The use of quantitative PCR, plant and earthworm bioassays, plating and chemical analysis to monitor 4-chlorobiphenyl biodegradation in soil microcosms

4-Chlorobiphenyl biodegradation was monitored using several methods includi ng molecular detection, microbiological and ecotoxicological techniques and analytical tools. Experiments were carried out in microcosms with artifici al soil and an uncultivated sandy loam soil, contaminated at a rate of 1 g kg(-1) of 4-chlorobiphenyl. Two strains were used for bioremediation: a 4-c hlorobiphenyl degrader, the bacterial strain Pseudomonas sp, strain B4 and the bacterial strain Pseudomonas sp, strain CBS3 which is able to mineraliz e 4-chlorobenzoate. Molecular tools were constructed for the detection and the quantification of dihydroxybiphenyl dioxygenase gene (bphC) from Pseudo monas sp. strain B4 and for the detection of the 4-chlorobenzoate coenzyme A dehalogenase gene from Pseudomonas sp. strain CBS3. Evidence was found fo r 4-chlorobiphenyl toxicity to barley and earthworms using standardized eco toxicological tests. When Pseudomonas sp. strain B4 was introduced alone in to microcosms, no decrease in toxicity occurred although 4-chlorobiphenyl w as entirely degraded. The introduction of Pseudomonas sp. strain CBS3 into inoculated microcosms resulted in the disappearance of the 4-chlorobenzoate accumulated during the degradation of 4-chlorobiphenyl by Pseudomonas sp. strain B4, and in the disappearance of any toxic effect indicating that rem ediation was complete. Similar results were obtained independent of the nat ure of the soil used in microcosms. These results underline the need for ta king biological effects into account in order to assess remediation efficie ncy. (C) 1999 Elsevier Science B.V, All rights reserved.