A novel bioaccessibility prediction method for PAHs in soil: Composite extraction with hydroxypropyl-β-cyclodextrin and extracellular polymer substances

Hydroxypropyl-β-cyclodextrin (HPCD) extraction of urban soils: mass balance, bioaccessibility, and cancer risk assessment of 71 polycyclic aromatic hydrocarbons (PAH) from petrogenic and pyrogenic sources

Bioaccessibility of polycyclic aromatic hydrocarbons (PAH) in soils is often determined by extraction with hydroxypropyl-β-cyclodextrin (HPCD), yet there is no standardized approach for determining bioaccessible concentrations (cbio), which are either calculated or directly measured. Additionally, most studies analyze solely the 16 EPA PAH, neglecting more carcinogenic PAH with higher relative potency factors (RPFs) and often disregarding PAH sources. This study examines optimal cbio determination by providing mass balances of HPCD extraction. Moreover, this study investigates the bioaccessibility of 71 PAH in five urban soils, considering their petrogenic to pyrogenic sources and their carcinogenic potential. Checking HPCD mass balances revealed that mechanical stress and residual HPCD can artificially increase the residual PAH content (cnon-bio), making cbio calculation using cnon-bio unfeasible. We therefore recommend re-extraction of HPCD extracts to measure cbio. The measured cbio of PAH depended on PAH sources, with lower cbio observed in petrogenic coal-containing soils. Within cbio, 7H-benzo[c]fluorene contributes most to toxicity equivalents (TEQs), while the most carcinogenic EPA PAH, benzo[a]pyrene, contributes little. Dibenzopyrenes, considered highly carcinogenic, were not bioaccessible. TEQs could only be calculated for 24 PAH with available RPFs. However, additional PAH with evidence for carcinogenicity were also bioaccessible, with 2-methylfluoranthene and benzo[c]phenanthrene reaching cbio of >1 mg/kg. Notably, benzo[c]phenanthrene is classified by the IARC as a group 2B carcinogen. These findings suggest that particularly 7H-benzo[c]fluorene and benzo[c]phenanthrene should be included in routine risk assessments due to their carcinogenic categorization and bioaccessibility. Future studies should focus on expanding carcinogenicity data and RPF values for additional PAH.

A novel bioaccessibility prediction method for complex petroleum hydrocarbon mixtures in soil

More evidence shows that bioaccessibility instead of total concentrations based on exhaustive extraction methods can better reflect the actual risk level of petroleum hydrocarbon contaminated sites, so it is essential to establish an effective assessment method for bioaccessibility. This study utilized Tenax extraction, butanol extraction, hydroxypropyl-β-cyclodextrin (HPCD) extraction, and a composite extraction method involving HPCD with LMWOAs (citric acid, CA) and surfactants (rhamnolipid, RL; Tween80, TW80; sodium dodecyl sulfate, SDS) at varying concentrations. These methods were employed to predict the bioaccessibility of earthworms to soil at different aging time of petroleum hydrocarbons. The results showed that traditional extraction methods such as Tenax 6h extraction and n-butanol extraction were ineffective in evaluating petroleum hydrocarbons' bioaccessibility. In contrast, the composite extraction of HPCD and solubilizer enhanced the extraction efficiency of HPCD greatly, and the extraction results showed a significant positive correlation with earthworm accumulation. By the comparison of the extraction results of different fractions of petroleum hydrocarbons, heavy fractions of petroleum hydrocarbons (C29-C40) are essential factors affecting chemical extraction effects. The correlation coefficients of four composite extraction methods and total petroleum hydrocarbons (TPH) of earthworm accumulation by linear regression analysis ranged from 1.1797 to 1.7990, and the slopes ranged from 0.8727 to 0.9792. Among them, the combined extraction method of 50 mmol/L HPCD and 0.5 mmol/L rhamnolipid had the best effect (r2 = 0.9792, slope = 1.1797), which could be used as an evaluation method suitable for the bioaccessibility of petroleum hydrocarbons in soil. This study could provide a new method for evaluating the bioaccessibility of organic pollutants and technically supporting risk assessment and bioremediation of complex petroleum hydrocarbons in soil.

Accurate prediction bioaccessibility of PAHs in soil-earthworm system by novel magnetic solid phase extraction technique

Conventional chemical extraction methods may lead to overestimate or underestimate bioaccessibility due to their inability to provide realistic kinetic information regarding PAHs in soils. In this study, we propose the use of magnetic solid phase extraction (MSPE) technique for assessing the bioaccessibility of PAHs in the soil-earthworm system. Firstly, a novel polydopamine-coated magnetic core-shell microspheres (Fe3O4-C16@PDA) was developed by a one-pot sol-gel and self-polymerization method. The PDA coatings not only enhance the hydrophilicity of material surfaces but also exhibit excellent biocompatibility. The maximum adsorption capacity of Fe3O4-C16@PDA for 16 PAHs was 52.72 mg g-1, indicating that the proposed material fulfills the assessment requirements for highly contaminated soil. To compare the measurement of PAHs and their uptake by earthworms (Eisenia fetida), experiments were conducted using four different soils with varying properties. The desorption kinetics data obtained from these experiments demonstrated that the capability of the MSPE in accurately predicting the bioavailable portions of PAHs. After a 28-day exposure, the best predictor of bioavailable PAHs in earthworms was MSPE method exhibited the highest correlation coefficient (R2 > 0.90), and its slopes in the four soils were 0.972, 0.961, 1.012, and 0.962, respectively, all close to 1. These results demonstrate that the MSPE method successfully mimics the conditions encountered in soil-earthworm systems and effectively assess bioaccessibility of PAHs in soils.

An evaluation model for in-situ bioremediation technology of petroleum hydrocarbon contaminated soil

Considering the interference of the complexity of underground environment to the bioremediation scheme, an evaluation model for bioremediation technology in the soil source area of oil contaminated sites was established. On the basis of traditional CDE model, a compartment model was coupled to express the adsorption and degradation process, and the spatial expression of biodegradation was enriched through environment-dependent factors. The visualization of the model was achieved based on COMSOL Multiphysics software platform. Two sets of indoor sandbox experiments on natural attenuation and bioaugmentation were carried out for 120 days to verify the prediction function of the model. The results showed that bioaugmentation greatly improved the remediation effect. Petroleum hydrocarbons with different occurrence states exhibited different spatial distributions under the influence of environmental factors. The prediction accuracy evaluation results of total petroleum hydrocarbons, bio available hydrocarbons and non extractable hydrocarbons showed excellent fitting degree, and the model had a good prediction function for petroleum hydrocarbon in soil under different bioremediation scenarios. This model can be used to screen bioremediation technical schemes, prevent pollution and assess risk of petroleum hydrocarbon contaminated sites.

Bioaccessibility and Toxicity Assessment of Polycyclic Aromatic Hydrocarbons in Two Contaminated Sites

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous soil contaminants, and their bioaccessibility determines their environmental risks in contaminated land. In the present study, the residual concentrations of PAHs in the soils of two industrial sites were determined, and their bioaccessibility was estimated by the hydroxypropyl-β-cyclodextrin extraction (HPCD) extraction method. The results showed heavy PAH contamination at both site S1 (0.38-3342.5 mg kg^-1) and site S2 (0.2-138.18 mg kg^-1), of which high molecular weight (HMW) PAHs (4-, 5-, and 6-ring compounds) accounted for approximately 80%. The average bioaccessibility of PAHs at sites S1 and S2 was 52.02% and 29.28%, respectively. The bioaccessibility of certain PAH compounds decreased with increasing ring number of the molecule. Lower PAH bioaccessibility was detected in loamy and silty soil textures than in sandy soil. Moreover, among the soil properties, the dissolved organic matter, total organic carbon, total potassium, and total manganese concentrations had significant effects on the bioaccessibility of PAHs. The toxicity analysis showed that the composition and bioaccessibility of PAHs could affect their potential toxicity in soil. We suggest that bioaccessibility should be taken into consideration when assessing the toxicity of PAHs in soil, and more attention should be given to low-ring PAHs with high bioaccessibility.

Inhalation Bioaccessibility of Polycyclic Aromatic Hydrocarbons in PM2.5 under Various Lung Environments: Implications for Air Pollution Control during Coronavirus Disease-19 Outbreak

Global spread of coronavirus disease-19 (COVID-19) is placing an unprecedented pressure on the environment and health. In this study, a new perspective is proposed to assess the inhalation bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 for people with various lung health conditions. In vitro bioaccessibility (IVBA) was measured using modified epithelial lung fluids simulating the extracellular environment of patients with severe and mild lung inflammation. The average PAH IVBA in PM2.5 of 24.5 ± 4.52% under healthy conditions increased (p = 0.06) to 28.6 ± 3.17% and significantly (p < 0.05) to 32.3 ± 5.32% under mild and severe lung inflammation conditions. A mechanistic study showed that lung inflammation decreased the critical micelle concentrations of main pulmonary surfactants (i.e., from 67.8 (for dipalmitoyl phosphatidylcholine) and 53.3 mg/L (for bovine serum albumin) to 44.5 mg/L) and promoted the formation of micelles, which enhanced the solubilization and competitive desorption of PAHs from PM2.5 in the lung fluids. In addition, risk assessment considering different IVBA values suggested that PAH contamination levels in PM2.5, which were safe for healthy people, may not be acceptable for patients with lung inflammation. Because of the large number of COVID-19 infections, and the fact that some survivors of COVID-19 were observed to still show symptoms of interstitial lung inflammation, the finding here can provide important implications for both the scientific community and policy makers in addressing health risk and air pollution control during the COVID-19 outbreak.

Magnetic solid-phase extraction as a novel method for the prediction of the bioaccessibility of polycyclic aromatic hydrocarbons

Chemical methods used to predict the bioaccessibility of hydrophobic organic compounds (HOCs) still need further development and improvement. In this work, magnetic solid-phase extraction (MSPE) based on poly(β-cyclodextrin)-coated magnetic polydopamine (Fe₃O₄@PDA@PCD) was first introduced to assess the bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in soils. Due to its good hydrophilicity and submicrometer scale, Fe₃O₄@PDA@PCD displayed a higher extraction rate for PAHs in an aqueous solution (equilibrium time < 5 min) than Tenax resin, which had an equilibrium time longer than 30 min. The merits of Fe₃O₄@PDA@PCD are beneficial to accelerate the desorption of PAHs from soil, especially for high molecular weight PAHs, in which the amounts extracted by Fe₃O₄@PDA@PCD were 1.2-2.8 times higher than those extracted by Tenax resin. The desorption kinetics data were well fitted with a two- or three-fraction model. The fitting results indicated that the MSPE method can be used to predict the bioaccessible fractions of PAHs. By comparing the prediction results obtained from the MSPE method with bioassays using earthworms, a significant linear correlation (R² = 0.98) with a slope statistically close to 1 was obtained. These results suggested that the MSPE method can act as a simple and efficient method to measure the bioaccessibility of PAHs in soil.

Pressurized liquid extraction followed by liquid chromatography coupled to a fluorescence detector and atmospheric pressure chemical ionization mass spectrometry for the determination of benzo(a)pyrene metabolites in liver tissue of an animal model of colon cancer

Since metabolism is implicated in the carcinogenesis of toxicants, an efficient extraction method together with an analytical method is warranted to quantify tissue burdens of a carcinogen and/or its metabolites. Therefore, the aim of this study was to validate a pressurized liquid extraction (PLE) method for measuring metabolites of benzo(a)pyrene [B(a)P; a food-borne carcinogen] from tissue samples. The sample extraction was performed separately by PLE and liquid-liquid extraction (LLE). PLE followed by high-performance liquid chromatography coupled to online fluorescence detector (HPLC-FLD) was used to quantify separated analytes; and by ultra-high-performance liquid chromatography (UHPLC) coupled to atmospheric pressure chemical ionization tandem mass spectrometry (UHPLC-APCI-MS/MS) were used for confirmation purposes. The UHPLC-MS/MS was set-up in the atmospheric pressure chemical ionization (APCI) positive interface with selective reaction monitoring (SRM). The analytical performance characteristics of the PLE technique was assessed at different temperatures, pressure, number of cycles and solvent types. A methanol + chloroform + water mixture (30:15:10, v/v/v) yielded greater recoveries at an extraction temperature range of 60-80°C, pressure of 10 MPa and an extraction time of 10 min. The PLE method was validated by the analysis of spiked tissue samples and measuring recoveries and limits of quantitation for the analytes of interest using HPLC-FLD equipment. The optimized PLE-HPLC-FLD method was used to quantify the concentrations of B(a)P metabolites in liver samples obtained from a colon cancer animal model. Overall, PLE performed better in terms of extraction efficiency, recovery of B(a)P metabolites and shortened sample preparation time when compared with the classic LLE method.

Biodegradation and Absorption Technology for Hydrocarbon-Polluted Water Treatment

Wastewaters polluted with hydrocarbons are an environmental problem that has a significant impact on the natural ecosystem and on human health. Thus, the aim of this research was to develop a bioreactor sorbent technology for treating these polluted waters. A lab-scale plant composed of three 1-L bioreactors with different sorbent materials inside (meltblown polypropylene and granulated cork) was built. Wastewater to be treated was recirculated through each bioreactor for 7 days. Results showed that hydrocarbon retention rates in the three bioreactors ranged between 92.6% and 94.5% of total petroleum hydrocarbons (TPHs) and that after one simple recirculation cycle, no hydrocarbon fractions were detected by gas chromatography/Mass Spectrometry (GC/MS) in the effluent wastewater. In addition, after the wastewater treatment, the sorbent materials were extracted from the bioreactors and deposited in vessels to study the biodegradation of the retained hydrocarbons by the wastewater indigenous microbiota adhered to sorbents during the wastewater treatment. A TPH removal of 41.2% was detected after one month of Pad Sentec™ carrier treatment. Further, the shifts detected in the percentages of some hydrocarbon fractions suggested that biodegradation is at least partially involved in the hydrocarbon removal process. These results proved the efficiency of this technology for the treatment of these hydrocarbon-polluted-waters.

Polydopamine-coated polyethylene sieve plate as an efficient and convenient adsorption sink for the bioaccessibility prediction of PAHs in soils

Bioaccessibility measurements of polycyclic aromatic hydrocarbons (PAHs) in soils are significant for exposure risk assessment. The current physicochemical methods require tedious operation processes, underestimate the actual risks, or are unsuitable for high organic content soils. In this work, an efficient and convenient method based on polydopamine-coated polyethylene sieve plate (PDA@PESP) and hydroxypropyl-β-cyclodextrin (HPCD) was developed to predict the bioaccessibility of PAHs in multi-type soils. The PDA@PESP can be prepared via in situ self-polymerization, allowing to extract PAHs from HPCD solution quantitatively and rapidly. When applied to evaluate the bioaccessibility with PDA@PESP as an adsorption sink and HPCD as a diffusive carrier, the proposed method can significantly improve the extractable fraction of PAHs compared to single HPCD extraction in particular for high organic carbon content soil and high-ring PAHs. The desorption kinetics data indicated that the method can predict the bioaccessible fraction of PAHs. In addition, the method predicted a satisfactory accumulation into earthworms (Eisenia fetida) with a slope statistically approximated to 1. A highly significant linear regression (R² = 0.95) was also found between the proposed method and Tenax desorption in historically contaminated soils, demonstrating that the method is an efficient and convenient approach for the bioaccessibility prediction of PAHs in soils.

Comparison of the bioavailability of benzo[a]pyrene (B[a]P) in a B[a]P-contaminated soil using the different addition approaches

Determination of the bioavailability of the hydrophobic organic contaminant benzo[a]pyrene (B[a]P) is extremely important for assessing its environmental risk. The effect of addition manner of B[a]P on the bioavailability and toxicity of B[a]P in soil remains unclear. In this study, soil samples, spiked with B[a]P by one-time or multiple-time additions, were tested to investigate the available fraction of B[a]P in soils, the uptake of B[a]P by red wiggler worms (Eisenia fetida), as well as superoxide dismutase (SOD) and peroxidase (POD) activities in earthworm coelomocytes at different periods. Results showed that the available fraction of B[a]P in soils and the amount of B[a]P assimilated by earthworms declined sharply from 1 d to 28 d during the incubation period and then decreased slowly from 28 to 56 d in both the one-time and the multiple-time addition tests. The available fraction of B[a]P in soils and its uptake by earthworms were significantly lower in multiple-time addition samples than those in one-time addition samples, a finding which was consistent with the SOD and POD activities in earthworms during the whole 56-d incubation period. These variations in the characteristics of the two addition treatments may be due to the differences in the way the B[a]P aged in the soil. These results indicated that the addition method was an important factor influencing the bioavailability of organic contaminants in soils.

Effect of extracellular polymeric substance components on the sorption behavior of 2,2',4,4'-tetrabromodiphenyl ether to soils: Kinetics and isotherms

Microbial extracellular polymeric substances (EPS) and persistent organic pollutants (POPs) commonly exist in the soil environment. Currently, there is a knowledge gap regarding the effect of EPS on the fate of POPs in soil. In the present study, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) was used as a model compound to investigate the effects of bovine serum albumin (BSA) and sodium alginate (SA) - mimicking the main components of EPS - on sorption of POPs to soils, through batch experiments. Irrespective of the concentration of BSA: the addition of BSA did enhance the sorption capacity of BDE-47 to soils, due to generation of more sorption sites. For SA, it increased the sorption capacity of BDE-47 at low BDE-47 concentrations, while the presence of SA negatively affected sorption of BDE-47 at high BDE-47 concentrations. The partition effect dominates the sorption of BDE-47 to soils, but after adding either BSA or SA, the sorption of BDE-47 to soils is dominated by surface sorption. Film diffusion and intra-particle diffusion were also involved in the sorption process with and without BSA or SA, with the latter being the rate-limiting step. The heterogeneous surface and nonlinear sorption behavior of BDE-47 to soils increased in the presence of either BSA or SA. The FTIR spectra indicated that the aromatic CC, H-bonds and OH groups may be involved in the sorption process. Therefore, BSA enhanced the retention of BDE-47 to soil, while SA's influence on BDE-47 sorption to soil depended on the concentration of BDE-47.

Effects of cationic surfactant on the bioaccumulation of polycyclic aromatic hydrocarbons in rice and the soil microbial community structure

Cetyltrimethylammonium bromide reduced the PAH bioaccumulation in rice from paddy soils and benefit the soil ecology in the short term.