| To evaluate the effect of contaminants in soils, this project proposes to measure soil enzymatic functions using the Relative Soil Stability Index (RSSI). In order to calculate this index, the dynamic response of extracellular enzymes, involved in reactions occurring in the biogeochemical cycles (C, N, P, and S), regulating the life cycle is monitored over a period of time when submitted to a thermal perturbation. Nevertheless, this index bears some deficiencies: (1) eventual stimulation or inhibition of enzyme activity due to the presence of contaminants in soil is not taken into account in the calculations, and (2) without a reference, the comparison between RSSI-values is difficult.;With artificially contaminated soils, the RSSIr shows more interesting results compared to the RSSI tool: calculated from the protease and urease potential monitoring, the RSSIr allows for discriminating between low and high creosote contaminated soils. Protease shows the best stability in the low contaminated soils (stability index values higher than 100%). In highly contaminated soils, the stability of this enzyme is inhibited, particularly in clay (values of 7,3 +/-8,3 % in the contaminated C3 soil sample versus 184,3 +/-17,2 % in the non-contaminated C0 soil sample). As for the RSSIr values measured with urease, in low contaminated soils values do not exceed the threshold of 53,7 +/-5,9 % (value obtained for the contaminated C2 sandy clay loam); urease activity is inhibited by the applied thermal stress. Overall stability values based on protease and urease decrease when contamination levels increase. These trends however vary in the three soils that were tested; this confirms that the toxic effects of PAHs change with soil composition, and specifically with varying organic matter or clay content.;In the site soil samples, the measured concentrations confirmed the efficiency of treatment: a decrease in PAH concentrations, up to 91 +/-4 % after co-composting treatment, and decrease of C10-C50 concentration of up to 89 +/-3 % between co-composting and phytoremediation treatments. RSSIr values were sensitive to contamination levels and to applied bioremediation treatments, calculated from the monitoring of protease and arylsulfatase potentials. Like the previous study, tools measuring enzymatic stabilities in soils after treatment (co-composting and phytoremediation) present values noticeably greater than 100 % when calculated with the RSSIr, and slightly lower than this threshold when calculated with the RSSI. These stability measurements therefore reflect a clear enhancement of functional stability after treatment. Moreover, stability values of the reference soil reach values significantly lower than those calculated for contaminated soils. For example, using arylsulfatase, an RSSIr value of 25,4 +/-2,7 % was obtained in the control soil sample (non-contaminated) and a RSSIr value of 48,7 +/-10,5 % was calculated for the contaminated soil sample. Consequently, the results showed the importance of reference soil choice. Biological treatment applications can lead to changes in soil structure and composition, making the choice of the reference soil, and the method to measure the enzymatic stability in a soil, rather arguable. (Abstract shortened by UMI.);Firstly, three soils of various grain size mixtures (sandy clay loam, clay, sandy loam) were artificially contaminated. Each soil type lead to five samples with different contamination levels (0; 0.17; 1.70; 24 and 60 mL creosote, dry soil kg-1), named C0, C1, C 2, C3 and C4, respectively, corresponding to theoretically respective PAH concentrations of 0, 87, 870, 12 432 and 31 173 mg total PAH, dry soil kg-1. Secondly, contaminated soil samples, (mostly by PAH) were collected at various points along the biological treatment process (prior to treatment, after cocomposting, during phytoremediation), along with a control soil sample. For both types of soil samples the experimental process was similar. A thermal perturbation (60°C, 24 hours) was applied to the soil samples. The impact of this perturbation was then monitored throughout a 12-day period by measuring the potential activity of three enzymes (protease, urease, arylsulfatase), and subsequently quantified by calculating RSSI and RSSIr values. The calculation of a RSSI value is based on the comparison made between enzyme activity in a contaminated soil following perturbation, and enzyme activity in the same contaminated soil, but not perturbed. As for the RSSIr tool, the reference soil is modified: the calculation of a RSSIr value is based on the comparison between the enzyme activity in a contaminated soil following a perturbation and the enzyme activity in the same uncontaminated and non-perturbed soil (the reference soil). Statistical analyses were used to examine the results. |
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