Co-exposure of di(2-ethylhexyl) phthalate (DEHP) decreased the submicron plastic stress in soil–plant system

The widespread use of agricultural plastic films has made micro- and nanoplastics (MNPs) and phthalate esters (PAEs) contaminants of emerging concern in agroecosystems. However, the interactive mechanisms underlying their combined pollution in soil-plant systems remain elusive. To fill this gap, this study investigated the interaction between submicron plastics (SMPs, 0.01% and 0.1% w/w) and di(2-ethylhexyl) phthalate (DEHP) in soil-lettuce systems. Contrary to the anticipated synergistic toxicity, DEHP significantly reduced SMP uptake into and by cracked surface cells of lettuce roots (with root concentration factors decreasing by 19%-64%), i.e., DEHP alleviated SMP-induced oxidative stress, as evidenced by reduced levels of reactive oxygen species (-26.8% and -66.7%) and antioxidant enzyme activities (-118% and -128%). Metabolomic profiling revealed that SMP exposure significantly dysregulated multiple metabolic pathways (amino acid, carbohydrate, energy, glycan, lipid, and nucleotide metabolism), while SMP ​+ ​DEHP co-exposure selectively attenuated these metabolic disturbances, showing enrichment only in glycan biosynthesis/metabolism and suppressing SMP-induced perturbations in other pathways (biosynthesis of secondary metabolites, energy metabolism, and signal transduction). Microbial community analysis showed that high-level SMP exposure significantly diminished bacterial α-diversity and amplicon sequence variant (ASV) richness, whereas DEHP supplementation enhanced those of <i>Myxococcota</i> in the soil, potentially counterbalancing SMP-induced microbial dysbiosis. These findings collectively demonstrate that co-contamination by MNPs and plastic additives may produce antagonistic interactions rather than uniformly synergistic effects, and provide a more comprehensive evaluation of the risks of PAEs and MNPs to food security, human health, and ecological environment.