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Non-biodegradable microplastics (MPs) pollution long-termly existed in soils, and was only concerned in recent years. In order to better understand MP behavior in soils, the sources, migration, distribution, biological effects, degradation and analytical methodology of non-biodegradable MPs in soils were quantificationally summarized from 170 publications based on Web of Science in 1950–2020. From the publications, we found these studies were mainly carried out in the Asia (60.0%) and Europe (23.3%), and most were on agricultural soils (68.5%). Polyethylene-MP (78.8% of the studies), Polypropylene-MP (78.8%), and Polystyrene-MP (45.5%) were the MPs most frequently found in the soils, with a MP size of 20–5000 µm being most common. Of the soil samples 64.3% contained MP 1000–4000 items kg-1, and the colour frequency ranking is blue (66.7%) > white (61.1%) ≈ red ≈ black. MPs changed the soil microenvironment and microorganism activity, and caused the negative effects on both soil animals (100%) and plants (57.9%). MP degradation was influenced by the photooxidation reactions, microorganism activities, enzymatic effects, environmental conditions, and by the composition, size and morphology of the MPs. An optional analytical method was suggested in this study. At the end of paper, the urgent and important research work in the future was prospected. ga1 • PE-MP, PP-MP, PS-MP with blue, white, red, black were most frequently found in soils. • MPs of 1000–4000 items kg−1 at size of 20–5000 µm took of 50% of soil samples. • MPs caused the negative effects on both soil animals (100%) and plants (57.9%). • An optional analytical method of soil MPs was suggested in this study. • Future prospects and challenging for follow up research have been discussed. [ABSTRACT FROM AUTHOR]

Highlights • A new EK remediation technology was developed. • MCD and citric acid enhanced the formation of MCD- and citrate-metals complexes. • Compared with MCD, citric acid better facilitated the migration of Cu in soil. Abstract This work investigated the influences of citric acid and methyl-β-cyclodextrin (MCD) as enhancing agents during the electrokinetics (EK)-persulfate process on the remediation of soil artificially contaminated with decabromodiphenyl ether (BDE-209) and copper (Cu) with an initial concentration of 50 and 1000 mg/kg, respectively. The results clearly demonstrate the efficiency of the process while at the same time, the distribution of the residual contaminants in soil and the EK parameters were greatly influenced by the presence of persulfate, MCD and citric acid. The results show that there was significant removal of BDE-209 and Cu from the soil. MCD-assisted process gave the highest BDE-209 removal (88.6%) and the third largest Cu removal (54.3%) from the soil. Comparatively, the highest Cu removal (92.5%) and the second largest BDE-209 removal (85.6%) were achieved by the joint application of MCD and citric acid in anolyte during the EK-persulfate treatment. MCD and citric acid could increase soil electrical current and electroosmotic flow during EK. The alkalization of soil near cathode was alleviated by the acidic byproducts of persulfate decomposition which could be transported to the soil by electroosmosis and electromigration. This integration process may provide a green efficient technology for remediating co-contaminated soil. [ABSTRACT FROM AUTHOR]

A 2-year greenhouse study was conducted to remediate an actual wastewater-irrigated soil co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cd and Zn). The remediation methods included microbial remediation, phytoremediation, and microbe-assisted phytoremediation. The maximum PAH removal (96.4%), PAH mineralization, and metal phytoextraction (36.1% Cd and 12.7% Zn) were obtained by interplanting ryegrass with Seduce alfredii with regular re-inoculation with Microbacterium sp. KL5 and Candida tropicalis C10 in the co-contaminated soil. The plants shoots were harvested at a 4-month interval. After 2 years, the concentrations of 16 individual PAHs were reduced to below the limit of Chinese soil quality standard for agricultural use (grade II, pH 6.5–7.5), and the metal concentrations in ryegrass shoots were below the Chinese national limit for animal feeds (GB13078-2001). The exogenous microbes gradually disappeared with time, and thus a 2-month re-inoculation interval was applied for a purpose to maintain high cell density and activity of the inoculants. KL5 introduction increased soil enzyme activity, plant growth, PAH removal and metal phytoextraction, while C10 promoted soil enzyme activity and removal of high-molecular-weight PAHs. Interplanting with S. alfredii reduced metal concentrations in ryegrass tissues. Ryegrass showed stronger rhizosphere effects than S. alfredii did. [ABSTRACT FROM AUTHOR]