Micro- and nano-plastics in hydroponic environment are critical for plants: A meta-analysis

The presence of microplastics (MPs) and nanoplastics (NPs) in the environment is ubiquitous, and as such, the toxicity of these plastics, exposure scenarios, and mechanisms of plant response is to be determined. Hereby, a meta-analysis is performed to investigate the effects of MPs and/or NPs on different plant species under hydroponics and soil conditions to assess the current scenario. We examined the response level of root system, photosynthetic parameters, and antioxidant system of plants against MPs/NPs. Root response level in soil condition against various concentrations and types of MPs was higher than in hydroponics however, this response was opposite for the types of MPs. Photosynthetic parameters, including chlorophyll a and b, carotenoids, total chlorophyll, and maximum quantum efficiency of PSII were higher in soil conditions than in hydroponics. Antioxidant parameters, such as malondialdehyde (MDA) and H2O2 contents were higher in hydroponics plants, while, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) showed a mix trend of response level. In addition, proline content was significantly higher in soil and ascorbic acid (ASA) in hydroponic cultured plants under different types, sizes, and concentrations of MPs. These three systems i.e., root, photosynthesis, and antioxidant parameters were also compared between different species, however, the results are generally consistent with the above mentions one. Overall, these analyses suggest that plants grown in hydroponics are more sensitive to the plastic pollution than in the soil environment.