Short Duration Exposure of 3 µm Polystyrene Microplastics Affected Morphology and Physiology of Watermilfoil (sp. Roraima)

<title>Abstract</title> 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, <italic>Watermilfoil</italic> (sp. <italic>Roraima</italic>) under controlled environmental conditions. Plants were exposed to 0 mg L^{− 1} (control), 0.05 mg L^{− 1}, 0.25 mg L^{− 1}, 1.25 mg L^{− 1}, and 6 mg L^{− 1} of 3 µm polystyrene microspheres for seven days. The oxidative stress, antioxidant response, pigmentations, Fv/Fm, and growth parameters in 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 mg L^{− 1} and 6 mg L^{− 1} concentrations. The response trends mostly followed the second-order polynomial distributions. Under the 1.25 mg 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.