Clean Energy, Contaminated Oysters? The Wind Farm Question

The idea looks like an obvious win. Offshore wind farms fence off large areas of sea, with turbines spaced far apart and open water between them. Oysters, mussels and seaweed grow well in those waters. Farm them between the turbines and the same patch of sea produces both clean energy and food, with no extra space taken. Governments around the North Sea have promoted exactly that kind of "co-location".

In January 2025, researchers led by the University of Portsmouth published a study of what the turbines put into the water, and what happens when a filter feeder that concentrates metals is grown right next to them.¹ Their answer is a warning: the risk could be serious, and the monitoring needed to know for sure mostly does not exist.

The Corrosion Problem

Steel makes up about 90% of an offshore wind turbine, and steel corrodes fast in seawater. Underwater it can be protected in several ways: coatings, extra-thick steel, an electrical system called impressed current cathodic protection, or galvanic anodes.¹ Galvanic anodes are blocks of more reactive metal, mostly aluminum with some zinc and indium, bolted to the foundation so that they corrode instead of the steel. That is their whole job. Over the turbine's life they dissolve into the sea.

The Portsmouth team worked out how much. For Europe's current offshore wind capacity of about 30 gigawatts, they estimate annual inputs of 3,219 metric tons of aluminum, 1,148 metric tons of zinc and 1.9 metric tons of indium. By 2050, with Europe's capacity expected to grow nine- to twelve-fold, those figures rise to roughly 30,000–38,000 metric tons of aluminum, 10,800–13,600 metric tons of zinc and 11–14 metric tons of indium a year. Today's wind-farm zinc is already about two-thirds of what rivers and direct discharges carry into the North Sea, the Channel, the Kattegat and the Skagerrak combined, 1,662–1,754 metric tons a year.¹

Indium is the odd one out. It is a scarce metal best known from touchscreens and semiconductors, and it has no known biological role. The researchers could find no published data on indium in the tissue of oysters, mussels or kelp, so for now its effects on these animals simply are not known.¹

Why Oysters Are the Sharp End

Oysters feed by pumping large volumes of water across their gills, and many metals that pass through build up in their tissue. That is why they are used worldwide as sentinels of water quality. Pacific oysters are exceptional zinc accumulators, carrying concentrations at least ten times those of blue mussels from the same kinds of sites.¹

No one has yet published tissue measurements from oysters grown beside wind turbines. So the study used concentrations from the wider scientific literature, one range for typical, low-impact waters and one for heavily contaminated sites. It then asked how much of an adult's tolerable weekly intake of zinc a standard six-oyster portion would supply.¹

The first row deserves more attention than it usually gets. Even from clean water, a plate of Pacific oysters can take a person past the tolerable weekly zinc level in one sitting. Tolerable intakes build in large safety margins and are designed around long-term exposure, so one plate is no emergency. But it also means oysters start with less headroom than almost any other seafood, and any extra zinc in their water pushes them higher still.

The evidence from the field is thin and does not all point one way. A Belgian North Sea study recorded very low zinc in sediments around wind farms, though its authors cautioned that it was "too limited to conclude" that turbines had not raised zinc levels.¹

What Could Change

The Portsmouth researchers are not arguing against offshore wind. Their paper calls renewables the most appropriate response to the need to decarbonize.¹ What they want is better information and better choices of material. Impressed current systems, which protect steel with an applied electrical current instead of dissolving metal, contribute negligible amounts to their totals, and coatings reduce how much anode is needed.¹ They also want water, sediment and seafood monitored around operating farms before co-located aquaculture is approved, not after.

What It Means for Oysters

For growers, the risk is practical and reputational. A farm between turbines could face harvest restrictions if tissue metals exceed food-safety limits, a cost nobody priced into the original idea. And much of the oyster's appeal, as a food that cleans its own water, depends on that water being clean.

None of the underlying science is new. The same trait that makes oysters good monitors of polluted water can make them unwise to eat from it. The possible new source is what gives the study its weight: the infrastructure of the energy transition itself. Co-location can still work if developers measure first, choose low-emission corrosion protection where they can, and keep testing the oysters.