Abstract
Microplastics are one of the most widely discussed environmental issues worldwide. Several studies have shown the effect of microplastic exposure on the marine environment; however, studies on freshwater systems are lacking. This study was conducted to investigate the effect of microplastics on hydroponically growing emergent freshwater macrophytes, watermilfoil (sp. roraima) under controlled environmental conditions. Plants were exposed to 0mg L-1 (control), 0.05mg L-1, 0.25mg L-1, 1.25mg L-1, and 6mg L-1 of 3-µm polystyrene microspheres for 7days. The oxidative stress, antioxidant response, pigmentations, Fv/Fm, and growth parameters in the above-water and below-water parts were analyzed separately. Microscopic observations were performed to confirm the tissue absorbance of the microplastics. Exposure to microplastics altered some parameters; however, growth was not affected. The effect of microplastics was not linear with the exposure concentration for most of the parameters and between 1.25 and 6mg L-1 concentrations. The response trends mostly followed the second-order polynomial distributions. Under the 1.25mg L-1 exposure, there were significant changes in root length, H2O2 content, catalase activity, anthocyanin content, and Fv/Fm. There were differences in parameters between the above-water and below-water parts, and the responses of the microplastics followed different trends. Microscopic observations confirmed the attachment of microplastic particles onto newly formed roots, except for older roots or shoot tissues.
Highlights
The release of plastics into the environment is currently a serious issue worldwide
The degraded plastic particles have sizes ranging from 1 μm to 5 mm and are typically called microplastics (MPs); there can be different definitions when considering the size of MPs (Hartmann et al 2019)
Microscopic observation of roots confirmed that MPs were absorbed into the roots and the number of MP particles observed inside the roots increased with increasing MP concentration (Fig. 2); the stem cross-sections observed did not confirm the existence of MPs in tissues
Summary
The release of plastics into the environment is currently a serious issue worldwide. numerous actions have been taken to prevent its environmental risk, there are still significant plastics in the environment from already released plastics and currently releasing plastics owing to the mismanagement of plastic wastes (Thompson et al 2009; Lebreton and Andrady 2019). Regardless of source, MPs have contaminated most parts of the land and water (rivers, lakes, oceans, and groundwater) worldwide. They have recently been recognized as a significant concern for aquatic systems (Lambert and Wagner 2018). The increased presence of MPs has been reported in freshwater systems worldwide, including in Japan (Wagner et al 2014; Kataoka et al 2019). In such environments, MPs can be considered as one of the abiotic factors in modern aquatic ecosystems
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