Phytotoxic Effects of Polyethylene Microplastics on the Growth of Food Crops Soybean (Glycine max) and Mung Bean (Vigna radiata)

Abstract

Accumulation of micro-plastics (MPs) in the environment has resulted in various ecological and health concerns. Nowadays, however, studies are mainly focused on toxicity of MPs on aquatic organisms, but only a few studies assess the toxic effects of micro-plastics on terrestrial plants, especially edible agricultural crops. The present study was aimed to investigate the adverse effects of polyethylene (PE) microplastics on the germination of two common food crops of China, i.e., soybean (Glycine max) and mung bean (Vigna radiata). Both the crops were treated with polyethylene microplastics (PE-MPs) of two sizes (6.5 μm and 13 μm) with six different concentrations (0, 10, 50, 100, 200, and 500 mg/L). Parameters studied were (i) seed vigor (e.g., germination energy, germination index, vigor index, mean germination speed, germination rate); (ii) morphology (e.g., root length, shoot length) and (iii) dry weight. It was found that the phyto-toxicity of PE-MPs to soybean (Glycine max) was greater than that of mung bean (Vigna radiata). On the 3rd day, the dry weight of soybean was inhibited at different concentrations as compared to the control and the inhibition showed decline with the increase in the concentration of PE-MPs. After the 7th day, the root length of soybean was inhibited by PE-MPs of 13 μm size, and the inhibition degree was positively correlated with the concentration, whereas the root length of mung bean was increased, and the promotion degree was positively correlated with the concentration. Present study indicated the necessity to explore the hazardous effects of different sizes of PE-MPs on the growth and germination process of agricultural crops. Additionally, our results can provide theoretical basis and data support for further investigation on the toxicity of PE-MPs to soybean and mung bean.

Influence of Microplastics on Seedling Growth of Blackgram under Different Soil Types

“…The decrease in germination rate could be due to physical or chemical interference of microplastics with seed imbibition or water uptake [20]. In previous studies, microplastics were reported to reduce germination rate in cress [20,29,30], rye grass [31], soybean [25] and lettuce [22]. The time taken for shoot emergence was significantly affected by different concentrations of microplastics in both of the soils.…”

“…The presence of microplastics around the plant roots is more likely to promote phytotoxicity of other soil contaminants. The influence of microplastics on soil-plant system varies based on the shape, size, type and concentration of microplastics [20,[23][24][25] and soil type [17,26]. Yet, the studies focusing on the impacts of microplastics on plant system in different soil types is scarce.…”

Microplastic/nanoplastic toxicity in plants: an imminent concern

“…In contrast, Lian et al ( 2020b ) observed the opposite effect of MPs/NPs on seed germination and stated in previous experiments that PS-based NPs significantly assisted wheat seedling growth rather than inhibited seed germination. Moreover, the phytotoxicity of PE-based MPs on food crops such as mung bean ( Vigna radiata ) and soybean ( Glycine max ) has been experimented where soybean crops are more affected than mung beans (Wang et al, 2021a , b , c ). Furthermore, a reduction in biomass was observed in different studies with different crops such as maize ( Zea mays L.) (Wang et al, 2020a , b ), wheat ( Triticum aestivum ) (Qi et al, 2018 ), and onion ( Allium fistulosum ) (de Souza Machado et al, 2018 ).…”

“…Another study on rice found that high concentrations of PS-based MPs significantly inhibited the germination percentage, germination index, and germination vigor of rice seeds when compared to low concentrations of PS (Zhang et al, 2021a , b ). Another study found that PE-based MPs can reduce the vigor index, germination energy, and germination index of soybean (Wang et al, 2021a , b , c ). Potential causes, in this case, include the presence of MPs in the seed coat, which inhibited water absorption capacity, blocked available pores, and ultimately slowed seed germination (Bosker et al, 2019 ).…”

“…Thus, for maintaining normal homeostatic conditions, the plant antioxidant system is activated to remove ROS and thus survive under adverse conditions (Judy et al, 2019 ). Generally, oxidative burst occurs in plants when the production of ROS exceeds the level of the antioxidant defense system (Wang et al, 2021a , b , c ). Thus, to build up resistance in the plant body, they produce several beneficial elements such as enzymatic and nonenzymatic antioxidants accordingly (Ogbe et al, 2020 ).…”