Pentachlorophenol transformation in soil: a toxicological assessment

Bioremediation is recognised as an economically viable method to treat cont aminated soil and the use of microbial inoculants, in particular, white-rot fungi, has been proposed to enhance the remediation process. During biorem ediation, a variety of pollutant transformation products will be created wh ich may have toxic synergistic interactions and may not at all be detected by chemical analysis. This work examined the potential for formation of tox ic breakdown products during pentachlorophenol (PCP) transformation in soil after inoculation with Phanerochaete chrysosporium; a frequently used fung al inoculant. To monitor toxicity during bioremediation, changes in soil de hydrogenase activity and effects of soil methanol extracts on the growth of a common soil bacterium Bacillus megaterium in liquid culture were determi ned. After 6 weeks of remediation, soil PCP levels had dropped from an init ial 250 mg kg(-1) to 2 mg kg(-1), and inoculation with P. chrysoporium did not improve PCP remediation over uninoculated PCP-contaminated soil. Soil d ehydrogenase activity remained very low in all soils containing PCP and did not recover throughout the experiment (6 weeks) despite the decrease in PC P levels. Soil methanol extracts varied in their toxicity towards growth of B. megaterium and were most toxic after 6 weeks incubation when extracts o btained from PCP-contaminated soil inoculated with P. chrysosporium complet ely inhibited B. megaterium. A longer incubation time would probably result in removal of toxic products and as soil methanol extracts were used in gr owth inhibition studies, the bioavailability of these toxic compounds remai ns in question. However, this work indicates that toxic transformation prod ucts may be formed during bioremediation and that ecotoxicological assays a n useful to complement chemical analysis during bioremediation of contamina ted soil. (C) 2000 Elsevier Science Ltd. All rights reserved.