Laboratory trials on the bioremediation of aged pentachlorophenol residues

The variable nature of field-contaminated soil requires reliable assessments or treatability studies to optimise the bioremediation process in the field. In a series of laboratory-based studies, experiments were developed and conducted to determine fungal isolate variations, optimum fungal inoculum concentration, optimum treatable contaminant concentration and predict pentachlorophenol (PCP) degradation over time. Generally, biodegradation of PCP in old (>30 years) field-contaminated soil (i.e. aged residues) was similar between New Zealand native isolates compared to the American isolates of Phanerochaete chrysosporium or P. sordida. A concentration of up to 2786 mg freshly added PCP kg−1-soil was readily biodegraded if augmented with live or dead white-rot isolates. However, no biodegradation or soil colonisation was observed at these high PCP concentrations when aged residues were used. Increasing the amount of fungal inoculum (>30%; v/v) for soil augmentation with white-rot fungi did not improve colonisation of field-contaminated PCP soil. Generally, soil colonisation by white-rot fungi did not correlate with PCP decline. However, soil colonisation and PCP biodegradation were isolate dependent. When aged residues were used, the variation between repeated residue analyses was high and similar to the variance among isolates and among isolates within sampling dates. Therefore stratified sampling protocols were developed for PCP residue analysis to be able to determine differences between fungal treatments. The results of the described experiments were then used to standardise treatability studies.