# Which radionuclides contribute most to seafood ingestion dose ?

Mathew P Johansen, Justin P Gwynn, Julia G Carpenter, Sabine Charmasson, Airi Mori, Blake Orr, Marie Simon-Cornu, Iolanda Osvath, Paul Mc Ginnity

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Mathew P Johansen, Justin P Gwynn, Julia G Carpenter, Sabine Charmasson, Airi Mori, et al.. Which radionuclides contribute most to seafood ingestion dose?. Journal of Environmental Radioactivity, 2025, 287, pp.107706. 10.1016/j.jenvrad.2025.107706. hal-05216955

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# Which radionuclides contribute most to seafood ingestion dose?

Mathew P. Johansen<sup>a,*</sup>, Justin P. Gwynn<sup>b</sup>, Julia G. Carpenter<sup>c</sup>, Sabine Charmasson<sup>d</sup>, Airi Mori<sup>e</sup>, Blake Orr<sup>c</sup>, Marie Simon-Cornu<sup>f</sup>, Iolanda Osvath<sup>g</sup>, Paul Mc Ginnity<sup>g</sup>

## ARTICLE INFO

### Keywords:

Seafood consumption

Radiological ingestion dose

Polonium-210

Radionuclide levels in seafood

ICRP dose coefficients

## ABSTRACT

Radiological ingestion doses from eating seafood are regularly evaluated near coastal nuclear facilities, following accidents/events and frequently in national studies worldwide. However, a recent global review found that published seafood doses varied greatly depending on which radionuclides were selected for evaluation and that there has been a tendency to omit important radionuclides or focus on less significant ones. This indicates a need for clear guidance on which radionuclides to prioritise in such studies. Here, we use worldwide data for 16 key radionuclides contributing to typical background seafood ingestion dose. We account for the loss of radionuclides during cooking and the radioactive decay of the short-lived <sup>210</sup>Po.

Results indicate that for the typical world consumer, naturally-occurring radionuclides account for >99 % of the total seafood ingestion dose, of which about 84 % comes from <sup>210</sup>Po and 8 % from <sup>210</sup>Pb. About 5 % comes from <sup>228</sup>Ra, a far greater proportion than the more frequently-assessed <sup>226</sup>Ra (<1 %). Other Th- and U-series radionuclides provide far lower contributions (0.07 %–0.70 %), while <sup>14</sup>C provides about 0.09 %. In comparison, the contribution to total seafood ingestion dose from background anthropogenic radionuclides is <1 %, with <sup>137</sup>Cs contributing most (0.08 %) and <sup>90</sup>Sr, <sup>99</sup>Tc, <sup>110m</sup>Ag and <sup>239</sup>Pu adding a further 0.05 % together. These percentage contributions to dose can vary somewhat depending on consumption patterns (e.g., differing proportions of fish, bivalves, etc.). However, <sup>210</sup>Po is the dominant contributor irrespective of country-specific diets or restricted diet scenarios (fish-only, seaweed-only, etc.). Study results provide new guidance to improve the design, interpretation and communication of seafood ingestion dose assessments.

## 1. Introduction

Numerous radionuclides are typically present in the tissues of marine organisms, each contributing to total ingestion dose when humans consume seafood. However, their relative contributions to ingestion dose vary greatly—ranging over many orders of magnitude—due to differences in their activity concentrations in seafood (IAEA, 2023), differing absorption rates after ingestion (ICRP, 2012) and also the variation in their emission types and energies (Delacroix et al., 2002).

Many radionuclides have been flagged as important for the

assessment of seafood ingestion dose including the naturally-occurring radionuclide <sup>210</sup>Po which was highlighted as a main dose contributor as early as the 1970s (Heyraud and Cherry, 1979) and subsequently recognised as globally significant in the 1990s (Aarkrog et al., 1997; Carvalho, 1995; IAEA, 1995). Various studies have reported that <sup>210</sup>Po contributes from 75 % to 99 % of total seafood ingestion doses (e.g., Aarkrog et al., 1997; Hassona et al., 2008; Komperad et al., 2020; McDonald et al., 1993). However, the relative contribution of <sup>210</sup>Po depends on which other radionuclides are selected for assessment, and these vary widely among published studies.

<footnote><sup>a</sup> Australian Nuclear Science and Technology Organisation, Kirrawee DC, 2232, NSW, Australia</footnote>

<footnote><sup>b</sup> Norwegian Radiation and Nuclear Safety Authority, The Fram Centre, Tromsø, Norway</footnote>

<footnote><sup>c</sup> Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), Yallambie, VIC, 3085, Australia</footnote>

<footnote><sup>d</sup> French Authority for Nuclear Safety and Radiation Protection (ASNR), PSE-ENV/STAAR/LRTA 13115 Saint Paul lez Durance, France</footnote>

<footnote><sup>e</sup> Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki, 319-1195, Japan</footnote>

<footnote><sup>f</sup> French Authority for Nuclear Safety and Radiation Protection (ASNR), PSE-ENV/SERPEN 13115 Saint Paul lez Durance, France</footnote>

<footnote><sup>g</sup> IAEA Marine Environment Laboratories, Department of Nuclear Sciences and Applications, IAEA, 4 Quai Antoine 1er, 98000, Monaco</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: Mathew.Johansen@ansto.gov.au (M.P. Johansen), justin.gwynn@dsa.no (J.P. Gwynn), Julia.Carpenter@arpansa.gov.au (J.G. Carpenter), sabine.charmasson@asnr.fr (S. Charmasson), mori.airi@jaea.go.jp (A. Mori), Blake.orr@arpansa.gov.au (B. Orr), marie.simoncornu@asnr.fr (M. Simon-Cornu), I. Osvath@iaea.org (I. Osvath), P.Mc-Ginnity@iaea.org (P. Mc Ginnity).</footnote>
In addition to $^{210}$Po, other naturally-occurring radionuclides often listed as important for seafood dose include $^{210}$Pb, $^{226}$Ra and $^{232}$Th, appearing in 30%, 25% and 17% of assessments respectively in a recent global review of seafood dose studies (Johansen et al., 2024). Many additional radionuclides from predominantly natural sources are ubiquitous in marine systems and have been variably applied to such studies (e.g., $^{14}$C, $^{22}$Na, $^{228}$Ra, $^{228}$Th, $^{230}$Th, $^{234}$U, $^{238}$U among others, see SI for an extended list). The anthropogenic radionuclide $^{137}$Cs appears in about 40% of seafood dose assessments (Johansen et al., 2024) due to its radiological significance in routine and accidental releases from nuclear facilities, its background presence due to global fallout and its relative ease of measurement. Other radionuclides of predominantly anthropogenic origin (e.g., $^{3}$H, $^{90}$Sr, $^{60}$Co, $^{99}$Tc, $^{131}$I, $^{134}$Cs, $^{110}$mAg, $^{239}$Pu and $^{241}$Am among others, see SI for an extended list) have been assessed as they can be present in seafood after discharges from nuclear power plants (NPPs), research reactors, radiopharmaceutical production, and other nuclear facility releases (e.g., CEFAS, 2023; IRSN, 2023; Renaud et al., 2015; Sun et al., 2021; Takata et al., 2019; Veliscek Carolan et al., 2011; Wada et al., 2016; Whicker, 1982).

Given the many different radionuclides that can be present in seafood and their highly variable contributions to ingestion dose, selecting which radionuclides to include in seafood dose assessments can be challenging. A recent review of 124 seafood dose studies worldwide found that important radionuclides were frequently omitted. For example, 20 recently published seafood dose studies omitted the more dose-important $^{210}$Po, while focusing instead on less significant naturally-occurring radionuclides (e.g., $^{226}$Ra and $^{232}$Th) leading to the underestimation of dose by large margins (Johansen et al., 2024). Across such studies, published dose estimates vary by many orders of magnitude due largely to the assessment's selection or omission of radionuclides, which reflects methodological uncertainty rather than real-world factors (Johansen et al., 2024).

The omission of dose-important radionuclides and the wide variation in published seafood ingestion dose estimates highlights that, despite more than five decades of study, no publication has provided guidance on which radionuclides should be prioritised in such studies. While there is some guidance on the contributions of various radionuclides to ingestion doses across all foods not limited to marine sources (e.g., IAEA, 2021), similar recommendations specifically for seafood are lacking.

In this paper, we establish reference data on the relative contributions to ingestion dose from the radionuclides commonly found in seafood. We test for the relative importance of anthropogenic vs naturally-occurring radionuclides in normal background conditions for the typical global seafood diet as well as across specific national diets and seafood consumption scenarios. Sixteen radionuclides (screened from 62) are evaluated taking into account loss from cooking along with the decay of $^{210}$Po that may occur before consumption due to its relatively short half-life. This paper provides important guidance for improving the design of seafood ingestion dose assessments leading to better interpretation and communication when evaluating the risk of routine and accidental radiological releases to the marine environment.

## 2. Methods

Sixty-two radionuclides were initially screened and evaluated based on their use in previously published seafood dose studies (Johansen et al., 2024) and from marine monitoring programs as recorded in the global IAEA Marine Radioactivity Information System (MARIS; IAEA, 2023). A listing of all 62 radionuclides is included in the SI, along with their categorisation with respect to the following screening criteria for this study.

* Include naturally-occurring radionuclides that provided more than ~0.1% (1/1000th) of total seafood ingestion dose based on an initial extraction of their activity concentration data from MARIS (edible portions, accessed 2021).

* Include commonly monitored anthropogenic radionuclides that provided more than ~0.01% (1/10,000th) of total seafood ingestion dose based on an initial download of their activity concentration data from MARIS (edible portions, accessed 2021).

* Exclude other radionuclides that monitoring data indicate are sometimes detected but are not widely present in global seafood supplies at significant levels due to their infrequent production/ release (e.g., $^{54}$Mn, $^{65}$Zn, $^{144}$Ce) and/or their short half-lives (e.g., $^{106}$Ru, $^{131}$I, $^{134}$Cs).

Following screening, 16 radionuclides were retained for further analysis including 11 radionuclides from predominantly natural sources ($^{14}$C, $^{210}$Po, $^{210}$Pb, $^{224}$Ra, $^{226}$Ra, $^{228}$Ra, $^{228}$Th, $^{230}$Th, $^{232}$Th, $^{234}$U and $^{238}$U), and five anthropogenic radionuclides ($^{90}$Sr, $^{99}$Tc, $^{110}$mAg, $^{137}$Cs, and $^{239}$Pu). For this study on generic background conditions, the five anthropogenic radionuclides that passed screening are generally detectable in seafood, but often at very low activity concentrations. Detecting such low levels of these radionuclides can require radiochemical pre-concentration and/or highly sensitive analytical methods (e.g., accelerator mass spectrometry for Pu isotopes in marine organisms such as in Hamilton et al., 2008; Johansen et al., 2020; Mietelski et al., 2008). $^{14}$C is grouped with the naturally-occurring radionuclides because we estimate that only approximately 5–10% of the $^{14}$C in the upper layers of oceans/seas (and by extension in seafood) is as a result of human activities such as nuclear weapons testing (derived from Graven et al., 2012; Lassey et al., 1996; Pookkandy et al., 2023). Similarly, some human activities (e.g., offshore oil and gas production and processing of phosphate ore) can give rise to additional sources of other naturally-occurring radionuclides (e.g. $^{210}$Po, $^{210}$Pb, $^{226}$Ra and $^{228}$Ra). These are also referred to here as “naturally-occurring” because while such discharges are not insignificant (MacIntosh et al., 2022), their impacts are highly localised against the overall dominant natural background inventories of the same radionuclides in the marine environment (Belahbib et al., 2025; OSPAR, 2022).

Of the radionuclides that did not pass our screening, some can still be important for seafood dose on local or acute scales. These include $^{131}$I, which can be important for specific discharge locations and limited time periods but does not persist in the marine environment in the long term due to its short 8-day half-life (Veliscek Carolan et al., 2011). $^{134}$Cs was present in releases from Fukushima and Chernobyl and can be a significant contributor to dose in interim timeframes (for longer periods than $^{131}$I), but, with a 2.1-year half-life, it is not generally detectable in the typical background conditions and for seafood as assessed here. $^{3}$H was also excluded as our screening calculations indicated that its background contribution to seafood ingestion dose was minuscule, although this can vary locally depending on the nature of specific discharges (Akata et al., 2024; Bezhenar et al., 2021) with elevated levels in some coastal waters (Fiévet et al., 2020; Ma et al., 2024). Although these radionuclides were excluded from this study based on our screening criteria, these and other discharged radionuclides should not be excluded from seafood ingestion dose assessments (based on this paper) for specific situations where they are known or expected to be present at higher concentrations.

The radionuclide $^{40}$K is ubiquitous in the environment and an important component of overall ingestion dose from total foods and water (IAEA, 2021). However, it has been inappropriately factored into some seafood ingestion dose studies owing to the levels of potassium in the body (including $^{40}$K) being regulated under homeostatic control. Therefore, the $^{40}$K ingestion dose is relatively constant (~0.17 mSv for a typical adult) regardless of whether or not seafood is consumed. As a result, by convention, $^{40}$K is normally not included in the ingestion dose estimates for specific food categories such as seafood, but rather added separately in total foods studies (IAEA, 2021).

For the selected 16 radionuclides of potential significance, the activity concentrations for this study were sourced from worldwide locations via the IAEA MARIS database (final access 2024, https://maris.ia
ea.org/home/news/2145). Activity concentrations were assembled for the six seafood categories of fish, crustaceans, bivalves, gastropods, cephalopods and seaweed. Multiple seafood categories are needed because radionuclide accumulation rates differ greatly depending on seafood type. The six seafood categories encompass the types of seafood commonly consumed worldwide. Exceptions can include consumption of marine mammals (e.g., whale and seal) (Gwynn et al., 2012; Hansen et al., 2022), seabirds and their eggs and echinoderms (e.g., sea urchins and sea cucumber) (Elvevoll et al., 2022; MHLW, 2019; Sirot et al., 2009). However, data for these additional seafoods are scarce and consumption is often limited to specific groups with small populations which are best assessed separately (Gwynn et al., 2012; Hansen et al., 2022; Inkret et al., 2000). Within the six seafood categories used here, the Bq kg⁻¹ data (in fresh mass of the edible portions) can vary widely and therefore the data are represented as distributions (see SI). As this study is on typical background conditions, data from near major discharge locations and accidents were excluded. The ²¹⁰Po data were corrected for losses between catch and consumption (decay and cooking losses) using the factors in Johansen et al. (2023). Specifically, a decay loss factor of 0.19 (0.81 retained) was applied for ²¹⁰Po, which represents a generic mix of fresh, frozen, canned, dried and smoked preservation methods based on global data (see Supplement for cooking factor data).

Because the main purpose of this study is to describe background or typical conditions, the main scenario considered here is based on the typical, average consumption profile for the world population based on a series of science papers listed in the SI and UN Food and Agriculture Organisation (FAO) data and reports such as Cai and Leung (2017). From these, the average consumption proportions used here are 63.6 % fish, 12.0 % Crustaceans, 13.1 % Bivalves, 2.1 % Gastropods, 4.0 % cephalopods and 5.2 % Seaweed. However, seafood consumption patterns vary across different populations and, to address this, five additional examples are assessed based on dietary survey data from China, France, Japan, Portugal and the United Kingdom (see SI). These countries were selected because diet survey data are available for all six seafood categories including valid survey data for seaweed consumption which is lacking for most other national populations. In addition, we consider a series of bounding scenarios in which a consumer eats exclusively from only one of the six different seafood categories (fish-only, crustaceans-only, etc.). Although most consumers do not limit themselves to only one type of seafood, these scenarios provide estimates on the variation in results that could be caused by seafood diet preferences.

Given the many data distributions involved, the basic ingestion dose equation (see SI) was solved in a Monte Carlo framework using Goldsim® software (www.Goldsim.com). For each scenario, 10,000 realisations were made to ensure robust representation across the Bq kg⁻¹ data distributions for the various radionuclide-seafood type combinations. As an example, the calculation for ²¹⁰Po in a single realisation is: [(fish consumption fraction) x (²¹⁰Po activity concentration) x (²¹⁰Po DCF) + repeat across all seafoods]. Then, the % contribution for ²¹⁰Po was simply calculated compared to the total dose from all 16 radionuclides. It follows that a higher % dose contribution from ²¹⁰Po would result if the population being assessed consumes a higher proportion of the seafood types with elevated ²¹⁰Po levels (e.g., bivalves). The dose coefficients for ingestion (or dose conversion factors, DCFs, used here interchangeably with “dose coefficients”) were sourced from the ICRP (2012). The DCFs include the doses from the radioactive progeny produced in vivo following ingestion. Further, since the DCFs for an adolescent (10 yrs) are different than those for adults, we have assessed how the proportional contributions of the various radionuclides to a seafood ingestion dose for an adolescent would compare with those for an adult.

This paper is focused on the specific objective of determining which radionuclides are important for seafood dose and quantifying their typical % contributions. The approach is such that the results

appropriately do not depend on the total amount of seafood ingested (results are valid whether the consumer eats 1 kg, 10 kg or 50 kg, etc. of seafood per year). It therefore does not include the estimation of current worldwide seafood ingestion dose levels (e.g., mSv per annual intake) as that topic requires additional global dietary data. In addition, a compilation of worldwide seafood ingestion doses from previous studies (1980–2024) has already been published in Johansen et al. (2024).

# 3. Results and discussion

## 3.1. World-representative seafood diet

The main study result indicates that the contributions from three radionuclides, ²¹⁰Po (84.1 %), ²¹⁰Pb (8.4 %) and ²²⁸Ra (5.1 %) make up more than 97 % of the total ingestion dose for the world-representative seafood diet (Fig. 1). The 84 % result for ²¹⁰Po clarifies previous estimates ranging from 75 % to 99 % (e.g., Aarkrog et al., 1997; Hassona et al., 2008; Komperad et al., 2020; McDonald et al., 1993), with the main difference being that this study assessed a broader range of radionuclides and seafood types and used the extensive available global activity concentration data in MARIS. The uncertainty around the ²¹⁰Po contribution of 84 % ranges from 72 % to 90 % for the 25th–75th percentiles and 52 % to 96 % for the 5th–95th percentiles, reflecting for the world typical diet the inherent variation in reported Bq kg⁻¹ activity concentrations across global data in the six seafood types.

## 3.2. Selected national diets

The main result here (Fig. 1) is for a typical world-representative seafood diet pattern consisting of six seafood types at proportions matching world average consumption data (see methods and SI). The results in Fig. 1 are relative and apply equally whether a consumer ingests small or large amounts of seafood (e.g., 1, 10 or 50 kg yr⁻¹). However, because radionuclides accumulate at differing rates in different types of seafood, their % contributions to ingestion dose are influenced by the relative proportions of the six seafood groups consumed (fish vs crustaceans vs bivalves, etc.). Such patterns in seafood diets vary between different world populations. When applying the seafood dietary data from China, France, Japan, Portugal and the United Kingdom (countries from which diet survey data are available for all seafood categories including seaweed), the overall result is that their profiles are similar to that of the typical world-representative seafood diet with some relatively minor differences across the various radionuclides (Fig. 2).

In these country-specific seafood diets, the relative dose contributions from ²¹⁰Po ranged from 77 % to 87 %, with Japan and China being the lowest and highest respectively. This result is consistent with higher bivalve/gastropod consumption in China than in the other assessed countries (MHLW, 2019; Wang et al., 2022). However, for ²¹⁰Pb, the highest contribution (12 %) was in the Japanese diet reflecting proportionally higher fish and seaweed consumption (MHLW, 2019). While the UK diet contains a relatively low seaweed consumption rate, its proportion of fish consumption is relatively high and thus ranked highest of the diets for the percentage contribution of ¹³⁷Cs, which tends to accumulate in fish muscle to a higher degree than the other assessed radionuclides (IAEA, 2023). For some countries, the relative contribution from ¹³⁷Cs would be higher than the baseline estimate given here if, for example, their seafood is sourced from areas impacted by Chernobyl fallout. See supplemental for further data on the national seafood diet analysis.

Overall, the analysis of the five representative national seafood diets supports the generic world estimate with the relatively minor differences resulting from their respective national seafood diet trends. Additional country-specific analyses should be pursued, provided that consumption data are available across all six seafood categories assessed in this study.
<figure><img src="image_2.png" /><figcaption>**Fig. 1.** (A) Percentage contributions to seafood ingestion dose from 16 radionuclides and assuming a typical world-representative seafood diet pattern (see Methods). The insert (B) repeats the same results using a log scale for the y-axis to fully display the whisker bars which indicate 25th and 75th percentiles. Anthropogenic radionuclides ($^{137}$Cs, $^{90}$Sr, $^{99}$Tc, $^{110}$Ag and $^{239}$Pu) are shown in lighter blue. See SI for details. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Range of dose contributions when considering the representative diets from China, France, Japan, Portugal and the United Kingdom as compared to the typical world-representative seafood diet. The vertical axis uses a log scale. The five anthropogenic radionuclides ($^{137}$Cs, $^{90}$Sr, $^{99}$Tc, $^{110}$Ag and $^{239}$Pu) are grouped on the right.</figcaption></figure>

### 3.3. Individual seafoods

The influence of diet choice on results was further investigated by assessing individual seafood category diets (e.g., fish-only, crustaceans-only, etc.). Most seafood consumers do not limit themselves to one type of seafood. However, some dose studies consider single-category seafood consumption (e.g., CEFAS, 2023; Dewar et al., 2021) and the use of

such diets are presented here mainly for the purpose of better understanding the range of possible dose-contribution profiles.

The main result is that $^{210}$Po is still the dominant contributor to seafood ingestion doses regardless of the individual seafood category eaten (Fig. 3). The highest dose contribution from $^{210}$Po was from the bivalve-only diet (94 %). Firstly, this reflects the fact that bivalves can accumulate comparatively higher $^{210}$Po activity concentrations due to
<figure><img src="image_4.png" /><figcaption>Fig. 3. Proportions of ingestion dose from $^{210}$Po, $^{210}$Pb, $^{224}$Ra and other radionuclides under the highly-specific seafood diets of Fish-only, Bivalves-only, and Seaweed-only. See SI for other diet categories.</figcaption></figure>

the adsorption of $^{210}$Po to small particles/nekton that can then be trapped by their filter feeding behaviours (Carvalho, 2011; Uddin and Behbehani, 2014). Secondly, part of the typical consumption practice when eating bivalves is to consume all soft tissues, including the hepatopancreas and digestive tracts in which most of the bioaccumulated $^{210}$Po resides. In contrast, lower dose contributions from $^{210}$Po occur in the cephalopod-only and seaweed-only diets (61 % and 68 %). Although $^{210}$Po accumulates in cephalopods (Bustamante et al., 2023), it is primarily concentrated in their internal organs, with only minimal amounts observed in the commonly consumed mantle and other edible tissues (Carvalho, 2011). Seaweeds, as primary producers lack a dietary intake pathway and tend to accumulate comparatively low levels of $^{210}$Po with only minor differences in activity concentrations among consumed parts (Collison, 2025). The fish-only diet also had relatively low contributions from $^{210}$Po (75 %) (and relatively higher levels of $^{210}$Pb) as the fish muscle tends to have lower $^{210}$Po activity concentrations than the edible parts of crustaceans, bivalves, and gastropods (Carvalho, 2011; IAEA, 2023).

### 3.4. $^{210}$Pb and other natural radionuclides

When focusing on $^{210}$Pb, study results indicate that it contributes significantly to seafood dose at ~8 % in the world-representative seafood diet and 7–12 % among the country-specific diets. When assessing category-only diets, the highest relative $^{210}$Pb contribution is in the Cephalopod-only diet (26 %), followed by fish-only (13 %) and seaweed-only (12 %).

For $^{228}$Ra, its ~5 % contribution to seafood ingestion dose is important in the world representative seafood diet and rises to 8–11 % in the fish-only, cephalopod-only, and seaweed-only diets, but is relatively low for bivalve and gastropod-only diets (<1 %). In terms of guidance for the design of seafood dose assessments, a significant finding of this study is that $^{228}$Ra has a greater contribution to total seafood ingestion doses than $^{226}$Ra. Despite this, $^{226}$Ra is more frequently measured in marine monitoring programs such as the nearly four times more $^{226}$Ra than $^{228}$Ra edible tissues data available for this study (IAEA, 2023). The meagre contribution of $^{226}$Ra in the world-representative seafood diet (~0.73 %) is comparable with that of $^{232}$Th (0.69 %) and $^{224}$Ra (0.45 %). Combined, these three radionuclides ($^{224}$Ra, $^{226}$Ra and $^{232}$Th) only contribute about 2.0 % on average to the total seafood ingestion dose and a combined maximum of about 5 % when considering category-only

diets (seaweed-only diet). Their individual contributions in the category-only diets equalled or surpassed 1 % in only the following diet scenarios: fish-only ($^{232}$Th = 1.3 %), cephalopod-only ($^{224}$Ra = 1.0 %) and seaweed-only ($^{226}$Ra = 3.0 % and $^{224}$Ra = 1.0 %).

Of the remaining U and Th series radionuclides, $^{228}$Th, $^{230}$Th, $^{234}$U and $^{238}$U together contribute about 0.3 % of total seafood ingestion dose on average and in only one of the category-only diets does their individual contribution surpass 1 % ($^{228}$Th = 1.6 %, seaweed-only diet).

$^{14}$C is a much-studied radionuclide (Hua et al., 2022) and while it is ubiquitous in oceans and seafood (Graven et al., 2012; IAEA, 2023), its dose contribution is relatively minor at about 0.09 %. In normal background situations, almost all this minor contribution comes from naturally-occurring $^{14}$C (90–95 % in 2020 by our estimate—see methods) rather than anthropogenic sources such as nuclear weapons testing or discharges from nuclear facilities.

### 3.5. Anthropogenic radionuclides

Results indicate that for background conditions and the world-representative seafood diet (in the 2010–2020 timeframe), the combined contribution from the five selected anthropogenic radionuclides is about 0.1 % (1/1,000th) of the overall total seafood ingestion dose. Of these, $^{137}$Cs has the highest contribution at about 0.08 % with $^{90}$Sr, $^{99}$Tc, $^{110}$mAg and $^{239}$Pu each contributing <0.02 % (Fig. 1). In the category-only diets, the contributions of the anthropogenic radionuclides were similarly low but variable with the highest single contribution at 0.16 % from $^{137}$Cs in the fish-only diet. This is consistent with observed data indicating most $^{137}$Cs in fish is concentrated in the edible muscle tissues (~73 %) compared with other anthropogenic radionuclides such as $^{90}$Sr which demonstrate far lower accumulation in the muscle tissues (Iwata et al., 2013; Johansen et al., 2015; Tateda et al., 2015).

While the above results are for normal background conditions the relative dose contribution from anthropogenic radionuclides can increase locally after accidents or other releases. The highest published values of such site-specific ingestion doses were to critical groups living near the Sellafield nuclear fuel reprocessing facility in the UK during the 1970s when authorised discharges were at far higher levels than they are today. In this situation, almost the entire seafood ingestion dose (approaching 100 % of the dose) was due to the anthropogenic radionuclides that had been discharged at that time (peak doses were estimated to be 2–3 mSv for annual seafood ingestion; Hunt, 1997; Jackson
et al., 2000).

Releases from the Chernobyl accident led to increased levels of anthropogenic radionuclides in the Baltic Sea—especially $^{134,137}$Cs. At their peak levels in Baltic Sea seafood, the Chernobyl-derived radionuclides contributed about 50–60 % of the total seafood ingestion dose, with the remainder coming from the usually dominant naturally-occurring radionuclides (peak doses were estimated to be about 0.2 mSv for annual seafood ingestion in 1986 (Nielsen et al., 1999)).

After the accident at the Fukushima Daiichi NPP (FDNPP), when taking into account the seafood actually available in the marketplace in Japan (after fishing and food restrictions), estimates of the contribution of anthropogenic radionuclides from the accident releases to total seafood ingestion doses were very low (e.g., about 0.002–0.004 mSv per annual intake; Terada et al., 2020; Mori et al. 2025). Across a number of such assessments on typical Japanese consumers, the additional anthropogenic radionuclides released from the accident only contributed <5 % of the assessed total seafood ingestion doses (summarised in Johansen et al., 2024). Even in the first years after the accident, total seafood ingestion doses were still dominated by the contribution from naturally-occurring radionuclides. Additionally, some studies considered hypothetical scenarios in which consumers were assumed to consistently eat fish from the restricted local areas near the FDNPP (Johansen et al., 2015; Povinec and Hirose, 2015). These are considered to be upper bounding estimates, which are often evaluated in dose assessments, and suggest that at most, during 2011–2013, about 50 % of the total seafood ingestion doses could have come from released radionuclides even in the hypothetical scenario of eating fish from restricted areas as close as 3 km to the FDNPP (summarised in Johansen et al., 2024).

Overall, the historical occurrence of waste discharges and accidental releases to the marine environment indicate that it is possible for anthropogenic radionuclides to give rise to localised seafood ingestion doses at levels that equal or exceed that from background levels of naturally-occurring radionuclides, particularly when corrective measures are not applied (e.g., discharge controls, monitoring and restrictions on fishing/consumption).

### 3.6. Implications of omitting $^{210}$Po, $^{210}$Pb and $^{228}$Ra

In recent publications, a significant proportion of studies focused on the seafood ingestion dose derived from minor natural radionuclides, especially $^{226}$Ra and $^{232}$Th, while excluding the more dose-important naturally-occurring radionuclides ($^{210}$Po and $^{210}$Pb). The main reason for this appears to be that $^{226}$Ra and $^{232}$Th are often considered to be easy to measure via gamma spectrometry (although in practice this can be challenging), while $^{210}$Po and $^{210}$Pb require more involved radiochemical analysis methods when assessing levels in seafoods. As the body cannot selectively absorb only $^{226}$Ra and $^{232}$Th, including only these radionuclides accounts for only ~1 % of the total seafood ingestion dose. A potential consequence of such fractional estimates is that the total seafood doses are vastly underestimated (by ~99 % when considering only $^{226}$Ra, $^{232}$Th) and, when published, may cause misunderstanding in assessing risk. When including naturally-occurring radionuclides in any seafood ingestion dose assessment, we recommend including $^{210}$Po, $^{210}$Pb and $^{228}$Ra at a minimum. This ensures that about 97 % (92 % to 99 % for various diets) of total seafood ingestion dose is captured depending on the seafood diet of the study population. If additional refinement is needed, we recommend adding $^{224}$Ra, $^{226}$Ra and $^{232}$Th.

Environmental impact assessments on radiological risk often focus on released anthropogenic radionuclides (e.g., $^{137}$Cs) and on the seafood dose increases specific to those releases (e.g., Men et al., 2020; Terada et al., 2020). Such studies are important for assessing the safety of nuclear facility operations. While it is not necessary for these studies to also calculate the seafood ingestion dose contribution from background levels of naturally-occurring radionuclides, doing so allows for a useful

comparison of the doses from the releases to that from the natural background as has been done in numerous studies (e.g., Deiaa et al., 2020; Fisher et al., 2013; Gwynn et al., 2012; Johansen et al., 2015; Povinec and Hirose, 2015; Urban et al., 2015; Wesley and Khan, 2012). In such comparisons, we recommend including $^{210}$Po, $^{210}$Pb, and $^{228}$Ra at a minimum when selecting natural radionuclides to evaluate. The inclusion of these prioritised naturally-occurring radionuclides is also paramount when assessing the local or acute impact on seafood ingestion doses from discharges of naturally-occurring radionuclides associated with human activities.

### 3.7. Adolescent (~10yr old) consumer

When considering the adolescent seafood consumer of about 10 yrs age, the relevant ICRP dose coefficients are different to those for adults. Elevated gastrointestinal absorption of the alkaline earth elements can occur during periods of rapid growth (ICRP, 1993). When applying adolescent DCFs, $^{210}$Po is still the dominant contributor to total seafood ingestion dose, but at a lower proportion (~75.9 %) than that of an adult. The difference is due to the relatively higher adolescent DCFs for $^{210}$Pb and $^{228}$Ra which respectively contribute 9.7 % and 12.1 % (higher than for adults, Table 1). Given these differences, it is useful to include adolescent specific calculations in seafood dose ingestion studies.

### 3.8. Effect of proposed changes to ICRP ingestion dose coefficients

The ICRP has reviewed the derivation of DCFs for ingestion by members of the public and has proposed updated DCF values in consultation processes which completed in 2024 (https://www.icrp.org/consultations.asp). The proposed DCF values are publicly available and include updated coefficients for $^{210}$Po, $^{210}$Pb, and $^{228}$Ra (the radionuclides that are most important for seafood ingestion dose). However, because the new values cannot be referenced at the time of writing this paper, we cannot include detailed information here on the effect these changes may have on the results of this study. We repeated the evaluation presented here using the proposed new DCFs, and in general terms, the overall conclusions—that the typical seafood ingestion dose derives overwhelmingly from natural radionuclides, with the greatest contributions from $^{210}$Po, $^{210}$Pb, and $^{228}$Ra— remain largely unchanged, although the specific contribution amounts would change. Of potentially greater significance is that any changes in the proposed DCFs of $^{210}$Po, $^{210}$Pb, and $^{228}$Ra would be strongly reflected in the results of any

<caption>Table 1</caption>

Contributions from individual radionuclides to total seafood ingestion dose for 1) Adult and Adolescent (~10 yrs). The 25th to 75th range indicated for Adult reflects the variation in the activity concentrations of the 16 radionuclides assessed in world seafood. All values in this table relate to a typical world diet. Data for diet differences is presented elsewhere in the text and in the SI.

<table><thead><tr><th rowspan="2"></th><th colspan="2">Adult</th><th>Adolescent</th></tr><tr><th>50th</th><th>25th - 75th</th><th>50th</th></tr></thead><tbody><tr><td><sup>210</sup>Po</td><td>84.1 %</td><td>71.9 % - 89.5 %</td><td>75.9 %</td></tr><tr><td><sup>210</sup>Pb</td><td>8.4 %</td><td>3.1 % - 13.6 %</td><td>9.7 %</td></tr><tr><td><sup>228</sup>Ra</td><td>5.1 %</td><td>2.8 % - 9.9 %</td><td>12.1 %</td></tr><tr><td><sup>226</sup>Ra</td><td>0.73 %</td><td>0.32 % - 1.20 %</td><td>0.87 %</td></tr><tr><td><sup>232</sup>Th</td><td>0.69 %</td><td>0.07 % - 0.94 %</td><td>0.37 %</td></tr><tr><td><sup>224</sup>Ra</td><td>0.45 %</td><td>0.25 % - 0.88 %</td><td>0.75 %</td></tr><tr><td><sup>238</sup>U</td><td>0.11 %</td><td>0.06 % - 0.20 %</td><td>0.07 %</td></tr><tr><td><sup>228</sup>Th</td><td>0.09 %</td><td>0.04 % - 0.15 %</td><td>0.07 %</td></tr><tr><td><sup>14</sup>C</td><td>0.09 %</td><td>0.07 % - 0.16 %</td><td>0.05 %</td></tr><tr><td><sup>230</sup>Th</td><td>0.07 %</td><td>0.05 % - 0.13 %</td><td>0.03 %</td></tr><tr><td><sup>234</sup>U</td><td>0.07 %</td><td>0.03 % - 0.10 %</td><td>0.04 %</td></tr><tr><td><sup>137</sup>Cs</td><td>0.076 %</td><td>0.012 % - 0.096 %</td><td>0.025 %</td></tr><tr><td><sup>90</sup>Sr</td><td>0.017 %</td><td>0.005 % - 0.019 %</td><td>0.015 %</td></tr><tr><td><sup>99</sup>Tc</td><td>0.011 %</td><td>0.003 % - 0.018 %</td><td>0.009 %</td></tr><tr><td><sup>110m</sup>Ag</td><td>0.011 %</td><td>0.003 % - 0.023 %</td><td>0.008 %</td></tr><tr><td><sup>239</sup>Pu</td><td>0.009 %</td><td>0.003 % - 0.014 %</td><td>0.005 %</td></tr></tbody></table>
seafood dose assessment because of the predominance of these three radionuclides in such studies. We, therefore, recommend that, when any new proposed DCFs become available for reference, an evaluation is performed that details the changes in % contributions of radionuclides to ingestion dose as well as the magnitude of the changes in ingestion dose estimates.

## 4. Conclusions

Results indicate that for the typical world consumer, naturally-occurring radionuclides account for >99 % of the total seafood ingestion dose. Typically, about 84 % of the total seafood ingestion dose comes from $^{210}$Po, with an additional ~8 % derived from $^{210}$Pb. Of the Ra radionuclides, $^{228}$Ra contributes to a greater degree (~5 %) than the more frequently-assessed $^{226}$Ra (0.7 %). The other Th- and U-series radionuclides provide smaller fractional dose contributions (all <1.0 %), while $^{14}$C provides about 0.09 %. Of the anthropogenic radionuclides that we evaluated in normal background situations, $^{137}$Cs has the greatest contribution to total seafood dose (~0.08 %), with $^{90}$Sr, $^{99}$Tc $^{110m}$Ag and $^{239}$Pu adding about 0.05 % together.

The percentage contributions of radionuclides to dose can vary somewhat depending on seafood consumption patterns (e.g., differing proportions ingested of fish, bivalves, etc.). However, the overall result—that $^{210}$Po is the dominant contributor to total seafood ingestion dose by far—held true when considering country-specific diet examples as well as various bounding individual seafood category diet scenarios. The ICRP have proposed updated ingestion dose coefficients (DCFs) which are not expected to change the overall results of this paper. However, some changes are expected to the percentage contributions of specific radionuclides and we therefore recommend re-calculating the relative contributions of key radionuclides to seafood ingestion dose after the ICRP have finalised their work.

### CRediT authorship contribution statement

**Mathew P. Johansen:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Justin P. Gwynn:** Writing – review & editing, Writing – original draft, Project administration, Formal analysis, Conceptualization. **Julia G. Carpenter:** Writing – review & editing, Methodology, Investigation. **Sabine Charmasson:** Writing – review & editing, Validation, Methodology. **Airi Mori:** Writing – review & editing, Methodology, Investigation, Data curation. **Blake Orr:** Writing – review & editing, Validation, Conceptualization. **Marie Simon-Cornu:** Writing – review & editing, Validation, Methodology. **Iolanda Osvath:** Writing – review & editing, Validation, Supervision, Project administration. **Paul Mc Ginnity:** Writing – review & editing, Supervision, Project administration, Methodology, Investigation, Conceptualization.

### Declaration of competing interest

The authors declare there are no conflicts of interest.

### Acknowledgements

The authors are grateful to the Principality of Monaco for the support provided to the IAEA Marine Environment Laboratories. We thank Tri-sha Zimmerman for the thoughtful and clear work on the graphical abstract. The primary data for this study came from many research teams worldwide with compilation and assessment performed within the IAEA-Coordinated Research Project “LAMER—Behaviour and Effects of Natural and Anthropogenic Radionuclides in the Marine Environment and their Use as Tracers for Oceanography Studies.”

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jenvrad.2025.107706.

### Data availability

Data will be made available on request.

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