Bioaccumulation of polonium‐210 in marine copepods

Stewart, Gillian; Fisher, Nicholas S.

doi:10.4319/lo.2003.48.5.2011

Cited by 66 publications

(38 citation statements)

References 40 publications

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“…1A and B show an inverse relationship between organism size and 234 Th and 210 Po activity concentrations when considering the entire range of size-fractionated plankton examined. The decrease of activity concentration with increasing particle size suggests an adsorption-driven behavior for both radioisotopes; this observation is consistent with previous findings for 234 Th (Fisher et al 1987), but it is in contrast with the presumed bioaccumulative behavior of 210 Po in zooplankton food chains (Stewart and Fisher 2003). However, as indicated already (Results section), in the case of 210 Po, this inverse relationship is entirely due to the higher specific activities measured in the 1-33-mm size fractions, and therefore it cannot be considered as representative of the actual behavior over the entire size range.…”

Section: Discussionsupporting

confidence: 91%

Particulate organic carbon : natural radionuclide ratios in zooplankton and their freshly produced fecal pellets from the NW Mediterranean (MedFlux 2005)

Baena¹,

Fowler²,

Miquel³

2007

Limnology & Oceanography

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To discern controls on particulate organic carbon (POC) : natural radionuclide (RN) ratio variability in order to enhance the accuracy of water column radionuclide-based carbon flux estimates, 234 Th, 210 Po, and POC were analyzed in seven size classes of mixed micro-and mesoplankton (1-1,500-mm size range), in larger zooplankton from different taxa (salps, euphausiids, copepods, pteropods), and in freshly produced feces from zooplankton collected during spring in the NW Mediterranean. POC : RN ratios in zooplankton ranged between 120 and 11,600 and between 89 and 9,200 mmol dpm 21 for 234 Th and 210 Po, respectively. In fecal pellets, POC : RN ratios were one to three orders of magnitude lower for 234 Th and 3-fold to 30-fold lower for 210 Po; the only exception was euthecosome pteropods, which had a higher POC : 210 Po ratio in their pellets than in their whole bodies. Significant increases in POC : RN ratios with organism size were best described by a power relationship for POC : 234 Th (p , 0.0006) and a saturation exponential equation for POC : 210 Po (with a constant POC : 210 Po ratio above 70 mm; p , 0.004), suggesting that the observed trend most likely results from surface adsorption processes for 234 Th and food chain bioaccumulation for 210 Po. This inference is further supported by the observation that, for the .33-mm size classes, 210 Po specific activity correlates negatively with the surface : volume ratio, while 234 Th correlates positively with it (p , 0.004 and p , 0.001, respectively). POC : RN ratios vary greatly among species and to a lesser extent among fecal pellet types, most probably due to differences in zooplankton feeding strategies. Partial removal of most zooplankton ''swimmers'' from trap samples would not likely confound assessment of 234 Th flux; however, it could considerably bias similar measurements of 210 Po flux as well as those of POC : RN ratios.Given the interest in climate change and the potential role of the oceans in sequestering carbon, 234 Th and to a minor extent 210 Po have been increasingly used to assess particle fluxes, especially particulate organic carbon (POC) out of surface waters (e.g., Kim and Church 2001;Friedrich and Rutgers van der Loeff 2002;Murray et al. 2005). When using natural radiotracers such as 234 Th and 210 Po to study carbon export and cycling in the oceans, it is necessary to determine both the activity concentration of the radionuclides in the water column and their ratio to carbon in the particles responsible for carbon sequestration and export (Moran et al. 2003).Although information on POC : 234 Th ratios in a variety of particles from different size classes and regions is available (for review, see Buesseler et al. 2006), similar data on POC : 234 Th and POC : 210 Po in zooplankton and fecal pellet material are extremely sparse (Fowler and Fisher 2004). This is somewhat surprising, considering that (1) many studies show that POC : 234 Th variability is much greater in surface waters than at depths below the euphotic zone (Bu...

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Section: Discussionsupporting

confidence: 91%

Particulate organic carbon : natural radionuclide ratios in zooplankton and their freshly produced fecal pellets from the NW Mediterranean (MedFlux 2005)

Baena¹,

Fowler²,

Miquel³

2007

Limnology & Oceanography

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“…Further, we obtained nearly identical Hg-assimilation efficiencies in separate experiments using 4-h and 10-h pulse feeding periods, and the calculated assimilation efficiencies were very close whether using the y-intercept of the fitted depuration curve or the 4-h time point. Others have also found these assimilation efficiency calculations to yield similar results (Stewart and Fisher 2003). Therefore, we believe that the trends noted between protozoa and phytoplankton prey are not attributable to differences in methods of calculating assimilation efficiencies.…”

Section: Discussionsupporting

confidence: 68%

“…3). A close relationship between metal partitioning in phytoplankton prey and assimilation within mesozooplankton has been observed with these and other metals (Reinfelder and Fisher 1991;Hutchins et al 1995;Stewart and Fisher 2003). Although the correlation between these two parameters is not quite as close when protozoa are used as food, the higher protozoan assimilation efficiencies are matched by a higher percentage of metals within the protozoan cells (Fig.…”

Section: Subcellular Distribution Of Metals In Prey-mentioning

confidence: 57%

Trophic transfer of trace metals from protozoa to mesozooplankton

Twining

Fisher

2004

Limnology & Oceanography

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Radiotracer techniques were used to quantify the assimilation and subsequent efflux of silver, cadmium, iron, mercury, thallium, and zinc by mesozooplankton fed ciliates, heterotrophic dinoflagellates, or heterotrophic flagellates, and the results were compared with published values measured for phytoplankton prey. The subcellular distribution of the metals within the prey cells was also determined and related to their bioavailability. Marine copepods assimilated 59-82% of Ag, 83-92% of Cd, 32-66% of Fe, 14-49% of Hg, and 71-78% of Zn ingested with protozoan prey. Higher Ag, Cd, Fe, and Hg assimilation efficiencies were observed for at least one of the species of protozoa than reported in the literature for phytoplankton. Significant differences in assimilation were not observed for Zn or for Tl fed to freshwater Ceriodaphnia in either protozoa or phytoplankton. The higher assimilation efficiencies of protozoan metals, when observed, were matched by higher fractions of metals in the cytoplasm of protozoa. A biokinetic model used to calculate steady-state metal concentrations in copepods indicates that copepods may contain 119% more Ag and 44% more Zn when feeding on ciliates instead of diatoms, possibly resulting in sublethal toxic effects at Ag and Zn concentrations reported for the Hudson River estuary. Further, higher assimilation and efflux rates of protozoan Fe may enhance remineralization of this limiting nutrient by mesozooplankton in high nutrient, low chlorophyll regions.Aquatic animals can accumulate metals both directly from their aqueous environment and from the prey they ingest, but metals accumulated through these two routes can have different physiological effects and geochemical fates. Food is often the dominant uptake pathway for metals in crustacean zooplankton (Munger and Hare 1997;Wang and Fisher 1998), and zooplankton can be more sensitive to metals accumulated through this pathway (Hook and Fisher 2001a,b). In addition to having greater physiological effects, metals that are ingested and assimilated by zooplankton can build up in food chains or be biologically recycled; these metals generally display longer residence times in surface waters than unassimilated metals, which get packaged into fecal pellets and sink out of surface waters (Fowler and Knauer 1986;Fisher et al. 1991). Metals bound to the exoskeleton may also be exported with molts (Fowler 1977).Most studies that have examined the assimilation of metals by zooplankton grazers have focused on phytoplankton prey (e.g., Sick and Baptist 1979;Fisher et al. 1991;Wang et al. 1996), but heterotrophic protists can also serve as an important food source for mesozooplankton. As the dominant grazers of heterotrophic and autotrophic picoplankton in many aquatic systems (Sherr and Sherr 1994), protozoa are an important trophic link between the microbial loop and the metazoan food web (Stoecker and Capuzzo 1990). Mi-

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“…These results support the well documented preference for 210 Po uptake over 210 Pb in marine 734 31 organisms and that 210 Po is both particle-reactive and bio-reactive, whereas 210 Pb is only 735 particle-reactive (Fisher et al, 1983;Heyraud et al, 1976;Heyraud and Cherry, 1979;Larock 736 et al, 1996;Stewart and Fisher, 2003;Wilson et al, 2009). The known bio-reactive behavior 737 of 210 Po and its association with sulfur (Balistrieri et al, 1995;Cherrier et al, 1995;Harada 738 et al, 1989), both suggest its cycling in particles is more complicated than 210 Pb cycling and 739 supports our hypothesis that important end-members were missing for the model of K d (Po).…”

supporting

confidence: 80%