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Effects of Microplastics on Soil and on Lettuce and Tomato, Depending on Type, Size, and Concentration
Summary
An 8-week pot experiment showed that microplastic type, size, and concentration produce species-specific, dose-dependent responses in lettuce and tomato, with tomato reaching 100% mortality at 10% concentration primarily because microplastics disrupted soil water-holding capacity rather than acting as direct chemical toxicants. This physical disruption mechanism means even low microplastic levels in agricultural soils may progressively degrade water availability for crops and threaten food security.
Microplastics (MPs) have emerged as pervasive pollutants in terrestrial environments, yet their effects on crops and soil remain poorly understood. This study investigated how microplastic type (PE, PP), particle size (1.2 μm, 6.5 μm, 150 μm), and concentration (1%, 10%) influence physiological responses of Lactuca sativa and Solanum lycopersicum. Using both germination assays and an 8-week pot cultivation experiment, we found species-specific and dose-dependent responses. Lettuce exhibited enhanced growth under certain MP treatments, while tomato showed high sensitivity—especially at 10% concentration, resulting in 100% mortality. Critically, our results revealed that MPs function primarily as physical disruptors of soil architecture rather than solely as chemical toxicants. Soil moisture content declined significantly in MP-treated soils, particularly in the upper layers where moisture dropped from 50% to approximately 12%, suggesting MPs disrupted water holding capacity. This water deficit was more detrimental to tomatoes, potentially explaining their higher mortality. Additionally, MPs tended to accumulate in upper soil layers due to their buoyant properties following irrigation events. These findings have important implications for agricultural sustainability, as even low MP concentrations may progressively concentrate in surface soils over time. Our results highlight the complex and species-specific phytotoxic effects of MPs and underscore the urgent need for research on long-term MP–soil–plant interactions in agricultural systems.