Plastic films widely used in agricultural production are becoming one of the main sources of microplastic pollution in soil. These plastic fragments remaining in the soil can not only disrupt soil structure and affect water permeability but may also enter the food chain through plant absorption, threatening soil health and food security. To address this issue, oxo-degradable plastics (ODPs) have been introduced as a "more sustainable alternative" to traditional plastics. These plastics theoretically undergo oxidative degradation through the addition of pro-oxidants, breaking down under conditions of light and heat, and are then biodegraded by microorganisms into carbon dioxide and water. However, what is their actual degradation efficiency? Will they negatively impact crop growth and soil quality in the soil environment?
Recently, a team led by Professor Davey L. Jones from Bangor University conducted a study that systematically revealed the effects of oxo-degradable plastics of different sizes and concentrations on soil and corn growth, providing important evidence to address these concerns. The study has been published in Frontiers of Agricultural Science and Engineering ( DOI: 10.15302/J-FASE-2025623 ).
Unlike previous studies that mainly focused on traditional plastics or single-size plastics, this research is unique in its "dual-dimensional comparison": it compares the differences between microplastics and macroplastics while covering a range from actual field concentrations to extreme concentrations. The research team selected corn as a model crop and monitored key indicators such as soil pH, electrical conductivity, and nitrate content over a 6-week experimental period. They analyzed plant growth, chlorophyll content, and nutrient absorption, and tracked the degradation process of the plastics using infrared spectroscopy.
The experimental results yielded several key findings. Firstly, at low concentrations commonly found in actual fields, oxo-degradable plastics had almost no impact on soil quality and corn growth. However, when concentrations exceeded 1%, significant changes in soil properties were observed—soil pH in the microplastic treatment group increased by nearly 1 unit, electrical conductivity doubled, and nitrate content significantly increased, while the impact of macroplastics was much weaker. This may be related to the larger surface area of microplastics, which allows for more extensive contact with soil, thereby altering soil structure and chemical environment more easily.
Secondly, the effects of microplastics on plants were more pronounced. High concentrations of both microplastics and macroplastics led to a decrease in corn height and chlorophyll content, but the inhibitory effect of microplastics was more evident. Nonetheless, corn biomass only slightly decreased at the highest concentration, indicating a certain level of tolerance. Notably, corn root biomass in the microplastic treatment group was higher at low concentrations, possibly due to increased soil nitrate promoting root growth.
Furthermore, the study revealed the "degradation limitations" of oxo-degradable plastics. Infrared spectroscopy analysis showed that 6 weeks of soil burial only resulted in mild chain scission of the plastics, with no significant production of oxidation products such as ketones or aldehydes detected. This suggests that in the absence of light in the soil environment, the degradation process of oxo-degradable plastics is very slow, potentially leading to long-term persistence and accumulation. Additionally, the study examined the additive components in the plastics and found that they primarily contained antioxidants and lubricants, with very low heavy metal content, ruling out significant direct toxicity from the additives affecting the experimental results.
This study not only fills the research gap regarding the "size-concentration-impact" relationship of oxo-degradable plastics in soil but also provides scientific support for policy-making through multidimensional data. As the paper states, "A cautious approach is needed regarding the use of oxo-degradable plastics"—until truly efficient and environmentally friendly alternative materials are found, reducing the excessive use of plastic films may still be the most direct choice for protecting soil health.
