Sorptive physiologically based extraction of contaminated solid matrices: incorporating silicone rod as absorption sink for hydrophobic organic contaminants

Endocrine disrupting potential of total and bioaccessible extracts of dust from seven different types of indoor environment

Information on the indoor environment as a source of exposure with potential adverse health effects is mostly limited to a few pollutant groups and indoor types. This study provides a comprehensive toxicological profile of chemical mixtures associated with dust from various types of indoor environments, namely cars, houses, prefabricated apartments, kindergartens, offices, public spaces, and schools. Organic extracts of two different polarities and bioaccessible extracts mimicking the gastrointestinal conditions were prepared from two different particle size fractions of dust. These extracts were tested on a battery of human cell-based bioassays to assess endocrine disrupting potentials. Furthermore, 155 chemicals from different pollutant groups were measured and their relevance for the bioactivity was determined using concentration addition modelling. The exhaustive and bioaccessible extracts of dust from the different microenvironments interfered with aryl hydrocarbon receptor, estrogen, androgen, glucocorticoid, and thyroid hormone (TH) receptor signalling, and with TH transport. Noteably, bioaccessible extracts from offices and public spaces showed higher estrogenic effects than the organic solvent extracts. 114 of the 155 targeted chemicals were detectable, but the observed bioactivity could be only marginally explained by the detected chemicals. Diverse toxicity patterns across different microenvironments that people inhabit throughout their lifetime indicate potential health and developmental risks, especially for children. Limited data on the endocrine disrupting potency of relevant chemical classes, especially those deployed as replacements for legacy contaminants, requires further study.

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.

Correlation analysis between the in vivo bioavailability and in vitro bioaccessibility of nitro PAHs in soil: Application of simplified FOREhST in vitro methods based on the Chinese pharmacopoeia

In this study, the relative bioavailability (RBA) of nitrated polycyclic aromatic hydrocarbons (NPAHs) in soil samples (n = 30) was assessed using an in vivo mouse model. Based on the correlation between the bioaccessibility data obtained from the Tenax improved traditional Fed ORganic Estimation human Simulation Test (FOREhST) in vitro method (TITF) and the bioavailability data obtained from in vivo experiments, the TITF method was further optimized and simplified by referring to the "Pharmacopoeia of the People's Republic of China: Volume IV, 2020" to adjust the formulation and parameters of the gastrointestinal fluid (GIF) in order to establish a simpler and lower cost in vitro method for the determination of the bioaccessibilities of NPAHs. The dose-accumulation relationship of the in vivo experiment showed that the linear dose-response was better in adipose tissue (R2 = 0.77-0.93), and the accumulation of NPAHs in adipose tissue was higher than that in kidney or liver tissue. Depending on the mouse adipose model, the NPAHs-RBA ranged from 1.88 % to 73.92 %, and a strongly significant negative relationship (R2 = 0.94, p < 0.05) was found between the NPAHs-RBA and Log Kow. The simplified experiment of the TITF showed that the composition of the GIF medium had a significant effect on the bioaccessibilities of NPAHs. The NPAH bioaccessibilities measured by the Tenax improved simplified FOREhST method (TISF) (9.0-36.5 %) were higher than that of the traditional FOREhST method (6.8-22.8 %) but significantly lower than that of the TITF method (16.8-55.2 %). With an increase in the bile concentration in the GIF (from 6 to 10 g/L), the bioaccessibilities of NPAHs increased from 9.0 to 36.5 % to 12.9-42.4 %. The accuracies of the four in vitro methods for predicting the bioavailabilities of NPAHs was in the following order: Tenax improved simplified FOREhST method with increased bile concentration (TITF-IB) (R2 = 0.54-0.87) ≈ TITF (R2 = 0.55-0.85) > TISF (R2 = 0.41-0.77) > FOREhST (R2 = 0.02-0.68). These results indicated that the simple in vitro method could also effectively predict the bioavailabilities of NPAHs.

Evaluation of the oral bioaccessibility of legacy and emerging brominated flame retardants in indoor dust

Indoor dust is the main source of human exposure to brominated flame retardants (BFRs). In this study, in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax as a sorptive sink was applied to evaluate the oral bioaccessibility of twenty-two polybrominated diphenyl ethers (PBDEs) and seven novel BFRs (NBFRs) via indoor dust ingestion. The mean bioaccessibilities of two NBFRs pentabromotoluene (PBT) and 1,2-Bis(2,4,6-tribromophenoxy) ethane (BTBPE) were first proposed, reaching 36.0% and 26.7%, respectively. In order to maintain homeostasis of the gastrointestinal tract, 0.4 g Tenax was added in CE-PEBT, which increased BFRs bioaccessibility by up to a factor of 1.4-1.9. The highest bioaccessibility of legacy PBDEs was tri-BDEs (73.3%), while 2-ethylhexyl-tetrabromo-benzoate (EHTBB), one of penta-BDE alternatives, showed the highest (62.2%) among NBFRs. The influence of food nutrients, liquid to solid (L/S) ratio, and octanol-water partition coefficient (Kow) on bioaccessibility was assessed. The oral bioaccessibility of BFRs increased with existence of protein or carbohydrate while lipid did the opposite. The bioaccessibilities of PBDEs and NBFRs were relatively higher with 200:1 L/S ratio. PBDEs bioaccessibility generally decreased with increasing LogKow. No significant correlation was observed between NBFRs bioaccessibility and LogKow. This study comprehensively evaluated the bioaccessibilities of legacy and emerging BFRs via dust ingestion using Tenax-assisted CE-PBET, and highlighted the significance to fully consider potential influencing factors on BFRs bioaccessibility in further human exposure estimation.

Effect of Microplastic Types on the In Vivo Bioavailability of Polychlorinated Biphenyls

As MPs are released into the soil, various equilibrium statuses are expected. MPs could play roles as a "source," a "cleaner," or a "sink" of HOCs. Three types of MPs (LDPE, PLA, and PS) were selected to study their effect on polychlorinated biphenyl (PCBs) relative bioavailability (RBA) measured by a mouse model. As a "source" of HOCs, exposure to MP-sorbed PCBs resulted in their accumulation in adipose tissue with PCB RBA as 101 ± 6.73% for LDPE, 76.2 ± 19.2% for PLA, and 9.22 ± 2.02% for PS. The addition of 10% MPs in PCB-contaminated soil led to a significant (p < 0.05) reduction in PCB RBA (52.2 ± 16.7%, 49.3 ± 4.85%, and 47.1 ± 5.99% for LDPE, PLA, and PS) compared to control (75.0 ± 4.26%), implying MPs acted as "cleaner" by adsorbing PCBs from the digestive system and reducing PCB accumulation. MPs acted as a "sink" for PCBs in contaminated soil after aging, but the sink effect varied among MP types with more pronounced effect for LDPE than PLA and PS. Therefore, the role played by MPs in bioavailability of HOCs closely depended on the MP types as well as the equilibrium status among MPs, soil, and HOCs.

Bioaccessibility of Organic Compounds Associated with Tire Particles Using a Fish In Vitro Digestive Model: Solubilization Kinetics and Effects of Food Coingestion

Tire and road wear particles (TRWP) account for an important part of the polymer particles released into the environment. There are scientific knowledge gaps as to the potential bioaccessibility of chemicals associated with TRWP to aquatic organisms. This study investigated the solubilization and bioaccessibility of seven of the most widely used tire-associated organic chemicals and four of their degradation products from cryogenically milled tire tread (CMTT) into fish digestive fluids using an in vitro digestion model based on Oncorhynchus mykiss. Our results showed that 0.06-44.1% of the selected compounds were rapidly solubilized into simulated gastric and intestinal fluids within a typical gut transit time for fish (3 h in gastric and 24 h in intestinal fluids). The environmentally realistic scenario of coingestion of CMTT and fish prey was explored using ground Gammarus pulex. Coingestion caused compound-specific changes in solubilization, either increasing or decreasing the compounds' bioaccessibility in simulated gut fluids compared to CMTT alone. Our results emphasize that tire-associated compounds become accessible in a digestive milieu and should be studied further with respect to their bioaccumulation and toxicological effects upon passage of intestinal epithelial cells.

Microplastics-sorbed phenanthrene and its derivatives are highly bioaccessible and may induce human cancer risks

Microplastics (MPs) are ubiquitous in environmental media and human diets and can enrich organic contaminants, including polycyclic aromatic hydrocarbons (PAHs) and their derivatives. The bioaccessibilities and triggering cancer risks of MP-sorbed PAHs and PAH derivatives are closely linked with human health, which, however, were rarely focused on. This study explored the sorption behaviors of phenanthrene (PHE) and PHE derivatives on polyethylene (PE), polypropylene (PP), and polystyrene (PS) MPs, and assessed their bioaccessibilities in gastrointestinal fluids as well as their inducing human cancer risks. PE MPs harbored the highest sorption capacity, secondly the PP MPs, then the PS ones. Sorption of PHE and PHE derivatives on MPs was positively correlated with their hydrophobicities. The bioaccessibilities of sorbed PHE and PHE derivatives could reach 53.59 %±0.46 %-90.28 %±0.92 % in gastrointestinal fluids and 81.34 %±0.77 %-98.72 %±1.44 % in gastrointestinal fluids with the addition of Tenax (more close to the bioavailability). The hydrophobicities also controlled the bioaccessibilities of PHE and PHE derivatives in gastric fluids, and those in intestinal fluids with Tenax for PS MPs. The incremental lifetime cancer risk (ILCR) values for PHE, PHE-Cl, and PHE-NO2 on MPs at tested concentrations were all higher than the USEPA-suggested safety limit (10-6), and most of them were even higher than 10-4, which thus indicates serious cancer risks. This study promoted our understanding of the potential health threats posed by organic pollutant-bearing MPs in the environment.

Evaluating the inhalation bioaccessibility of traffic-impacted particulate matter-bound PAHs in a road tunnel by simulated lung fluids

Polycyclic aromatic hydrocarbons (PAHs) are the most highly concerned pollutants bound on traffic-impacted particulate matter (TIPM). The inhaled TIPM-bound PAHs risk has attracted much attention, whereas the inhalation bioaccessibility, a method to refine the exposure risk assessment, has not yet been extensively introduced in the exposure risk assessment. Thus, in vitro assays using artificial lung fluids including artificial lysosomal fluid (ALF), Gamble's solution (GS), and modified GS (MGS) were conducted to assess the inhalation bioaccessibility of USEPA 16 PAHs in TIPM collected from an expressway tunnel, the influence factors of PAHs' inhalation bioaccessibility were explored, and the exposure risk of TIPM-bound PAHs was estimated based on inhalation bioaccessibility. Results showed that the average PAHs concentrations were 30.5 ± 12.9 ng/m³, 36.2 ± 5.19 ng/m³, and 39.9 ± 4.31 ng/m³ in the tunnel inlet PM_2.5, TSP, and tunnel center PM_2.5, respectively. Phe, Flt, Pyr, Nap, Chr, BbF, and BkF were found as the dominant species in TSP and PM_2.5, indicating a dominant contribution of PAHs from diesel-fueled vehicular emissions. The bioaccessible fractions measured for different PAH species in tunnel PM_2.5 and TSP were highly variable, which can be attributed to PAHs' physicochemical properties, size, and carbonaceous materials of TIPM. The addition of Tenax into SLF as an "adsorption sink" can greatly increase PAHs' inhalation bioaccessibility, but DPPC has a limited effect on tunnel PM-bound PAHs' bioaccessibility. The incremental lifetime carcinogenic risk (ILCR) of tunnel inlet PM_2.5-bound PAHs evaluated according to their total mass concentration exceeded the threshold (1.0 × 10^-6) set by the USEPA, whereas the ILCRs estimated based on the inhalation bioaccessibility were far below the threshold. Hence, it is vitally important to take into consideration of pollutant's bioaccessibility to refine health risk assessment.

Incorporating Tenax into the in vitro method to improve the predictive capability of bioaccessibility of triazole fungicides in grape

In vitro bioaccessibility assays have been developed for high-throughput prediction of relative bioavailability (RBA). However, methods to reliably and efficiently assess pesticide residues remain limited, hindering the precise estimation of pesticide exposure risk. The inclusion of a sorption sink material to simulate intestinal sorption could be a promising approach to optimize in vitro bioaccessibility methods. The current study aimed to explore the feasibility of incorporating Tenax into the Rijksinstituut voor Volksgezondheid en Milieu (RIVM) method for accurate evaluation of the bioaccessibility of triazole fungicides. The use of 1.0 g of Tenax enabled the valid trapping of triazole fungicides released from grape, resulting in a significant increase of 23.59-38.51 % in the value of bioaccessibility. A strong in vivo-in vitro correlation was observed between pesticide RBA and bioaccessibility, suggesting that the Tenax-assisted RIVM method is a suitable replacement for time-consuming and laborious in vivo alternatives. In addition, the exposure assessment indicated that the hazard quotients for triazole fungicides in grape may be overestimated by 5.79-27.34 % without considering bioaccessibility based on the Tenax-assisted RIVM method. These results provide further insights into the assessment of bioaccessibility-based human exposure to pesticides as well as dietary exposure and related risk for human health.

Assessment of DDT and its Metabolites Bioaccessibility in Historically Contaminated Soils Using Unfed and Fed in Vitro Methods

Bioaccessibility of hydrophobic organic contaminants (HOCs) from unintentional ingestion of soil is increasingly assessed with in vitro gastrointestinal models incorporating a sorption sink. In this study, the bioaccessibility of DDTs in contaminated soils (n = 11) was determined using "unfed" unified bioaccessibility method (UBM) and fed organic estimation human simulation test (FOREhST) with/without Tenax as an absorbent. By adding Tenax, the bioaccessibility of DDTs determined using UBM was significantly increased from 4.9-30.6% to 31.6-86.0%. In contrast, the bioaccessibility of DDTs determined using FOREhST without/with Tenax were similar with values of 20.0-60.9% vs 31.5-47.6%, implying that the influence of food components on the absorption efficiency of the sink should not be overlooked. Much high fraction of DDTs (bioaccessibility: 11.7-24.8%) remained in FOREhST supernatant after Tenax collection, suggesting that prediction of bioavailability through bioaccessibility obtained by absorbent needs to be treated with caution when bioaccessibility is determined using a "fed state" in vitro method.

Evaluating the adsorption performance of Tenax TA® in different containers: An isolation tool to study the bioaccessibility of nitro-PAHs in spiked soil

The improved in vitro gastrointestinal simulation methods, with the addition of the adsorption sink, are considered as a promising tool for predicting the bioaccessibility of contaminants. However, the problem associated with the recovery of the adsorption sink from the complex matrix needs more understand. Although previous studies tried to solve this shortcoming by using the containers (a vessel to hold the adsorption sink), there is no systematic comparison study on the impact of containers on bioaccessibility till now, especially for nitro-polycyclic aromatic hydrocarbons (nitro-PAHs). In order to understand the problem, commonly used containers in previous studies (dialysis bags and stainless-steel screen) were selected and deployed in the Fed Organic Estimation Human Simulation Test (FOREhST) method to compare the effects of these containers on the bioaccessibility of nitro-PAHs desorbed from the five different types of soils into the gastrointestinal fluid (GIF). Results showed that in order to maintain a constant sorptive gradient for the high molecular weight (MW) nitro-PAHs, 0.25 g of Tenax TA® were required in FOREhST. Compared with Tenax TA® encapsulated in dialysis bag (Tenax-EDBG), the use of Tenax TA® encapsulated in dissolution basket (Tenax-EDBT) significantly increased the bioaccessibility of nitro-PAHs in the soil from 5.6-31.4% to 17.2-70.6%, due to the better diffusion performance. The bioaccessibility of nitro-PAHs by FOREhST extraction with Tenax-EDBT showed a significant negative correlation with soil total organic carbon (TOC), whereas a weak correlation with pH. This study provides the researchers with a more standardized in vitro method to quantify the bioaccessibility of PAHs and their derivatives in soil.

Coupling polydimethylsiloxane vials with a physiologically based extraction test to predict bioavailability of hydrophobic organic contaminants in soils

As alternatives to in vivo assays, physiologically based in vitro methods have been developed to measure bioaccessibility of hydrophobic organic contaminants (HOCs) in soils. However, bioaccessibility can usually be underestimated since in vitro tests fail to provide sufficient affinity for HOCs. Sorption sink was therefore included to simulate intestinal cell absorption and to promote the mobilization of HOCs from soils. In this study, polydimethylsiloxane (PDMS) vials, widely used as passive dosing, were introduced as a sorption sink to improve the performance of physiologically based extraction test (PBET). The bioaccessibility of PCBs (representatives of HOCs) in 13 lab-spiked soils measured by PBET coupled with PDMS vials ranged from 56.5 ± 2.7% to 109.3 ± 1.5%. Correlation was conducted between the bioaccessibility and relative bioavailability (RBA) of PCBs assessed using an in vivo mouse model. A significant correlation (p < 0.001, R² = 0.72, slope = 0.85 ± 0.16) was observed between in vitro and in vivo data, indicating that the proposed method here can be a robust in vitro method to predict PCB RBA in soils. The accuracy of this novel method was further shown by extracting one field contaminated soil with environmental relevant levels of PCBs. The relative standard deviation of bioaccessibility measured by PBET with PDMS vials was 1.2-9.8%, and much lower than those by PBET alone with values of 17.1-63.6%. In addition, the PDMS vials can be reusable as sorption sink, and no significant variation (p = 0.44) in PCB bioaccessibility was observed among 5 cycles of extracting soils with PBET coupled with PDMS vials. Due to the high sorption capacity of PDMS and flexibility of PDMS mass used for vials, the novel method here is expected to be applicable in soils with a wide range of contamination levels.

A review on in-vitro oral bioaccessibility of organic pollutants and its application in human exposure assessment

Generally, human oral exposure assessments of contaminants have not considered the absorption factor in the human gastrointestinal tract, thus overestimating human exposure and associated health risk. Currently, more researchers are adding the absorption factor into human exposure assessment, and bioaccessibility measured by in-vitro methods is generally replacing bioavailability for estimation because of the cheap and rapid determination. However, no single unified in-vitro method is used for bioaccessibility measurement of organic pollutants, although several methods have been developed for these pollutants and have shown good in vitro-in vivo correlation between bioaccessibility and bioavailability. The present review has focused on the development of in-vitro methods, validation of these methods through in-vivo assays, determination of factors influencing bioaccessibility, application of bioaccessibility in human exposure assessment, and the challenges faced. Overall, most in-vitro methods were validated using bioavailability, and better in vitro-in vivo correlations were obtained when absorption sinks were added to the digestion solution to mimic dynamic absorption of organic chemicals by small intestine. Incorporating bioaccessibility into the estimation of human exposure by oral ingestion significantly decreases the estimated exposure dose. However, more investigations on bioaccessibility of hydrophobic organic compounds are urgently needed because many challenges for in-vitro methods remain to be overcome.

Evaluating oral and inhalation bioaccessibility of indoor dust-borne short- and median-chain chlorinated paraffins using in vitro Tenax-assisted physiologically based method

Though ingestion and inhalation of dust have been suggested as important exposure routes contributing chlorinated paraffins (CPs) build-up in humans, the bioaccessibility of dust-borne CPs in the organ environment has not been well-studied, which may hinder an accurate estimation of exposure risks. In this study, the ingestion and inhalation bioaccessibility of dust-borne short- and median-chain CPs (SCCPs and MCCPs) was assessed using (colon-extended) physiologically based extraction test with the addition of Tenax. The ingestion bioaccessibility of SCCPs 51.5 %Cl, SCCPs 63 %Cl, MCCPs 42 %Cl, and MCCPs 57 %Cl was in ranges of 21.1-44.0 %, 11.7-45.8 %, 21.9-36.6 %, and 7.9-32.9 %, respectively. Multiple linear regression analysis demonstrated statistically significant associations of ingestion bioaccessibility with carbon chain length and chlorine substitution. The ingestion bioaccessibility of CPs also increased with co-existence of carbohydrate/protein. The inhalation bioaccessibility of SCCPs (16.7-38.7 % in artificial lysosomal fluid and 15.5-34.1 % in modified Gamble solution) was significantly higher than MCCPs (<5 %), and varied with dust particle size/total organic carbon content. Our study indicates that modest bioaccessible fractions of CPs in dust should be taken into account to refine the estimation of human exposure, and their bioaccessibility may be affected by CP molecular size, nutritional content and dust property.

A review of organophosphate esters in indoor dust, air, hand wipes and silicone wristbands: Implications for human exposure

The ubiquity of organophosphate esters (OPEs) in various environmental matrices inevitably pose human exposure risks. Numerous studies have investigated human exposure pathways to OPEs, including air inhalation, dust ingestion, dermal contact, and dietary and drinking water intake, and have indicated that indoor dust and indoor air routes are frequently the two main human exposure pathways. This article reviews the literature on OPE contamination in indoor air and dust from various microenvironments and on OPE particle size distributions and bioavailability in dust conducted over the past 10 years. Ways in which sampling strategies are related to the uncertainty of exposure assessment results and comparability among different studies in terms of sampling tools, sampling sites, and sample types are addressed. Also, the associations of OPEs in indoor dust/air with human biological samples were summarized. Studies on two emerging matrices, hand wipes and silicone wristbands, are demonstrated to be more comprehensive and accurate in reflecting personal human exposure to OPEs in microenvironments and are summarized. Given the direct application of some diester OPEs (di-OPEs) in numerous products, research on their existence in indoor dust and food and on their effects on human urine are also discussed. Finally, related research trends and avenues for future research are prospected.

Bioaccessibilities of metal(loid)s and organic contaminants in particulates measured in simulated human lung fluids: A critical review

Particle-bound pollutants can pose a health risk to humans. Inhalation exposure evaluated by total contaminant concentrations significantly overestimates the potential risk. To assess the risk more accurately, bioavailability, which is the fraction that enters into the systemic circulation, should be considered. Researchers have replaced bioavailability by bioaccessibility due to the rapid and cost-efficient measurement for the latter, especially for assessment by oral ingestion. However, contaminants in particulates have different behavior when inhaled than when orally ingested. Some of the contaminants are exhaled along with exhalation, and others are deposited in the lung with the particulates. In addition, a fraction of the contaminants is released into the lung fluid and absorbed by the lung, and another fraction enters systemic circulation under the action of cell phagocytosis on particulates. Even if the release fraction, i.e., release bioaccessibility, is considered, the measurement faces many challenges. The present study highlights the factors influencing release bioaccessibility and the incorporation of inhalation bioaccessibility into the risk assessment of inhaled contaminants. Currently, there are three types of extraction techniques for simulated human lung fluids, including simple chemical solutions, sequential extraction techniques, and physiologically based techniques. The last technique generally uses three kinds of solution: Gamble's solution, Hatch's solution, and artificial lysosomal fluid, which are the most widely used physiologically based simulated human lung fluids. External factors such as simulated lung fluid composition, pH, extraction time, and sorption sinks can affect release bioaccessibility, whereas particle size and contaminant properties are important internal factors. Overall, release bioaccessibility is less used than bioaccessibility considering the deposition fraction when assessing the risk of contaminants in inhaled particulates. The release bioaccessibility measurement poses two main challenges: developing a unified, accurate, stable, simple, and systematic biologically based method, and validating the method through in-vivo assays.

The Influence of Food on the In Vivo Bioavailability of DDT and Its Metabolites in Soil

Incidental soil ingestion is considered to be an important route of exposure to hydrophobic organic contaminants (HOCs), such as dichlorodiphenyl-trichloroethane (DDT). Contaminant ingestion often occurs during food consumption; however, knowledge on the influence of food on DDT bioavailability remains limited. In this study, the relative bioavailability (RBA) of soil DDTr (i.e., DDT and metabolites) was determined using an in vivo mouse model in the presence of eight kinds of food including rice, egg, pork, pear, soybean, bread, spinach, and milk powder. The values of DDTr-RBA ranged from 19.8 ± 10.9 to 114 ± 25.1%. DDTr-RBA was positively correlated with fat (r = 0.71) and negatively correlated with fiber (r = 0.63) content in food. A mechanistic study showed that fat enhanced micellarization and promoted the formation of chylomicron, which facilitated the dissolution and transport of DDTr in the intestinal tract. Bioaccessibility of DDTr was determined using a physiologically based in vitro method. The addition of lipase significantly improved the ability of the method to predict DDTr-RBA, indicating that the "fasted state" in vitro method required optimization for food scenarios. To the best of our knowledge, this is the first study to explore the mechanistic influence of food on DDTr-RBA and provide important knowledge on dietary approaches for reducing exposure to HOCs.

Membrane Enhanced Bioaccessibility Extraction (MEBE) of hydrophobic soil pollutants - Using a semipermeable membrane for separating desorption medium and acceptor solvent

Bioaccessibility extractions are increasingly applied to measure the fraction of pollutants in soil, sediment and biochar, which can be released under environmentally or physiologically relevant conditions. However, the bioaccessibility of hydrophobic organic chemicals (HOCs) can be markedly underestimated when the sink capacity of the extraction medium is insufficient. Here, a novel method called "Membrane Enhanced Bioaccessibility Extraction" (MEBE) applies a semipermeable membrane to physically separate an aqueous desorption medium that sets the desorption conditions from an organic medium that serves as acceptor phase and infinite sink. The specific MEBE method combines HOC (1) desorption into a 2-hydroxypropyl-β-cyclodextrin solution, (2) transfer through a low-density polyethylene (LDPE) membrane and (3) release into ethanol, serving as analytical acceptor phase. The surface to volume ratio within the LDPE membrane is maximized for rapid depletion of desorbed molecules, and the capacity ratio between the acceptor phase and the environmental sample is maximized to achieve infinite sink conditions. Several experiments were conducted for developing, optimizing and pre-testing the method, which was then applied to four soils polluted with polycyclic aromatic hydrocarbons. MEBE minimized sample preparation and yielded a solvent extract readily analyzable by HPLC. This study focused on the proof-of-principle testing of the MEBE concept, which now can be extended and applied to other samples and desorption media.

In vitro gastrointestinal mobilization and oral bioaccessibility of PAHs in contrasting soils and associated cancer risks: Focus on PAH nonextractable residues

The gastrointestinal mobilization and oral bioaccessibility of polycyclic aromatic hydrocarbon (PAH) nonextractable residues (NERs) from soils remain unexplored, including associated incremental lifetime cancer risks. This study investigated the gastrointestinal mobilization of PAHs and their NERs from contrasting soils, using a physiologically based extraction test that incorporates a silicone-rod (Si-Org-PBET) as PAH sink. Associated cancer risks following soil ingestion were also evaluated. Four solvent-spiked and aged soils, and four long-term contaminated manufactured gas plant (MGP) soils, were utilized. Total-extractable PAH concentrations were measured after exhaustive solvent extractions of soils. We evaluated the PAH sorption efficiency of the silicone rods and associated sorption kinetics, using PAH-spiked silica sand as the contaminated matrix. We then assessed gastrointestinal mobilization of benzo[a]pyrene and benzo[a]pyrene NERs from the solvent-spiked soils, and mobilization of six PAHs and their NERs from the MGP soils. PAH oral bioaccessibility was determined. The incremental lifetime cancer risks (ILCRs), using Si-Org-PBET- and total-extractable PAH concentrations from the MGP soils, were calculated. Sorption kinetics modelling showed that 95% of mobilized PAHs sorbed to the silicone rods within 2-19 h, depending on PAH physico-chemical properties. Total-extractable and Si-Org-PBET extractable PAH concentrations exceeded health investigation levels (3 mg/kg based on benzo[a]pyrene toxic equivalent quotients) in soils. PAH oral bioaccessibility approached 100% for solvent-spiked soils, but only 24-36% for the MGP soils. Associated ILCRs exceeded target levels (10^-5) for one MGP soil, particularly for 2-3 year olds, despite oral bioaccessibility considerations. In contrast, mobilized PAH NERs did not exceed health investigation and ILCR levels, as the NERs were highly sequestered, especially in the MGP soils. PAH nonextractable residues in long-term contaminated soils are unlikely to be mobilized in concentrations that pose cancer risks to humans following soil ingestion, and do not need to be considered in risk assessments.

When Fluorescence Is not a Particle: The Tissue Translocation of Microplastics in Daphnia magna Seems an Artifact

Previous research reported the translocation of nano- and microplastics from the gastrointestinal tract to tissues in Daphnia magna, most prominently of fluorescent polystyrene beads to lipid droplets. For particles >300 nm, such transfer is biologically implausible as the peritrophic membrane retains these in the daphnid gut. We used confocal laser scanning microscopy to study tissue transfer applying the setup from a previous study (neonates exposed to 20 and 1000 nm polystyrene beads at 2 µg L^-1 for 4 and 24 h), the same setup with a fructose-based clearing, and a setup with a 1000-fold higher concentration (2 mg L^-1 ). We used passive sampling to investigate whether the beads leach the fluorescent dye. Although the 1000 nm beads were visible in the gut at both exposure concentrations, the 20 nm beads were detectable at 2 mg L^-1 only. At this concentration, we observed fluorescence in lipid droplets in daphnids exposed to both particle types. However, this did not colocalize with the 1000 nm beads, which remained visible in the gut. We further confirmed the leaching of the fluorescent dye using a passive sampler, a method that can also be applied in future studies. In summary, we cannot replicate the original study but demonstrate that the fluorescence in the lipid droplets of D. magna results from leaching of the dye. Thus, the use of fluorescence as a surrogate for particles can lead to artifacts in uptake and translocation studies. This highlights the need to confirm the stability of the fluorescence label or to localize particles using alternative methods. Environ Toxicol Chem 2019;38:1495-1503. © 2019 SETAC OPEN PRACTICES: The present study has earned Open Data/Materials badges for making publicly available the digitally shareable data necessary to reproduce the reported results. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki.

Ingestion bioaccessibility of indoor dust-bound PAHs: Inclusion of a sorption sink to simulate passive transfer across the small intestine

In this study, we investigated the levels of 12 priority polycyclic aromatic hydrocarbons (PAH₁₂) pollutants, bioaccessible PAH₁₂, and sorption sink for PAH₁₂ by a silicone sheet of indoor dust samples, which were collected from teachers' offices (n = 17), students' offices (n = 17), laboratory (n = 11), and experimental center (n = 9), using an in vitro digestive model. In PAH₁₂, bioaccessible PAH₁₂, and sorption sink PAH₁₂, benzo[b]fluoranthene (BbF), phenanthrenes (Phe), and fluoranthene (FLA) were labeled respectively the most significant PAHs (6.61 ± 4.42 μg/g, 0.16 ± 0.11 μg/g, and 0.08 ± 0.06 μg/g) after indoor dust ingestion, whereas the proportions of anthracene (Ant), benzo(g,h,i)perylene (BghiP), and BghiP (0.34 ± 0.17, 0.03 ± 0.03 and 0.01 ± 0.01 μg/g) were low. Based on benzo[a]pyrene- equivalent carcinogenic concentrations, the mean daily exposure of bioaccessible PAH₁₂ and sorption sink for PAH₁₂ by indoor dust ingestion was 4.07 × 10^-3 ± 1.73 × 10^-3 and 3.23 × 10^-3 ± 1.36 × 10^-3 μg/day in the experimental center; 4.01 × 10^-3 ± 2.05 × 10^-3 and 1.46 × 10^-3 ± 6.72 × 10^-4 μg/day in students' offices; 8.25 × 10^-4 ± 2.33 × 10^-4 and 5.15 × 10^-4 ± 1.37 × 10^-4 μg/day in laboratory; and 7.05 × 10^-4 ± 4.12 × 10^-5 and 2.82 × 10^-4 ± 4.36 × 10^-5 μg/day in teachers' offices, respectively. Our results indicated that the passive transfer fraction of PAH₁₂ (44.07%-67.36% in this case) is therefore large and needs to be considered in exposure and risk assessments.

Relationships between the bioavailability of polybrominated diphenyl ethers in soils measured with female C57BL/6 mice and the bioaccessibility determined using five in vitro methods

Several in vitro methods for simulating human gastrointestinal digestion have been validated for predicting the bioavailability of heavy metals, but the methods for successfully predicting the bioavailability of organic pollutants are still limited. In this study, we used an adapted fasting in vitro digestion method (Fa-VDM) from the Simulator of the Human Intestinal Microbial Ecosystem and four other in vitro methods comprising In Vitro Gastrointestinal, a physiologically-based extraction test, the unified BARGE method, and Deutsches Institut für Normung e.V. in order to measure the bioaccessibility of polybrominated diphenyl ethers (PBDEs) in soils from an e-waste dismantling town, China, with a Standard Reference Material (SRM2585) as the control. Furthermore, the bioaccessibility data were compared with the bioavailability measured using female C57BL/6 mice. The bioavailability of PBDEs in the soils and SRM2585 were 1.7% to 38.1% and 3.9% to 48.8%, respectively, and the bioaccessibility determined using Fa-VDM were 1.6-55.4% and 6.7-32.1%. There were negative and parabolic correlations between octanol/water partition coefficient for PBDEs and the bioavailability and bioaccessibility, respectively, whereas the H/C ratios and organic matter contents of the soils did not correlate with them. The bioaccessibility data determined by Fa-VDM were generally higher than those obtained using the other four methods, mainly due to the higher bile concentration and larger liquid to solid ratio in the digestion solution in Fa-VDM. There was a significant linear relationship between the results according to the in vivo and in vitro method of Fa-VDM where the slopes varied from 0.83 to 1.16 (R² > 0.73) and intercepts from 0.3%-7.7% for BDE47, 99, 100, and 153 measured using Fa-VDM, thereby indicating that the bioaccessibility assessed by this method can potentially be used to predict the bioavailability of moderately brominated congeners in soils.

Comparison of sorption kinetics of PAHs by sorptive sinks and caco-2 cell and the correlation between bioaccessibility and bioavailability of PAHs in indoor dust

Sorptive sinks are extensively used in the bioaccessibility of organic contaminants, but their suitability for simulating the intestinal cell is seldom reported. In the present study, the sorption efficiency of PAHs by sorptive sinks including silica, poly(ethylene-co-vinyl acetate) (polyE), tenax, and C18 were compared with that by caco-2 cells. The elimination rate constants of phenanthrene, fluoranthene, pyrene, benzo(a)pyrene by caco-2 cell were 0.0417 ± 0.006 min^-1, 0.0411 ± 0.0074 min^-1, 0.0362 ± 0.006 min^-1, and 0.0526 ± 0.0037 min^-1, respectively, which were more closely to that of silica and polyE compared to other materials. This indicated that these materials might be the preferable sorptive sinks to simulate absorption of PAHs by intestinal cells. The bioaccessibility of phenanthrene, fluoranthene, pyrene, benzo(a)pyrene in indoor dust ranged from 15.5-43.5%, 9.10-38.8%, 10.0-37.9%, and 6.00-21.9%, respectively, based on physiologically based extraction test (PBET) and the sorptive sinks added in the intestinal solution led to 1.17 to 8.47-fold enhancement of bioaccessibility. The correlation of in vivo PAHs relative bioavailability (RBA) and in vitro digestion bioaccessibility with or without the sorptive sinks of indoor dust were measured, and the results indicated that silica and polyE were more likely to predict PAHs RBA of indoor dust, which was consistent with the results of sorption kinetics assay. The present results indicate that silica and polyE have the potential to simulate caco-2 cell and the inclusion of these materials in the PBET is likely to predict PAHs RBA in indoor dust. Capsule: Silica and polyE were more likely to simulate absorption of PAHs by intestinal cells, and to predict PAHs RBA of indoor dust.

In vitro assessment of pyrethroid bioaccessibility via particle ingestion

Due to their intensive use in agricultural and residential pest control, human exposure to residues of multiple pyrethroids frequently occurs. Pyrethroids have exceptionally high affinity for solid particles, highlighting the need to understand human exposure through oral ingestion of contaminated soil or dust particles. In this study, we used artificial gastrointestinal fluids to measure the desorption or bioaccessibility of eight current-use pyrethroids in soil and dust samples. Tenax was further included as a sink in parallel treatments to simulate the effect of removal due to transfer of pyrethroids to lipid membranes. The use of 0.4 g of Tenax in 20 mL digestive fluids resulted in rapid and efficient trapping of pyrethroids, and further, greatly increased bioaccessibility. In the artificial digestive fluids without Tenax, 6.0-48.0% of pyrethroids were desorbed over 21 h, and the fractions increased by 1.6-4.1 folds to 21.5-79.3% with the Tenax sink. Therefore, 6.0-79.3% of soil or dust-borne pyrethroids may be considered bioavailable upon ingestion. While protein and sucrose increased the estimated bioaccessibility, co-presence of lipid (vegetable oil) decreased the bioaccessibility of pyrethroids, likely due to competitive phase partition. Pyrethroids were also found to be unstable in the artificial intestinal fluid containing pancreatin, further decreasing the potential bioaccessibility of pyrethroids on soil or dust particles. The limited bioaccessibility should be considered to refine the prediction of human exposure and risk through oral ingestion of pyrethroid residues.

Oral bioaccessibility of semi-volatile organic compounds (SVOCs) in settled dust: A review of measurement methods, data and influencing factors

Many semi-volatile organic compounds (SVOCs), suspected of reprotoxic, neurotoxic or carcinogenic effects, were measured in indoor settled dust. Dust ingestion is a non-negligible pathway of exposure to some of these SVOCs, and an accurate knowledge of the real exposure is necessary for a better evaluation of health risks. To this end, the bioaccessibility of SVOCs in dust needs to be considered. In the present work, bioaccessibility measurement methods, SVOCs' oral bioaccessibility data and influencing factors were reviewed. SVOC bioaccessibilities (%) ranged from 11 to 94, 8 to 100, 3 to 92, 1 to 81, 6 to 52, and 2 to 17, for brominated flame retardants, organophosphorus flame retardants, polychlorobiphenyls, phthalates, pesticides and polycyclic aromatic hydrocarbons, respectively. Measurements method produced varying results depending on the inclusion of food and/or sink in the model. Characteristics of dust, e.g., organic matter content and particle size, also influenced bioaccessibility data. Last, results were influenced by SVOC properties, such as octanol/water partition coefficient and migration pathway into dust. Factors related to dust and SVOCs could be used in prediction models. To this end, more bioaccessibility studies covering more substances should be performed, using methods that are harmonized and validated by comparison to in-vivo studies.

Applying no-depletion equilibrium sampling and full-depletion bioaccessibility extraction to 35 historically polycyclic aromatic hydrocarbon contaminated soils

Assessing the bioaccessibility of organic pollutants in contaminated soils is considered a complement to measurements of total concentrations in risk assessment and legislation. Consequently, methods for its quantification require validation with historically contaminated soils. In this study, 35 such soils were obtained from various locations in Switzerland and Cuba. They were exposed to different pollution sources (e.g., pyrogenic and petrogenic) at various distance (i.e., urban to rural) and were subject to different land use (e.g., urban gardening and forest). Passive equilibrium sampling with polyoxymethylene was used to determine freely dissolved concentrations (C_free) of polycyclic aromatic hydrocarbons (PAHs), while sorptive bioaccessibility extraction (SBE) with silicone rods was used to determine the bioaccessible PAH concentrations (C_bioacc) of these soils. The organic carbon partition coefficients of the soils were highest for skeet soils, followed by traffic, urban garden and rural soils. Lowest values were obtained from soil exposed to petrogenic sources. Applicability of SBE to quantify C_bioacc was restricted by silicone rod sorption capacity, as expressed quantitatively by the Sorption Capacity Ratio (SCR); particularly for soils with very high K_D. The source of contamination determined bioaccessible fractions (f_bioacc). The smallest f_bioacc were obtained with skeet soils (15%), followed by the pyrogenically influenced soils, rural soils, and finally, the petrogenically contaminated soil (71%). In conclusion, we present the potential and limitations of the SBE method to quantify bioaccessibility in real soils. These results can be used for additional development of this and similar bioaccessibility methods to guarantee sufficient sorption capacity to obtain reliable results.

Bioaccessibility of PBDEs present in indoor dust: A novel dialysis membrane method with a Tenax TA® absorption sink

Human uptake of flame retardants (FRs) such as polybrominated diphenyl ethers (PBDEs) via indoor dust ingestion is commonly considered as 100% bioaccessible, leading to potential risk overestimation. Here, we present a novel in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax TA® as an absorptive "sink" capable to enhance PBDE gut bioaccessibility. A cellulose-based dialysis membrane (MW cut-off 3.5kDa) with high pH and temperature tolerance was used to encapsulate Tenax TA®, facilitating efficient physical separation between the absorbent and the dust, while minimizing re-absorption of the ingested PBDEs to the dust particles. As a proof of concept, PBDE-spiked indoor dust samples (n=3) were tested under four different conditions; without any Tenax TA® addition (control) and with three different Tenax TA® loadings (i.e. 0.25, 0.5 or 0.75g). Our results show that in order to maintain a constant sorptive gradient for the low MW PBDEs, 0.5g of Tenax TA® are required in CE-PBET. Tenax TA® inclusion (0.5g) resulted in 40% gut bioaccessibility for BDE153 and BDE183, whereas greater bioaccessibility values were seen for less hydrophobic PBDEs such as BDE28 and BDE47 (~60%). When tested using SRM 2585 (n=3), our new Tenax TA® method did not present any statistically significant effect (p>0.05) between non-spiked and PBDE-spiked SRM 2585 treatments. Our study describes an efficient method where due to the sophisticated design, Tenax TA® recovery and subsequent bioaccessibility determination can be simply and reliably achieved.

In vitro prediction of polycyclic aromatic hydrocarbon bioavailability of 14 different incidentally ingested soils in juvenile swine

Predicting mammalian bioavailability of PAH mixtures from in vitro bioaccessibility results has proven to be an elusive goal. In an attempt to improve in vitro predictions of PAH soil bioavailability we investigated how energetic input influences PAH bioaccessibility by using a high and low energetic shaking method. Co-inertia analysis (COIA), and Structural Equation Modeling (SEM) were also used to examine PAH-PAH interactions during ingestion. PAH bioaccessibility was determined from 14 historically contaminated soils using the fed organic estimation of the human simulation test (FOREhST) with inclusion of a silicone rod as a sorption sink and compared to bioavailability estimates from the juvenile swine model. Shaking method significantly affected PAH bioaccessibility in the FOREhST model, with PAH desorption from the high energy FOREhST almost an order of magnitude greater compared to the low energy FOREhST. PAH-PAH interactions significantly influenced PAH bioavailability and when these interactions were used in a linear model, the model predicted benzo(a)anthracene bioavailability with an slope of 1 and r² of 0.66 and for benzo(a)pyrene bioavailability has a slope of 1 and r² of 0.65. Lastly, to confirm the effects as determined by COIA and SEM, we spiked low levels of benzo(a)anthracene into historically contaminated soils, and observed a significant increase in benzo(a)pyrene bioaccessibility. By accounting for PAH interactions, and reducing the energetics of in vitro extractions, we were able to use bioaccessibility to predict bioavailability across 14 historically contaminated soils. Our work suggests that future work on PAH bioavailability and bioaccessibility should focus on the dynamics of how the matrix of PAHs present in the soil interact with mammalian systems. Such interactions should not only include the chemical interactions discussed here but also the interactions of PAH mixtures with mammalian uptake systems.

Bioaccessibility of PAHs in contaminated soils: Comparison of five in vitro methods with Tenax as a sorption sink

For hydrophobic organic contaminants, physiologically based in vitro methods may need to include a sorption sink to simulate in vivo intestinal uptake. We compared PAH bioaccessibility in contaminated soils using five in vitro methods including physiologically based extraction test (PBET), in vitro digestion assay (IVD), method from Deutsches Institut für Normung (DIN), unified bioaccessibility method (UBM), and fed organic estimation human simulation test (FOREhST) in the absence and presence of Tenax as a sorption sink. The PAH bioaccessibility without Tenax were pretty low with values ranging from below detection limit to 13.4%, indicating the limited capacity of these in vitro models to accommodate PAHs. With addition of Tenax, bioaccessibility increased to 0.59-75.5% for all PAH congeners. Even with the dominant effect of sorption sink, bioaccessibility values significantly varied among all the five methods with DIN result being the highest at 7.0-34.8%. Based on multiple linear regression, Tenax, incubation time, and bile contents are identified to be the most important factors in controlling bioaccessibility. The understanding of these key factors for bioaccessibility is highly necessary to standardize in vitro methods, which helps to refine the assessment of health risk through exposure to ingested contaminants.

Relative bioavailability and bioaccessibility of PCBs in soils based on a mouse model and Tenax-improved physiologically-based extraction test

In this study, bioavailability of polychlorinated biphenyls (PCBs) in soil samples aged for various time intervals (7 days, 1 and 5 months) was assessed by in vivo tests using mice. The in vivo bioavailability of PCBs in soil ranged from 45% (PCB180 in soil aging for 5 month) to 119% (PCB52 in soil aging for 1 month), indicating that not all PCBs was available for absorption after ingestion of soil samples. The bioaccessibility was assessed using both physiologically-based extraction test (PBET) and Tenax improved PBET (TI-PBET). Acceptable in vivo-in vitro correlation (r² = 0.70 and slope = 1.30 ± 0.20) was observed for TI-PBET, not for PBET. Due to dominant role played by Tenax and bile, the TI-PBET was further simplified to Tenax and Tenax-bile extraction methods. However, poor in vivo-in vitro correlation (r² = 0.14 and 0.05) was observed for the two simplified methods, which may be attributed to the combined effect between sorption sink and components in PBET. Therefore, in order to simply TI-PBET or standardize in vitro methods, it is highly necessary to explore the mechanism about the interaction between in vitro method components and sorption sink, or to screen key factors for bioaccessibility results in the future studies.

Bioavailability and bioaccessibility of polycyclic aromatic hydrocarbons from (post-pyrolytically treated) biochars

Bioaccessibility data of PAHs from biochar produced under real world conditions is scarce and the influence of feedstock and various post-pyrolysis treatments common in agriculture, such as co-composting or lacto-fermentation to produce silage fodder, on their bioavailability and bioaccessibility has hardly been studied. The total (C_total), and freely dissolved (i.e., bioavailable) concentrations (C_free) of the sum of 16 US EPA PAHs of 43 biochar samples produced and treated in such ways ranged from 0.4 to almost 2000 mg/kg, and from 12 to 81 ng/L, respectively, which resulted in very high biochar-water partition coefficients (4.2 ≤ log K_D ≤ 8.8 L/kg) for individual PAHs. Thirty three samples were incubated in contaminant traps that combined a diffusive carrier and a sorptive sink. Incubations yielded samples only containing desorption-resistant PAHs (C_res). The desorption resistant PAH fraction was dominant, since only eight out of 33 biochar samples showed statistically significant bioaccessible fractions (f_{bioaccessible} = 1 - C_res/C_total). Bioavailability correlated positively with C_total/surface area. Other relationships of bioavailability and -accessibility with the investigated post-pyrolysis processes or elemental composition could not be found. PAH exposure was very limited (low C_free, high C_res) for all samples with low to moderate C_total, whereas higher exposure was determined in some biochars with C_total > 10 mg/kg.

Significance of Cooking Oil to Bioaccessibility of Dichlorodiphenyltrichloroethanes (DDTs) and Polybrominated Diphenyl Ethers (PBDEs) in Raw and Cooked Fish: Implications for Human Health Risk

The present study examined the bioacessibility of DDTs and PBDEs in cooked fish (yellow grouper; Epinephelus awoara) with and without heating using the colon extended physiologically based extraction test. The bioaccessibility of DDTs and PBDEs increased from 60 and 26% in raw fish to 83 and 63%, respectively, after the addition of oil to raw fish. However, they decreased from 83 to 66% and from 63 to 40%, respectively, when oil-added fish were cooked. Human health risk assessment based on bioaccessible concentrations of DDTs and PBDEs in fish showed that the maximum allowable daily fish consumption rates decreased from 25, 59, and 86 g day^-1 to 22, 53, and 77 g day^-1 for children, youths, and adults, respectively, after fish were cooked with oil. These findings indicated that the significance of cooking oil to the bioaccessibility of DDTs and PBDEs in food should be considered in assessments of human health risk.

Bioaccessibility of nitro- and oxy-PAHs in fuel soot assessed by an in vitro digestive model with absorptive sink

Ingestion of soot present in soil or other environmental particles is expected to be an important route of exposure to nitro and oxygenated derivatives of polycyclic aromatic hydrocarbons (PAHs). We measured the apparent bioaccessibility (B_app) of native concentrations of 1-nitropyrene (1N-PYR), 9-fluorenone (9FLO), anthracene-9,10-dione (ATQ), benzo[a]anthracene-7,12-dione (BaAQ), and benzanthrone (BZO) in a composite fuel soot sample using a previously-developed in vitro human gastrointestinal model that includes silicone sheet as a third-phase absorptive sink. Along with B_app, we determined the 24-h sheet-digestive fluid partition coefficient (K_s,24h), the soot residue-fluid distribution ratio of the labile sorbed fraction after digestion (K_r,lab), and the maximum possible (limiting) bioaccessibility, B_lim. The B_app of PAH derivatives was positively affected by the presence of the sheet due to mass-action removal of the sorbed compounds. In all cases B_app increased with imposition of fed conditions. The enhancement of B_app under fed conditions is due to increasingly favorable mass transfer of target compounds from soot to fluid (increasing bile acid concentration, or adding food lipids) or transfer from fluid to sheet (by raising small intestinal pH). Food lipids may also enhance B_app by mobilizing contaminants from nonlabile to labile states of the soot. Compared to the parent PAH, the derivatives had larger K_r,lab, despite having lower partition coefficients to various hydrophobic reference phases including silicone sheet. The B_lim of the derivatives under the default conditions of the model ranged from 65.5% to 34.4%, in the order, 1N-PYR > ATQ > 9FLO > BZO > BaAQ, with no significant correlation with hydrophobic parameters, nor consistent relationship with B_lim of the parent PAH. Consistent with earlier experiments on a wider range of PAHs, the results suggest that a major determinant of bioaccessibility is the distribution of chemical between nonlabile and labile states in the original solid.

Oral relative bioavailability of Dichlorodiphenyltrichloroethane (DDT) in contaminated soil and its prediction using in vitro strategies for exposure refinement

In this study, the bioavailability of DDTr (sum of DDT, DDD and DDE isomers) in pesticide-contaminated soil was assessed using an in vivo mouse model. DDTr relative bioavailability (RBA) ranged from 18.7±0.9 (As35) to 60.8±7.8% (As36) indicating that a significant portion of soil-bound DDTr was not available for absorption following ingestion. When DDTr bioaccessibility was assessed using the organic Physiologically Based Extraction Test (org-PBET), the inclusion of a sorption sink (silicone cord) enhanced DDTr desorption by up to 20-fold (1.6-3.8% versus 18.9-56.3%) compared to DDTr partitioning into gastrointestinal fluid alone. Enhanced desorption occurred as a result of the silicone cord acting as a reservoir for solubilized DDTr to partition into, thereby creating a flux for further desorption until equilibrium was achieved. When the relationship between in vivo and in vitro data was assessed, a strong correlation was observed between the mouse bioassay and the org-PBET+silicone cord (slope=0.94, y-intercept=3.5, r(2)=0.72) suggesting that the in vitro approach may provide a robust surrogate measure for the prediction of DDTr RBA in contaminated soil.

Advances in in vitro methods to evaluate oral bioaccessibility of PAHs and PBDEs in environmental matrices

Cleanup goals for sites contaminated with persistent organic pollutants (POPs) are often established based on total contaminant concentrations. However, mounting evidence suggests that understanding contaminant bioavailability in soils is necessary for accurate assessment of contaminant exposure to humans via oral ingestion pathway. Animal-based in vivo tests have been used to assess contaminant bioavailability in soils; however, due to ethical issues and cost, it is desirable to use in vitro assays as alternatives. Various in vitro methods have been developed, which simulate human gastrointestinal (GI) tract using different digestion fluids. These methods can be used to predict POP bioavailability in soils, foods, and indoor dust after showing good correlation with in vivo animal data. Here, five common in vitro methods are evaluated and compared using PAHs and PBDEs as an example of traditional and emerging POPs. Their applications and limitations are discussed while focusing on method improvements and future challenges to predict POP bioavailability in different matrices. The discussions should shed light for future research to accurately assess human exposure to POPs via oral ingestion pathway.

Oral Bioavailability, Bioaccessibility, and Dermal Absorption of PAHs from Soil-State of the Science

This article reviews the state of the science regarding oral bioavailability, bioaccessibility, and dermal absorption of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in soil by humans, and discusses how chemical interactions may control the extent of absorption. Derived from natural and anthropomorphic origins, PAHs occur in a limited number of solid and fluid matrices (i.e., PAH sources) with defined physical characteristics and PAH compositions. Existing studies provide a strong basis for establishing that oral bioavailability of cPAHs from soil is less than from diet, and an assumption of 100% relative bioavailability likely overestimates exposure to cPAHs upon ingestion of PAH-contaminated soil. For both the oral bioavailability and dermal absorption studies, the aggregate data do not provide a broad understanding of how different PAH source materials, PAH concentrations, or soil chemistries influence the absorption of cPAHs from soil. This article summarizes the existing studies, identifies data gaps, and provides recommendations for the direction of future research to support new default or site-specific bioavailability adjustments for use in human health risk assessment.

How to Determine the Environmental Exposure of PAHs Originating from Biochar

Biochars are obtained by pyrolyzing biomass materials and are increasingly used within the agricultural sector. Owing to the production process, biochars can contain polycyclic aromatic hydrocarbons (PAHs) in the high mg/kg range, which makes the determination of the environmental exposure of PAHs originating from biochars relevant. However, PAH sorption to biochar is characterized by very high (10(4)-10(6) L/kg) or extreme distribution coefficients (KD) (>10(6) L/kg), which makes the determination of exposure scientifically and technically challenging. Cyclodextrin extractions, sorptive bioaccessibility extractions, Tenax extractions, contaminant traps, and equilibrium sampling were assessed and selected methods used for the determination of bioavailability parameters for PAHs in two model biochars. Results showed that: (1) the KD values of typically 10(6)-10(9) L/kg made the biochars often act as sinks, rather than sources, of PAHs. (2) Equilibrium sampling yielded freely dissolved concentrations (pg-ng/L range) that were below or near environmental background levels. (3) None of the methods were found to be suitable for the direct measurement of the readily desorbing fractions of PAHs (i.e., bioacessibility) in the two biochars. (4) The contaminant-trap method yielded desorption-resistant PAH fractions of typically 90-100%, implying bioaccessibility in the high μg/kg to low mg/kg range.

Predicting the Relative Bioavailability of DDT and Its Metabolites in Historically Contaminated Soils Using a Tenax-Improved Physiologically Based Extraction Test (TI-PBET)

Due to their static nature, physiologically based in vitro assays often fail to provide sufficient sorption capacity for hydrophobic organic contaminants (HOCs). The addition of a sorption sink to in vitro intestinal solution has the potential to mimic dynamic intestinal uptake for HOCs, thereby increasing their desorption from soil. However, the effectiveness of sorption sinks for improving in vitro assays needs to be compared with in vivo data. In this study, Tenax was added as a sorption sink into the physiologically based extraction test (PBET), while DDT and its metabolites (DDTr) were investigated as typical HOCs. Tenax added at 0.01-0.2 g to the PBET intestinal solution sorbed ∼100% of DDTr in 6.3-19 min, indicating its ability as an effective sorption sink. DDTr bioaccessibility in six contaminated soils using Tenax-improved PBET (TI-PBET; 27-56%) was 3.4-22 fold greater than results using the PBET (1.2-15%). In vivo DDTr relative bioavailability (RBA) was measured using a mouse adipose model with values of 17.9-65.4%. The inclusion of Tenax into PBET improved the in vivo-in vitro correlation from r(2) = 0.36 (slope = 2.1 for PBET) to r(2) = 0.62 (slope = 1.2 for TI-PBET), illustrating that the inclusion of Tenax as a sorption sink improved the in vitro prediction of DDTr RBA in contaminated soils.

Using in vitro bioaccessibility to refine estimates of human exposure to PAHs via incidental soil ingestion

PAH bioaccessibility in contaminated soil was determined using the organic physiologically based extraction test with the inclusion of a sorption sink. Silicone cord was incorporated into the assay in order to overcome the limited capacity of the in vitro medium to accommodate desorbable PAHs. Initially, silicone cord sorption efficacy was determined by assessing sorption kinetics using PAH-spiked sand (phenanthrene, pyrene and benzo[a]pyrene; 10-1000mgkg(-1)). Irrespective of PAH and concentration, >95% of the initial PAH mass partitioned into the silicone cord within 12h although rates were lower at higher concentration and with increasing hydrophobicity. When PAH bioaccessibility was assessed in contaminated soil (n=18), contamination source (i.e. pyrogenic versus petrogenic) influenced PAH bioaccessibility. Individual PAH bioaccessibility ranged up to 81.7±2.7% although mean values ranged from 2.1 (acenaphthalene) to 20.8% (benzo[k]fluoranthene) with upper 95% confidence intervals of the means of 4.5 and 28.3% respectively. Although a PAH in vivo-in vitro correlation is yet to be established, bioaccessibility approaches incorporating sorption sinks represent a robust approach for estimating PAH bioavailability as the desorbable fraction may be a conservative measure of the absorbable fraction.

Bioaccessibility of PAHs in Fuel Soot Assessed by an in Vitro Digestive Model with Absorptive Sink: Effect of Food Ingestion

We investigated the effects of changing physiological conditions in the digestive tract expected with food ingestion on the apparent bioaccessibility (Bapp) of 11 polycyclic aromatic hydrocarbons (PAHs) in a fuel soot. A previously established in vitro digestive model was applied that included silicone sheet as a third-phase absorptive sink simulating passive transfer of PAHs to intestinal epithelium in the small intestine stage. The Bapp is defined as the fraction found in the digestive fluid plus sheet after digestion. We determined that Bapp was independent of gastric pH and addition of nonlipid milk representing dietary proteins and carbohydrates, whereas it increased with bile acids concentration (2.0-10 g/L), small intestinal pH (5.00-7.35), and addition of soybean oil representing dietary lipid (100% and 200% of the mean daily ingestion by 2-5 year olds in the U.S.). Bapp of PAHs increases with small intestinal pH due to the combined effects of mass transfer promotion from nonlabile to labile sorbed states in the soot, weaker sorption of the labile state, and increasingly favorable partitioning from the digestive fluid to the silicone sink. Under fed conditions, Bapp increases with inclusion of lipids due to the combined effects of mass transfer promotion from nonlabile to labile states, and increasingly favorable partitioning into bile acid micelles. Our results indicate significant variability in soot PAH bioaccessibility within the range of physiological conditions experienced by humans, and suggest that bioaccessibility will increase with coconsumption of food, especially food with high fat content.

'Towards a unified approach for the determination of the bioaccessibility of organic pollutants'

Bioaccessibility studies have been widely used as a research tool to determine the potential human exposure to ingested contaminants. More recently they have been practically applied for soil borne toxic elements. This paper reviews the application of bioaccessibility tests across a range of organic pollutants and contaminated matrices. Important factors are reported to be: the physiological relevance of the test, the components in the gut media, the size fraction chosen for the test and whether it contains a sorptive sink. The bioaccessibility is also a function of the composition of the matrix (e.g. organic carbon content of soils) and the physico-chemical characteristics of the pollutant under test. Despite the widespread use of these tests, there are a large number of formats used and very few validation studies with animal models. We propose a unified format for a bioaccessibility test for organic pollutants. The robustness of this test should first be confirmed through inter laboratory comparison, then tested in-vivo.

Bioacessibility of PAHs in fuel soot assessed by an in vitro digestive model: effect of including an absorptive sink

Polycyclic aromatic hydrocarbons (PAHs) associated with soot or black carbon can enter the human digestive tract by unintentional ingestion of soil or other particles. This study investigated the bioaccessibility of 11 PAHs in a composite fuel soot sample using an in vitro digestive model that included silicone sheet as an absorptive sink during the small intestinal digestion stage. The sheet was meant to simulate the passive transfer of PAHs in lumen fluid across the small intestinal epithelium, which was postulated to promote desorption of labile PAHs from the soot by steepening the soot-fluid concentration gradient. We show that the presence of silicone sheet during a 4 h default digestion time significantly increased the apparent bioaccessible fraction (Bapp, %), defined as the sum in the sheet and digestive fluid relative to the total PAH determined. The ability to increase Bapp for most PAHs leveled off above a sheet-to-soot ratio of 2.0 g per 50 mg, indicating that the sheet is an effective absorptive sink and promotes desorption in the mentioned way. Enhancement of Bapp by the sheet correlated positively with the octanol-water partition coefficient (Kow), even though the partition coefficient of PAH between sheet and digestive fluid (which contains bile acid micelles) correlated negatively with Kow. It was hypothesized that PAHs initially in the soot exist in labile and nonlabile states. The fraction of labile PAH still sorbed to the soot residue after digestion, and the maximum possible (limiting) bioaccessibility (Blim) could be estimated by varying the sheet-to-soot ratio. We show conclusively that the increase in bioccessibility due to the presence of the sheet is accounted for by a corresponding decrease in fraction of labile PAH still sorbed to the soot. The Blim ranged from 30.8 to 62.4%, independent of molecular size. The nonlabile fraction of individual PAHs (69.2-37.6% in this case) is therefore large and needs to be taken into account in risk assessment.

Determining high-quality critical body residues for multiple species and chemicals by applying improved experimental design and data interpretation concepts

Ecotoxicological effect data are generally expressed as effective concentrations in the external exposure medium and do thus not account for differences in chemical uptake, bioavailability, and metabolism, which can introduce substantial data variation. The Critical Body Residue (CBR) concept provides clear advantages, because it links effects directly to the internal exposure. Using CBRs instead of external concentrations should therefore reduce variability. For compounds that act via narcosis even a constant CBR has been proposed. Despite the expected uniformity, CBR values for these compounds still show large variability, possibly due to biased and inconsistent experimental testing. In the present study we tested whether variation in CBR data can be substantially reduced when using an improved experimental design and avoiding confounding factors. The aim was to develop and apply a well-defined test protocol for accurately and precisely measuring CBR data, involving improved (passive) dosing, sampling, and processing of organisms. The chemicals 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 2,3,4-trichloroaniline, 2,3,5,6-tetrachloroaniline, 4-chloro-3-methylphenol, pentylbenzene, pyrene, and bromophos-methyl were tested on Lumbriculus variegatus (California blackworm), Hyalella azteca (scud), and Poecilia reticulata (guppy), which yielded a high-quality database of 348 individual CBR values. Medians of CBR values ranged from 2.1 to 16.1 mmol/kg wet weight (ww) within all combinations of chemicals and species, except for the insecticide bromophos-methyl, for which the median was 1.3 mmol/kg ww. The new database thus covers about one log unit, which is considerably less than in existing databases. Medians differed maximally by a factor of 8.4 between the 7 chemicals but within one species, and by a factor of 2.6 between the three species but for individual chemicals. Accounting for the chemicals' internal distribution to different partitioning domains and relating effects to estimated concentrations in the target compartment (i.e., membrane lipids) was expected to but did not decrease the overall variability, likely because the surrogate partition coefficients for membrane lipid, storage lipid, protein, and carbohydrate that were used as input parameters did not sufficiently represent the actual partitioning processes. The results of this study demonstrate that a well-designed test setup can produce CBR data that are highly uniform beyond chemical and biological diversity.

Tenax as sorption sink for in vitro bioaccessibility measurement of polycyclic aromatic hydrocarbons in soils

Physiologically based in vitro methods have been developed to measure bioaccessibility of organic contaminants in soils. However, bioaccessibility of hydrophobic organic contaminants (HOCs) can be underestimated by in vitro tests if gastrointestinal (GI) solution fails to provide sufficient sorption sink for HOCs. To circumvent this drawback, Tenax was included in GI solution as sorption sink to trap mobilized HOCs and maintain the desorption gradient between soil and GI solution. Polycyclic aromatic hydrocarbons (PAHs) were selected as target HOCs, and physiologically based extraction test (PBET) was selected as the in vitro method. Inclusion of Tenax in GI solution increased bioaccessibility of PAHs in five spiked soils from 8.25-20.8% to 55.7-65.9% and the bioaccessibility of PAHs in a field contaminated soil from 3.70-6.92% to 16.3-31.0%. Our results demonstrated the effectiveness of Tenax as sorption sink to enhance PAH mobilization in bioaccessibility measurement in soils.

Evaluating the bioaccessibility of flame retardants in house dust using an in vitro Tenax bead-assisted sorptive physiologically based method

Exposure to house dust is a significant source of exposure to flame retardant chemicals (FRs), particularly in the US. Given the high exposure there is a need to understand the bioaccessibility of FRs from dust. In this study, Tenax beads (TA) encapsulated within a stainless steel insert were used as an adsorption sink to estimate the dynamic absorption of a suite of FRs commonly detected in indoor dust samples (n = 17), and from a few polyurethane foam samples for comparison. Organophosphate flame retardants (OPFRs) had the highest estimated bioaccessibility (∼ 80%) compared to brominated compounds (e.g., PBDEs), and values generally decreased with increasing Log K(ow), with <30% bioaccessibility measured for BDE209. These measurements were in very close agreement with reported PBDE bioavailability measures from an in vivo rat exposure study using indoor dust. The bioaccessibility of very hydrophobic FRs (Log K(ow) > 6) in foam was much less than that in house dust, and increasing bioaccessibility was observed with decreasing particle size. In addition, we examined the stability of more labile FRs containing ester groups (e.g., OPFRs and 2-ethylhexyl-tetrabromo-benzoate (EH-TBB)) in a mock-digestive fluid matrix. No significant changes in the OPFR concentrations were observed in this fluid; however, EH-TBB was found to readily hydrolyze to tetrabromobenzoic acid (TBBA) in the intestinal fluid in the presence of lipases. In conclusion, our study demonstrates that the bioaccessibility and stability of FRs following ingestion varies by chemical and sample matrix and thus should be considered in exposure assessments.