Ambient Seawater Concentrations Research Articles

Hydrothermal amorphous silica, barite and orpiment from the crater area of seamount (SM-13) off Nicobar island, Andaman sea: Indications for the development of a new hydrothermal field

The Andaman sea characterized by trench-arc-backarc elements (Andaman-Nicobar island-arc, the Andaman back-arc spreading center, the seamount complex, and the back-arc basin) is a complex active basin and is known for hydrothermal activity in some of the seamounts (subaerial and submarine) of the volcanic arc. In the present study, 13 submarine seamounts (SM1- SM13) in the southern Andaman volcanic arc, extending from 6°47′N: 94°43′E to 7° 56′ N: 94° 2.47′E, were surveyed onboard RV Sindhu Sadhana (November 2021) to find the evidences for the hydrothermal activity. Out of the 13 seamounts, at one crater seamount (SM-13) we have observed evidence for hydrothermal activity characterized by plumes rich in dissolved gases (mainly CO2) in the water column, live chemosymbiotic organisms (Bathymodiolus species), and neoforming minerals such as amorphous silica, barite and orpiment. We observed two plumes rich in dissolved gases (mainly CO2), called GP1 and GP2, in the water column at two different water depths i.e. 400 and 380 mbsl respectively. Geochemical analysis of the water samples shows enhanced TCO2 concentrations within the plumes rich in dissolved gases (mainly CO2) observed in sub-bottom profiler data, however, the dissolved methane concentrations do not show any enrichment when compared with ambient seawater concentrations. Apart from the enhancement in the TCO2 concentrations, pH and total alkalinity data also show fluctuations within the same depth zone which may be attributed to the hydrothermal plume exhausting from the crater seamount. The occurrence of live chemosymbiotic organism Bathymodiolus species indicate an active and continuous supply of H2S. The precipitation of neoforming hydrothermal minerals such as amorphous silica, tabular barite, and orpiment on the surface of the rock samples further supports the hydrothermal activity. Previous studies carried out in 2007 have reported hydrothermal ferromanganese oxides precipitated from low-temperature hydrothermal fluids (Surya prakash et al., 2012) and inferred SM-13 as a dormant submarine volcano (Kamesh Raju et al., 2012). However, after 14 years, we observe volatile emissions to the water column, hydrothermal mineral precipitation and live chemosymbiotic organisms from the same seamount. These observations of the present study infer development of a new hydrothermal field in the least explored Andaman Sea. This study adds up a new active site to the global hydrothermal inventory which may allow better estimation of global hydrothermal flux and its role in oceanic elemental cycle.

Seasonal variability of δ18O and δ13C of planktic foraminifera in the Bering Sea and central subarctic Pacific during 1990–2000

AbstractWe evaluated a 10 year time series of δ18O and δ13C records from three planktic foraminifers (Neogloboquadrina pachyderma, Globigerina umbilicata, and Globigerinita glutinata) in the Bering Sea and central subarctic Pacific with a focus on their responses to environmental changes. Foraminiferal δ18O followed the equilibrium equation for inorganic calcite, with species‐specific equilibrium offsets ranging from nearly zero (−0.02‰ for N. pachyderma and −0.01‰ for G. umbilicata) to −0.16‰ (G. glutinata). Equilibrium offsets in our sediment trap samples were smaller than those from plankton tow studies, implying that foraminiferal δ18O was modified by encrustation during settling. Habitat/calcification depths varied from 35–55 m (N. pachyderma and G. umbilicata) or 25–45 m (G. glutinata) during warm, stratified seasons to around 100 m during winter, when the mixed layer depth increases. Unlike δ18O, foraminiferal δ13C showed species‐specific responses to environmental changes. We found a dependency of δ13C in G. umbilicata on CO32− concentrations in ambient seawater that agreed reasonably well with published laboratory results, suggesting that δ13C of G. umbilicata is subject to vital effects. In contrast, δ13C of N. pachyderma and G. glutinata are likely affected by other species‐specific biological activities. Seasonal flux patterns reveal that fossil records of N. pachyderma and G. glutinata represent annual mean conditions, whereas that of G. umbilicata most likely indicates those of a specific season. Because none of these three taxa was abundant from December to February, their fossil records likely do not reflect isotope signals from cold seasons.

Linking trace element variations with macronutrients and major cations in marine mussels Mytilus edulis and Perna viridis.

Marine mussels have long been used as biomonitors of contamination of trace elements, but little is known about whether variation in tissue trace elements is significantly associated with those of macronutrients and major cations. The authors examined the variability of macronutrients and major cations and their potential relationships with bioaccumulation of trace elements. The authors analyzed the concentrations of macronutrients (C, N, P, S), major cations (Na, Mg, K, Ca), and trace elements (Al, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Ba, Pb) in the whole soft tissues of marine mussels Mytilus edulis and Perna viridis collected globally from 21 sites. The results showed that 12% to 84% of the variances in the trace elements was associated with major cations, and the tissue concentration of major cations such as Na and Mg in mussels was a good proxy for ambient seawater concentrations of the major cations. Specifically, bioaccumulation of most of the trace elements was significantly associated with major cations, and the relationships of major cations with trace cations and trace oxyanions were totally opposite. Furthermore, 14% to 69% of the variances in the trace elements were significantly associated with macronutrients. Notably, more than half of the variance in the tissue concentrations of As, Cd, V, Ba, and Pb was explained by the variance in macronutrients in one or both species. Because the tissue macronutrient concentrations were strongly associated with animal growth and reproduction, the observed coupling relationships indicated that these biological processes strongly influenced the bioaccumulation of some trace elements. The present study indicated that simultaneous quantification of macronutrients and major cations with trace elements can improve the interpretation of biomonitoring data.

Variation in soft tissue chemistry among scyphozoan and cubozoan jellyfishes from the Great Barrier Reef, Australia

Bioaccumulation of trace elements in jellyfish has so far received little attention, despite their being prey for many animals from multiple trophic levels and targeted by commercial jellyfish fisheries. Scyphozoan and cubozoan jellyfish were collected over a three year period from across-shelf and along the northern and central Great Barrier Reef, Australia. To test the hypotheses that jellyfishes were able to accumulate elements above ambient background levels, and if there were spatial or temporal variations among species, soft tissue concentrations of 14 trace elements were compared with ambient seawater concentrations. Most elements, including aluminium, arsenic, barium, cadmium, chromium, copper, iron, manganese and zinc were measured at concentrations above ambient seawater levels indicating bioaccumulative capacity. Results showed some regulation of lithium in Cassiopea sp., Cyanea sp. and Mastigias sp., while calcium, magnesium and strontium reflected ambient conditions for all species. Accumulation varied significantly among species and sampling locations. For Mastigias sp. and Netrostoma sp., tissue concentrations of Al, As, Cu, Fe and Zn decreased with distance from the mainland. The hypothesis that jellyfishes are capable of accumulating trace elements was accepted, and their use as biomonitors should be investigated further.

Flesh residue concentrations of organochlorine pesticides in farmed and wild salmon from British Columbia, Canada

The present study reports measured levels of organochlorine pesticides (OCPs) in commercial salmon feed (n = 8) and farmed Atlantic, coho, and chinook salmon (n = 110), as well as wild coho, chinook, chum, sockeye, and pink salmon (n = 91). Flesh residue concentrations (ng/g wet weight) of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, chlorobenzenes (CBz) and cyclodiene pesticides (e.g., dieldrin, mirex) were 2 to 11 times higher (p < 0.05) in farmed salmon compared with wild salmon. Concentrations were positively correlated with flesh lipid levels. Farmed Atlantic salmon (12-15% lipid) typically exhibited the greatest OCP burdens compared with other salmon species. However, when expressed on a lipid weight basis, concentrations of OCPs (ng/g lipid weight) in wild salmon, in many cases, exceeded those levels in farmed salmon. Observed interspecies and site-specific variations of OCP concentrations in farmed and wild salmon may be attributed to divergent life history, prey/feed characteristics and composition, bioenergetics, or ambient environmental concentrations. Calculated biomagnification factors (BMF = C(F)/C(D), lipid wt) of OCPs in farmed salmon typically ranged between two and five. Biomagnification of chemicals such as DDTs, chlordanes, and mirex was anticipated, because those compounds tend to exhibit high dietary uptake and slow depuration rates in fish because of relatively high octanol-water partition coefficients (K(OW)s > 10⁵). Surprisingly, less hydrophobic pesticides such as hexachlorocyclohexanes and endosulfans (K(OW) s < 10⁵) consistently exhibited a high degree of biomagnification in farmed salmon species (BMFs > 5). This is contrary to previous laboratory and field observations demonstrating fish BMFs less than 1 for low K(OW) chemicals, because of efficient respiratory elimination of those compounds via gills. The results suggest that ambient seawater concentrations and bioconcentration-driven accumulation may play a key role in the bioaccumulation of these relatively more water-soluble contaminants in farmed salmon. Finally, OCP exposure through consumption of British Columbian salmon is found to be low relative to United States national average per capita total exposure levels and provisional tolerable daily intakes.

The influence of environmental factors and nutrient concentrations in tissues of the seaweed Ahnfeltia tobuchiensis (Rhodophyta: Ahnfeltiales) on the primary production and dark respiration of its population

Complex investigations of the influence of environmental factors, viz., the temperature, photosynthetically active radiation (PAR), ambient seawater concentrations of ammonium (NH4), and orthophosphate (PO4), as well as the contents of organic carbon (C), nitrogen, phosphorus, and a-chlorophyll (Ch) on the rate of photosynthesis (Pn) and dark respiration (Rd) in the tissues of the unattached red seaweed Ahnfeltia tobuchiensis (Rhodophyta: Ahnfeltiales) population, were performed in the summers of 2000 and 2008 in Izmeny Bay (Kunashir Island) under in situ conditions. The dependence of photosynthesis on PAR intensity (P-I dependence) is described by the equation of a hyperbolic tangent. The population of A. tobuchiensis forms a layer up to 50 cm thick with an area of 23.3 km2 and a biomass of 125 000 tons. The Pn rate of seaweed population during daylight hours varies within a wide range, with an average of 1.04 mg O2 O2/(gdry weight h) and largely depends on PAR intensity and availability (r = 0.70–0.98). The maximum photosynthesis rate (Pmax) is substantially defined by the ambient concentration of NH4 (r2 = 0.91, p < 0.01). The rate of Rd during the night is on average 0.1 mg O2/(gdry weight h) and mainly depends on the content of Ch in seaweed tissues (r2 = 0.83, p < 0.01), which, in its turn, is regulated by the ambient concentration of PO4 (r2 = 0.86, p < 0.01). With average biomass values of 5.4 kg/m2 or 1.8 kgdry weight/m2, the net primary production (Pn) of seaweed population is estimated to be on average 22.5 g O2/(m2 day) or 8.4 g C/(m2 day). Based on these indices, the investigated population is one of the most productive ecosystems of the World Ocean. It is supposed that such indices of the A. tobuchiensis population are attained due to the highly efficient use of weak light and a low light-saturation level of photosynthesis, compared to other seaweeds.

Oil well produced water discharges to the North Sea. Part I: Comparison of deployed mussels (Mytilus edulis), semi-permeable membrane devices, and the DREAM model predictions to estimate the dispersion of polycyclic aromatic hydrocarbons

The oil companies operating in the Norwegian sector of the North Sea have conducted field studies since the mid-1990s to monitor produced water discharges to the ocean. These studies have been used to refine monitoring methods, and to develop and validate a dispersion and impact assessment model. This paper summarizes monitoring data from surveys conducted in two major oil and gas production areas, and compares the results to concentrations of polycyclic aromatic hydrocarbons (PAH) in surface waters predicted by the dose-related risk and effect assessment model (DREAM). Blue mussels and semi-permeable membrane devices (SPMDs) were deployed in the Ekofisk and Tampen Regions and analyzed for more than 50 PAH. PAH concentrations in ambient seawater were estimated based on the mussels and SPMD concentrations, and compared to model predictions. Surface water total PAH concentrations ranged from 25 to 350 ng/L within 1 km of the platform discharges and reached background levels of 4-8 ng/L within 5-10 km of the discharge; a 100,000-fold dilution of the PAH in the discharge water. The PAH concentrations in surface water, predicted by three methods, compared well for the Ekofisk Region. The model predicted higher concentrations than the field-based methods for parts of the Tampen Region; particularly the most tidally influenced areas. Tidally-mediated fluctuations in PAH concentrations in surface water must be considered because they affect the estimation of PAH concentrations from mussel and SPMD residue data, and the predictions by the DREAM model. Predictions using mussels, SPMDs, and modeling support and complement each other; all are valuable tools for estimating the fate and impact of chemical contaminants in produced water that are discharged to the ocean.

Evolutionary aspects of intestinal bicarbonate secretion in fish

Experiments compared intestinal HCO 3 − secretion in the intestine of marine teleost Gulf toadfish, Opsanus beta, to representatives of early chondrostean and chondrichthyan fishes, the Siberian sturgeon, Acipenser baerii, and white-spotted bamboo shark, Chiloscyllium plagiosum, respectively. As seen in marine teleosts, luminal HCO 3 − concentrations were 10-fold plasma levels in all species when exposed to hyperosmotic conditions. While intestinal water absorption left Mg 2+ and SO 4 2− concentrated in intestinal fluids up to four-fold ambient seawater concentrations, HCO 3 − was concentrated up to 50 times ambient levels as a result of intestinal HCO 3 − secretion. Reduced luminal Cl − concentrations in the intestine of all species suggest that HCO 3 − secretion also occurs via Cl −/HCO 3 − exchange in chondrostean and chondrichthyan fishes. Sturgeon began precipitating carbonates from the gut after only 3 days at 14‰, a mechanism utilized by marine teleosts to reduce intestinal fluid osmolality and maintain calcium homeostasis. Analysis of published intestinal fluid composition in the cyclostome Lampetra fluviatilis reveals that this species likely also utilize intestinal HCO 3 − secretion for osmoregulation. Analysis of existing cyclostome data and our results indicate that intestinal Cl −/HCO 3 − exchange plays an integral role in maintaining hydromineral balance not only in teleosts, but in all fish (and perhaps other animals) with a need to drink seawater.

The chemistry of lava-seawater interactions II: the elemental signature

The flow of lava into the ocean at the shoreline of Kilauea Volcano during the ongoing Pu’u O’o eruption has allowed a detailed study of the geochemical interaction between lava and seawater. This paper focuses on the chemistry of the major and minor elements in the fluids that resulted from this interaction. The elemental enrichments in these fluids are dominated by three processes: (1) evaporation of water from seawater, which creates solutions enriched in the major elements found in seawater, (2) congruent dissolution of the basalt glass matrix, which is limited by the solubility of some of the elements in seawater, and (3) removal of volatile phases from the lava on contact with seawater.Using a simple model of volatile emanation (using published emanation coefficients) and congruent dissolution, we are able to explain the concentrations observed for the majority of elements in precipitation from the steam plume at the shoreline lava entry and in water allowed to interact with molten lava in controlled experiments. Fe, Al, Ti, and some of the rare earth elements (REEs) in precipitation samples from the steam plume at the lava entry were > 10,000-times enriched over their ambient seawater concentrations, suggesting that these elements may be useful for identifying submarine eruptions. The flux of elements from the Kilauea ocean lava entry is greater than that from a typical midocean ridge hydrothermal vent field for Al, Cd, Co, and the REEs, whereas the opposite is true for the remainder of the elements studied.

Formula omitted]Pu and [formula omitted]Cs concentrations for zooplankton and nekton in the Northwest Pacific and Antarctic Oceans (1993–1996)

The concentrations of 239+240 Pu and 137 Cs in zooplankton and nekton in the Northwest Pacific and Southern Oceans were measured during the period 1993–1996. The object of the sampling was to assess the potential impacts of existing submerged anthropogenic-radioactive materials in the western North Pacific as well as the East China Sea. Samples from the Bransfield Strait of the Antarctic Ocean provided a control source impacted by only atmospheric bomb fallout. No particularly elevated levels of 239+240 Pu were found in zooplankton samples from the Northwest Pacific, although significantly lower levels of 239+240 Pu were found in three mixed zooplankton samples from the Bransfield Strait. The body burden of 239+240 Pu in zooplankton appears to reflect concentrations in ambient seawater with some variation. Some additional measurements of 137 Cs in fish are also reported here to complement existing databases and for future reference in the regional marine environmental radioactivity monitoring effort.

Imposex development in response to TBT pollution in Hinia incrassata (Ström, 1768) (Prosobranchia, Stenoglossa)

The stenoglossan prosobranch Hinia incrassata, collected along the coast of Brittany and Normandy between 1988 and 1997, exhibits imposex also known as pseudohermaphroditism (the occurrence of male parts in addition to the female genital system) in response to tributyltin (TBT) pollution. Excluding some normal females (stage 0), different imposex stages as defined by Fioroni et al. (1991a)(1a, 1b, 2a, 3a and 4) can be distinguished and have been documented for the first time using scanning electron micrographs. Additional malformations of the genital tract are described. Neither TBT-induced sterilization nor sex change occur in the analyzed samples. TBT accumulation in soft parts was analyzed and bioconcentration factors (BCF) were found to be between 4.68 · 10 4 and 1.22 · 10 5. The VDS (vas deferens sequence) index, RPL (relative penis length) index and the average female penis length (FPL) in populations exhibit a significant dependence on both TBT concentrations in ambient sea water and TBT body burden. An interspecific comparison between imposex intensities in sympatrically living populations of Hinia incrassata, Nucella lapillus and Hinia reticulata reveals that H. incrassata exhibits the lowest TBT sensitivity of the three species. But even in this relatively unsensitive species the threshold concentration for imposex development is below 1.5 ng TBT as Sn l −1. The VDS index is recommended as the most suited biological parameter for effect monitoring purposes because this index is characterized by the lowest deviation of data points from calculated concentration-effect-equations and shows no seasonal variations. Hinia incrassata is proposed for large large-scale TBT surveys in the Mediterranean being planned by OSPARCOM for the North Atlantic. Furthermore the species can be used for TBT temporal trend monitoring. Studies in France, for example, where TBT was partially banned in 1982, show little or no recovery from TBT contamination in H. incrassata and two other prosobranch species between 1989 and 1997.

98/00701 Coal characterization for NO x prediction

Samples of seaweed Fucus vesiculosus collected from Cumbria and the Isle of Man in 1980 have been analysed for their alpha and gamma radioactivity, using a combination of chemical separation and alpha and gamma spectrometry. The source of artificial radioactivity in the Irish Sea is primarily the effluent discharge from the nuclear fuel reprocessing facility at Windscale, and significant decreases in activity were seen with increased distance from the source. Seaweed measurements, used as a marker of the ambient seawater concentrations, allowed comparison of the environmental behaviour of different radionuclides on entering the marine environment. The nuclides could be divided into two categories: (a) 137Cs, 134Cs, 238Pu, 239 + 240Pu and 241Am and (b) 106Ru, 95Nb, 95Zr and 144Ce, dependent on their concentration distribution amongst the samples. Using the 134Cs/137Cs ratio, a relative time scale was established between the samples which allowed correction of all activities for decay during the time period since discharge, enabling comparison of the transport behaviour of the different radionuclides. It was found that the degree of conservation of the nuclides in seawater decreased in the sequences: zirconium > cerium > ruthenium and caesium > plutonium > americium.

Experimental and observational studies of radiolarian physiological ecology, 6. Effects of silicate-supplemented seawater on the longevity and weight gain of spongiose radiolarians Spongaster tetras and Dictyocoryne truncatum

Radiolaria occur abundantly in surface water with low silicate concentrations (ca. 1 μM), yet they construct remarkably robust siliceous skeletons. This indicates they compete very effectively for the available silicate. To examine the effects of variation in silicate concentration on skeletal growth and vitality, two spongiose radiolarians Spongaster tetras and Dictyocoryne truncatum, collected in surface plankton tows near Barbados, West Indies, were maintained in plastic tissue culture dishes, each well of the dishes containing ca. 15 ml seawater emended with additional sodium silicate of 0 μM (control), 50 μM, 100 μM and 150 μM. Their longevity and skeletal weight gain, the latter calculated from equations relating skeletal weight to a linear dimension of the skeleton, are reported with descriptions of their living features. The addition of silicate up to 100 μM had no statistically significant effect on the weight of silicate deposited per shell for either S. tetras or D. truncatum. However, noticeable detrimental effects resulted in earlier death in both S. tetras and D. truncatum at 150 μM. Early death was more frequent in D. truncatum. Spongaster tetras that grew skeletons may survive longer when cultured in 50 μM silicate-enriched seawater compared to 150 μM enriched seawater, but not longer than those cultured in unsupplemented seawater. D. truncatum has the longest longevity in unsupplemented seawater. In addition, scanning electron microscopy of shells collected from individuals that grew in culture revealed no evidence of enhanced skeletal growth or structures with silicate enrichment of the culture medium. These data add further evidence that S. tetras and D. truncatum are capable of competing very effectively for silica in ambient seawater concentrations of approximately 1.0 μM, and also that changes in seawater silicate may not have a dramatic effect on longevity, skeletal size, or weight of some radiolarians. Thus other environmental variables, such as variations in temperature and salinity, may more likely impress a relatively more salient signal in the microfossil record. Daily mean weight gain values at the four treatments ranged from 4.3 ng to 6.3 ng in S. tetras and from 19.7 ng to 27.1 ng in D. truncatum. For the control group, mean total weight gain was 0.035 μg in S. tetras and 0.083 μg in D. truncatum. Compared to the previously published results for S. tetras, using larger glass vials, the weight gain values seem to be significantly smaller. However, estimated silicate consumption ratios with respect to the available amount in the culture vessel by S. tetras agree substantially with each other. This suggests that observed radiolarian skeletal growth in the previous and present experiments was rather substantially affected by other environmental factors, such as available micronutrients, related to the water volume used in the culture vessel.

Lava‐seawater interactions at shallow‐water submarine lava flows

Hydrothermal plumes associated with nearshore lava flows from Kilauea Volcano, Hawaii were studied on five occasions during 1989–1990 to address the current lack of data on direct lava‐seawater interactions. The following enrichments were found in the sea‐surface hydrothermal plumes above the active underwater lava flows: H2, 15,000x ambient seawater concentrations; Mn, 250x; and Si, 20x. Water temperatures reached 46°C. Lower concentrations and temperatures were observed in the plumes with increasing distance from shore, with H2, Si, and Mn concentrations linearly related to seawater temperature. Unlike deep sea spreading center hydrothermal plumes, no CH4 enrichment was observed. The elevated H2 is likely to be from water‐rock reactions, rather than from the release of magmatic gas. The plume mass/heat ratios presented here suggest that submarine flood basalts, although aerially large, should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust.

Nutrient uptake in the reef-building coral Acropora palmata at natural environmental concentrations

Experiments were carried out over 15 mo to assess the net exchange of dissolved inorganic nitrogen (DIN) by the symbiotic coral Acropora palmata (Lamarck) under near-natural environmental conditions. Specimens were enclosed in situ in transparent acrylic chambers and changes in the ambient seawater concentrations of nitrate, nitrite and ammonium determined over 1 h closed incuba- tion~. There was a consistent depletion of nitrate and a more variable but significant mean depletion of ammonium within the experimental chambers, indicating simultaneous net uptake of both ions by the coral. No exchange of nitrite could be detected. No significant changes in concentration of any form of DIN occurred in ambient seawater control chambers. Contrary to previous predictions from studies of uptake kinetics in isolated zooxanthellae and other coral species, mean net rates of nitrate uptake exceeded that of ammonium uptake by a factor of 2. Nitrate uptake was dependent on substrate concentration, with a linear response over the range of ambient seawater concentrations encountered in the study. Rate of ammonium uptake was apparently independent of substrate concentration and the rate of uptake of each ion was independent of the concentration of the others. A diurnal rhythm was noted in nitrate uptake rates, after changes in concentration had been taken into account, which suggests that although uptake continued over the complete 24 h period, maximal rates of uptake were not maintained throughout the night. These results support previous studies which have demonstrated the capability for dual uptake of both nitrate and ammonium by zooxanthellae, but suggest that under natural conditions nitrate rather than ammonium provides the primary external source of dissolved inorganic nitrogen in this species.

Selenium content of marine food chain organisms from the coast of China

Over 250 samples of phytoplankton, zooplankton, other invertebrates, fish and macroalgae were collected from coastal waters of the southeast China Sea and analyzed for their selenium (Se) content. Phytoplankton (1·2 ppm) contained about twice as much Se as seaweeds (0·08 to 0·6 ppm) and both of these algal groups accumulated Se to concentrations three to four orders of magnitude above the ambient concentration in seawater. The Se content of zooplankton (∼ 4 ppm) was three to four times higher than phytoplankton, and juvenile stages (nauplii) and small zooplankton had the highest Se content. Fish often contained less Se than zooplankton on a dry weight basis. The Se content of various tissues and organs in fish varied from a maximum in liver (1·4–28·3 ppm) to a minimum in muscle and hard tissues (1–3 ppm and 0·1–6 ppm, respectively). There was little evidence for the bioaccumulation of Se in organisms of higher trophic status. The major concentrating step in the food web was Se incorporation by phytoplankton and zooplankton, up to four orders of magnitude above ambient seawater concentrations.

Alpha and gamma radioactivity in Fucus vesiculosus from the Irish sea

Samples of seaweed Fucus vesiculosus collected from Cumbria and the Isle of Man in 1980 have been analysed for their alpha and gamma radioactivity, using a combination of chemical separation and alpha and gamma spectrometry. The source of artificial radioactivity in the Irish Sea is primarily the effluent discharge from the nuclear fuel reprocessing facility at Windscale, and significant decreases in activity were seen with increased distance from the source. Seaweed measurements, used as a marker of the ambient seawater concentrations, allowed comparison of the environmental behaviour of different radionuclides on entering the marine environment. The nuclides could be divided into two categories: (a) 137Cs, 134Cs, 238Pu, 239 + 240Pu and 241Am and (b) 106Ru, 95Nb, 95Zr and 144Ce, dependent on their concentration distribution amongst the samples. Using the 134Cs/ 137Cs ratio, a relative time scale was established between the samples which allowed correction of all activities for decay during the time period since discharge, enabling comparison of the transport behaviour of the different radionuclides. It was found that the degree of conservation of the nuclides in seawater decreased in the sequences: zirconium > cerium > ruthenium and caesium > plutonium > americium.

Bioaccumulation factors of chlorinated hydrocarbons between mussels and seawater

The bioaccumulation of PCB and DDT compounds by mussels, Mytilus spp., from ambient seawater was determined by measuring concentrations of these chlorinated hydrocarbons in both mussels and seawater at four sites on the Mediterranean coast of France and two sites in California. Bioaccumulation factors were found to vary over an order of magnitude. Ratios of the concentrations of PCB in mussels, consisting predominantly of pentachloro-and hexachlorobiphenyls, to concentrations in ambient seawater ranged between 69 000 and 690 000; the corresponding ratios of concentrations of p, p′-DDE or p, p′-DDT ranged from 40 000 to 690 000. Although mussels appear to be appropriate and convenient indicator organisms of local chlorinated hydrocarbon contamination levels, the factors contributing to this variance must be determined before mussels are widely used in global monitoring programmes.