Microplastics deplete soil available nutrients: a global meta-analysis with machine learning reveals critical thresholds and interactive controls

Summary

This global meta-analysis of 206 studies synthesised evidence on microplastics effects on soil nutrient bioavailability across diverse agricultural systems, integrating random-effects meta-analysis with machine learning to identify non-linear relationships and threshold effects. Microplastics significantly depleted available nitrogen, phosphorus, and potassium across controlled experiments, though field studies showed no significant effects. Critical thresholds emerged: particle size effects plateaued above 100 μm, concentration impacts saturated beyond 10 g kg⁻¹, and soil pH determined whether depletion or enrichment occurred, with biodegradable plastics causing nutrient immobilization comparable to or exceeding conventional polymers.

Regional applicability

The study is geographically concentrated in East Asia (92% of data), with predominantly controlled laboratory and pot experiments (99% of observations), limiting direct applicability to United Kingdom field conditions. Findings on soil pH-dependent responses and microplastics concentration thresholds may inform UK soil protection policy, but field validation across temperate agricultural systems would be needed to establish realistic risk profiles for practical UK farming contexts.

Key measures

Log response ratios (ln RR) for soil available nitrogen, phosphorus, and potassium; XGBoost model R² values (0.44–0.62); relative importance scores; particle size thresholds; soil pH effects; microplastics concentration impacts

Outcomes reported

The study quantified the effects of microplastics on soil available nitrogen (5.3% depletion), phosphorus (9.4% depletion), and potassium (7.0% depletion) across 206 studies, and identified context-dependent responses and critical threshold effects using machine learning.

Topic tags