Bioremediation of chemically contaminated soil : extraction/analysis methodology development.

Abstract

The efficacies of soil extraction methods, namely, Soxhlet, sonication, agitation, alkaline digestion and the ethyl acetate micro-method, for monitoring soil bioremediation were evaluated using three soil types, Swartland, Rensburg and Hutton, encompassing the mineralogical range prevalent in Kwa Zulu Natal. Phenol, atrazine and the BTEX component of petrol were the molecules used in this study and were extracted under different spiking concentrations, after prolonged ageing times up to 21 days and after changing the composition of the spiking solution. It was concluded that extraction methods must be validated for the specific conditions under which they would be used, taking into consideration, soil type, spiking solutions, moisture content, weathering times and the analyte(s) in question. A preliminary appraisal of atrazine degradation in a Hutton soil was then made under the conditions of sterilized, fertilized/non-fertilized and non-sterilized, fertilized/nonfertilized soils. The predominant pathway of atrazine degradation was deemed to be chemically/abiotically mediated due to the soil pH and the presence of iron and aluminium oxides as well as the high levels of manganese in the soil. The results obtained prompted further study into atrazinecatabolism using soil-slurry reactors, under the conditions of carbon-limitation, nitrogen limitation, carbon/nitrogen non-limitation and carbon/nitrogen limitation. A comparison was made between inoculated and non-inoculated bioreactors. The ability of the indigenous microbial population to return the Hutton soil to its original pristine state was confirmed. The expense of inoculation and culture maintenance could be avoided since carbon and nitrogen supplementation would be as equally effective as inoculation.