Interaction between temperature and cadmium toxicity in the isopod Porcellio scaber

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 degrees C), and four different exposures to cadmium (0.016, 0.071, 0.14 and 0.31 mu mol 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 mu mol g(-1) it disturbed the temperature-induced growth enhancement. 3. There was a tendency for cadmium to be least toxic at intermediate temperature (16 degrees 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 mu mol g(-1) and EC10 = 0.041 mu mol 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 mu mol 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.