Slurry-phase ozonation for remediation of sediments contaminated by polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic, persistent, bioaccumulating organic compounds containing two or more fused aromatic rings. They are listed by the U.S. Environmental Protection Agency as priority pollutants because of their carcinogenicity and toxicity. Employing ozonation as a remediation technique, this work investigated the treatability of a sediment sample from a freshwater boat slip subjected to coal tar contamination over a long period. The contaminated sediment sample contained high levels of PAHs in the forms of naphthalene, phenanthrene, pyrene, and benzo[a]pyrene, among other byproducts present in the humic and solid phases of the sediment. The objectives of this work were to examine (1) the degradation of PAHs in the contaminated sediment as treated by ozonation in the slurry form, (2) the effects of ozonation upon the soil matrix and the biodegradability of the resultant PAH intermediates, and (3) the feasibility of a combined technique using O3 as a pretreatment followed by biological degradation. The sediment was made into 3% w/w soil slurries and ozonated in a 1.7-L semi-batch, well-stirred reactor equipped with pH control and a cold trap for the gaseous effluent. Samples were collected after different ozonation durations and tested for biochemical oxygen demand (BOD), chemical oxygen demand (COD), UV absorbance, and toxicity, along with quantitative and qualitative determinations of the parent and daughter intermediates using gas chromatography/flame ionization detection (GC/FID), GC/mass spectrometry (MS), and ion chromatography (IC) techniques. The GC/MS technique identified 16 compounds associated with the humic and solid phases of the sediment. Intermediates identified at different ozonation times suggested that the degradation of PAHs was initiated by an O3 attack resulting in ring cleavage, followed by the intermediates' oxidation reactions with O3 and the concomitant OH radical toward their mineralization. Results suggested that ozonation for 2 hr removed 50-100% of various PAHs in the solid and liquid phases (as well as the aqueous and gaseous media resulting from the treatment process) of the sediment sample and that organic and inorganic constituents of the sediment were also altered by ozonation. Measurements and comparisons of BOD, COD, UV absorbance, and toxicity of the samples further suggested that ozonation improved the bioavailability and biodegradability of the contaminants, despite the increased toxicity of the treatment effluent. An integrated chemical-biological system appeared to be feasible for treating recalcitrant compounds.     

Desorption of polycyclic aromatic hydrocarbons from carbon nanomaterials in water

Desorption behavior of pyrene, phenanthrene and naphthalene from fullerene, single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) was examined. Available adsorption space of carbon nanotubes (CNTs) was found to be the cylindrical external surface, neither the inner cavities nor inter-wall spaces due to impurities in the CNTs and restricted spaces (0.335nm) of the MWCNTs, respectively. Desorption hysteresis was observed for fullerene but not for CNTs. Deformation-rearrangement was proposed to explain the hysteresis of polycyclic aromatic hydrocarbons (PAHs) for fullerene, due to the formation of closed interstitial spaces in spherical fullerene aggregates. However, long, cylindrical carbon nanotubes could not form such closed interstitial spaces in their aggregates due to their length, thus showing no significant hysteresis. High adsorption capacity and reversible adsorption of PAHs on CNTs imply the potential release of PAHs if PAH-adsorbed CNTs are inhaled by animals and humans, leading to a high environmental and public health risk.     

Desorption kinetics for selected PCB congeners from river sediments

Desorption of PCBs from sediment can significantly affect the ultimate fate and effects of PCBs in aquatic systems. Using a gas purging technique to strip soluble and sorbed polychlorinated biphenyls (PCBs) from solutions and sediment suspensions, Henry's law constants, approach to equilibrium, and desorption rate constants for four PCB congeners were measured. Henry's law constants were on the order of 10⁻⁴ m³ atm mole⁻¹. Desorption rate constants measured for a predominantly kaolinitic, low-organic carbon sediment were on the order of 0.03–0.1 days⁻¹. In contrast, desorption rate constants measured for a sediment composed of montmorillonite with a 3% organic carbon content were on the order of 0.009–0.04 days⁻¹. Desorption data suggest that equilibration times for PCBs with low chlorine content are on the order of six weeks, and months to years for PCBs with a significantly higher chlorine content.     

Leaching characteristics of polycyclic aromatic hydrocarbons (PAHs) from spiked sandy soil

In order to evaluate the factors affecting leachability of hydrophobic organic pollutants (HOPs), we performed leaching tests under a variety of conditions using sandy soil contaminated with phenanthrene and pyrene. The results obtained were: (1) the shaking time, temperature, and dissolved humic matter (DHM, as coexisting matter) increased leachability; (2) ionic strength reduced leachability; and (3) the liquid-to-solid ratio and pH level had no effect on leaching concentration of HOPs. In DHM-added leaching tests assuming equilibrium with HOPs, DHM, and solid matrix, the partitioning (binding) coefficient of HOPs to DHM was accurately calculated with the equations proposed in this study. While we recommend taking into consideration the coexistence of DHM, it is difficult to use universally because its properties differ according to origin and extracting method. It is therefore reasonable to use an alternative reagent having an effect similar to that of DHM.     

Removal of pyrene from contaminated sediments by mangrove microcosms

The potential of mangrove wetland systems to remove pyrene from surface- or bottom-contaminated sediments was investigated by microcosm studies. The performance of two mangrove plant species, Kandelia candel and Bruguiera gymnorrhiza in pyrene removal was also compared. During the six-months experimental period, the growth of both species in the surface-contaminated microcosms was not significantly different from that in the bottom-contaminated ones, and was comparable to the control (without any pyrene contamination). At the end of six-months treatment, pyrene concentrations in contaminated sediments declined from an initial 3 microg g(-1) to less than 0.4 microg g(-1), indicating that pyrene was successfully removed by mangrove microcosms. Around 96.4% and 92.8% pyrene in microcosms planted with K. candel were removed from the surface- and bottom-contaminated sediments, respectively. The removal percentages were slightly lower in microcosms planted with B. gymnorrhiza. Significant accumulation of pyrene in roots was only found in microcosms having bottom-contaminated sediments, and pyrene concentrations were 3.05 microg g(-1) and 4.50 microg g(-1) in roots of K. candel and B. gymnorrhiza, respectively. These values were much higher than that in control microcosms (without pyrene contamination, root pyrene concentrations were 0.27 microg g(-1) for K. candel and 0.34 microg g(-1) for B. gymnorrhiza) and in microcosms with contaminated sediments placed at the surface layer. Nevertheless, the overall contribution of root accumulation and plant uptake to the removal of pyrene from contaminated sediments was insignificant.     

Formation of chlorinated hydrocarbons from the reaction of chlorine atoms and activated carbon

The reactions of chlorine atoms and activated carbon have been studied over the temperature range of 200-400 degrees C using an isothermal flow reactor in conjunction with 337 nm laser photolysis of Cl2. These studies have shown that carbon tetrachloride is the major product, with chloroform, methylene chloride, and methyl chloride being formed in progressively decreasing yields. Trace quantities of methane, ethane, and dichloroethylenes were also observed. Mechanisms of carbon fragmentation by successive addition of chlorine atoms are proposed. The formation of small chlorinated hydrocarbons by the direct reaction of chlorine with carbon may be a key link in both the de novo and precursor pathways of formation of PCDD/F.     

Regiospecific dechlorination of spiked tetra- and trichlorodibenzo-p-dioxins by anaerobic bacteria from PCDD/F-contaminated Spittelwasser sediments

Samples were taken from sediment of the River Spittelwasser (district Bitterfeld, Germany), which is highly polluted with PCDD/Fs and other chloroorganic compounds. The sediment cores were separated into 10-20 cm thick layers, spiked with 50 microM of 1,2,3,4-tetrachlorodibenzo-p-dioxin and incubated for 8 months under anaerobic conditions in the presence of cosubstrates. Reductive dechlorination of the tetrachlorinated congener and formation of tri- and dichlorinated products were observed in all biologically active incubations. Analysis of subcultures spiked with 1,2,3- and 1,2,4-trichlorodibenzo-p-dioxin, respectively, revealed two different dechlorination pathways within the sediment cores. Pathway M was characterized by the simultaneous dechlorination of peri- and lateralchlorine atoms, whereas sequence SP was restricted to the dechlorination at positions flanked by chlorine atoms on both sides.     

Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride

Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) released from combustion of polyvinylchloride (PVC) at different furnace temperatures were investigated. A laboratory-scale tube-type furnace with electric heating was utilized to control combustion conditions. Glass fabric filters and adsorbents were used to collect the combustion emissions. Following Soxhlet extraction, concentration and column chromatography purification, isomers separation, selective detection and identification of Cl-PAHs were performed on GC/MS system on the basis of retention data and mass spectra. Their quantification was accomplished by using external standard calibration technique. About 18 Cl-PAHs were determined, most of which were monochlorinated derivatives of naphthalene, biphenyl, fluorene, phenanthrene, anthracene, fluoranthene and pyrene. Only two dichlorophenanthrenes or anthracenes were identified. The possible positions of chlorine atoms attached to the aromatic rings are predicted by quantitative structure-property relationship. The levels of these compounds were in the range of 0.30-29.08 microg/g PVC. The relationship between the formation of Cl-PAHs and PAHs was discussed.     

Toxic chlorinated and polyaromatic hydrocarbons in simulated house fires

Toxic chlorinated hydrocarbons (polychlorinated biphenyls, benzenes and dioxins and furans) and polyaromatic hydrocarbons were examined in combustion gas and deposited soot wipe samples from simulated house fires. Concentrations of these substances were high during the fires, the amounts of polychlorinated dioxins and furans (PCDD/Fs) in the combustion gas varying from 1.0 to >7.2 ng/m3 (I-TEQ) and those of polyaromatic hydrocarbons from 6.4 to 470 mg/m3. Thus large amounts of organic compounds may be released in house fires. As a result, there is a need for careful personal protection of fire-fighters and remediation workers against combustion gases during a fire and on contaminated surfaces after it.     

Uptake of polycyclic aromatic hydrocarbons (PAHs) in salt marsh plants Spartina alterniflora grown in contaminated sediments

Polycyclic aromatic hydrocarbon (PAH) concentrations were measured in Spartina alterniflora plants grown in pots of contaminated sediment, plants grown in native sediment at a marsh contaminated with up to 900 microg/g total PAHs, and from plants grown in uncontaminated control sediment. The roots and leaves of the plants were separated, cleaned, and analyzed for PAHs. PAH compounds were detected at up to 43 microg/g dry weight in the root tissue of plants grown in pots of contaminated soil. PAH compounds were detected at up to 0.2 microg/g in the leaves of plants grown in pots of contaminated soil. Concentrations less than 0.004 microg/g were detected in the leaves of plants grown at a reference site. Root concentration factor (RCF) values ranged from 0.009 to 0.97 in the potted plants, and from 0.004 to 0.31 at the contaminated marsh site. Stem concentration factor (SCF) values ranged from 0.00004 to 0.03 in the potted plants and 0.0002 to 0.04 at the contaminated marsh. No correlation was found between the RCF value and PAH compound or chemical properties such as logKOW. SCF values were higher for the lighter PAHs in the potted plants, but not in the plants collected from the contaminated marsh. PAH concentrations in the roots of the potted plants are strongly correlated with soil concentrations, but there is less correlation for the roots grown in natural sediments. Additional plants were grown directly in PAH-contaminated water and analyzed for alkylated PAH homologs. No difference was found in leaf PAH concentrations between plants grown in contaminated water and control plants.     

Polycyclic aromatic hydrocarbons in lake sediments from the High Tatras

European alpine lake systems are used as indicators of air quality over the continent. Preliminary data showed high polycyclic aromatic hydrocarbons (PAH) loads in the High Tatras (Eastern Europe) in comparison to other mountain regions. Here, insight on the spatial distribution of PAH is provided from analysis of top-core sediments of 27 alpine lakes distributed along the High Tatras.Top-core sediment concentrations were higher than those in deep-cores, and they were higher than those observed in other European high mountain regions. The PAH profiles were uniform and comparable to those observed in aerosols and snow, indicating that atmospheric deposition was the predominant PAH input pathway to the lakes. Good agreement between estimated atmospheric deposition and sedimentation fluxes was observed. However, in several lakes in the western range higher sediment fluxes may correspond to higher PAH depositions levels. The higher concentrations may also reflect inputs from potential emission source areas.     

Pressure-assisted ozonation of PCB and PAH contaminated sediments

Sediment contamination by recalcitrant organics such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) is prevalent and of a great concern. Remediation efforts are hampered by the hydrophobic nature of the contaminants that limits their availability as well as by the sediment matrix that limits their exposure to treatment agents. Using contaminated sediment samples from the Passaic River, St. Louis River, Waukegan Harbor, and Wells National Estuarine Research Reserve, this research demonstrated a new ozonation technique that incorporates rapid, successive cycles of pressurization (690 kPa) and depressurization, enabling more effective treatment than conventional ozonation would. Conventional ozonation reached maximum 60% and 40% removal of PAHs from the Passaic River (40 mg kg(-1) initially) and St. Louis River sediment (520 mg kg(-1) initially), respectively, in 1h; however, removals ceased despite prolonged treatment for 2h. The pressure-assisted technique removed 96% of PAHs from both river sediments within 1h; it completely removed both PAHs (16 mg kg(-1) initially) and PCBs (5.1 mg kg(-1) initially) from the Waukegan Harbor sediment in 0.5 h. The heightened treatment is explained by soil aggregate fracturing upon pressure cycles that exposes the contaminants as well as by the confluence of hydrophobic contaminants and O(3) at the gas-liquid interface in the presence of microbubbles. The technique is expected to accelerate O(3) treatment of a wide range of organic contaminants, and it may provide treatment to dredged and stored contaminated sediment.     

Mineralisation of target hydrocarbons in three contaminated soils from former refinery facilities

This study investigated the microbial degradation of ¹⁴C-labelled hexadecane, octacosane, phenanthrene and pyrene and considered how degradation might be optimised in three genuinely hydrocarbon-contaminated soils from former petroleum refinery sites. Hydrocarbon mineralisation by the indigenous microbial community was monitored over 23 d. Hydrocarbon mineralisation enhancement by nutrient amendment (biostimulation), hydrocarbon degrader addition (bioaugmentation) and combined nutrient and degrader amendment, was also explored. The ability of indigenous soil microflora to mineralise ¹⁴C-target hydrocarbons was appreciable; ≥16% mineralised in all soils. Generally, addition of nutrients or degraders increased the rates and extents of mineralisation of ¹⁴C-hydrocarbons. However, the addition of nutrients and degraders in combination had a negative effect upon ¹⁴C-octacosane mineralisation and resulted in lower extents of mineralisation in the three soils. In general, the rates and extents of mineralisation will be dependent upon treatment type, nature of the contamination and adaptation of the ingenious microbial community.     

Desorption of sediment-associated polychlorinated dibenzo-p-dioxins, dibenzofurans, diphenyl ethers and hydroxydiphenyl ethers from contaminated sediment

The transport and bioavailability of sediment-associated contaminants are often controlled by the contaminants' desorbing behaviour. This study examines the desorption kinetics of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), diphenyl ethers (PCDEs) and hydroxydiphenyl ethers (HO-PCDEs) from the highly contaminated River Kymijoki sediment in Finland. The desorption kinetics data were generated using Tenax((R)) extraction, and a first-order three-compartment kinetic model was fitted to the data. The desorption data was compared to the previously published accumulation data from this same location to investigate the relationship between the rapidly desorbing fraction (F(r)) and biota-sediment accumulation factors (BSAFs) as well as semipermeable membrane device sediment accumulation factors (SSAFs). The PCDDs, PCDFs, PCDEs and HO-PCDEs were tightly attached to sediment particles and formed a large very slowly desorbing fraction (F(vs)). Rapidly desorbing fractions (F(r)) varied between 0.8% and 8% of total amount in sediment. The size of the desorbing fraction was congener-specific and F(r) decreased with the increasing lipophilicity of congeners. The size of the F(r) was unable to explain the small variation in the BSAFs of Lumbriculus variegatus but may help to explain the observed variation in the SSAFs. To our best knowledge, this study is the first effort to investigate the desorption of PCDDs, PCDFs, PCDEs and HO-PCDEs in field-contaminated sediments. The major finding that the very slow desorption of these chemicals will continue years, provides essential information for the modern risk assessment process.     

Atmospheric background of chlorinated hydrocarbons studied in Swedish lichens

Lichens $\text{Cladonia}$$\text{alpestris}$ collected in the northern part of Sweden were analyzed over a 10-year period for chlorinated hydrocarbons. Results show a delay of 2–3 years between the production of PCBs and the deposition of these compounds in the lichen. They confirm the low solubility of PCBs in water and the predominance of atmospheric transport of these chlorinated compounds far away from industrialized areas.     

Dissolution of resin acids, retene and wood sterols from contaminated lake sediments

The dissolution potency of hydrophobic resin acids (RAs), retene and wood sterols from sediments was studied. These wood extractives and their metabolites are sorbed from pulp and paper mill effluents to downstream sediments. With harmful components like these, sediments can pose a hazard to the aquatic environment. Therefore, sediment elutriates with water were produced under variable conditions (agitation rate and efficiency, time), and concentrations of the dissoluted compounds were analyzed. Both naturally contaminated field sediments and artificially spiked sediments were studied. By vigorous agitation RAs can be released fast from the sediment matrix and equilibrium reached within 3 days. Compared to RAs, desorption of retene from lake sediment was slower and did not completely reach equilibrium in 23 days. Sterols spiked to pristine sediment with a 33-day contact time desorbed faster than those associated authentically with industrial sediment of from a contaminated lake. Simulating the water turbulence adjacent to a sediment surface by low and high rate of agitation in the laboratory, an increase in the mixing rate after 43-day elutriation suddenly released a high amount of wood sterols. The results indicate wide variation between hazardous chemicals in their tendency to dissolution from sediment solids. Erosion and hydrology adjacent to the sediment surface, as well as risks from dredging activities of sediments, may expose lake biota to bioactive chemicals.     

Risks from sediments contaminated with organochlorine pesticides in Hangzhou,China

In September 2009, we investigated the residues, enantiomer fractions (EFs) and biological risks of organochlorine pesticides (OCPs), including dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs), in three different depth ranges (0–5 cm, 5–10 cm and 10–15 cm) of sediments from 15 sites in Hangzhou, China. The concentration (ng g^?1 dry weight) ranges of HCHs and DDTs in surface sediments were 0.74–5.8 and 0.76–17, respectively. The vertical distribution of mean OCP concentrations was in the order of 10–15 cm > 5–10 cm > 0–5 cm and implied that the residues of HCHs and DDTs gradually decreased after they were banned. The residues of OCPs in the study area mainly originated from the historical OCP use. The isomer ratios of <alpha>-HCH (α-HCH)/<gamma>-HCH (γ-HCH) (0.10–7.6) implied that HCH residues were derived not only from historical technical HCH use but also from additional use of lindane in this area. The isomer ratios of o,p′-DDT/p,p′-DDT (51% of samples were in the range of 0.3–1.3) suggested that both dicofol-type DDT and technical DDT applications may be present in most study areas. The (+)-enantiomers of α-HCH and o,p′-DDT were more prevalent than (?)-enantiomer in most samples with the fractions contain different enantiomers greater than 0.5. DDTs, especially p,p′-DDE, are the main OCP species of more ecotoxicological concern in Hangzhou.     

Supercritical fluid extraction of polycyclic aromatic hydrocarbons from marine sediments and soil samples

Supercritical fluid extraction (SFE) was used to extract polycyclic aromatic hydrocarbons (PAH) from a certified sample of marine sediment. This sample contains a great number of organic pollutants that are present in low concentrations. The extractions were carried out at 50 and 80 degrees C, at a pressure varying from 230 to 600 bar and using CO2 in the supercritical phase and the effect of three organic modifiers (methanol, n-hexane and toluene), added at 5%/vol, at the same temperature and pressure conditions, were then considered. PAHs were characterized by GC-MS and the recover yield was estimated for 6 PAHs that were representative of those present in the sample, according to their molecular weight and to the number of condensed rings. The analytical conditions giving the best recovery efficiency were used on an unpolluted soil sample spiked with 11 PAHs of environmental importance at a concentration similar to that certified for the sediment sample. An increase in the yield of recovered PAHs, using methanol as co-solvent, was observed while higher temperatures caused a negative effect on the quantity of recovered pollutants. The recovery yield for PAHs from the spiked soil sample was measured and found to be greater than 90%. Better recoveries were obtained for those compounds with higher molecular weight.     

Behaviour of pharmaceuticals in spiked lake sediments - effects and interactions with benthic invertebrates

The behaviour and effects of atorvastatin (ATO), carbamazepine (CBZ), and 17α-ethinylestradiol (EE2) were investigated in spiked lake sediments, at concentrations up to 56.5 mg kg⁻¹ dry weight (dw), with the benthic invertebrates Chironomus dilutus and Hyalella azteca. Desorption constants were calculated in the presence and absence of animals, using linear isotherms, yielding K_d values of 28.2, 189.0 and 125.1 L kg⁻¹ (ATO), 73.7, 201.7 and 263.2 L kg⁻¹ (CBZ), and 114.9, 114.2 and 519.2 L kg⁻¹ (EE2) for C. dilutus, H. azteca, and without animals, respectively. For ATO and CBZ, K_d values were smaller in the presence of C. dilutus, indicating greater desorption to the overlying water from bioturbation, which is consistent with the predominantly benthic occurrence of C. dilutus compared to H. azteca. In contrast, due to its greater hydrophobicity, bioturbation did not significantly affect desorption of EE2. No significant toxicity was observed, indicating decreased bioavailability of the chemicals sorbed to sediments compared with water-only toxicity assays.     

多环芳烃污染土壤生物修复的强化方法

生物降解是去除环境中多环芳烃(PAHs)的重要途径,通过采取一些强化措施,如使用表面活性剂,添加营养物质和提供共代谢底物等,可显著提高PAHs降解速度和程度,为生物修复技术的成功应用提供前提。在分析中,对近年来国内外在PAHs污染土壤生物修复强化方面的研究进展进行了综述。