The Deep Ocean as a Radioactive Rubbish Dump

For decades, governments treated the deep ocean as though it were the planet's ultimate rubbish dump. If something was dangerous enough that nobody wanted it on land, there was always another possibility: put it into a steel drum, mix it with concrete or bitumen, take it hundreds of kilometres offshore and throw it overboard into several kilometres of water. That sounds like the premise of an environmental horror film. Unfortunately, it was once perfectly respectable government policy.

Scientists are now returning to one of the great radioactive graveyards of the twentieth century, in the abyssal plains of the North-East Atlantic. The numbers involved are extraordinary. More than 200,000 drums of radioactive waste were dumped into this region during the decades when ocean disposal was permitted. Some estimates for the broader Atlantic dumping record run closer to 300,000 drums. Britain alone dumped more than 140,000 barrels during 34 operations between 1949 and 1982, Belgium about 55,000 and France more than 46,000 in two operations during the 1960s.

This was not some secret operation conducted by criminals in the middle of the night. Radioactive waste disposal at sea became an internationally supervised activity. Eight European countries participated in dumping solidified radioactive wastes at designated North-East Atlantic sites, and the OECD's Nuclear Energy Agency maintained records and reviewed the suitability of disposal areas. As late as 1980, an expert review concluded that the principal North-East Atlantic site remained suitable for continued radioactive-waste dumping under specified conditions.

The practice now looks extraordinary, but the reasoning at the time was straightforward. The ocean is enormous. The deep seabed is remote. The waste being dumped was predominantly low- and intermediate-level radioactive material rather than spent reactor fuel or the intensely radioactive high-level waste that usually comes to mind when people hear the words "nuclear waste." The material could be immobilised in concrete or bitumen, enclosed in roughly 200-litre steel drums and dropped into water four or five kilometres deep.

Out of sight, out of mind. Except steel does something remarkably predictable when left in salt water for half a century. It rusts.

The French-led NODSSUM project has now gone back to see what happened. During its 2025 expedition, an autonomous deep-sea vehicle surveyed part of a vast disposal region and located 3,355 barrels. Popular Mechanics reports that only about two per cent of the approximately 14,500-square-kilometre area was mapped, yet thousands of barrels were found. Scientists returned in 2026 with the crewed submersible Nautile to inspect selected barrels directly and collect samples of water, sediment, microorganisms and marine animals.

What they found eliminates any comforting idea that these containers remain pristine little nuclear coffins sitting intact on the seabed. Researchers have documented drums in advanced stages of degradation. Some are heavily corroded. Most significantly, they have photographed at least one seriously degraded drum with its contents visibly spilling onto the surrounding seabed. This raises the obvious question: what happens when all these containers eventually rust through?

The first thing to understand is that the steel barrel was never necessarily intended to remain an impermeable containment vessel for thousands of years. Much of the radioactive material was immobilised within concrete, bitumen or another matrix inside the drum. Consequently, failure of the outer steel does not mean that 200 litres of concentrated radioactive liquid suddenly pours into the Atlantic.

Instead, deterioration creates pathways through which seawater can reach the solidified waste and radionuclides can potentially migrate into the surrounding environment. How rapidly that happens depends upon the waste matrix, the radionuclides present, corrosion, water chemistry and the physical condition of individual packages.

Then radioactive decay enters the story. Some radionuclides originally dumped will already have decayed substantially during the forty to seventy years they have spent underwater. Others have much longer half-lives and consequently remain relevant for decades, centuries or longer. The environmental problem therefore cannot be reduced to saying that the barrels are either "radioactive" or "safe." What matters is which isotopes remain, at what concentrations, how mobile they are and whether organisms incorporate them.

The enormous volume of the Atlantic provides equally enormous dilution. At depths approaching five kilometres, this is not comparable to a leaking radioactive drum sitting beside a town's drinking-water reservoir. Any material released into the surrounding water is entering an immense marine environment, and much of it may remain at concentrations posing little or no meaningful threat to humans.

But dilution is not the whole story. The deep ocean is not the lifeless wasteland that earlier generations sometimes imagined it to be. The barrels themselves demonstrate the point rather beautifully. Photographs show them colonised by anemones, sponges, crabs and other organisms. What humans regarded as dead industrial rubbish has become hard substrate upon which deep-sea communities establish themselves.

That creates the possibility of a biological pathway for radionuclides. If radioactive elements migrate from degraded waste into sediments or seawater, microorganisms may interact with them. Benthic organisms can potentially take them up. Those organisms can be eaten by other organisms. Some radionuclides can therefore move through food webs rather than simply dispersing uniformly through an effectively infinite body of water.

This does not mean that scientists have discovered some gigantic radioactive plume poisoning the Atlantic. They have not. Indeed, one of the most important points about the present expeditions is that the detailed radioecological answer is still being worked out.

Researchers sampled the sediments immediately adjacent to barrels, surrounding water, microbial communities and organisms. Scientists from France, Norway, Germany and Spain are analysing the samples to identify radionuclides and determine how far contamination has migrated and how it interacts with the ecosystem. The NODSSUM researchers describe this as one of the first detailed radioecological investigations of its kind in the deep sea.

There is an important distinction here between container failure and environmental catastrophe. The first is already occurring. The second has not been demonstrated. That distinction matters because nuclear stories easily become sensationalised. "Hundreds of thousands of radioactive barrels at the bottom of the Atlantic" sounds terrifying, and photographs of corroded drums leaking material make it more so. But most of this material was classified as low- or intermediate-level waste, the sites are extremely deep and remote, and radioactive decay and oceanic dilution work strongly in favour of reducing risk. Yet none of that makes the original policy look particularly wise.

The deeper problem is temporal. Governments made a decision lasting decades, centuries or potentially longer using containers whose deterioration over much shorter periods was entirely foreseeable. They effectively transferred the monitoring problem to future generations.

And the North Atlantic is only part of the story. The International Atomic Energy Agency's historical inventory records sea disposal beginning in the Pacific in 1946 and continuing until the last North-East Atlantic operation in 1982. Across 36 years, 12 states used 47 sites to dispose of approximately 46 petabecquerels of mainly solid or solidified low-level radioactive waste. The European North-East Atlantic dumps were therefore one component of a much larger twentieth-century experiment in using the oceans as a repository for radioactive material.

Ocean dumping did not finally disappear because someone discovered that steel rusts. International attitudes towards marine pollution changed. Disposal of radioactive waste at sea was progressively restricted and ultimately prohibited internationally, with the global prohibition taking effect in the 1990s.

The barrels, however, did not disappear when the regulations changed. They remain where governments left them. That is what makes the NODSSUM expeditions so fascinating. They are not merely environmental surveys. They are an archaeological investigation of the nuclear age. Scientists are visiting decisions made by governments half a century ago and discovering what those decisions look like after decades of corrosion, radioactive decay and biological colonisation.

The results may ultimately prove reassuring. Perhaps radionuclide migration will turn out to be extremely localised, environmental concentrations tiny and biological effects difficult to distinguish from background radiation. Given the depth, dilution and predominantly lower-level nature of the waste, that is entirely possible.

Alternatively, researchers may identify particular radionuclides accumulating in sediments or organisms around degraded barrels. The fact that material can now be seen escaping from severely deteriorated containers makes determining that question more than an academic exercise.

There is also little realistic prospect of simply cleaning the place up. Recovering hundreds of thousands of ageing radioactive drums scattered across enormous areas of seabed four or five kilometres underwater would be an immense technical undertaking. Disturbing badly degraded packages might sometimes release more material than leaving them alone. Monitoring and understanding the sites may therefore be more practical than attempting wholesale recovery.

That leaves us with a peculiar inheritance. The generation that built the nuclear age also inherited an older environmental assumption: that sufficiently large oceans could absorb almost anything humans put into them. Radioactive waste, industrial chemicals, sewage and ordinary rubbish could disappear over the horizon and thereby disappear politically.

Nature does not recognise that particular definition of disappearance. The waste is still there. The steel is rusting. Some barrels are already spilling their contents. Marine organisms have colonised them, and scientists are only now beginning to establish in detail where the radionuclides go when their containers finally fail.

Perhaps the ultimate environmental effects will prove modest. We should hope so. But the story remains an extraordinary example of technological confidence combined with institutional short-termism. Hundreds of thousands of containers were dropped into the abyss on the assumption that four or five kilometres of seawater constituted an adequate answer to a waste problem. Half a century later, scientists have descended into that abyss to discover that the problem was not disposed of at all. It was merely postponed.

https://www.popularmechanics.com/science/environment/a73467447/north-atlantic-radiation-barrels/