农田残留地膜源微塑料对土壤中莠去津生物有效性的影响及机制

As a type of emerging pollutants, microplastics are generally considered to have the potential adverse ecological effects by themselves. Meanwhile, there is growing concern over microplastics as carriers for co-existing organic pollutants and may cause new combined pollution. Plastic mulching films and pesticides are widely used in China. However, it is still unclear about the effects of farmland residual microplastics on the environmental fate and bioavailability of co-existing pesticides. Systematic studies will be performed on the sorption and desorption behavior of atrazine on farmland residual mulch derived-microplastics and microplastics-soil mixtures, the uptake process and accumulation level of microplastics and atrazine in different soil systems by earthworms, in order to explore the effect of microplastics on the occurrence state and bioaccumulation of atrazine in farmland. The earthworm subchronic toxicity test under different experimental conditions will also be performed to reveal the toxicity effect of microplastics on earthworms in single and combined pollution with atrazine. This study will help to understand the interaction effects and mechanisms of residual mulch and pesticide combined pollution, and provide scientific support for improving the ecological risk assessment of microplastics in soil.

作为一类新型污染物，微塑料不仅自身被发现具有潜在不良生态效应，其对共存有机污染物的载带作用也可能带来新的复合污染问题。塑料地膜和农药在我国被大量应用。然而，农田微塑料残留对共存农药环境归趋和生物有效性的影响及作用机制仍不清晰。本项目拟以农田残留地膜源微塑料和典型除草剂—莠去津为研究对象，以蚯蚓为模型生物，通过研究莠去津在微塑料及微塑料-土壤复合体系上的吸附/解吸行为与关键控制因素，以及蚯蚓对不同土壤体系中微塑料和莠去津的摄入过程与富集水平，探究微塑料对农田环境中莠去津赋存状态及生物富集的影响机制；并通过不同实验条件下蚯蚓亚慢性毒性测试，从生化、分子和基因水平出发，揭示微塑料与莠去津单一及复合污染对蚯蚓的毒性效应及其微观机制。本项目将有助于深入认识残留地膜与农药复合污染下的交互作用效应与机制，并可为完善土壤环境微塑料的生态风险评估提供科学支撑。

作为一类新型污染物，农田微塑料残留对共存农药环境归趋和生物有效性的影响及作用机制仍不清晰。本项目分别以未老化聚乙烯地膜源微塑料（PE MPs）和田间老化聚乙烯地膜源微塑料（PE-aged MPs）为研究对象，选取莠去津作为土壤中典型的有机污染物，以山东农田棕壤作为受试介质，研究了地膜源微塑料对土壤中莠去津吸附/解吸行为、蚯蚓富集的影响以及地膜源微塑料与莠去津单一及复合污染对蚯蚓的毒性效应。研究结果表明：（1）莠去津在土壤、PE MPs和PE-aged MPs上的吸附过程符合准二级动力学模型；Langmuir模型较Freundlich模型能更好地描述莠去津在土壤、PE MPs和PE-aged MPs上的吸附特性；土壤、PE MPs和PE-aged MPs对莠去津的吸附能力大小顺序为PE-aged MPs>PE MPs>土壤；土壤、PE MPs和PE-aged MPs在模拟消化液中对莠去津的解吸量和解吸率均显著高于CaCl2溶液，且在不同背景溶液中土壤、PE MPs和PE-aged MPs对莠去津的解吸量和解吸率均呈现出PE-aged MPs>PE MPs>土壤的规律；添加地膜源微塑料增加了土壤对莠去津的吸附/解吸能力，且增加程度受添加量和田间老化过程的影响。（2）当富集浓度达到最大值时，PE MPs和PE-aged MPs处理组蚯蚓体内莠去津的浓度较未添加地膜源微塑料的染毒对照组显著升高，且不同处理组Metaphire guillelmi体内莠去津的浓度高于Eisenia fetida体内莠去津的浓度。（3）地膜源微塑料（PE MPs和PE-aged MPs）与莠去津（0.02和2.0 mg·kg-1）单一及复合暴露均能够诱导E. fetida产生氧化胁迫效应，造成DNA损伤，并导致生理相关基因相对表达水平发生显著变化；且大部分复合暴露组，尤其是PE-aged MPs与2.0 mg·kg-1莠去津复合暴露组，E. fetida的综合生物标志物响应指数IBR值（氧化胁迫效应）和Olive尾矩（OTM）值均高于相应的单一暴露组，表明地膜源微塑料与莠去津复合暴露能够增强其对E. fetida的氧化胁迫效应和DNA损伤。本研究可为全面评价土壤环境中微塑料与其他典型农药复合污染的环境风险提供科学依据。