Microplastic abundance in sludge-treated fields: Variance and estimated half-life

Area of Science:

• Environmental Science
• Soil Science
• Polymer Science

Background:

• Agricultural soils can accumulate microplastics (MPs) through sludge application.
• Long-term sludge fertilization poses risks of persistent MP contamination.

Purpose of the Study:

• To quantify microplastic abundance and mass in agricultural soil after long-term sludge application.
• To assess the impact of sampling strategy on MP concentration measurements.
• To estimate the environmental persistence and degradation rates of microplastics in soil.

Main Methods:

• Analysis of microplastic counts and mass in soil samples from three long-term sludge-fertilized fields.
• Application of Monte Carlo simulations to determine optimal soil sampling strategies.
• Estimation of microplastic half-life based on counts and mass over time.

Main Results:

• Microplastic concentrations ranged from 2392 to 48,791 counts kg⁻¹.
• Polyester and acrylic comprised over 50% of the identified microplastics.
• Monte Carlo simulations indicated a high risk of outliers with fewer than ten subsamples.
• Estimated microplastic half-life was approximately 2.5 years for counts and 4 years for mass.

Conclusions:

• Long-term sludge application leads to significant microplastic accumulation in agricultural soils.
• Adequate soil sampling (≥10 subsamples) is crucial for reliable microplastic quantification.
• Microplastics exhibit varying degradation or migration rates, with smaller particles disappearing faster.