Macro- and microplastic leachates show a slightly toxic effect on seed germination of cotton.

Utilizing degradable mulching film effectively decreases the accumulation of plastic residuals in agriculture fields and their impacts on plant growth. However, the chemical risks to plants raised by leached substances from different microplastics are still unknown. This work determined the characteristics of macro- and microplastic leachates from different degradation (PE, PO, and Bio) and size (1 × 1 cm, 450-600 µm and <355 µm), as well as their impact on the germination of two varieties of cotton seeds. Our study revealed that degradable characteristics of macro-plastic significantly affect its leachates. Leachates of Bio gained higher dissolved organic carbon (DOC) concentration, aromatic, and values of slope ratios (SR) compared with PO and PE. The particle size of Bio macro- and microplastics also influences indicators such as SR, E250/E365, E253/E203, and Fmax value; however, fluctuations of those indicators were significantly lower than that induced by different degradable traits. Leachates of PE, PO, and Bio seem to have little impact on the germination of two varieties of cotton seeds, only mean germination time (MGT) and shoot height were slightly different among each treatment. A slight fluctuation of enzyme activities also indicates that plastic leachate did not generate excessive oxidative stress in cotton during germination. Leachates of macro- and microplastic under the tested concentration exhibited a slight toxic impact on cotton, which has high-stress tolerance. Thus, further studies should concentrate on the effects of plastic leachate on sensitive plants.

[Characterization of Microplastic Leachate from Different Polymers and Its Effect on Seed Germination of Lettuce].

Accumulation of microplastics in soil could interfere with the germination and growth of plants. However, the chemical risks raised by leachate of microplastics remain unknown. Here, we prepared microplastic leachate at different extraction temperatures (25 and 50℃) using microplastic fibers derived from polyamide (PA) and polyethylene (PE) and conducted the seed germination test of microplastic leachates to investigate the toxic effects of microplastic leachates on lettuce (Lactuca sativa L.). Furthermore, characteristics of the microplastic leachate, such as DOC and DON concentrations and parameters of UV-vis, were measured. The results revealed that the concentration of DOC and DON in the leachate of PA was significantly higher than that of PE. DOC and DON concentration in the leachate of PA increased with extraction temperature. Additionally, the aromaticity, hydrophobic component content, and molecular weight of leachates were significantly affected by the polymers of microplastic, whereas the extraction temperature had no effect. Compared to those in CK, the microplastic leachates reduced the indicators such as germination vigor, germination index, and vigor index of lettuce seeds; however, it had no impact on agronomic traits, such as plant height, root length, fresh weight, and dry weight. Meanwhile, some seeds had abnormal developments of radicles and cotyledons under the microplastic leachate treatments. This demonstrates that the substances leached from microplastics could interfere with the germination process of lettuce seeds. Therefore, the chemical risks exerted by the microplastics to the soil and plant system require further attention.