典型电子废物塑料机械再生过程中多溴联苯醚污染风险与释放机理研究

As a primary recycling method of electrical and electronic waste (e-waste) plastics in China, mechanical recycling is an imperative contamination resource of polybrominated diphenyl ethers (PBDEs). The investigation on the emission properties and pollution risk of PBDEs during the mechanical recycling process of e-waste plastics is of great importance to effectively controll PBDEs. This research focuses on the TV casing as the typical e-waste plastics, and the experimental simulation of mechanical recycling is conducted in laboratory. The emission properties, relative abundances and distribution of PBDE congeners in raw material, gas, cooling water and recycled product is studied. The influence of recycling frequency and temperature on PBDEs contamination properties is analyzed. Based on the characterization of concentration profiles of typical lower brominated congeners in certain temperature range or reclycling frequency, the debromination course is discussed. The migration fate and environmental risk of PBDEs carried by gas is analyzed by adopting multi-media fugacity model, and the human intake of PBDE congeners via exposure to the gas and daily articles by using of recycled plastic is estimated by establishing exposure model. The debromination pathway and decomposition course of higher brominated congeners are studied by conduct the thermal experiment of BDE-209 combined with quantitative structure-activity relationship (QSAR) method. The preferred debromination pathway of PBDEs during the mechanical recycling process is revealed. The research results can provide a scientific basis and theoretical guidance for the risk management and comprehensive pollution control on e-waste plastic recycling.

机械再生是我国电子废物塑料最主要的资源化利用方式，也是多溴联苯醚(PBDEs)释放的重要污染源，研究电子废物塑料机械再生过程中PBDEs污染风险对于PBDEs的有效控制具有十分重要的意义。本项目以电视机外壳作为典型电子废物塑料，实验室模拟机械再生工艺，分析PBDEs同系物的释放规律，及其在原料、烟气、冷却水和再生产品中的相对组分与污染分布特性；研究循环再生与加热熔融对PBDEs同系物释放规律的影响，探讨特定温度区间与再生次数条件下，典型低溴代同系物组分及其脱溴分解过程；运用逸度模型分析烟气中PBDEs的迁移归趋与环境风险；运用暴露评价模型研究烟气释放与再生塑料的风险暴露量；通过BDE-209加热反应实验结合定量构效关系(QSAR)，揭示机械再生过程中PBDEs的优先脱溴路径。研究结果为电子废物塑料回收处理环节的污染防治和风险管理提供了科学依据和理论指导。

随着多溴联苯醚(PBDEs)在全球范围内的禁产和禁用，以及我国废塑料再生行业的快速发展，电子废物塑料机械再生已成为当前PBDEs污染的主要途径，及其全过程风险管理和综合污染防治的重要环节。然而，现有的国内外研究只集中于环境介质中PBDEs的污染特性，对于电子废物塑料再生利用环节的污染释放研究相对较少。针对此，本项目围绕电子废物塑料机械再生环节，通过实际处理企业采样分析与实验室模拟相结合，开展了PBDEs污染与释放特性研究。实际机械再生处理产生冷却水中PBDEs浓度高出自然水体3-6个数量级，土壤受污染程度与电子废物拆解区和PBDEs生产区污染负荷相当。根据实际工况条件，模拟机械再生过程，采集再生料、冷却水和烟气样品，分析发现PBDEs在三相中的分配关系为70:0.01:3.35，烟气中PBDEs浓度呈现出随温度升高而增加的趋势，其中，气相/颗粒相占比为35/65。冷却水和烟气中PBDEs排放因子分别为1.08E-04和1.9E-02~3.4E-02，据此可估算得到我国每年因电子废物回收拆解进入再生塑料制品的PBDEs总量约为673吨，进入大气环境的释放量约632kg。电子废物塑料经机械再生处理表现出显著的脱溴过程，再生料中三溴~七溴含量高于原料，十溴占比减少44%，气相中低溴代同系物占比随温度升高而增加。为进一步明确再生过程中PBDEs释放机理，针对电子废物塑料中主要同系物BDE-209开展实验，分析不同温度和加热时间，烟气中同系物组成，结果表明，当温度未达到200℃时，脱溴产物主要为六溴和七溴同系物，当温度升高达到200℃时，四溴和五溴同系物产生，且该脱溴过程会在温度升高至250℃时加快。在明确电子废物塑料机械再生过程中PBDEs释放规律的基础上，运用暴露评价模型研究了烟气与再生塑料回用于日用塑料制品造成的PBDEs潜在暴露风险，其中，再生塑料制品对人体健康影响较小，在可接受范围内，但是烟气因呼吸吸入的暴露风险非常高，需加强风险监管。本研究结果对于电子废物塑料再生环节PBDEs总量控制和源头减排具有实际指导意义。