Availability Of Polycyclic Aromatic Hydrocarbons Research Articles

Effect of sorption properties on the content, ecotoxicity, and bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in bottom sediments.

Polycyclic aromatic hydrocarbons (PAHs) tend to accumulate in the sediment due to their high hydrophobicity. Despite PAHs have been the subject of several reviews, PAH sorption processes in bottom sediments has not been comprehensively discucorrelation coefficients between sorption parameters and contessed. Understanding the dependencies governing PAH sorption processes will allow to predict, monitor, and mitigate the ecological effects of PAH contamination and the associated risks to humans or wildlife. The objectives of the study were to assess the relationship between the sorption properties and the content of PAHs in bottom sediments and mussels. The PAH profile was dominated by higher-molecular hydrocarbons, which accounted for 73% of the total concentration of PAHs. Potentiometric studies revealed the steric-based PAH sorption mechanism that strongly depended on the presence of negatively dissociating structures such as carboxylic or phenolic functional groups. Based on the changes in Q8 values, the size-exclusion effect was more likely for 5- and 6-ring compounds. Pores <5µm, which had the largest share in the specific surface area, were the preferred sites for PAH sequestration and stabilization in bottom sediments. The availability of PAHs was reduced in sediments with high organic matter content. The PAH bioaccumulation factor significantly decreased with increasing TOC content in sediments. Higher mortality and growth inhibition of H. incongruens were observed in samples with high and medium TOC contents than in those with low TOC content.

Characterization of Different Molecular Size Fractions of Glomalin-Related Soil Protein From Forest Soil and Their Interaction With Phenanthrene.

As a natural organic compound secreted by arbuscular mycorrhizal fungi (AMF), glomalin-related soil protein (GRSP) is an important part in soil, affecting the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in it. Previous research have demonstrated that GRSP could enhance the availability of PAHs in the soil and favor their accumulation in plant roots. However, a scarcity of research exists on the different molecular weights of GRSP interacting with PAHs due to their complexation and heterogeneity. In this research, the extracted GRSP in soil was divided into three molecular weight (Mw) fractions of GRSP (<3,000, 3,000–10,000, and >10,000 Da), whose characteristics and binding capacity of PAHs were conducted by using UV–visible absorption, quenching fluorometry and, Fourier transform infrared spectroscopy. The results showed that the GRSP was composed of abundant compounds, it has a wide distribution of molecular weight, and the >10,000 Da Mw fraction was dominant. For three Mw fractions of GRSP, they have some difference in spectral features, for example, the >10,000 Da fraction showed higher dissolved organic carbon (DOC) contents, more phenolic hydroxyl groups, and stronger UV adsorption capacity than the low and middle Mw fractions. In addition, the interaction between GRSP and phenanthrene is related to the characteristics of the Mw fractions, especially the phenolic hydroxyl group, which has a significantly positive correlation with a binding coefficient of KA (k = 0.992, p < 0.01). Simultaneously, hydrophobic, NH-π, and H-bound also played roles in the complexation of phenanthrene with GRSP. These findings suggested that different GRSPMw fractions could influence the fate, availability, and toxicity of PAHs in soil by their interaction.

Assessment of marine sediment remediation efficiency with SPME-based passive sampling measurement

Passive sampling has been shown to be a suitable procedure to assess the risk of contaminated sediments through the measurement of freely dissolved concentrations (CFree) and remedial actions involving amendments such as activated carbon (AC). Here we report results of the application of simple, solvent-free solid phase micro extraction methodology (SPME) to assess the performance of different materials for the remediation of selected Norwegian harbour sediments contaminated with polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). AC amendments enabled a reduction of the availability of PAHs and/or PCBs by a factor of ten to over one hundred in Aker Brygge sediments (Oslo) and sediments from Elkembukta, impacted by industrial emissions of PAHs with/from coal tar pitch. Another material, anthracite, slightly less effective in this set of experiment than AC, showed nonetheless great promise as capping material. The SPME data are put in perspective with equilibrium measurements of CFree for PAHs and organochlorines with silicone rubber in other Elkembukta sediments collected in the vicinity of those used for the remediation experiments. A reduction of sediment Cfree for pyrene, benzo[a]pyrene and benzo[ghi]perylene in inner Elkembukta sediment from on average 407, 6.3 and 0.82 ng L−1 to values of/or below 1.3, 0.15 and 0.076 ng L−1, respectively can be expected upon remediation with AC. For the outer, less contaminated Elkembukta sediment, Cfree would reduce from 36, 0.81 and 0.13 ng L−1 to value of or below 0.06, 0.03 and 0.005 ng L−1 for these three compounds, respectively. Differences in pattern of PAH and organochlorine contamination of inner and outer Elkembukta sediments are discussed.

Enhancement of PAHs biodegradation in biosurfactant/phenol system by increasing the bioavailability of PAHs

The poor bioavailability of polycyclic aromatic hydrocarbons (PAHs) is the main limiting factor for their biodegradation in contaminated sites. The addition of biosurfactant is an effective method for enhancing the bioavailability of PAHs. Suitable low molecular weight (LMW) organic matters have been shown to increase the bioavailability of PAHs. Therefore, we investigated the effect of phenol, which often co-exists with PAHs, on the biodegradation of PAHs in biosurfactant solution. The results show that the critical micelle concentration (CMC) of the biosurfactant decreased after phenol was added. The formation of mixed micelles resulted in enhancement of PAHs dissolution. The weight solubilization ratio (WSR) values of biosurfactant for Phe, Pyr and BaP in phenol solution are approximately 1.34, 1.40 and 1.67 times that of the control group, respectively. Phenol, therefore, can assist biosurfactant to increase the availability of PAHs by microbes. The bioavailability of PAHs in sludge increased from 27.7% to 43.1% after the biosurfactant was added, and reached a maximum of 49.2%, following the simultaneous addition of phenol and biosurfactant. Phenol also improved the degradation of PAHs by Stenotrophomonas sp. N5 in biosurfactant solution.

Effects of sediment manipulation on freely dissolved concentrations of hydrophobic organic chemicals

The freely dissolved concentration (Cfree) of hydrophobic organic chemicals (HOCs) in pore water is an important parameter in the risk assessment and management of contaminated sediments and soils. It can be determined most conveniently through ex situ passive sampling, i.e., in the laboratory. For this purpose, samples are taken from the field and transported to the laboratory, where they are stored and possibly manipulated by sieving, freezing, drying and/or grinding. Although the objective of ex situ passive sampling often is to determine a Cfree that reflects the metric under in situ conditions, hardly any information is available on possible effects of sample manipulation. Hence, the present study investigated the impact of freezing, freeze-drying, and grinding on Cfree of HOCs in field sediments, as determined with solid phase microextraction (SPME). Freezing increased the Cfree of 3- and 4-ring polycyclic aromatic hydrocarbons (PAHs) with up to a factor of 4, whereas for 5- and 6-ring PAHs hardly any effects were observed. Generally, additional freeze-drying did not further increase Cfree, but subsequently grinding the samples (further) increased Cfree of all PAHs with up to a factor of 4, leading to an overall maximum observed increase in Cfree of a factor of 16. Probably, these effects are caused by a structural change in the sorption matrix, enhancing PAH availability. The results indicate that freezing, freeze-drying, and grinding prior to ex situ Cfree determinations should be avoided, as these treatments may considerably increase the Cfree of HOCs, leading to an overestimation of risks.

The Impact of Organic Matter on Polycyclic Aromatic Hydrocarbon (PAH) Availability and Persistence in Soils.

Polycyclic aromatic hydrocarbons (PAHs) exhibit persistence in soils, and most of them are potentially mutagenic/carcinogenic and teratogenic for human beings but also influence the growth and development of soil organisms. The PAHs emitted into the atmosphere are ultimately deposited (by dry or wet deposition processes) onto the soil surface where they tend to accumulate. Soil organic matter (SOM) plays an important role in the fate and transformation processes of PAHs, affecting their mobility, availability, and persistence. Therefore, the aim of this research was to investigate the influence of SOM fractional diversification (fulvic acids—FA, humic acids—HA, and humins—HN) on PAH availability and persistence in soils. Twenty soil samples (n = 20) were collected from upper horizons (0–30 cm) of agricultural soils exposed to anthropogenic emissions from industrial and domestic sources. The assessment of PAH concentrations included the determination of medium-molecular-weight compounds from the US EPA list: fluoranthene—FLA, pyrene—PYR, benz(a)anthracene—BaA, and chrysene—CHR. The assessment was conducted using the GC-MS/MS technique. Three operationally defined fractions were investigated: total extractable PAHs (TE-PAHs) fraction, available/bioavailable PAHs (PB-PAHs) fraction, and nonavailable/residual PAHs (RE-PAHs) fraction, which was calculated as the difference between total and available PAHs. TE-PAHs were analyzed by dichloromethane extraction, while PB-PAHs were analyzed with a hydrophobic β-cyclodextrin solution. SOM was characterized by total organic carbon content (Turin method) and organic carbon of humic substances including FA, HA, HN (IHSS method). Concentrations of PAHs differed between soils from 193.5 to 3169.5 µg kg−1, 4.3 to 226.4 µg kg−1, and 148.6 to 3164.7 µg kg−1 for ∑4 TE-PAHs, ∑4 PB-PAHs, and ∑4 RE-PAHs, respectively. The ∑4 PB-PAHs fraction did not exceed 30% of ∑4 TE-PAHs. FLA was the most strongly bound in soil (highest content of RE-FLA), whereas PYR was the most available (highest content of PB-PYR). The soils were characterized by diversified total organic carbon (TOC) concentration (8.0–130.0 g kg−1) and individual SOM fractions (FA = 0.4–7.5 g kg−1, HA = 0.6–13.0 g kg−1, HN = 0.9–122.9 g kg−1). FA and HA as the labile fraction of SOM with short turnover time strongly positively influenced the potential ∑4 PAH availability (r = 0.56 and r = 0.52 for FA and HA, respectively). HN, which constitutes a stable fraction of organic matter with high hydrophobicity and poor degradability, was strongly correlated with ∑4 RE-PAHs (r = 0.75), affecting their persistence in soil.

Availability of Polycyclic Aromatic Hydrocarbons in Environment and Food Chains: A Review

Availability of Polycyclic Aromatic Hydrocarbons in Environment and Food Chains: A Review

Agro-Environmental Benefit and Risk of Manure- and Bone Meal-Derived Pyrogenic Carbonaceous Materials as Soil Amendments: Availability of PAHs, PTEs, and P

The worldwide boom of biochar and pyrogenic carbonaceous material application as a potential soil additive has brought about not only agricultural benefits such as enhanced crop yield, nutrients supply (P), and soil organic carbon increase, but also, on the other hand, environmental risk of organic (polycyclic aromatic hydrocarbons (PAHs)) and potentially toxic element (PTE) penetration into arable soils. Therefore, our study assessed pyrogenic carbonaceous materials (PCM) produced from the P-rich feedstocks—chicken manure (CM) and bone meal (BM)—as promising and safe alternatives for inorganic P fertilizers. Pyrogenic materials produced in the process of slow pyrolysis at residence time 2 h, 400 and 500 °C, were characterized by determination of pH, electrical conductivity (EC), elemental analysis of total C, H, N, S scanning electron microscopy (SEM), total content of P, selected potentially toxic elements (PTEs), and available forms of PTEs and P by diethylenetriaminepentaacetic acid (DTPA) and calcium-acetate-lactate (CAL) extractions. CMPCM4, CMPCM5, BMPCM4, and BMPCM5 were characterized by determination of total 16 US-EPA (U.S. Environmental Protection Agency) PAHs by toluene extraction protocol and available concentrations by Tenax resin approach. Additionally, CMPCM4, CMPCM4, BMPCM4, and BMPCM5 were tested in earthworm avoidance test with Eisenia foetita and short-term rye-seedling germination test. Obtained results showed decreasing of total carbon in the order of BM &gt; BMPCM4 &gt; BMPCM5 and increasing in the order of CM &lt; CMPCM4 &lt; CMPCM5. Total phosphorus content increased from 56.8 ± 1.7 g kg−1 (BM) to 85.2 ± 4.2 g kg−1 (BMPCM4) to 110.5 ± 7.0 g kg−1 (BMPCM5). In the case of chicken manure-derived pyrogenic materials, total phosphorus content increased in the order of CM (22.9 ± 2.0 g kg−1) &lt; CMPCM4 (37.0 ± 4.5 g kg−1) &lt; CMPCM5 (40.0 ± 3.4 g kg−1). Availability of selected PTEs and P decreased in pyrogenic materials compared to feedstock. Total concentration of ∑16-US-EPA PAHs in BMPCM4 and BMPCM5 was 3.92 mg kg−1; CMPCM4, 7.33 mg kg−1; and CMPCM, 6.69 mg kg−1. The Tenax-available ∑16-PAHs showed concentrations of 0.53 mg kg−1 for BMPCM4, 0.26 mg kg−1 for BMPCM5, 1.13 mg kg−1 for CMPCM4, and 0.35 mg kg−1 for CMPCM5. Total P concentrations determined in rye aboveground tissues showed the highest accumulation ability in the case of CMPCM5 compared to other samples. Pyrogenic carbonaceous materials produced from chicken manure and bone meal at 400 and 500 °C have the potential to be P slow release fertilizers and may be ecologically safe.

Evaluating the effect of different modified microplastics on the availability of polycyclic aromatic hydrocarbons

Microplastics (MPs) discharged into the natural environment undergo various wearthering pathways, such as mechanical abrasion and ultraviolet (UV) irradiation. However, little is known about the effects of such aged MPs on the bioavailability of hydrophobic organic compounds (HOCs) in aqueous environments. To simulate the natural oxidation and UV-ageing process of MPs, three kinds of modified polyethylene MPs were obtained by plastic etching processes common in industry and UV irradiation, namely, etched MPs (EMPs), UV-aged MPs (UV-MPs), and etched MPs followed by UV ageing (UV-EMPs). The modified MPs showed a higher content of surface oxygen-containing groups than the pristine MPs, and the specific surface area and pore volume increased significantly after etching and ultraviolet ageing, especially for the EMPs (1.67 m2 g−1 and 0.0049 cm³ g−1) and UV-EMPs (2.37 m2 g−1 and 0.0089 cm³ g−1). The effect of modified MPs on the availability of 10 polycyclic aromatic hydrocarbons (PAHs, logKow 4.18–6.20) was evaluated by negligible-depletion solid-phase microextraction (nd-SPME). The free concentrations (Cfree) of most PAHs (except for less hydrophobic PAHs, logKow 4.18 and 4.56) decreased with an increasing concentration of MPs. The logarithms of the sorption coefficients of PAHs with various MPs (logKMPs, logKUV-MPs, logKEMPs and logKUV-EMPs) were linearly correlated with logKow, suggesting that the sorption is hydrophobicity dependent. Compared with the results for pristine MPs (logKMP 3.80–4.95), UV ageing only slightly enhanced the sorption of PAHs by MPs (logKUV-MPs 3.71–4.98), whereas the plastic etching processes significantly enhanced sorption (logKEMPs 3.85–5.18 and logKUV-EMPs 3.90–5.28). The sorption of PAHs to MPs is mainly based on partitioning; however, a mechanism of adsorption also likely takes place in EMPs and UV-EMPs due to hydrogen bonding and π-π interactions. Desorption study indicated that PAH desorption from MPs are dominated by film diffusion. However, intraparticle diffusion also takes great part for the EMPs. These results suggest that modification of MPs in the natural environment will change the availability of HOCs.

Modelling PAHs removal in activated sludge process: effect of disintegration.

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Impacts of activated carbon amendments, added from the start or after five months, on the microbiology and outcomes of crude oil bioremediation in soil

The use of activated carbon (AC) amendments to reduce exposure risks for hydrophobic contaminants like polycyclic aromatic hydrocarbons (PAHs) by adsorption is an innovative soil remediation approach. However, AC amendment side-effects on the pollution biodegradation are poorly understood. This study assessed for optimized nutrient ratio conditions, effects of 5% soil wet weight AC amendments, if added from the beginning or after five months, on the outcomes of one year of crude oil polluted soil bioremediation. CO2, residual hydrocarbon concentrations and microbial community structure analysis revealed how AC amendment hindered crude oil biodegradation much more, if added from the start, as compared to after 5 months, i.e. after the initial phase of biodegradation. Putative crude oil degrading microorganisms from the genera Marinobacter, Parvibaculum, Salinibacterium, Muricauda, and Alcanivorax were more sensitive to the AC amendment than those from the genus Rhodococcus. Rhodococci possess hydrophobic cell walls which may enable them to accumulate hydrocarbons in the AC amended soil, despite of their reduced availability. AC amendment from the start had the highest alkane and total US EPA PAH residues, but was more effective than one year of bioremediation, with or without AC amendment after 5 months, in reducing PAH availability in the soil.

Natural and assisted dissipation of polycyclic aromatic hydrocarbons in a long-term co-contaminated soil with creosote and potentially toxic elements

An enhanced bioremediation strategy was applied to an industrial soil co-contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) and Potentially Toxic Elements (PTEs). Hydroxypropyl-β-cyclodextrin (HPBCD) and a natural mixture of two rhamnolipids (RL) were added to increase PAHs bioavailability, and combined with a microbial consortium (MC) to biodegrade soil PAHs. Bioavailability of only six PAHs (3-, 4-ring PAHs) increased when using HPBCD, with a maximum increase about 2.8-fold higher. The highest dose of HPBCD (5%) enhanced PAH degradation, with the best results for 4-ring PAHs with treatments of HPBCD + MC (up to 48% degradation for pyrene and 43% for fluoranthene), whereas dissipation for 5-ring PAHs was very low and for 6-ring was negligible. The use of RL increased the bioavailability of 13 of the 16 PAHs studied, reaching up to 60-fold higher values for phenanthrene or 18-fold higher for acenaphtene. RL addition did not show degradation improvement in any situation, and even inhibited the scarce degradation observed in the control treatment. The high increase in availability of both PAHs and mainly PTEs when using RL as amendment could make them toxic for microorganisms. In fact, Microtox Acute Toxicity test using Aliivibrio fischeri and the absence of colony forming units (CFUs) of indigenous bacteria demonstrated the extremely high levels of toxicity in RL treated soil.

Glomalin-related soil protein influences the accumulation of polycyclic aromatic hydrocarbons by plant roots

Studies have demonstrated that the inoculation of soil with arbuscular mycorrhizal fungi (AMF) enhances the content of glomalin-related soil protein (GRSP), which in turn elevates the availability of polycyclic aromatic hydrocarbons (PAHs) in soil. However, few studies have examined the influence of GRSP on PAH accumulation by plants and their tissues. Understanding of this issue would provide new perspectives on the role of GRSP in PAH uptake by plants at contaminated sites. This investigation was the first observational study of the GRSP-influenced PAH accumulation in roots of ryegrass (Lolium multiflorum Lam.). GRSP (0–120 mg/L) enhanced the root PAH accumulation in a GRSP-concentration-dependent manner, based on the observed root concentrations and root concentration factors (RCFs). The greatest enhancement of ΣPAH accumulation appeared at 40 mg/L of the total GRSP (T-GRSP) and 80 mg/L of the easily extracted GRSP (EE-GRSP), respectively. The weakly and strongly adsorbed fractions accounted for 88.8–94.4%, while the absorbed fraction contributed no >11.2% of total PAH accumulation in roots. The capacity of PAH adsorption on roots was enlarged in the presence of GRSP (0–120 mg/L). As the adsorbed fraction dominated the total PAH contents in roots overwhelmingly, the GRSP-induced changes in root PAH accumulation were ascribed to GRSP-affected PAH sorption by roots.

Co-application of activated carbon and compost to contaminated soils: toxic elements mobility and PAH degradation and availability

This work assesses the suitability of three commercial activated carbons (ACs) and their combination with olive mill waste compost (AC + C) as amendments for the remediation of two different contaminated soils. The treatments were applied to a mining soil, and their ability to immobilize trace elements was evaluated. Besides, the efficiency of the amendments to degrade and reduce the availability of polycyclic aromatic hydrocarbons (PAHs) was investigated in a soil from a wood creosote treatment plant. To this aim, trace elements mobility and PAH degradation and availability were evaluated. Ecotoxicological assays were performed to assess potential toxicity risks in the untreated and the amended soils. In the mining soil, the ACs were able to immobilize metals and As, but the AC + C treatments were more effective than AC. In the PAH-polluted soil, AC treatments promoted the degradation of high molecular weight PAH, but the AC + C amendments further enhanced the degradation of total PAH and reduced the availability of those with 3-rings. The ecotoxicological tests demonstrated an improvement of soil quality when AC and compost were applied together. In conclusion, the co-application of AC and compost reduces the mobility of potentially toxic elements in the polluted mine soil and enhances PAH degradation and reduces PAH availability in the creosote-contaminated soil.

Modelling the fate of PAH added with composts in amended soil according to the origin of the exogenous organic matter

A new model that was able to simulate the behaviours of polycyclic aromatic hydrocarbons (PAH) during composting and after the addition of the composts to agricultural soil is presented here. This model associates modules that describe the physical, biological and biochemical processes involved in PAH dynamics in soils, along with a module describing the compost degradation resulting in PAH release. The model was calibrated from laboratory incubations using three 14C-PAHs, phenanthrene, fluoranthene and benzo(a)pyrene, and three different composts consisting of two mature and one non-mature composts. First, the labelled PAHs were added to the compost over 28days, and spiked composts were then added to the soil over 55days. The model calculates the proportion of biogenic and physically bound residues in the non-extractable compartment of PAHs at the end of the compost incubation to feed the initial conditions of the model for soil amended with composts. For most of the treatments, a single parameter set enabled to simulate the observed dynamics of PAHs adequately for all the amended soil treatments using a Bayesian approach. However, for fluoranthene, different parameters that were able to simulate the growth of a specific microbial biomass had to be considered for mature compost. Processes that occurred before the compost application to the soil strongly influenced the fate of PAHs in the soil. Our results showed that the PAH dissipation during compost incubation was higher in mature composts because of the higher specific microbial activity, while the PAH dissipation in amended soil was higher in the non-mature compost because of the higher availability of PAHs and the higher co-metabolic microbial activity.

Availability of polycyclic aromatic hydrocarbons to earthworms in urban soils and its implications for risk assessment

Polycyclic aromatic hydrocarbons (PAHs) are a global problem, and in urban soils they can be found at potentially hazard levels. Nevertheless, the real risks that these contaminants pose to the environment are not well known, since the bioavailability of PAHs in urban soils has been poorly studied. Therefore, the bioavailability of PAHs in some selected urban soils from Lisbon (Portugal) was evaluated. Moreover, the applicability of a first screening phase based on total contents of PAHs was assessed. Results show that bioavailability of PAHs is reduced (low levels in earthworms, low accumulation percentages, and low biota-to-soil accumulation factors values), especially in more contaminated soils. The aging of these compounds explains this low availability, and confirms the generally accepted assumption that accumulation of PAHs in urban areas is mostly related with a long-term deposition of contaminated particles. The comparison of measured PAHs concentrations in earthworm tissues with the ones predicted based on theoretical models, reinforce that risks based on total levels are overestimated, but it can be a good initial approach for urban soils. This study also highlights the need of more reliable ecotoxicological data.

Glomalin-related soil protein enhances the availability of polycyclic aromatic hydrocarbons in soil

This is the first observation of glomalin-related soil protein (GRSP)-enhanced availability of phenanthrene as a representative polycyclic aromatic hydrocarbon (PAH) in soils based on an n-butanol extraction procedure and a desorption batch assay. The butanol-extractable amount of phenanthrene increased ∼204.4% in soils with GRSP added at 0–25 mg/kg. Phenanthrene desorption in soils increased monotonically with the increase of added GRSP concentration (0–50 mg/L) in solution. GRSP addition led to reduced soil organic matter in soil solids and increased concentrations of dissolved organic matter in solution, which dominates the mechanism of GRSP-enhanced phenanthrene availability. The results provide insight into the role of GRSP in soil PAH availability, and will be beneficial for risk assessment and remediation strategies at PAH-contaminated sites.

Characteristics of PAH tar oil contaminated soils—Black particles, resins and implications for treatment strategies

Tar oil contamination is a major environmental concern due to health impacts of polycyclic aromatic hydrocarbons (PAH) and the difficulty of reaching acceptable remediation end-points. Six tar oil-contaminated soils with different industrial histories were compared to investigate contamination characteristics by black particles. Here we provide a simple method tested on 6 soils to visualize and identify large amounts of black particles (BP) as either solid aggregates of resinified and weathered tar oil or various wood/coke/coal-like materials derived from the contamination history. These materials contain 2–10 times higher PAH concentrations than the average soil and were dominantly found in the sand fraction containing 42–86% of the total PAH. The PAH contamination in the different granulometric fractions was directly proportional to the respective total organic carbon content, since the PAH were associated to the carbonaceous particulate materials. Significantly lower (bio)availability of PAH associated to these carbonaceous phases is widely recognized, thus limiting the efficiency of remediation techniques. We provide a conceptual model of the limited mass transfer of PAH from resinated tar oil phases to the water phase and emphasize the options to physically separate BP based on their lower bulk density and slower settling velocity.

Application of sewage sludge and sewage sludge biochar to reduce polycyclic aromatic hydrocarbons (PAH) and potentially toxic elements (PTE) accumulation in tomato.

The effects of sewage sludge (SS) and its derived biochar (SSBC) on the availability and uptake of polycyclic aromatic hydrocarbons (PAHs) and potential toxic elements (PTEs) by Solanum lycopersicum (tomato) fruits grown in contaminated urban soil were investigated. Increasing application rates of SS and SSBC (2, 5, and 10%) decreased PAH availability and, correspondingly, PAH accumulation (22-39 and 48-62%, respectively) into tomato. SSBC was more effective in this regard. The available concentrations of PAHs (Σ16PAH) in the SSBC treatments were significantly reduced (from 30.0-47.3%) as compared to the control treatment. The availability of high-molecular-weight PAHs (containing four to six benzene rings) was greatly affected, while low-molecular-weight PAHs (containing two to three benzene rings) was less affected by SSBC amendments. The addition of SSBC showed the least effect on bioaccumulation of naphthalene (two-ring PAH; 24.5-32.6%), while the highest effect was observed for benzo(b)fluoranthene (five-ring PAH; 3.1-86.8%) and benzo(g,h,i)perylene (six-ring PAH; 51.8-84.2%). In contrast, increasing application rates of SS successively increased PTE (As, Cd, Cu, Pb, and Zn) availability and accumulation (15-139%) into tomato while SSBC successively decreased PTE availability and accumulation (17-91%). Changes in accumulation varied with PTE and the extent to which PTE concentrations in soil was elevated.

Low-molecular-weight organic acids enhance the release of bound PAH residues in soils

Understanding the release and availability of bound residues of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere is essential when assessing their fate and risk in the soil environment. However, limited information is available regarding the impact of root-secreted low-molecular-weight organic acids (LMWOAs) on the release of bound PAH residues in soils. The aim of this study was to investigate the LMWOA-influenced release of soil bound PAH residues. An n-butanol extraction procedure was used to evaluate the release of soil bound PAH residues. LMWOAs can dramatically promote the release of bound PAH residues and enhance the extractability and availability of PAHs in soil. The addition of LMWOAs significantly increased the extractable concentrations of ΣPAH and each individual PAH in soils containing bound PAH residues in a LMWOA-concentration dependent manner. Compared with control treatments without addition of LMWOA, the concentrations of butanol-extractable ΣPAH and each PAH in soils following the addition of 10–100mmol/kg LMWOAs were 54–745% and 58–605% larger after 40 and 80 days, respectively. Citric acid always generated the largest PAH release from soil bound PAH residues, while malic acid generated the lowest release among the three LMWOAs tested. The results of this work provide important information regarding the fate of bound PAH residues in the soil environment, and will be useful for the risk assessment of PAH-contaminated soils and the development of remedial strategies for contaminated sites.