Toxicity orchestrated by alkyl chain length of plasticizers and exposure time: Transfer mechanisms of microplastic-plasticizer co-contamination across the full life cycle of rye

The contamination of water sources by microplastics (MPs) and phthalate esters (PAEs) presents a growing concern for agricultural water safety and groundwater quality. This study examined the toxicity of polystyrene MPs (PS-MPs) combined with PAEs of different alkyl chain lengths (DEP, DBP, DEHP) on rye (Secale cereale L.) through integrated short-term hydroponic and long-term experiments. Combined with multi-omics analyses, a clear "time-medium-alkyl chain length" dependent toxicity was observed. Short-term hydroponic exposure indicated the strongest combined toxicity for short-chain DEP with MPs, significantly suppressing plant growth and inducing severe chloroplast damage. In long-term experiments, the combination of long-chain DEHP and MPs exhibited the greatest adverse effects, resulting in a 50 % reduction in tillers, a 38.16 % decrease in grain weight, delayed heading, and MP accumulation in seeds (0.217 ± 0.231 mg/kg). Mechanistically, MPs served as "carriers" of PAEs, enhancing their bioavailability in aqueous and soil porewater environments via van der Waals interactions (binding energy up to -10.74 kcal/mol for DEHP). Co-exposure activated defense pathways such as MAPK signaling and the AsA-GSH cycle, but suppressed photosynthetic and nitrogen metabolism genes, leading to significant oxidative stress (MDA increased 2.3-fold) and impaired reproductive development. These findings highlight the risk that PAE-MP combined pollution poses to agricultural irrigation water systems and groundwater, providing critical insights for water quality risk assessment in farmland environments.