How do controlled-release fertilizer coated microplastics dynamically affect Cd availability by regulating Fe species...

Area of Science:

• Environmental Science
• Soil Science
• Ecotoxicology

Background:

• Microplastics (MPs) influence soil environments and heavy metal accumulation.
• Limited research exists on the dynamic effects of MPs on heavy metal bioavailability in soil.
• The synergistic impact of controlled-release fertilizer coated MPs on heavy metal states, soil properties, and microbial communities is understudied.

Purpose of the Study:

• To investigate the dynamic effects of polyurethane (PU) MPs on the available state of soil cadmium (Cd).
• To analyze the influence of PU MP particle size and concentration on Cd bioavailability and soil properties.
• To understand the role of soil physicochemical properties and microbial communities in mediating MP-Cd interactions.

Main Methods:

• In situ study using diffusive gradient in thin-films (DGT) to measure effective Cd concentration (DGT-Cd).
• Analysis of soil chemical properties including pH, dissolved organic carbon (DOC), zeta potential, Fe(II), and Mn(II).
• Correlation and path analysis to link soil properties, microbial community structure, and Cd availability.

Main Results:

• PU MP addition, particularly at high concentrations (≥1%), significantly increased DGT-Cd.
• PU MPs altered soil properties: decreased pH and DOC, increased absolute zeta value, Fe(II), and Mn(II) in a dose- and time-dependent manner.
• Fe(II) content and DOC were identified as key factors controlling Cd activation, with significant correlations between soil properties, heavy metal availability, and microbial community composition.

Conclusions:

• PU MP concentration and particle size critically influence Cd bioavailability and soil properties.
• PU MPs indirectly affect Cd activity by altering soil physicochemical properties and microbial communities involved in C and Fe cycling.
• Enhanced ecological risk assessment and management are crucial for combined pollution of controlled-release fertilizer coated MPs and heavy metals in agricultural soils, especially when MP concentrations exceed 1%.