AEESP Spotlight: Early 2025

The “spotlight” column draws attention to selected articles in Environmental Engineering Science (EES), the official journal of the Association of Environmental Engineering and Science Professors (AEESP). Spotlight articles appear three times per year in the journal as well as in the AEESP newsletter. Through the publication of high-quality peer-reviewed research, the EES journal helps AEESP achieve its mission of developing and disseminating knowledge in environmental engineering and science. In this entry, we shine the spotlight on selected articles from the August through November 2024 issues of EES. Congratulations to those whose work is highlighted.

A recent special issue of EES dealt with microplastics. Leading the issue was Salehi et al., 2024, who critically evaluated the status of microplastics research and outlined various environmental phenomena promoted by microplastic interactions with the environment. The ubiquitous presence of microplastics in all environmental compartments has emerged as an environmental challenge in recent decades. Large quantities of microplastics are being released into the environment where they undergo numerous transformations through various degradation processes, often releasing byproducts of adverse health concerns and toxic effects. To develop effective strategies for microplastics management, a deeper knowledge of the inherent chemical and physical characteristics and their interaction with the environment is required. The authors identified critical knowledge gaps in understanding the links between the intrinsic properties of microplastics and their environmental fate and human exposure. Molecular and structural characteristics of the polymer influence their degradation rates. Degradation may take place through physicochemical, photochemical, and biodegradation routes. The nature and kinetics of degradation depend on the various chemical bonds, physical properties including molecular weights, and environmental factors. Most of the reviewed research reported environmental degradation of pure plastic materials; however, additives are often used to improve the functional properties and performance of various plastic products, which add to the increased complexity of their degradation kinetics. More research is required in the additive arena. Increased efforts to understand the physicochemical degradation and its impacts on the diversity, composition, and abundance of microbial communities during biodegradation of microplastics are recommended. Similarly, studies focusing on understanding the linkage between intrinsic microplastic properties and mechanical degradation provide new insights into further reaction pathways. Finally, long-term effects of degradation byproducts on the environment are critical for assessing their ecological and health risks and informing policy and technological interventions.

One of the papers in the special issue discussed microplastics, abundant in aquatic systems, being covered in natural organic matter (NOM), often called eco-coronas (McColley and Nason, 2024). The eco-corona coating can alter the fate and effects of microplastics in water bodies, but the mechanism of eco-corona formation is poorly understood. In addition, UV radiation from the sun can photooxidize microplastics in water, potentially changing how they interact with eco-coronas. McColley and Nason, 2024, aimed to shed light on the mechanisms underlying the formation of eco-coronas on pristine and UV-photooxidized microplastics. They used polystyrene and polyvinyl chloride (PVC) as model microplastics; and selected Suwannee River humic acid (SRHA) and bovine serum albumin (BSA) as NOM. The plastics were spin-coated onto the sensor of a quartz crystal microbalance with dissipation apparatus, which was then used to measure the shifts in frequency and dissipation upon depositing the two types of NOM. While BSA’s affinity for polystyrene microplastics increased after photooxidation, photooxidation decreased the affinity of BSA for PVC, showing a clear impact of microplastic polymer on the affinity of eco-coronas. In addition, while photooxidation did not have much impact on the affinity of SRHA for polystyrene, it decreased its affinity for PVC. The interactions were mediated by electrostatic attractions, hydrophobic interactions, hydrogen bonding, and divalent cation bridging.

Another special issue article discussed a novel, greener chemical for drinking water treatment, with a focus on microplastic removal (Panigrahi et al., 2024). Chemical coagulants and flocculants used for water treatment have high economic and environmental costs. In addition, the efficacy of currently used coagulants and flocculants for removing microplastics from drinking water depends on their physicochemical properties. Several greener alternative coagulants have been proposed for water treatment. Seeds from Moringa oleifera, a fast-growing tropical plant, contain cationic proteins (Moringa oleifera cationic protein or MOCP) that have been successfully used for coagulation in water treatment. Compared with conventional chemical coagulants such as alum, MOPC is more accessible and has less environmental impact. Panigrahi et al., 2024, investigated the efficacy of MOCP for removing pristine and photooxidized polyethylene microplastics from water. They used MOCP either as a suspension (for coagulation) or by immobilizing it on sand for flocculation. Using a series of carefully planned jar tests performed with microplastics dispersed in distilled water, they found that MOCP is a viable alternative to alum. However, sand-immobilized MOPC was less effective in incorporating microplastics into flocs compared with polyacrylamide, a widely used flocculant. When the tests were repeated with the microplastics dispersed in Mississippi River water instead of distilled water, MOCP was less effective than alum. Overall, the authors concluded that charge neutralization was an important mechanism for microplastic removal by MOPC, and the natural coagulants were promising for mitigating microplastic pollutants in aquatic environments.

Aside from those microplastic-focused entries, the final article we spotlight here deals with soil microbiology after wildfires (Patrick et al., 2024). The devastation of a wildfire leaves obvious signs in the form of charred trees, scorched vegetation, and perhaps burned-out homes. However, some effects are subtler and harder to study than those obvious signs. Patrick et al., 2024, evaluated what happens just below the subsurface among microbial communities inhabiting the soil. They took samples a year after the Woolsey Fire in the Santa Monica Mountains National Recreation Area in California, which burned 95,000 acres from November 2018 to January 2019. They saw that 6 families and 17 genera of microbes were reduced in abundance when wildfire severity increased. Interestingly, 3 families and 6 genera increased with wildfire severity, perhaps because they filled niches left by the declination of others. Gene abundance and expression data also indicated that high-severity wildfires negatively impact nitrogen-cycling bacteria, and this persisted a year after the fire. This study paves a path toward understanding microbial community dynamics during ecosystem recovery. As this summary is being written (January 9, 2025), new fires are blazing in California, making this research further relevant.