The role of algal-EPS in modifying the short-term and long-term toxicity of binary mixtures of TBBPA and GFNs towards marine Chlorella sp.: cellular toxicity, uptake, and environmental risk assessment

Abstract

The increasing occurrence of graphene family nanomaterials (GFNs) such as graphene oxide (GO), reduced graphene oxide (rGO), and graphene, along with the widespread flame retardant tetrabromobisphenol A (TBBPA), poses a growing threat to marine ecosystems. Both types of contaminants are known to induce toxicity in algae primarily through oxidative stress, membrane impairment, and photosynthetic disruption. This study provides the first systematic evidence of EPS-mediated detoxification of GFNs, TBBPA, and their combinations in the marine alga Chlorella sp. over both short-term (72 h) and long-term (360 h) exposures. EPS were added only once at the beginning, demonstrating their ability to provide sustained protection in a batch culture system. Detoxification was evident through reduced growth inhibition, significant suppression of reactive oxygen species (ROS) and lipid peroxidation (MDA), stabilisation of photosynthetic efficiency, and normalisation of biochemical responses, including proteins, carbohydrates, and antioxidant enzyme activities. UPLC-based uptake studies further confirmed that EPS reduced cellular accumulation of TBBPA, indicating a barrier or binding effect that limited bioavailability of TBBPA. Supporting analyses, including zeta potential, wettability, UPLC analysis, and 3D-EEM, revealed that EPS modulated surface interactions and minimised direct contaminant–cell contact. Clustered heatmap, correlation analysis, and PCA also showed the correlation. Among the GFN treatment groups, rGO revealed the highest toxicity, although in the presence of TBBPA and EPS, the toxicity was higher in the presence of GO. Ecological risk assessment highlighted the broader environmental relevance of these findings. Overall, this work establishes EPS as natural and effective detoxification agents capable of mitigating the long-term toxic impacts of emerging contaminants, thereby emphasising their potential as a sustainable ecological defense mechanism in aquatic systems.