A comparison of test systems for assessing effects of metals on isopod ecological functions.

The effects of metals on the isopod Porcellio scaber and the implication of metal pollution for the functioning of isopods in soil decomposition processes were determined. The experiments were carried out using two test systems, a simple test container without natural substrate and a micro-ecosystem with leaf litter, the latter being more comparable to the field situation. Metals were offered to the isopods by feeding artificially contaminated litter and litter from contaminated field sites. The Cd concentrations in isopods in test containers with ground litter as food were similar to those in isopods in micro-ecosystems with intact leaves as food. Exposure to artificially contaminated litter with Cd alone or litter from contaminated field sites with Cd, Pb, Zn, and Cu resulted in comparable Cd concentrations in the isopods. Growth of the isopods was not affected by Cd or by the combination of Cd, Pb, Zn, and Cu, but differed between the test systems. Fragmentation activity of isopods decreased in litter containing 155 nmol/g Cd and 33500 nmol/g Zn, sampled at a contaminated field site. CO2 production from micro-ecosystems decreased at a concentration of 1010 nmol/g Cd, but NH4 and NO3 concentrations in the litter did not respond to Cd. Isopod growth was better in micro-ecosystems. These systems are therefore recommended for ecotoxicity tests using isopods. After comparison with literature data it was concluded that the bioavailability of Cd in laboratory tests is often higher than the bioavailability in the field at the same total concentrations. This may be due to environmental heterogeneity; this gives animals food choice and is absent in many laboratory test systems. For the quantification of a laboratory-field extrapolation factor for general use, more detailed information is needed than is available now.