Influence of Temperature on the Regulation and Toxicity of Zinc in Folsomia candida (Collembola) C. E. Smit 1 and C. A. M. Van Gestel Department of Ecology and Ecotoxicology, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands Received October 28, 1996 To generate reproducible and reliable results, most protocols for standardized toxicity tests prescribe strict limits for test con- ditions such as temperature and relative humidity. In the field, however, variability of climate can influence the functioning of organisms and induce changes in sensitivity. To evaluate the in- fluence of temperature on the ecotoxicity of zinc, the springtail Folsomia candida was exposed to zinc-contaminated soil at differ- ent temperatures. In one experiment, the toxicity of ZnCl 2 was determined at a constant temperature and under alternating tem- perature conditions. Although control performance of F. candida was influenced by the temperature treatment, effect concentra- tions for reproduction were not significantly different between treatments. Levels of internal zinc regulation were higher in ani- mals exposed to alternating temperatures. Based on the observed influence of temperature on the accumulation of zinc, a second experiment was performed to determine the sensitivity of F. can- dida to zinc at four different exposure temperatures. A decrease in temperature led to an increase in sensitivity when sublethal pa- rameters such as growth and reproduction were considered. How- ever, animals were less sensitive at lower temperatures where mortality was concerned. Internal zinc concentrations in the ani- mals increased with decreasing temperatures, and when the effect on reproduction was based on internal zinc levels, differences between temperature treatments were not significant. From the results of this study it is concluded that for F. candida, constant temperature conditions form a good basis for the extrapolation of toxicity levels to fluctuating temperature conditions. Since the average exposure temperature can alter the sensitivity of F. can- dida for zinc, and changes in sensitivity are parameter dependent, exposure temperature should be chosen carefully. © 1997 Academic Press Key Words: soil; temperature; toxicity; zinc; Collembola; Fol- somia candida. INTRODUCTION Standardized laboratory toxicity tests are used on a large scale to evaluate the potential ecotoxicological risks of con- taminants. Results of these tests form the basis of statistical extrapolation methods to derive safe levels of chemicals in the environment (Aldenberg and Slob, 1993; Van Straalen and Denneman, 1989; Wagner and Løkke, 1991). To generate re- producible and reliable results, most test protocols prescribe strict limits for test conditions such as temperature and relative humidity. In the field, however, variability of climate can in- fluence the functioning of organisms and thereby induce changes in susceptibility for toxicant stress. An increase in temperature generally leads to increased activity, which in most cases will be accompanied by increased uptake rates of several substances, including toxicants, from the environment. If an organism is capable of active excretion, an increased elimination rate might compensate for the excess of chemical taken up, leading to no net change in internal concentration. If, however, uptake and elimination rates are not influenced by temperature to the same extent, the internal concentration will eventually change. For some terrestrial organisms like earth- worms and springtails, temperature has been found to affect uptake and elimination kinetics and tissue levels of heavy met- als (Bengtsson and Rundgren, 1992; Janssen and Bergema, 1991), but consequences for toxicity remain unclear. It can be assumed that by spending energy on maintaining a constant internal concentration, the organism has to reduce expenditure on other functions like growth or reproduction. Most studies investigating the interactions of temperature and toxicity have been conducted using a fixed test period for the respective temperatures. Since development time of all in- vertebrates is temperature dependent, the test period must be based on a physiological time scale, especially when sublethal parameters like growth or reproduction are considered (Ax- elsen, 1997). Nevertheless, the influence of temperature on toxicity is often evaluated at constant temperatures (Cairns et al., 1975) and knowledge about the effects of fluctuating tem- peratures on the sensitivity of organisms for toxicants is scarce. If, under similar average temperature conditions, fluctuations affect toxicity, extrapolation of toxicity data to field situations will be very difficult. In this paper results are presented from experiments in which the effects of zinc on survival, growth, and reproduction of Folsomia candida were estimated at several temperatures. F. candida, as a representative of the ecologically important group Collembola, is recommended as a test organism to 1 To whom correspondence and reprint requests should be addressed. Fax: +31 20 44 47123. E-mail: smit@bio.vu.nl. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 37, 213–222 (1997) ARTICLE NO. ES971558 213 0147-6513/97 $25.00 Copyright © 1997 by Academic Press All rights of reproduction in any form reserved.