塑料添加剂对微塑料土壤生物效应的影响研究—以增塑剂为例

In recent years, soil microplastic pollution as a new environmental issue has received increasing attention. Existing research has mainly focused on the ecological impacts of microplastics alone (without additives). Indeed, plastic products usually contain significant amounts of chemical additives that loosely incorporated into the polymer structure. These additives would have a direct effect on the toxicity of microplastics, but relevant research is still very limited. Plasticizers account for the largest fraction of additive consumption, which are predominantly used in PVC plastics. Thus, the aim of this study is to investigate how plastic additives affect the ecological impacts of microplastics in soil environments, by focusing on the effect of plasticizers on the toxicity of PVC microplastics to soil earthworms and microorganisms. Briefly, PVC microplastics with and without specific plasticizers will be prepared, and patterns of plasticizer release under simulated gut fluid and soil solution conditions will be studied; during the ecotoxicity tests, the relationships among plasticizer contents in microplastics, plasticizer accumulation in earthworm tissues and toxicity indices of earthworms will be analyzed, to evaluate the effect of plasticizers on the toxicity of microplastics to soil animals; high-throughput sequencing technologies will be utilized to analyze the responses of microbial communities in different soils, to elucidate the role of plasticizers in microplastic-induced impacts on soil microorganisms. The results of this study will help to clarify the importance of additives in determining the toxicity of microplastics, and contribute to reasonable evaluation of the ecological risks of microplastic-contaminated soils.

近年来，土壤微塑料污染作为新的环境问题逐渐受到重视。已有的研究多关注于微塑料自身的生态效应，而实际上塑料制品中通常含有大量疏松结合的化学添加剂，目前关于这些添加剂对微塑料生态效应的影响研究还十分缺乏。增塑剂是全球消耗量最大的添加剂，主要用于聚氯乙烯（PVC）塑料。基于此，本项目拟以增塑剂为例，考察塑料添加剂对微塑料土壤动物和微生物效应的影响。制备含和不含增塑剂的PVC微塑料，研究增塑剂的释放规律；进行暴露实验，通过分析增塑剂剂量与蚯蚓体内增塑剂累积、毒性效应指标之间的关系，评估增塑剂对土壤动物毒性效应的影响及作用机制；利用高通量测序技术分析土壤微生物多样性、组成和功能的变化，阐明增塑剂在微塑料土壤微生物效应中的作用。该研究结果将有助于揭示添加剂在微塑料毒性效应中的作用，为微塑料污染土壤的生态风险评价提供重要的科学依据。

微塑料作为一类新污染物在土壤环境中被广泛检出，但其对土壤微生物组成和功能的影响及作用机理尚不清楚，尤其是微塑料中化学添加剂的释放行为及其在微塑料效应中的贡献仍不明晰。本项目以常见的邻苯二甲酸酯类增塑剂为例，系统研究了聚氯乙烯（PVC）微塑料中增塑剂的释放规律，微塑料对土壤微生物群落和氮代谢功能的影响及增塑剂在其中所起的作用，以及土壤性质和增塑剂类型等因素对微塑料效应的影响。结果表明：（1）软质PVC微塑料具有很强的增塑剂（邻苯二甲酸二丁酯，DnBP）释放潜力，小塑料粒径、高增塑剂含量、光老化和富里酸的存在均有利于增塑剂释放，富里酸和盐离子共存可进一步促进增塑剂释放。（2）纯PVC微塑料（质量浓度为0.5%）对土壤微生物和氮代谢的影响很小，而软质PVC则可通过释放增塑剂重塑微生物组从而改变氮代谢过程，增塑剂释放是微塑料影响土壤微生物组成和功能的主要驱动力。（3）土壤类型/性质、温度和增塑剂类型对微塑料效应有重要影响。PVC微塑料在不同类型土壤中对氮代谢的影响存在差异，具体效应与土壤对增塑剂的降解能力有关，在降解能力强的土壤中脲酶活性和硝酸盐还原潜力提高，在降解能力弱的土壤中微生物数量和氮代谢活性降低，造成无机氮累积，在实验使用的土壤中硝化作用均被抑制，主要与氨氧化古菌（和全程氨氧化菌）数量降低有关；微塑料在实验室恒温（25℃）和室外自然变化温度（2-26℃）条件下产生相似的效应，表明实验室结果可用于预测微塑料在实际土壤中环境效应，但准确评估仍需考虑温度差异，室外温度下软质PVC微塑料在质量浓度为0.05%时即可对土壤微生物和氮代谢造成显著的或可观测的影响，表明需要严格控制软质PVC进入土壤环境；与DnBP相比，分子量更大的邻苯二甲酸酯增塑剂对PVC微塑料微生物效应的影响相对较小。本研究有助于确立影响微塑料效应的关键因子，为准确评估微塑料对土壤微生物和氮代谢的影响提供科学依据。