PREDICTING SOIL-ASSOCIATED CONTAMINANT BIOAVAILABILITY IN SINGLE AND MULTIPLE CONTAMINANT SYSTEMS

摘要

The aim of this study was to investigate the influence of a non-aqueous phase liquid (NAPL), namely diesel (applied over a log-concentration range from 20 to 20,000 mg kg-1), on the fate of soil-associated phenanthrene (applied at a concentration of 21 mg kg-1) after 1d, 50d, 100d and 225d. The impact of these co-contaminant mixtures on the soil microflora was also assessed. Further to these aims, the application of aqueous solutions of cyclodextrin to predict microbial bioavailability of soil-associated phenanthrene was investigated. With respect to compound fate, the results suggested that competitive effects between dissimilar co-contaminants did influence phenanthrene loss. Where diesel was present at 0, 20, 200 and 2,000 mg kg-1 losses were 67.3% ± 0.4%, 71.8% ± 0.6%, 70% ± 0.3% and 77.8% ± 0.3% after 225d, respectively. It is suggested that the observed loss was a direct result of increased bioavailability of soil-associated phenanthrene, through competitive desorption, and increased biodegradation of the displaced fraction. Following 225d soil-compound contact time, no significant difference could be determined (P > 0.95) between the amount of phenanthrene extracted using aqueous solutions of cyclodextrin and the amount of compound determined to be bioavailable for microbial degradation. In contrast, total phenanthrene residues, as determined by sample oxidation, were on average 20 times greater than the amount of phenanthrene determined to be bioavailable for microbial degradation. These results support the use of aqueous solutions of cyclodextrin to assess microbial bioavailability of phenanthrene in co-contaminant treatments and underline the fact that total compound residues do not represent the bioavailable fraction.