Recommandations for the quantitative assessment of metal inputs in the marine environment from the galvanic anodes of offshore renewable energy structures

The fast-growing offshore wind industry represents a potential new anthropogenic pressure for the marine environment. Despite the fact that it is considered as a green/clean energy source, the large-scale deployment of these devices could induce some environmental impacts that need to be studied. Understanding these impacts is in line with the Marine Strategy Framework Directive (MSFD) (European Commission, 2008) of the European Union which targets good environmental status for the marine environment. The development of offshore renewable energies (ORE), in particular floating and fixed offshore wind structures in France, gives rise to new and more precise questioning from the French public authorities and civil society. In particular, a lot of questions have emerged in relation to the use of Galvanic Anode Cathodic Protection (GACP) systems and about the release of heavy metals associated with their functioning. These anodes are composed of different metals which are more reducing than the metal to be protected. The anodes are generally made with magnesium, aluminium or zinc. In offshore industries such as offshore wind turbines or oil & gas platforms, the anodes used are mainly composed of an aluminium alloy which contains zinc and other trace metals. Their installation in fishing zones is a source of major concern and this affects several offshore wind farm projects (such as Île d’Yeu and Noirmoutier). This growing concern from public authorities and civil society has even led to galvanic anodes being abandoned in certain projects in order to overcome this problem. For example, the chosen solution for the jacket foundations of the Dieppe Le Tréport project is to implement cathodic protection by impressed current (ICCP) with titanium anodes). GACP has been replaced by ICCP in several projects although no scientific study has been conducted to prove the environmental impact of GACP in the ORE context, and no scientific study has proven that ICCP has no environment