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塑料由于轻便、耐腐蚀、化学性质稳定、成本低等优点，广泛应用于工业、医药、农业等各个领域[1 − 3]. 常用的微塑料种类按材料划分包括聚苯乙烯 （PS）、聚乙烯 （PE）、聚丙烯（PP）、聚氯乙烯（PVC）和聚对苯二甲酸乙二醇酯（PET）[4] . 预计到2025年，全球塑料的累计产量将达到2.5亿t[5]. 全球塑料产量由于成本低增长迅速，产生大量的塑料垃圾. 这些塑料垃圾会通过一系列自然过程破碎成更小的颗粒[6]. 微塑料 （microplastics,MPs） 通常指直径小于5 mm的颗粒、纤维或薄膜，其所占环境中塑料碎片数量最多[7]. 微塑料分布广泛、难以降解，目前构成严重的全球环境问题[8]. 研究表明，全球产生的塑料约有1.5%—4.5%直接释放到海洋中[2 − 3]. 不仅如此，每年释放到陆地上的微塑料质量可能超过40万t，是释放到海洋中的4—23倍[9 − 10]. 废弃的微塑料流入环境后易被生物体摄入，从而对其生长发育、氧化应激和生殖系统等造成负面影响[11, 12]. 因此，环境中微塑料造成的污染问题已引起海内外广泛重视.
环境中微塑料可以通过机械力、光照、化学物质、高温和生物等因素发生物理、化学和生物老化[13 − 15]. 老化后微塑料表面形貌和理化性质发生显著改变，例如表面形貌、粒径、比表面积和氧官能团等，从而影响其环境行为[16-17]. 首先，环境中微塑料老化后粒径减小，改变了生物体对微塑料的摄入方式和数量[18 − 20]，使其更易被生物体摄入，从而影响微塑料的生态毒性[21-22]. 例如微塑料老化过程中破碎为粒径更小的颗粒甚至为纳米塑料，更易被无脊椎动物（如贻贝和牡蛎幼虫）摄入，表现出更强的毒性[23 − 24]. 其次，环境中的微塑料可以作为载体富集环境中的污染物，主要包括有机污染物、重金属和微生物[25 − 30]. 老化过程显著改变了微塑料吸附有机污染物的能力. 微塑料老化后表面粒径减小、比表面积增大，吸附位点增多；同时表面生成更多含氧官能团，导致亲水性、极性和电负性增加，进而影响对有机污染物的吸附性能[13, 31]. 此外，老化过程不仅影响污染物富集有机污染物的性能，而且随着生物体的摄食行为，老化微塑料将污染物载带至生物体内，导致生物体的毒性增强，进一步增加了微塑料的生态风险[32 − 34]. 因此，微塑料的老化对环境行为和生态风险有重大影响.
微塑料自然老化过程缓慢且复杂，化学老化由于氧化能力强而用于模拟和加速微塑料的老化过程[35]. 在此，本文综述了化学老化微塑料物理化学性质的改变，探讨了化学老化微塑料吸附有机污染物的研究现状，结合吸附动力学模型和等温吸附模型，以期对化学老化微塑料的环境行为和生态风险评估提供参考.
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环境中微塑料经化学老化后表面发生氧化还原反应，进而导致微塑料的表面形貌、分子结构及化学组成等理化性质发生显著改变. 微塑料化学老化后表面粗糙度增加，出现裂缝和孔隙，粒径减小、比表面积增多；同时，表面生成的官能团增加，导致其亲水性增强，疏水性降低.
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化学老化改变了微塑料的表面特性. 通过扫描电子显微镜（SEM）表征老化前后微塑料的物理尺寸和形貌. 研究表明化学老化后微塑料的表面形态与紫外照射塑料3—72 h后的表面形态相似[36]，化学老化微塑料表面变得脆弱和粗糙，有不同程度小孔、裂纹和凹坑[37]. 例如用芬顿和H2O2分别处理PS1、3、5、7 d[38]，SEM显示老化前的PS颗粒是表面光滑均匀的球形，可随着老化时间的增加，PS表面逐渐变化[39]. 一些PS颗粒的表面逐渐变得粗糙，一些颗粒的表面有不同程度的折叠，甚至有个别颗粒已经断裂[30]. 例如将PS和PE微塑料分别经芬顿和热活化过硫酸盐老化，随着老化程度增加，微塑料表面逐渐产生裂纹和凹坑, 微塑料表面在老化10 d后表现出类似缺口的形状，老化30 d后会产生多个裂缝且纹理粗糙[40]. 例如研究低密度聚乙烯（LDPE）分别经过芬顿、热活化过硫酸盐和臭氧处理前后的表面形貌，发现原始微塑料表面相对平坦和光滑，老化后微塑料表面出现碎片和裂纹，变得更粗糙并呈现出更多的层状结构[41]. 总体而言，化学老化后微塑料表面粗糙度增加，并破碎为更小的碎片.
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微塑料化学老化后聚合物破碎成粒径更小颗粒，生成微米级甚至纳米级的亚微塑料. 与原始微塑料（40—250 μm）相比，芬顿老化微塑料粒径显著降低[40, 42]. Liu等[18]研究表明，纳米PS微塑料（（487 ± 18.3） nm）臭氧老化后粒径减小. Ren等[43]发现，紫外活化过硫酸盐老化PS的粒径下降（平均粒径为（
1161.8 ± 17.2 ） — （823.7 ± 16.3）nm）. 聚乳酸（PLA）微塑料在热活化过硫酸盐老化10d后，破碎成更小的碎片（约10 μm），甚至更小的纳米塑料（< 100 nm）[44]. Liu等[40]用热活化过硫酸盐老化微塑料30 d后，发现80.1%的PS和97.4%的PE的尺寸低于20 μm（原始微塑料平均尺寸为40—50 μm）. 微塑料化学老化后粒径减小导致比表面积（SSA）增大. Liu等发现与原始微塑料相比（SSA为7.419 m2·g−1），臭氧老化PS微塑料3 h后SSA显著增加（SSA 为12.94 m2·g−1）[18]. Kong等[44]发现热活化过硫酸盐老化PLA、PET 和PP微塑料后比表面积分别比原始微塑料提高了6.18倍、1.63 倍和 3.84 倍. -
化学老化微塑料表面官能团增加会导致微塑料疏水性降低，表面接触角测量是衡量老化微塑料亲疏水性改变的关键参数. 环境中微塑料经化学老化过程后接触角往往会减小，亲水性提高. 研究发现臭氧老化后PS的接触角从94.4°降至65.3°其疏水性降低[18]. 例如芬顿老化微塑料表面生成亲水性含氧官能团，疏水性显著下降[45]. 化学老化后微塑料表面疏水性降低、亲水性增强会进而降低对疏水性有机物的吸附能力，增强对亲水性有机污染物的吸附能力[46 − 47]. 研究表明芬顿老化微塑料后表面疏水性下降了10%左右，降低了对疏水性化合物的吸附[42]. 例如分别经热活化过硫酸盐老化[44]和H2O2[48]老化后，微塑料表面羟基和羰基增加导致亲水性增强，提高了对抗生素的吸附能力.
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研究老化微塑料的化学特性主要是为了观察官能团和元素的变化. 傅立叶变换红外（FTIR）光谱鉴定微塑料老化前后表面含氧官能团（如羰基（C=O）和羧基（O—C=O））的变化[49 − 50]. 研究表明化学老化后微塑料表面含氧官能团的峰强增强，表明微塑料老化程度提高[18 − 20, 38, 45, 51 − 53]. 羰基指数（Carbonyl Index，CI）常用于评价微塑料的老化程度. 例如与原始微塑料相比，分别经芬顿和H2O2老化后微塑料羰基指数值有不同程度的增加[54]. Liu等[40]研究热硫酸盐老化微塑料30d后，PS的羰基指数范围为0.03—0.69，PE羰基指数范围为0.01—0.36. 例如将LDPE用臭氧气体直接暴露1h，发现用臭氧气体直接处理的平均羰基指数值达到0.100 ± 0.002[55]. 因此，羰基指数可以较好描述微塑料化学老化程度的变化. 此外，与Fenton和臭氧相比，热活化过硫酸盐后微塑料老化程度更高，表明热活化过硫酸盐处理的氧化能力相对较强[41]. 另一方面， X射线光电子能谱分析（XPS）可以检测老化微塑料表面元素含量，尤其是氧含量的增加. O/C 包含除羰基以外的羟基和碳氧，利用XPS分析O/C比可进一步反映微塑料的老化程度[56]. Wang等[45]使用芬顿处理PS、PC后微塑料表面迅速氧化，O/C比增加，进一步证明PS、PC表面引入了含氧基团. Wu等[57]采用热活化过硫酸盐老化等规聚丙烯（iPP），结果表明老化40d后的iPP表面含氧官能团增加（O/C比为0.02—0.09），且O/C比与iPP微塑料老化时间呈线性相关（r= 0.964，P<0.01）. 未来可考虑结合羰基指数和O/C比证实AOPs是实验室加速微塑料老化过程的有效方法.
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化学老化指微塑料与氧化剂反应生成活性氧自由基（reactive oxygen species, ROS），诱导聚合物碳链断裂，随后引发的自由基链式反应[58]. 具体地说，首先羟基自由基（·OH）进攻聚合物碳链叔碳原子上的C-H键，生成烷氧自由基（R·）；其次，烷基自由基与氧气反应生成过氧自由基（ROO·），过氧自由基再从聚合物分子（RH）中提取氢原子形成氢过氧化物（ROOH）[59]，氢过氧化物断裂脱去—OH生成烷氧基自由基（RO·）和·OH[60]；烷氧基自由基作为重要的反应中间体，可通过夺氢、断链、重排反应形成醇类、羧基、过氧化物、酯类、酮类等产物. 其反应步骤如下[53]：
高级氧化过程（Advanced Oxidation Processes，AOPs）因具有较强氧化能力而被广泛应用于有机污染物的降解和矿化[61- 62]. AOPs是常用的化学老化微塑料方法，主要包括芬顿（Fenton）、过硫酸盐（K2S2O8）处理和臭氧（O3）等[63- 64]. 实验室采用AOPs通过不同激活方式产生高氧化电位的ROS（包括·OH，硫酸根自由基（SO4−·），超氧化物自由基（O2·−）和单线氧（1 O2）加速老化微塑料[65]. 此外，实验室将化学老化与光照射结合提高微塑料的老化程度.
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作为一种经典的氧化还原反应，芬顿反应广泛存在于自然环境中[39]. 芬顿反应是指使用 H2O2 和 Fe2+ 的混合物将有机物质氧化成无机状态. 它可以将大分子氧化成小分子，将小分子氧化成简单的无机物质，如 CO2 和 H2O [66]. 微塑料也是含碳有机物，因此，由芬顿反应引起的微塑料老化在自然界很常见. 芬顿反应在常温常压下进行，可以产生大量高氧化还原电位的自由基（如·OH（
$ {E}^{0} $ =1.8 V|SHE）[67]）攻击有机物骨架[68]. 芬顿反应的主要机理如下：在芬顿反应中H2O2激活Fe2+生成·OH和氢过氧自由基（HO2·），HO2·可以作为中间自由基与H2O2反应产生·OH，同时也与·OH反应，产生O2；而Fe3+被HO2·还原为Fe2+，Fe3+不仅促进·OH的生成，同时也是自由基的猝灭剂. 芬顿是最常用的微塑料化学老化方法，如PS[38, 40, 42, 45]、PE[40]、PVC[45]、PC[45]、PP [42]和高密度聚乙烯（HDPE）[42]等. 研究表明芬顿可以有效氧化PS和PC，实现微塑料的循环利用[45]. Lang等[38]在pH=4（中性和碱性条件下形成的氢氧化铁会抑制 Fe2+的催化活性）和室温下老化PS1、3、5、7 d，结果表明随着老化时间增加，PS表面产生裂纹、比表面积增大，含氧官能团增多，且芬顿老化效果好于H2O2.
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H2O2 作为一种高效清洁的氧化剂，因其价格低廉易得和环境友好性而在AOPs中得到了广泛的应用[69]. H2O2可以通过过渡金属、超声波、电解和光照射等激活方式产生高氧化性的·OH [70 − 73]. 研究表明H2O2对PS[38]、PVC [45, 51]等微塑料具有氧化能力. 例如在pH=4和室温下用（1.5%）H2O2老化PS分别震荡1、3、5、7 d，发现PS老化效果逐渐增强[38].
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过硫酸盐（PS），包括过氧单硫酸盐（PMS，HSO5−）和过硫酸盐（PS，S2O82−）可以经激活后产生SO4−·，称为基于硫酸根的高级氧化技术（SR-AOPs）[74]. 与·OH（
$ {E}^{0} $ =1.8—2.8 V）相比，SO4−·具有较高的氧化电位（$ {E}^{0} $ =2.5—3.1 V）[75]. 过硫酸盐的激活方法有多种，如紫外光、电化学氧化、热、碱和过渡金属等[76]. 过硫酸盐的热活化主要通过升高温度提供足够的活化能，O—O键在热辐射作用下发生断裂反应，生成2个分子量的使O－O键断裂产生SO4−·. 研究表明热活化过硫酸盐可老化多种类型的微塑料，如PS[40, 77]、PE[40, 77]、PP[44, 57]、PLA[44]和PET [44]. Liu等[40]根据CI和O/C计算，发现PS和PE经热活化过硫酸盐和自然老化过程中产生了类似的氧化产物，自然老化需要4.3—40年才能达到与热活化过硫酸盐30 d相同的老化程度. 例如PLA、PET 和PP微塑料热活化过硫酸盐老化10 d后表面粗糙度增加，生成羰基、羟基和酯基等官能团[44]. -
臭氧具有高氧化能力，主要产生·OH氧化降解顽固的有机污染物. 臭氧通过链式反应形成·OH、O2·-和HO2·. 城市污水消毒后出水中会残留许多小颗粒的微塑料，消毒过程中残留的微塑料可能与化学消毒剂反应，从而改变微塑料表面性质[5]. Liu等[18]观察到PS在0.1 g·min−1的臭氧中暴露3 h后破碎成更小颗粒，表面生成羟基、酮和羧基等含氧基团. 例如在臭氧中老化LDPE和PET微塑料96 h后表面含氧官能团增加，羰基指数提高，且臭氧气体直接氧化程度比在水体中更高[55]. 表明消毒工艺可以短期内改变微塑料性质，加速微塑料的老化.
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虽然AOPs可以模拟微塑料在环境中的自然老化，但处理过程单一，没有考虑光照在微塑料老化中的重要作用[35]. 其次，为稳定氧化速率，AOPs需反复添加氧化剂，老化微塑料收集率低. 为此人们开发了紫外（UV）与不同的氧化剂（芬顿、H2O2、过硫酸盐和臭氧）的组合，提高老化程度[78].
光-芬顿（UV/Fenton）是增强Fe3+/Fe2+还原循环的一种有效途径，通常将紫外引入芬顿系统实现[79]. H2O2直接吸收紫外后光解产生·OH，同时氧化Fe3+成Fe2+产生大量额外·OH. 研究表明光-芬顿老化PS微塑料发生破碎表面出现裂纹和凹坑，平均尺寸减少，含氧官能团增加[19].
光-H2O2（UV/ H2O2）指H2O2吸收紫外后光产生·OH进攻聚合物分子使碳链断裂，同时聚合物吸收辐射发生光氧化，光- H2O2的组合加速了聚合物链内C—H键的断裂和—OH、C—O和C—OH键的形成. 研究使用紫外照射H2O2老化PS，微塑料破碎断链生成羟基、烯烃和醛等产物[80 − 82]. 例如向PS微塑料添加H2O2（10%），然后将样品暴露于紫外光 （4×15W UVC-灯泡，最大波长在254 nm） 下96 h，羰基指数由0.36提高到1.61[80].
O3由于具有很强的氧化能力（
$ {E}^{0} $ =2.07 V），作为降解各种污染物的氧化剂，城市污水厂为了提高废水处理的消毒效率，开发了联合消毒工艺，例如采用紫外光-臭氧（UV/ O3），O3分解为ROS（·OH和O·−），参与消毒后水中微塑料的氧化[52]. UV/ O3体系机理如下:过硫酸盐中的O—O键在的紫外照射下可以产生断裂反应（UV/ PS），生成2个分子量的SO4−·. 当PMS作为氧化剂时，·OH是主要的反应物. 当PDS被用作氧化剂时，·OH和SO4−·都是主要的反应性物种. Ren等[43]发现与单独的紫外照射或过硫酸盐处理相比，紫外照射过硫酸盐老化由于加强了光引发的化学氧化作用而显示出协同效应，从而显著增强PS的老化程度.
总之，光复合老化是多种因素的结合，紫外光的氧化作用可能很强，所以不能完全归结为化学氧化作用，在探讨微塑料的化学氧化时，我们还应该考虑不同类型的光氧化过程. 本文总结了常见的微塑料化学老化方法，如表1所示，并通过羰基指数和O/C表明老化程度.
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目前微塑料中已鉴定出200多种有机化合物[83]. 水体中有机污染物主要分为疏水性有机污染物（Hydrophobic Organic Compounds，HOCs）和亲水性有机污染物. 进入环境的微塑料经化学老化后其表面特性发生变化，进而直接影响微塑料对有机物的吸附. 老化后微塑料表面粒径减小，比表面积增大，导致表面吸附位点增加；同时表面含氧官能团增加，从而使其亲水性、极性和电负性增强，并通过疏水相互作用、静电相互作用、π-π 相互作用和氢键等多种作用机制，进而影响其对HOCs和亲水性有机污染物的吸附能力. 此外，环境因素也会对化学老化微塑料吸附有机物产生影响. 本文总结了化学老化微塑料吸附有机污染物的研究现状，并结合吸附动力学模型和吸附等温线模型，如表2所示，进一步明确化学老化对微塑料吸附有机污染物的影响，为生态环境风险评估提供理论依据.
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微塑料对水体中HOCs具有较强的吸附能力[85 − 88]. 研究表明老化过程将影响微塑料对HOCs的吸附能力，如持久性有机污染物[89]、芳香族化合物[80]和农药[90-91]等. 原始微塑料对HOCs的吸附主要通过疏水相互作用和π—π相互作用，而老化微塑料形成的含氧官能团易与周围水分子形成氢键，减少其表面可利用吸附位点，降低了对HOCs的吸附能力. 首先，化学老化后微塑料表面产生含氧基团，O/C和亲水性增加，将抑制对HOCs的吸附[92]. Munoz等[42]发现原始PS在4种微塑料中对双氯芬酸（DCF）吸附量最高，而芬顿老化后微塑料对DCF的吸附量大幅下降，微塑料老化后表面产生大量酸性含氧基团导致亲水性增加. 研究表明微塑料表面的酸性氧团会减少对HOCs的吸附[93]，DCF具有疏水性，从而引起了污染物和水分子之间的竞争效应，极大抑制了DCF的有效吸附. Wu等[57]发现热活化过硫酸盐老化的iPP微塑料表面暴露出更多可用吸附位点,表面产生更多含氧官能团使其亲水性增加，增强对疏水有机物三氯生（TCS）的吸附能力, 吸附速率常数从0.21 min−1增加到 0.44 min−1. 例如紫外照射H2O2老化PS吸附21种芳香族化合物，发现与原始微塑料相比老化微塑料吸附系数显著降低（P<0.05），老化PS表面的含氧官能团与周围的水分子形成氢键，使HOCs难以取代被吸附的水分子，降低了PS表面吸附位点的可利用性，进而导致PS的吸附系数降低，从而降低对其吸附能力[80]. 其次，π-π相互作用是含有苯环的微塑料和芳香族化合物之间的主要作用机制[94]. 老化过程中聚合物链的断裂使骨架中苯环的含量降低，可能会削弱π-π相互作用[13, 95- 96]. 例如PS经光-芬顿老化后会降低微塑料的疏水性，导致苯环分子脱落，含有苯环的有机分子释放到水相中，导致π-π相互作用削弱，从而降低对药物的吸附能力[19- 20]. 例如PS经光-H2O2老化后表面产生极性含氧基团，导致亲水性增加，与BPA之间π-π相互作用和疏水相互作用削弱，从而对BPA的吸附能力下降[81]. 因此，化学老化微塑料疏水相互作用和π-π相互作用削弱，从而降低对水体中疏水性污染物的吸附能力.
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微塑料主要通过氢键和静电相互作用吸附亲水性有机污染物（如抗生素类氨氯地平[19]、环丙沙星[40]和三氯生[57]）. 微塑料化学老化后一些化学键被氧化生成含氧官能团（如羧基、羰基和羟基），使其极性、亲水性和电负性增强，并与有机物分子之间形成氢键，从而提高对亲水性有机污染物的吸附能力[97]. Munoz等[42]发现与原始微塑料相比，芬顿老化后微塑料对亲水性污染物甲硝唑 （MNZ）的吸附能力增加. MNZ由于极性较强，易与微塑料表面酸性含氧基团相互作用，增强吸附能力. Kong等[44]采用热活化过硫酸盐老化PLA、PET和PP微塑料吸附磺胺甲恶唑（SMX），发现与原始微塑料相比，老化微塑料对SMX的吸附容量呈增加趋势，且4种微塑料对SMX吸附能力分别提高了64.6%、187.8%和198%. Guo等[77]发现经热活化过硫酸盐老化后，聚对苯二甲酸丁二醇酯（PBAT）对四环素（TC）的吸附能力提高，老化后PBAT对污染物的吸附容量从
0.7980 mg·g−1 增加到1.2669 mg·g−1. Liu等[40]比较两种老化微塑料方式（芬顿和热活化过硫酸盐）对亲水性环丙沙星（CIP）的吸附性能，发现热活化过硫酸盐老化后吸附效果更好，老化后微塑料有效吸附位点增多，表面含氧基团的增加促使微塑料和CIP分子之间形成氢键，从而提高吸附容量. Song等[84]通过吸附动力学模型结果表明，与原始微塑料相比，老化微塑料对腐殖酸（HA）吸附能力更高，且由于PA极性比PP更强，经 H2O2老化后对HA吸附量更高. 另一方面，化学老化后微塑料表面电荷增加，静电相互作用在微塑料和带电污染物之间的吸附过程中可能起到关键作用[47]. Munoz等[42]认为带负电荷的MNZ和带正电荷的微塑料之间的静电相互作用增强了微塑料对MNZ的吸附能力. Liu等[19]发现，在光芬顿作用下，PS释放的大量衍生中间体通过与其之间的静电相互作用显著影响对阿托伐他汀 （ATV） 和氨氯地平 （AML）的吸附性能. 结果表明PS衍生中间体显著降低了PS对 ATV的吸附能力，但增加了对AML的吸附能力，PS经化学老化后释放的中间体增加了微塑料表面电负性，从而增强 PS 对带正电荷的 AML 的静电吸引和对带负电荷的 ATV 的静电排斥. 因此，化学老化微塑料表面含氧官能团增加导致极性、亲水性和电负性增强，与有机物分子间氢键和静电相互作用增强，提高了对亲水性有机物吸附能力. 总之，化学老化微塑料吸附有机污染物能力取决于不同吸附机制的贡献程度，随着老化程度的增加，静电相互作用和氢键在化学老化微塑料对有机污染物的吸附中起到关键作用，而疏水相互作用和π-π相互作用随着老化过程而被削弱.吸附过程包括物理吸附和化学吸附过程. 常用吸附动力学和等温吸附模型模拟化学老化微塑料吸附有机污染物过程. 例如原始微塑料对污染物吸附符合伪一级动力学模型，而伪二级动力学模型对化学老化微塑料吸附有机污染物拟合效果较好，说明该过程以化学吸附为主[40, 77]. 原始微塑料对污染物的吸附遵循Langmuir模型，吸附为单层吸附，活性位点分布均匀；而 Freundich模型化学对老化微塑料吸附过程拟合效果更好，说明该过程为多相多层的不均匀吸附[44].
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环境介质如离子强度（盐度）、pH和HA等都会对化学老化微塑料吸附有机物行为产生影响. 溶液的离子强度通过静电相互作用对微塑料吸附有机物能力产生影响. Wu等[57]发现随着Na+和Ca2+离子浓度的增加，老化PP微塑料对TCS的吸附能力提高. 环境中pH也会影响微塑料对有机物的吸附作用. pH不仅对微塑料表面官能团质子化程度产生影响，同时影响有机物在溶液中的存在形式. Kong等[44]认为，老化微塑料对SMX的吸附速率随pH的提高而降低. 微塑料表面发生去质子化具有电负性，SMX在碱性溶液中以阴离子形式存在，加剧了它们的静电排斥作用，抑制了微塑料对SMX的吸附. 水体中含有大量天然有机质（NOM），NOM污染会导致微塑料表面吸附位点堵塞，抑制微塑料对有机物的吸附能力. Munoz等[42]发现HA覆盖在微塑料表面占据吸附位点，显著降低微塑料对DCF吸附能力.
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环境中微塑料可经过光照、化学物质、生物膜和机械磨损等因素而老化，化学老化指微塑料与氧化剂反应产生活性氧引发的自由基链式反应. AOPs由于氧化性强常用于化学老化微塑料，包括芬顿、H2O2、热活化过硫酸盐、臭氧以及光复合老化等. 化学老化导致微塑料表面理化性质显著改变，进而影响其吸附有机污染物的能力. 微塑料化学老化后表面粗糙度增加，出现孔隙和裂纹，粒径减小，比表面积增大，有效吸附位点增多；同时老化微塑料表面含氧官能团增加，使其疏水性降低、电负性和极性增强，从而使疏水相互作用、π-π 相互作用削弱，静电相互作用和氢键等作用机制增强，从而改变微塑料吸附有机污染物的能力. 本文综述了微塑料化学老化的理化性质及常用方法，结合吸附动力学和等温吸附模型，梳理了老化微塑料吸附疏水性有机污染物和亲水性有机污染物的研究现状. 针对环境中微塑料化学老化的复杂性及对吸附行为的影响，本文对今后拟开展的重点工作提出了以下建议.
1）自然老化过程具有复杂性和缓慢性，实验室化学老化可以模拟和加速微塑料的自然老化过程. 化学老化操作条件简单，通过人为控制老化条件获得不同程度老化微塑料. 然而该方法技术过于简单只能模拟环境中单一老化过程，氧化剂用量多，应开发更多高效、友好的实验室技术模拟自然老化过程，可考虑多种老化过程结合，如将化学氧化和光照射结合，缩短老化周期，减少人力成本，提高老化效率. 从而减少实验室模拟与自然环境之间的差距，增加环境相关性.
2）有必要定量研究微塑料老化程度与微塑料吸附行为的潜在关系，明确老化微塑料理化性质变化对吸附污染物行为的影响，建立微塑料种类-老化程度（粒径和O/C）-吸附性能（平衡吸附量）的关系曲线与预测模型，结合吸附动力学和等温吸附模型进一步探讨微塑料的结构特性、老化程度对有机污染物的吸附贡献度，探究影响老化微塑料吸附行为的影响因素，实现微塑料环境行为的风险预测和评估.
3）还需要加强多种微塑料/有机污染物混合体系吸附行为的理论研究. 环境中有机污染物往往不是以单一形式存在，自然界中微塑料与多种有机污染物共存的情况时有发生，与环境污染物的结合可能会进一步增加老化微塑料的环境风险，因此需要加强微塑料与有机污染物的复合体系在环境中的吸附行为，对于阐明微塑料与有机污染物共存体系下的吸附行为和作用机制有重大意义.
4）探索环境介质（离子强度、温度、pH、HA浓度及生物膜等）与微塑料的协同老化，到目前为止，这些环境因素对老化微塑料的影响过程和作用机制还没有广泛研究，今后应在实验室中将这些因素与其他模拟老化过程一起进行类比研究.
微塑料的化学老化过程及吸附有机污染物的研究进展
Research progress on chemical aging microplastics and the adsorption of organic pollutants
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摘要: 微塑料的环境行为和生态影响如今备受瞩目，环境中微塑料受光照、化学物质、机械力和生物等因素而老化，影响其环境行为和归趋. 化学老化可以产生具有强氧化能力的活性氧引起自由基链式反应，导致微塑料物理化学性质发生显著改变，进而影响其对污染物的吸附性能. 高级氧化过程是常见的化学老化方法，用于模拟和加速微塑料的自然老化. 此外，微塑料作为载体吸附环境中的有机污染物是近年来研究的热点. 本文阐述了化学老化过程中微塑料的表面形貌、粒径、含氧官能团和亲疏水性等物理化学性质的变化，总结了微塑料化学老化的方法（例如芬顿、过氧化氢、过硫酸盐、臭氧和光复合老化）及机制；同时综述了化学老化微塑料吸附疏水性有机污染物和亲水性有机污染物的研究现状，并结合吸附动力学和吸附热力学模型，进一步明确化学老化对微塑料吸附有机污染物的影响. 最后，基于此对微塑料化学老化存在的问题和后续研究方向提供了展望.Abstract: The environmental behavior and ecological impact of microplastics have been in the spotlight nowadays. Microplastics are subject to aging by sunlight, chemical substances, mechanical forces, and biofilm, which affect their environmental behaviors and fate in the environment. Chemical aging can generate reactive oxygen species with strong oxidative capacity, which induces free radical chain reactions, resulting in significant changes in the physicochemical properties of microplastics, thereby affecting the absorption performance towards pollutants by microplastics. Advanced oxidation processes are common chemical aging methods used to simulate and accelerate the natural aging of microplastics. Additionally, the adsorption of organic pollutants in the environment by microplastics as carriers has been a hot research topic in recent years. This paper elaborates the variations of physicochemical properties, including surface morphology, particle size, oxygen-containing functional groups, hydrophilicity and hydrophobicity on microplastics chemical aging. We also summarize the methods and mechanisms of chemical aging microplastics (e.g., Fenton, hydrogen peroxide, persulfate, ozone, and combined technologies based on light irradiation and AOPs). Meanwhile, the current research status on the adsorption of hydrophobic organic pollutants and hydrophilic organic pollutants by chemical aging microplastics are reviewed, combined with adsorption kinetics and adsorption thermodynamics models to further clarify the effects of chemical aging on the adsorption of organic pollutants by microplastics. Finally, the existing problems and potential research directions about microplastics chemical aging in the future are proposed.
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Key words:
- microplastics /
- chemical aging /
- adsorption /
- organic pollutants /
- research status.
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表 1 微塑料的化学老化
Table 1. Various chemical aging process of MPs
化学老化方式
Chemical aging
Process微塑料类型
Type
of MPs时间
Time老化程度
Aging degree参考文献
Reference羰基指数
Carbon index氧碳比
O/C芬顿 PS 7 d C—O, H—O, C=O和O—C=O键形成 [38] PE,
PS30 d 0.01—0.4
0.03—0.200.01—0.13
0.01—0.1[40] PE,PP,
PS,PA,
PET1 d 0.006—0.0
0.001—0.02
0.003—0.013
0.64—0.47
7.34—7.36[54] H2O2 PS 7 d C—O, C=O和O—C=O键形成 [38] PVC 30 d C—O, C=O和H—C—Cl键形成 [51] 热活化过硫酸盐 PE,
PS30 d 0.01—0.36
0.03—0.690.01—0.26
0.01—0.34[40] PP 40 d 0.02—0.09 [57] 臭氧 PS < 1 d
（3 h）22.8—1.6 [18] LDPE 3 h 0.004—0.10 [55] 光-芬顿 PS 4.5 d 0.03—0.32 0.01—0.12 [19] PS 5 d 0.03—0.27 0.01—0.11 [20] 光- H2O2 PS 4 d 0.36—0.61 [81] PA 90 d 0.43—0.60 [82] 光活化过硫酸盐 PS 8 d 0.40—0.65 [43] 
下载: 导出CSV
表 2 化学老化微塑料吸附有机污染物的动力学和等温线模型研究
Table 2. Studies on kinetics and isotherm models in the adsorption of organic pollutants on chemical aging MPs
老化方式
Aging process微塑料类型
Type of MPs污染物
Pollutants最佳拟合模型
Best fit model参考文献
Reference动力学模型
Kinetic models等温线模型
Isotherm
models芬顿 PS，PET，
PP，HDPE双氯芬酸
甲硝唑伪二级模型 Langmuir模型 [42] PE，PS 环丙沙星 伪二级模型 Langmuir模型 [40] H2O2 PA，PP 腐殖酸 伪二级模型 Freundichm模型 [84] PS，PET 四环素 伪二级模型 Freundichm模型 [48] 热活化过硫酸盐 iPP 三氯生 伪一级模型 Freundichm模型 [57] PE，PS 四环素 伪二级模型 Freundichm模型 [77] 光-芬顿 PS 托伐他汀
氨氯地平伪二级模型 Langmuir模型
Freundichm模型[19] PS 牛血清蛋白 伪一级模型 Freundichm模型 [20] 光- H2O2 PS 双酚A 伪二级模型 Freundichm模型 [81] PS 芳香化合物 伪二级模型 Freundichm模型 [80]
下载: 导出CSV
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