When "biodegradable" is not benign: Microplastic-driven disruption of soil processes and plant-microbe interactions

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• Biodegradable plastics (BPs) are increasingly used, leading to the accumulation of biodegradable microplastics (BMPs) in terrestrial ecosystems.
• Contrary to expectations, BMPs can persist in soil and interact with crucial biological processes.
• Existing research shows inconsistencies in BMP effects, highlighting the need for a comprehensive understanding.

Purpose of the Study:

• To propose a mechanistic framework linking BMP aging, degradation, soil properties, and biological interactions.
• To critically evaluate factors causing variability in BMP impact studies.
• To advance the understanding of BMPs' ecological risks in soil environments.

Main Methods:

• Literature review and synthesis of existing studies on BMPs in soil.
• Development of a framework integrating polymer chemistry, aging, soil physics, and rhizosphere dynamics.
• Analysis of factors influencing BMP persistence, microbial community shifts, and plant responses.

Main Results:

• BMP effects are determined by polymer chemistry, additive composition, aging, soil properties, and rhizosphere processes.
• BMPs alter soil structure, nutrient cycling, enzyme activity, and microbial community composition and function.
• BMPs can act as niches for microbial biofilms, potentially facilitating pollutant and pathogen transport.

Conclusions:

• BMPs pose ecological risks in soils, and biodegradability does not equate to safety.
• Plant responses to BMPs are primarily indirect, mediated by rhizosphere changes, explaining response variability.
• Future research requires integrated, long-term studies considering aged BMPs and complex plant-soil interactions.