Aged polylactic acid microplastics with ultraviolet irradiation alleviated the toxic effect of Cd on pakchoi (Brassica chinensis L.) in hydroponics

Abstract

Biodegradable microplastics (BMPs) and cadmium (Cd) present substantial risks to agricultural systems, primarily affecting plants. Most current studies have focused on the ecological effects of virgin BMPs. However, the effects of ultraviolet (UV)-aged BMPs and their interactions with cadmium (Cd) on pakchoi remain largely unknown. Therefore, this study addressed this gap by aging polylactic acid (PLA) microplastics (MPs) through UV irradiation and conducting an indoor hydroponic experiment. The research systematically examined the individual and combined impacts of Cd, virgin, and UV-aged BMPs on pakchoi (Brassica chinensis L.), focusing on plant growth, photosynthesis, antioxidant systems, and Cd accumulation. The results showed that after 21 days of UV irradiation (UPLA MPs), UPLA MPs with a fractured surface had a more significant impact on pakchoi than untreated PLA MPs. Cd alone inhibited pakchoi growth, development, and photosynthesis, while PLA/UPLA MPs alone promoted these processes. Under the combination of Cd and PLA/UPLA MPs, UPLA MPs could effectively alleviate the toxic effect of Cd on pakchoi. Besides, Cd coexisted with PLA/UPLA MPs, and with the increase of Cd concentration, UPLA MPs(41.22 %, 66.80 %, 45.57 %) decreased the Cd content of pakchoi more significantly than PLA MPs(37.87 %, 55.91 %, 26.35 %). Meanwhile, the results of Partial least squares structural equation models (PLS-SEM) further showed that UPLA MPs could effectively reduce the accumulation of Cd in plants. Therefore, the results of this study can provide a new perspective and reference for the ecological risk evaluation of Cd and BMPs pollution in agricultural soils.