Partitioning of polycyclic aromatic hydrocarbons (PAH) to water-soluble soil organic matter

The mobility of polycyclic aromatic hydrocarbons (PAH) in soils can be influenced by the presence of dissolved organic matter. Partition coefficients of selected polycyclic aromatic hydrocarbons, ranging from 3-ring to 6-ring compounds, to water-soluble soil organic matter (WSSOM) were determined. Partition coefficients were determined for WSSOM obtained from two soils under agricultural use and forest and for commercially available humic acid (Aldrich), taking advantage of a reversed phase (C₁₈) separation method. The WSSOM was characterised with regard to charge and hydrophilic/hydrophobic properties with a dissolved organic matter (DOM) fractionation method. No sorption to WSSOM was found for the tri- and tetracyclic PAH, whereas the penta- and hexacyclic PAH showed a significant binding to both types of WSSOM and to Aldrich humic acid. The affinity of penta- and hexacyclic PAH to WSSOM was considerably lower compared to the affinity to Aldrich humic acid. This is suggested to be due to the lower amount of hydrophobic fractions, c. 30%, in the natural WSSOM as compared to Aldrich humic acid. Effective partition coefficients (Koc_eff) for the sorption of PAH to bulk soil calculated from K_DOC and DOM in the naturally occurring concentration range were only 60–70% of the K_oc values in pure water. The impact of DOM on pollutant transport is further influenced by non-equilibrium behaviour of PAH in soils and by sorption of DOM to the solid-soil matrix. Several scenarios are described in which the effect of DOM on pollutant transport may become important.     

Influence of sample pretreatment on the extractability of polycyclic aromatic hydrocarbons (PAH) from forest floor horizons

Extraction of PAH from Oh-horizon material after dispersion of air-dried samples in water resulted in a 80% higher yield of 20 PAH species compared to extraction of air-dried, freeze-dried or ground samples. Concurrently, the free surface area (BET method) of the organic matter increased. It was assumed that dispersion resulted in a disaggregation and/or stretching of organic aggregates, which makes interior aggregate regions available to the extractant that were pre-viously not accessible for the extractant due to diffusion barriers.     

The history of airborne polycyclic aromatic hydrocarbons (PAH) and perylene as recorded in dated lake sediments

Polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from five small forest lakes in Finland. The catchments of the lakes were undisturbed (2 lakes) or only very slightly disturbed by human activity (3 lakes). None of the lakes had runoff delivery of PAH from their shores. Lead-210 dating of four lakes enabled the calculation of individual PAH fluxes over the past 100 to 150 yr. The sedimentary distribution of abiotic PAH in these lakes appears to be indicative of the development of combustion-generated energy production in Finland and adjacent countries. This development is reflected in an overall increase in sedimentary PAH since about 1850. After World War II the rate of accumulation of PAH continues to increase. The large variation between the PAH fluxes of different lakes indicates different trapping efficiencies and/or different preservation of the PAH compounds due to limnological differences between the lakes.     

Fractionated extraction of polycyclic aromatic hydrocarbons (PAHs) from polluted soils: estimation of the PAH fraction degradable through bioremediation

Chemical extractions were tested to estimate the fraction of 15 polycyclic aromatic hydrocarbons (PAHs) in polluted soils degradable through bioremediation. Of 30 soil samples, differing in PAH concentrations, from 10 long‐term polluted sites, four were used in screening tests conducted with 14 different extractants. PAH extractability increased in the order salt solutions < surfactant solutions < organic solvents and organic solvent–water mixtures. Closest correlations (r = 0.73–0.91) and ratios of c. 1:1 of the extracted to the degradable PAH concentrations were found with aqueous solutions of two surfactants (Genapol UDD 88, Synperonic LF/RA 30). The PAH extractability by surfactant solutions increased with surfactant concentration (0–50 mg ml^?1) and with decreasing degree of PAH condensation (6–2 rings). Kinetic behaviour of PAH solubilization by surfactants resembled the kinetics of PAH degradation (r = 0.84–0.99). With repeated extractions, a finite fraction of PAHs was extracted, which is thought to be the mobile and mobilizable PAH fraction, the latter being controlled by back‐diffusion from intra‐ and inter‐particle sites. Experiments with all 30 soil samples and a priori testing with an additional 10 soil samples confirmed that single extractions with surfactant solutions (5 mg ml^?1; soil:solution ratio 1:20) were suitable for estimating the degradable fraction of PAHs in soil. With separate linear regression equations for PAHs grouped according to their degree of condensation, the extracted concentrations described the degradable concentrations with correlation coefficients (r) ranging from 0.62 to 0.80 (P < 0.001). PAH extractions with the surfactant solutions can be used to assess the prospects of bioremediation of PAH‐polluted sites.     

多环芳烃在土壤中的环境行为研究进展

综述了土壤环境中多环芳烃(PAHs)来源及其进入环境后的行为和归宿,并提出多环芳烃污染土壤的修复对策。     

The relationship of a coal fired power plant to the levels of polycyclic aromatic hydrocarbons (PAH) in the sediment of Cayuga Lake

Polychlorinated biphenyls (PCBs) are chlorinated hydrocarbons primarily used as dielectric fluids and coolants for electrical equipment. At present, it is estimated that 200 Gg of PCBs have been released into the environment. In 1976, the Toxic Substances Control Act was passed by Congress, requiring regulation of PCBs. EPA-approved methods for destruction/disposal of PCBs include high temperature combustion in incinerators and high efficiency boilers, landfilling, chemical dechlorination, and alternate disposal techniques which achieve a level of performance equivalent to an approved incinerator or boiler. A discussion of these methods is presented as well as various other disposal methods which are still in the research phases.     

Milk--blood transfer of (14)C-tagged polycyclic aromatic hydrocarbons (PAHs) in pigs

Polycyclic aromatic hydrocarbons (PAHs) are lipophilic organic pollutants occurring widely in the terrestrial environment. To study the transfer of PAHs in the food chain, pigs have been fed with milk spiked either with [(14)C]phenanthrene or with [(14)C]benzo[a]pyrene. The analysis of blood radioactivity showed that both PAHs were absorbed with a maximum concentration at 5--6 h after milk ingestion, similar to fat metabolism. The blood radioactivity then decreased to reach background levels 24 h after milk ingestion. Furthermore, the blood radioactivity was higher for phenanthrene (even if the injected load was the lowest) than for benzo[a]pyrene, in agreement with their solubility difference. These findings suggest that milk fat and PAHs were absorbed during the same time period.     

Distribution of polycyclic aromatic hydrocarbons in the soil-plant system

The content and composition of the polycyclic aromatic hydrocarbons (PAHs) in the conjugated systems of [arable soil]-[above-ground plant organs] in background (reference) and contaminated regions were studied. The coefficients of the biological uptake of PAHs by plants (K _bPAH) were determined for different PAH concentrations in the soil. Correlations of the PAH accumulation rate in plants with the physicochemical properties of the PAHs—the solubility, hydrophobicity, volatility, and chemical activity (polarizability and ionization potential)—were revealed. The high accuracy, sensitivity, and information value of the standardized parameters K _b were shown (with K _bPAH as an example) for the quantitative study of the accumulation mechanisms of substances by plants compared to the average arithmetic values of their concentrations in the plants.     

Metabolism of polycyclic aromatic hydrocarbons by the wood-feeding termite Coptotermes formosanus (Shiraki)

Polycyclic aromatic hydrocarbons (PAHs) are among the most prevalent and persistent pollutants in the environment. In this study, the wood-feeding termite (WFT) Coptotermes formosanus (Shiraki) was studied regarding the potential ability to degrade two selected low-molecular-weight PAHs, phenanthrene and anthracene. Pyrolysis-gas chromatography/mass spectrometry was employed for analysis of in vivo PAH degradation by three gut segments (fore-, mid-, and hindgut) of the WFT. The results revealed the capability of lower termite for PAH metabolism, which started from the foregut and mainly occurred in the midgut region. Remediation of phenanthrene by the termite has been proposed to be initiated via hydroxylation at the C-10 position. Anthracene metabolism first occurred at the C-3, C-5, and C-12 positions with the addition of aldehyde and carbonyl groups. Ring hydroxylation, methoxylation, esterification, carboxylation, and methylation were detected on both the PAHs for ring fission, suggesting the existence of effective PAH modification activity in the alimentary canal of C. formosanus . This new PAH degradation system of the WFT provides new insights for potential technologies for bioremediation of PAH-contaminated soil and sediment based on the related lingolytic enzymes.     

甜菜与牧草间作对多环芳烃污染土壤的修复作用

通过盆栽试验方法,选择经济作物甜菜和牧草类黑麦草、苏丹草、香根草为供试植物,研究了甜菜与3种牧草分别间作及各自单作对多环芳烃（PAHs）菲、荧蒽、芘和苯并[a]芘污染土壤修复作用。结果显示：经6个月连续两茬种植试验后,所有种植植物的处理中土壤PAHs的去除率均高于无植物种植组,间作种植土壤PAHs的去除率高于单作,黑麦草、苏丹草、香根草与甜菜间作对土壤PAHs的去除率分别达到84.85%、79.96%、84.11%;在土壤污染条件下,间作模式更有利于甜菜生长;种植植物增强了土壤中多酚氧化酶和过氧化氢酶的活性,间作模式下二者活性高于单作4.37%~43.07%,过氧化氢酶较多酚氧化酶对PAHs土壤污染更敏感,可作为关键酶用于评价土壤PAHs污染状况。在不影响农业生产的前提下,修复植物牧草和经济作物甜菜间作种植模式显著提高了土壤PAHs的降解率。     

Availability of polycyclic aromatic hydrocarbons in aging soils

Purpose  

The soil contamination by hydrophobic organic contaminants (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), poses great threats to human health and ecological security and attracts worldwide concerns. The total HOC concentrations overestimate its available fraction to the soil biota. Increased understanding of the availabilities of PAHs in soil environment will have considerable benefits for their risk assessment and be very instructive to food safety and remediation strategies in contaminated sites. However, the availability of PAHs in aging soils and particularly the correlations of the availabilities with their forms in soils have yet to be elucidated. In this work, the availabilities of PAHs in aging soils were evaluated using a sequential mild extraction technique.     

Contamination of pastures by polycyclic aromatic hydrocarbons (PAHs) in the vicinity of a highway

To assess PAH contamination pastures, grass and soil samples have been collected from 10 m (d1), 50 m (d2), and 150 m (d3) perpendicular to a French highway (70,000 vehicles per day) and at a control site in a rural area away from nearby contaminating sources. Total PAH concentration ranges from 767 ng/g dry weight to 3989 ng/g dry weight, according to the matrix and the distance from the highway. Distance is not a significant factor for PAH deposition on grass, while in soil it has an effect between d1 and d2 or d3. The total PAH concentration in highway samples is 8 times higher than in control site samples for grass and 7 to 4 times higher for soil. Fluoranthene, pyrene, and phenanthrene are the major PAHs in grass samples at the control site and the highway, but the concentrations are about 5 times higher near the highway. In soil samples collected near the highway, the values of concentrations between all compounds are not statistically different. PAH deposition on grass is linked to the physicochemical properties of the compounds, which lead to a specific distribution of each molecule (according to their volatility and the number of aromatic rings) while no specific behavior is revealed in soil.     

生物表面活性剂强化微生物修复多环芳烃污染土壤的初探

通过温室盆栽实验,单独或联合接种多环芳烃专性降解菌(DB)和添加生物表面活性剂-鼠李糖脂(RH),研究了生物表面活性剂强化微生物修复多环芳烃(PAHs)长期污染土壤的效果。结果表明,添加RH和接种DB能明显促进土壤中PAHs总量和各组分PAHs的降解。经过90 d培养后,添加RH、DB和RH+DB处理的PAHs的降解率分别为21.3%、32.6%、36.0%,较对照分别提高了333.0%、563.3%、633.0%。此外,随着苯环数的增加,土壤中15种PAHs平均降解率逐渐降低。同时也发现DB、RH+DB处理土壤中脱氢酶活性、多酚氧化酶活性和PAHs降解菌数量显著高于CK、RH处理,但是CK与RH处理没有显著差异,说明DB、RH在促进土壤中PAHs的降解方面有不同的机制。     

Phytotoxicity of polycyclic aromatic hydrocarbons to willow trees

The toxicity of PAH to willow trees(Salix alba, S. viminalis, S. viminalis x schwerinii) was investigated. Willow cuttings were grown in PH-saturated hydroponic solution (naphthalene NAP, phenanthrene PHEN and benzo(a)pyrene BaP). Toxicity was related to aqueous solubility and was highest for NAP. PHEN did not show significant effects, except in one case. Exposure of trees to BaP showed no effect in two cases, but increased transpiration and growth in two others. High dosages of NAP were fatal for the trees, the lowest dosage significantly stimulated growth. Soil samples were taken from several PAH contaminated sites, among them gas works sites and a former sludge basin. The PAH contents ranged from 1.76 mg/kg to 1451 mg/kg. None of the soils was lethally toxic to the trees, and difference between growth in control soils and growth in PAH contaminated soils was not apparent. Growth and water use efficiency were positively, but not significantly correlated to the PAH content of the soils. Outdoor growth of willows and poplars on the former sludge basin in Valby was monitored, with willows growing faster than poplars(Fopulus trichocarpa). Phytotoxic effects could be observed at some willows at the Valby sludge basin, but it is not sure whether these effects can be contributed to PAH.     

Sorption of polycyclic aromatic hydrocarbons to mineral surfaces

Minerals contribute crucially to the retention of polycyclic aromatic hydrocarbons (PAHs) in subsurface environments. To investigate the sorption behaviour to mineral surfaces batch sorption experiments were conducted using three PAHs (phenanthrene, pyrene, benzo(a)pyrene) and three mineral sorbents that were representative of subsurface materials (quartz, goethite‐coated quartz, quartz‐montmorillonite mixture). Sorption kinetics showed an instantaneous, considerable PAH sorption to all minerals, except for phenanthrene sorption to quartz at small aqueous‐phase concentrations. Apparent sorption equilibrium was achieved after 4 hours of contact time. The sorption characteristics were fitted to six isotherm models by applying Monte Carlo simulation and nonlinear regression. Best‐fit models were obtained by a model discrimination approach. Phenanthrene and pyrene sorption were best described by the Freundlich isotherm model, with the exception of phenanthrene sorption to quartz (linear isotherm). Good fit results for quartz were also obtained for the combined linear‐Freundlich isotherm. Benzo(a)pyrene sorption to all minerals followed linear high‐affinity isotherms. In the case of phenanthrene and pyrene, the Monte Carlo simulations resulted in mean values with small standard deviations for the isotherm parameters, indicating a negligible influence of the experimental uncertainties on the accuracy of the fitted parameters. For phenanthrene, (i) linear isotherms to quartz and goethite‐coated quartz and (ii) a nonlinear concave‐shaped isotherm to quartz–montmorillonite, assuming a pore‐filling process to micropores formed by clay aggregates, were confirmed. For pyrene, nonlinear convex‐shaped isotherms to the mineral surfaces were assessed. A specific sorption affinity of pyrene to the goethite surface indicated a non‐covalent cation‐π interaction. Small sorption affinities to quartz–montmorillonite support an unfavourable partitioning into the adjacent water.     

多环芳烃微生物降解机理研究进展

主要阐述了微生物降解PAHs的机理,比较了典型微生物种类芽孢杆菌(Bacillus)和分支杆菌(M.vanbaalenii PYR-1)对同种PAHs菲的代谢过程不同之处,并分析了分支杆菌(M.vanbaalenii PYR-1)对菲和芘的代谢机理,指出微生物氧化降解PAHs主要从其K区和湾区开始,而K区氧化是有毒PAHs降解的主要可能途径,资料显示真菌比细菌对苯并[a]芘的降解能力更强,同时给出了微生物代谢菲、芘和苯并[a]芘的降解图,以便做进一步研究。     

Extraction of polycyclic aromatic hydrocarbons from spiked soil

A homogenization method was evaluated for extracting polycyclic aromatic hydrocarbons (PAHs) from soils. Fifteen PAHs were spiked and recovered from 2 soils at concentrations ranging from 1 to 1000 micrograms/g, using the homogenization method and a Soxhlet extraction method. Each extraction method performed well in removing the 15 PAHs from both soils over a broad range of concentrations. In general, Soxhlet extraction yielded slightly but significantly (P less than 0.05) higher recoveries than did the homogenization method. The homogenization method, however, was easy to use, and the extraction step turnaround time was less than 15 min/sample. The method should be suitable for other applications requiring the extraction of hydrophobic organic compounds from soils.     

Distribution of polycyclic aromatic hydrocarbons (PAHs) in floodplain soils of the Mosel and Saar River

Background, Aim and Scope  Polycyclic aromatic hydrocarbons (PAHs) have gained serious attention in the scientific community due to their persistence and toxic potential in the environment. PAHs may pose a risk to ecosystem health. Along the Mosel River/Germany, a tributary of the river Rhine, PAHs were found at significantly high concentrations (> 20 mg kg⁻¹, German national guideline value Z2, LAGA 1998). These high concentrations were detected during the construction of a storm water retention basin, in which the contaminated soils had to be removed and treated as hazardous waste. This resulted in higher construction costs for implementing flood prevention measures, but did not address the origin of these PAHs and its distribution along Mosel River. Hence, for future flood prevention projects, it is necessary to estimate the extent of PAH contamination along the Mosel River. The aim of the study is to determine the extent of PAH contamination in soils collected along Mosel and Saar River, and to obtain a first insight into the origin of the PAH contamination in this region. Materials and Methods  In total twenty seven sample sites were investigated. Forty two single samples were collected along a 167 km distance of Mosel River and six samples were collected along a 20 km distance of Saar River. Soil samples were collected at a depth of 0 to 2 m with a stainless steel corer (▫ 8 cm). Each 2 m sample was further separated into two sub-samples (0–1 m and 1–2 m). The sixteen EPA PAHs and three additional PAHs (1methylnaphthalene, 2methylnaphthalene and perylene) were analysed with gas chromatography mass spectrometry (GC-MS). For soil characterisation, total organic carbon (TOC), grain size, microscope and X-ray diffraction (XRD) analysis were performed. Results  Grain size for all soil samples was classified as a mixture of sand and silt. XRD analysis showed that all samples were dominated by quartz. Some clay minerals, such as illite and montmorillonite and feldspars, i.e. anorthoclase and orthoclase, were found in minor quantities. TOC ranged from 0.1% to 13%. Microscope analysis showed black coal particles in the majority of the soils collected from the Saar River and part of the Mosel River (downstream of the confluence of Saar and Mosel River). The black particles were not found further upstream along Mosel River. The sum of nineteen PAHs in the soil samples was up to 81 mg kg⁻¹ dry weight (dw). Most soil samples showed a relationship between the presence of coal particles and PAH concentrations. Discussion  Elevated PAH concentrations were found in all soil samples collected from Saar River and downstream Mosel River. Due to former coal mining activities in the Saarland, Germany, there is a strong evidence that the majority of the PAH contamination in the soils downstream Mosel River are linked to these mining activities. Upstream Mosel River coal particles were hardly found although PAH concentrations were high. Therefore another PAH source has to be responsible for these concentrations. PAH distribution patterns indicate a pyrogenic PAH input upstream Mosel River and a mixed input (petrogenic and pyrogenic) downstream Mosel River. Conclusions  Due to PAH distribution patterns, the contamination along the upstream of the Mosel River is probably linked to atmospheric depositions and other sources not linked to coal mining activities. Downstream Mosel River the PAH distribution patterns reflect former coal mining activities. We could corroborate for the first time that coal mining resulted in a serious problem of an extensive PAH contamination at Saar and Mosel River floodplain soils. Recommendations and Perspectives  Coal mining activities have a strong impact on the neighbouring regions (Johnson and Bustin 2006, Short et al. 1999, Stout et al. 2002). It is known that coals exhibit relative high PAH concentrations, especially in the low molecular weight PAHs (Chapman et al. 1996, Radke et al. 1990). However, PAHs in coals are hardly bioavailable (Chapman et al. 1996) and hence may have less adverse effects on exposed biota. They can act as sink for other hydrophobic contaminants. For the assessment of the environmental impact, a detailed study of the sorption and desorption behaviour of PAHs linked to coal particles should be carried out. ESS-Submission Editor: Dr. Ralph Portier (rportie@lsu.edu)