Microplastic Contamination in Agricultural Soils: Impacts on soil properties and plant performance

The continuous use of plastics in agriculture has led to the accumulation of microplastics (MPs) in soils. However, the extent of MP contamination and its impacts on soil properties and plant growth remain poorly understood. Soils are complex matrices that interact with MPs, presenting three significant challenges. First, accurately quantifying MPs is difficult due to their uneven distribution and interference from soil components. Second, MPs can alter soil physical, chemical, and biological properties, which may compromise soil health and function. Third, the effects of MPs on plant growth and physiology are highly variable and not well characterized. This research aimed to address these three major gaps: the absence of reliable quantification methods for MPs in agricultural soils, the limited understanding of their effects on soil chemical properties, and the lack of knowledge on their impacts on plant growth. Existing MP quantification methods for solid matrices were reviewed and compared to identify or develop an optimal approach for agricultural soils. A method based on Total Organic Carbon–Solid Sample Combustion Unit (TOC-SSM) was developed for quantifying polyethylene (PE) MPs. This method successfully quantified field-relevant concentrations of PE-MPs in strawberry farm soils during a case study. Using these relevant concentrations and different particle sizes, soil microcosm experiments were conducted to examine the chemical responses of soil properties to MP contamination. The results showed a notable reduction in cation exchange capacity (CEC) and a negative priming effect in dissolved organic matter (DOM), indicating potential disruptions in soil nutrient availability and cycling. Additionally, phthalate acid esters (PAEs) were detected, suggesting toxic leachates originating from MPs. Glasshouse experiments further revealed species-dependent responses to MP-contaminated soils, highlighting varying sensitivities among crops. These findings demonstrate that MPs can alter soil chemistry and affect plant health. Despite increasing evidence of such impacts, there are currently no effective mitigation strategies or regulatory policies for MPs in soils. This study highlights the urgent need for improved monitoring and informed policy development to address MP pollution in agricultural environments.