A CRITICAL-EVALUATION OF SAMPLE PRETREATMENT FOR STORAGE OF CONTAMINATED SEDIMENTS TO BE INVESTIGATED FOR THE POTENTIAL MOBILITY OF THEIR HEAVY-METAL LOAD

The identification of the geochemical forms of heavy metals in contami nated sediments gives information on their availability. This requires the use of a geochemical speciation procedure such as the one develop ed by Tessier et al. (1979). In addition to the imperfections of these protocols, their results can vary depending on the technique used for the preservation of sediments which must be suited to the materials s tudied and to particularities of the investigation. This study was car ried out on superficial river sediments, seriously polluted by Cu, Cd and Pb. Compared to fresh sediment, none of the drying methods studied (freeze-drying, air-drying and oven-drying at 105 degrees C) complete ly preserve the distribution of Cu, Pb, Zn and Cd in the various geoch emical fractions of the sediment. The modifications depend directly on the quantities of metals present in the various fractions of the sedi ment, the effects being more marked when the quantity is smallest. Thi s results in a decrease in metals in the exchangeable fraction and in those bound to carbonates under the action of atmospheric oxygen and a corresponding increase in the other fractions. To minimize this, free ze-drying and air-drying are satisfactory techniques which enable pres ervation of sediments representative of the environment.