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Carrier effects of microplastics in a hydroponic system: Amplifying diethyl phthalate toxicity and endophytic dysbiosis in Rye (Secale cereale L.) with implications for aquatic ecosystems
Summary
Researchers found that polystyrene microplastics and diethyl phthalate (a common plasticizer) interact synergistically to cause severe toxicity in hydroponically grown rye, far exceeding the damage from either pollutant alone. The study revealed a bidirectional mechanism where microplastics adsorb the plasticizer while the plasticizer enhances microplastic uptake by roots, leading to photosynthetic collapse and disrupted endophytic microbial communities.
Microplastics (MPs) and diethyl phthalate (DEP) co-contamination poses a growing threat to agricultural water systems, with potential risks for aquatic environments via groundwater infiltration and drainage. This study systematically investigates the individual and combined toxicological effects of polystyrene MPs and DEP on hydroponically cultivated rye (Secale cereale L.) by integrating physiological profiling, transcriptomics, endophytic microbiome analysis, and computational modeling. Co-exposure to MPs and DEP induced severe synergistic toxicity, significantly exceeding individual treatments. This was manifested as drastic growth inhibition, photosynthetic collapse due to "stomatal-non-stomatal" limitation, and exacerbated oxidative damage linked to the direct inhibition of ascorbate peroxidase (APX) by DEP. Crucially, a bidirectional interaction mechanism was uncovered: MPs adsorbed DEP, reducing its phytoaccumulation, while DEP enhanced MPs root uptake and upward translocation by altering their surface charge, leading to synergistic subcellular damage, including chloroplast disintegration. Molecular dynamics simulations revealed that non-specific lipid transfer proteins (nsLTPs) facilitate DEP apoplastic transport. Furthermore, pollutants reshaped the endophytic microbiome, reducing diversity and enriching specific taxa (e.g., Rhizobiaceae), changes strongly correlated with oxidative stress and photosynthetic decline. The new insights reside in demonstrating that the synergistic toxicity stems from a bidirectional MP-DEP interaction (adsorption versus enhanced penetration), facilitated DEP transport via nsLTPs, and the consequential linkage between endophytic community disruption and the decline of plant physiological function. These findings imply that composite pollution risks are not additive but can be synergistically amplified through physicochemical and biological interactions. The study provides a mechanistic framework for assessing multipollutant risks, with broader relevance for the sustainability of hydroponic agriculture, safety of wastewater-irrigated systems, and understanding of pollutant transfer in aquatic-terrestrial food webs.