Soil's complex challenge: micro/nanoplastics exhibit dual impact on terrestrial microbiomes
Research emphasizes the intricate balance of harm and potential support, calling for a refined understanding of environmental risk assessment
image: Micro/nanoplastics contamination of the terrestrial environment: exposure routes, dose, and co-contaminants complicate the risk calculus
Credit: Xiaoli Zhao, Xiaowei Wu & Jason C. White
Micro/Nanoplastics Reshape Terrestrial Ecosystems
Microplastics and nanoplastics are pervasive in terrestrial environments, influencing the delicate balance of soil ecosystems. A recent perspective article in Carbon Research, authored by Xiaoli Zhao, Xiaowei Wu, Zhi Tang, and Fengchang Wu from the State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, and Jason C. White from The Connecticut Agricultural Experiment Station, addresses the complex nature of these contaminants. The paper explores how the diverse array of plastic types, varied exposure doses, and the presence of co-contaminants significantly complicate the assessment of their impact on soil microbiomes.
Unpacking the Adverse Effects on Microbes
For many terrestrial microorganisms, micro and nanoplastics pose a considerable threat. The paper details how exposure can inhibit reproduction and development, as seen in bacterial and fungal communities. Nanoplastics, due to their smaller size, can enter cells and disrupt mitochondrial metabolism, leading to oxidative stress and cell apoptosis. Microplastics, larger in size, can damage microbial cell membranes directly. These interactions can lead to increased reactive oxygen species production, causing intracellular oxidative stress and inflammatory responses.
The Role of Co-Contaminants
A significant factor contributing to the complexity of risk assessment is the presence of co-contaminants. Plastics frequently contain various toxic additives and can sorb other hazardous substances from the environment, such as arsenic, lead, or perfluoroalkyl sulfonate PFAS. These co-existing contaminants can dramatically alter the overall toxicity profile of the plastics. The interaction of plastics and these associated pollutants can activate intracellular signaling pathways, potentially causing metabolic dysregulation, reduced cell viability, and even cell death in microorganisms.
Unexpected Benefits and Microbial Adaptations
Surprisingly, plastics can also offer certain advantages to some components of the terrestrial microbiome. As complex carbon-based materials, their rough surfaces and carbon-rich structures can provide a physical substrate for microbial colonization, forming a unique "plastisphere." Certain bacteria, including Pseudomonas, Flavobacteriaceae, and Bacillus, can even mediate plastic biodegradation, utilizing the plastics as a carbon and energy source. This process can involve biofilm formation, enzyme secretion for degradation, and subsequent conversion of plastic components into CO₂ and H2O.
Dynamic Shifts in Microbial Communities
The interaction between plastics and soil microorganisms is dynamic. While some microbial populations may be inhibited by plastics, others can simultaneously increase. This phenomenon is often not due to direct benefits from the plastics, but rather because sensitive species decline, freeing up resources and reducing competition. Such shifts can influence predator species, nutrient cycling, and redox conditions, fundamentally altering the basic microbial community structure in ways that are currently not fully understood.
A Call for Comprehensive Research
The authors emphasize the urgent need for more comprehensive research to unravel these intricate dynamics. Future studies should focus on understanding short- and long-term dose-response relationships for both prokaryotic and eukaryotic soil microbiomes. Investigations must also consider the combined impact of plastics with their additives and co-contaminants under environmentally relevant concentrations. Microcosm studies that assess 'omic' parameters over extended periods are essential to fully grasp the long-term consequences of plastics on soil microbiome function.
Corresponding Author:
Xiaoli Zhao
Original Source:
https://doi.org/10.1007/s44246-023-00059-z
Contributions:
Xiaoli Zhao: Writing original draft, Funding acquisition, Supervision, Writing—review & editing; Xiaowei Wu: Writing original draft, Visualization, Writing review & editing. Jason C. White: Investigation, Writing—review & editing.Fengchang Wu: Investigation, Writing—review & editing.