*2.3. Median Effective Concentrations (EC50)*

The concentrations of BDE-47 and nickel/BDE-47 mixtures that induced a 50% reduction in *P. tricornutum* biomass after 72 h of exposure were calculated according to the Organization for Economic Cooperation and Development (OECD) guidelines [32] by estimating cell numbers. EC50-72 h values were estimated with a sigmoidal curve and the OriginPro 2018 software program (OriginLab Corporation, Northampton, MA, USA).
