Focus on the toxicology of deep-sea mining: Biotoxicity of heavy metals to Vibrio fischeri released from disturbed surface sediments of the western Clarion-Clipperton zone, Pacific Ocean

With the growing interest in deep-sea mining from industry, environmental risk assessments of deep-sea mining activities urgently require refinement. This study focuses on the biotoxicity effects of heavy metals released from disturbed surface sediments in the Clarion-Clipperton Fracture Zone (CCZ) of the eastern Pacific Ocean, using Vibrio fischeri as a model organism to simulate deep-sea mining tailings discharge conditions. Through leaching experiments, we identified heavy metals with higher release concentrations (Rb, Li, Mn, Mo, V, Cs) and those with higher toxicity (Cu, Cd, Cr), and investigated their individual and binary combined toxicities under simulated deep-sea low-temperature (4 °C) and surface ambient-temperature (20 °C) conditions. Results showed that the concentrations of Cd, Cu, and Cr released from disturbed sediments (0.035, 1.75, 1.06 μg/L) were significantly lower than their EC 50 (36.95, 1.72, 14.43 mg/L). However, low-toxicity heavy metals such as Mn markedly enhanced the toxicity of Cd, Cu and Cr (up to 230 %), while Rb and Mo exhibited inhibitory effects. Low temperature (4 °C) significantly reduced the toxicity of Cd (reductions of 32 %–85 %) but enhanced Cu and Cr toxicity by 31 %–170 %. This study reveals the complex interactive effects of heavy metal combined toxicity in deep-sea low-temperature environments and provides critical data for defining toxicity thresholds and ecological risk assessments of heavy metals in deep-sea mining tailings discharges.