Plastic films, extensively utilized in agricultural production, have emerged as significant contributors to microplastic pollution in soil. These plastic remnants can disrupt soil structure, affect water permeability, and potentially enter the food chain via plant absorption, posing threats to soil health and food security. In response to these concerns, oxo-degradable plastics (ODPs) have been introduced as a “more sustainable alternative” to conventional plastics. These materials are designed to break down through oxidative degradation, facilitated by pro-oxidants, under light and heat, eventually biodegrading into carbon dioxide and water by microorganisms. However, questions remain about their actual degradation efficiency and potential impacts on crop growth and soil quality.
Recently, a study led by Professor Davey L. Jones from Bangor University has provided crucial insights into these concerns. Published in the journal Frontiers of Agricultural Science and Engineering, the research systematically examined the effects of oxo-degradable plastics of varying sizes and concentrations on soil and corn growth (DOI: 10.15302/J-FASE-2025623).
Innovative Dual-Dimensional Comparison
Unlike previous studies focusing solely on traditional plastics or single-size plastics, this research is unique in its “dual-dimensional comparison.” It evaluates the differences between microplastics and macroplastics while spanning a range from actual field concentrations to extreme levels. Corn was chosen as a model crop, with key indicators such as soil pH, electrical conductivity, and nitrate content monitored over a six-week period. The team also assessed plant growth, chlorophyll content, nutrient absorption, and tracked the degradation process of the plastics using infrared spectroscopy.
Key Findings and Implications
The study’s findings are significant. At low concentrations typical of real-world conditions, oxo-degradable plastics showed minimal impact on soil quality and corn growth. However, when concentrations exceeded 1%, notable changes in soil properties were observed. For instance, soil pH in the microplastic treatment group increased by nearly one unit, electrical conductivity doubled, and nitrate content rose significantly. The impact of macroplastics was comparatively weaker, likely due to the larger surface area of microplastics, which facilitates more extensive soil contact and alteration of soil structure and chemistry.
“At high concentrations, both microplastics and macroplastics reduced corn height and chlorophyll content, but microplastics had a more pronounced inhibitory effect.”
Interestingly, corn biomass only slightly decreased at the highest concentration, indicating a degree 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.
Degradation Limitations of Oxo-degradable Plastics
The study also highlighted the “degradation limitations” of oxo-degradable plastics. Infrared spectroscopy revealed that after six weeks of soil burial, only mild chain scission of the plastics occurred, with no significant oxidation products like ketones or aldehydes detected. This suggests that without light exposure, the degradation process in soil is slow, potentially leading to long-term persistence and accumulation.
Additionally, the research examined the additive components in the plastics, finding primarily antioxidants and lubricants with very low heavy metal content, ruling out significant direct toxicity from these additives affecting the results.
Policy Implications and Future Directions
This study not only addresses the “size-concentration-impact” relationship of oxo-degradable plastics in soil but also provides valuable scientific data to inform policy decisions. As the authors caution, “A cautious approach is needed regarding the use of oxo-degradable plastics.” Until truly efficient and environmentally friendly alternatives are developed, reducing the excessive use of plastic films remains a prudent strategy for protecting soil health.
“Reducing the excessive use of plastic films may still be the most direct choice for protecting soil health.”
The findings underscore the need for further research into alternative materials and more comprehensive strategies to mitigate the environmental impacts of agricultural plastics. As the agricultural sector continues to seek sustainable solutions, studies like this play a crucial role in guiding both policy and practice towards more environmentally responsible choices.
