W5 PM Toxicity of Complex Mixtures
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 321-323

(SAU-1117-774576) Toxicity Interactions of Cadmium, Copper and Lead on Urease and Dehydrogenase Activity in Soils.

Chaperon, S¹, Sauvé, S¹, ¹ Université de Montréal, Montréal, QC, Canada

ABSTRACT- Soil quality criteria for contaminated sites are presently based on the toxicity observed from single pollutants. However, most contaminated soils are exposed to many chemicals simultaneously. Few data are published on the toxicity of pollutant mixtures in soils, even fewer looking at metal mixtures. To better understand the real toxicity encountered in soils, the effects of speciation and interactions between components must be known. In this study, the toxicity of single metals (Pb, Cd, Cu) and their mixtures on microbial enzyme processes such as urease and dehydrogenase were determined. A forest soil was spiked with CdCl2 (1, 2, 10 and 20 mg Cd kg-1 dry soil), PbCl2 (100, 500, 1000 and 2000 mg Pb kg-1 dry soil) and CuCl2 (50, 250, 500 and 1000 mg Cu kg-1dry soil). We also used a factorial set up to contaminate soils using combinations of the two higher concentrations of each metal. We have chosen to use urease and dehydrogenase activities because of their relative sensitivity and stability. Preliminary results indicate that the measured toxicity of combined metals on microbial activity is less than additive. For example, urease showed an inhibition of 8% for 2000 mg Pb kg-1 and 48% for 10 mg Cd kg-1. The additive model would predict an addition of the toxicity of each component without any interaction. According to this model, the combination of the two metals should present an inhibition of 56%. However, in this case a stimulation of 51% is observed. This trend was observed for both urease and dehydrogenase activities at each concentration. The combinations of Pb, Cu and Cd have important, yet hard to predict, effects on microbial activities. The toxicity observed for those two enzyme assays does not follow a simple additive model.

Key words: Enzyme, Soil, Mixture, Quality criteria