Response of <i>Brassica chinensis L</i> to the stress of combined pollution of microplastics and cypermethrin

Microplastics (MPs) can coexist with pesticides in soil for a long period, forming combined pollution. <i>Brassica chinensis L</i> was used as the test plant and the differences in the effects of traditional microplastic polyethylene (PE MPs) and biodegradable microplastic polylactic acid (PLA MPs) alone and combination with cypermethrin pesticide on plants were studied. The results showed that the inhibitory effect of the PLA MPs on <i>Brassica chinensis L</i> was greater than PE MPs and that the inhibitory effect of microplastics in combination with cypermethrin pesticides was greater than that of microplastics alone. <i>Brassica chinensis L</i> avoided oxidative damage by increasing the stress level at a low PE MP concentration (2%) and the antioxidant defense capability gradually weakened as the concentration increased. As the concentration of PLA MPs increased, the oxidative damage of plant roots was further aggravated. The biomass and quality of <i>Brassica chinensis L</i> showed the pattern of 'low promotion and high inhibition' whether PE MPs were treated alone or combined with cypermethrin pesticides. While PLA MPs treatment groups showed a pattern of 'stronger inhibition with increasing microplastic concentration'.