Polycyclic aromatic hydrocarbon (PAH) biodegradation was investigated in contaminated soils from two different industrial sites under simulated land treatment conditions. Soil samples from a former impregnation plant (soil A) showed high degradation rates of PAHs by the autochthonous microorganisms, whereas PAHs in material of a closed-down coking plant (soil B) were not degraded even after inoculation with bacteria known to effectively degrade PAHs. As rapid PAH biodegradation in soil B was observed after PAHs were extracted and restored into the extracted soil material, the kind of PAH binding in soil B appears to completely prevent biodegradation. Sorption of PAHs onto extracted material of soil B follows a two-phase process (fast and slow); the latter is discussed in terms of migration of PAHs into soil organic matter, representing less accessible sites within the soil matrix. Such sorbed PAHs are suggested to be non-bioavailable and thus non-biodegradable. By eluting soil B with water, no biotoxicity, assayed as inhibition of bioluminescence, was detected in the aqueous phase. When treating soil A analogously, a distinct toxicity was observed, which was reduced relative to the amount of activated carbon added to the soil material. The data suggest that sorption of organic pollutants onto soil organic matter significantly affects biodegradability as well as biotoxicity.

Bacterial mixed cultures able to degrade the polycyclic aromatic hydrocarbons (PAH) phenanthrene, fluorene and fluoranthene, were obtained from soil using conventional enrichment techniques. From these mixed cultures three pure strains were isolated: Pseudomonas paucimobilis degrading phenanthrene; P. vesicularis degrading fluorene and Alcaligenes denitrificans degrading fluoranthene. The maximum rates of PAH degradation ranged from 1.0 mg phenanthrene/ml per day to 0.3 mg fluoranthene/ml per day at doubling times of 12 h to 35 h for growth on PAH as sole carbon source. The protein yield during PAH degradation was about 0.25 mg/mg C for all strains. Maximum PAH oxidation rates and optimum specific bacterial growth were obtained near pH 7.0 and 30 degrees C. After growth entered the stationary phase, no dead end-products of PAH degradation could be detected in the culture fluid.

The degradation of fluoranthene by pure cultures ofAlcalioenes denitrificans WW1, isolated from contaminated soil samples, was investigated. The strain showed m a x i m u m degradation rates of 0.3 mg fluoranthene/ml per day. A. denitrificans was able to utilize also naphthalene, 1-and 2-methylnaphthalene, phenanthrene, and anthracene as sole carbon sources and to co-metabolize fluorene, pyrene, and benzo(a)anthracene. During growth on fluoranthene in batch culture two metabolic products that were completely degraded before growth entered the stationary phase were detected in the culture fluid. Analyses by UV, mass and N M R spectroscopy identified the products as acenaphthenone and 3-hydroxymethyl-4,5-benzocoumarine. Fluoranthene-grown resting cells of A. denitrificans showed degradative activity towards 2,3-dihydroxybenzoic acid, pyrogallol, salicylic acid, and catechol. The enzymatic activities in extracts of fluoranthene-induced cells indicate a meta ring fission involved in the degradation of fluoranthene. From these data new aspects of the biodegradative pathway of fluoranthene have been predicted.

Ecotoxicological and Human Toxicological Risk Assessment of PAH-contaminated Soils Before and After Biological TreatmentThe goal of the present work is to assess the adverse effects of soil bound polycyclic aromatic hydrocarbons (PAH) which remain in soils after biological remediation. We focus on risk assessment for mammalian species with respect to the oral uptake of contaminated soil particles and compare the results of a biomarker test with those of an ecotoxicological assay, the bioluminescence inhibition test with Vibrio fischeri. As a biomarker effect in mammals, we determined the liver microsomal cytochrome P450 enzyme CYPIA1 which is induced by PAH in exposed rats. After biological soil treatment, different amounts of PAH remain in the soil depending on the soil properties and initial pollutant composition. Particularly, higher condensated PAH resists biological treatment due to its hydrophobicity. In addition, high amounts of organic carbon in the soils affect remediation efficiency. In the bioluminescence inhibition test, eluates of all biologically treated soils studied do not reveal any or only low inhibitory effects. In contrast, the oral uptake of biologically treated contaminated soils leads to induction levels for CYPIA1 similar to those in the untreated samples. A good correlation is obtained between CYPIA1 levels and the amount of 5 and 6-ring PAH in the soil samples. The main result is that the remediation efficiency determined by the luminescence test is not reflected by the biomarker test, a finding which indicates the high bioavailabiliry of residual PAH in soils. Consequently, new criteria for human risk assessment can be delineated,

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