Microplastics deplete soil available nutrients: a global meta-analysis with machine learning reveals critical...

Area of Science:

• Environmental Science
• Soil Science
• Ecotoxicology

Background:

• Microplastic (MP) contamination is a growing global concern impacting soil ecosystems.
• Understanding the quantitative effects of MPs on soil nutrient bioavailability is crucial but fragmented.
• Diverse agricultural systems and environmental contexts complicate the assessment of MP impacts.

Purpose of the Study:

• To quantitatively synthesize the impacts of MPs on soil available nitrogen (AN), phosphorus (AP), and potassium (AK).
• To identify key controlling factors and non-linear relationships governing MP effects on soil nutrients.
• To establish quantitative thresholds for risk assessment of MP contamination in soils.

Main Methods:

• Conducted a meta-analysis of 206 studies (2853 observations) across diverse agricultural systems and countries.
• Employed random-effects meta-analysis with log response ratios (lnRR).
• Integrated eXtreme Gradient Boosting (XGBoost) machine learning and SHapley Additive exPlanations (SHAP) for advanced analysis.

Main Results:

• Across all setups, MPs significantly depleted AN (5.3%), AP (9.4%), and AK (7.0%).
• Effects were context-dependent: significant depletion in pot/incubation studies, but not in field studies.
• Soil pH and MP concentration were identified as dominant factors, with critical thresholds for particle size and concentration.

Conclusions:

• MPs pose a significant threat to soil nutrient availability, particularly in controlled experimental settings.
• Quantitative thresholds and interactive effects highlight the complexity of MP impacts.
• Findings necessitate interventions to prevent soil fertility degradation, though field-scale validation is essential.