Physiological responses of lettuce (Lactuca sativa L.) to microplastic pollution

Concerns about the pollution of farmlands by microplastics and the associated toxicology have increased in recent times; however, studies on this topic are scarce. In this study, two kinds of PVC microplastics with different particle sizes (PVC-a with particle sizes from 100 nm to 18 μm, and PVC-b with particle sizes from 18 to 150 μm) and different content levels (0.5%, 1%, and 2%) were used to analyze the effects of PVC microplastics on the physiological characteristics of the lettuce root system and leaves. The results showed that PVC-a and PVC-b had no significant effect on the lettuce root activity. However, 0.5%a and 1%a significantly increased the total length, surface area, volume, and diameter of roots. In terms of leaves, PVC-a and PVC-b had no significant effect on the malondialdehyde content, but 1%a significantly increased the superoxide dismutase activity. Carotenoid synthesis was promoted by PVC-a but inhibited by PVC-b. Furthermore, 1%a could reduce the ability of light energy absorption, dissipation, capture, and electron transfer. The gray correlation analysis indicated that PVC-a correlated to a considerable degree with the indices related to photosynthesis, while PVC-b was significantly correlated with the indices related to root morphology. This study provides insights into the ecotoxicological effect of microplastics on farmland crops and associated ecological risk assessment.