Ocean Policy · Deep Sea Mining

The Deep Sea’s Overlooked Hazard: A New Report on Radioactivity and Seabed Mining

As the International Seabed Authority returns to negotiations, the Deep Sea Mining Campaign says one risk has gone almost entirely unstudied: what happens when mining mobilises the natural radioactivity locked in the seafloor.

By SEVENSEAS MediaOcean Conservation

When scientists weigh the risks of deep sea mining, the conversation usually turns to sediment plumes, the loss of species found nowhere else on Earth, and habitats that may take geological timescales to recover. A report released at the end of June by the Deep Sea Mining Campaign argues that one hazard has been left almost entirely out of that conversation: radioactivity.

The timing is deliberate. The report arrived just ahead of the International Seabed Authority’s July session in Kingston, Jamaica, where member states are again working through the draft exploitation regulations, the so called Mining Code, that would govern commercial mining in international waters. Those negotiations have repeatedly stalled over gaps in environmental knowledge. This report argues that one of the largest gaps has barely been named.

What is settled, and what is not

The starting point is not in dispute. Polymetallic nodules and seafloor massive sulphides, the two mineral deposits that mining companies are most interested in, naturally concentrate radioactive elements from the uranium and thorium decay chains. It happens through a slow process called scavenging, the same chemistry that builds the metal-rich nodules in the first place. A 2023 study in Scientific Reports led by Jessica Volz and colleagues at the Alfred Wegener Institute found that the surface layers of nodules from the Clarion-Clipperton Zone carry activity concentrations high enough to exceed the exemption levels that regulators apply to other naturally occurring radioactive materials, in some cases by a wide margin. Most of the isotopes involved are alpha emitters.

Alpha particles are easy to underestimate. They are stopped by something as thin as skin or a sheet of paper, which makes them close to harmless outside the body. Swallowed, inhaled, or absorbed across a membrane, they are a very different matter, delivering dense and highly localised damage to living tissue.

Here is where the report parts company with the existing science. Volz’s work, and more recent studies, focused mainly on the people who would handle and process nodules aboard ships and at ports. That is a real and studied question. The one the campaign wants answered is what happens to the ocean itself. According to the report, no peer-reviewed study has yet examined the uptake, dose, or ecological effect of mining-mobilised radioactivity in marine ecosystems.

“There is zero research on how radiation mobilised by deep sea mining will impact marine ecosystems. Marine life cannot escape polluted water. They will breathe it in and swallow it, and eat prey contaminated by mining operations.”

Dr Helen Rosenbaum, Deep Sea Mining Campaign

How the material would spread

The concern rests on how mining would move that material through the water. Extraction generates a plume of disturbed sediment at the seafloor. Several operators, including The Metals Company, also plan to pump the dewatered slurry left after processing back into the ocean at depths of one to two kilometres, creating a second plume in the midwater. Other companies that do not intend to discharge wastewater would still lift crushed nodules and rock through the entire water column, shedding fragments and fine particles along the way.

How far those plumes travel is still being investigated, but independent modelling, including peer-reviewed work published in 2025, suggests midwater discharge could reach well beyond the mining site, potentially across hundreds or even thousands of kilometres. Because the surface layers of nodules are the most radioactive part, and because those are the layers most likely to fragment, the report argues that mining would disperse enriched material into a water column that migrating fish, filter feeders, and deep-sea animals cannot avoid.

A double exposure

Mining would not release radioactive isotopes in isolation. It would mobilise heavy metals at the same time. Both classes of contaminant can build up in the tissue of marine organisms and concentrate as they move up the food chain, a process well documented for radionuclides such as polonium-210 and radium-226 in marine systems generally. The report’s point is that almost no research has looked at their combined effect, especially the chronic, low-level exposure that would run for the decades a mining licence would last. Whether the two would simply add together or amplify each other is, on the current evidence, unknown.

That uncertainty carries into the food that reaches people. Polonium-210 in particular is known to accumulate in seafood and can contribute meaningfully to the radiation dose a human consumer receives. For Pacific communities, where fish is a staple rather than an occasional meal, the question is not abstract.

“It’s frequently suggested that activities such as air travel expose people to greater levels of radiation than those associated with nodules. Such comparisons divert attention away from important scientific questions about the impact of radioactive isotopes released by deep sea mining within the marine environment.”

Alanna Matamaru Smith, Te Ipukarea Society, Cook Islands

Matamaru Smith, whose own government supports seabed mining, frames the report as a call for the kind of hard data that leaders need before they decide. That is the report’s most careful move, and its most defensible one.

An argument built on an absence

It is worth being clear about what the report does and does not claim. It does not say that deep sea mining has been shown to poison marine food webs with radiation. It says the opposite: that the effect has not been studied, and that an unstudied risk of this kind is not a reason to proceed. The distinction matters for a readership that can tell the difference between evidence of harm and evidence of ignorance.

The Deep Sea Mining Campaign is an advocacy coalition, supported by MiningWatch Canada and hosted by The Ocean Foundation, that has spent fifteen years opposing commercial seabed mining, so the report is written to make a case. Its authors include the marine scientist Dr Andrew Thaler alongside researchers in geoscience and radiation. The central claim, that the ecosystem-level radiological effects of mining have simply not been measured, is consistent with the peer-reviewed literature the report draws on, and with how little of the deep sea has been studied at all. Industry proponents, for their part, argue that nodule mining may disturb less habitat than terrestrial mining and that the radioactivity involved is low-level natural material, points the report does not accept but which remain part of the debate the ISA is trying to resolve.

The report closes with ten research questions it wants answered before any commercial licence is granted:

For a report whose main finding is an absence, the request is modest and specific: look before mining. As Rosenbaum put it, deep sea mining is on the verge of exposing the ocean commons to elevated and unregulated radioactivity, and the knowledge gaps should be filled before commercial extraction is allowed to start.

The report, Critical Questions about the Risks of Radiation Toxicity from Deep Sea Mining, was published in June 2026 by the Deep Sea Mining Campaign. The full report, media release, and backgrounder are available at dsm-campaign.org.

SEVENSEAS Media · Conservation Journalism for the Ocean