Notizen: Abstract Seastars, which are known to accumulate transuranium nuclides to relatively high levels, were used in laboratory radiotracer experiments (April–May, 1982) designed to determine the subcellular distribution of tissue-incorporated californium-252 and americium-241. Mediterranean asteroids (Marthasterias glacialis), collected in April 1982 and fed prey contaminated with 252Cf and 241Am, accumulated and retained large fractions of these radionuclides (252Cf, 91 to 98%; 241Am, 82 to 88%) in their pyloric caeca, the glandular complex involved with digestive and food storage processes. Differential centrifugation demonstrated an association of 252Cf and 241Am with the lysosome-mitochondrial fraction of plyoric caeca cells. Partial separation of lysosomes and mitochondria by isopycnic gradient centrifugation suggests a somewhat different subcellular fractionation of the two transuranics; 252Cf is associated primarily with the mitochondria, whereas 241Am is accumulated in both lysosomes and mitochondria. From comparison with analogous studies in mammalian systems, it is hypothesized that the long biological half-lives reported for ingested transuranics in seastars result in large part from the radionuclide association with mitochondria in the pyloric caeca.

Notizen: Abstract In a series of laboratory experiments, the biokinetics of 241Am, an important transuranium element, was studied in Meganyctiphanes norvegica, a euphausiid common in the northwestern Mediterranean. The euphausiids accumulated Am from water by passive adsorption onto exoskeletons, achieving wet weight concentration factors on the order of 102 after 1 wk exposure; concentration factors varied inversely with the size of the euphausiids and linearly with their surface area:wet weight ratios. Essentially all (96±10%) of the Am taken up from water was associated with the exoskeleton, so that negligible Am was retained by the euphausiids after molting. The retention half-time of Am in molts was 2.9 d. Euphausiids could also concentrate Am from feeding suspensions by ingesting Am-labelled diatom cells, although there was negligible Am assimilation (3±2% after 4 d feeding); after passage through the gut, virtually all (≃99%) of the ingested Am was defecated within 1 wk. The retention half-time of Am in fecal pellets was 41 and 51 d at 13° and 5°C, respectively. In oceanic waters, where the preponderance of 241Am is in the dissolved phase, uptake of Am from water by euphausiids would be the dominant route of bioaccumulation. The results underscore the importance of sinking biogenic debris from zooplankters in mediating the vertical transport of Am in the sea. Given their retention half-times for 241Am and their rapid sinking rates, fecal pellets and discarded molts have the potential to deliver most of their Am to the sediments.

Notizen: Abstract Radiotracer experiments were performed (February–April, 1982) to study the assimilation and metabolism of the transuranium nuclide americium-241 in the marine teleosts Serranus scriba (Linnaeus, 1758) and Scorpaena notata Rafinesque, 1810, caught off the Monaco coast. Fish fed with 241Am-labelled food showed that assimilation of this radionuclide takes place through the gastrointestinal walls and that the small fraction accumulated is incorporated mainly in the skin, muscle and skeleton. Gut-transfer coefficients were similar in both species and averaged 0.7% (range 0.1 to 1.7%) of the ingested activity. The calculated biological half-lives for loss of the absorbed fraction ranged between 49 and 61 d for Serranus scriba and 12 and 117 d for Scorpaena notata. Results from an intramuscular injection experiment indicated that 241Am was retained mainly in the liver, skin and skeleton; the fraction accumulated by muscle was very low. Liver displayed a relatively short biological half-time for 241Am loss of roughly 24 d. Routes of 241Am excretion from the teleosts appear to be through the kidneys, gills and feces with bile serving as a possible excretion route from the liver. From the limited amount of published information available for comparison, experimental evidence is presented which suggests that 241Am taken up via the food chain is more biologically available to marine fish than is plutonium.

Notizen: Abstract The subcellular distribution of technetium was studied using the seastar Marthasterias glacialis which had previously ingested prey labelled with 95mTc either as pertechnetate (VII) or in the reduced state (IV). The majority of the Tc [98% (IV) and 96% (VII)] was taken up and retained in the pyloric caeca, the gland responsible for digestive and food storage processes. Differential centrifugation and separation techniques have demonstrated that, at the subcellular level, technetium in the pyloric caeca was largely associated with the lysosomes. 95mTc (IV) was distributed between the lysosomes and the soluble fraction to roughly the same degree, whereas pertechnetate was more strongly associated with the lysosomal fraction. Chromatography of the cytosol by gel filtration indicated the presence of two distinct protein compounds which were responsible for binding virtually all of the technetium in the soluble fraction. Technetium had a greater relative affinity for the low molecular weight compound, more so for Tc (VII) than for Tc (IV). This anionic protein had an apparent molecular weight of approximately 10 000, and thus may play a role in metal detoxification mechanisms at the cellular level.

Notizen: Abstract A detailed study of 210Po, the predominant alpha-emitting nuclide found in most marine organisms, has been undertaken in a particular zooplanktonic species, the euphausiid Meganyctiphanes norvegica. The purpose was to obtain information concerning the origin, the localization and the flux of the nuclide in and through this organism. Measurements of 210Po were made in euphausiids of different sizes, in dissected organs and tissues, and in excretion products. The results show higher concentrations in the smaller specimens; this fact cannot be explained on the basis of surface adsorption, but is probably related to the ingestion of food. Dissection results show that the distribution of 210Po in euphausiids is not homogeneous, but that the majority is concentrated in the internal organs, the alimentary tract and the hepatopancreas in particular. The natural radiation dose received by these organs is in consequence much higher than that received by the whole animal. Use of a dynamic model allowed the flux of 210Po through M. norvegica to be calculated. The calculations confirm that food is the principal source of 210Po for this species, and clearly show that fecal pellets constitute the major elimination route. Extrapolation of the data to zooplankton in general leads to the conclusion that zooplankton metabolic activity plays an important role in transporting 210Po from the surface layers of the ocean to depth.

Notizen: Abstract The polychaete Nereis diversicolor O.F. Müller was exposed to marine sediments which had been contaminated with plutonium and americium either through the testing of nuclear devices or by the release of liquid waste effluent from a nuclear fuel reprocessing plant. The uptake of both plutonium and americium was small, about 0.5% of the concentration of these transuranics in the sediments. The degree of relative uptake of plutonium from both sediments was comparable; relative uptake of americium from sediments contaminated by waste effluent was greater than that from nuclear sediment and those previously determined from water-uptake experiments to environmentally determined plutonium concentrations in sediments and overlying waters leads to the tentative conclusion that water may be the predominant pathway for plutonium accumulation by deposit-feeding worms like N. diversicolor.

Notizen: Abstract Experiments were designed to assess the effect of different techniques of radiotracer labelling on subsequent radioisotope excretion rates in marine crustaceans. A small amphipod (Gammarus locusta) that accumulated 65Zn under a close approximation of natural conditions excreted the radiotracer during a 3-month period at a markedly different rate than those of comparable amphipods labelled with 65Zn in the laboratory via different combinations of radioactive food and seawater. Shrimp (Lysmata seticauda) administered 65Zn by three different methods in the laboratory displayed different excretion kinetics during the first 2 months of loss. The difference between excretion rates most likely was a reflection of the degree to which the various zinc pools within the shrimp had equilibrated with the radiotracer. During the next several months all 65Zn loss rates were quite similar, probably indicating that radiotracer excretion was taking place from similar zinc pools within the shrimp. The importance of adequate radiotracer labelling techniques as well as proper design of subsequent excretion experiments, used to gain reliable information on flux rates of the corresponding stable metal, is discussed. It is concluded that laboratory radiotracer experiments which are intended to supply information on actual situations in the sea require careful design and execution.

Notizen: Abstract Comparisons were made of the accumulation of a polychlorinated biphenyl (PCB) mixture from sediments and from water by the benthic worm Nereis diversicolor. Uptake from sediments was dose-dependent, attaining equilibrium concentration factors of approximately 3 to 4 after 2 months. Subsequent PCB elimination rates were concentration-dependent, with higher initial loss rates evident in the worms containing higher levels of PCBs. Accumulation of PCBs from water was much more rapid; concentration factors reached approximately 800 after only 2 weeks. Estimates were made of the relative importance of sediments and water as a source of PCBs to worms exposed to these contaminants in the natural environment. Calculations based on experimentally derived PCB concentration factors and ambient PCB levels in sediments and water suggest that compared to water, sediments contribute the bulk of these compounds to the worms. The possible mechanisms involved in the uptake of sediment-associated PCBs are discussed.

Notizen: Abstract Radiotracer experiments were designed to study the effect of certain factors on the accumulation and loss of methyl and inorganic mercury in mussels (Mytilus galloprovincialis) and benthic shrimp (Lysmata seticaudata). Methyl mercury was accumulated from both food and water to a greater degree than inorganic mercury by both species. There was a tendency for small mussels to concentrate more mercury than larger individuals, but the reason for this difference remains unclear. A trend towards greater mercury accumulation at higher temperatures was noted for mussels, but the temperature effect was relatively small over a 10 Co range between 8° and 19°C. Methyl mercury residues were eliminated by both species more slowly than those of the inorganic form. Loss from mussels was somewhat more rapid at higher temperatures; however, as in the case of accumulation, the effect of temperature was relatively small. Loss rates for small mussels were not significantly different from those for large individuals. Enhanced methyl mercury elimination was noted for the group of mussels maintained in their natural environment. The more rapid metal turnover in these individuals compared with mussels held in the laboratory was attributed to differences in the availability of natural particulate food matter and, hence, subsequent growth of the animals in the two experimental systems. The observed differences underscore the need for caution in predicting in situ flux of metals such as mercury in certain species based solely on data derived from laboratory experiments.

Notizen: Abstract Many pure samples of natural fecal pellets have been collected from mixed small copepods and from the pontellid copepod Anomalocera patersoni in the Ligurian Sea, using a specially designed pellet collection device. Sinking rates of fresh pellets and pellets aged up to 33 days have been determined at 14°C, the mean temperature of the essentially isothermal water column in the Ligurian Sea. Sinking rates of pellets collected during calm sea states increased with increasing pellet volume, but sinking rates of pellets collected during rough sea (Beaufort scale ≃6) showed little correlation with pellet size. Much of the variability in the sinking rate-pellet size relationships was the result of different pellet composition and compaction, but not pellet age. Pellets produced from laboratory diets of phytoplankton and phytoplankton-sediment mixes showed the expected wide variability in sinking rates, with sediment-ballasted pellets sinking much faster than pellets produced from pure algal diets; thus determination of vertical material fluxes in the sea using laboratory-derived fecal pellet sinking rates is unwarranted. Natural pellet sinking data for small copepods and A. patersoni have been combined with similar data for euphausiids, to yield sinking rates of roughly two orders of magnitude over three orders of magnitude in pellet volume. Pellets from small copepods sank at speeds too slow to be of much consequence to rapid material flux to the deep sea, but they undoubtedly help determine upper water distribution of materials. Recalculation of fecal pellet mass flux estimates from the literature, using our sinking rate data for natural small copepod pellets, yielded estimates about half those of previously published values. Earlier studies had concluded that small fecal pellets were of lesser significance to total material flux than fecal matter; our recalculation strengthens that conclusion. Pellets from large copepods and euphausiids, however, have the capability to transport materials to great depths, and probably do not substantially recycle materials near the surface. The fact that the majority of pellets which had previously been collected in deep traps by other workers were of a size comparable to pellets from our large copepods supports the contention that these larger pellets are the main ones involved in vertical flux.