Graphene family nanomaterials - atrazine - extracellular polymeric substances: a triangular interplay during short-...

The co-occurrence of graphene family nanomaterials (GFNs) and organic pollutants in aquatic environments raises concerns regarding their individual as well as combined effects on marine primary producers. The present research investigates the toxicity of graphene, graphene oxide (GO), and reduced graphene oxide (rGO), both individually and in combination with atrazine (ATZ), in the marine microalga Chlorella sp. over short-term (72 h) and long-term (360 h) exposure periods, with a particular focus on the protective role of algal extracellular polymeric substances (EPS). For the determination of toxicity, growth, photosynthesis, reactive oxygen species (ROS), malondialdehyde (MDA), and antioxidant enzyme activities were studied. The results show that GFNs in various combinations with ATZ can inhibit growth, hinder photosynthesis, induce oxidative stress and accelerate lipid peroxidation. Among the three GFNs studied, rGO was the most toxic, followed by GO and graphene. Exposure to binary mixtures of GFNs and ATZ resulted in different responses compared to the individual pollutants, indicating the effect of the combination of GFNs and ATZ, as well as the exposure duration. Importantly, EPS markedly alleviated the adverse effects of ATZ, GFNs and their combination by reducing oxidative stresses and improving photosynthesis and biochemical responses. The uptake study revealed decreased accumulation of ATZ in cells in the presence of EPS. Finally, the current work concludes that algal EPS is an important natural defence system that regulates the bioavailability and toxicity of GFNs and other organic contaminants such as ATZ, even when they co-occur in the environment for a long duration.