Time-dependent relative potency factors for polycyclic aromatic hydrocarbons and their derivatives in the H4IIE-luc bioassay

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

Lung cancer associated with combustion particles and fine particulate matter (PM2.5) - The roles of polycyclic aromatic hydrocarbons (PAHs) and the aryl hydrocarbon receptor (AhR)

Air pollution is the leading cause of lung cancer after tobacco smoking, contributing to 20% of all lung cancer deaths. Increased risk associated with living near trafficked roads, occupational exposure to diesel exhaust, indoor coal combustion and cigarette smoking, suggest that combustion components in ambient fine particulate matter (PM2.5), such as polycyclic aromatic hydrocarbons (PAHs), may be central drivers of lung cancer. Activation of the aryl hydrocarbon receptor (AhR) induces expression of xenobiotic-metabolizing enzymes (XMEs) and increase PAH metabolism, formation of reactive metabolites, oxidative stress, DNA damage and mutagenesis. Lung cancer tissues from smokers and workers exposed to high combustion PM levels contain mutagenic signatures derived from PAHs. However, recent findings suggest that ambient air PM2.5 exposure primarily induces lung cancer development through tumor promotion of cells harboring naturally acquired oncogenic mutations, thus lacking typical PAH-induced mutations. On this background, we discuss the role of AhR and PAHs in lung cancer development caused by air pollution focusing on the tumor promoting properties including metabolism, immune system, cell proliferation and survival, tumor microenvironment, cell-to-cell communication, tumor growth and metastasis. We suggest that the dichotomy in lung cancer patterns observed between smoking and outdoor air PM2.5 represent the two ends of a dose-response continuum of combustion PM exposure, where tumor promotion in the peripheral lung appears to be the driving factor at the relatively low-dose exposures from ambient air PM2.5, whereas genotoxicity in the central airways becomes increasingly more important at the higher combustion PM levels encountered through smoking and occupational exposure.

Benzo[b]naphtho[d]thiophenes and naphthylbenzo[b]thiophenes: Their aryl hydrocarbon receptor-mediated activities and environmental presence

Polycyclic aromatic sulfur heterocyclic compounds (PASHs) belong among ubiquitous environmental pollutants; however, their toxic effects remain poorly understood. Here, we studied the aryl hydrocarbon receptor (AhR)-mediated activity of dibenzothiophene, benzo[b]naphtho[d]thiophenes, and naphthylbenzo[b]thiophenes, as well as their presence in two types of environmental matrices: river sediments collected from both rural and urban areas, and in airborne particulate matter (PM_2.5) sampled in cities with different levels and sources of pollution. Benzo[b]naphtho[2,1-d]thiophene, benzo[b]naphtho[2,3-d]thiophene, 2,2-naphthylbenzo[b]thiophene, and 2,1-naphthylbenzo[b]thiophene were newly identified as efficient AhR agonists in both rat and human AhR-based reporter gene assays, with 2,2-naphthylbenzo[b]thiophene being the most potent compound identified in both species. Benzo[b]naphtho[1,2-d]thiophene and 3,2-naphthylbenzo[b]thiophene elicited AhR-mediated activity only in the rat liver cell model, while dibenzothiophene and 3,1-naphthylbenzo[b]thiophene were inactive in either cell type. Independently of their ability to activate the AhR, benzo[b]naphtho[1,2-d]thiophene, 2,1-naphthylbenzo[b]thiophene, 3,1-naphthylbenzo[b]thiophene, and 3,2-naphthylbenzo[b]thiophene inhibited gap junctional intercellular communication in a model of rat liver epithelial cells. Benzo[b]naphtho[d]thiophenes were dominant PASHs present in both PM_2.5 and sediment samples, with benzo[b]naphtho[2,1-d]thiophene being the most abundant one, followed by benzo[b]naphtho[2,3-d]thiophene. The levels of naphthylbenzo[b]thiophenes were mostly low or below detection limit. Benzo[b]naphtho[2,1-d]thiophene and benzo[b]naphtho[2,3-d]thiophene were identified as the most significant contributors to the AhR-mediated activity in the environmental samples evaluated in this study. Both induced nuclear translocation of the AhR, and they induced CYP1A1 expression in a time-dependent manner, suggesting that their AhR-mediated activity may depend on the rate of their intracellular metabolism. In conclusion, some PASHs could be significant contributors to the overall AhR-mediated toxicity of complex environmental samples suggesting that more attention should be paid to the potential health impacts of this group of environmental pollutants.

Extensive chemical and bioassay analysis of polycyclic aromatic compounds in a creosote-contaminated superfund soil following steam enhanced extraction

Polycyclic aromatic compounds (PACs) are organic compounds commonly found in contaminated soil. Previous studies have shown the removal of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soils during steam enhanced extraction (SEE). However, less is known about the removal of alkyl-PAHs and heterocyclic compounds, such as azaarenes, and oxygen- and sulfur-heterocyclic PACs (OPACs and PASHs, respectively). Further, the impact of SEE on the freely dissolved concentration of PACs in soil as well as the soil bioactivity pre- and post-SEE have yet to be addressed. To fulfil these research gaps, chemical and bioanalytical analysis of a creosote-contaminated soil, collected from a U.S. Superfund site, pre- and post-SEE were performed. The decrease of 64 PACs (5-100%) and increase in the concentrations of nine oxygenated-PAHs (OPAHs) (150%) during SEE, some of which are known to be toxic and can potentially contaminate ground water, were observed. The freely dissolved concentrations of PACs in soil were assessed using polyoxymethylene (POM) strips and the concentrations of 66 PACs decreased post-SEE (1-100%). Three in vitro reporter gene bioassays (DR-CALUX®, ERα-CALUX® and anti-AR CALUX®) were used to measure soil bioactivities pre- and post-SEE and all reporter gene bioassays measured soil bioactivity decreases post-SEE. Mass defect suspect screening tentatively identified 27 unique isomers of azaarenes and OPAC in the soil. As a remediation technique, SEE was found to remove alkyl-PAHs and heterocyclic PACs, reduce the concentrations of freely dissolved PACs, and decrease soil bioactivities.

Identification of AhR agonists in sediments of the Bohai and Yellow Seas using advanced effect-directed analysis and in silico prediction

Novel aryl hydrocarbon receptor (AhR) agonists were identified in coastal sediments in the Yellow and Bohai Seas by use of a combination of effect-directed analysis (EDA) and in silico prediction. A total of 125 sediments were screened for AhR-mediated potencies using H4IIE-luc bioassay. Great potencies were observed in organic extracts, mid-polar fraction (F2), and subfractions of F2 (F2.6-F2.9) of sediments collected from Nantong, Qinhuangdao, and Yancheng. Less than 15% AhR potencies could be explained by detected dioxin-like PAHs. Full-scan screening analysis was conducted for the more potent fractions using GC-QTOFMS to investigate the presence of unmonitored AhR agonists. A five-step prioritization strategy was applied; 92 candidate compounds satisfied all criteria. Among these chemicals, thirteen were evaluated for AhR efficacy. Six compounds; benz[b]anthracene, 6-methylchrysene, 2-methylbenz[a]anthracene, 1-methylbenz[a]anthracene, 1,12-dimethylbenzo[c]phenanthrene, and indeno[1,2,3-cd]fluoranthene, exhibited significant AhR-mediated efficacies. 1,12-dimethylbenzo[c]phenanthrene and indeno[1,2,3-cd]fluoranthene were identified as novel AhR agonists. Potency balance analysis showed that the six newly identified AhR agonists explained 0.4-100% of the total AhR-mediated potencies determined. Overall, combining EDA and in silico prediction applied in this study demonstrated the benefits of assessing the potential toxic effects of previously unidentified AhR agonists in sediments from the coasts of China and Korea.

Examination of aryl hydrocarbon receptor (AhR), estrogenic and anti-androgenic activities, and levels of polyaromatic compounds (PACs) in tire granulates using in vitro bioassays and chemical analysis

Tire granulates recovered from end-of-life tires contain a complex mixture of chemicals, amongst them polyaromatic compounds (PACs), of which many are recognized to be toxic and persistent in the environment. Only a few of these PACs are regularly monitored. In this study a combined approach of chemical analysis and a battery of CALUX® in vitro bioassays was used to determine PAC concentrations and estrogenic, (anti)-androgenic and aryl hydrocarbon receptor (AhR) activities in tire granulates. Tire granulates from a recycling company was analyzed for PAHs, alkyl-PAHs, oxy-PAHs and heterocyclic PACs (NSO-PACs), in total 85 PACs. The concentrations of PACs were between 42 and 144 mg/kg, with major contribution from PAHs (74-88%) followed by alkyl-PAHs (6.6-20%) and NSO-PACs (1.8-7.0%). The sum of eight priority PAHs were between 2.3 and 8.6 mg/kg, contributing with 4.7-8.2% of ∑PACs. Bioassay analysis showed presence of AhR agonists, estrogen receptor (ERα) agonists, and androgen receptor (AR) antagonists in the tire granulate samples. Only 0.8-2.4% of AhR-mediated activities could be explained by the chemical analysis. Benzo[k+j]fluoranthenes, benzo[b]fluoranthene, indeno[1,2,3-cd]pyrene, 2-methylchrysene, and 3-methylchrysene were the major contributors to the AhR-mediated activities. The high contribution (98-99%) of unknown bioactive compounds to the bioassay effects in this study raises concerns and urges for further investigations of toxicants identification and source apportionment.

Observed and predicted embryotoxic and teratogenic effects of organic and inorganic environmental pollutants and their mixtures in zebrafish (Danio rerio)

Risk assessment of chemicals is still primarily focusing on single compound evaluation, even if environmental contamination consists of a mixture of pollutants. The concentration addition (CA) and independent action (IA) models have been developed to predict mixture toxicity. Both models assume no interaction between the components, resulting in an additive mixture effect. In the present study, the embryo toxicity test (OECD TG no. 236) with zebrafish embryos (Danio rerio) was performed to investigate whether the toxicity caused by binary, ternary, and quaternary mixtures of organic (Benzo[a]pyrene, perfluorooctanesulfonate, and 3,3´,4,4´,5-pentachlorobiphenyl 126) and inorganic (arsenate) pollutants can be predicted by CA and IA. The acute toxicity and sub-lethal alterations such as lack of blood circulation were investigated. The models estimated the mixture toxicity well and most of the mixtures were additive. However, the binary mixture of PFOS and PCB126 caused a synergistic effect, with almost a ten-fold difference between the observed and predicted LC₅₀-value. For most of the mixtures, the CA model was better in predicting the mixture toxicity than the IA model, which was not expected due to the chemicals' different modes of action. In addition, some of the mixtures caused sub-lethal effects not observed in the single compound toxicity tests. The mixture of PFOS and BaP caused a division of the yolk and imbalance was caused by the combination of PFOS and As and the ternary mixture of PFOS, As, and BaP. Interestingly, PFOS was part of all three mixtures causing the mixture specific sub-lethal effects. In conclusion, the present study shows that CA and IA are mostly resulting in good estimations of the risks that mixtures with few components are posing. However, for a more reliable assessment and a better understanding of mixture toxicity, further investigations are required to study the underlying mechanisms.

Instrumental and bioanalytical characterization of dioxin-like activity in sediments from the Yeongsan River and the Nakdong River estuaries, South Korea

In the present study, we investigated the contamination status of dioxin-like chemicals (DLCs) and potential toxic effects associated with river and coastal sediments from two large estuaries of South Korea. Sediments collected from the Yeongsan River and the Nakdong River estuaries were analyzed for several DLCs, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), coplanar polychlorinated biphenyls (co-PCBs), and polycyclic aromatic hydrocarbons (PAHs). Greater concentrations of target DLCs (except for PCDDs in Nakdong River) were found in the inland creeks with decreasing trends towards estuarine and coastal areas in both regions. The result indicated that the elevated DLCs were attributable to the surrounding land use activities, such as point sources of industrial and municipal areas from the inland regions. Principal component analysis and positive matrix factorization model revealed that major sources of PCDD/Fs and PAHs in sediments were fly ash and dust, and petroleum and diesel emission, respectively. The dioxin-like activities of the sediments ranged from 0.98 to 88% of the maximal induction elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin, which generally explained the sedimentary contamination by the target DLCs. Dioxin-like activity in sediments from the artificial lake and inland creek of the Nakdong River Estuary was mostly explained by the targeted DLCs (~75%). However, the contribution of known DLCs from the sediments of the Yeongsan River Estuary was relatively low (~35%) compared to that of the Nakdong River Estuary, suggesting the presence of unknown DLCs in sediments. Overall, the distribution of DLCs quite varied by region, generally reflecting the difference in the surrounding land use activity. In the future, it is needed to study the distribution, sources, and potential ecological effects of unknown toxic substances in coastal sediments.

Identification of novel polar aryl hydrocarbon receptor agonists accumulated in liver of black-tailed gulls in Korea using advanced effect-directed analysis

Although bioaccumulation of persistent organic pollutants in seabirds has been examined, few studies have been conducted to identify previously unidentified substances. Here, aryl hydrocarbon receptor (AhR) agonists were identified in livers of black-tailed gulls from South Korea using effect-directed analysis combined with full-scan screening analysis. Significant AhR-mediated potencies were observed in the polar fractions of liver extracts using H4IIE-luc bioassay. Eight known polar AhR agonists accounted for 11-20% of the total AhR-mediated potencies in the polar fractions; hydrocortisone and rutaecarpine were the major contributors. Twenty-two AhR agonist candidates in the polar fractions were identified using liquid chromatography-quadrupole time-of-flight mass spectrometry during a six-step selection process. Of these, [10]-gingerol, angelicin, corticosterone, eupatilin, etofenprox, oxadixyl, and tretinoin were identified as novel AhR agonists. The contribution to potencies increased with inclusion of novel AhR agonists (27-52%); corticosterone and [10]-gingerol contributed significantly. Quantitative structure-activity relationship suggested that the novel AhR agonists have other potential toxic effects, including carcinogenicity and mutagenicity. Polar AhR agonists have been used for pharmaceuticals and pesticides. Some novel AhR agonists have log K_OW > 2 and log K_OA ≥ 6, which indicates that these compounds can be biomagnified in air-breathing organisms, such as seabirds.

Characterization of polycyclic aromatic compounds in historically contaminated soil by targeted and non-targeted chemical analysis combined with in vitro bioassay

Soil samples from a contaminated site in Sweden were analyzed to identify the presence of 78 polycyclic aromatic compounds (PACs) using gas chromatography coupled with mass spectrometry (GC-MS). The target analysis revealed large contributions not only from polycyclic aromatic hydrocarbons (PAHs), but also from alkylated- and oxygenated-PAHs (alkyl- and oxy-PAHs, respectively), and N-heterocyclics (NPACs). PAC profiles indicated primarily pyrogenic sources, although contribution of petrogenic sources was also observed in one sample as indicated by a high ratio of alkylated naphthalene compared to naphthalene. The aryl hydrocarbon receptor (AhR)-activity of the soil extracts was assessed using the H4IIe-pGudluc 1.1 cells bioassay. When compared with the calculated total AhR-activity of the PACs in the target list, 35-97% of the observed bioassay activity could be explained by 62 PACs with relative potency factors (REPs). The samples were further screened using GC coupled with Orbitrap™ high resolution MS (GC-HRMS) to investigate the presence of other PACs that could potentially contribute to the AhR-activity of the extracts. 114 unique candidate compounds were tentatively identified and divided into four groups based on their AhR-activity and environmental occurrence. Twelve substances satisfied all the criteria, and these compounds are suggested to be included in regular screening in future studies, although their identities were not confirmed by standards in this study. High unexplained bio-TEQ fractions in three of the samples may be explained by tentatively identified compounds (n = 35) with high potential of being toxic. This study demonstrates the benefit of combining targeted and non-targeted chemical analysis with bioassay analysis to assess the diversity and effects of PACs at contaminated sites. The applied prioritization strategy revealed a number of tentatively identified compounds, which likely contributed to the overall bioactivity of the soil extracts.

Novel polar AhR-active chemicals detected in sediments of an industrial area using effect-directed analysis based on in vitro bioassays with full-scan high resolution mass spectrometric screening

Studies investigating aryl hydrocarbon receptor (AhR)-active compounds in the environment typically focus on non- and mid-polar substances, such as PAHs; while, information on polar AhR agonists remains limited. Here, we identified polar AhR agonists in sediments collected from the inland creeks of an industrialized area (Lake Sihwa, Korea) using effect-directed analysis combined with full-scan screening analysis (FSA; using LC-QTOFMS). Strong AhR-mediated potencies were observed for the polar and latter fractions of RP-HPLC (F3.5-F3.8) from sediment organic extracts in the H4IIE-luc in vitro bioassays. FSA was performed on the corresponding fractions. Twenty-eight tentative AhR agonists were chosen using a five-step process. Toxicological confirmation using bioassay revealed that canrenone, rutaecarpine, ciprofloxacin, mepanipyrim, genistein, protopine, hydrocortisone, and medroxyprogesterone were significantly active. The relative potencies of these AhR-active compounds compared to that of benzo[a]pyrene ranged from 0.00002 to 2.0. Potency balance analysis showed that polar AhR agonists explained, on average, ~6% of total AhR-mediated potencies in samples. Some novel polar AhR agonists also exhibited endocrine-disrupting potentials capable of binding to estrogen and glucocorticoid receptors, as identified by QSAR modeling. In conclusion, the focused studies on distributions, sources, fate, and ecotoxicological effects of novel polar AhR agonists in the environment are necessary.

Bioanalytical equivalents and relative potencies for predicting the biological effects of mixtures

Bioanalytical equivalents (BEQs) of mixtures and environmental samples are widely used to reflect the potential threat of pollutants in the environment and can be obtained by bioassays or using chemical analysis combined with relative potencies (REPs). In this study, the relationships between bioassay-detected BEQs (Bio-BEQs) and chemically analyzed BEQs (Chem-BEQs) were studied. BEQs and REPs are correlated with effect level and the concentration-response curves of the reference standard and sample. Thus, effect level (e.g., EC₁₀, EC₂₅ and EC₅₀) should be addressed for the BEQ values obtained from bioassays or chemical analyses. The previous prerequisites for REPs application (i.e., curves that are parallel and have the same maximum response) are redundant, and the use of REPs for the calculation of BEQs or in risk assessment should instead be based on the same effect level. For a complex mixture with many components, all active components can be regarded as dilutions of a standard compound for inducing a specific effect. Relative toxicity estimates based on EC₅₀ ignore the contribution of weak-active components with maximum response below EC₅₀ of the reference standard, especially in complex mixtures or environmental samples. REPs based on an effect level EC₁₀ that can be clearly discriminated from background response are recommended for BEQ calculation. As an example, the aryl hydrocarbon receptor (AhR)-mediated activity of US EPA priority polycyclic aromatic hydrocarbons (PAHs) in RTL-W1 cells was used to assess the reliability of REPs for mixture toxicity prediction based on the effect level EC₁₀.

Impurities in technical mixtures of chlorinated paraffins show AhR agonist properties as determined by the DR-CALUX bioassay

Chlorinated paraffins (CPs) are produced at more than one million tons per year. Technical CPs mixtures may contain impurities, which end up in consumer products. In the present study, 17 technical CPs mixtures were investigated for the potential occurrence of potential impurities. By applying the DR-CALUX bioassay, 3 out of 17 technical mixtures were shown to elicit responses at 4 h exposure time, but much lower at 48 h. Constitutional defined CPs materials did not show responses. Subsequently different groups of known AhR-agonists and compounds suspected to be present in technical CPs mixtures were investigated. Benzene, (poly)chlorobenzene, non-dioxin like polychlorinated naphthalenes (PCNs), and three-ringed polyaromatic hydrocarbons (PAHs) did not result in a significant response at 4 h or 48 h. TCDD, non-ortho PCBs, dioxin-like PCNs, four or five ringed PAHs and their chlorinated analogues resulted in a significant response. TCDD and the non-ortho PCBs showed the highest potency and stability, while dioxin-like PCNs, PAHs, and the chlorinated PAHs were clearly inactivated (metabolized) at longer incubation. Altogether, the present findings substantiate that AhR-mediated responses of CPs technical mixtures in the DR-CALUX bioassay are caused by impurities, most likely some intermediate stable AhR-agonists such as dioxin-like PCNs or (chlorinated) PAHs. The current study shows that impurities in CPs technical mixtures need to be investigated for assessing the safety of technical CPs mixtures.

A polycyclic aromatic hydrocarbon-enriched environmental chemical mixture enhances AhR, antiapoptotic signaling and a proliferative phenotype in breast cancer cells

Emerging evidence suggests the role of environmental chemicals, in particular endocrine-disrupting chemicals (EDCs), in progression of breast cancer and treatment resistance, which can impact survival outcomes. However, most research tends to focus on tumor etiology and the effect of single chemicals, offering little insight into the effects of realistic complex mixture exposures on tumor progression. Herein, we investigated the effect of a polycyclic aromatic hydrocarbon (PAH)-enriched EDC mixture in a panel of normal and breast cancer cells and in a tumor organoid model. Cells or organoids in culture were treated with EDC mixture at doses estimated from US adult intake of the top four PAH compounds within the mixture from the National Health and Nutrition Examination Survey database. We demonstrate that low-dose PAH mixture (6, 30 and 300 nM) increased aryl hydrocarbon receptor (AhR) expression and CYP activity in estrogen receptor (ER) positive but not normal mammary or ER-negative breast cancer cells, and that upregulated AhR signaling corresponded with increased cell proliferation and expression of antiapoptotic and antioxidant proteins XIAP and SOD1. We employed a mathematical model to validate PAH-mediated increases in AhR and XIAP expression in the MCF-7 ER-positive cell line. Furthermore, the PAH mixture caused significant growth increases in ER-negative breast cancer cell derived 3D tumor organoids, providing further evidence for the role of a natural-derived PAH mixture in enhancing a tumor proliferative phenotype. Together, our integrated cell signaling, computational and phenotype analysis reveals the underlying mechanisms of EDC mixtures in breast cancer progression and survival.

Assessing the receptor-mediated activity of PAHs using AhR-, ERα- and PPARγ- CALUX bioassays

Polycyclic aromatic hydrocarbons (PAH) are a complex group of organic compounds, consisting of at least three fused aromatic rings, which are formed during combustion of organic matter. While some PAHs have been reported to have carcinogenic and/or mutagenic properties, another possible negative health impact is their endocrine disrupting potential. Therefore, the aim of this study was to determine both the agonistic and antagonistic endocrine activity of 9 environmentally relevant PAHs using three different CALUX bioassays: The AhR-CALUX, The ERα-CALUX and PPARγ-CALUX. For the PPARγ-CALUX anthracene, fluoranthene, pyrene and fluorene showed weak agonistic activity, whilst benzo(a)pyrene (B(a)P) was the only one exhibiting weak antagonistic activity. For the AhR-CALUX, chrysene was the only PAH that showed relatively strong agonist activity (except for B(a)P which was used as a standard). Pyrene, anthracene and fluoranthene showed weak AhR agonist activity. In the ERα-CALUX bioassay, fluoranthene had agonistic activity whilst B(a)P exhibited both agonistic and antagonistic activity (lowering E2 activity by 30%). Phenanthrene and anthracene had weak ERα agonist activities. These results indicate that certain PAHs have multiple modes of action and can activate/inhibit multiple receptor signaling pathways known to play critical roles in mediating endocrine disruption.

Major AhR-active chemicals in sediments of Lake Sihwa, South Korea: Application of effect-directed analysis combined with full-scan screening analysis

This study utilized effect-directed analysis (EDA) combined with full-scan screening analysis (FSA) to identify aryl hydrocarbon receptor (AhR)-active compounds in sediments of inland creeks flowing into Lake Sihwa, South Korea. The specific objectives were to (i) investigate the major AhR-active fractions of organic extracts of sediments by using H4IIE-luc in vitro bioassay (4 h and 72 h exposures), (ii) quantify known AhR agonists, such as polycyclic aromatic hydrocarbons (PAHs) and styrene oligomers (SOs), (iii) identify unknown AhR agonists by use of gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOFMS), and (iv) determine contributions of AhR agonists to total potencies measured by use of the bioassay. FSA was conducted on fractions F2.6 and F2.7 (aromatics with log K_ow 5-7) in extracts of sediment from Siheung Creek (industrial area). Those fractions exhibited significant AhR-mediated potency as well as relatively great concentrations of PAHs and SOs. FSA detected 461 and 449 compounds in F2.6 and F2.7, respectively. Of these, five tentative candidates of AhR agonist were selected based on NIST library matching, aromatic structures and numbers of rings, and available standards. Benz[b]anthracene, 11H-benzo[a]fluorene, and 4,5-methanochrysene exhibited significant AhR-mediated potency in the H4IIE-luc bioassay, and relative potencies of these compounds were determined. Potency balance analysis demonstrated that these three newly identified AhR agonists explained 1.1% to 67% of total induced AhR-mediated potencies of samples, which were particularly great for industrial sediments. Follow-up studies on sources and ecotoxicological effects of these compounds in coastal environments would be required.

Aryl hydrocarbon receptor-mediated activity of gas-phase ambient air derived from passive sampling and an in vitro bioassay

The gaseous fraction of hydrophobic organic contaminants (HOCs) in ambient air appears to be responsible for a significant portion of aryl hydrocarbon receptor (AhR)-mediated activity, but the majority of compounds contributing to this activity remain unidentified. The present study investigated the use of polyethylene passive samplers to isolate gaseous HOCs from ambient air for use in in vitro bioassays and to improve our understanding of the toxicological relevance of the gaseous fraction of ambient air in urban and residential environments. Concentrations of polycyclic aromatic hydrocarbons (PAHs) and organic flame retardants were measured in polyethylene passive sampler extracts. Extracts were also analyzed using an in vitro bioassay to measure AhR-mediated activity. Bioassay-derived benzo[a]pyrene (BaP) equivalents (BaP-Eq_bio ), a measure of potency of HOC mixtures, were greatest in the downtown Cleveland area and lowest at rural/residential sites further from the city center. The BaP-Eq_bio was weakly correlated with concentrations of 2-ring alkyl/substituted PAHs and one organophosphate flame retardant, ethylhexyl diphenyl phosphate. Potency predicted based on literature-derived induction equivalency factors (IEFs) explained only 2 to 23% of the AhR-mediated potency observed in bioassay experiments. Our results suggests that health risks of gaseous ambient air pollution predicted using data from targeted chemical analysis may underestimate risks of exposure, most likely due to augmentation of potency by unmonitored chemicals in the mixture, and the lack of relevant IEFs for many targeted analytes. Environ Toxicol Chem 2019;38:748-759. © 2019 SETAC.

Methylated PACs are more potent than their parent compounds: A study of aryl hydrocarbon receptor-mediated activity, degradability, and mixture interactions in the H4IIE-luc assay

Twenty-six polycyclic aromatic compounds (PACs; including native polycyclic aromatic hydrocarbons [PAHs], hydroxylated PAHs, alkylated and oxygenated PAHs, and [alkylated] heterocyclic compounds) were investigated for their aryl hydrocarbon receptor (AhR)-mediated potencies in the H4IIE-luc bioassay. Potential degradabilities of PACs were investigated by use of various durations of exposure (24, 48, or 72 h), and various mixtures of PACs including PAHs, alkylated and oxygenated PAHs, and heterocyclic compounds were tested for their joint AhR-mediated potency. Additive behaviors of PACs in mixtures were studied by comparing observed mixture potencies with mixture potencies predicted by use of the concentration addition model. Methylated derivatives were more potent than their parent compounds in the H4IIE-luc assay. A time-dependent decrease in relative potency was observed for all AhR-active compounds, which may be indicative of in vitro biotransformation. Monomethylated compounds seemed to be more rapidly transformed than analogous unsubstituted compounds. In addition, the results showed that the predictive power of the concentration addition model increased with the number of compounds, suggesting additivity in multicomponent mixtures. Due to the greater potency of methylated derivatives and their ubiquitous occurrence, there is a need for further research on the toxicity and mixture behavior of these environmentally and toxicologically relevant compounds. Environ Toxicol Chem 2018;37:1409-1419. © 2018 SETAC.

Occurrence and leachability of polycyclic aromatic compounds in contaminated soils: Chemical and bioanalytical characterization

An important concern regarding sites contaminated with polycyclic aromatic compounds (PACs) is the risk of groundwater contamination by release of the compounds from soils. The goal of this study was to investigate the occurrence and leachability of 77 PACs including polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic compounds (NSO-PACs) among total aryl hydrocarbon receptor (AhR) agonists in soils from historical contaminated sites. A novel approach combining chemical and bioanalytical methods in combination with characterization of leachability by use of a column leaching test was used. Similar profiles of relative concentrations of PACs were observed in all soils, with parent PAHs accounting for 71 to 90% of total concentrations in soils. Contribution of oxy-PAHs, alkyl-PAHs and N-PACs ranged from 2 to 9%, 3 to 9% and 1 to 14%, respectively. Although the contributions of groups of PACs were small, some compounds were found in similar or greater concentrations than parent PAHs. Leachable fractions of 77 PACs from soils were small and ranged from 0.002 to 0.54%. Polar PACs were shown to be more leachable than parent PAHs. The contribution of analyzed PACS to overall AhR-mediated activities in soils and leachates suggests presence of other AhR agonists in soils, and a potential risk. Only a small fraction of AhR agonists was available in soils, indicating an overestimation of the risk if only total initial concentrations in soils would be considered in risk assessment. The results of the study strongly support that focus on 16US EPA PAHs may result in inadequate assessment of risk and hazard of PACs in complex environmental samples.

Methylated polycyclic aromatic hydrocarbons and/or their metabolites are important contributors to the overall estrogenic activity of polycyclic aromatic hydrocarbon-contaminated soils

In the present study 42 polycyclic aromatic compounds (PACs) were investigated for their estrogenic potential using the VM7Luc4E2 transactivation assay. Relative potencies were determined for mass-balance analysis. In addition, compounds were tested in combination with the estrogen receptor (ER) antagonist ICI182,780 (ICI) and the aryl hydrocarbon receptor antagonist/CYP1A1 inhibitor α-naphthoflavone. Luciferase induction and CYP1A1-dependent ethoxyresorufin-O-deethylase (EROD) activity were measured to assess whether the estrogenic activity was elicited by the compound itself and/or by its metabolites. Relative potencies ranged between 10^-7 and 10^-4 . The ability of ICI to decrease luciferase activity stimulated by all compounds indicated that the induction responses were ER-dependent. The aryl hydrocarbon receptor antagonist/CYP1A1 inhibitor α-naphthoflavone decreased luciferase induction and EROD activity by several compounds, including the methylated chrysenes, suggesting that metabolites of these chemicals contributed to ER activation. Several PACs, such as acridine and its derivatives, appear to directly activate the ER. Furthermore, extracts of soils from industrial areas were examined using this bioassay, and estrogenic activity was detected in all soil samples. Mass-balance analysis using a combination of relative potencies and chemical analysis of the samples suggested that polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs, such as 1- and 3-methylchrysene, are important contributors to the overall estrogenic activity. However, these results revealed that a considerable proportion of the estrogenic activity in the soil remained unexplained, indicating the presence of other significant estrogenic compounds. Environ Toxicol Chem 2018;37:385-397. © 2017 SETAC.

Comparative developmental toxicity of a comprehensive suite of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that occur in complex mixtures. Several PAHs are known or suspected mutagens and/or carcinogens, but developmental toxicity data is lacking for PAHs, particularly their oxygenated and nitrated derivatives. Such data are necessary to understand and predict the toxicity of environmental mixtures. 123 PAHs were assessed for morphological and neurobehavioral effects for a range of concentrations between 0.1 and 50 µM, using a high throughput early-life stage zebrafish assay, including 33 parent, 22 nitrated, 17 oxygenated, 19 hydroxylated, 14 methylated, 16 heterocyclic, and 2 aminated PAHs. Additionally, each PAH was evaluated for AHR activation, by assessing CYP1A protein expression using whole animal immunohistochemistry (IHC). Responses to PAHs varied in a structurally dependent manner. High-molecular weight PAHs were significantly more developmentally toxic than the low-molecular weight PAHs, and CYP1A expression was detected in five distinct tissues, including vasculature, liver, skin, neuromasts and yolk.

Long-term changes in distributions of dioxin-like and estrogenic compounds in sediments of Lake Sihwa, Korea: Revisited mass balance

In the late 1990s, severe pollution by persistent organic contaminants (POCs) was observed in Lake Sihwa by use of a combination of instrumental analyses and in vitro bioassays. To determine long-term changes (>15-year gaps) in distributions of POCs and their potential toxic potencies in the given region, sediment assessments were reconducted. Target chemicals include polycyclic aromatic hydrocarbons (PAHs), alkylphenols (APs), and recently reported emerging chemicals, styrene oligomers (SOs). We employed in vitro bioassays (such as H4IIE-luc and MVLN) to determine potential sediment toxicities. The reduction rates of mean concentrations of APs and SOs in sediments between the two sampling years (1998 vs. 2015) were estimated to be 99% and 67%, respectively. Although APs and SOs significantly declined over the 15-year period, concentrations of PAHs were consistent. Results of the bioassays were consistent with the instrumental data, with relatively great concentrations of all target compounds being detected, particularly in inland creeks. Compositions of all target compounds exhibited changes in homologue patterns over the 15 years considered. This result indicated varying and/or continuing sources in this region. In particular, PAHs were dominated by higher-molecular-weight PAHs (e.g., benzo[g,h,i]perylene and benzo[b]fluoranthene) in recent years. This result might indicate consumption of oil-related fuels. Quantitative potency balance analysis revealed that concentrations of instrumentally-derived equivalents accounted for as little as 18.5% of bioassay-derived equivalents, which indicated significant amounts of unknown and/or unmeasured compounds were present. The present study documented the continuing severe pollution by selected POCs in the Lake Sihwa region over the last 15 years, indicating a lack of management in the area studied.

Assessment of potential biological activities and distributions of endocrine-disrupting chemicals in sediments of the west coast of South Korea

The west coast of Korea has experienced environmental deterioration for more than half a century. In the present study, we specifically aimed to: i) evaluate potential toxicities of contaminants in sediments that cause effects mediated through the aryl hydrocarbon receptor (AhR) and estrogen receptor (ER); ii) determine spatio-temporal distributions of polycyclic aromatic hydrocarbons (PAHs) and alkylphenols (APs); and iii) identify causes of greater potencies of samples. From 2010 to 2014, sediments were collected from 12 major estuarine and coastal regions along the west coast of South Korea. In vitro cell bioassays were performed to determine AhR- and ER-mediated potencies using H4IIE-luc and MVLN cells, respectively. Fifteen PAHs and six APs in sediments were identified by GC/MSD. Results of bioassays generally showed a low-to-moderate degree of contamination, however, greater AhR- and ER-mediated potencies were measured at some locations. Concentrations of PAHs and APs varied among locations, which indicated that sources were independently affected by the surrounding environment (e.g., industrial complex and cities). Results of bioassays were generally well correlated with concentrations of putative causative chemicals. Benzo[k]fluoranthene, dibenz[a,h]anthracene, and benzo[b]fluoranthene were the major AhR agonists, explaining approximately 30% of the bioassay-derived benzo[a]pyrene equivalent concentration (BaP-EQ). Unknown AhR and ER agonists and potential mixture effects remain in question. Overall, the present study provides baseline information on chemical contaminations and potential toxicity of sediments in a fairly wide geographical region of the west coast of South Korea.

Assessment of the aryl hydrocarbon receptor-mediated activities of polycyclic aromatic hydrocarbons in a human cell-based reporter gene assay

Activation of the aryl hydrocarbon receptor (AhR)-mediated activity is one of key events in toxicity of polycyclic aromatic hydrocarbons (PAHs). Although various classes of AhR ligands may differentially activate human and rodent AhR, there is presently a lack of data on the human AhR-inducing relative potencies (REPs) of PAHs. Here, we focused on estimation of the AhR-mediated activities of a large set of environmental PAHs in human gene reporter AZ-AhR cell line, with an aim to develop the human AhR-based REP values with potential implications for risk assessment of PAHs. The previously identified weakly active PAHs mostly failed to activate the AhR in human cells. The order for REPs of individual PAHs in human cells largely corresponded with the available data from rodent-based experimental systems; nevertheless, we identified differences up to one order of magnitude in REP values of PAHs between human and rodent cells. Higher REP values were found in human cells for some important environmental contaminants or suspected carcinogens, such as indeno[1,2,3-cd]pyrene, benz[a]anthracene or benzo[b]fluoranthene, while lower REP values were determined for methyl-substituted PAHs. Our results also indicate that a different rate of metabolism for individual PAHs in human vs. rodent cells may affect estimation of REP values in human cell-based assay, and potentially alter toxicity of some compounds, such as benzofluoranthenes, in humans. We applied the AZ-AhR assay to evaluation of the AhR-mediated activity of complex mixtures of organic compounds associated with diesel exhaust particles, and we identified the polar compounds present in these mixtures as being particularly highly active in human cells, as compared with rodent cells. The present data suggest that differences may exist between the AhR-mediated potencies of PAHs in human and rodent cells, and that the AhR-mediated effects of polar PAH derivatives and metabolites in human cell models deserve further attention.

Are styrene oligomers in coastal sediments of an industrial area aryl hydrocarbon-receptor agonists?

Effect-directed analysis (EDA) was performed to identify the major aryl hydrocarbon receptor (AhR) agonists in sediments collected from a highly industrialized area (Lake Shihwa, Korea). Great AhR-mediated potencies were found in fractions containing aromatic compounds with log Kow values of 5-8, and relatively great concentrations of styrene oligomers (SOs) and polycyclic aromatic hydrocarbons (PAHs) were detected in those fractions. Until now, there was little information on occurrences and toxic relative potencies (RePs) of SOs in coastal environments. In the present study; i) distributions and compositions, ii) AhR binding affinities, and iii) contributions of SOs to total AhR-mediated potencies were determined in coastal sediments. Elevated concentrations of 10 SOs were detected in sediments of inland creeks ranging from 61 to 740 ng g(-1) dry mass (dm), while lesser concentrations were found in inner (mean = 33 ng g(-1) dm) and outer regions (mean = 25 ng g(-1) dm) of the lake. Concentrations of PAHs in sediments were comparable to those of SOs. 2,4-diphenyl-1-butene (SD3) was the predominant SO analogue in sediments. SOs and PAHs were accumulated in sediments near sources, and could not be transported to remote regions due to their hydrophobicity. RePs of 3 SOs could be derived, which were 1000- to 10,000-fold less than that of one representative potent AhR active PAH, benzo[a]pyrene. Although concentrations of SOs in sediments were comparable to those of PAHs, the collective contribution of SOs to total AhR-mediated potencies were rather small (<1%), primarily due to their smaller RePs. Overall, the present study provides information on distributions and AhR binding affinities for SOs as baseline data for degradation products of polystyrene plastic in the coastal environment.

Induction and inhibition of human cytochrome P4501 by oxygenated polycyclic aromatic hydrocarbons

Our data represent the first demonstration that oxy-PAHs can be potent inhibitors of CYP1 expression and function.

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are found in the environment together with PAHs. However, less is known concerning their biological activity including their impact on aryl hydrocarbon receptor (AHR) signalling and the subsequent modulation of the cytochrome P450 monooxygenases (CYP). In this study, the effects of 15 environmentally relevant oxy-PAHs on the induction and activity of the CYP1 enzymes were determined in vitro by measuring gene expression levels and enzyme activity. We found that nine of the tested oxy-PAHs significantly induced CYP1A1 and CYP1B1 gene expression in human keratinocytes (HaCaT cells) while only five of these also were potent inducers of CYP1-dependent ethoxyresorufin-O-deethylase (EROD) activity suggesting that some of the oxy-PAHs are both activators of AHR signalling and inhibitors of CYP1 function. Using a recombinant human CYP1A1 enzyme we showed that eleven of the oxy-PAHs potently inhibited enzyme activity with benz[a]anthracene-7,12-quinone (7,12-BAQ) and benzo[a]fluorenone (BFLO) being the most potent inhibitors (IC₅₀ = 0.037 and 0.061 μM, respectively). We further exposed HaCaT cells to binary mixtures of oxy-PAHs and the model AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to investigate potential interaction effects. The results showed that oxy-PAHs can interfere with the TCDD-mediated effects leading to reduced CYP1A1 and 1B1 expression and EROD activity. These data represent the first demonstration that oxy-PAHs can be potent inhibitors of CYP1 expression and function and make important contributions towards understanding the mechanisms through which oxy-PAHs can contribute to the overall risk of polycyclic aromatic compounds.

Measured and predicted affinities of binding and relative potencies to activate the AhR of PAHs and their alkylated analogues

Polycyclic aromatic hydrocarbons (PAHs) and their alkylated forms are important components of crude oil. Both groups of PAHs have been reported to cause dioxin-like responses, mediated by aryl hydrocarbon receptor (AhR). Thus, characterization of binding affinity to the AhR of unsubstituted or alkylated PAHs is important to understand the toxicological consequences of oil contamination on ecosystems. We investigated the potencies of major PAHs of crude oil, e.g., chrysene, phenanthrene and dibenzothiophene, and their alkylated forms (n=17) to upregulate expression of AhR-mediated processes by use of the H4IIE-luc transactivation bioassay. In addition, molecular descriptors of different AhR activation potencies among PAHs were investigated by use of computational molecular docking models. Based on responses of the H4IIE-luc in vitro assay, it was shown that potencies of PAHs were determined by alkylation in addition to the number and conformation of rings. Potencies of AhR-mediated processes were generally greater when a chrysene group was substituted, especially in 1-methyl-chrysene. Significant negative correlations were observed between the in vitro dioxin-like potency measured in H4IIE-luc cells and the binding distance estimated from the in silico modeling. The difference in relative potency for AhR activation observed among PAHs and their alkylated forms could be explained by differences among binding distances in the ligand binding domain of the AhR caused by alkylation. The docking model developed in the present study may have utility in predicting risks of environmental contaminants of which toxicities are mediated by AhR binding.

Potency of polycyclic aromatic hydrocarbons (PAHs) for induction of ethoxyresorufin-O-deethylase (EROD) activity in hepatocyte cultures from chicken, Pekin duck, and greater scaup

The potency of tetrachlorodibenzo-p-dioxin (TCDD) and 18 polycyclic aromatic hydrocarbons (PAHs) for induction of ethoxyresorufin-O-deethylase (EROD) activity was assessed in primary hepatocyte cultures prepared from chicken (Gallus domesticus), Pekin duck (Anas platyrhynchos domesticus), and greater scaup (Aythya marila). TCDD and 8 of the PAHs induced EROD activity in a concentration-dependent manner. Seven of these were previously shown to be acutely toxic to avian embryos, while the 10 congeners that did not produce an EROD response caused limited mortality. The rank order potency of the EROD-active congeners in all three species was as follows: TCDD>dibenz[ah]anthracene>benzo[k]fluoranthene>indeno[1,2,3-cd]pyrene>benzo[a]pyrene>chrysene≈benz[a]anthracene≈benz[ghi]perylene>benzo[b]naphtho[2,3-d]thiophene. Chicken hepatoctyes were more sensitive than duck hepatocytes to EROD induction by all test compounds, but the gap in species sensitivity was 100-fold for TCDD, and generally ≤10-fold for PAHs. This study is the first to use in vitro methods to rank the AHR-mediated potency of PAHs in birds. These data may be useful for assessing risks associated with exposure to PAHs in the environment.

Aryl hydrocarbon receptor activation and developmental toxicity in zebrafish in response to soil extracts containing unsubstituted and oxygenated PAHs

Many industrial sites are polluted by complex mixtures of polycyclic aromatic compounds (PACs). Besides polycyclic aromatic hydrocarbons (PAHs), these mixtures often contain significant amounts of more polar PACs including oxygenated PAHs (oxy-PAHs). The effects of oxy-PAHs are, however, poorly known. Here we used zebrafish embryos to examine toxicities and transcriptional changes induced by PAC containing soil extracts from three different industrial sites: a gasworks (GAS), a former wood preservation site (WOOD), and a coke oven (COKE), and to PAH and oxy-PAH containing fractions of these. All extracts induced aryl hydrocarbon receptor (Ahr)-regulated mRNAs, malformations, and mortality. The WOOD extract was most toxic and the GAS extract least toxic. The extracts induced glutathione transferases and heat shock protein 70, suggesting that the toxicity also involved oxidative stress. With all extracts, Ahr2-knock-down reduced the toxicity, indicating a significant Ahr2-dependence on the effects. Ahr2-knock-down was most effective with the PAH fraction of the WOOD extract and with the oxy-PAH fraction of the COKE extract. Our results indicate that oxy-PAH containing mixtures can be as potent Ahr activators and developmental toxicants as PAHs. In addition to Ahr activating potency, the profile of cytochrome P4501 inhibitors may also determine the toxic potency of the extracts.

Differential expression of CYP1A1 and CYP1A2 genes in H4IIE rat hepatoma cells exposed to TCDD and PAHs

Rat hepatoma cells H4IIE were treated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polycyclic aromatic hydrocarbons (PAHs) (dibenz(a,h)anthracene, benzo(a)pyrene, benz(a)anthracene, chrysene), low-concentration mixtures of PAHs and TCDD, and environmental mixtures contaminated by PAHs and their derivatives. Expression of the gene battery comprising cytochrome P450 Cyp1a1, Cyp1a2, Cyp1b1, and glutathione-s-transferase Gsta2 and Gstp was investigated using quantitative real time polymerase chain reaction (qRT-PCR) analysis. The results revealed that TCDD induce Cyp1a1>Cyp1a2>Cyp1b1, while PAHs and PAH-containing environmental mixtures induce Cyp1a2>Cyp1a1>Cyp1b1 gene expression pattern. While low-concentration mixtures elicited a more pronounced response in comparison to single treatments, the typical gene expression patterns were not observed. In all samples, Gsta2 was predominantly expressed relative to Gstp. These findings indicate that differential Cyp1a1 and Cyp1a2 expression in the H4IIE cells might be used for detection of PAHs in highly contaminated environmental mixtures, but not in low-concentration mixtures of these compounds.

AhR-mediated activities of polycyclic aromatic compound (PAC) mixtures are predictable by the concept of concentration addition

Risk assessments of polycyclic aromatic hydrocarbons (PAHs) are complicated because these compounds exist in the environment as complex mixtures of hundreds of individual PAHs and other related polycyclic aromatic compounds (PACs). In this study, the hypothesis that concentration addition (CA) can be used to predict the aryl hydrocarbon receptor (AhR)-mediated activity of PACs in mixtures containing various combinations of PACs was tested. AhR-mediated activities of 18 mixtures composed of two to 23 PACs, which included PAHs, azaarenes and oxygenated PAHs, were examined by the use of the AhR-based H4IIE-luc bioassay. Since greater AhR-mediated activities have been observed in soils contaminated by PAHs, investigations were done to test whether soil extract matrix or the presence of non-effect PACs might affect responses of the H4IIE-luc bioassay. Our results showed that AhR-mediated activities of mixtures of PACs could be predicted by the use of concentration addition. Additive activities of PACs in multi component mixtures along with the insignificant effect of the soil matrix support the use of concentration addition in mass balance calculations and AhR-based bioassays in risk assessment of environmental samples. However, independent action (IA) could not be used to predict the activity of mixtures of PACs.

Methylated and unsubstituted polycyclic aromatic hydrocarbons in street dust from Vietnam and India: occurrence, distribution and in vitro toxicity evaluation

Methylated polycyclic aromatic hydrocarbons (MePAHs), unsubstituted PAHs and AhR-mediated activities were determined in street dust collected from Vietnam and India using a combined approach of chemical analysis and in vitro reporter gene assay. MePAHs and PAHs diagnostic ratios indicated that the main sources of MePAHs in Vietnam were pyrogenic emissions, whereas in India there were mixed sources of pyrogenic and petrogenic emissions. AhR-mediated activities determined by using DR-CALUX assay were observed in urban street dust at mean 40, 29 and 20 ng CALUX-TEQ/g dw for Hanoi, Bangalore and New Delhi, respectively. MePAHs and PAHs contributed only 5% or less to AhR-mediated activity in street dust, indicating the occurrence of unknown AhR agonists. The principal contributors to Theoretical-TEQs among target compounds were methyl benz[a]anthracene, benzo[b]- and benzo[k]fluoranthene. The present study indicates importance of MePAHs in evaluation of toxic risk related to AhR-mediated activity in urban polluted areas.