Considerations on the sample size of wood mice used to biomonitor metals.

The concentrations of various metals (Zn, Cu, Mn and Cr) in liver, kidneys and brain from specimens of the wood mouse Apodemus sylvaticus captured from 5 sites were measured. Two of the sites were in a restored mine dump, another in an area characterized by serpentized soils and the remaining two were control sites. The sample size required for statistical differentiation of the sampling sites was calculated from the mean values and the variability in bioaccumulation corresponding to each of the sites. The relationship between the sample size and the results of the statistical test used to reveal significant differences between the mean concentrations of metals in organs from A. sylvaticus is demonstrated. The homeostatic control exerted by the wood mice on the tissue levels of metals reduced the interpopulational variability, thereby homogenizing the mean bioaccumulation corresponding to the different sampling stations. The sample size, tissue regulation of the levels of heavy metals and the patterns of variability are of vital importance in evaluating the usefulness of A. sylvaticus as a biomonitor of heavy metals.