Cobalt and nickel in marine and coastal systems: A quantitative review of occurrence, bioaccumulation and ecotoxicological impacts

This review synthesizes studies published up to 2025 on cobalt (Co) and nickel (Ni) contamination in marine and coastal environments, identified through major scientific databases. After duplicate removal, 183 unique studies were included. Of these, 142 reported Co and/or Ni concentrations in water and/or sediments, 18 included organism-based data, and 28 were laboratory-based investigations. Environmental concentrations ranged from 0.0001 to 101 μg/L for Co and from 0.001 to 550 μg/L for Ni, whereas laboratory exposures ranged from 0.035 to 171,660 μg/L for Co and from 0.12 to 162,985 μg/L for Ni. Most studies addressed bioaccumulation and toxicity in marine invertebrates, particularly bivalves, copepods, corals, and other taxa. Bivalves, including Mytilus galloprovincialis, M. edulis, and M. trossulus, were the most frequently investigated organisms because of their filter-feeding behaviour, broad distribution, and established value as bioindicators. Under controlled exposure, M. galloprovincialis accumulated up to 33 μg/g Co and 25 μg/g Ni in tissues. Overall, Co and Ni exposure induced oxidative stress, enzymatic alterations, and cellular damage, affecting fertilisation, embryonic and larval development, growth, calcification, and reproduction. However, responses varied according to metal, dose, species, and endpoint. In corals, adverse effects were mainly associated with Co or high Ni concentrations, whereas low to moderate Ni exposure often stimulated calcification, growth, photosynthetic performance, or symbiont-related responses. Given the increasing industrial and municipal releases, especially from lithium-ion battery production, this review highlights the need for improved monitoring, source control, wastewater treatment, metal speciation assessment, and long-term ecological risk evaluation.