Radioactivity in the Marine Environment (1971) / Chapter Skim
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ACCUMULATION AND REDISTRIBUTION OF RADIONUCLIDES BY MARINE ORGANISMS
ACCUMULATION AND REDISTRIBUTION OF RADIONUCLIDES BY MARINE ORGANISMS
Pages 161-199
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From page 161... ...
Because several radionuclides are accumulated by marine organisms to concentrations several thousand times the amounts in the water, several investigators have suggested that biological transport may be a factor in altering their distribution in the sea. Investigations of the presence of radionuclides in the marine environment have been concerned mainly with the release of contaminants produced by nuclear technology, including testing of nuclear weapons, as well as reactor cooling and fuel processing.
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From page 162... ...
168 Radioactivity in the Marine Environment TABLE 1 Average Concentration Factors for Benthic Algae, Plankton, and Mollusc, Crustacean, and Fish Muscle" Chemical Group Benthic algae Phytoplankton Zooplankton Mollusc Muscle or Soft Parts Crustacean Muscle Fish Muscle IA Li 0.28 1.2 0.47 Na -- -- -- 0.2 0.3 0.13 K 8 13 13 Rb 16 13 17 Cs 8 23 15 Ir IB Cu 100 30,000 6,000 5,000 1,000 Ag 23,000 9.000 7,100 7 An 470 -- 400 400 60 IIA Be 110 1,000 15 Mg 2 2 4 1 0.2 Ca 2 2.5 5 0.4 120 1.5 Sr 96 -- 1 3 0.1 Ba 17,000 900 -- 8 Ra 1,400 1 2,000 190 1,300 140 130 1111 "Zn 410 15,000 8,000 11,000 2,000 500 Cd 200 -- 1,000 Hg 1IIA B
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From page 163... ...
Elements associated with biological material also are distributed by these processes but, in addition, are transported by vertical and horizontal migrations of animals, are anchored in place on the bottom through incorporation by benthic organisms, or are carried to the bottom from the surface by the effect of gravity on dead organisms, fecal pellets, moulted exoskeletons, and other organic detritus. Any influence of marine organisms (or of physical or chemical processes)
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From page 164... ...
These concentration factors are of the same order of magnitude as those observed for the uptake of several radionuclides by these and other plankton. Thus, an examination of the distribution patterns of nitrogen, phosphorus, carbon, and silicon in the waters of areas of high biological productivity may provide an insight into possible effects of biological activity upon radionuclide transport and distribution, provided turnover rates for the nutrient elements and the radiocontaminants are comparable.
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From page 165... ...
The turnover rates for nitrogen and phosphorus may equal or exceed, in a short-time interval, the annual average, and the fractions of both elements that are not passed to higher trophic levels or to the bottom through the sinking of fecal pellets, moults, and dead organisms are probably recycled between the primary producers and the water several times during an annual cycle. Even the degree of association suggested by the annual average for the accumulation of other elements is sufficient that local populations with movements independent of the motion of the water would be expected to contain and transport significant amounts of total phosphorus and nitrogen accumulated in the euphotic layer.
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From page 166... ...
. In summary, the vertical distribution of phosphorus, nitrogen, and silica in the sea is affected by biological transport, and the concentrations of the three elements are not related to salinity or the distribution of the conservative elements.
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From page 167... ...
He tentatively attributed these variations to differences in the production of particles in the euphotic zone and their subsequent sinking and horizontal transport by currents. Uptake of Nonstructural Elements and Their Radionuclides by Phytoplankton Twenty-six elements have been reported to be concentrated in marine organisms by factors approximately equal to or greater than that for carbon.
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From page 168... ...
These organisms constitute the largest biomass, have the greatest total exposed biological surface areas, exhibit the highest concentration factors and turnover rates for many trace elements, and, in the case of zooplankton, migrate vertically. The magnitude and extent of diurnal vertical migration of zooplankton living in the upper layers, however, is often overestimated, and the plankton populations are sometimes considered to correspond to a large biological "blotter," which daily moves up and down to great depths, scavenging and redistributing radionuclides and trace elements in its path.
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From page 169... ...
For these radionuclides, biological transport from the bottom waters upward would be significantly lower than physical transport in all open ocean areas cited in Table 4 because of the relatively low concentration factors that exist for these elements. In the nearshore areas, including the Gulf of Maine, coastal waters, and the North African Upwelling, physical transport from deeper waters to the surface is at least one order of magnitude greater than the Atlantic average, and here also, physical transport would be more effective than biological transport in moving radioactive contaminants from the deeper waters to the surface.
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From page 170... ...
For those zoopiankton that do not undergo vertical migration in and out of the upper mixed layer, all of the biological transport of radionuclides into the deeper water would result from the influence of gravity upon fecal pellets, moulted exoskeletons, and dead animals. At equilibrium, the only fraction of the ingested radionuclides that would not be carried down by this mechanism would be that incorporated by growth and the amounts excreted by the animals back into the water of the mixed layer in soluble or colloidal form plus the fraction of the radionuclides dissociated into solution or colloidal suspension from the fecal pellets and moults as they settled.
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From page 171... ...
A conversion factor of 50 percent for organic material (based on carbon) does not necessarily indicate an equal conversion factor for all of the trace elements and radionuclides incorporated into, or associated with, food.
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From page 172... ...
Fecal pellets appear to provide the major transport mechanism for these trace elements and their radionuclides out of the mixed layer into the deeper waters. This agrees with the observations that those elements with low conversion factors, including barium, cerium, silicon, and 210Pb, have been shown to occur in larger amounts in deeper waters than in surface layers of the sea (Chow and Goldberg, 1960; Hogdahl et al., 1968; Rama etal., 1961; Goldberg and Koide, 1963)
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From page 173... ...
^Structural elements. Relative Uptake of Radionuclides by Zooplankton from Food and Water The calculation of conversion factors in zooplankton from concentration factors is based on the assumption that the zooplankton receive a major part of their trace elements and corresponding radionuclides from food.
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From page 174... ...
If the zooplankter is capable of extracting daily the element from a volume of water only 20 to 25 times its body volume, then 99 percent, or more, of the 95Zr would be accumulated from the food. Transport by Zooplankton, Fecal Pellets, Moults, and Dead Organisms Calculations may be made to determine the relative roles of diurnal vertical migration, fecal pellet production, moulting, and death upon the transport of radionuclides.
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From page 175... ...
Transport of iron out of mixed layer by vertical migration , 3X103 9.2 : 3.26 X104 days = 89 yr. Transport of iron out of mixed layer by fecal pellets, excretion, and dead organisms : 2.86 X 103 days = 7.8 yr.
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From page 176... ...
3 I Q ! | c oi Eastern Diurnal Vertical o M 0 0 0 0 0 O •o "5b £ S «l ® *
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From page 177... ...
Those elements that are relatively insoluble in seawater or form insoluble salts would be retained to a high degree in the fecal pellets. The proposal here that the effect of gravity on fecal pellets constitutes a major biological mechanism for the transport of some radionuclides and trace elements to the deeper waters from the surface is not new.
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From page 178... ...
proposed that a significant fraction of the energy contained in marine communities was channeled into the production of fecal pellets and that the quantitative sinking of this material out of the euphotic zone would result in rapid transport of large quantities of phosphate into the deeper waters, provided the element was not rapidly redissolved from the pellets. They also postulated that the rate of downward transport of phosphate would be reduced if fecal pellets were utilized by other zooplankton.
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From page 179... ...
These include silicon, barium, rare earths, and lead. Silver, on the basis of concentration factors in phytoplankton and zooplankton, would be transported only about 91 percent by fecal pellets, moults, and dead organisms, yet it appears to have a vertical distribution pattern in areas of upwelling similar to the elements listed above.
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From page 180... ...
Upwelling areas may provide sinks for biologically important elements. Because surface currents transport phytoplankton and zooplankton downwind from TABLE 7 Calculations of Transport of Trace Elements and Radionuclides Downward by Vertical Diurnal Migration of Zooplankton and by Sinking of Fecal Pellets, Moults, and Dead Animals and Time Required for Zooplankton to Transport Radionuclides, Introduced at the Surface, out of the Upper Mixed Layer" Percent of Vertical Transport by Zooplankton Time in Years to Transport Element out of the Mixed Zone by Biological Processes6 Radionuclide Diurnal Vertical Migration Fecal Pellets, Moults, and Dead Animals Eastern North Pacific Upwelling Areas 14C 12 88 94 3.8 32p 6 94 9.6 0.4 Si <1 >99 17 0.7 54Mn 5 95 74 3 55Fe 8 92 7.2 0.3 60Co 7 93 220 8.8 Ni 9 91 66 2.6 64Cu 3 97 11 0.4 65Zn 4 96 12 0.5 95Zr 6 94 5.4 0.2 n0Ag 9 91 11 0.4 140Ba <1 >99 17 0.7 144Ce <1 >99 73 2.9 210pb <1 >99 7.3 0.3 "See Figure 4 for method of calculation.
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From page 181... ...
Influence of Sedimentation upon Biological Availability of Radionuclides Estuarine areas differ from the open sea in several features that alter the relative influence of the water, organisms, and bottom sediments upon trace element and radionuclide transport and distribution in the two environments. In the sea, limited sedimentation processes are slow, and the depth-solubility relationships for elements in the deeper waters plus the length of time required for particles to sink to the bottom result in the return of most elements to the water as ions or colloids before they reach the bottom.
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From page 182... ...
r~ v> oo o *
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From page 183... ...
In similar experiments with clay, 27 to 55 percent of cobalt, 14 to 25 percent of silver, and 15 to 35 percent of selenium supplied by the streams would be carried to the bottom sediments by settling clay particles in the marine environment. Manganese hydroxide, in general, was least effective in coprecipitating several trace elements, with 20 percent of total stream cobalt, 4 percent of total stream silver, and 34 percent of total stream selenium remaining associated with the particles in salt water.
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From page 184... ...
These concentration factors were 100 to 200 times as great as those measured in the benthic alga Porphyra for the same radionuclides (CF 95Zr, 410; CF 95Nb, 430) , and the higher values measured in the sediments are as great as or greater than any reported for any marine organisms, for 95Zr or 95Nb.
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From page 185... ...
For the large amounts of epiphyton in sediments to significantly influence the distribution of added trace elements or radionuclides, these organisms must be capable of accumulating the contaminants at concentration factors comparable to those of inorganic adsorptive mechanisms that operate on the sediment surfaces. Marine periphyton are known to accumulate several trace elements efficiently.
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From page 186... ...
Some of the highest concentration factors for trace elements in marine organisms have been reported for benthic filter feeders. Oysters have been reported to concentrate 65Zn up to 250,000 times the amounts present in water (Chipman et al., 1958; Preston, 1966)
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From page 187... ...
of fecal pellets per m2. The top centimeter of bottom sediment in a square meter weighs about 15 kg; thus, a physical sedimentation rate of about 1 cm per year would be required to equal the biological sedimentation from fecal pellets under the oyster rafts.
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From page 188... ...
Biological transport of some trace elements and radionuclides has been attributed to these organisms. One reason is that they are capable of concentrating several elements to levels much greater than their concentration levels in the water; in addition, many zooplankton undergo vertical migration and produce detritus in the form of fecal pellets, moults, and carcasses, which sink because of the influence of gravity.
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From page 189... ...
Considerations related to biomass, feeding rates, conversion efficiencies, and migratory habits of zooplankton, as well as the chemical characteristics of the elements of interest, suggest that the major downward transport of these elements and radionuclides is effected through the influence of gravity on fecal pellets, moults, and carcasses, with direct biological transport accounting for 10 percent or less of the total movement toward the bottom of the sea. In estuarine and other nearshore marine regions, the bottom sediments are close to the sites of photosynthesis and to the sites of the introduction of fallout and terrestrial additions of radionuclides.
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From page 190... ...
1966. Composition and nutritive value of fecal pellets of a marine crustacean.
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From page 191... ...
1967a. The effects of river outflows upon the distribution pattern of fallout radioisotopes in marine organisms, p.
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From page 192... ...
1965a. The investigation of the geographical and vertical distribution of several trace elements in sea water using neutron activation analysis.
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From page 193... ...
1939. Diurnal vertical migrations of deepwater plankton.
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From page 194... ...
The purely homocentric approach to decisions about safe levels of radionuclide concentrations in the oceans is an incomplete one; nevertheless, we know of no evidence that it has not provided for the protection of man and of the food chains of the sea on which he depends for sustenance. We believe that the probably large gene pools of most oceanic species, and their efficient recruitment from oceanic areas, provide oceanic ecosystems with considerable resistance in the face of local introductions of radioactivity.
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From page 195... ...
exposition of the potentialities and realities of ecological modeling in resource management. In more theoretical ecology, however, it seems that in the use of models that actively involve organic matter of the biosphere, living and dead, research may be in a stage comparable with that of box models for the physical world 10 years or more ago.
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From page 196... ...
The major divisions of the marine environment, pelagic and benthic, have subdivisions that are largely a function of water depth. Light intensity decreases rapidly with depth so that most photosynthetic plants are found in near-surface waters in the photic zone.
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From page 197... ...
Availability is dependent upon two factors: the foci of introduction of radioactivity and the physicochemical environment into which it is introduced. It is possible that the physical and chemical characteristics of radionuclides introduced near shore are systematically different from those introduced to the pelagic or to the benthic environments.
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From page 198... ...
Because of the small size of fallout particles, their settling rates would be too slow to account for the radioactivity of the sea cucumbers at this great depth. The authors therefore attributed the increased sinking rates to the processing of fallout radionuclides into fecal pellets by zooplankton, thereby increasing the particle size and the sinking rate.
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From page 199... ...
Benthic organisms that ingest sediment particles may or may not remove the radionuclides from the sediments, depending in part on the pH of their digestive systems. It seems clear that unless plants and animals associated with the sedimentwater interface can remove radioactive trace elements from sediment particles, most of the radionuclides introduced into the ocean will eventually end up in the sediments.
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