BIOREMEDIATION IN FIELD BOX PLOTS OF A SOIL CONTAMINATED WITH WOOD-PRESERVATIVES: A COMPARISON OF TREATMENT CONDITIONS USING TOXICITY TESTING AS A MONITORING TECHNIQUE THERESA M. PHILLIPS 1,3 , DICKSON LIU 2 , ALAN G. SEECH 1 , HUNG LEE 3,∗ and JACK T. TREVORS 3,∗ 1 GRACE Bioremediation Technologies, Mississauga, Ontario, Canada, L5C 4P9; 2 National Water Research Institute, Burlington, Ontario, Canada, L7R 4A6; 3 Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1 ( ∗ authors for correspondence, e-mail: jtrevors@uoguelph.ca or hlee@uoguelph.ca) (Received 25 March 1999; accepted 2 September 1999) Abstract. A soil contaminated with polycyclic aromatic hydrocarbons, petroleum hydrocarbons and chlorophenols was bioremediated in field box plots. Three different bioremediation treatments (tillage and irrigation alone (box plot 2) or in addition to amendment with nitrogen and phosphorus (box plots 3 and 4) and additional organic amendment composed of agricultural crop residues (box plot 4)) were compared using chemical analysis for target contaminants and six toxicity tests (seed germination, earthworm survival, SOS Chromotest, Toxi-Chromotest, solid-phase Microtox  and red blood cell (RBC) haemolysis assay). Degradation was enhanced, and toxicity was generally the most reduced, in box plots 3 and 4. Although chemical analysis indicated that the two amendment protocols were equally effective, soil toxicity was generally the most reduced in box plot 4. The earthworm survival and seed germination assays were the most reliable and relevant toxicity tests. Difficulties arising with the other tests included insensitivity to changes in soil contaminant levels, inconsistency and interference by soil particles and other soil constituents. Because of the lack of agreement between toxicity tests, these results support the use of a battery of toxicity tests in conjunction with chemical analysis, when assessing the efficacy of bioremediation. Keywords: bioassays, bioremediation, microbiology, soil contamination, soil toxicity 1. Introduction Finding suitable methods to remediate wood treatment sites where concentrated chemical spills have occurred, is a significant concern. Chemicals used for wood preservation such as pentachlorophenol (PCP) or many compounds found in creo- sote (a complex mixture consisting mainly of polycyclic aromatic hydrocarbons (PAHs)) are toxic and are included on the US EPA priority pollutants list (Keith and Telliard, 1979). In situ bioremediation can be an effective and inexpensive approach, provided microorganisms capable of mineralizing the constituents of creosote are present. Microorganisms capable of degrading PAHs and PCP have been isolated and are widely distributed in nature (Mueller et al., 1989; Cerniglia, 1992; Kiyohara et al., 1992; Leung et al., 1997). Water, Air, and Soil Pollution 121: 173–187, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.