Paradoxical Effect of High-Concentration Soil Microplastics on Tomato (Solanum lycopersicum) Yield: A Follow-Up Study

Overview

Microplastics (MPs) are pervasive environmental pollutants that can accumulate in living organisms. Their levels in agricultural soils are expected to increase exponentially, but the impacts of extremely high MP soil concentrations on tomatoes (Solanum lycopersicum)—the most produced vegetable crop—remain poorly understood. Research using MP levels similar to those found in agricultural soils usually results in decreased tomato yield, though there are exceptions. The author’s preceding study, “Plastic Fruit: Effect of Microplastics on Tomato (Solanum lycopersicum) Growth and Yield” (Cowan, 2025) found that a 10% MP soil concentration—much higher than current agricultural soil levels—increased yield compared with 0% and 20% MP concentrations. The primary hypothesis was that if tomato plants are grown in soil with concentrations of 0%, 5%, 10%, and 15% polyethylene (PE) MPs, then at a 10% MP concentration, yield will increase compared with the other concentrations. The number of fruit and plant height were recorded over 39 days. Plants grown at the 10% MP concentration exhibited the greatest average percent change in yield, supporting the primary hypothesis. This result is consistent with those of the preceding study. A one-way ANOVA did not reach statistical significance, F(3, 16) = 2.32, p = 0.115, but the effect size was moderate-to-large (η² = 0.303). This, along with the replication of results across both studies, suggests that the effect is real, but a larger sample size is needed to reach statistical significance. Future research should also include longer study durations, additional MP concentrations, and expanded plant health metrics.

Competition history

• CSEF 2026 Plant Biology (Junior Division) · Entry J-18-15

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