Leaching of organic matter from microplastics and its role in disinfection by-product formation

Natural organic matter (NOM) is the primary precursor of disinfection by-products (DBPs). However, as emerging environmental contaminants continue to increase in natural waters, there is a possibility of new precursors of DBPs. We investigated the potential of microplastics (MPs), a growing environmental concern, for leaching organic matter (OM) and subsequent DBP formation. Two experimental setups were used, including chlorinated water containing MPs (Cl2-MP), and non-chlorinated water containing MPs (Non-Cl2-MP), using polyethylene (PE), polyethylene tetrahydrate (PET), polypropylene (PP), and polyvinyl chloride (PVC) as MP materials. The UV absorbance spectra of Cl2-PET/PP/PVC showed peaks at 218 nm, which were significantly correlated with dissolved organic carbon (DOC), indicating lower aromaticity of the leached OM. The DOC concentrations in Cl2-MP samples were several times higher than those in Non-Cl2-MP samples. The leached OM from MPs formed trihalomethanes (THMs) and haloacetic acids (HAAs) in Cl2-MP samples. Among the MPs tested, PVC showed the highest total THM formation after 7 days, followed by PET, PE, and PP. Brominated THMs were predominant, while HAAs were highly chlorinated. THM formation increased with contact time for PE, PET, and PVC, and decreased for PP. Compared to THMs, the concentration of HAAs was low (highest total THM = 185.5 μg/L per g-MP and highest total HAA = 120.7 μg/L per g-MP). Further, the total THM concentration decreased and the total HAA concentration increased over the reaction period, indicating the leaching of different types of OM with increasing contact time. Additionally, the differences in the pattern of DOC leaching and DBP formation among different MPs suggested changes in the leached OM.

Treatment processes to eliminate potential environmental hazards and restore agronomic value of sewage sludge: A review

Land application of sewage sludge is increasingly used as an alternative to landfilling and incineration owing to a considerable content of carbon and essential plant nutrients in sewage sludge. However, the presence of chemical and biological contaminants in sewage sludge poses potential dangers; therefore, sewage sludge must be suitably treated before being applied to soils. The most common methods include anaerobic digestion, aerobic composting, lime stabilization, incineration, and pyrolysis. These methods aim at stabilizing sewage sludge, to eliminate its potential environmental pollution and restore its agronomic value. To achieve best results on land, a comprehensive understanding of the transformation of organic matter, nutrients, and contaminants during these sewage-sludge treatments is essential; however, this information is still lacking. This review aims to fill this knowledge gap by presenting various approaches to treat sewage sludge, transformation processes of some major nutrients and pollutants during treatment, and potential impacts on soils. Despite these treatments, overtime there are still some potential risks of land application of treated sewage sludge. Potentially toxic substances remain the main concern regarding the reuse of treated sewage sludge on land. Therefore, further treatment may be applied, and long-term field studies are warranted, to prevent possible adverse effects of treated sewage sludge on the ecosystem and human health and enable its land application.

Sources of Antibiotic Resistant Bacteria (ARB) and Antibiotic Resistance Genes (ARGs) in the Soil: A Review of the Spreading Mechanism and Human Health Risks

Soil is an essential part of our ecosystem and plays a crucial role as a nutrient source, provides habitat for plants and other organisms. Overuse of antibiotics has accelerated the development and dissemination of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). ARB and ARGs are recognized as emerging environmental contaminants causing soil pollution and serious risks to public health. ARB and ARGs are discharged into soils through several pathways. Application of manure in agriculture is one of the primary sources of ARB and ARGs dissemination in the soil. Different sources of contamination by ARB and ARGs were reviewed and analyzed as well as dissemination mechanisms in the soil. The effects of ARB and ARGs on soil bacterial community were evaluated. Furthermore, the impact of different sources of manure on soil microbial diversity as well as the effect of antibiotics on the development of ARB and ARGs in soils was analyzed. Human health risk assessments associated with the spreading of ARB and ARGs in soils were investigated. Finally, recommendations and mitigation strategies were proposed.