Ecotoxicological effects of deep-sea sediments from polymetallic nodule fields in the marine mussel Mytilus galloprovincialis

Deep-sea mining (DSM) has the potential to become the next global scale extractive industry. Besides directly removing habitat in the area where the ores will be collected, DSM activities in the deep seafloor are likely to cause a plume of sediments. This sediments plume may also affect the fauna in the surrounding areas of the mining site. In this context, this work assesses the ecotoxicological effects of deep-sea sediments from polymetallic nodule fields, collected in the Clarion-Clipperton Zone (CCZ), Pacific Ocean, in the coastal mussel Mytilus galloprovincialis. Mussels were exposed for 14 days to deep-sea sediments (10 mg/L and 50 mg/L) in seawater. An array of metals (As, Cd, Co, Cu, Mn, Ni, Pb, V, and Zn) and biomarkers (SOD-Superoxide dismutase, CAT-Catalase, GPx-Glutathione peroxidase, GST-Glutathione-S-transferase, LPO-Lipid peroxidation, AChE-Acetylcholinesterase, MT-Metallothionein and DNA damage) were analysed in the mussels' gills and digestive glands. Additionally, metals (Cd, Co, Cu, Ga, Mn, U, and V) and REY (rare earth elements + Yttrium) concentrations were measured in the sediments and seawater. Results show that deep-sea sediments released bioavailable metals and REY into seawater, with Mn being the most accumulated especially in the 50 mg/L treatment and after 14 days of exposure. A dose-dependent, and tissue-specific response was observed for the antioxidant and detoxification biomarkers. Results indicate that deep-sea sediments from the CCZ trigger genetic and neurotoxicity in coastal mussels. These findings support the idea that ecotoxicological harm can manifest even at low concentrations of these deep-sea sediments meaning that during full scale DSM operations, impacts might be greatly enhanced.