenase and ribulose-1,5-bishosphate carboxylase activities. This study provides a theoretical basis for using arginine to enhance degradation in microplastic-contaminated farmland. • PS inhibits the uptake and metabolism of DBP in pumpkins. • DBP and PS trigger oxidation bursts in pumpkins and reduce their biomass. • DBP and PS promote oxalic acid secretion in the root system. • The combined toxicity of DBP and large size PS is antagonistic, while DBP and small size PS is synergistic.