A field study on stress indices in the sea mussel, Mytilus edulis: application of the "stress approach" in biomonitoring.

Sea mussels, Mytilus edulis, collected from a relatively unpolluted area of the Eastern Scheldt, were transplanted along contaminated sites of the Western Scheldt for 2 1/2 and 5 months. Several established stress indices were determined such as accumulation of pollutants, adenylate energy charge (AEC), and condition index. Following field exposure, mussels were also subjected to an additional lethal or sublethal stress. The data show that environmental exposure alters the mussel's response to stress, viz., aerial exposure and increased temperature, at the organismal (anoxic survival time), biochemical (AEC), and molecular (heat shock protein synthesis) level. The "stress approach" to assessment of environmental contamination appears to be a promising method to disclose early changes in the organism at a stage when conventional parameters (condition index, AEC) remain still unchanged.

Effects of cadmium on metal composition and adenylate energy charge in the sea star Asterias rubens L.

Sea stars, Asterias rubens, were exposed to 200 micrograms Cd/L or fed with mussels which contained about 70 micrograms Cd/g dry wt. After 5 weeks, cadmium in the pyloric caeca of directly and indirectly exposed sea stars had reached levels of 12 and 9 micrograms Cd/g dry wt, respectively. For both types of exposure, a reduction of 30% of the zinc levels in the pyloric caeca was found, which was correlated with a comparable displacement of zinc from the metallothionein-like proteins. Copper levels were increased in the pyloric caeca of directly exposed sea stars. In gonads, stomachs, and body wall of directly exposed sea stars, cadmium concentrations were 4 to 9 times higher than those in animals fed with Cd-contaminated mussels. Cadmium exposure also affected metal composition in these tissues. The ovaries contained relatively large amounts of zinc. Gel filtration chromatography revealed that this zinc and the accumulated cadmium were distributed over a large range of high-molecular-weight proteins. Both direct and indirect cadmium exposure resulted in a small, but significant decrease of the adenylate energy charge (AEC) in the pyloric caeca. In the gonads, no effect of the cadmium exposure could be demonstrated on the AEC, but in the ovaries a reduction of the adenylate pool was found. In semi-field experiments, stars were exposed to 25 micrograms Cd/L or fed with mussels collected from the heavily polluted Dutch Western Scheldt. After 6 months of direct or indirect exposure, cadmium in the pyloric caeca had reached comparable levels of 8 and 7 micrograms/g dry wt, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of stress proteins under normal and heat shock conditions in gill tissue of sea mussels (Mytilus edulis) after chronic exposure to cadmium.

1. Sea mussels were exposed to 16.5 micrograms Cd/1 under semi-field conditions for almost one year. The isolated gills were incubated with 35S-methionine or -cysteine. 2. Chronic exposure to cadmium neither altered the rate of amino acid incorporation nor induced expression of heat shock proteins in the gills. 3. Heat shock imposed after chronic exposure to cadmium resulted in an increased synthesis of heat shock proteins, especially those of high molecular weight. 4. Synthesis of cadmium-binding, low molecular weight proteins was observed at any point of the exposure time. Their cadmium-binding capacity and rate of synthesis, after the initial increase, remained unchanged throughout the exposure.

Effects of cadmium in freshwater clams. II. Ultrastructural changes in the renal system ofAnodonta cygnea.

An ultrastructural study was made of the renal system of freshwater clams,Anodonta cygnea, that had been exposed to cadmium chloride (50 µg Cd/L) for 12 weeks. By stereological analysis an extended lysosomal system and a decreased number of mitochondria was apparent in the epithelial cells lining the proximal compartment of the kidney. The increase of the lysosomal system was mainly accountable to the appearance of a distinct type of lysosome, that accumulated in the apical cell region. The decrease of the mitochondrial population was accompanied by a considerable swelling of the individual mitochondria. Finally, a severe reduction of the glycogen stores was noticed. Similar, but less obvious, changes occurred in the distal kidney compartment. The results suggest that long-term exposure ofAnodonta cygnea to cadmium stimulates the lysosomal system and disturbs the function of organelles involved in the energy metabolism of resorptive kidney cells.

Effects of cadmium in freshwater clams. I. Interaction with essential elements inAnodonta cygnea.

The elemental composition of the freshwater clam,Anodonta cygnea, was investigated in response to exposure to cadmium at 50 ppb (µg/L) Cd during 12 weeks. Accumulation of cadmium affected the composition in various tissues and hemolymph. From 2 to 8 weeks of exposure considerable loss of sodium occurred, to about half the levels in control animals. During the last four weeks of exposure, sodium concentrations stabilized at the decreased level while those of potassium started to decline. Minor changes were noticeable for other elements. Calcium and iron tended to increase in all organs examined while magnesium levels remained constant. Zinc increased slightly during exposure to cadmium. For some elements, especially zinc and sulphur, hemolymph concentrations showed a response opposite to those in tissues. Concentrations of Al, B, Ba, Be, Ce, Co, Cr, Cu, Li, Mn, Mo, Ni, P, Pb, Sn, Sr, Ti, V, Y, and Zr did not change during Cd exposure. Possible sites of cadmium interaction with ionic regulation are discussed.

Effects of cadmium in freshwater clams. III. Interaction with energy metabolism inAnodonta cygnea.

Freshwater clams,Anodonta cygnea, were exposed to cadmium, at 50 ppb (µg/L), to investigate the effects of semi-chronic exposure on energy metabolism. Parameters examined included: adenylate energy charge (AEC), glycogen content, blood glucose and protein concentration, the accumulation of anaerobic metabolic end products,viz. lactate and succinate, and mitochondrial NADH-oxidase activity. In all tissues, AEC was significantly lowered after 12 weeks. Glycogen contents of the separate organs, except for the gills, were diminished to one half those of control animals. Hemolymph glucose increased between 4 and 8 weeks, whereas protein in hemolymph steadily decreased, to about one half the concentration of controls at 12 weeks. Lactate increased in mantle and midgut gland, whereas in gill only an initial accumulation was found after 2 weeks of exposure. Succinate concentrations increased in all organs between 4 and 8 weeks of Cd exposure. Thereafter, no further accumulation occurred. From the onset of exposure to cadmium there was a gradual reduction of NADH-oxidase activity of gill mitochondria, down to 60% of the control value after 12 weeks. The data indicate an impairment of oxidative carbohydrate metabolism that is brought about by a metabolic blockade, rather than by (partial) anaerobiosis as a consequence of shell closure.

Effects of cadmium and PCBs on reproduction of the sea star Asterias rubens: aberrations in the early development.

In semifield experiments sea stars, Asterias rubens, were exposed to 25 micrograms Cd/liter or fed with mussels containing 0.6 microgram/g wet wt PCBs (Clophen A50). After 5 months of exposure, Cd concentrations in testes and ovaries were respectively 17 and 50 times higher than those in unexposed sea stars. PCB concentrations were respectively 7 and 9 times higher. With spermatozoa obtained from Cd- or PCB-exposed sea stars, normal fertilization could be achieved. However, maturation of oocytes from Cd-exposed animals was delayed and early development of embryos from Cd- or PCB-exposed animals was disturbed. Due to aberrations during the early development only 24 and 30% of the embryos obtained from Cd- or PCB-exposed sea stars, respectively, had developed to normal bipinnaria larvae after 1 week.

Toxicity of heavy metals to early life stages of Daphnia magna.

This study was designed to investigate the susceptibility of the parthenogenetic eggs of Daphnia magna to cadmium, zinc, copper, and lead. Early life stages of D. magna proved to be highly tolerant to heavy metal toxicity in comparison with later stages. This relatively high tolerance might be explained by the structural constitution of the eggs.

Effects of cadmium exposure on feeding of freshwater planktonic crustaceans.

1. Effects of cadmium exposure (0.010-0.100 ppm) on food consumption and assimilation rates of crustacean zooplankton from 2 lakes were studied in laboratory using radioisotope (14C) technique. 2. The inhibiting effects were significant 48 hr after Cd-exposure, but not after 20 hr exposure. 3. Daphnia spp. were the most affected cladocerans; copepods, especially the cyclopoids, appeared less sensitive. 4. The decrease in assimilation rates was much more marked than in the consumption rates. 5. The 14C-technique offers quick and sensitive means of studying the effects of heavy metal toxicity.

Effects of cadmium on consumption, assimilation and biochemical parameters of Daphnia magna: possible implications for reproduction.

1. The effects of cadmium on consumption, assimilation rates and biochemical parameters of Daphnia magna were determined. 2. The consumption and assimilation rates of 14 days 1.0 ppb Cd treated animals tended to decrease slightly, the decline of these rates at 5.0 ppb Cd (14 days), however, was highly significant (P less than 0.001). 3. The assimilation efficiencies of daphnids exposed to cadmium did not significantly differ from control. 4. No notable changes in the biochemical composition of daphnids could be noticed after 7, 14 and 21 days of cadmium exposure. 5. It seems as if not one metabolic process in particular was depressed due to cadmium, but metabolic activities seemed to be inhibited on the whole. 6. Results are discussed in relation with data of a previous study on the reproduction of D. magna under cadmium stress.

Facultative anaerobiosis in molluscs.

The glycolytic fermentation of molluscs is rather complex. Multiple end products accumulate (lactate, alanine, octopine, succinate, propionate, acetate and CO2), which are partly formed in the cytoplasm and partly in the mitochondrion. Various schemes have been presented to account for these end products as well as for the maintenance of the redox balance. With respect to the role of alanine there are two opinions: (1) alanine accumulation is continuous and is essential for the generation of the mitochondrial NADH required in the reduction of fumarate and (2) succinate and alanine (initial end products) accumulate in different compartments and their accumulation occurs independently. Both statements are evaluated in the light of the latest experimental observations including the regulatory properties at the phosphoenolpyruvate branchpoint and the effect of pH and 'energy charge'. For nervous tissue the function of oxygen can be replaced by the lipochrome pigment, which enables carbohydrates to be totally oxidized to CO2 and water. The simultaneous mobilization of carbohydrates and amino acids is not supported by the experimental data. Various advantages of the glycolytic fermentation in molluscs as compared with classical glycolysis in skeletal muscle are discussed.