Wen Qiong, Liu Na, Qu Ruohua, Ge Fei
College of Environment and Resources, Xiangtan University, Xiangtan 411105, China.
College of Environment and Resources, Xiangtan University, Xiangtan 411105, China; Hunan Provincial University Key Laboratory for Environmental Behavior and Control Principle of New Pollutants, Xiangtan 411105, China.
Sci Total Environ. 2023 Nov 25;901:165741. doi: 10.1016/j.scitotenv.2023.165741. Epub 2023 Jul 22.
The photoaging of microplastics (MPs) accumulated in the sea can be influenced by humic acid (HA). However, the role of salinity cannot be ignored, as it may potentially disrupt the interaction between MPs and HA, thereby altering the photoaging of MPs. Herein, this study investigated how salinity influences the effect of humic acid (HA, derived from lignite) on the photoaging of polystyrene microplastics (PS MPs) in artificial and natural seawater. The results revealed that HA promoted the photoaging of PS MPs under both low (5 PSU) and high salinity (35 PSU) in light conditions (L), reflected in the formation of fragments, the production of oxygen-containing functional groups (OH, CO, and OCO), and the increase in hydrophilicity of PS MPs. Furthermore, high salinity promoted the photoaging of PS MPs with HA more significantly, as evidenced by the similar indicators and the order of oxygen/carbon atom ratio (O/C): L-HA-High (0.15) > L-HA-Low (0.10) > Unaged (0.02). Interestingly, due to the reduction of electrostatic repulsion, the adsorption of HA on photoaged PS MPs in natural and artificial high salinity seawater was 1.77 mg/g and 0.39 mg/g, respectively, which was significantly higher than those PS MPs photoaged in the low salinity seawater. Furthermore, the electron spin resonance (ESR) results confirmed that more hydroxyl radicals (OH) were generated after adsorbing HA under high salinity conditions, thus promoting the fragmentation and oxidation of PS MPs. Overall, our findings highlight the crucial role of salinity in influencing the photoaging of MPs with HA and help to assess the marine risk of MPs accurately.
海洋中积累的微塑料（MPs）的光老化会受到腐殖酸（HA）的影响。然而，盐度的作用也不容忽视，因为它可能会破坏MPs与HA之间的相互作用，从而改变MPs的光老化过程。在此，本研究调查了盐度如何影响腐殖酸（源自褐煤的HA）对人工海水和天然海水中聚苯乙烯微塑料（PS MPs）光老化的影响。结果表明，在光照条件下（L），HA在低盐度（5 PSU）和高盐度（35 PSU）条件下均促进了PS MPs的光老化，表现为碎片的形成、含氧官能团（OH、CO和OCO）的产生以及PS MPs亲水性的增加。此外，高盐度更显著地促进了HA存在下PS MPs的光老化，氧/碳原子比（O/C）的类似指标及顺序证明了这一点：L-HA-High（0.15）> L-HA-Low（0.10）>未老化（0.02）。有趣的是，由于静电排斥的减少，在天然和人工高盐度海水中，HA在光老化PS MPs上的吸附量分别为1.77 mg/g和0.39 mg/g，显著高于在低盐度海水中光老化的PS MPs。此外，电子自旋共振（ESR）结果证实，在高盐度条件下吸附HA后会产生更多的羟基自由基（OH），从而促进PS MPs的碎片化和氧化。总体而言，我们的研究结果突出了盐度在影响MPs与HA光老化过程中的关键作用，并有助于准确评估MPs的海洋风险。
