Acute toxicities of eleven metals to early life-history stages of the yellow crab Cancer anthonyi

We report findings from the first laboratory experiments to assess toxicities of metals found in drilling muds to embryos and prezoeae of a brachyuran crab. Embryos of Cancer anthonyi are brooded externally on the abdomen of female crabs; thus, embryos may be continuously exposed to pollutants contained in sediments of contaminated benthic habitats. Lethal concentrations of metals to embryos after 7 d exposures were: iron and barium (sulfate), 1 000 mg l^–1; barium (chloride), 100 mg l^–1; aluminum and nickel, 10 mg l^–1; copper and lead, l mg l^–1; cadmium, chromium VI and manganese, 0.01 mg l^–1; mercury, 0.001 mg l^–1. All metals effectively retarded embryos from hatching at concentrations equal or lower to those causing mortality, except for cadmium. Particularly impressive was iron, which suppressed hatching at l to 10 mg l^–1, concentrations previously found non-deleterious to marine organisms and 100 times more dilute than concentrations causing significant embryo mortality. The effects of metals on embryos increased as a function of exposure duration. Embryo mortality was delayed for at least 120 h at concentrations 1.0 mg l^–1, with the exception of mercury. Lethal concentrations established at 96 h were meaningless for crab embryos, because acute toxic thresholds were not attained by that time. Larval survivorship to chromium VI, copper, and zinc increased following exposure of embryos to these metals at low concentrations (1.0 mg l^–1), suggesting induction of biochemical pathways for products which bind or metabolize metals. Identical exposures of embryos to lead failed to enhance subsequent larval survivorship, showing that inductions may be metal-specific. We suggest that exposures of brachyuran embryos at field sites and the success of their subsequent hatching in the laboratory may be a means of assessing environmental contamination otherwise difficult to monitor.     

Feeding and assimilation kinetics of Artemia franciscana fed Isochrysis galbana (clone T. Iso)

Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l⁻¹) for 11 d at 26 to 28 °C, and 34 ppt salinity. Three groups of brine shrimp were used in the feeding experiments: metanauplius III and IV (Group 1), post-metanauplius II and III (Group 2) and post-metanauplius VIII (Group 3), corresponding to 4-, 7- and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages at different concentrations of ¹⁴C-labeled I. galbana ranging from 0.05 to 30 mg C l⁻¹. The handling time of algae was determined for all three groups. The ingestion rate (I, ng C ind⁻¹ h⁻¹) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maximum level (I _max) and remained constant at food concentrations ≥10 mg C l⁻¹ (saturated food concentrations). The clearance rate (CR, μl ind⁻¹ h⁻¹) increased with increasing food concentration up to a maximum rate (CR _max), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consistent with Holling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2 and 3) differed significantly from a Type 2 response (p < 0.05). The gut passage time for the three groups of A. franciscana, feeding on saturated food concentration (20 mg C l⁻¹), varied between 24 and 29 min. As the nauplii developed to pre-adult stage the handling time of the algae increased as a function of animal size. The assimilation rate (ng C ind⁻¹ h⁻¹) in the youngest stages (Group 1 and 2) increased with increasing food concentrations, reaching a maximum level close to 10 mg C l⁻¹. At higher food concentrations the assimilation rate decreased, and the proportions of defecated carbon increased, reaching 60 to 68% in the post-metanauplius stages (Group 3). The assimilation efficiency (%) was high at the lowest food concentrations in all three groups (89 to 64%). At higher concentrations, the assimilation efficiency decreased, reaching 56 to 38% at the highest concentrations. Received: 2 February 2000 / Accepted: 25 March 2000     

Laboratory studies on the accumulation of inorganic mercury and methylmercury by the mussel (Mytilus galloprovincialis Lam) in relation to the presence of sediment

A comparative study on the accumulation of inorganic mercury and methylmercury by the mussel Mytilus galloprovincialis was based on nine days of exposure to 25 µg L^?1 HgCl₂ or to 2.5 µg L^?1 methylmercury in laboratory microcosms. Mercury (Hg) content was evaluated in the gills, digestive gland, and mantle. A higher accumulation occurred in the gills than in other tissues. The effect of the sediment on the bioaccumulation of the Hg species was evaluated. The results showed that the sediment accumulated the inorganic Hg more efficiently than the methylmercury. In both cases, the bioaccumulation in the tissues was reduced. The observed differences emphasized the need for caution when field results are compared with the results of laboratory experiments. The fate of either inorganic or organic Hg was depicted considering the absolute total amount given and the amount found in all the matrices (organism, sediment, and seawater).     

Modulation of the free amino acid pool and protein content in populations of the brine shrimp Artemia spp.

 Free amino acid (FAA) and protein content were measured in various developmental stages of Artemia franciscana, from cysts to Instar III metanauplii. In addition, decapsulated cysts of 15 Artemia populations from different localities were compared with respect to their FAA and protein content. Furthermore, the content and composition of the FAA pool were modulated by hatching the cysts at various salinities, and by enriching the nauplii with algae or a lipid-enrichment emulsion. The FAA content increased threefold from cysts to nauplii, and Instar III metanauplii contained nearly 50% taurine of total FAA. Cysts of A. franciscana were found to contain one-third the amount of FAA compared to the other Artemia species investigated. The content and pool composition of FAA was successfully modulated in 11 of 13 populations, where by the content of FAA was significantly increased when hatched at high salinity. Finally, enrichment elevated the content of FAA and changed the pool composition, thereby showing a dietary effect. Algal enrichment also increased the protein content. Received: 27 September 1999 / Accepted: 17 July 2000     

城市污水厂污泥倾倒对海洋生物的毒性研究

以广州市和佛山市的5个城市污水处理厂的污泥为实验对象,选取费氏弧菌、蒙古裸腹溞、卤虫、裸项栉鰕虎鱼仔鱼4种不同营养级的海洋生物为受试对象,结合化学分析方法,研究广州区域周边污水污泥浸出液的生物毒性效应。结果显示各污水污泥浸出液的毒性均较大,且浸出液的Cu污染浓度较高;广州市污水污泥对4种受试生物的毒性效应要高于佛山市。从污泥毒性对受试生物的选择性方面分析,发现卤虫筛分能力强且灵敏度高,而费氏弧菌则相关性好且方法简捷。研究结果为反映城市污泥的生物毒性强度和选择合适毒性评价受试生物提供基础数据。     

Disinfection efficacy on cyst viability of<Emphasis Type="Italic"> Artemia franciscana</Emphasis> (Crustacea),<Emphasis Type="Italic"> Hexarthra fennica</Emphasis> (Rotifera) and<Emphasis Type="Italic"> Fabrea salina</Emphasis> (Ciliophora)

Resting stages (cysts) of Artemia franciscana, Hexarthra fennica and Fabrea salina were exposed for two periods (acute and chronic exposures) to different concentrations of five aquaculture disinfectants (formalin, sodium hypochlorite, potassium permanganate, organic iodine, copper sulphate). The effects of chemical treatments were ranked according to their action on cyst hatching: total inhibition (no cyst hatching), heavy inhibition (significant decrease of cyst hatching), alteration of hatching synchrony, and occurrence of anomalous hatching (death of emerging individuals or birth of malformed organisms). Resting-stage viability was not completely impaired by disinfectant exposures at the ordinary doses used in aquaculture, so that usual treatments are possibly ineffective against the protist and metazoan cysts potentially present in breeding systems. On the other hand, the high resistance shown by cysts suggests the possibility of using these chemicals in live-feed disinfection.     

Factors affecting methyl and inorganic mercury dynamics in mussels and shrimp

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 C^o 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.     

Free amino acid and protein contents of start-feeding larvae of turbot (Scophthalmus maximus) at three temperatures

The contents of free amino acids (FAA) and total protein, together with growth and gut-content, of turbot (Scophthalmus maximus L.) larvae reared at 14, 18 and 22 °C were studied from first-feeding to approximately 140 effective day-degrees post hatch (D_eff ^∘). Artemia franciscana nauplii and two species of rotifers were used as prey. Protein content accounted for about 42 and 26% of dry body mass in the A. franciscana nauplii and the rotifers, respectively. The FAA pool constituted 5.6 and 4.8% of the total amino acids in the same animals. The dry body mass of turbot larvae was exponentially related to D_eff ^∘. Protein and FAA contents were linearly related to dry body mass, and were independent of rearing temperature between 14 and 18 °C. At the end of the experiment, however, turbot larvae at 22 °C had lower gut content values, retarded growth rates, and decreased FAA contents and concentrations. Thus, at this high temperature, turbot larvae seem unable to catch and ingest sufficient prey, or to sustain an amino acid assimilation rate from the intestine sufficient to meet metabolic demands. Received: 2 January 1997 / Accepted: 25 September 1998     

Effect of total cadmium and organic complexing on the uptake of cadmium by the brine shrimp,Artemia franciscana

The effect of total cadmium and organic complexing on the rate of cadmium uptake by the brine shrimp, Artemia franciscana has been studied in chemically defined saltwater solutions. The uptake of cadmium from solution by the laboratory-reared brine shrimp displays saturable uptake kinetics. Uptake of cadmium is linear in time up to a total cadmium concentration of 200 moll^-1 and saturates above 800 moll^-1. Complexation of cadmium with organic ligands decreases the uptake of the metal by the brine shrimp. This is in agreement with the view that the availability of cadmium to aquatic organisms is related to the activity of the free cadmium ion in the solution. There is no evidence that the direct uptake of cadmium complexes is important in determining uptake of cadmium. Cadmium uptake is not, however, a mere function of the free cadmium ion activity in the solution, i.e., cadmium uptake rates may differ by an order of magnitude for the same free cadmium ion activity depending on the complexation conditions. In addition to controlling the free cadmium ion activity, the role of organic ligands in metal ion buffering and metal ion masking appear important factors in determining the availability of the metal to the organism.     

Atmospheric mercury at mediterranean coastal stations

Mercury in air has been measured at five coastal Mediterranean sites, involving measurements in Spain, France, Italy, Slovenia and Israel. Four two-weeks long measurements campaigns were performed at the five sites. The measurements were carried out during autumn 2003 and winter, spring and summer 2004. Total gaseous mercury/elemental gaseous mercury, particulate mercury and divalent gaseous mercury were measured in parallel at the five sites. The activities constituted a subtask of the EU funded MERCYMS research project, which also included Mediterranean Sea cruises where both mercury in air and water were measured. The result from an evaluation of all the coastal air data is presented. Mercury concentrations from the different sites are compared with similar data obtained in northern Europe and elsewhere. The result shows that the background concentration of mercury in Mediterranean coastal air is lower than earlier anticipated. Background concentrations of TGM, RGM and TPM corresponded to 1.75–1.80 ng m⁻³, 1–13 and 3–23 pg m⁻³, respectively. The measurements also showed that the mercury concentration occasionally can be very high in some areas due to local anthropogenic emissions. It is proposed that diurnal variation in RGM concentrations observed during situation with nocturnal inversion merely is an effect of meteorology rather than due to local photochemistry.     

A model of mercury contamination in a woodland stream

A model for the accumulation of mercury in four compartments of woodland stream has been set up. The four components considered are sediments, detritus, invertebrates and fish. The model inputs are concentrations of dissolved monomethyl mercury and dissolved inorganic mercury (Hg²⁺) in the water. The model predicts that some reevaluation of current safe mercury concentrations in water may be needed in order to keep mercury concentrations in fish below current actions levels.     

Inorganic mercury and methylmercury in surface sediments and mussel tissues from a microtidal lagoon (Bizerte, Tunisia)

The aim of this study was to investigate the distribution of mercury compounds in marine sediments and mussel tissues collected in the lagoon of Bizerte, Tunisia, during two seasons (summer and winter). Inorganic mercury (Hg²⁺) concentrations in sediments were found to be highly variable, ranging from 0.04 nmol.g¹ to 3.22 nmol.g⁻¹ (dry weight) with a mean value of 0.52 nmol.g⁻¹. Anthropogenic sources of Hg²⁺, most probably metallurgy or tire production industries, have been evidenced. The mean concentration of monomethylmercury (MeHg⁺) in the surface sediments is 2.32 pmol g⁻¹ ranging from below the detection limit (0.45 pmol.g⁻¹) to 14.6 pmol.g⁻¹. No significant variation was observed between winter and summer seasons for both mercury species concentration in the sediments. The Hg²⁺ concentrations in mussel tissues are also variable, ranging from 0.007 to 1.347 nmol.g⁻¹ (dry weight). The mean concentration is 0.70 nmol.g⁻¹. In these tisssues, Hg²⁺ is generally the major compound, making up ca. 88% of total mercury concentrations. However, methylmercury concentrations are significant and homogeneous, ranging from 62 to 121 pmol.g⁻¹ (mean 96 pmol.g⁻¹). The results suggest that a fraction of the inorganic mercury load in the sediments of the lagoon undergoes methylation pathways. MeHg⁺ produced is assimilated in the mussels more readily than Hg²⁺.     

Principal Biogeochemical Factors Affecting the Speciation And Transport of Mercury through the terrestrial environment

It is increasingly becoming known that mercury transport and speciation in the terrestrial environment play major roles in methyl-mercury bioaccumulation potential in surface water. This review discusses the principal biogeochemical reactions affecting the transport and speciation of mercury in the terrestrial watershed. The issues presented are mercury-ligand formation, mercury adsorption/desorption, and elemental mercury reduction and volatilization. In terrestrial environments, OH^–, Cl^– and S^– ions have the largest influence on ligand formation. Under oxidized surface soil conditions Hg(OH)₂, HgCl₂, HgOH⁺, HgS, and Hg⁰ are the predominant inorganic mercury forms. In reduced environments, common mercury forms are HgSH⁺, HgOHSH, and HgClSH. Many of these mercury forms are further bound to organic and inorganic ligands. Mercury adsorption to mineral and organic surfaces is mainly dictated by two factors: pH and dissolved ions. An increase in Cl^– concentration and a decrease in pH can, together or separately, decrease mercury adsorption. Clay and organic soils have the highest capability of adsorbing mercury. Important parameters that increase abiotic inorganic mercury reduction are availability of electron donors, low redox potential, and sunlight intensity. Primary factors that increase volatilization are soil permeability and temperature. A decrease in mercury adsorption and an increase in soil moisture will also increase volatilization. The effect of climate on biogeochemical reactions in the terrestrial watershed indicates mercury speciation and transport to receiving water will vary on a regional basis.     

Are monoalgal diets inferior to plurialgal diets to maximize cultivation of the calanoid copepod Temora stylifera?

Temora stylifera adult copepods were fed with four different monoalgal diets and six combinations of the same cultures for 15 days. Fecundity, hatching success, number of cannibalized embryos, fecal pellet production, adult mortality and naupliar recruitment were compared, in order to find the best diet for this species. Phytoplankton species tested were Prorocentrum minimum (PRO); Isochrysis galbana (ISO); Tetraselmis suecica (TETRA) and Rhodomonas baltica (RHO) which were supplied alone or in different combinations and at various concentrations ranging from a minimum of 1 mg C L⁻¹ day⁻¹ to a maximum of 66 mg C L⁻¹ day⁻¹. Of the ten diets tested, ISO was the worst and was unable to sustain egg production and adult survival possibly because adults were unable to ingest this alga due to its small size. TETRA was also a poor food since it negatively impacted egg production and adult survival, as well as egg hatching success, possibly due to the lack of essential compounds necessary for optimal embryogenesis. RHO and PRO were the best foods inducing highest egg production, hatching success and naupliar recruitment. Even if mean egg production rates were similar to those obtained with some mixed diets, carbon intake concentrations with mixed diets were from 3 to 33 and from 6.6 to 66 times higher than with RHO and PRO given alone, respectively. Mixed diets of ISO and PRO, especially when supplied at higher concentrations (66 mg C L⁻¹ day⁻¹), had a negative effect on egg hatching success and adult survival, with a corresponding reduction in naupliar recruitment. On the other hand, mixed diets of TETRA and PRO promoted high naupliar recruitment but values were similar to PRO offered alone. Our results indicate that a good monoalgal diet such as RHO and PRO can be as effective as a mixed diet to sustain the mass cultivation of T. stylifera.     

Effect of temperature on the escape responses of larval herring,Clupea harengus

Herring (Clupea harengus L.) larvae from spring and autumn spawning stocks were reared at different constant temperatures from 5° to 17 °C. At equivalent developmental stages, the spring larvae were longer than the autumn larvae and the larvae reared at low temperatures were longer than those reared at high temperatures. At hatching and at the end of the yolk-sac stage, the larvae were induced, by a probe, to make C-start escape responses, which were recorded and analysed using a high-speed video recording at 400 frames s^-1. The response was rapid and of short duration. The tailbeat frequency and swimming speed were measured during the burst of swimming following the C-start at different test temperatures and in larvae with different temperature histories. The tail-beat frequency was strongly temperature-dependent, rising from 19 Hz at 5 °C to 37 Hz at 17 °C with no effect of temperature history, season or developmental stage. The burst-swimming speed ranged at hatching from 75 to 90 mm s^-1 at 5 °C to 110 to 160 mm s^-1 at 17 °C and at yolk resorption from 90–115 mm s^-1 at 5 °C to 175–190 mm s^-1 at 17 °C. The longer, spring-spawned larvae swam faster than the shorter autumn-spawned larvae. When the swimming speeds were expressed as body lengths (L) s^-1, these differences disappeared. Larvae swam from 7–9 L s^-1 at 5 °C to 15–20 L s^-1 at 17 °C at hatching, and from 8–9 L s^-1 at 5 °C to 15–17 L s^-1 at 17 °C at yolk resorption. There was, however, a significantly faster specific swimming speed by the larvae reared at 12 °C in spring 1991.Honorary Research Fellow of the Scottish Association for Marine ScienceUnfortunately, Karen Fretwell was drowned in an accident on 9 January 1993     

Effect of temperature on the proliferation of Gymnodinium breve and Gomphosphaeria aponina

The effect of temperature on the growth and proliferation of two marine microorganisms, the toxigenic dinoflagellate Gymnodinium breve, and a potential bio-control organism, the blue-green alga Gomphosphaeria aponina, was determined by culturing the organisms in thermal gradients established by heating and cooling the opposite ends of an aluminum bar that had been adapted to hold culture tubes. Gradients were linear and stable for the duration of each trial. There was no relationship between variations in light and growth of the organisms. Gymnodinium breve showed optimum growth at 22°C, and proliferated over a range of temperatures (17° to 30°C). Below 17°C cultures of G. breve declined in growth, and at 4°C the organisms died within 5 h. Above 31°C there was rapid decline in viability of cells, and at 33.5°C the organism died within 24 h. Gomphosphaeria aponina showed optimum growth between 24° and 29°C, with a maximum at 27°C. Growth at temperatures greater than 31°C was minimal, but the organism survived. Limitation may be due to repression of the bio-synthesis of an iron-transport compound.     

Effects of mercury on the behaviour and oxygen consumption of Monodonta articulata

The trochid snail Monodonta articulata Lamarck was exposed to mercuric sulphate at concentrations of 0.2, 0.5, 0.8 and 1 ppm Hg⁺⁺. At 24 h, retraction into the shell was observed in 0.8 and 1 ppm Hg⁺⁺; this retraction increased in these concentrations at 36 h. Retracted snails died if retained in the solutions, but generally recovered within 24 to 48 h if transferred to uncontaminated sea water. Immersionemersion behaviour and interface activity were studied over 24 h by means of an aktograph; snails in normal sea water spent more time below than above the water surface, and exhibited frequent periods of activity. Exposure to mercuric sulphate at concentration of 0.25, 0.5, 0.8 and 1 ppm Hg⁺⁺ progressively reduced both the length and frequency of activity periods. From 0.5 ppm Hg⁺⁺ upwards, emersion periods increased, and immersion periods decreased. Oxygen consumption of snails was measured in sea water and in mercuric sulphate at concentrations of 0.2, 0.5, 0.8 and 1 ppm Hg⁺⁺. Oxygen consumption decreased significantly with each progressive rise in mercury concentration. It is considered that mercury affects M. articulata by interfering with respiration, initially reducing interface activity, then forcing the snail for longer and longer periods out of the water. Retraction occurs when activity is no longer possible. It is concluded that respiratory and behavioural alterations of this nature would afford a good indicator of the presence of sub-lethal concentrations of pollutants.     

Nitrate toxicity toPenaeus monodon protozoea

Increased levels of nitrate occur in natural waters due to pollution, and in aquaculture systems from nitrification and addition of microalgal cultures for feeding. Static bioassays showed that significant mortality of larvalPenaeus monodon (Fabricius) occurred within 40 h at nitrate concentrations as low as 1 mg NO ₃ ^- l^–1. Sublethal effects of this concentration resulted in changes to ganglionic neuropiles and muscles. At higher concentrations (10 and 100 mg NO ₃ ^- l^–1), additional tissues were affected including the hypodermis, midgut and proventriculus. This is the first report of toxicity to a marine organism of nitrate at concentrations normally present in enclosed seawater and mariculture systems. The results are discussed in terms of management of culture systems and of natural marine ecosystems containing elevated levels of nitrate.     

Effects of inorganic and organic phosphates on feeding, feeding absorption, nutrient allocation, growth and righting responses of the sea urchin Lytechinus variegatus

The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l⁻¹, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l⁻¹. However, chronic exposure to low (0.8 mg l⁻¹ inorganic and 10 mg l⁻¹ organic phosphate), medium (1.6 mg l⁻¹ inorganic and 100 mg l⁻¹ organic phosphate) or high (3.2 mg l⁻¹ inorganic and 1,000 mg l⁻¹ organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate. Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only, while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues. Received: 10 April 2000 / Accepted: 2 October 2000     

Biochemical correlates of dissolved mercury uptake by the oyster Ostrea edulis

From previous work, the equilibrium concentration factor for dissolved mercury in the digestive gland of Ostrea edulis Linnaeus was found to be three to four times higher than that in the gills. In the present study, an analysis of soluble protein revealed values of 49.3±14.2 mg g wet tissue^-1 for the digestive gland and 0.7 ±0.1 mg g wet tissue^-1 for the gills. Starvation significantly reduces the soluble protein level of the digestive gland to 31.1±6.4 mg g^-1 and that of the gills to below the limit of detection. These results suggest that the difference in concentration factors between the gills and digestive gland may be based on a quantitative difference in macromolecular binding sites. However, the uptake of dissolved mercury over a period of 48 h was considerably greater in the gills, so that although the soluble protein content of the tissue may influence the final concentration factor, it does not appear to affect the rate at which this equilibrium is achieved. A more detailed investigation of the mechanism of dissolved mercury uptake by oyster gills has been carried out using isolated tissues. The process is inhibited by 5mM 2–4 dinitrophenol, by the absence of a readily metabolizable substrate (dextrose) in the uptake medium, and by 30mM K⁺. The effect of K⁺ necessitated further investigation with a specific inhibitor of K⁺ transport. Strophanthin G (ouabain), at a concentration of 0.01 mM, caused a significant increase in mercury uptake.