Microplastics in wastewater treatment plants and their contributions to surface water and farmland pollution in China.

Wastewater treatment plants (WWTPs) are usually considered gateways for microplastics (MPs) to enter the environment because large amounts of sewage are produced and MPs are incompletely removed during treatment processes. However, the contribution of effluent MPs to aquatic environmental pollution and that of sludge application to MPs in agricultural soil are still unknown. This study examines the presence of MPs in sewage and sludge in Shenzhen WWTPs and estimates the annual mass loading of MPs from WWTPs to surface water and farmland soil in China. According to our results, for Shenzhen, the annual contribution of MPs from WWTPs (which was obtained by multiplying the annual treated sewage volume by the estimated MP density in the treated sewage) to surface water could be 70.6-302 tons. With a normalized extrapolation model of population density, the contribution of national urban WWTPs to MPs in surface water was estimated to be 734 -3.10 × 103 tons/year, of which 220-950 tons/year entered the marine environment. Furthermore, the riverine flux of MPs from WWTPs to the ocean amounts to at least 7.0%-30% based on the maximum value of WWTP contribution to MPs in surface water. For sludge, the potential contribution of MPs to agricultural soil from Shenzhen WWTPs is (1.00-2.80) × 103 tons/year. With the above calculation procedure, it was estimated that the contribution of MPs to farmland from sludge application in China is (1.30-3.90) × 104 tons/year. The source appointment results for MPs in China's agricultural soil suggested that the contributions of the main four sources, namely, atmospheric deposition, agricultural mulch film, sludge application, and organic fertilizers, are 52%, 30%, 11%, and 7.0%, respectively.

Biodeterioration of Microplastics by Bacteria Isolated from Mangrove Sediment.

As a kind of ubiquitous emerging pollutant, microplastics (MPs) are persistent in the environment and have a large impact on the ecosystem. Fortunately, some microorganisms in the natural environment can degrade these persistent MPs without creating secondary pollution. In this study, 11 different MPs were selected as carbon sources to screen the microorganisms for degradable MPs and explore the possible mechanism of degradation. After repeated domestication, a relatively stable microbial community was obtained after approximately 30 days later. At this time, the biomass of the medium ranged from 88 to 699 mg/L. The growth of bacteria with different MPs ranged from 0.030 to 0.090 optical density (OD) 600 of the first generation to 0.009-0.081 OD 600 of the third generation. The weight loss method was used to determine the biodegradation ratios of different MPs. The mass losses of polyhydroxybutyrate (PHB), polyethylene (PE), and polyhydroxyalkanoate (PHA) were relatively large, at 13.4%, 13.0%, and 12.7%, respectively; these figures for polyvinyl chloride (PVC) and polystyrene (PS) were relatively slight, 8.90% and 9.10%, respectively. The degradation half-life (t1/2) of 11 kinds of MPs ranges from 67 to 116 days. Among the mixed strains, Pseudomonas sp., Pandoraea sp., and Dyella sp. grew well. The possible degradation mechanism is that such microbial aggregates can adhere to the surface of MPs and form complex biofilms, secrete extracellular and intracellular enzymes, etc., break the hydrolyzable chemical bonds or ends of molecular chains by attacking the plastic molecular chains, and produce monomers, dimers, and other oligomers, leading to the reduction of the molecular weight of the plastic itself.

Effects of microplastic sorption on microbial degradation of halogenated polycyclic aromatic hydrocarbons in water.

Halogenated PAHs (HPAHs) are ubiquitous in the environment and have a toxicity similar to that of dioxin. Microplastics exist widely in the environment, and their sorption allows them to act as carriers of HPAHs, potentially changing the bioavailability of HPAHs. However, to the best of our knowledge related studies are limited. In this study, degrading bacteria of five HPAHs were cultivated from mangrove sediments. Among them, the Hyphomicrobium genus has good degradation ability on 9-BrAnt, 2-BrPhe and 2-ClPhe. The degradation process is in line with the first-order degradation kinetic characteristics. The kinetic equations of five kinds of HPAHs showed that the degradation half-lives are 0.65 days (2-BrFle), 0.79 days (9-ClPhe), 1.50 days (2-ClAnt), 5.94 days (9-BrPhe) and 14.1 days (9-BrAnt). The greater the number of benzene rings and the heavier the halogen substituents, the slower the degradation of HPAHs. The sorption of microplastics inhibited the biodegradation of HPAHs, and the degradation half-life of HPAHs will be extended from 0.65 to 14.1 days (the average is 4.59 days) to 1.71-9.93 days (average 5.40 days) for PA, 0.70-35.2 days (average 12.8 days) for PE, 6.02-28.2 (average 15.7 days) days for POM, and 4.60-24.0 (average 19.2 days) days for PP, which is mainly related to the partition coefficient between microplastics and water. This study provides a reference for reducing the uncertainty of the ecological risk assessment of HOCs in the aquatic environment.

A method for measuring the emissions of in situ agricultural plastic film microplastics by ultraviolet and mechanical abrasion.

Agricultural plastic film (APF) is widely used in modern agriculture. Under natural environmental conditions, the structure, surface properties and mechanical properties of APFs change because of sunlight, wind and other factors and gradually break into debris, resulting in the generation of microplastics (MPs). Studies have reported that the MPs concentration in soil is positively correlated with the use intensity and duration of APFs. Unfortunately, to the best of our knowledge, no method to measure the emissions of in situ APFs has been developed. In this study, the effects of mechanical abrasion driven by wind on MPs fragmentation by polyethylene (PE) and polyvinyl chloride (PVC) APFs with the increase of exposure time were investigated. Meanwhile, based on the release rate model of PS fragmented MPs under natural sunlight, a modified model to quantify the effect of ultraviolet (UV) radiation exposure duration on the production of APF fragmented MPs was developed. Based on these models, the amount of MPs produced from APFs in farmland in China was estimated. The national annual MPs mass emissions from APFs in agricultural soil were approximately 5 × 104 to 6.8 × 104 tons in 2018 due to wind and 6.5 × 103 tons due to sunlight, and the total emission level due to both wind and sunlight was 5.1 × 104 to 7.0 × 104 tons. Compared with that of wind, the contribution of UV radiation to MPs emission is smaller. Our estimates are comparable to data reported in previous studies, indicating that our models have good practical applications and are of great significance for predicting MPs production from APFs in farmland.

Contribution of mulch film to microplastics in agricultural soil and surface water in China.

Agricultural mulch film (AMF) is deemed an important source of microplastics (MPs) in agricultural soil (AS). However, quantitating the contribution of AMFs to MPs in farmland soil and surface water remains a considerable challenge to date. In the present study, a basic framework was developed to address these concerns. First, the concentrations of MPs in soil derived from AMF abrasion (CMP) and the total MPs from all sources in AS (CTMP) were measured. Then, the ratios of CMP to CTMP, i.e., the contribution of AMFs to MPs in AS, were calculated. The contribution of AMFs to MPs in surface water via soil erosion was calculated based on CTMP values, the ratios of CMP to CTMP, soil erosion intensities (SEIs), and farmland areas. Furthermore, the potential contribution of soil erosion to MPs in the ocean was estimated. In China, the inventory of MPs in surface AS in 2018 ranged from 4.9 × 106 to 1.0 × 107 tons according to our results. AMFs contributed 10%-30% of the CTMP with certainties of 60-95%. Assuming that all MPs in AS can be exhaustively transferred to surface water via soil erosion, the national mass transfer amount of MPs (MTTMP) from AS to surface water reached 1.2 × 105-2.2 × 105 tons (∼2% of the inventory of MPs in the AS of China); the fluxes of MPs into the ocean from AS were 3.4 × 104-6.6 × 104 tons, assuming that all MPs in the AS of coastal provinces enter the ocean. It is likely that AMFs contributed 10%-30% MTTMP and fluxes of MPs to the ocean according to the ratios of CMP to CTMP. Apparently, approximately 30% of the national MTTMP (i.e., the rate of MP flux to the ocean to MTTMP) was input to the ocean.

Incidence of microplastics in personal care products: An appreciable part of plastic pollution.

Microplastic had been commonly used in personal care products (PCPs) until it was documented to be a pollutant. The relative contents of microplastics in PCPs decrease in the order of the USA, Europe, and Asia. The geometric means of the abundance and mass of microplastics found in PCPs were 2162 particles/g and 0.04 g/g, respectively. Diameters of PCP-derived microplastics are less than 350 µm. To quantify the exact contribution of PCPs to microplastic pollution, this review surveyed the existing scientific literature and statistically integrated the findings from 88 literatures. Overall, approximately 1500 tons/year of microplastics from PCPs escape from WWTPs and enter the global aquatic environment. According to the PCP consumption and microplastics levels, the mass emission of global PCP-derived microplastics reach up to 1.2 × 104 tons/year. The two figures account for ~0.1% and ~ 0.8% of the annual global release of primary microplastics in the world oceans (~1.5 × 106 tons/year). In the last 50 years (1970-2019), up to 3.00 × 105 tons of PCP-derived microplastics have accumulated in the environment. The main plastic in PCPs is polyethylene, which is known for being a remarkably resistant polymer to degradation. Even if microbeads are completely banned globally in 2020, microplastics that have been discharged into the environment will still persist for a long time and claim our highest attention. This review provided primary information to deal effectively with the problem of PCP-derived microplastic both now and in the future.

A minimalist approach to quantify emission factor of microplastic by mechanical abrasion.

Plastic film has allowed manufacturers to meet varied marketplace demands. Typically, its usage can be divided into two general categories-packaging (food, nonfood and other) and nonpackaging. The microplastics emission resulting from wearing of plastic film is unavoidable in the process of production and use. Currently, no reliable method exists for measure emission factor (EF) of microplastics by mechanical abrasion (MA). In the present study, a simple but effective approach to quantify EF of microplastic by MA was developed. Specifically, the relative light transmittance (RLT) of the plastic film is decreased with increase of MA degree. This quantitative relationship between the two factors can be applied to determine EFs of microplastics induced by MA. The method developed in this study is easy and feasible, but it still has limitations in the standpoint and range, the direction of worthiness of theory.

Effects of soybean oligosaccharides on antioxidant enzyme activities and insulin resistance in pregnant women with gestational diabetes mellitus.

The effects of soybean oligosaccharides (SBOS) on antioxidant enzyme activities and insulin resistance in pregnant women with gestational diabetes mellitus (GDM) were investigated. Ninety-seven pregnant women with GDM were randomly divided into two groups, the control group (51 cases) and the SBOS group (46 cases). Before the group separation, the blood sugar level in patients was maintained stable by regular diet and insulin treatment. The control group was continued with the insulin treatment, while the SBOS group was treated with the combination of insulin and SBOS. Results showed that SBOS were able to reduce oxidative stress and alleviate insulin resistance in pregnant women with GDM, which indicates that SBOS may play an important role in the control of GDM complications.