The impact of polystyrene nanoplastics on plants in the scenario of increasing temperatures: The case of Azolla filiculoides Lam

There are great concerns for the accumulation in the environment of small dimension plastics, such as micro- and nanoplastics. Due to their small size, which facilitates their uptake by organisms, nanoplastics are of particular concern. The toxic effects of nanoplastics on plants are already reported in the literature, however nothing is known, to date, about the possible effects of climate change, in particular of increasing temperatures, on their toxicity for plants. To address this issue, plants of the water fern Azolla filiculoides were grown at optimal (25 °C) or high (35 °C) temperature, with or without polystyrene nanoplastics, and the effects of these stressors were assessed using a multidisciplinary approach. Green fluorescent polystyrene nanoplastics were used to track their possible uptake by A. filiculoides. The development and physiology of our model plant was adversely affected by both nanoplastics and high temperatures. Overall, histological, morphological, and photosynthetic parameters worsened under co-treatment, in accordance with the increased uptake of nanoplastics under higher temperature, as observed by fluorescence images. Based on our findings, the concern regarding the potential for increased toxicity of pollutants, specifically nanoplastics, at high temperatures is well-founded and warrants attention as a potential negative consequence of climate change. Additionally, there is cause for concern regarding the increase in nanoplastic uptake at high temperatures, particularly if this phenomenon extends to food and feed crops, which could lead to greater entry into the food chain.