Dear Editor,

As discussions continue about polymetallic nodules and American Samoa’s potential role as a transshipment hub, concerns about natural radioactivity have been raised. To address these directly and transparently, I conducted an interview with Thomas Lüttke, a geoscientist formerly with the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover, Germany, and lead author of a recent peer-reviewed study published in Scientific Reports.

Lüttke’s research provides conservative, scenario-based assessments of radiation exposure for workers and nearby residents in realistic transshipment operations. The Q&A below responds to questions tailored to our local context including our tropical climate, port operations in Pago Pago, and community priorities for safety and transparency. I believe this expert perspective will help separate fact from fear and support informed public dialogue.

Q&A with Thomas Lüttke
(Based on the study: Lüttke, T., Kunze, C., Flesch, K. et al. Estimations of effective doses received from naturally occurring radioactivity in polymetallic nodules from the deep sea. Sci Rep 15, 32303 (2025). https://doi.org/10.1038/s41598-025-10842-0)

Q 1. For our audience in American Samoa who may be hearing about polymetallic nodules for the first time: in simple terms, what is the main message of your study about the natural radioactivity in these nodules?

A: Radioactivity is part of our daily lives and background radiation from environment and cosmic origin is everywhere around us. The radioactivity of polymetallic nodules is nothing new to science. Researchers have been using the naturally occurring radionuclides in nodules for decades to determine how slowly they grow, sometimes just a few millimeters over a million years. In all that time, handling nodules in a research context has never raised safety concerns, precisely because they are a natural material that scavenges trace amounts of metals and radioactive nuclides from the surrounding seawater and sediment during their growth.

Upon mining any rock radiation protection is one of many safety considerations that have to be taken care of to ensure safe work environments. The applicable term is “naturally occurring radioactive material” (NORM).

While single nodules generally do not pose any radiation risk at all, industrial scale operations will handle large amounts of nodules, which may lead to increased exposure when handled carelessly. Radiation protection aims to reduce additional exposure as much as reasonably possible and our study shows that if the nodules are handled accordingly, the exposure to workers will be very low.

Q 2. Your paper directly responds to an earlier study (Volz et al., 2023) that raised serious health concerns. What was the key misunderstanding in that earlier work, and why does it matter for places like American Samoa that are considering handling these nodules?

A: The researchers measured the activity concentrations of individual radionuclides in nodules and compared them against exemption levels that apply to materials specifically manufactured or used because of their radioactivity, such as radiation sources in medical instruments, smoke detectors, or nuclear fuels. These exemption levels were never intended for NORM like polymetallic nodules.

NORM is treated under a completely different regulatory framework. For these materials, the relevant question is not whether individual radionuclide concentrations exceed an exemption threshold, as NORM commonly exhibit elevated activity concentrations by nature. Therefore, for NORM it is of interest, what effective dose a person actually receives in a realistic exposure scenario. When you apply that correct approach, the claims of serious health risks made by Volz et al. do not hold up.

Q 3. American Samoa would likely serve as a transshipment point — nodules coming off mining ships, being stored briefly at the port, and then loaded onto bulk carriers. Based on your calculations, what radiation dose would a typical port worker or ship-crew member (e.g., stevedores, crane operators, or engine-room staff) actually receive in a realistic transshipment scenario?

A: In our assessment, we have been conservative and considered several scenarios that are rather unlikely in reality and tendentially overestimate the true radiation dose. For example, we assumed that there is no shielding provided by the driver’s cabs, i.e. workers standing at a distance of 1 meter from the stored nodules without anything in between for 400 hours per year.

One realistic scenario for elevated exposure to radon gas is the storage of nodules in closed and unventilated places. Measurements of radon were carried out in a bulk carrier containing nodules in a closed compartment and the values were very high. The easy solution to that is opening the compartments and ventilating – if for any reason a worker has to go into these compartments. One important parameter in the calculation of the radiation dose is time: Shorter exposure means lower doses.

According to our study the effective dose is expected to be below 1 Millisievert (mSv) per year, which is the international threshold for a worker to be considered as occupationally exposed to radiation. Even under conservative assumptions the effective doses will be way below 20 mSv per year, which is the annual limit for occupational exposure.

In order to make workers and also inhabitants feel safe, we advise to carry out realistic dose assessments when operations start and make them publicly available.

Q 4. In your conservative “transport vessel” scenario, you calculated only 0.7 mSv per year from gamma radiation for someone in the engine room. How does that compare to natural background radiation in American Samoa or to other common port jobs (e.g., handling phosphate, bauxite, or other ores)?

A: 0.7 Millisieverts per year is well below the occupational dose limit of 20 mSv per year for workers. To put that in context: in our scenario we assumed the engine room to be situated directly next to the storage hold, with only a few centimeters of shielding from steel and cabinets, and the worker being present for 2000 hours per year. These are deliberately conservative assumptions.

I don’t have specific background radiation figures for American Samoa, but the global average is around 2.3 mSv per year, with considerable variation depending on local geology and altitude. When comparing nodules to other bulk materials like phosphate or bauxite the effective dose at a port facility will fall within a similar range, and expected to be lower compared to our onshore scenario within a processing plant.

Q 5. You assumed nodules would be stored dry in cargo holds or port stockpiles. In our tropical climate with high humidity and frequent rain, would the actual radiation exposure (especially from radon and dust) be lower than your conservative estimates? What simple steps could keep exposure even lower?

A: Yes, and the tropical climate of American Samoa actually works in your favor here. Radon exhalation from nodules decreases as moisture content increases, so the natural humidity and rainfall will already reduce radon release compared to our conservative dry-storage assumptions. Wet nodules also generate significantly less dust.
Storing nodules in the open air is the most effective single measure, as it prevents both radon and dust from accumulating to any meaningful concentration. If enclosed storage is unavoidable for operational reasons, adequate ventilation must be ensured. Beyond that, reducing the time workers spend in direct proximity to stored nodules and wearing standard dust masks during bulk handling operations are simple and cost-effective measures that lower exposure further.

Q 6. If nodules are stored temporarily in open piles or Big Bags at the port (as is common in transshipment), what are the main exposure pathways your study identified (gamma, dust, radon)? How significant are they under real-world conditions?

A: For nodules stored in the open air in those humid climates, radon and dust are the least concerning pathways. Both disperse rapidly and do not accumulate to meaningful concentrations when there is no enclosed space to contain them. Under typical open-air port conditions they are unlikely to contribute significantly to worker exposure.

In that setting, gamma radiation is the more relevant pathway. The dose depends on four factors: the size of the stockpile, the distance between the worker and the material, any shielding in between and the aforementioned time of exposure. In our processing plant scenario we assumed a worker standing at a distance of one meter from heaps of nodules with no shielding whatsoever. In reality, port operations rely on machinery to move bulk materials, which both increases the distance between workers and the stockpile and provides additional shielding through the equipment itself. Actual exposures at a transshipment facility are therefore expected to be lower than our conservative model suggests.

Q 7. Your paper recommends standard industrial measures like wetting the material, ventilation, shielding, and personal protective equipment. Which of these would be most practical and cost-effective for a small-island transshipment hub like Pago Pago?

A: The answer depends on where workers are. For open-air stockpiles, gamma radiation is the dominant pathway and is best managed through distance and machinery, as I just described. The picture changes as soon as nodules are moved into enclosed spaces. Radiation protection is guided by the ALARA principle: exposures should be kept as low as
reasonably achievable. For a transshipment hub like Pago Pago, that translates into a small number of practical priorities.

The single most important measure is avoiding enclosed, unventilated storage. In a closed space, both radon and dust can accumulate to concentrations that are not possible in the open air, and radon in particular represents the highest potential single source of exposure in that situation. The solution is straightforward: open-air stockpiling where possible, or adequate mechanical ventilation in any warehouse.

For workers handling nodules directly during loading and unloading operations, dust is the more practical day-to-day concern. Suppressing dust through wetting with seawater is essentially cost-free given the setting, provided local environmental guidelines permit its use for this purpose. Standard dust masks during bulk handling provide an additional layer of protection.

To complement these measures, equipping storage areas with continuous air quality monitors for dust concentration and radon monitors for any enclosed areas is a transparent and relatively inexpensive step. It generates a documented record, reassures both workers and the surrounding community, and provides early warning if conditions change.

Q 8. Under German and EU rules, the key threshold for workers handling naturally occurring radioactive material (NORM) is 1 mSv per year. Your study shows that even the most conservative industrial scenarios can stay below that limit with normal safety practices. Would you expect the same outcome for American Samoan workers if international best practices are followed?

A: Yes, I would expect the same outcome. As our results show, the calculated doses remain well below the relevant thresholds even under deliberately pessimistic assumptions. Those thresholds are not specific to German or EU law but reflect the guidance of the International Commission on Radiological Protection, which forms the scientific basis for radiation protection frameworks worldwide. The conclusion therefore transfers regardless of which specific regulatory system applies in American Samoa, as long as the basic operational measures we recommend are actually implemented.

Q 9. Many people in the Pacific are understandably worried about any form of radioactivity near their homes and families. How would you reassure our community that nodule transshipment does not pose the kind of health risks that some headlines have suggested?

A: I completely understand that concern. The radionuclides present in polymetallic nodules have been part of the seafloor for millions of years. What matters for health is not whether radioactivity is detectable, but whether exposure during transshipment reaches levels that are harmful. The doses we are talking about for port workers and nearby residents are a small fraction of the natural background radiation that everyone on Earth receives every day from soil, building materials, nutrition and cosmic rays. These doses are measurable and should be measured transparently by independent parties when the operations start.

Q 10. Are there any groups of workers (e.g., longshoremen doing maintenance inside holds, or people living very close to storage areas) who would need extra monitoring or protection?

A: Workers who regularly access enclosed spaces containing nodules, such as maintenance crews working inside cargo holds, represent the group most likely to experience elevated exposure, particularly from radon. If exposure times for these tasks are significant, additional monitoring is warranted. As recommended throughout, a dedicated dose assessment using realistic variables for these specific work situations is the most reliable way to determine whether additional protective measures are needed.

For residents living in close proximity to storage areas, a separate dose assessment is equally advisable. Not because the doses are expected to be significant, but because documented evidence is the most effective way to address legitimate public concern and maintain community trust. Transparency in this regard costs little and is worth a great deal.

Q 11. What kind of radiation monitoring program would you recommend for a transshipment hub – continuous radon monitors, periodic gamma surveys, personal dosimeters for certain workers? How expensive or complicated would that be to set up?

A: Given that effective doses are expected to remain well below the 1 mSv per year threshold, a full occupational monitoring program with personal dosimeters and regular medical surveillance is not warranted. That level of infrastructure is designed for workers with meaningful radiation exposure, which is not the situation we are dealing with here.

What is practical and advisable is a more targeted approach. Before operations begin, a baseline survey of the facility establishes what background levels look like without any nodules present. Repeating that survey once transshipment is underway immediately shows whether the nodules are making any measurable difference. This is straightforward, inexpensive, and generates a documented record.

For any enclosed storage areas, radon monitors are the most relevant instrument. They are available for a few hundred dollars, require minimal technical expertise to operate, and provide continuous reassurance that ventilation is working as intended. If readings ever indicate elevated levels, the response is simple: increase ventilation or reduce the time workers spend in that space.

Q 12. Your study was done under German/EU regulations. How do those compare with U.S. or international maritime/port regulations that would apply in American Samoa? Are there any gaps or additional safeguards we should consider?

A: Our study was conducted within the European regulatory framework, specifically German radiation protection law and EU Euratom standards, which are closely aligned with IAEA international safety standards. In that sense, the scientific basis is internationally transferable even if the specific legal instruments differ.

How that translates into the specific regulatory context of American Samoa, as a US territory with a distinct legal status, is beyond my expertise. For specific guidance on US requirements I would defer to the Nuclear Regulatory Commission, who can clarify which federal and territorial regulations apply to NORM handling in a port setting.

A useful next step would be a direct regulatory mapping exercise: take the activity concentrations we measured, apply both the EU thresholds and whatever thresholds apply under US federal and territorial law, and identify explicitly whether any gaps exist. Wherever one framework is more conservative than the other, those specific points should be adopted as voluntary safeguards regardless of what local law requires.

Q 13. Looking ahead, if commercial nodule mining ramps up, what data or studies would you like to see from actual transshipment operations (perhaps right here in American Samoa) to confirm your modeling?

A: The most valuable data would come from systematic measurements during actual transshipment operations, compared against the baseline established before nodules arrive. Specifically, personal air sampling for dust concentrations in the breathing zone of workers during bulk handling, continuous radon measurements in any enclosed storage areas, and gamma dose rate surveys at varying distances from stockpiles would allow us to test directly whether our modeled estimates hold up under real conditions.

Q 14. Your paper concludes that, with standard radiation-protection measures already common in other industries, effective doses can be kept “well below” occupational limits. If American Samoa decides to move forward as a transshipment hub, what one or two pieces of practical advice would you give our local authorities and workforce?

A: Two things come to my mind: First, be as transparent about the topic as possible. Establish a baseline through independent monitoring at the facility under normal operating conditions. Then repeat those measurements during the first transshipment operations. If the numbers do not change meaningfully, that is your answer, documented and publicly accessible. If they do change, you catch it early and can respond proportionally. Building that transparency into the operating license from the start is straightforward and goes a long way toward maintaining public confidence.

Second, while Deep-Sea Mining is an emerging industry, NORM-related protocols are well established concepts in industry with decades of experience. Dust suppression, enclosed conveyor systems, basic respiratory protection during bulk handling are not exotic measures. They are standard practice in phosphate fertilizer plants, rare earth processing, and heavy mineral sand mining. For the workforce handling nodules directly, standard industrial respirators and basic dust protection are sufficient, and I would frame these not as radiation-specific measures but as general good practice for bulk mineral handling.

Q 15. Is there anything else you think the people of American Samoa should know about the radioactivity aspect of polymetallic nodules that didn’t make it into the published paper?

A: Our results show that even under conservative assumptions, the radiological contribution from nodules is a small fraction of what people already receive from natural background radiation every day. Radiation protection frameworks are deliberately built with large safety margins, and the nodules fall comfortably within those margins.

There are legitimate and serious questions surrounding deep-sea mining, ecological impacts, sediment plumes, long-term biodiversity effects. These deserve careful scrutiny and honest debate. Based on the current state of evidence, however, radioactivity is not on that list. It is a concern I understand completely given the associations the word carries, but one that the data, at this point, does not support.

Thomas Lüttke
Geoscientist, formerly Federal Institute for Geosciences and Natural Resources (BGR),
Hannover, Germany
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This interview addresses one specific technical question: the level of naturally occurring radioactivity associated with handling and transshipment of polymetallic nodules. It does not cover the broader and equally important considerations including environmental stewardship, fisheries protection, and community decision-making that remain central to any discussion of deep-sea minerals in American Samoa.

In closing, as a community we are best served by remaining committed to openness, independent verification, and trust in the information we receive. The science shows that radioactivity risks from nodule transshipment are low and can be managed effectively through standard, low-cost industrial practices already used successfully in other bulk material industries. I encourage continued questions and open dialogue as we thoughtfully work through these issues as a community.

Sincerely,
Michael McDonald