Abstract-Temperature is an important controlling factor in the metabolism of ectotherms, and it may interact with the toxicity of heavy metals in a variety of ways. In this work, a study on the effect of different zinc concentrations (0.3, 13, 26, and 40 mol/ g dry litter) on growth (body weight) of the isopod Porcellio scaber was conducted using four temperature levels (12, 16, 20, and 24ЊC). The results demonstrated a significant effect for both zinc and temperature on the growth rate; the interaction between zinc and temperature was also significant. The Arrhenius function was used to describe the temperature-growth rate relationship, from which estimates for the activation energy were derived. A tendency for activation energy to decrease with increasing zinc concentration was observed. Isopods exposed to 13 mol Zn/g had the highest activation energy and the highest growth rate. To analyze the effect of temperature on the internal body concentration of zinc, the exposure time was transformed into physiological time, calibrated at 15ЊC, for all experimental groups using the activation energies estimated earlier. The rate of zinc accumulation was derived from the relationship between internal body concentration and physiological exposure time. Differences between isopods cultured at different temperatures could be explained well by the effect of physiological exposure time. The interaction between temperature and zinc toxicity seems to be due not to increased accumulation of zinc at higher temperatures as such but to a physiological interaction with the energy metabolism.
1. Temperature has an important effect on all physiological processes in animals that rely on external sources of heat (ectotherms). In an attempt to elucidate the interaction between temperature and the response of ectotherms to heavy metals, a study was made of growth (increase of body mass) of the isopod Porcellio scaber under four constant temperature regimes (12, 16, 20, 24 °C), and four different exposures to cadmium (0·016, 0·071, 0·14 and 0·31 μmol g–1 in the diet), in a factorial experiment. 2. There were significant effects on growth rate for both cadmium and temperature, and the interaction between cadmium and temperature was also significant. The average growth rate per week increased with increasing temperature, but the results showed that when cadmium was present at concentrations higher than 0·071 μmol g–1, it disturbed the temperature‐induced growth enhancement. 3. There was a tendency for cadmium to be least toxic at intermediate temperature (16 °C), but the 50% and 10% effect concentrations in the diet, estimated by loglogistic curve fitting, did not significantly vary with temperature. The average values were EC50 = 0·330 μmol g–1 and EC10 = 0·041 μmol g–1. 4. The Arrhenius model was used to describe the temperature–growth rate relationship, and activation energies were estimated for each cadmium exposure. At the highest cadmium concentration the Arrhenius model did not describe the data very well. The lowest activation energy was observed at 0·14 μmol g–1. 5. Cadmium accumulation in isopods was linearly related to the cadmium concentration in food, for all temperature levels. The significant increase in cadmium concentration with temperature indicates that the effect of temperature on cadmium accumulation is stronger than its effect on body growth. As a whole the data illustrate the importance of taking temperature into account when conducting ecotoxicological studies with soil invertebrates.
Temperature is an important controlling factor in the metabolism of ectotherms, and it may interact with the toxicity of heavy metals in a variety of ways. In this work, a study on the effect of different zinc concentrations (0.3, 13, 26, and 40 μmol/g dry litter) on growth (body weight) of the isopod Porcellio scaber was conducted using four temperature levels (12, 16, 20, and 24°C). The results demonstrated a significant effect for both zinc and temperature on the growth rate; the interaction between zinc and temperature was also significant. The Arrhenius function was used to describe the temperature–growth rate relationship, from which estimates for the activation energy were derived. A tendency for activation energy to decrease with increasing zinc concentration was observed. Isopods exposed to 13 μmol Zn/g had the highest activation energy and the highest growth rate. To analyze the effect of temperature on the internal body concentration of zinc, the exposure time was transformed into physiological time, calibrated at 15°C, for all experimental groups using the activation energies estimated earlier. The rate of zinc accumulation was derived from the relationship between internal body concentration and physiological exposure time. Differences between isopods cultured at different temperatures could be explained well by the effect of physiological exposure time. The interaction between temperature and zinc toxicity seems to be due not to increased accumulation of zinc at higher temperatures as such but to a physiological interaction with the energy metabolism.
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