The programmed sequence-based oxygenase screening for polypropylene degradation.

Enzymatic degradation of plastic is an effective means of plastic recycling and pollution control. However, the strong chemical inertness of polypropylene plastic (PP) severely impedes its oxidative cleavage, making it resistant to degradation. In this study, based on sequence screening of Hidden Markov Model (HMM), a dioxygenase (HIS1) was identified and characterized to be effective in PP oxidation. Various kinds of PP products, including plastic films, microplastics, and disposable water cups or bags, were HIS1-degraded with cracks and holes on the surface. The hydrophobic binding was the primary force driving oxidative degradation in the specific cavity of HIS1. The discovery of HIS1 achieved a zero breakthrough in PP biodegradation, providing a promising candidate for the selection and evolution of degrading enzymes.

Urban Microplastic Pollution Revealed by a Large-Scale Wetland Soil Survey.

Microplastics (MPs), as a new persistent pollutant, can be emitted and accumulated in urban environments, but there is no detailed information on the driving factors of MP pollution. In this study, through a large-scale wetland soil survey, the features of MPs were characterized in each urban area. The results showed an average abundance to be 379 n/kg in wetland soil. Polypropylene, fiber or fragment, and black color were common composition, shape, and color, respectively. The spatial distribution information showed that MP abundance was significantly relevant to the distance from the urban economic center. Furthermore, the correlation and regression analysis revealed that MP abundance was related to soil heavy metal and atmospheric particle (PM10 and PM2.5) concentrations (P < 0.05), while the promotion of socioeconomic activities (urbanization level, population density, etc.) may aggravate the pollution degree. Additionally, by using structural equation modeling, it was found that the urbanization level was the dominant factor driving the MP pollution degree, with a total effect coefficient of 0.49. Overall, this work provides multi-sided environmental information regarding MP pollution in urban ecosystems, which is significant for follow-up studies of MP pollution control and restoration.

Time-dependent effects of microplastics on soil bacteriome.

Microplastic threats to biodiversity, health and ecological safety are adding to concern worldwide, but the real impacts on the functioning of organisms and ecosystems are obscure owing to their inert characteristics. Here we investigated the long-lasting ecological effects of six prevalent microplastic types: polyethylene (PE), polypropylene (PP), polyamide (PA), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) on soil bacteria at a 2 % (w/w) level. Due to the inertia and lack of available nitrogen of these microplastics, their effects on bacteriome tended to converge after one year and were strongly different from their short-term effects. The soil volumes around microplastics were very specific, in which the microplastic-adapted bacteria (e.g., some genera in Actinobacteria) were enriched but the phyla Bacteroidetes and Gemmatimonadetes declined, resulting in higher microbial nitrogen requirements and reduced organic carbon mineralization. The reshaped bacteriome was specialized in the genetic potential of xenobiotic and lipid metabolism as well as related oxidation, esterification, and hydrolysis processes, but excessive oxidative damage resulted in severe weakness in community genetic information processing. According to model predictions, microplastic effects are indirectly derived from nutrients and oxidative stress, and the effects on bacterial functions are stronger than on structure, posing a heavy risk to soil ecosystems.

Combined toxicity of zinc oxide nanoparticles and cadmium inducing root damage in Phytolacca americana L.

In recent years, nano-contamination in the soil environment has aroused concern. But it is still uncertain whether the interactions of nano- and metal-pollutants would have a combined toxic effect on plants. In this study, we investigated the effects of joint exposure to zinc oxide nanoparticles (ZnO NPs) and Cd on the root tissue of Phytolacca americana L. Spin-polarized density functional theory simulations assumed that the plant may undergo metal toxicity or acidosis upon joint exposure to ZnO NPs/Cd. Subsequently, experimental exposure of P. americana verified the combined toxic effects. The plant grew normally with a single treatment of ZnO NPs (500 mg/kg) or low doses of Cd (10 mg/kg). However, root growth was significantly inhibited with the combined treatments (up to 43% reduction); additionally, Cd ions were transported to the shoot, leading to shoot growth inhibition (translocation factor > 1). The antioxidant enzymes in the root (superoxide dismutase, peroxidase, and catalase) were highly activated to resist stress, accompanied by a greater than two-fold increase in thiobarbituric acid reactive substances. Corresponding to physiological indicators, biological transmission electron microscopy revealed severe damage to the root cells. Moreover, ZnO NPs/Cd accumulation was observed in the root cytoderm, which confirmed the toxicity of the combined effects. Our study provides insight into the potential combined toxicity of ZnO NPs and heavy metals in polluted environments, such as mining areas and electronic waste sites, and agricultural soils.

Net global warming potential and greenhouse gas intensity as affected by different water management strategies in Chinese double rice-cropping systems.

This study provides a complete account of global warming potential (GWP) and greenhouse gas intensity (GHGI) in relation to a long-term water management experiment in Chinese double-rice cropping systems. The three strategies of water management comprised continuous (year-round) flooding (CF), flooding during the rice season but with drainage during the midseason and harvest time (F-D-F), and irrigation only for flooding during transplanting and the tillering stage (F-RF). The CH4 and N2O fluxes were measured with the static chamber method. Soil organic carbon (SOC) sequestration rates were estimated based on the changes in the carbon stocks during 1998-2014. Longer periods of soil flooding led to increased CH4 emissions, reduced N2O emissions, and enhanced SOC sequestration. The net GWPs were 22,497, 8,895, and 1,646 kg CO2-equivalent ha-1 yr-1 for the CF, F-D-F, and F-RF, respectively. The annual rice grain yields were comparable between the F-D-F and CF, but were reduced significantly (by 13%) in the F-RF. The GHGIs were 2.07, 0.87, and 0.18 kg CO2-equivalent kg-1 grain yr-1 for the CF, F-D-F, and F-RF, respectively. These results suggest that F-D-F could be used to maintain the grain yields and simultaneously mitigate the climatic impact of double rice-cropping systems.