Feasibility Study on the Application of Biodegradable Plastic Film in Farmland Soil in Southern Xinjiang, China-Planting Tomatoes as an Example

In recent years, polybutylene adipate-co-terephthalate (PBAT) mulch film has become one of the most commonly used biodegradable mulch films in agriculture in an attempt to combat plastic film pollution. However, its degradation characteristics and impact on the soil environment and crop growth are affected by many factors such as its composition, soil and crop types, local climate characteristics, etc. In this study, PBAT mulch film and ordinary polyethylene (PE) film were used as test materials, with non-mulching treatment (CK) as a control, to study the applicability of PBAT film in Moyu County, Southern Xinjiang region, using tomato growth as an example. The results showed that PBAT film started its induction period after 60 days, and 60.98% of the PBAT film was degraded within 100 days. Generally, the soil temperature and humidity preservation functions of this film were comparable to that of PE film in the seedling and flowering-fruiting stages of tomato growth. In the mature stage, the soil humidity under PBAT film was significantly lower than that of PE film due to its substantial degradation rate. However, this did not have any significant negative effects on tomato growth, yield, and quality. The tomato yield of 667 m² with BPAT was insignificantly lower than that of PE film by 3.14%, and both were significantly higher than that of the CK treatment by 63.38% and 68.68%, respectively, indicating that it is feasible to use PBAT film to cultivate crops such as tomato in the arid region of Southern Xinjiang, China.

Spectral Characteristics of Dissolved Organic Matter in Farmland Soils around Urumqi, China

The dissolved organic matter (DOM) is one of the most sensitive indicators of changes in the soil environment, and it is the most mobile and active soil component that serves as an easily available source of nutrients and energy for microbes and other living organisms. In this paper, DOM structural characteristics and main properties were investigated by three-dimensional fluorescence spectroscopy (EEM) and UV-visible spectrum technology in the farmland soils around Urumqi of China, and its possible sources and pathways were analyzed by spectroscopic indices. The results showed that humic-like substances were the main composition of the soil DOM, and its autogenesis characteristics were not obvious. Main DOM properties such as aromatability, hydrophobicity, molecular weight, molecular size, and humification degree in the southern region of Urumqi were higher than those of the northern region of Urumqi and Fukang in China, and higher on the upper layers of the soil (0-0.1 and 0.2 m) than in the deeper layer (0.2-0.3 m).This may be because the tilled layer is more subjected to fertilization and conducive to microbial activities. The spectroscopic analysis showed that the source of DOM of these regions is mainly from microbial metabolites. These results provide basic scientific data for the further research on the environmental chemical behavior of pollutants and pollution control in this region.

Distinct soil microplastic distributions under various farmland-use types around Urumqi, China

Very little is known about the occurrence of microplastics in the soils of various land uses, especially their distributional characteristics in the soils of arid areas. In this study, 24 sampling sites across three soil layers were investigated for three different farmland-use types (greenhouses, crop fields and vegetable fields) in the main agricultural and pastoral areas around Urumqi, China. The results demonstrated that the dominant sizes of soil microplastics were 0.2-0.5 and 0.5-1.0 mm, the main shape was film (85.93 %), the main color was white, and the main polymer was polyethylene (93.1 %), indicating that most microplastics derive from the damage to residual mulches. The microplastics abundance was highest in the greenhouse plots (7763 ± 2773 items/kg), followed by the vegetable plots (4128 ± 2235 items/kg) and then the crop fields (3178 ± 3172 items/kg). No significant differences were observed among the abundances of microplastics in the 0-10 cm (1822 ± 1345 items/kg), 10-20 cm (1566 ± 1139 items/kg) and 20-30 cm (1309 ± 1028 items/kg) layers, suggesting that microplastics can migrate to the deeper soil layer and are strongly influenced by tillage disturbance. The abundance of microplastics in the north of Urumqi was found to be higher than in the south, which is closely related to the division of agricultural functional zones and the intensity of agricultural management practices. It was found that different cropping characteristics and modes of agricultural use affect the abundance and migration of microplastics in various farmland-use types, and thus their distribution. This study provides important data for follow-up research on microplastics in arid terrestrial ecosystems, and corresponding policy-making on the management of these materials.

Isolation and Degradation Characteristics of PBAT Film Degrading Bacteria

In recent years, PBAT (polybutylene adipate-co-terephthalate) mulch has become one of the most commonly used biodegradable mulching films. In this paper, five potential strains of PBAT film degrading bacteria were screened from the soil sample using PBAT film as the sole carbon source. A highly efficient PBAT degrading strain JZ1 was isolated by comparing the degradation performance of PBAT mulching film identified as Peribacillus frigoritolerans S2313 by 16S rDNA sequence analysis. The capacity of the strain to degrade PBAT film was optimized by adjusting the cultivation conditions such as nitrogen source, pH, and inoculum volume. After 8 weeks of cultivation, the actual degradation rate of the strain to PBAT mulch film reached 12.45%. SEM (scanning electron microscopy) coupled with EDX (energy dispersive spectroscopy) analysis showed that microbial degradation is an oxidation process and is mainly due to the amorphous regions of the PBAT film. The biodegradation of PBAT film by Peribacillus frigoritolerans may provide a promising method for regulating the degradation progress of PBAT film in the farmlands.

The Binding Ability of Mercury (Hg) to Photosystem I and II Explained the Difference in Its Toxicity on the Two Photosystems of Chlorella pyrenoidosa

Mercury (Hg) poses high toxicity to organisms including algae. Studies showed that the growth and photosynthesis of green algae such as Chlorella are vulnerable to Hg stress. However, the differences between the activities and tolerance of photosystem I and II (PSI and PSII) of green microalgae under Hg exposure are still little known. Responses of quantum yields and electron transport rates (ETRs) of PSI and PSII of Chlorella pyrenoidosa to 0.05−1 mg/L Hg2+ were simultaneously measured for the first time by using the Dual-PAM-100 system. The photosystems were isolated to analyze the characteristics of toxicity of Hg during the binding process. The inhibition of Hg2+ on growth and photosystems was found. PSII was more seriously affected by Hg2+ than PSI. After Hg2+ exposure, the photochemical quantum yield of PSII [Y(II)] decreased with the increase in non-photochemical fluorescence quenching [Y(NO) and Y(NPQ)]. The toxic effects of Hg on the photochemical quantum yield and ETR in PSI were lower than those of PSII. The stimulation of cyclic electron yield (CEF) was essential for the stability and protection of PSI under Hg stress and played an important role in the induction of non-photochemical quenching (NPQ). The results showed a strong combination ability of Hg ions and photosystem particles. The number of the binding sites (n) of Hg on PSII was more than that of PSI, which may explain the different toxicity of Hg on PSII and PSI.

Characteristics and distribution of microplastics in shoreline sediments of the Yangtze River, main tributaries and lakes in China-From upper reaches to the estuary

Microplastics (MPs) pervade the environment and increasingly threaten both natural ecosystems and human health. In this study, we investigated MP particle concentrations in sediment samples collected from 54 sites along the banks of the Yangtze River and its major tributaries and on lakeshores. The main polymer types found in the samples were polypropylene (PP), polystyrene (PS) and polyethylene (PE). MP particle abundance in the various types of locations was 35-51,968 particles/kg dry weight (d.w.) on the banks of the main river, 52-1463 particles/kg (d.w.) on the banks of tributaries and 2574-23,685 particles/kg (d.w.) on lakeshores. Correlation between MP abundance and mean annual runoff of each upstream tributary was significant, which suggests that increased runoff brings more microplastic waste to streambank sediments. The most common shape of MP particles in all upstream samples was flake, and in downstream samples it was foam. Small microplastic particles (< 0.50 mm) were predominant at all sites in this study, and the minimum particle size in samples from the Yangtze river banks was 0.065 mm. Average abundance of MP particles on the shores of the source lake was 9069 particles/kg around the inlet but only 866 particles/kg around the outlet; the difference was due to interception associated with sedimentation and precipitation in the lake. Our study represents the large-scale study of MPs contamination in sediment along the Yangtze River and provides important data regarding the accumulation and distribution of MPs in shoreline sediments of the upper, middle and lower reaches of the Yangtze River, main tributaries and lakes in China.

Cadmium Caused Different Toxicity to Photosystem I and Photosystem II of Freshwater Unicellular Algae Chlorella pyrenoidosa (Chlorophyta)

Heavy metals such as Cd pose environmental problems and threats to a variety of organisms. The effects of cadmium (Cd) on the growth and activities of photosystem I (PSI) and photosystem II (PSII) of Chlorella pyrenoidosa were studied. The growth rate of cells treated with 25 and 100 µM of Cd for longer than 48 h were significantly lower than the control, accompanying with the inhibition of photosynthesis. The result of quantum yields and electron transport rates (ETRs) in PSI and PSII showed that Cd had a more serious inhibition on PSII than on PSI. Cd decreased the efficiency of PSII to use the energy under high light with increasing Cd concentration. In contrast, the quantum yield of PSI did not show a significant difference among different Cd treatments. The activation of cyclic electron flow (CEF) and the inhibition of linear electron flow (LEF) due to Cd treatment were observed. The photochemical quantum yield of PSI and the tolerance of ETR of PSI to Cd treatments were due to the activation of CEF around PSI. The activation of CEF also played an important role in induction of non-photochemical quenching (NPQ). The binding features of Cd ions and photosystem particles showed that Cd was easier to combine with PSII than PSI, which may explain the different toxicity of Cd on PSII and PSI.

Ecotoxicological Effects of Microplastics on Bird Embryo Development by Hatching without Eggshell

Microplastics are an emerging global pollutant type that poses a great health threat to animals due to their uptake and translocation in animal tissues and organs. Ecotoxicological effects of microplastics on the development of bird embryos are not known. The bird egg is a complete development and nutrition system, and the entire embryo development occurs in the eggshell. Therefore, a direct record of bird embryo development under the stress of pollutants such as microplastics is highly limited by the opaque eggshell in traditional hatching. In this study, the effects of microplastics on quail embryo development were visually monitored by hatching without an eggshell. The main steps include the cleaning and disinfection of fertilized eggs, the incubation before exposure, the short-term incubation after exposure, and the sample extraction. The results show that compared with the control group, the wet weight and body length of the microplastics-exposed group displayed a statistical difference and the liver proportion of the whole exposed group significantly increased. Additionally, we evaluated external factors that affect the incubation: temperature, humidity, egg rotation angle, and other conditions. This experimental method provides valuable information on the ecotoxicology of microplastics and a novel way to study the adverse effects of pollutants on the development of embryos.

Microplastics in agricultural soils: Extraction and characterization after different periods of polythene film mulching in an arid region

Plastic film mulching has been extensively used in farmland, especially in arid regions, for over half-century. However, this has led to heavy pollution of soils by microplastics (MPs). Currently, efficient extraction of MPs from the organo-mineral soil matrix is a problem because microsize clay particles tightly adhere to MPs. It is therefore extremely challenging to investigate, identify, quantify, and characterize MP particles and their behavior in agricultural soils. In this study, we developed a simple and effective method of separating and extracting MPs from the soil matrix. Clean polyethylene (PE) MPs were obtained after a series of treatments including pressure leaching, flotation, electrostatic adsorption, and concentrated sulfuric acid (98% H₂SO₄) carbonization. The characteristics of MP pollutants, such as abundance, size, and morphology, in soils that have been continuously mulched with PE film for various periods of time were determined after extraction. The highest abundance of MPs (40.35 mg/kg) with sizes ranging from 0.9-2.0 mm was found in soil samples that had been continuously mulched with plastic film for 30 years. The sampled MP particles are in the microplastic size (0.8-0.3 mm) range, and the size of MPs decreases gradually as the period of mulching increased. Scanning electron microscopy analysis showed that the surface of the MP particles showed visible cracks, with round holes, and the particle surface roughened as the number of years of continuous mulching increased. Fourier-transform infrared spectroscopy results showed that the absorption peak area of hydrocarbyl (-CH₂) of PE MPs decreased significantly, and the typical oxidation characteristic peak area increased as the mulching period increased. The concentration of mesoplastics also increased, from 91.20 mg/kg to 308.50 mg/kg, when the mulching period increased from 5 to 30 years.

A survey of uranium levels in urine and hair of people living in a coal mining area in Yili, Xinjiang, China

Recent reports have drawn attention to the uranium contamination arising from coal mining activities in the Yili region of Xinjiang, China due to the mixed distribution of uranium and coal mines, and some of the coal mines being associated with a high uranium content. In this study, we have collected water samples, solid samples such as soil, mud, coal, and coal ash, and hair and urine samples from local populations in order to evaluate the uranium level in this environment and its implications for humans in this high uranium coal mining area. Our results showed that uranium concentrations were 8.71-10.91 μg L^-1 in underground water, whereas lower levels of uranium occurred in river water. Among the solid samples, coal ash contained fairly high concentrations of uranium (33.1 μg g^-1) due to enrichment from coal burning. In addition, uranium levels in the other solid samples were around 2.8 μg g^-1 (the Earth's average background value). Uranium concentrations in hair and urine samples were 22.2-634.5 ng g^-1 (mean: 156.2 ng g^-1) and 8.44-761.6 ng L^-1 (mean: 202.6 ng L^-1), respectively, which are significantly higher than reference values reported for unexposed subjects in other areas. Therefore, these results indicate that people living in this coal mining area have been subjected to uranium exposure for long periods of time.

Uranium Bioreduction and Biomineralization

Following the development of nuclear science and technology, uranium contamination has been an ever increasing concern worldwide because of its potential for migration from the waste repositories and long-term contaminated environments. Physical and chemical techniques for uranium pollution are expensive and challenging. An alternative to these technologies is microbially mediated uranium bioremediation in contaminated water and soil environments due to its reduced cost and environmental friendliness. To date, four basic mechanisms of uranium bioremediation-uranium bioreduction, biosorption, biomineralization, and bioaccumulation-have been established, of which uranium bioreduction and biomineralization have been studied extensively. The objective of this review is to provide an understanding of recent developments in these two fields in relation to relevant microorganisms, mechanisms, influential factors, and obstacles.