Assessment of phosphogypsum impact on the salt-marshes of the Tinto river (SW Spain): Role of natural attenuation processes

► Natural attenuation of contaminants occurs in phosphogypsums disposed on salt-marshes. ► Metals are highly mobile in superficial zones under oxidizing conditions. ► Mobility and toxicity strongly decrease in deep zones under oxygen-restricted conditions. ► Metal removal occurs by sulphate reduction and precipitation of metallic sulphides. ► Salt-marsh sulphate-reducing bacteria likely catalyse these natural processes.