Constructed wetlands as neglected fixed source of microplastics and antibiotic resistance genes in natural water bodies?

Research advances of biodegradable microplastics in wastewater treatment plant: Current knowledge and future directions

Plastic and microplastic pollution in the environment has become a significant global concern. Biodegradable plastics (BPs), as environmentally friendly alternatives to conventional plastics, have also emerged as a crucial topic of global discussion. The successful application of BPs appears to offer a solution to the potential ecological risks posed by conventional plastics. However, BPs have negative impacts on the ecological environment and human health. BPs can gradually degrade into biodegradable microplastics (BMPs) in the environment. Wastewater treatment plants (WWTPs) have become an undeniable source and sink of microplastics. With the production and application of BPs, BMPs will inevitably enter WWTPs. This paper reviews the pollution status, degradation behavior of BMPs, and their potential impact on wastewater treatment performance. The focus is on the environmental behavior of BMPs in wastewater treatment systems. The influences of BMPs on microbial communities, sludge treatment, and disposal are thoroughly discussed. The results indicate that BMPs are more easily decomposed into micro/nanoplastics and release additives compared to conventional microplastics. The effects of BMPs on microbial communities and wastewater treatment depend on their characteristics. The numerous oxygen-containing functional groups on the surface of BMPs enable them to serve a dual purpose as transport media and potential sources of environmental pollutants. Finally, in light of existing knowledge gaps, suggestions and prospects for future research on BMPs are proposed.

Livestock and poultry breeding farms as a fixed and underestimated source of antibiotic resistance genes

The excessive use of antibiotics, disinfectants, and drugs in livestock and poultry breeding has resulted in a rise in the presence of antibiotic resistance genes (ARGs). Antibiotic-resistant bacteria (ARB) and ARGs have been widely found in animal feces, farm wastewater, and farm air. ARGs can not only spread across media through adsorption and migration, but also transfer resistance across bacterial genera through horizontal gene transfer. Livestock breeding has become a fixed and unavoidable source of ARGs in the environment. Existing technologies for controlling ARGs, such as composting, disinfection, and sewage treatment, are not efficient in removing ARB and ARGs from waste. Furthermore, the remaining ARGs still possess a strong capacity for dissemination. At present, antibiotics used in animal husbandry are difficult to replace in a short period of time. The growth and potential risks of resistance genes in livestock and poultry breeding sources in the receiving environment are not yet clear. In this paper, we summarize the current situation of ARGs in the livestock and poultry breeding environment. We also explain the key environmental processes, main influencing factors, and corresponding ecological risks associated with ARGs in this environment. The advantages and disadvantages of current technologies for the removal of ARGs are primarily discussed. There is a particular emphasis on clarifying the spatiotemporal evolution patterns and environmental process mechanisms of ARGs, as well as highlighting the importance and urgency of developing efficient pollution control technologies.

Research advances on the toxicity of biodegradable plastics derived micro/nanoplastics in the environment: A review

The detrimental effects of plastic and microplastic accumulation on ecosystems are widely recognized and indisputable. The emergence of biodegradable plastics (BPs) offers a practical solution to plastic pollution. Problematically, however, not all BPs can be fully degraded in the environment. On the contrary, the scientific community has demonstrated that BPs are more likely than conventional plastics (CPs) to degrade into micro/nanoplastics and release additives, which can have similar or even worse effects than microplastics. However, there is very limited information available on the environmental toxicity assessment of BMPs. The absence of a toxicity evaluation system and the uncertainty regarding combined toxicity with other pollutants also impede the environmental toxicity assessment of BMPs. Currently, research is focused on thoroughly exploring the toxic effects of biodegradable microplastics (BMPs). This paper reviews the pollution status of BMPs in the environment, the degradation behavior of BPs and the influencing factors. This paper comprehensively summarizes the ecotoxicological effects of BPs on ecosystems, considering animals, plants, and microorganisms in various environments such as water bodies, soil, and sediment. The focus is on distinguishing between BMPs and conventional microplastics (CMPs). In addition, the combined toxic effects of BMPs and other pollutants are also being investigated. The findings suggest that BMPs may have different or more severe impacts on ecosystems. The rougher and more intricate surface of BMPs increases the likelihood of causing mechanical damage to organisms and breaking down into smaller plastic particles, releasing additives that lead to a series of cascading negative effects on related organisms and ecosystems. In the case of knowledge gaps, future research is also proposed and anticipated to investigate the toxic effects of BMPs and their evaluation.

Is the application of organic fertilizers becoming an undeniable source of microplastics and resistance genes in agricultural systems?

The application of organic fertilizers is becoming an undeniable source of microplastics and antibiotic resistance genes (ARGs) in agricultural soils. The complex microbial activity further transfers resistance genes and their host bacteria to agricultural products and throughout the entire food chain. Therefore, the current main focus is on reducing the abundance of microplastics and ARGs in organic fertilizers at the source, as well as managing microplastics and ARGs in soil. The control of microplastic abundance in organic fertilizers is currently only achieved through pre-composting selection and other methods. However, there are still many shortcomings in the research on the distribution characteristics, propagation and diffusion mechanisms, and control technologies of ARGs, and some key scientific issues still need to be urgently addressed. The high-temperature composting of organic waste can effectively reduce the abundance of ARGs in organic fertilizers to a certain extent. However, it is also important to consider the spread of ARGs in residual antibiotic-resistant bacteria (ARB). This article systematically explores the pathways and interactions of microplastics and resistance genes entering agricultural soils through the application of organic fertilizers. The removal of microplastics and ARGs from organic fertilizers was discussed in detail. Based on the limitations of existing research, further investigation in this area is expected to provide valuable insights for the development and practical implementation of technologies aimed at reducing soil microplastics and resistance genes.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.