[en] A radiotracer technique using ²¹⁰Pb was applied to quantify the transfer and distribution of lead in the asteroid Asterias rubens following a single ingestion of radio-labelled mussels under controlled laboratory conditions. Approximately 50% of the ²¹⁰Pb accumulated by mussels in their soft tissues from seawater was transferred to the asteroid through the food pathway resulting in a transfer factor less than unity. Loss kinetics of ²¹⁰Pb in the asteroid were best described by a two-component exponential model. A. rubens eliminated 56%±5% of the ingested ²¹⁰Pb in a few days while the remaining fraction (42%±5%), was absorbed and eliminated very slowly. Following ingestion, ²¹⁰Pb was accumulated in the pyloric caeca and the body wall with little radioisotope found in the coelomic fluid. Lead-210 was then transferred to the organic matrix of the body wall through the general body cavity via the coelomic fluid, and then to the skeleton. In this way, lead appears to be progressively eliminated from the organic matrix of the body wall while it is efficiently trapped in the calcite skeleton. The sequestration and retention of lead in the skeleton is considered as a detoxification process, but it also prevents lead transfer to higher trophic levels of the marine food chain since the skeleton is not digested by higher consumers. In addition, the skeleton of asteroids can be regarded as a bioindicator of long-term dietary lead contamination

[en] Uptake and loss of cobalt-57 were investigated in the starfish Asterias rubens, in order to assess its value as a sentinel organism for nearshore radionuclide contamination. Whole-body uptake from sea water was linear over a 32-day exposure period and reached wet weight concentration factor (CF) of 23 ± 5. Bioaccumulation of ⁵⁷Co was dependent upon body compartment, the aboral part of the body wall concentrating cobalt to the greatest degree (wet weight CF: 77 ± 16). After restoration of uncontaminated conditions, radiocobalt was released following an exponential loss kinetics characterized by a biological half-life (T_b1/2) of 27 ± 6 day. Dietary radiocobalt (taken up during a short-term feeding for 24 h on radiolabelled mussels) showed a much more rapid turnover time (T_b1/2: 14 ± 4 d), suggesting that A. rubens accumulates this radionuclide predominantly from sea water. A. rubens, and more particularly the aboral part of its body wall, would readily reveal the presence of an environmental contamination by radiocobalt and could preserve this information over a period of few months

[en] The distribution and behaviour of the natural-series alpha-emitter polonium-210 in the marine environment has been under study for many years primarily due to its enhanced bioaccumulation, its strong affinity for binding with certain internal tissues, and its importance as a contributor to the natural radiation dose received by marine biota as well as humans consuming seafoods. Results from studies spanning nearly 5 decades show that ²¹⁰Po concentrations in organisms vary widely among the different phylogenic groups as well as between the different tissues of a given species. Such variation results in ²¹⁰Po concentration factors ranging from approximately 10³ to over 10⁶ depending upon the organism or tissue considered. ²¹⁰Po/²¹⁰Pb ratios in marine species are generally greater than unity and tend to increase up the food chain indicating that ²¹⁰Po is preferentially taken up by organisms compared to its progenitor ²¹⁰Pb. The effective transfer of ²¹⁰Po up the food chain is primarily due to the high degree of assimilation of the radionuclide from ingested food and its subsequent strong retention in the organisms. In some cases this mechanism may lead to an apparent biomagnification of ²¹⁰Po at the higher trophic level. Various pelagic species release ²¹⁰Po and ²¹⁰Pb packaged in organic biodetrital particles that sink and remove these radionuclides from the upper water column, a biogeochemical process which, coupled with scavenging rates of this radionuclide pair, is being examined as a possible proxy for estimating downward organic carbon fluxes in the sea. Data related to preferential bioaccumulation in various organisms, their tissues, resultant radiation doses to these species, and the processes by which ²¹⁰Po is transferred and recycled through the food web are discussed. In addition, the main gaps in our present knowledge and proposed areas for future studies on the biogeochemical behaviour of ²¹⁰Po and its use as a tracer of oceanographic processes are highlighted in this review.

[en] Highlights: • Depurating dogfish transfer radionuclides to eggs over six months. • Transfers even enhanced for ⁶⁵Zn and ¹³⁴Cs. • Progeny more exposed to radionuclides with greater assimilation from food. -- Abstract: Cartilaginous dogfish Scyliorhinus canicula continued to transfer four anthropogenic radionuclides (⁶⁵Zn, ⁶⁰Co, ¹³⁴Cs and ²⁴¹Am) to their eggs for over six months, after two months of continued maternal exposure to radio-labelled food. Unexpectedly, rates of radionuclide transfers to eggs and their yolk & embryo during maternal depuration were equivalent for ⁶⁰Co and ²⁴¹Am, or even enhanced for ⁶⁵Zn and ¹³⁴Cs by factors of c.200–350%, over two-three months, compared to their maximal transfer rates at the end of the maternal uptake phase. These rates of maternal transfer of radionuclides to yolk & embryo were positively associated with their previously determined efficiencies of assimilation (AE) from ingested radio-labelled food. Thus progeny may be more exposed via maternal transfer to those radionuclides which have greater rates of maternal assimilation from food. As maternal depuration continued beyond 60–80 up to 180–200 days the transfers of all four radionuclides to eggs did diminish but were still substantial at mean values of 18% for ²⁴¹Am, 17% for ¹³⁴Cs and 9 and 8% for ⁶⁰Co and ⁶⁵Zn, respectively. In the yolk & embryo the mean rates of transfer over this period were further reduced for ²⁴¹Am (13.5%), ⁶⁰Co (2.5%) and ⁶⁵Zn (5.8%), but were still appreciable for ¹³⁴Cs at 56%. These results for S. canicula have demonstrated a potential enhanced radiological risk of extended duration due to the particular biokinetics of maternal transfer in this species. This study draws further attention to the current paucity of knowledge about the maternal: progeny transfer pathway, particularly in the context of the known heightened radio-sensitivity of early life stages in fish and other vertebrates, compared to later life stages.

[en] Highlights: • The review summarizes laboratory studies carried out on Cs bioaccumulation in aquatic organisms. • It outlines key results of previous experiments as a toolbox for modelers. • A database is included and compiles data from 125 publications dating back to 1950s. • Gaps of knowledge still exists to fully understand Cs accumulation process in marine organisms. - Abstract: A better understanding of the fate of radiocesium in aquatic organisms is essential for making accurate assessments of potential impacts of radiocesium contamination on ecosystems and human health. Studies of the accumulation of ¹³⁴Cs, ¹³⁶Cs and ¹³⁷Cs in diverse biota have been the subject of many field investigations; however, it may often be difficult to understand all the mechanisms underlying the observations reported. To complement field investigations, laboratory experiments allow better understanding the observations and predicting dynamics of Cs within aquatic ecosystems by accurately assessing bioaccumulation of Cs in living organisms. The present review summarizes selected relevant laboratory studies carried out on Cs bioaccumulation in aquatic organisms over a period of more than 60 years. To date, 125 experimental studies have been carried out on 227 species of aquatic organisms since 1957. The present review provides a synthesis of the existing literature by highlighting major findings and identifying gaps of key information that need to be further addressed in future works on this topic. Thus, influences of some environmental parameters such as water chemistry both for marine and freshwater ecosystems, and biotic factors such as the life-stages and size of the organisms on radiocesium bioaccumulation should be examined and become priority topics for future research on Cs accumulation in aquatic organisms.

[en] Maternal transfer of radionuclides to progeny is one of the least known sources of contamination in marine biota and more information is needed to assess its radiological significance. A radiotracer study on spotted dogfish, Scyliorhinus canicula, evaluated the hypothesis that four anthropogenic radionuclides (Cobalt-60, Zinc-65, Americium-241 and Cesium-134) could be maternally transferred to eggs and each of their major components during maternal ingestion of radiolabelled food. The linear regressions between cumulative radioactivity that had been maternally ingested and the level in subsequently laid eggs were used to derive maternal-to-egg transfer factors (mTFs). These maternal transfers varied over an order of magnitude and were ranked "1"3"4Cs > "6"5Zn > "6"0Co > "2"4"1Am. This ranking was the same as their relative assimilation efficiencies in radiolabelled food consumed by adults. Among these four radionuclides the potential radiological exposure of embryos is accentuated for "6"5Zn and "1"3"4Cs due to their predominant transfer to egg yolk where they are available for subsequent absorption by the embryo as it develops prior to hatching from the egg capsule. Thus, for cartilaginous fish like shark, the potential radioecological consequences of a pulsed release of these radionuclides into the marine environment may extend beyond the temporal duration of the release. - Highlights: • Dogfish maternally transfer anthropogenic radionuclides to eggs. • Transfers are ranked "1"3"4Cs > "6"5Zn > "6"0Co > "2"4"1Am. • Both "6"5Zn and "6"0Co are mainly deposited in yolk

[en] Monthly sampling in northwestern Mediterranean coastal waters was undertaken to better understand the relationship between zooplankton biomass and the cycling of the natural radionuclide ²¹⁰Po/²¹⁰Pb pair during a one-year period (October 1995–November 1996). In conjunction with mesozooplankton collections and ²¹⁰Po/²¹⁰Pb measurements in seawater, zooplankton and their fecal pellets, the biochemical composition of particulate organic matter (POM) was also examined at three depths (0, 20 and 50 m) as an indicator of trophic conditions. During May 1996, a strong zooplankton “bloom” was observed which was preceded by a prolonged increase in POM (protein + carbohydrates + lipids) starting at the end of March, and further demonstrated by a concomitant increase in the concentration of smaller particles, two features that are typical of mesotrophic waters. Simultaneous measurements of ²¹⁰Po in sea water and zooplankton showed an inverse trend between these two parameters during the sampling period, with the two lowest ²¹⁰Po concentrations in the dissolved phase of seawater coincident with the highest radionuclide concentrations in the zooplankton; however, this apparent relationship was not statistically significant over the entire year. Freshly excreted mesozooplankton and salp fecal pellets, which have been strongly implicated in the removal and downward transport of these radionuclides from the upper water column, contained ²¹⁰Po and ²¹⁰Pb levels ranging from 175 to 878 and 7.5–486 Bq kg⁻¹ dry weight, respectively. Salp pellets contained 5 and 10 times more ²¹⁰Po and ²¹⁰Pb than in fecal pellets produced by mixed zooplankton, a finding most likely related to their different feeding strategies. During the zooplankton biomass peak observed in May, the ²¹⁰Po concentration in zooplankton was at a minimum; however, in contrast to what has been reported to occur in some open sea oligotrophic waters, over the year no statistically significant inverse relationship was found between zooplankton biomass and ²¹⁰Po concentration in zooplankton. This observation may have resulted from the general lack of very low biomass concentrations (<1 mg m⁻³) measured in these coastal waters, biomass levels which commonly occur in open ocean oligotrophic regions. - Highlights: ► This a one year sampling of zooplankton and water at 3 different depths to study 210Po and 210Pb in them. ► A zooplankton bloom was present in May after an extended period of a higher primary productivity proxy. ► An inverse trend was found for 210Po in zooplankton and water or the dissolved phase. ► Maximum zooplankton biomass showed minimum 210Po in zooplankton and a maximum in the dissolved phase. ► A dilution phenomenon is present in zooplankton and water, depending zooplankton or particle concentration.

[en] Sediment cores from a hydrothermal vent zone off Milos Island in the Aegean Sea were dated using the ²¹⁰Pb method. The average unsupported ²¹⁰Pb inventory in the cores was calculated to be 3256 Bq m^-2. The corresponding mean annual ²¹⁰Pb flux of 105 Bq m^-2 year^-1 is comparable to estimates of the atmospheric flux given in the literature. ²¹⁰Pb fluxes calculated from the unsupported ²¹⁰Pb inventories in cores are also comparable with the ²¹⁰Pb vertical fluxes determined from settling particles off the coast of Milos Island. The highest unsupported ²¹⁰Pb concentrations (89 Bq kg^-1) were measured in the sediments nearest to the hydrothermal vent area suggesting that the sedimentation rate is lowest at this site. Direct gamma measurements of ²¹⁰Pb were used to date three sediment cores that are located at different distances from the vent zone: one is in the immediate vicinity of the vent; and others are outside the zone. Sedimentation rates for these cores, calculated using the CRS and CIC models, ranged from 0.088±0.008 cm year^-1 to 0.14±0.01 cm year^-1. Where both models were applicable, the results given by the two methods were in good agreement. ¹³⁷Cs concentrations in all three cores generally declined with depth but showed no clear signal of either the period of maximum fallout from weapons testing or the Chernobyl accident. ²¹⁰Po activities were also measured and the maximum ²¹⁰Po concentration was in the sediment surface layer (166 Bq kg^-1)

[en] To clarify the relationship between zooplankton biomass and the environmental kinetics of the natural radionuclide ²¹⁰Po during a one-year period (October 1995 to November 1996) in northwestern Mediterranean coastal waters, a modelling analysis was applied. Using ²¹⁰Po concentrations in seawater and zooplankton, the ²¹⁰Po uptake rate constant from food for zooplankton was evaluated using a biokinetics calculation involving the uptake and the excretion rate constants between seawater and zooplankton. Using the transfer constants obtained, the ²¹⁰Po concentrations in zooplankton were reconstructed and validated by observed concentrations. The simulation results were in good agreement with the measured ²¹⁰Po concentrations in zooplankton. Assuming that ²¹⁰Po fecal excretion represents the majority of the excretion of ²¹⁰Po from zooplankton, the fecal matter associated ²¹⁰Po vertical flux was calculated, and compared with the observed vertical fluxes of ²¹⁰Po measured in sediment traps. The modelling evaluation showed that fecal pellet vertical transport could not fully explain the observed sinking fluxes of particulate organic matter at 150 m depth, suggesting that other sinking biodetrital aggregates are also important components of the plankton-derived vertical flux of ²¹⁰Po. The relationship between ²¹⁰Po concentration in seawater and that in rain and dry fallout and their potential effect on ²¹⁰Po concentrations in zooplankton at this location were also examined. A similar, but diphased trend between ²¹⁰Po in zooplankton and ²¹⁰Po in rain and dry fallout deposition rate was demonstrated. ²¹⁰Po concentrations in the dissolved phase of seawater tended to diminish as mean daily rainfall increased suggesting that rain inputs serve as a ²¹⁰Po dilution mechanism in seawater at this location. - Highlights: • Biokinetics calculation used to estimate ²¹⁰Po in zooplankton. • Estimates were in agreement with the measured ²¹⁰Po concentrations. • Fecal pellet vertical transport could not explain observed fluxes at 150 m depth. • Other sinking aggregated biodetritus are also important. • ²¹⁰Po in seawater and that in rain and dry fallout were also examined.

[en] Highlights: • This is the first experimental assessment on loss of ²¹⁰Po in seafood from Kuwait. • The Study provides a realistic assessment of dose to humans from cooked seafood. • The seafood consumption in Kuwait varied between 35 and 203 g. • The CED in Kuwait varies between 37 and 240 μSv.y-1 from seafood consumption. - Abstract: An experimental study was conducted to assess loss of ²¹⁰Po due to cooking fresh seafood, and provide a more realistic and reliable dose estimate that humans may receive from consuming cooked seafood. Fresh fish and shrimp samples from Northern Gulf waters were grilled and boiled to simulate the effect of different cooking methods. Sixteen different species of fish were compared and significant differences in ²¹⁰Po concentration in uncooked samples were observed between species (ANOVA I, F_15,79 = 362.81, p 210Po concentration ranging from 14 to 58% compared to the uncooked samples, with no difference between grilled or boiled treatments. The effect of the cooking and shrimp treatment on ²¹⁰Po concentration was tested using ANOVA II after logarithmic transformation. Cooking led to a significant 38% reduction of ²¹⁰Po concentration as compared to uncooked treatments with no difference between grilled and boiled samples (ANOVA I: F_3,99 = 14.72, p 210Po concentration as compared to all other treatments. As a consequence, cooked deveined shrimp contained an 84% lower ²¹⁰Po concentration than whole uncooked shrimp. As ²¹⁰Po is known to be the major contributor to radiation dose in humans consuming seafood, based on the results obtained, it is evident there is a need to re-examine how committed effective doses (CEDs) are best calculated for seafood consuming populations considering that most populations consume fish and shellfish cooked.