Characterization of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash using different extraction methods

In this study, traditional Soxhlet, automatic Soxhlet and ultrasonic extraction techniques were employed to determine the speciation and concentration of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash samples collected from the baghouse of a spreader stoker boiler. To test the efficiencies of different extraction methods, LSD ash samples were doped with a mixture of 16 US EPA specified PAHs to measure the matrix spike recoveries. The results showed that the spike recoveries of PAHs were different using these three extraction methods with dichloromethane (DCM) as the solvent. Traditional Soxhlet extraction achieved slightly higher recoveries than automatic Soxhlet and ultrasonic extraction. Different solvents including toluene, DCM:acetone (1:1 V/V) and hexane:acetone (1:1 V/V) were further examined to optimize the recovery using ultrasonic extraction. Toluene achieved the highest spike recoveries of PAHs at a spike level of 10 microg kg(-1). When the spike level was increased to 50 microg kg(-1), the spike recoveries of PAHs also correspondingly increased. Although the type and concentration of PAHs detected on LSD ash samples by different extraction methods varied, the concentration of each detected PAH was consistently low, at microg kg(-1) levels.     

Analysis of polycyclic aromatic hydrocarbons in sediment reference materials by microwave-assisted extraction

The microwave-assisted extraction (MAE) of polycyclic aromatic hydrocarbons (PAHs) from harbor sediment reference material EC-1, marine sediment reference material HS-2 and PAH-spiked river bed soil was conducted. The extraction conditions for EC-1 were carried out at 70 degrees C and 100 degrees C under pressure in closed vessels with cyclohexane acetone (1:1), cyclohexane-water (3:1), hexane acetone (1:1), and hexane-water (3:1) for 10 min. A comparison between MAE and a 16-h Soxhlet extraction (SX) method showed that both techniques gave comparable results with certified values. MAE has advantages over the currently used Soxhlet technique due to a faster extraction time and lower quantity of solvent used. The consumption of organic solvent of the microwave method was less than one-tenth compared to Soxhlet.     

Modeling in situ ozonation for the remediation of nonvolatile PAH-contaminated unsaturated soils

Mathematical models were developed to investigate the characteristics of gaseous ozone transport under various soil conditions and the feasibility of in situ ozone venting for the remediation of unsaturated soils contaminated with phenanthrene. On the basis of assumptions for the mass transfer and reactions of ozone, three approaches were considered: equilibrium, kinetic, and lump models. Water-saturation-dependent reactions of gaseous ozone with soil organic matter (SOM) and phenanthrene were employed. The models were solved numerically by using the finite-difference method, and the model parameters were determined by using the experimental data of Hsu [The use of gaseous ozone to remediate the organic contaminants in the unsaturated soils, PhD Thesis, Michigan State Univ., East Lansing, MI, 1995]. The transport of gas-phase ozone is significantly retarded by ozone consumption due to reactions with SOM and phenanthrene, in addition to dissolution. An operation time of 156 h was required to completely remove phenanthrene in a 5-m natural soil column. In actual situations, however, the operation time is likely to be longer than the ideal time because of unknown factors including heterogeneity of the porous medium and the distribution of SOM and contaminant. The ozone transport front length was found to be very limited (< 1 m). The sensitivity analysis indicated that SOM is the single most important factor affecting in situ ozonation for the remediation of unsaturated soil contaminated with phenanthrene. Models were found to be insensitive to the reaction mechanisms of phenathrene with either gas-phase ozone or dissolved ozone. More study is required to quantify the effect of OH* formation on the removal of contaminant and on ozone transport in the subsurface.     

Treatment system for solid matrix contaminated with fluoranthene. I--Modified extraction technique.

A laboratory-scale ultrasonication technique was developed for fluoranthene extraction from soils and sediments where the utilized organic solvent would be recovered after the extraction process. Therefore, the remedied soils and sediments would be free from toxicant and trace of added chemicals. The developed ultrasonication technique outlined here is an integrated part of a complete remediation system consisting of extraction and solar detoxification reactors. This paper investigates extraction efficiencies under different conditions, outlines solvent recovery technique and compares extraction efficiency of the developed ultrasonication technique with a commercially available laboratory-scale sonication bath. The spiked soil sample with fluoranthene (19.4 microg g(-1)) and organic solvent was ultrasonicated at 40 degrees C for 20 min. The sonicated mixture was allowed to settle for 10 min before the extract gravitated into the modified solar reactor for fluoranthene detoxification. The added solvents were removed from the remedied soil before it was released to site. The mixture of cyclohexane and ethanol (CH:ETOH) (3:1) was the favorable solvent from among 10 organic solvents because of its high extraction efficiency, safety and low cost. Preliminary results indicated that the developed extraction technique recovered more than 93% of fluoranthene from soil samples.     

Comparative study of extraction methods for the determination of PAHs from contaminated soils and sediments

The following four methods were compared on the extraction efficiency of 16 EPA (US Environmental Protection Agency) polycyclic aromatic hydrocarbons (PAHs): German method of the Verband Deutscher Landwirtschaftlicher Untersuchungs und Forschungsanstalten (VDLUFA), two methods of the International Organization for Standardization using shaking (ISO A) and Soxhlet extraction (ISO B) and an ultrasonic method. Recovery rates of 16 PAHs were determined in two soils. Extraction efficiency was evaluated in five soils and three sediments. Effect of drying soils and sediments on extraction efficiency was tested using the VDLUFA and the ultrasonic methods. Our study shows that the number of aromatic rings, rather than extraction procedures, significantly influenced recovery rates of individual PAHs. No significant differences in extraction efficiency of the four methods were observed for less polluted samples. For highly polluted soils, extraction efficiency decreased in the following order: VDLUFA method > ISO A > ultrasonic method > ISO B. Influence of soil moisture on extraction efficiency depended to some extent on both solvent used and content of PAHs in samples. A mixture of dichloromethane/acetone (5:1) is recommended for PAH extraction from moist samples when the ultrasonic method is used.     

Sonochemical degradation of 2,3,7,8-tetrachlorodibenzo-p-dioxins in aqueous solution with Fe(III)/UV system

2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) was rapidly decreased by sonication in aqueous solution. The degradation efficiency was strongly influenced by ultrasonic power and reaction temperature. An initial 2,3,7,8-TeCDD concentration of 20 ng l(-1) was completely degraded within 60 min under sonochemical conditions using a 20 kHz frequency with a 150 W ultrasound power. The activation energy is 21.9 kJ/mol in the temperature range of 10-40 degrees C, suggesting a diffusion-controlled reaction. To increase the efficiency of 2,3,7,8-TeCDD treatment, degradation system combined ultrasound with Fe(III) (2 x 10(-4)mol l(-1)) and UV irradiation. Both UV and Fe(III) induced Fenton, Fenton-like and photo-Fenton reactions, leading to additional OH radicals and rapid 2,3,7,8-TeCDD removal.     

Study of factors affecting on the extraction efficiency of polycyclic aromatic hydrocarbons from soils using open-vessel focused microwave-assisted extraction

As part of an evaluation of focused microwave-assisted extraction (FMAE) using an open-vessel system, the effects of matrix, moisture content, ageing, and solvent have been studied on the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) from spiked soils. PAHs were spiked onto three different uncontaminated air dried and originally wet soil matrices with 1- and 20-day ageing periods. Solvents used were hexane–acetone (1:1), cyclohexane–acetone (1:1) and dichloromethane. FMAE only required a small amount of solvent (20 ml) and short extraction time (10 min) in the open cell under 90 W of microwave power. The results revealed that the extraction efficiency strongly depends on the nature of soil matrix; moisture content may enhance the recoveries of PAHs for many cases; and, the influence of the type of solvent is not significant. A comparison between microwave extraction and 16-h Soxhlet extraction has been made on spiked soils. It evidenced that the microwave method under ambient pressure is a suitable alternative to Soxhlet method for the analysis of PAHs in soils. For the evaluation of the developed FMAE method, three reference materials were used. The PAHs recovered from three reference materials were in a good agreement with reference values.     

The degradation of parathion and DDT in aqueous systems containing organic additives

Abstract

Laboratory studies were conducted to investigate some of the factors influencing pesticide degradation in‐ aqueous systems. Parathion added to natural water in ethanol, acetone or without organic solvent, was completely degraded within 2 wk. While most of the parathion was reduced to amino‐parathion when added in ethanol, no amino‐parathion was detected in the presence of acetone or when no solvent was added, suggesting that in the latter two cases the insecticide was aerobically degraded to other metabolites. No paraoxon was detected. When ethanol concentration was increased from 1% to 2 and 4%, the rate of parathion degradation was inversely related to the ethanol concentration. In the presence of glucose as a carbon source, approximately 50% of the parathion was reduced to aminoparathion. DDT degradation in natural water was more rapid when it was added in ethanol than when added in acetone. The only DDT metabolite detected was TDE, with about 36% conversion in presence of ethanol, and 20% when the DDT was added in acetone.     

Correlations of nonlinear sorption of organic solutes with soil/sediment physicochemical properties

The estimation of solute sorptive behaviors is essential when direct sorption data are unavailable and will provide a convenient way to assess the fate and the biological activity of organic solutes in soil/sediment environments. In this study, the sorption of 2,4-dichlorophenol (2,4-DCP) on 19 soil/sediment samples and the sorption of 13 organic solutes on one sediment were investigated. All sorption isotherms are nonlinear and can be described satisfactorily by a simple dual-mode model (DMM): q(e)=KpCe+Q0 . bCe/(1+bCe), where Kp (mlg(-1)) is the partition coefficient; Ce (microgml(-1)) is the equilibrium concentration; Q0 (microgg(-1)) is the maximum adsorption capacity; Q0 . b (mlg(-1)) is the Langmuir-type isotherm slope in the low concentration (Henry's law) range and b (mlmicrog(-1)) is a constant related to the affinity of the surface for the solute. Based on these nonlinear sorption isotherms and similar other nonlinear isotherms, it is observed that, for both polar 2,4-DCP and nonpolar phenanthrene, Kp, Q0 and Q0 . b are linearly correlated with soil/sediment organic carbon content (f(oc) in the range of 0.118-53.7%). The results indicate that the nonlinear sorption of organic solutes results primarily from interactions with soil/sediment organic matter. The K*oc K*oc=Kp/f(oc)), Qoc (Qoc=Q0/f(oc)), Loc (Loc=Q0 . b/f(oc)) and b for a given organic solute with different soils/sediments are largely invariant. Furthermore, logK*oc, logb and logLoc for various organic solutes are correlated significantly with the solute logKow or logSw (logKow in the range of 0.9 to 5.13 and logSw in the range of -6.176 to -0.070). A fundamental empirical equation was then established to calculate approximately the nonlinear sorption from soil/sediment f(oc) and solute Sw for a given solute equilibrium concentration.     

Sequential UV-biological degradation of polycyclic aromatic hydrocarbons in two-phases partitioning bioreactors

A method based on UV-irradiation in organic solvent followed by transfer of the remaining pollutants into silicone oil for subsequent biodegradation in a biphasic system inoculated with a phenanthrene degrading Pseudomonas sp. was tested for the treatment of various mixtures of PAHs. Acetone was first selected as the most suitable solvent compared to methanol, acetonitrile and silicone oil for the removal of pyrene and phenanthrene. The sequential treatment was then applied to the treatment of a mixture of fluorene, phenanthrene, anthracene, fluoranthrene, pyrene, benzo(a)anthracene and benzo(a)pyrene in acetone. These compounds were photodegraded in the following order of initial removal rates (mg l(-1) d(-1)): benzo(a)pyrene (7.8) > anthracene (5.0) > benzo(a)anthracene (2.5) > fluoranthrene (1.8) > pyrene (1.5) > phenanthrene (1.2) > fluorene (0.2). UV-treatment allowed complete removal of, anthracene, benzo(a)anthracene and benzo(a)pyrene and removals of 63% of pyrene and 37% of fluorene after 434 h or irradiation. The subsequent biological treatment removed the remaining phenanthrene and fluorene by 100% and 90%, respectively, after 790 h of cultivation. Although less efficient due to the presence of interfering compounds, the UV-biological treatment of a soil extract allowed a 63% removal of the seven PAHs named above. Microbial growth did not occur when the pollutants were directly supplied to the microorganism showing that biphasic systems reduced the toxicity effects cause by mixtures of PAHs at high concentrations. This study demonstrates the potential of selective UV treatment of high molecular weight PAHs followed by biological treatment of the low molecular weight species in biphasic systems.     

Enzymatic degradation of anthracene, dibenzothiophene and pyrene by manganese peroxidase in media containing acetone

The high hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) greatly hamper their degradation in liquid media. The use of an organic solvent can assist the degradative action of ligninolytic enzymes from white rot fungi. The enzymatic action of the enzyme manganese peroxidase (MnP) in media containing a miscible organic solvent, acetone (36% v/v), was evaluated as a feasible system for the in vitro degradation of three PAHs: anthracene, dibenzothiophene and pyrene. These compounds were degraded to a large extent after a short period of time (7, 24 and 24h, respectively), at conditions maximizing the MnP-oxidative system. The initial amount of enzyme present in the reaction medium was determinant for the kinetics of the process. The order of degradability, in terms of degradation rates was as follows: anthracene>dibenzothiophene>pyrene. The intermediate compounds were determined using gas chromatography-mass spectrometry and the degradation mechanisms were proposed. Anthracene was degraded to phthalic acid. A ring cleavage product of the oxidation of dibenzothiophene, 4-methoxybenzoic acid, was also observed.     

Photocatalytic degradation of volatile organic compounds at the gas-solid interface of a TiO2 photocatalyst

In the present work, photocatalytic degradation of volatile organic compounds including gas-phase trichloroethylene (TCE), acetone, methanol and toluene over illuminated TiO2 was closely examined in a batch photoreactor as a function of water vapor, molecular oxygen and reaction temperature. Water vapor enhanced the photocatalytic degradation rate of toluene, but was inhibitive for acetone, and, there was an optimum water vapor concentration in the TCE and methanol removal. In a nitrogen atmosphere, it showed lower photocatalytic degradation rate than in air and pure oxygen. Thus, it could be concluded that oxygen is an essential component in photocatalytic reactions by trapping photogenerated electrons on the semiconductor surface and by decreasing the recombination of electrons and holes. As for the influence of reaction temperature, it was found that photocatalytic degradation was more effective at a moderate temperature than at an elevated temperature for each compound.     

Competitive sorption of organic contaminants in chalk

In the Negev desert, Israel, a chemical industrial complex is located over fractured Eocene chalk formations where transfer of water and solutes between fracture voids and matrix pores affects migration of contaminants in the fractures due to diffusion into the chalk matrix. This study tests sorption and sorption competition between contaminants in the chalk matrix to make it possible to evaluate the potential for contaminant attenuation during transport in fractures. Single solute sorption isotherms on chalk matrix material for five common contaminants (m-xylene, ametryn, 1,2-dichloroethane, phenanthrene, and 2,4,6-tribromophenol) were found to be nonlinear, as confirmed in plots of Kd versus initial solution concentration. Over the studied concentration ranges, m-xylene Kd varied by more than a factor of 100, ametryn Kd by a factor of 4, 1,2-dichloroethane Kd by more than a factor of 3, phenanthrene Kd by about a factor of 2, and 2,4,6-tribromophenol Kd by a factor of 10. It was earlier found that sorption is to the organic matter component of the chalk matrix and not to the mineral phases (Chemosphere 44 (2001) 1121). Nonlinear sorption isotherms indicate that there is at least some finite sorption domain. Bi-solute competition experiments with 2,4,6-tribromophenol as the competitor were designed to explore the nature of the finite sorption domain. All of the isotherms in the bi-solute experiments are more linear than in the single solute experiments, as confirmed by smaller variations in Kd as a function of initial solution concentration. For both m-xylene and ametryn, there is a small nonlinear component or domain that was apparently not susceptible to competition by 2,4,6-tribromophenol. The nonlinear sorption domain(s) is best expressed at low solution concentrations. Inert-solvent-normalized single and bi-solute sorption isotherms demonstrate that ametryn undergoes specific force interactions with the chalk sorbent. The volume percent of phenanthrene sorbed at the liquid solubility limit is calculated to be 13% v:v in both the single and bi-solute experiments. This value exceeds what may be reasonably interpreted as partitioning of phenanthrene into organic matter, despite the relative linearity of the phenanthrene sorption isotherm (compared with other compounds) in both single and bi-solute systems.     

Cosolvent effects on sorption isotherm linearity

Sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic polymers associated with soils and sediments. In this study, aqueous and mixed solvent systems were used to investigate the effects of a cosolvent, methanol, on sorption isotherm linearity with natural organic matter (NOM), and to evaluate whether these results support, or weaken, the rubbery/glassy polymer conceptualization of NOM. All of the sorption isotherms displayed some nonlinear character. Our data indicates that all of the phenanthrene and atrazine isotherms were nonlinear up to the highest equilibrium solution concentration to solute solubility in water or cosolvent ratios (Ce/Sw,c) used, approximately 0.018 and 0.070, respectively. Isotherm linearity was also observed to increase with volumetric methanol content (fc). This observation is consistent with the NOM rubbery/glassy polymer conceptualization: the presence of methanol in NOM increased isotherm linearity as do solvents in synthetic polymers, and suggests that methanol is interacting with the NOM, enhancing its homogeneity as a sorptive phase so that sorption is less bimodal as fc increases. When the equilibrium solution concentration was normalized for solute solubility in water or methanol-water solutions, greater relative sorption magnitude was observed for the methanol-water treatments. This observation, in conjunction with the faster sorption kinetics observed in the methanol-water sediment column systems, indicates that the increase in relative sorption magnitude with fc may be attributed to the faster sorption kinetics in the methanol-water systems, and hence, greater relative sorptive uptake for the rubbery polymer fraction of NOM at similar time scales.     

Investigation of the solvent extracts of humic organic matter (HOM) isolated from the Ravenna Lagoon to study environmental pollution and microbial communities

Solvent extracts of HOM isolated from highly polluted sediments from the Ravenna Lagoon were studied. Diagnostic indicators included polycyclic aromatic hydrocarbons (PAHs) and nonylphenols as hazardous organic pollutants to characterize anthropogenic pollution, as well as fatty acids (FA, analysed as methyl esters, FAME) to characterize microbial communities responsible for natural attenuation processes. The distribution of PAHs including cyclopentafused surrogates pointed to a significant pyrogenic origin, characteristic for methane combustion. The PAH distribution was characterized by high concentrations of highly carcinogenic analytes with molecular weights of 276Da (benzo[ghi]perylene prevailing) and 300Da (coronene prevailing). The PAH pattern as obtained by solvent extraction was very different from that obtained from pyrolysis/thermochemolysis of the HOM polymeric matrix. The FA pattern indicated strong bacterial input, with a significant contribution from methanotrophic bacteria as revealed by monounsaturated members with n:1omega8 and n:1omega5 double bonds in the alkyl chain. Terrestrial inputs as revealed by FAME analysis beyond C(20) with pronounced even-over-odd discrimination were of minor significance. This was confirmed by the pattern of nC(24)-nC(30) alcohols in strong even-over-odd prevalence occurring in relatively low concentrations. The hopane hydrocarbon distribution reflected a distinctive impact from industrial processes utilizing heavy fractions of petroleum as feedstock. Hopanols along with the 17beta(H),21beta(H)-bishomohopanoic acid pointed to hopane producers, including methanotrophic and sulfate-reducing bacteria. Nonylphenols, which could not be detected in the pyrograms of solvent-extracted HOM matrix, had a total concentration of about 70microg g(-1) referred to the HOM in the solvent extract. In addition to common phytosterols including beta-sitosterol, coprostanol could be detected in the solvent extracts pointing to human fecal matter contamination. Concentration of resin acids turned out to be very low, thus no harmful environmental effects are to be expected from these compounds.     

A comparative study on the recovery of polycyclic aromatic hydrocarbons from fly ash and lignite coal

The recovery of polycyclic aromatic hydrocarbons (PAHs) from lignite coal burnt in Greek power stations and the fly ash produced is examined comparatively using Soxhlet, ultrasonic and accelerated solvent extraction procedures with various organic solvents. Soxhlet using toluene/methanol mixture and accelerated solvent extraction/toluene were found to be the most efficient methods for fly ash PAHs, yielding average recoveries of about 80%. The accelerated solvent extraction/toluene procedure was superior for lignite PAHs, yielding 96% average recovery, whereas ultrasonic and Soxhlet extraction yielded relatively lower recoveries (75% and 67%, respectively).     

水中有机污染物超声强化氧化技术研究进展

超声波技术在化学、环境、制药以及生物等领域有着广阔的应用前景。在降解水中难降解有机污染物方面 ,超声强化氧化技术有一定优势 ,降解效果显著 ,符合绿色环保技术的要求。超声强化氧化技术主要可分为超声空化技术、超声强化化学 (催化 )氧化技术、超声强化电化学 (催化 )氧化技术、超声强化光化学 (催化 )氧化技术、超声 生物降解等几大类 ,本文对各类技术的优缺点进行了评述。     

Study of metabolites from the degradation of polycyclic aromatic hydrocarbons (PAHs) by bacterial consortium enriched from mangrove sediments

The PAH metabolites produced during degradation of fluorene, phenanthrene and pyrene by a bacterial consortium enriched from mangrove sediments were analyzed using the on-fiber silylation solid-phase microextraction (SPME) combining with gas chromatography–mass spectrometry (GC–MS) method. Seventeen metabolites at trace levels were identified in different PAH degradation cultures based on the full scan mass spectra. In fluorene degradation cultures, 1-, 2-, 3- and 9-hydroxyfluorene, fluorenone, and phthalic acid were detected. In phenanthrene and pyrene degradation cultures, various common metabolites such as phenanthrene and pyrene dihydrodiols, mono-hydroxy phenanthrene, dihydroxy pyrene, lactone and 4-hydroxyphenanthrene, methyl ester, and phthalic acid were found. The detection of various common and novel metabolites demonstrates that SPME combining with GC–MS is a quick and convenient method for identification as well as monitoring the real time changes of metabolite concentrations throughout the degradation processes. The knowledge of PAH metabolic pathways and kinetics within indigenous bacterial consortium enriched from mangrove sediments contributes to enhance the bioremediation efficiency of PAH in real environment.     

Tracing the transformation of labelled [1-13C]phenanthrene in a soil bioreactor

[1-(13)C]-labelled phenanthrene was incubated in a closed bioreactor to study the flux and biotransformation of polycyclic aromatic hydrocarbon (PAH) in contaminated soils on a bulk and molecular level. The degradation of extractable phenanthrene was observed by GC-MS measurements and the mineralisation was monitored by (13)CO(2) production. The transformation of the (13)C-label into non-extractable soil-bound residues was determined by carbon isotopic measurements. With these data we were able to calculate a carbon budget of the (13)C-label. Moreover, the chemical structure of non-extractable bound residues was characterised by applying selective chemical degradation reactions to cleave xenobiotic subunits from the macromolecular organic soil matrix. The obtained low molecular weight products yielded (13)C-labelled compounds which were identified using IRM (isotope ratio monitoring)-GC-MS and structurally characterised with GC-MS. Most of the (13)C-labelled products obtained by chemical degradation of non-extractable bound residues are well-known metabolites of phenanthrene. Thus, metabolites of [1-(13)C]phenanthrene formed during biodegradation appear to be reactive components which are subsequently involved in the bound residue formation. Hydrolysable amino acids of the soil residues were significantly labelled with (13)C as confirmed by IRM-GC-MS measurements. Therefore, phenanthrene-derived carbon was transformed by anabolic microbial processes into typical biologically derived compounds. These substances are likely to be incorporated into humic-like material after cell death.     

Bioavailability and degradation of phenanthrene in compost amended soils

Bioavailability in soil of organic xenobiotics such as phenanthrene is limited by mechanisms of diffusion of the xenobiotics within soil micropores and organic matter. The agricultural utilization of compost may reduce the risk connected to organic xenobiotic contamination by means of: (i) a reduction of the bioavailable fraction through an increased adsorption and (ii) an enhanced degradation of the remaining bioavailable fraction through an inoculum of degrading microorganisms. Aim of this work is to test this hypothesis by assessing the effects of compost amendment on the bioavailability and degradation of phenanthrene in soil. Experiments were carried out in both sterilized and non-sterilized conditions, and chemical and microbiological analyses were carried out in order to determine the extent of degradation and bioavailability and to monitor the evolution of the soil micro flora in time. Bioavailability was assessed in sterilized microcosms, in order to assess the physical effects of compost on aging processes without the influence of microbial degradation. Results showed that bioavailability is significantly reduced in soils amended with compost, although no differences were found at the 2 doses of compost studied. In non-sterilized soils the amount of phenanthrene degraded was always higher in the amended soils than in the non-amended one. Microbiological analyses confirmed the presence of a higher number of phenanthrene degraders in the amended soils and in samples of compost alone. These results suggest that compost induces the degradation in soils of easily degradable compounds such as phenanthrene, when the proper bacteria are in the compost; more resistant xenobiotics may instead be trapped by the compost organic matter, thus becoming less available.