Effects of Soil Plastic Contamination on the Early Growth of Pea Plant (Pisum sativum)

Technical Summary: Effects of Soil Plastic Contamination on the Early Growth of Pea Plant (Pisum sativum)

Problem Statement
While marine plastic pollution has long been a focus of environmental research, terrestrial ecosystems are increasingly recognized as significant sinks for microplastics (particles <5 mm). Agricultural soils are particularly vulnerable due to the extensive use of plastic mulch films, irrigation equipment, greenhouse covers, and the application of sewage sludge and compost. Once in the soil, plastics fragment and alter physical soil characteristics (porosity, bulk density, water retention), disrupt hydrological regimes, and interfere with soil microbiota and nutrient supply. These changes pose a threat to seed germination and early plant development, stages where seedlings are most sensitive to environmental stress. Despite existing literature showing varied plant responses to microplastics—ranging from growth inhibition to neutral effects—there remains a need for controlled studies examining specific crop responses to different plastic contamination scenarios to better understand the complexity of these interactions.

Methodology
This study employed a controlled laboratory experiment to evaluate the impact of plastic-contaminated soil on the germination and early growth of garden peas (Pisum sativum). The plant species was selected for its rapid germination, predictable growth patterns, and economic importance.

• Experimental Design: Four treatment groups were established:
  1. Control: Soil only.
  2. Plastic 1: Soil with Plastic 1 contamination.
  3. Plastic 2: Soil with Plastic 2 contamination.
  4. Plastic + Soil: A specific combination of soil and plastic.
• Variables: The independent variable was the type/condition of plastic contamination. Dependent variables included seed germination success rate, root length (cm), shoot length (cm), and plant biomass (g).
• Controls: To isolate the effect of plastic, all other environmental factors were held constant, including irrigation schedules (three times weekly), light intensity, temperature, soil volume, and container size.
• Procedure: Ten healthy seeds were planted per treatment. The experiment ran from June 3 to June 22, 2026. Measurements were taken weekly, with final biomass recorded upon harvest.

Key Results
The study revealed significant variability in plant responses depending on the specific plastic treatment, challenging the notion of a uniform negative effect across all plastic-contaminated scenarios.

• Root Development: The Plastic 2 treatment resulted in the most significant inhibition of root growth, with the shortest average root length recorded at 1.63 cm. In contrast, the Plastic + Soil treatment yielded the longest average root length (2.96 cm), surpassing the control group (2.64 cm). The Plastic 1 treatment (2.68 cm) showed root development comparable to the control.
• Shoot Growth: Variability was also observed in shoot lengths, indicating that plastic pollution influenced above-ground development, though specific quantitative averages for shoots were not highlighted as distinct outliers in the summary data.
• Plant Biomass: Contrary to the initial hypothesis that plastic would universally reduce growth, the Plastic + Soil treatment produced the highest average plant biomass (3.6 g). The Plastic 1 and Plastic 2 treatments resulted in the lowest mean biomass (1.8 g), while the control group averaged 2.6 g.

Significance and Claims
The paper positions itself as a contribution to the growing body of literature regarding terrestrial microplastic pollution and its specific effects on agricultural crops. The authors claim that their findings:

1. Highlight Context-Dependency: The results demonstrate that the impact of plastic on plant growth is not monolithic; it depends heavily on the interaction between soil properties, the specific type of plastic, and the plant's physiological response. The unexpected increase in biomass in the "Plastic + Soil" treatment suggests that under certain conditions, plastic presence may alter soil aeration or moisture in ways that temporarily benefit growth, or that the specific plastic-soil interaction mitigated negative effects.
2. Identify Root Sensitivity: The significant reduction in root length in the Plastic 2 treatment supports the theory that roots, as the primary interface with soil, are highly sensitive to microplastic-induced changes in soil structure and water/nutrient availability.
3. Educational and Foundational Value: Acknowledging the study's limitations—specifically the small sample size, short duration, and laboratory setting—the authors assert that this work provides a foundational piece of evidence. It serves as a basis for future research that should expand to include larger sample sizes, diverse crop species, longer experimental periods, and a deeper analysis of plastic properties (type, size, concentration) and soil microbial communities.

The paper concludes that while plastic contamination clearly influences plant development, the direction and magnitude of this influence are complex and contingent on multiple environmental and material factors.