Isoxaflutole is a herbicide activated in soils and plants to its diketonitrile derivative, the active herbicide principle. The diketonitrile derivative undergoes cleavage to the inactive benzoic acid analogue. In this paper, it is established that an oxidative mechanism implicating two successive reactions in the presence of dimethyldioxirane can chemically initiate the cleavage of the diketonitrile. It is also shown that two white rot strains, Phanerochaete chrysosporium and Trametes versicolor, are able to convert the diketonitrile to the acid when cultured in liquid media. This main metabolite amounts to 24.6 and 15.1% of initial herbicide content after 12-15 days of culture. Another polar metabolite represents <3.7% of the parent compound amount during the same period. Oxidative enzymes produced by the fungi show a time course similar to that of diketonitrile degradation. Purified laccase (EC 1. 10.3.2), in the presence of 2 mM 2, 2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) acting as a redox mediator at pH 3 supports the reaction with rates of 0.3-0.4 nmol h(-)(1) unit(-)(1).

Solid carriers have been developed to inoculate Trametes versicolor andCunninghamella elegans into manufactured gas plant site soils. Pelleted wheat bran carriers were very efficient in stimulating the growth of fungi in an industrial soil containing about 2800 mg kg -1 PAHs. Fungal biomass and activity of extracellular laccases, enzymes produced by T. versicolor as markers of metabolic activity in the contaminated soil, both decreased after 2 weeks of incubation. Supplementing the soil with a mixture of carbon, nitrogen and phosphorus enhanced the fungal activity period.A 38% decrease of solvent extractable PAHs was observed in manufactured gas plant site soils when supplemented with T. versicolor, Glucidex 19 TM , ammonium nitrate, lime phosphate and Montanox 80 TM , after 20 weeks. Then, the degradation proceeded more slowly during the following 30 weeks, and reached 43% of initial extractable PAHs. Some factors governing a limited PAH biotransformation in the soil are discussed.

The biotransformation of benzo [a]pyrene by purified extracellular laccase of Pycnoporus cinnabarinus was investigated in bench scale reactors. The reaction required the presence of exogenous mediator ABTS. Most of 95% of the substrate was converted within 24 hours. The enzyme preparation oxidised the substrate mainly to benzo[a]pyrene 1,6-3,6-and 6,12-quinones in a 2/1/1 ratio after 24 hours incubations.

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The efficiency of soil remediation is often limited by the low aqueous solubility of Polycyclic Aromatic Hydrocarbons, PAHs. Surfactants can then be used to enhance the removal of PAHs from soils. The dissolution of pure solid deposit of benzo(a)pyrene, B(a)P, has shown that cationic surfactants are the most efficient to increase the aqueous solubility of B(a)P, when compared to neutral or anionic surfactants. In this paper we compare by using soil suspension washings, the efficiency of two surfactants (i) a cationic surfactant, the benzyldimethyl dodecylammonium bromide, BDDA, and (ii) a neutral one, the t-octylphenoxypolyethoxy ethanol, triton X-1 00. The losses of surfactant, by adsorption on soil or precipitation, were measured together with the release of B(a)P, chosen as a model molecule, representative of all the PAHs. The efficiency of surfactants used in blend was then compared to the efficiency of surfactants alone.