concentrations of contaminants in this sample. Toxicity in this sample
could be related either to its geochemical soil properties and low
nutrient availability or to the presence of contaminants not analyzed
in this research. The effects due to differences in soil properties could
be resolved with the use of a reference soil with similar properties
to contaminated soils but without contaminants. However, such a soil
was not available.
Effects of soil on microorganisms did not relate to element concentrations
in the soil. Sample S5, sited in the most distant zone, showed
similar effects to S2 and S3 on the respiration rate induced by glucose
and dehydrogenase (DHA) activity, whereas S4 toxicity was lower.
The effects on phosphatase were not correlated with the other effects
measured inmicroorganisms and showed different behavior in the tested
soils. Thus, soil S2 showed inhibition of enzymatic activity, soil S3
showed enzymatic activation and no significant effects were observed
in soil S5. Dehydrogenase is very sensitive to element pollution,whereas
acid phosphatase is less affected by it. Moreover, other authors
have found that some of these elements may exert a positive effect
(e.g., hormesis) on soil microbial activity at lowelement concentrations
(Antunes et al., 2011). This fact could explain the activation observed in
soil S4. It is recognized that element toxicity is more related to the