Short-duration exposure of 3-µm polystyrene microplastics affected morphology and physiology of watermilfoil (sp. roraima)

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 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 7 days. 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 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.