ALBERT

Notes: SUMMARY. The accumulation of cadmium from an experimental medium by the freshwater amphipod Gammarus pulex is described.Much of the uptake is internal as opposed to adsorption on the body surface, and after an apparent saturation of the exoskeleton the hepatopancreas becomes an increasingly important site of cadmium storage. The haemolymph cadmium concentration reaches a high level compared with marine crustaceans, achieving a concentration factor (ratio of internal Cd/ external Cd) of 100 after about 60 h uptake.The cadmium uptake process is severely inhibited after exposure of experimental animals to 0.5 mM 2:4 Dinitrophenol, indicating the mediation of an active process. This fact together with the negative relationship between cadmium uptake rate and the calcium concentration of the animal suggests that cadmium accumulation by this species may be at least partially accounted for by a process of ‘accidental’ active cadmium uptake, with cadmium substituting for calcium on a calcium regulatory mechanism.As yet it has not been possible to establish a true stoichiometric relationship between the two metals. Although calcium influx and cadmium uptake (influx) rates are similar over a wide range of external concentrations, calcium influx is clearly inhibited by a low external ratio of cadmium to calcium. This indicates that the relationship between the two metals is far from an equimolar one and the possibility of non-competitive inhibition of calcium influx by cadmium cannot be eliminated.

Notes: SUMMARY. Adult Gammarus pulex lose about 42% body calcium into solution over a 2–3-day period preceding the moult. A further 54% body calcium is lost with the exuviae, leaving c. 4% in the newly moulted animal.Nearly all of the body calcium in a stage A (post moult) animal is contained in the hepatopancreas and a transient increase in the calcium content of this tissue is seen in some individuals. The haemolymph calcium compartment is heavily depleted at this stage. In stage B animals the hepatopancreas calcium level has returned to, or even fallen below, the intermoult level while the haemolymph calcium concentration remains lower than in intermoult animals.Animals switch from a strongly negative calcium balance to a state of rapid calcium uptake immediately following moult. Uptake at 10°C proceeds at a rate of between 3 and 10 μmol g−1 h−1 depending on the calcium concentration of the external medium. The lower rate is found in starved animals in 0.1 mM calcium and this concentration is probably close to a minimum for the satisfactory restoration of body calcium. Recalcification is completed in 10–14 days in 0.1 mM calcium and is apparently enhanced by the presence of food in the form of a portion of oak leaf together with the cast exuviae. In 1.0 mM calcium the recalcification period is shortened to 3–4 days. This is considerably longer than the time recorded for French populations of this species (Vincent, 1969), although reasons for this are offered.

Notes: The rates of drying of cut perennial ryegrass (Lolium perenne L.) herbage over short periods of time were measured in four experiments in a controlled environment room. Standard weights of 33·7 g grass dry matter (DM) were placed in half the area of wire-mesh trays (0·5 m long × 0·3 m wide × 0·07 m high with 11-mm-square mesh) which, so as to simulate conditions in a swath, were supported on wooden frames within dark plastic boxes 25 mm above 35-mm-thick wet sponges. The trays of grass in the controlled environment room were weighed hourly for 7 h, drying rate being assessed by the change in grass fresh weight. Light was supplied from 400-W mercury vapour lamps, while an air conditioning unit within the controlled environment room allowed control of vapour pressure deficit (VPD). Only one particular VPD could be created on any one day and resource limitations restricted the study to one replicate per day. The first experiment correlated drying rates under the mercury vapour lamps with drying rates in the open air under sunshine over 3 d. This work showed that a distance of 200 mm between the tray and lamps equated to 1081 W m–2, 400 mm to 432 W m–2 and 600 mm to 281 W m–2. Experiment 2, conducted with previously frozen grass, was a 4 × 4 factorial design with light intensity and VPD as factors. The third experiment (Experiment 3) compared the drying rate of freshly cut grass with grass that had previously been frozen in a 2 × 2 × 2 factorial design with the two grasses, two light intensities and two wind speeds as factors. The final experiment (Experiment 4) was a 3 × 2 × 2 factorial design with light intensity, VPD and wind speed as factors. A wind of approximately 3 m s–1 was simulated using a 22-mm, 30 W fan set in a fixed position 600 mm from each tray plus grass. Fresh grass was cut each morning of the experiment. There were six replicates of each treatment. The effect of the three radiation intensities on grass DM concentration in Experiment 2 was highly significant (P 〈 0·001). VPD had less effect (P 〈 0·05). Results from Experiment 3 showed that previously frozen material dried much more rapidly than fresh grass and as a result would not simulate actual grass drying in the field. Consequently in Experiment 2 fresh grass was used as opposed to previously frozen material. In Experiment 4, light intensity had the greatest influence on grass drying followed by VPD and wind speed. However, the influence of wind speed was variable. A wind speed of ≈3 m s–1 increased the rate of water loss from grass with a low initial DM concentration (〈160 g kg–1) receiving low levels of solar radiation (281 W m–2), while at higher initial DM concentrations (〉210 g kg–1) and higher solar radiation levels (432 W m–2) the effect of wind was to slow grass drying. The results from Experiments 2 and 4 also indicated that high levels of either wind (3 m s–1) or VPD (〉6 mbars), when associated with low levels of solar radiation, resulted in large increases in grass DM concentration. However, these extreme weather conditions are unlikely to occur in practice.

Notes: The rates of drying of perennial ryegrass, subjected to different treatments at mowing and after mowing, were assessed in the field by weight change of grass fresh weight in wire-mesh trays over 3·5 d (76 h). In a 5 × 3 × 3 factorial experimental design, the effects of five weights of grass per unit area [1·5, 3, 6, 12 and 24 kg fresh material (FM) m−2], three treatments at mowing (no treatment, mower-conditioned, flail-treated) and three treatments after mowing (no treatment, inverted, mixed) were examined. The experiment was replicated twice on 16 occasions in 1992 at the Agricultural Research Institute of Northern Ireland. This gave a total of thirty-two replicates per treatment. The trays were weighed at 2-h intervals from 09.00 to 17.00 h each day. Data sets were restricted to rain-free days and also to the first day after mowing (day 1). On day 1, grass weight per unit area was a major factor dictating drying; reducing the grass weight per unit area of unconditioned grass from 6 to 3 kg FM m−2 increased grass drying rate by 47%. There was no significant (P 〉 0·05) benefit over the untreated grass on day 1 from mixing or turning mower-conditioned or the unconditioned grass. Mixing of the flail-treated grass improved drying rate significantly (P 〉 0·001) over the control. Over the whole 76-h period, the relative benefit from either mower conditioning or flail treatment over no treatment was dependent upon both grass weight per unit area and initial dry-matter (DM) concentration. At higher initial DM concentrations (〉150 g kg−1) and lower grass weights (〈6 kg FM m−2) both mower conditioning using a nylon brush type conditioner and intensive conditioning by flail treatment gave substantial increases in drying over no treatment. Moisture regain of grass exposed to overnight dew was small. Rain had a much greater effect than dew on subsequent moisture regain. Unconditioned grass at 12 kg m−2 retained 82% less water following rainfall than unconditioned grass at 3 kg m−2.

Notes: [Auszug] WE have recently measured the Hall coefficient R and the conductivity σ in oxide coatings sprayed on a magnesia base. By drawing D.C. and pulsed thermionic emission, we have been able to activate the coatings satisfactorily, obtaining a D.C. work function near 1,000° K. of ...

Notes: The effects of tributyltin (TBT) compounds on gill morphology were examined in the mummichog, Fundulus heteroclitus, in 96-h LC50 and 6-week sublethal exposures. Morphometry was used for the identification and quantification of effects with the light microscope. A 96-h LC50 of 17.2 μg 1 1 was determined. Morphometric analysis of gill tissues revealed hypertrophy of the lamellar epithelium in fish exposed to 17.2 μg 1–1. Relative diffusing capacity was significantly decreased (−41 %); (P〈0.05, ANOVA, Bonferroni t-test). At 35.6 μg 1−1, TBT exposure resulted in a significant reduction (− 40%) in the volume of the lamellar blood channels. Both of these observations occurred in fish that showed signs of acute poisoning including loss of equilibrium. In fish exposed to sublethal concentrations of 0.105–2.000 μg TBT 1−1 for 6 weeks, there were no pathological changes in the gill. There were no treatment-related changes in the surface morphology of the gills of fish from both experiments upon scanning electron microscopic examination. Although gill pathology was observed in acutely toxic exposures, it does not appear to be a major mechanism of TBT toxicity.

Notes: Hatchery reared larval striped bass, Morone saxatilis, 8-days-post-hatching were subjected to various feeding/starvation regimes over a period of 14 days.Batches of larvae from each treatment were sampled over the 14-day period and subdivided for determination of notochord length and RNA:DNA ratio. The best growth was found in fully fed F1000 larvae (exposed to 1000 Artermia nauplii l−1), which reached 8.2 mm after 11 days and 9.6 mm after 14 days. Starved animals after 11 days had notochord lengths of 4.9 mm. Growth curves from feeding-delayed larvae indicated that animals fed after up to 5 days starvation were capable of complete recovery. F100 larvae (exposed to 100 Anemia nauplii 1−l) had a slower growth rate than F1000 larvae, reaching a notochord length of 7.3 mm after 14 days. RNA:DNA ratios over time closely followed notochord growth curves, with clear differences between starved, F100 and F1000 larvae being established after only 2 days. Equilibrium RNA:DNA ratios of 3.0 and 2.25 were established in F1000 and F100 larvae, respectively, 6.8 days after the beginning of the experiment. The average lag time between a change from the starved to the fed condition and a change in RNA:DNA ratio as determined by the divergence of the nucleic acid curve from the starved condition was 0.66 days.In treatments where starvation followed various periods of feeding, larvae regressed in notochord length such that the final length at 14 days reflected the degree of feeding. RNA:DNA ratios in these animals again closely followed growth curves with a lag time of 0.81 days.It was concluded that RNA:DNA ratios provided very accurate indices of growth in striped bass larvae which were highly sensitive to feeding status.

Notes: Abstract During cadmium uptake by the shore crab Carcinus maenas (L.), cadmium appears in both haemolymph and urine within 1 h, and comes into equilibrium with the haemolymp after some 60 h. The equilibrium concentration for haemolymph cadmium is always considerably less than that of the external medium, whether the latter is close to background level or at the artificially high concentration of 2.2 mg l-1. Despite earlier evidence that cadmium entering the haemolymph is mainly bound to protein, current results show most of this to be freely labile and quickly displaced by cadmium taken up subsequently. There is some evidence to suggest that cadmium is passed on from the haemolymph to the hepatopancreas. A large proportion of whole-body cadmium is adsorbed onto the exoskeleton and gills. The comparatively rapid efflux of 109Cd from loaded crabs over a period of 1 week is mainly due to desorption of this cadmium from the outer body surface.