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Microplastics enter the soil in a variety of shapes and polymer types altering soil properties with known consequences for plant growth. However, the effects of a range of different microplastic shapes and types on seed germination are mostly unknown. Here, we established a glasshouse experiment that included 12 microplastic types representing different shapes (fibers, films, foams and fragments) and polymers, and mixed each of them with soil at a concentration of 0.4% (w/w). Fifty seeds of Daucus carota were sown and monitored for 49 days to evaluate different germination parameters. Our results showed that microplastic films and fibers decrease seed germination velocity as they may affect soil water status, likely interfering with different phases of seed germination: Seeds may imbibe toxic microplastic leachates, and be affected by a physical blockage; testa rupturing may be delayed as this also depends on water uptake. Microplastic toxic leachates may affect activity of enzymes key for seed germination, and delay embryo growth and radicle emergence. Microplastics, irrespective of their shape and polymer type, increase synchrony of seed germination, which might be linked with microplastics exerting a mild stress on seeds. The final percentage of germination was not affected by microplastics in soil, implying that microplastics did not affect seed viability. Our results showed that microplastics affect seed germination mainly as a function of their shape.

This study investigated small microplastic particle (SMP, < 350 μm) contamination in the surface seabed sediment of the inner part of Tokyo Bay. The SMP concentration during the rainy season (May) was 100.3 ± 45.8 pieces g−1 dry weight and higher in the inner side of the bay, whereas that of the dry season (January) was 147.6 ± 19.5 pieces g−1 dry weight.There was no seasonal difference. The main plastic types found in the rainy season were polypropylene (PP), polyethylene (PE), and polyamide (PA). In the dry season (January), the concentration of PP decreased while that of PA increased.The mean SMP diameter did not change by site or season. Our results indicate that the seabed sediments in the inner part of Tokyo Bay are contaminated with relatively high concentrations of SMPs.Furthermore, the deposition rate of SMPs in the inner part of the bay was 12.4 mg cm−2 y−1., 公開日: 2023-09-01