Leaching Of Polycyclic Aromatic Hydrocarbons Research Articles

Leaching of polycyclic aromatic hydrocarbons and heavy metals from stored reclaimed asphalt pavement

The construction, maintenance, and expansion of roads results in the generation of huge quantities of milled asphalt viz. reclaimed asphalt pavement (RAP). However, recycling of RAP is rarely followed in developing countries such as India. Due to rainfall, stockpiled RAP in open areas may generate leachate containing polycyclic aromatic hydrocarbons (PAHs) and heavy metals, raising concern about the stockpiling of RAP. This study addresses the environmental concerns associated with the possible leaching of PAHs and heavy metals from RAP by batch leaching procedures. The leachate predominantly contained three-, and five-ring PAHs. ΣBenzo(k)fluoranthene (ΣBkF) showed the highest concentration (397 µg/kg), followed by ΣPhenanthrene (ΣPHE) (290 µg/kg) among the all sixteen PAH compounds analysed. The results showed that the leaching potential of RAP was rather weak; hence RAP cannot be classified as hazardous waste. Further, none of the samples exceeded the soil risk-based threshold (RBT) values of PAH for residential or commercial settings indicating negligible risk.

Presence and leaching of PAHs in soils of high Andean grasslands affected by intentional burning

Shepherds intentionally burn certain high Andean grasslands to stimulate the regrowth of grass. Nevertheless, this practice results in the generation of Polycyclic Aromatic Hydrocarbons (PAHs), which contaminate and can leach into the soil and be absorbed by plants. Ultimately, this adversely affects the livestock graze on these contaminated plants. The objective of this study was to evaluate the presence of 15 PAHs at the surface, 10, 20, and 30 cm depth, immediately and three months after burning natural grasses in Somoa, Carumas-Peru, during the year 2021. UHPLC-FLD determined PAHs, and the QuEChERS method was used to extract the PAHs from soil samples. Twelve of the 15 PAHs listed by the USEPA were found. The highest concentration was found at the surface, followed by the 10, 20, and 30 cm (759,63, 157,99, 85,86, and 68,04 ng g−1, respectively). On the other hand, Acenaphthene presented higher leaching concerning the rest of the compounds, showing 1.80 ng g−1 at 0 cm, 3.86 ng g−1 at 10 cm, 3.70 ng g−1 at 20c, and 3.44 ng g−1 at 30 cm of depth. The ∑12PAHs at the surface at T1 (first collection after burning) were 669.74 ng g−1, and T2 (second collection, three months after burning) was 759.63 ng g−1; that indicates these soils are contaminated with mean values between 600 and 1000 ng g−1. Additionally, according to the Canadian soil criteria, Fluoranthene slightly exceeded the established limits (157.99 ng g−1).

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons in biochar, biocrude, and biogas obtained from pyrolysis of agricultural residues

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons (PAHs) in pyrolysis steams (biochar, biocrude, and biogas) of three agricultural residues was investigated at pyrolysis temperatures of 400–800 °C. Increasing PAHs formation was observed in the narrow temperature range (500–600 °C) in all feedstocks due to temperature-induced dehydration, decarboxylation, and dehydrogenation reactions. Low molecular weight PAHs (naphthalene, phenanthrene) were dominant in all product streams while high molecular weight PAHs were found in negligible concentrations. Leaching studies showed that pyrolyzed biochars produced at lower temperatures are more prone to leaching due to the presence of hydrophilic amorphous uncarbonized structures, while the presence of hydrophobic carbonized matrix with denser and stronger polymetallic complex prevents the leaching of PAHs in the high temperature pyrolyzed biochar. Low leaching potential, low toxic equivalency, and permissible total PAHs values in biochar derived from all three feedstocks warrant the broader application and ensure ecological safety.

Chemical fingerprints and implicated cancer risks of Polycyclic aromatic hydrocarbons (PAHs) from fine particulate matter deposited in human lungs

Exposure to fine particles (PM2.5) and associated PAHs are frequently linked with lung cancer, which makes the understanding of their occurrence and health risk in human lungs urgently important. Using the ultrasonic treatment and sequencing centrifugation (USC) extraction method coupled with gas chromatography-tandem mass spectrometry (GC - MS/MS) analysis, we revealed the molecular fingerprints of PM-accumulated PAHs in human lungs from a cohort of 68 patients with lung cancer in a typical air-polluted region, China. Sixteen priority PAHs can be grouped by concentrations as ∼ 1 × 104 ng/g (ANT/BkF/ACE/DBA/BgP/PHN/PYR), 2–5 × 103 ng/g (BaP/FLE/NaP/BbF), and ∼ 1 × 103 ng/g (IND/Acy/CHR/FLT/BaA). The sum concentration of 16 PAHs was approximately equaled to 13% of those in atmospheric PM2.5, suggesting significant pulmonary leaching of PAHs deposited in lungs. Low- and high-molecular weight PAHs accounted for ∼ 41.8% and ∼ 45.1% of the total PAHs, respectively, which indicated that atmospheric PM2.5, tobacco and cooking smoke were likely to be important sources of pulmonary PAHs. The evident increasing concentrations of NaP and FLE in pulmonary PM were significantly correlated with smoking history among smokers. The implicated carcinogenic potency of PM-accumulated PAHs among the participants aged 70–80 was 17 times that among participants aged 40–50 on the basis of BaP equivalent concentration (BaPeq) evaluation. The particulate enrichment factor (EFP), the PAH content in pulmonary PM relative to the bulk lung tissue, was equaled to 54 ∼ 835 and averaged at 436. The high value of EFP suggested that PAHs were essentially accumulated in pulmonary PM and exhibited a pattern of “hotspot” distribution in the lungs, which would likely increase the risk of monoclonal tumorigenesis. The chemical characteristics of PM-accumulated PAHs in human lungs together with their implicated lung cancer risks could provide significant information for understanding health effects of particulate pollution in the human body.

Leaching behavior of polycyclic aromatic hydrocarbons (PAHs) from oil-based residues of shale gas drill cuttings

Cuttings are the main solid residues which are generated from drilling operations. Due to the presence of heavy and radioactive elements, the environment risk posed by cuttings has attracted increasing attention. In this work, a short-term static immersion experiment was carried out to investigate the leaching of polycyclic aromatic hydrocarbons (PAHs) from oil-based residues of shale gas drilling cuttings. Furthermore, the effects of some relevant environmental factors controlling the leaching behavior were evaluated, including the different particle sizes, pH, extraction time, solid-to-liquid (S/L) ratio and dissolved organic matter (DOM) concentration. The results showed that (1) the concentrations of leached PAHs gradually increased with prolonged leaching time, but the cumulative amount of PAHs released during leaching was less than 3% of the total. (2) The Elovich, parabolic diffusion and power function models were found to fit the experimental data better than the first-order kinetic equation, indicating that the leaching of PAHs was controlled by the coupling of diffusion and chemical reactions at the source surface. (3) Different environmental factors had different impacts on the leaching of PAHs: the shaking time and presence of DOM increased leachability, the particle size and S/L ratio decreased leachability, and the pH did not affect the leachability of PAHs. Therefore, PAHs leaching was a complex process, and it is of scientific and environmental interest to conduct the leaching tests under the simulated environmental conditions.

Environmental impact of rejuvenators in asphalt mixtures containing high reclaimed asphalt content

ABSTRACT The use of reclaimed asphalt pavement (RAP) is of increasing importance due to fast-growing amounts of demolished road materials. However, reclaimed asphalt can contain relevant amounts of pollutants such as carcinogenic polycyclic aromatic hydrocarbons (PAHs) and toxic metals. In order to improve the mechanical properties of recycled asphalt, rejuvenators are used to reduce the stiffness of the aged binder. These rejuvenators in turn may potentially mobilise pollutants like PAHs and facilitate their leaching to surface and ground waters. The environmental impact of three rejuvenators with good mechanical performance was studied. The environmental impact was assessed by determining metal- and PAH contents in the RAP and in leachates. Chemical analyses showed that rejuvenators did not mobilise PAHs from RAP materials for 2–3 ring PAHs. However, some 4–6 ring PAHs that are relatively less toxic indeed leached more easily from unaged material. Ageing reduced the tendency for PAH leaching, without and with rejuvenator.

Biochar produced from wood waste for soil remediation in Sweden: Carbon sequestration and other environmental impacts.

The use of biochar to stabilize soil contaminants is emerging as a technique for remediation of contaminated soils. In this study, an environmental assessment of systems where biochar produced from wood waste with energy recovery is used for remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAH) and metal(loid)s was performed. Two soil remediation options with biochar (on- and off-site) are considered and compared to landfilling. The assessment combined material and energy flow analysis (MEFA), life cycle assessment (LCA), and substance flow analysis (SFA). The MEFA indicated that on-site remediation can save fuel and backfill material compared to off-site remediation and landfilling. However, the net energy production by pyrolysis of wood waste for biochar production is 38% lower than incineration. The LCA showed that both on-site and off-site remediation with biochar performed better than landfilling in 10 of the 12 environmental impact categories, with on-site remediation performing best. Remediation with biochar provided substantial reductions in climate change impact in the studied context, owing to biochar carbon sequestration being up to 4.5 times larger than direct greenhouse gas emissions from the systems. The two biochar systems showed increased impacts only in ionizing radiation and fossils because of increased electricity consumption for biochar production. They also resulted in increased biomass demand to maintain energy production. The SFA indicated that leaching of PAH from the remediated soil was lower than from landfilled soil. For metal(loid)s, no straightforward conclusion could be made, as biochar had different effects on their leaching and for some elements the results were sensitive to water infiltration assumptions. Hence, the reuse of biocharremediated soils requires further evaluation, with site-specific information. Overall, in Sweden's current context, the biochar remediation technique is an environmentally promising alternative to landfilling worth investigating further.

Leaching of polycyclic aromatic hydrocarbons (PAHs) from sewage sludge-derived biochar

Polycyclic aromatic hydrocarbons (PAHs), a family of persistent organic pollutants with various negative health effects, are inherently formed during biochar pyrolysis. However, the knowledge regarding the leaching potentials and mechanisms of PAHs remains limited for biochar implementation to soil. In this study we evaluated the leaching behaviors of PAHs from sewage sludge-derived biochar pyrolyzed at different temperatures (300–700 °C) using the protocol of Synthetic Precipitation Leaching Procedure (SPLP) with deionized water. Leachate concentrations of sixteen U.S. Environmental Protection Agency PAHs increased with the increasing pyrolysis temperature, exhibiting an opposite pyrolytic temperature dependence with their concentrations in biochar. The total leachate PAH concentration peaked at 700 °C with 11.75 μg/L, corresponding to 15.9% of total PAHs present in biochar. PAH leaching was associated with the release of hydrophobic organic compounds (HOCs) that created a mobile phase to facilitate the mobilization of PAHs into water. The enhanced release of calcium, aluminum, and barium from the biochars with pyrolysis temperature could also favor the leaching of biochar PAHs, due to the destruction of HOCs-(metal ions)-mineral linkages, which improved the release of HOCs and HOCs-bound PAHs; and because the extent of metal cross-linking in biochar is reduced, enabling better diffusion of PAHs through the inner matrix and thus accelerating their desorption.

Inhibition of naphthalene leaching from municipal carbonaceous waste by a magnetic organophilic clay.

Municipal solid waste conversion into biofuels via gasification is one of the latest technologies to divert waste from landfills. The byproduct of the process is a carbonaceous material, which is often tainted with polycyclic aromatic hydrocarbons (PAH) such as naphthalene that can leach into the environment and have toxic effects on aquatic organisms. In this paper, we present a novel method to address the issue of leachable naphthalene in a carbonaceous waste produced from a gasification process, using a magnetic sorbent. The sorbent was fabricated by the coprecipitation of iron oxide nanoparticles on an organophilic clay under atmospheric conditions. The characterization results show that the intercalated nanoparticles are predominantly magnetite with a diameter of 15-20 nm, and increase the clay specific surface area from 0.4 to 17 m2 g-1. Toxicity characteristic leaching procedure results indicate that the magnetic composite has a high naphthalene inhibition efficiency comparable to that of the original clay. As opposed to the clay alone, the magnetic hybrid can be separated from the carbonaceous waste with a magnet, regenerated by heat treatment, and reused without compromising its naphthalene removal efficiency. Thus, these composites may provide a cost-effective method to curtail leaching of PAH from contaminated carbonaceous waste.

Residue pattern of polycyclic aromatic hydrocarbons during green tea manufacturing and their transfer rates during tea brewing

ABSTRACTResidues of polycyclic aromatic hydrocarbons (PAHs) in green tea and tea infusion were determined using gas chromatography-tandem mass spectrometry to study their dissipation pattern during green tea processing and infusion. Concentration and evaporation of PAHs during tea processing were the key factors affecting PAH residue content in product intermediates and in green tea. PAH residues in tea leaves increased by 2.4–3.1 times during the manufacture of green tea using the electric heating model. After correction to dry weight, PAH residue concentrations decreased by 33.5–48.4% during green tea processing because of PAH evaporation. Moreover, spreading and drying reduced PAH concentrations. The transfer rates of PAH residues from green tea to infusion varied from 4.6% to 7.2%, and PAH leaching was higher in the first infusion than in the second infusion. These results are useful for assessing exposure to PAHs from green tea and in formulating controls for the maximum residue level of PAHs in green tea.

Combined effects of land reclamation, channel dredging upon the bioavailable concentration of polycyclic aromatic hydrocarbons (PAHs) in Victoria Harbour sediment, Hong Kong

The up-to-date concentration of polycyclic aromatic hydrocarbons (PAHs) in sediment materials of Victoria Harbour was investigated so as to evaluate the pollution potential associated with the reclamation projects in Hong Kong. A total of 100 sediment samples were collected at 20 locations. Except the control point in reservoir, the PAHs concentrations were detectable levels all sites (131–628.3ng/g, dw) and such values were higher than Dutch Target and Intervention Values (the New Dutch standard in 2016). The PAHs concentration indicating that construction waste and wastewater discharges were the main pollutant sources. Results of correlation in single cell gel electrophoresis assay (comet assay) studies also revealed that the PAHs concentration was highly correlated (<0.01) with DNA migration (i.e. the length of tail moment of fish cells) in 5mg/ml of PAHs. The above observation indicates that the PAHs present in the sediment may substantially effect the marine ecosystem. Although the dredged sediment can be a useful sea-filling material for land reclamation; however, the continuing leaching of PAHs and its impact on the aquatic environment need to be studied further.

Leaching of PAHs from agricultural soils treated with oil shale combustion ash: an experimental study.

The present study focuses on the fate of polycyclic aromatic hydrocarbons (PAHs) in soils amended with oil shale ash (OSA). Leachability studies to assess the release of PAHs to the environment are essential before the application of OSA in agriculture. A quantitative estimation of the leaching of PAHs from two types of soil and two types of OSA was undertaken in this study. Two leaching approaches were chosen: (1) a traditional one step leaching scheme and (2) a leaching scheme with pretreatment, i.e.., incubation of the material in wet conditions imitating the field conditions, followed by a traditional leaching procedure keeping the total amount of water constant. The total amount of PAHs leached from soil/OSA mixtures was in the range of 15 to 48μg/kg. The amount of total PAHs leached was higher for the incubation method, compared to the traditional leaching method, particularly for Podzolic Gleysols soil. This suggests that for the incubation method, the content of organic matter and clay minerals of the soil influence the fate of PAHs more strongly compared to the traditional leaching scheme. The amount of PAHs leached from OSA samples is higher than from soil/OSA mixtures, which suggests soils to inhibit the release of PAHs. Calculated amount of PAHs from experimental soil and OSA leaching experiments differed considerably from real values. Thus, it is not possible to estimate the amount of PAHs leached from soil/OSA mixtures based on the knowledge of the amount of PAHs leached from soil and OSA samples separately.

Enhanced Immobilization of Polycyclic Aromatic Hydrocarbons in Contaminated Soil Using Forest Wood-Derived Biochar and Activated Carbon under Saturated Conditions, and the Importance of Biochar Particle Size

Leaching behavior of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) can be altered in the presence of organic amendments through enhanced sorption of PAHs to the amended soil. The aim of the present study was to investigate the influence of biochar in two forms (i.e., crushed and pulverized), and granular activated carbon on immobilization and leaching behavior of selected PAHs from contaminated soil into water using the column leaching test. The influence of biochar particle size on leaching behavior of PAHs in biochar-amended soil was also evaluated for the first time in this study. Results showed relatively high initial concentrations of naphthalene, fluorene, and pyrene for unamended column (B1). Strong sorption of all PAHs to soil was observed in this study. At the end of the experiment less than one percent of the solid phase content of the sum of PAHs was released into water in columns B3 and B4. Change in pH due to the application of organic amendments did not affect PAH leaching results. The addition of pulverized biochar and granular activated carbon to soil remarkably reduced mobilization and leaching of the studied PAHs in most cases; however, higher molecular weight PAHs (i.e., pyrene, benzo(b)fluoranthene, and indeno(1,2,3cd)) were mobilized in the presence of crushed biochar in soil. The controlling role of biochar particle size on mobilization and release of PAHs in soil was observed. The application of pulverized biochar and activated carbon increased colloid content of the column effluents while reducing their dissolved organic carbon (DOC) content, suggesting a more significant role of colloid-facilitated transport than DOC-associated transport of PAHs in their leaching from carbon-amended soils, particularly for higher molecular weight PAHs. Based on the obtained results, pulverized biochar and granular activated carbon demonstrated promising and comparable performance in immobilizing PAHs in soil and reducing their leaching from soil into water through enhanced sorption of PAH compounds, which is markedly favorable in terms of soil remediation.

Ionic Liquid as Green Solvent for Leaching of Polycyclic Aromatic Hydrocarbons from Petroleum Source Rock

Microwave-assisted extraction of polycyclic aromatic hydrocarbons (PAHs) from petroleum source rock using ionic liquids was investigated and the conditions for optimum yields of the analytes were determined. Three ionic liquids showed similar extraction efficiencies and for further work 1-butyl-3-methylimidazolium bromide (BmimBr) was selected. The results showed that concentration and extraction temperature have significant effects on extraction yields of the PAHs. The 3.0 M ionic liquid solution was the best concentration for extraction of the PAHs. The highest yields of PAHs were obtained at an extraction time of 30 min. The optimum temperature for microwave-assisted ionic liquid extraction of all the PAHs from petroleum source rock was 100 °C. The results also show that microwave-assisted ionic liquid extraction is more efficient than accelerated solvent extraction and Soxhlet extraction. This study showed that microwave-assisted ionic liquid extraction (MAILE) is an efficient green analytical sample ...

PAHs in leachates from thermal power plant wastes and ash-based construction materials.

The focus of the current study is to characterise the leaching behaviour of polycyclic aromatic hydrocarbons (PAHs) from oil shale ashes (OSAs) of pulverised firing (PF) and circulating fluidised-bed (CFB) boilers from Estonian Thermal Power Plant (Estonia) as well as from mortars and concrete based on OSAs. The target substances were 16 PAHs from the EPA priority pollutant list. OSA samples and OSA-based mortars were tested for leaching, according to European standard EN 12457-2 (2002). European standard CEN/TC 15862(2012) for monolithic matter was used for OSA-based concrete. Water extracts were analysed by GC-MS for the concentration of PAHs. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene were detected. Still, the release of PAHs was below the threshold limit value for inert waste. The amount of the finest fraction (particle size <0.045 mm), the content of the Al-Si glass phase and the surface characteristics were the main factors, which could affect the accessibility of PAHs for leaching. The mobility of PAHs from OSA of CFB and PF boilers was 20.2 and 9.9%, respectively. Hardening of OSA-based materials did not lead to the immobilisation of soluble PAHs. Release of PAHs from the monolith samples did not exceed 0.5 μg/m(2). In terms of leaching of PAHs, OSA is safe to be used for construction purposes.

Effects of pollution sources and soil properties on distribution of polycyclic aromatic hydrocarbons and risk assessment

In this study, the concentrations of polycyclic aromatic hydrocarbons (PAHs) in soil profiles and the soil properties were analyzed in Hunpu, a typical wastewater irrigation area, northeast of China. The total concentrations of 16 priority control PAHs ranged from 7.88 to 2,231.42μg/kg. Among 16 PAHs, the most abundant was Phenanthrene and the 3- or 4- ring PAHs were predominant. The PAH concentrations were higher in the upland fields near the oil wells, whereas leaching of PAH into the groundwater caused low concentrations in the paddy fields. The geochemical indices and the results from the principal component analysis of all 16 PAHs indicated that PAHs were mainly from atmospheric dusts in the top soil in I-1P/I-3P/I-7P and through soil profiles in I-4U/I-5P/I-8U, whereas those in the bottom layers were mainly from petroleum production and wastewater irrigation in I-1P/I-3P/I-7P and through soil profiles in I-2U and I-6U. In the redundancy analysis, PAHs exhibited negative correlation with pH, depth, silt, and clay, but had positive correlation with sand and organic matter. Finally, total toxic equivalent in the soil profiles and the calculated health risk of PAHs in the surface soil using contaminated land exposure assessment model elucidated the cancer risk that PAHs pose on human health in the Hunpu region.

Enhanced Dissipation of Polycyclic Aromatic Hydrocarbons in the Rhizosphere of the Athel Tamarisk (Tamarix Aphylla L. Karst.) Grown in Saline-Alkaline Soils of the Former Lake Texcoco

Remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated alkaline saline soil with phreatophyte or “water loving plants” was investigated by spiking soil from the former lake Texcoco with 100 mg phenanthrene (Phen) kg−1 soil, 120 mg anthracene (Ant) kg−1 soil and 45 mg benzo(a)pyrene (BaP) kg−1 soil and vegetating it with Athel tamarisk (Tamarix aphylla L. Karst.). The growth of the Athel tamarisk was not affected by the PAHs. In soil cultivated with Athel tamarisk, the leaching of PAHs to the 32–34 cm layer decreased 2-fold compared to the uncultivated soil. The BaP concentration decreased to 39% of the initial concentration at a distance smaller than 3 cm from the roots and to 45% at a distance larger than 3cm, but 59% remained in unvegetated soil after 240 days. Dissipation of Ant and Phen decreased with depth, but not BaP. The biodegradation of PAHs was affected by their chemical properties and increased in the presence of T. aphylla, but decreased with depth.

Factors Controlling Leaching of Polycyclic Aromatic Hydrocarbons from Petroleum Source Rock Using Nonionic Surfactant

The extraction of polycyclic aromatic hydrocarbons (PAHs) from petroleum source rock by nonionic surfactants with the assistance of microwave irradiation was investigated and the conditions for maximum yield were determined. The results showed that the extraction temperatures and type of surfactant have significant effects on extraction yields of PAHs. Factors such as surfactant concentration, irradiation power, sample/solvent ratio and mixing surfactants (i.e., mixture of surfactant at specific ratio) also influence the extraction efficiencies for these compounds. The optimum temperature for microwave-assisted nonionic surfactant extraction of PAHs from petroleum source rock was 120 °C and the best suited surfactant was Brij 35. The new method showed extraction efficiencies comparable to those afforded by the Soxhlet extraction method, but a reduction of the extraction times and environmentally friendliness of the new nonionic surfactant extraction system are clear advantages. The results also show that microwave-assisted nonionic surfactant extraction is a good and efficient green analytical preparatory technique for geochemical evaluation of petroleum source rock.

Determination of Retardation Effect of SOM on Aqueous Leaching of Polycyclic Aromatic Hydrocarbons Using Confocal Laser Scanning Microscope

Influence of soil organic matter (SOM) on the adsorption, desorption and transport of polycyclic aromatic hydrocarbons (PAHs) has already been given full investigation in soils. In this paper, confocal laser scanning microscope (CLSM) was used to elucidate aqueous leaching of PAHs in different types of soil with soil columns, which enhanced understanding on transport of PAHs appreciably. Four typical soils in China including fluvo-aquic soil (FAS), aquic brown soil (ABS), red soil (RS) and black soil (BS) were selected in the experiment. Target pollutants of phenanthrene and pyrene were extracted from the leachate by solid phase extraction (SPE) and then determined by high performance liquid chromatography (HPLC). The experimental results showed that the retardation ability of pollutants to the four selected types of soil increased in the order: FAS H” ABS < RS < BS. To better expatiate the dissimilar ability of the PAHs transported in the four typical soils, the retardation factor (R), distribution constant (Kd) and partition coefficient (Koc) were evaluated based on the observed breakthrough curves (BTCs). Furthermore, CLSM was used to visualize the effects of SOM on the transport ability of PAHs in different types of soil. All the results provided vivid understanding with mathematical and especially optical measures that SOM was considered the single most important factor limiting the availability and mobility of PAHs in soil over the duration of the experiment.

Determination of leaching behaviour of polycyclic aromatic hydrocarbons from contaminated soil by column leaching test

Column leaching tests become increasingly important for assessing the risk of release of pollutants from a wide variety of solid materials into water. In this study a column leaching test was designed to provide insight into the fate of selected polycyclic aromatic hydrocarbons (PAHs) in soils and their leaching behaviour. The results showed relatively high initial concentrations of naphthalene, anthracene, and pyrene for column B2. Two proportions of contaminated soil (5 and 20%) used in the columns yielded different leaching behaviour. Different contact time applied in columns B1 and B2 affected the initial amounts of leached PAHs. Results indicated that the distribution pattern of PAH compounds in solid phase considerably affected leached concentrations of PAHs. Released amounts of PAH compounds decreased with increasing molecular size, or rather the hydrophobicity of the compound. The effect of dissolved organic carbon on PAH leaching was also investigated in this study. The mobilization of colloids did not show any significant effect on leached concentrations of PAH compounds. Approximately 4.6 and 2.2% of the total initial amounts of studied PAHs in the soil were leached in columns B1 and B2, respectively. Therefore high PAH concentrations in the solid phase does not imply serious groundwater contamination risk during a leaching event (e.g. raining) and significant amount of contaminants may stay in the soil layer for a long time and do not leach down into groundwater.