Comparaison de quatre procedures d'extraction pour evaluer les concentrations en arsenite et arseniate dans les sols contamines

The research hypotheses for this project are : (1) the methods employed for the extraction of inorganic arsenic in contamined soils have an influence on the oxidation of As(III) to As(V) during the extraction, (2) the physico-chemical properties of contamined soils have an influence on the oxidation of As(III) to As(V) during the extraction of inorganic arsenic species. The first objective of this research is to identify, among the published extraction procedures, an extraction method which preserves the oxidation state of arsenic. The second objective of this study is to assess the influence of the physiochemical properties of soils on the performance of the extraction method.;The results of the characterization of the CCA-contamined soils have shown that the total arsenic content was between 93+/-9 mg/kg and 147+/-112 mg/kg. These values were two or three times higher than the criteria set in the province of Quebec (50 mg/kg) for commercial and industrial use.;After the first stage, the results have shown that there was no speciation change of the standard As(III) solution for the three extraction method : 15% (v/v) H3PO4, 10 mM Phosphate + 0,5% (p/v) NaDDC and 1M H3PO4 + 0,5M C6H8O 6. However, for the 10M HCl extraction method, there was 18+/-1% of the As(III) which were oxidized in As(V). These results have shown that the 10M HC1 was responsible for the oxidation of As(III). It was therefore concluded that this method was not adapted to extract inorganic arsenic from soils. This method was eliminated for the others stages.;In the second stage, the arsenic extracted in all CCA-contamined soils was As(V). The soils were collected in surface immediately adjacent to the CCA-treated utility poles with CCA-C solution which contained arsenate. Generally, As(V) is a major arsenic species under oxidizing conditions, therefore, the presence of As(V) in the five subsurface collected soils was to be expected. For the two reference materials, the five collected soils, the 15% (v/v) H 3PO4, 10mM Phosphate + NaDDC 0.5% (w/v), and 1M H3PO 4 + 0,5M C6H8O6 extraction methods, total As was 107+/-18%, 13+/-8%, 83+/-11%, respectively. The two extraction methods which used phosphoric acid in the extraction solution allowed the extraction of the totality or quasi-totality of total arsenic in the soils. On the other hand, the 10 mM Phosphate + 0,5% (p/v) extraction method was too weak to extract arsenic from soils.;After the third stage, the same results were found for the extraction of total arsenic. For the 15% (v/v) H3PO4 extraction method, an important oxidation of the doped As(III) was observed while for the 10 mM Phosphate + 0,5% (p/v) extraction method, the doped As(III) was well preserved. Theses results have shown that these extraction methods were able to extract ancient or recent contamination but not in the same time. These two extraction methods were not adapted for the extraction of inorganic arsenic from soils. For the 1M H3PO4 + 0,5M C6 H8O6 extraction method, between 0% and 40+/-1% of the doped As(III) were oxidized. These results have shown that this extraction method seem adapted because it minimises the oxidation of As(III) during extraction.;The oxidation of As(III) was more important for soils C and D. These soils have a high content of Fe and Mn, which may have an influence on the oxidation of As(III). The results have shown that the manganese oxides were responsible because high correlations were found between manganese fractions extracted by citrate dithionine (CD), ammonium oxalate (AO), hydroxylamine hydrochloride (HH) and the extracted As(V) (r = 0,90, p = 0,01, n = 6) as well as the total Mn content (r = 0,91, p = 0,01, n = 7). The soil C high clay content (18%) could be responsible of the oxidation of As(III). The manganese proved to be an effective oxidant of As(III), more so than the others soils physicochemical properties. As a matter of fact, it was the most important factor on the performance of extraction methods. (Abstract shortened by UMI.)...