The report for industry and permitting authorities provides an overview of the hazardous substances that can be released into the marine environment during the installation, operation and decommissioning of offshore wind turbines, including transformer stations, converter platforms and cables. The substances relevant to operation were identified and listed. These substances were assessed for their potential risk to the aquatic environment based on the following criteria: ⁠PBT⁠ criteria, H-phrases for aquatic toxicity, listing on ⁠REACH⁠, ⁠OSPAR⁠, ChemSec and ECHA contaminant lists. Applications in open systems such as galvanic corrosion protection and fire extinguishing foams, but also accidents with fuels and hydraulic oils are possible sources of emissions of hazardous substances into the marine environment.