Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang, 110044, PR China.
Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang, 110044, PR China.
Environ Pollut. 2020 Jul;262:114270. doi: 10.1016/j.envpol.2020.114270. Epub 2020 Feb 25.
Current understanding on the fate and behavior of microplastics (MPs) in complex soil media remains inadequate. We characterized the aging and hetero-aggregation of a MP sampled in farmland soil, and explored its vertical downward transport in natural loamy sand. The MP was identified with FTIR spectrum as polypropylene, a plastic lighter than water. FTIR spectrum combined with SEM imaging confirmed the MP was highly aged, generating colloidal plastic fibers and carbonyl groups. SEM imaging coupled with EDX analysis suggested hetero-aggregation of the MP with soil minerals. Soil leaching tests performed with the clean MP (without soil minerals) (CMP), the raw MP (RMP) (with soil minerals), and the RMP with humic acid (HA) (RMP + HA) demonstrated that the mobility was insignificant for the CMP, moderate for the RMP and highest for the RMP + HA, resulting in a maximal downward traveling distance of 0 cm, 3-4 cm, and 9-10 cm, respectively. Correlation between the maximal traveling distance and zeta potential of the CMP, RMP, and RMP + HA confirmed surface charge as a dominant control on the MP mobility; while the increasing density of the MP, due to hetero-aggregation with soil minerals, was identified as a driving mechanism for its downward transport, despite its intrinsic density lower than water. Occurrence of only the lower-sized rod-shaped plastic fibers at the maximal traveling distance suggested the natural aging, a process leading to plastic vibration and fragmentation, was conducive to plastic translocation. The three explored classes of antibiotic resistance genes (ARGs) (tetracycline, beta-lactam and sulfonamide) were all detected in the plastic surface, suggesting the MP may function as a potential pathway for the dissemination of ARGs to the deeper soil layer. These findings are important to understand the concentration distribution of both the MPs and ARGs in agriculture impacted soils, a natural reservoir of both emerging contaminants.
目前，人们对微塑料（MPs）在复杂土壤介质中的归宿和行为的认识还不够充分。本研究以农田土壤中采集的 MP 为研究对象，对其老化和异质聚集行为进行了表征，并探索了其在天然壤土中的垂直向下迁移。傅里叶变换红外光谱（FTIR）分析表明，该 MP 为聚丙烯，一种比水轻的塑料；SEM 成像结合 FTIR 光谱分析证实，该 MP 高度老化，生成胶体状塑料纤维和羰基；SEM 成像结合能谱（EDX）分析表明，MP 与土壤矿物质发生了异质聚集。对纯净 MP（无土壤矿物质）（CMP）、原始 MP（含土壤矿物质）（RMP）和含腐殖酸的 RMP（RMP+HA）进行土壤淋洗实验的结果表明，CMP 的迁移性可以忽略不计，RMP 的迁移性中等，而 RMP+HA 的迁移性最强，导致最大向下迁移距离分别为 0cm、3-4cm 和 9-10cm。CMP、RMP 和 RMP+HA 的最大迁移距离与zeta 电位之间的相关性证实，表面电荷是控制 MP 迁移性的主要因素；而由于与土壤矿物质的异质聚集，MP 的密度增加被认为是其向下迁移的驱动力，尽管其固有密度低于水。在最大迁移距离处仅发现较低尺寸的棒状塑料纤维的存在，这表明自然老化过程导致塑料振动和破碎，有利于塑料的转移。在所研究的三种抗生素抗性基因（ARGs）（四环素、β-内酰胺和磺胺类）中，都在塑料表面检测到了这些基因，这表明 MP 可能成为 ARGs 向深层土壤层传播的潜在途径。这些发现对于理解农业土壤中 MPs 和 ARGs 的浓度分布具有重要意义，因为农业土壤是新兴污染物的天然储存库。
