Zinc (Zn) is an essential element for corals. We investigated the effects of ocean acidification on zinc incorporation, photosynthesis, and gross calcification in the scleractinian coral Stylophora pistillata. Colonies were maintained at normal pHT (8.1) and at two low-pH conditions (7.8 and 7.5) for 5 weeks. Corals were exposed to 65Zn dissolved in seawater to assess uptake rates. After 5 weeks, corals raised at pHT (8.1) exhibited higher 65Zn activity in the coral tissue and skeleton, compared with corals raised at a lower pH. Photosynthesis, photosynthetic efficiency, and gross calcification, measured by 45Ca incorporation, were however unchanged even at the lowest pH.

Ocean acidification poses a threat to marine calcifiers, but their response varies widely. An analysis of Mediterranean corals and molluscs now shows that the ability to continue shell and skeleton growth in corrosive seawater is determined in part by the existence of outer organic protective layers. High temperatures, however, modify resistance to acidification.

Nuclear techniques and isotopes can be efficiently exploited for studying pollution processes of different origin and their connected mechanisms of diffusion. The IAEA Environment Laboratories through its Marine laboratories is since almost fifty years applying these methodologies for environment assessment to sustain member states in a sustainable development of their environment.This review does not pretend to report in an exhaustive manner on the effectiveness of the use of isotope for environmental studies, but it provides a short summary of the application of isotope analysis as tools to track the source and the levels of chemical and biological contamination. Emphasis is placed, in particular, on the use of isotope analysis for the determination and the tracking of organic pollutants. (C) 2011 Elsevier B.V. All rights reserved.

The Chilean blue mussel (Mytilus chilensis, Hupe 1854) represents the most important bivalve exploited along the Chilean coast and is a major food source for the Chilean population. Unfortunately, local fish and shellfish farming face severe problems as a result of bioaccumulation of toxic trace metals into shellfishes. Blue mussels collected along the Chilean coasts contain levels of Cd above the regulatory limits for human consumption. In this study, we examined the bioaccumulation, depuration and organ distribution of Cd in the M. chilensis, from 109Cd-labelled bulk seawater and from feeding with 109Cd-labelled algae. The uptake of 109Cd via seawater displayed a simple exponential kinetic model suggesting that cadmium activity tends to reach an equilibrium value of 1.838 ± 0.175 ng g−1 (mean ± asymptotic standard error, p < 0.001) after 78 ± 9 days. The depuration rate for 109Cd accumulated via seawater was slow, with only 21% of the total 109Cd accumulated in the whole mussel being eliminated after 52 days. Total elimination of Cd in mussels was adequately described by a double component kinetic model, in which the biological half-life for the long-lived component represents more than 6 months. In contrast, depuration after radiolabelled food uptake was fast, reaching only 20% of retention in 10 days. This knowledge of the long half-life of cadmium accumulated via seawater as well as the non-negligible level of cadmium accumulated into the shells is relevant to the management of Cd levels in this species and the refinement of detoxification processes in order to comply with authorized Cd levels.

In Chile, upwellings occur periodically along the coasts, resuspending metals from the seafloor and reintroducing them to the food web. Chilean blue mussels, Mytilus chilensis, accumulate these toxic compounds and show high concentrations of cadmium. An in vitro simulated digestion method has been applied to specimens of M. chilensis previously contaminated with 109Cd, to measure the bioaccessibility of cadmium for humans. The effects of the cooking process on the cadmium content of this species and on the resulting change in dietary bioaccessibility have also been evaluated. While cooking resulted in an increase in cadmium concentration in mussel flesh, cadmium remaining in the cooked flesh was also significantly less bioaccessible than cadmium occurring in the raw tissue. Estimations made in this study show that the intake of Cd from mussels by the Chilean population does not exceed the toxicological reference values established by the FAO/WHO; consequently, a health risk situation is not indicated.

The uptake kinetics of zinc (Zn), an essential nutrient for both photosynthesis and calcification, in the tissue of S. pistillata showed that the transport of Zn is composed of a linear component (diffusion) at high concentrations and an active carrier-mediated component at low concentrations. The carrier affinity (K m=28 pmol l−1) was very low, indicating a good adaptation of the corals to low levels of Zn in seawater. Zn accumulation in the skeleton was linear; its level was dependent on the length of the incubation as well as on the external concentration of dissolved Zn. There was also a light-stimulation of Zn uptake, suggesting that zooxanthellae, through photosynthesis, are involved in this process. An enrichment of the incubation medium with 10 nM Zn significantly increased the photosynthetic efficiency of S. pistillata. This result suggests that corals living in oligotrophic waters might be limited in essential metals, such as zinc.

Strontium thermometry has been suggested as a powerful tool for reconstructing seawater surface temperature (SST). In corals, an inverse relationship between SST and skeletal Sr/Ca ratios has been found. However, this ratio might also vary with calcification, which in turn is dependent on light and temperature. The aim of this study was to improve our knowledge of the uptake of Sr2+ as a function of light and temperature in the scleractinian coral Acropora verweyi. Two experiments were performed in which nubbins were acclimated over 4 wk either to 3 light intensities (100, 200 and 400 mumol m(-2) s(1)) or to 3 temperatures (20, 25, and 29degreesC) and growth rates were monitored. At the end of the 4 wk, nubbins were incubated, under the above light levels and temperatures, in individual beakers containing seawater spiked with the radiotracer Sr-85. Parallel incubations were carried out in dark beakers, in order to compare rates of Sr2+ incorporation in light and dark. The results obtained showed that growth rates were significantly higher under high light (0.16 +/- 0.01 and 0.27 +/- 0.01% d(-1) for 100 and 400 mumol photons m(-2) s(-1)) and under high temperature (0.06 +/- 0.01% d(-1) at 20degreesC to 0.35 +/- 0.03% d(-1) at 29degreesC). Rates of Sr2+ incorporation into the coral skeleton were also higher under high light (32.4 +/- 3.0, 72.9 +/- 13.5 and 91.2 +/- 9.0 nmol (g dry weight, DW)(-1) d(-1), for corals cultured at 100, 200 and 400 mumol m(-2) s(-1) respectively) and high temperature (89 +/- 14, 224 +/- 38 and 436 +/- 58 nmol (g DW)(-1) d(-1) for corals cultured at 20, 25 and 29degreesC respectively). Rates of Sr2+ uptake were also 2 to 3 times lower in the dark than in the light, comparable with the incorporation of calcium. Our results finally show a strong correlation between Sr2+ uptake and growth rates. Strontium uptake therefore follows the same pattern as calcium uptake, both ions being regulated by the calcification biochemistry.

The bioaccumulation of cadmium in the oyster Crassostrea gigas originating from a clean (Bourgneuf Bay) and a chronically Cd-contaminated area (Gironde estuary) experimentally exposed to 109 Cd-labeled bulk seawater (dissolved and particulate pathways combined) was examined over 21 d. A single-component first-order kinetic model describing the behavior of the bioaccumulation factor (BAF) throughout the experiment showed that the estimated Cd BAF at 21 d was 47% higher for oysters originating from the contaminated estuary than for oysters from the clean area, suggesting an influence of the previous chronic exposure to Cd contamination in the estuarine environment. From the experimental results, the potential adaptive mechanism suggested cannot be attributed to a reduction in Cd permeability but rather to a higher Cd turnover due to the synergy between lysosomes and metallothioneins which, through chelation, are responsible for the reduction in bioavailability and toxicity of cd in oysters. The lower BAF observed for soft parts of oysters previously exposed to chronic Cd contamination corresponded to a faster response to the experimental Cd contamination due to the presence of pre-existing metallothioneins induced by the Cd present in the estuarine environment. Furthermore, based on a 2-component exponential loss kinetic model, Cd complexation to metallothioneins and lysosomes was probably responsible for the slow turnover in the long-term compartment of loss (biological half-life, T b1/b2 = 495 and 198 d for the Bourgneuf and the Gironde oysters, respectively). Of the total Cd accumulated, 40 to 60% was in the soluble form and 30 to 40% of this fraction had been detoxified by the Gironde oysters through chelation to metallothioneins or to lysosomes, which means that approximately 12 to 24% of the total Cd accumulated was potentially bioavailable to humans through oyster consumption. However, through depuration, it was also more efficiently eliminated from oyster soft parts (the edible portion) previously exposed to Cd than from control oysters. Therefore, in the light of these results, it is suggested that the way in which regulatory thresholds of Cd in oysters are presently calculated should be reconsidered and should take into account the level of Cd already detoxified by the oysters through complexation processes.

The relative importance of dissolved and food pathways and the influence of food type in the bioaccumulation and retention of lead in the shrimp Palaemonetes varians were examined using a radiotracer method. Shrimp were exposed to 210Pb-labelled seawater or fed two types of 210Pb-labelled food, viz. mussels or worms. The amount of radiotracer accumulated by shrimp was examined over a 7-day period, followed by a 1-month and a 7-day depuration period for the dissolved and food source, respectively. Steady state in the uptake was reached after 2 days exposure to dissolved lead, with a resultant estimated concentration factor of 98+/-3. Transfer factors following ingestion of contaminated mussels and worms were lower than unity for both food types, with lead transfer from worms being significantly higher than that from mussels. Accumulation of dissolved Pb by shrimp was found to occur mainly through adsorption on the exoskeleton with a minor accumulation in the internal tissues probably resulting from the intake of seawater for osmoregulation. In contrast, lead taken up from contaminated food was readily absorbed and bound in the internal tissues of P. varians. Although the transfer of lead to P. varians through the ingestion of contaminated food was low (TF<1%), it still represented 4 to 8% of the lead content in the prey which is a significant additional contribution of lead to the shrimp body burden. Independent of food type, following ingestion of contaminated food, approximately 23-27% of total lead accumulated in shrimp was located in the edible parts (e.g. muscle). Therefore, the food pathway is suggested to be a significant contributor to the lead transfer to humans through ingestion of contaminated shrimp. After exposure to contaminated food, lead loss kinetics were described by a two-component model, whereas Pb loss following direct uptake from seawater was best described by a three-component model. The additional compartment representing 64% of total Pb retained and characterized by a turnover<10 min, corresponded to lead weakly adsorbed on the exoskeleton and incorporated in the hepatopancreas. Nevertheless, a significant fraction of lead accumulated from the dissolved (2%) and food (52-57%) pathways remained irreversibly retained in the tissues, suggesting that this organism could also serve as an effective long-term bioindicator of lead contamination in marine waters.

Reef-building corals are very sensitive to changes in their environment and have been identified as potential accurate recorders of environmental changes. They form aragonitic carbonate skeletons that contain relatively high amounts of strontium (Sr2+). The ratio of Sr2+/calcium (Ca2+) has been proved to be useful for paleoclimatic studies since it has been suggested to vary with the seawater temperature. However, no correlation can be established between skeletal Sr2+ content and environmental parameters due to the lack of knowledge concerning the extent to which skeletal chemistry is controlled by physiological parameters. In this study, we investigated the pathway of Sr2+ incorporation by the scleractinian coral Stylophora pistillata. For this purpose, we used Sr-85 and a non-destructive NaI gamma detector. Sr2+ skeletal incorporation was found to be linear during the 9 experimental days of incubation with natural concentrations of Sr2+. The incorporation of Sr2+ versus external Sr2+ concentration was also linear up to 3.42 mM (i.e. a concentration 37.5 times higher than normal seawater concentration). However, the uptake of Sr2+ at high concentrations (> 1 mM) decreased with an increase in Ca2+ concentration in the seawater. Moreover, Verapamil, a Ca2+ channel inhibitor, also inhibits the incorporation of Sr2+ with the same I-c50 (12 muM) as for Ca2+. Incorporation of Sr2+ is therefore inversely correlated to the rate of calcification, suggesting interactions between these 2 ions, which should be taken into account during paleoclimatic studies.

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.

To quantify the potential enhancement of naturally-occurring 210Po and 210Pb that may result from the high sulfur-reducing and sulfur-oxidizing regimes associated with hydrothermal vents, sinking particles from both inside and outside vent areas and benthic molluscs grazing on or living near bacterial mats in the vent zone were collected off Milos Island (Aegean Sea) and analyzed for their 210Po and 210Pb content. There was no significant difference in the range of 210Po specific activities measured in particulate material collected by sediment traps in a control area and in the vent area; the resultant 210Po levels were of the same order of magnitude as literature values reported for other Mediterranean coastal areas. 210Pb levels in sinking particles from the control site tended to be higher than those measured in the vent zone, as demonstrated by the lower 210Po/210Pb ratios observed in particles from the control site. Nevertheless, these 210Pb levels were also comparable with similar 210Pb data reported for the northwestern Mediterranean Sea. The 210Po and 210Pb vertical particulate fluxes were, on average, higher in the vent zone as a consequence of the higher particle flux. This observation indicates that vents can indirectly control the flux of these natural radionuclides by affecting the types and amount of particles produced in hydrothermal areas. The 210Po levels measured in a gastropod and a bivalve living on or near the microbial mat in the vent zone were higher than values reported for non-vent gastropods and bivalves from the NW Mediterranean Sea, an observation which suggests that an enhanced food chain transfer of 210Po may occur in the vicinity of vents off Milos Island. Nevertheless, the lack of a general enhancement of 210Po and 210Pb in the marine particulate samples collected indicates that any input of these radionuclides through venting activity may have a minimal effect in the surrounding environment.

The disposal of large quantities of radioactive wastes in Arctic Seas by the former Soviet Union has prompted interest in the behavior of long-lived radionuclides in polar waters. Previous studies on the interactions of radionuclides prominent in radioactive wastes have focused on temperate waters; the extent to which the bioconcentration factors and sediment partitioning from these earlier studies could be applied to risk assessment analyses involving high latitude systems is unknown. Here we present concentrations in seawater and calculated in situ bioconcentration factors for (90)Sr, (137)Cs, and (239+240)Pu (the three most important radionuclides in Arctic risk assessment models) in macroalgae, crustaceans, bivalve molluscs, sea birds, and marine mammals as well as sediment K(d) values for 13 radionuclides and other elements in samples taken from the Kara and Parents Seas. Our data analysis shows that, typically, values for polar and temperate waters are comparable, but exceptions include 10-fold higher concentration factors for (239+240)Pu in Arctic brown macroalgae, 10-fold lower K(d) values for (90)Sr in Kara Sea sediment than in "typical" temperate coastal sediment, and 100-fold greater Ru K(d) values in Kara Sea sediment. For most elements application of temperate water bioconcentration factors and K(d) values to Arctic marine systems appears to be valid.

As a prerequisite for most evaluations of radionuclide transport pathways in marine systems, it is necessary to obtain basic information on the sorption potential of contaminants onto particulate matter. Kd values for use in modeling radionuclide dispersion in the Kara Sea have been determined as part of several international programs addressing the problem of radioactive debris residing in Arctic Seas. Field and laboratory Kd experiments were conducted for the following radionuclides associated with nuclear waste: americium, europium, plutonium, cobalt, cesium and strontium. Emphasis has been placed on two regions in the Kara Sea: (i) the Novaya Zemlya Trough (NZT) and (ii) the mixing zones of the Ob and Yenisey Rivers (RMZ). Short-term batch Kd experiments were performed at-sea on ambient water column samples and on samples prepared both at-sea and in the laboratory by mixing filtered bottom water with small amounts of surficial bottom sediments (particle concentrations in samples = 1-30 mg/l). Within both regions, Kd values for individual radionuclides vary over two to three orders of magnitude. The relative particle affinities for radionuclides in the two regions are americium approximately equal to europium > plutonium > cobalt > cesium > strontium. The values determined in this study agree with minimum values given in the IAEA Technical Report [IAEA, 1985. Sediment Kd's and Concentration Factors for Radionuclides in the Marine Environment. Technical Report No. 247. International Atomic Energy Agency, Vienna.]. Given the importance of Kd's in assessments of critical transport pathways for radionuclide contaminants, we recommend that Kd ranges of values for specific elements rather than single mean values be incorporated into model simulations of radionuclide dispersion.

In order to assess the adaptation to metals previously observed in the bioindicator organism, Macoma balthica, subjected to chronic contamination by silver and mercury in the French Loire estuary, the bioaccumulation potential of individual organisms originating from the contaminated Loire estuary and a relatively uncontaminated control estuary (Somme) was evaluated using both radiotracers and stable isotopes of Ag (80 μg Ag litre−1) and Hg (100 μg Hg litre−1). Clams from the contaminated estuary were more sensitive to Ag (LT50 = 9d) than those originating from the Somme estuary (LT50 > 15d), even though the former bioaccumulated Ag to a significantly lower degree. This is attributed to a consequence of the chronic stress induced by Ag while clams were living in their natural environment. Therefore, past history of trace metal contamination should be considered when evaluating the susceptibility of M. balthica to heavy metal exposure. Lower uptake rates obtained for Hg (during the initial uptake phase only) and for Ag in clams from the polluted estuary suggest the presence of an adaptive trait for survival in contaminated areas. However, the lower degree of bioconcentration observed for Ag was not sufficiently low to reduce the sensitivity of the organisms to Ag and allow them to resist the toxic stress. Clams that survived Ag or Hg exposure at LT50 did not protect themselves against metal toxicity by accumulating a significantly lesser amount of these metals than clams which did not survive metal stress. The results suggest that the bioaccumulation potential of each individual was not a factor which can explain the survival ability of M. balthica exposed to chronic Ag and Hg contamination in estuaries. In this case, cellular, biochemical and genetic levels of adaptation are presumed to be of greater importance.

Bioaccumulation of lead in the mussel Mytilus galloprovincialis from 210Pb-labeled bulk seawater (dissolved and particulate pathways combined) was examined over 21 days. The lead bioaccumulation factor (BAF) at equilibrium was estimated to be 211 +/- 10 ml g-1. This value was two orders of magnitude lower than BAFs reported in the literature for other trace metals in this bivalve indicating that lead is not efficiently accumulated by mussels from bulk seawater. The resultant lead distribution in mussels was 49 +/- 10% in soft tissues and 46 +/- 16% in the shell suggesting similar uptake rates (Bq day-1) in both compartments throughout the exposure. Total elimination for lead in mussels was adequately described by a short-term compartment with a biological half-life for loss of 1.4 +/- 0.3 days and a long-term compartment which released lead only very slowly (Tb1/2 = 2.5 +/- 0.7 months). No difference was noted for lead elimination rates in shell and in soft parts. When experimentally exposed to lead under conditions representative of natural environmental lead levels in water, including both that in the dissolved phase and in the food, the shell compartment was shown to contain the major fraction of the total lead accumulated by mussels. Therefore mussels may be considered as good bioindicators of lead contamination accumulated from the dissolved rather than from the particulate source. Furthermore, the relatively slow uptake and the long depuration half-life of lead will limit the ability of mussels to accurately record short-term variations in lead concentrations in the surrounding waters, a fact which should be taken into consideration in order to define the appropriate sampling frequency for mussels used in biomonitoring programs involving lead.

Environmental parameters (salinity, sediment concentration, equilibration time) affecting radionuclide partitioning between sediment and seawater were experimentally investigated for Kara Sea sediments collected from nuclear waste dumping sites in Abrosimov and Stepovogo Bays off Novaya Zemlya. Adsorption kinetics were examined and the influence of salinity and sediment concentration were evaluated over the range of concentrations expected in the bays for the following radionuclides: 110 mAg; 241Am; 109Cd; 60Co; 57Co-cobalamine; 134Cs; 152Eu; 54Mn; 133Ba; 106Ru; and 85Sr. The major findings of this investigation are that 1. radionuclide distribution coefficients (Kds) were most sensitive to variations in sediment character (241Am, 60Co, 109Cd) and concentration (57Co-cobalamine, 85Sr, and 133Ba), 2. distribution coefficients generally decreased with increasing sediment concentration and 3. fast adsorption kinetics (near equilibrium ≈1 day) were observed only for 137Cs and 110 mAg. The observed differences in Kds for sediments from the two dumpsites exemplifies the importance of undertaking site-specific determinations of Kds. For purposes of confining radioactive wastes to the dumpsites in Stepovogo and Abrosimov Bays, the findings of this study indicate that based on sediment character alone, Stepovogo Bay will be more effective at retaining radionuclides than Abrosimov Bay. This is unfortunate since less radioactive waste resides in Stepovogo Bay (0.6 PBq) than in Abrosimov Bay (1.4 PBq).