Marine mining companies are in the starting blocks to dig up the immense treasure of non-ferrous metals that lie on the ocean floor in the form of manganese nodules at depths of 4,000 to 6,000 meters. The potato- to cabbage-sized structures accumulated metals such as copper, cobalt, manganese, nickel and molybdenum over millions of years. They grow at only a few millimeters per million years.
Harvesting the manganese nodules is not yet permitted. But the UN’s International Seabed Authority (ISA) in Jamaica wants to have binding rules in place next July under which mining should be allowed. The Canadian Metals Company is eagerly awaiting this and wants to start mining together with the Pacific island state of Nauru in the so-called Clarion-Clipperton Zone in the central Pacific east of Hawaii.
Experts warn of radiation damage
But experts warn. The currently possible mining methods for the manganese nodules threaten to destroy the deep-sea ecosystem that has developed over millions of years for millions more.
Not only that: people’s health could also be threatened. Because manganese nodules are radioactive. Their mining, their transportation, even their processing and purification on land, even the products made from the nodule metals could result in radiation damage.
The fact that the polymetallic nodules, as they are also known, efficiently intercept and store several naturally occurring radioisotopes of the uranium series, which emit mainly alpha radiation during decay, is not new.
Manganese nodule from the Northwest Pacific.
(Image: Jan Steffen / GEOMAR)
But so far no one has bothered about what this means for health protection against radiation. Alpha particles do not penetrate the skin; so they are not directly dangerous. However, alpha emitters are very energetic and particularly harmful if they enter the body through inhalation or ingestion. Then the body cells themselves become permanent radiation that damages the tissue.
Effects of industrial deep-sea mining
Scientists at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven have now addressed this knowledge gap.
Since 2015, deep-sea researchers from the institute, together with over 30 other institutes from all over the world, have been investigating in a project called MiningImpact2 what effects industrial deep-sea mining would have on the habitats and ecosystems of the sediments and the water column in the Pacific.
“Our new study on the radioactivity of manganese nodules now shows that, in addition to the consequences for marine ecosystems, there can also be health hazards for people in connection with the mining and processing of manganese nodules, but also the use of the products made from them,” explains Professor Sabine Kasten for sediment diagenesis and project manager of the MiningImpact project at the institute.
“With our study, we don’t really say anything about the extent to which this is dangerous. We simply relate our measured values to the currently applicable exemption limits for radioactivity. What that really means for health is beyond our expertise,” says first author and biogeochemist Jessica Volz present the results.
However, the measured level of radioactivity surprised the researchers. For example, the activity of radium-226 in the nodules exceeds the limit value of 0.01 becquerel per gram laid down in the German Radiation Protection Ordinance by a hundred to a thousand times. Sometimes the outside of manganese nodules even shone with more than five becquerels per gram.
“This is because the nodules consist mainly of manganese oxide. But manganese oxide is simply an extremely strong absorber of radioisotopes,” explains Volz.
When the manganese nodules are processed
It is not surprising that the outside shines particularly brightly. “Due to the fact that the nodules are extremely old, this of course exceeds the half-lives of the isotopes. We looked at isotopes that have relatively long half-lives, but a lot of those had already decayed in the center of a nodule,” says Volz.
According to the study, this also has consequences for those who work with it. Because after the nodules are recovered from the seabed, they are crushed and dried on top of the ship. Their strength decreases, and dust from abrasion disperses in the air that people breathe during operation. This fine dust is likely to originate primarily from the surface of the nodule fragments, where the activities of thorium-230, radium-226 and protactinium-231 are highest.
In addition, tailings from mining sludge – a mixture of seawater, sediment and fine nodules – returns to the ocean as runoff plume.
Actually, the processing ships should discharge this flushing cloud, which contains up to seven percent of ground-off nodule fragments, to greater depths. Nevertheless, marine organisms can absorb the radioactive particles, which thus enter the food chain and are ultimately consumed by humans.
In summing up their analyses, the authors express themselves very cautiously: “We show that the expected breakdown of nodules will adversely affect the health of workers and the general public through the probable inhalation or ingestion of radioactive nodule dust and escaping radon-222 gas, possibly through the ingestion of Alpha emitters via the marine food chain and possibly endangered by their accumulation during metal extraction on land.”
So if the deep-sea mining companies and processors now have to invest in additional safeguards against the radioactive risks, the costs of deep-sea mining are likely to continue to rise – and thus profitability will continue to fall.
(jl)