Gene expression induction of volatile organic compound and/or polycyclic aromatic hydrocarbon-metabolizing enzymes in isolated human alveolar macrophages in response to airborne particulate matter (PM2.5)

To contribute to improve the knowledge of the underlying mechanisms of action involved in air pollution particulate matter (PM)-induced cytotoxicity, we were interested in the metabolic activation of volatile organic compounds (VOC) and/or polycyclic aromatic hydrocarbons (PAH) coated onto Dunkerque City's PM2.5 in human alveolar macrophages (AM) isolated from bronchoalveolar lavage fluid (BALF). This in vitro cell lung model is closer to the normal in vivo situation than other lung cell lines, notably in the characteristics that AM display in terms of gene expression of phase I and phase II-metabolizing enzymes. The bronchoscopic examinations and BAL procedures were carried out without any complications. After 24, 48 and 72h of incubation, calculated lethal concentrations at 10% and 50% of collected airborne PM were 14.93microg PM/mL and 74.63microg PM/mL, respectively, and indicated the higher sensibility of such target lung cells. Moreover, VOC and/or PAH coated onto PM induced gene expression of cytochrome P450 (cyp) 1a1, cyp2e1, nadph quinone oxydo-reductase-1, and glutathione S-transferase-pi 1 and mu 3, versus controls, suggesting thereby the formation of biologically reactive metabolites. In addition, these results suggested the role of physical carrier of carbonaceous core of PM, which can, therefore, increase both the penetration and the retention of attached-VOC into the cells, thereby enabling them to exert a longer induction. Hence, we concluded that the metabolic activation of the very low doses of VOC and/or PAH coated onto Dunkerque City's PM2.5 is one of the underlying mechanisms of action closely involved in its cytotoxicity in isolated human AM in culture.     

Polycyclic aromatic hydrocarbons within airborne particulate matter (PM2.5) produced DNA bulky stable adducts in a human lung cell coculture model

To extend current knowledge on the underlying mechanisms of air pollution particulate matter (PM_2.5)‐induced human lung toxicity, the metabolic activation of polycyclic aromatic hydrocarbons (PAH) within PM_2.5 and PAH–DNA bulky stable adduct patterns in human alveolar macrophage (AM) and/or human lung epithelial L132 cells in mono‐ and cocultures were studied. In the coculture system, only human AM were exposed to air pollution PM_2.5, unlike L132 cells. Particles, inorganic fraction and positive controls [i.e. TiO₂, thermally desorbed PM (dPM) and benzo[a]pyrene, B[a]P, respectively] were included in the experimental design. Cytochrome P450 (CYP) 1A1 gene expression, CYP1A1 catalytic activity and PAH–DNA bulky stable adducts were studied after 24, 48 and/or 72 h. Relatively low doses of PAH within PM_2.5 induced CYP1A1 gene expression and CYP1A1 catalytic activity in human AM and, thereafter, PAH–DNA bulky stable adduct formation. Adduct spots in PM_2.5‐exposed human AM were higher than those in dPM‐exposed ones, thereby showing the incomplete removal of PAH by thermal desorption. PAH within air pollution PM_2.5 induced CYP1A1 gene expression but not CYP1A1 catalytic activity in L132 cells. However, despite the absence of PAH–DNA bulky stable adduct in L132 cells from human AM/L132 cell cocultures exposed to dPM_2.5 or PM_2.5, reliable quantifiable PAH–DNA bulky stable adducts were observed in L132 cells from human AM/L132 cell coculture exposed to B[a]P. Taken together, these results support the exertion of genotoxicity of highly reactive B[a]P‐derived metabolites produced within human AM not only in primary target human AM, but also in secondary target L132 cells. Copyright © 2011 John Wiley & Sons, Ltd.     

PM2.5-induced alterations of cell cycle associated gene expression in lung cancer cells and rat lung tissues

The aim of the current study was to investigate the expression of cell cycle-associated genes induced by fine particulate matter (PM_2.5) in lung cancer cell line and tissues. The pulmonary lymph node metastasis cells (H292) were treated with PM_2.5 in vitro. Wistar rats were used to perform an in vivo study. Rats were randomly assigned to experiment and control groups and those in the experiment group were exposed to PM_2.5 once every 15 d, while those in the control group were exposed to normal saline. The cell cycle-associated genes expression was analyzed by real-time PCR. Trachea and lung tissues of rats were processed for scanning electron microscopic (SEM) examinations. Exposure of H292 cells to PM_2.5 dramatically increased the expressions of p53 and cyclin-dependent kinase 2 (CDK2) after 24 h of exposure (p < 0.01) and markedly increased the expressions of the cell division cycle 2 (Cdc2) and cyclin B after 48 h of exposure (p < 0.01), while those genes expressions were significantly reduced after 72 h of exposure, at which time the expression of p21 was predominant (p < 0.01). In vivo studies further demonstrated these results. The results of SEM suggested that both of the trachea and lung tissues were damaged and the degree of damage was time-dependent. In conclusion, PM_2.5 can induce significantly alterations of p53 and CDK2 in the early phase, Cdc2 and cyclin B in mid-term and p21 in long-term exposure. The degree of PM_2.5-induced damage to the trachea and lung tissue was time-dependent.     

Fine particulate matter (PM2.5) enhances allergic sensitization in BALB/c mice

Ambient particulate matter (PM), a component of air pollution, exacerbates airway inflammation and hyperreactivity in asthmatic patients. Studies showed that PM possesses adjuvant-like properties that enhance the allergic inflammatory response; however, the mechanism (or mechanisms) by which PM enhances the allergic response remains to be determined. The aim of this study was to assess how exposure to fine PM collected from Sacramento, CA, shapes the allergic airway immune response in BALB/c mice undergoing sensitization and challenge with ovalbumin (OVA). Eight-week-old BALB/c male mice were sensitized/challenged with phosphate-buffered saline (PBS/PBS; n = 6), PM/PBS (n = 6), OVA/OVA (n = 6), or OVA + PM/OVA (n = 6). Lung tissue, bronchoalveolar lavage fluid (BALF), and plasma were analyzed for cellular inflammation, cytokines, immunoglobulin E, and heme oxygenase-1 (HO-1) expression. Mice in the OVA + PM/OVA group displayed significantly increased airway inflammation compared to OVA/OVA animals. Total cells, macrophages, and eosinophils recovered in BALF were significantly elevated in the OVA + PM/OVA compared to OVA/OVA group. Histopathological grading indicated that OVA + PM/OVA treatment induced significant inflammation compared to OVA/OVA. Both immunoglobulin (Ig) E and tumor necrosis factor (TNF) α levels were significantly increased in OVA/OVA and OVA + PM /OVA groups compared to PBS/PBS control. The number of HO-1 positive alveolar macrophages was significantly elevated in lungs of mice treated with OVA + PM /OVA compared to OVA/OVA. Our findings suggest that fine PM enhances allergic inflammatory response in pulmonary tissue through mechanisms involving increased oxidative stress.     

Role of nuclear factor-kappa B activation in the adverse effects induced by air pollution particulate matter (PM2.5) in human epithelial lung cells (L132) in culture

To contribute to improving knowledge on the adverse health effects induced by particulate matter (PM) air pollution, an extensive investigation was undertaken of the underlying mechanisms of action activated by PM(2.5) air pollution collected in Dunkerque, a strongly industrialized French seaside city. Their chemical and physical characteristics have been previously determined, and earlier in vitro short-term studies have shown them to cause dose-dependent and time-dependent oxidative damage, gene expression and protein secretion of inflammatory mediators, and apoptotic events in human lung epithelial cells (L132) in culture. Hence, this work studied the activation of nuclear factor-kappa B (NF-kappaB)/inhibitory kappa B (IkappaB) by Dunkerque city PM(2.5) in these target cells, by determination of phosphorylated p65 and phosphorylated IkappaBalpha protein levels in cytoplasmic extracts, and p65 and p50 DNA binding in nuclear extracts. In PM-exposed L132 cells, there were concentration- and/or time-dependent increases in nuclear p65 and cytoplasmic IkB-alpha phosphorylation, and nuclear p65 and p50 DNA binding. Taken together, these results showed that Dunkerque city PM(2.5) were involved in the activation of the NF-kappaB/IkappaB complex, notably through the occurrence of oxidative stress conditions, and, therefore, in the gene expression and protein secretion of inflammatory mediators in target L132 cells. Hence, these findings suggested that the activation of the NF-kappaB/IkappaB complex preceded cytotoxicity in Dunkerque city PM-exposed L132 cells.     

体外应用抑制性消减杂交技术克隆和筛选大气细颗粒物（PM2．5）污染相关基因

大气细颗粒物(Fine Particular Matter,PM2.5)是指空气动力学直径小于2.5μm的分散在大气中的固态或液态颗粒物物质.国外大量流行病学研究资料提示,颗粒物浓度的上升与疾病的发病率、死亡率关系密切,尤其是呼吸系统疾病及心血管疾病[1-2].     

Exposure to particulate matter 2.5 (PM2.5) induced macrophage-dependent inflammation,characterized by increased Th1/Th17 cytokine secretion and cytotoxicity

Particulate matter PM2.5 is a class of airborne particles and droplets with sustained high levels in many developing countries. Epidemiological studies have shown the association between sustained high level of PM2.5 and the risk of many diseases in the respiratory system, including lung cancer. However, the precise mechanisms through which PM2.5 induces respiratory diseases are still unclear. In this study, we demonstrated that CD4⁺ and CD8⁺ T cells following PM2.5 treatment demonstrated significantly elevated mRNA and protein levels of interferon (IFN)-γ, interleukin (IL)-10, IL-17, and IL-21 production. This increase in cytokines required the presence of macrophages, such that CD4⁺ and CD8⁺ T cells treated with PM2.5 in the absence of macrophages did not present higher IFN-γ, IL-10, or IL-21 expression. In contrast, PM2.5-treated macrophages could significantly upregulate T cell cytokine secretion, even when excess PM2.5 was removed from cell culture. We also observed a macrophage-dependent upregulation of granzyme A and granzyme B expression by CD4⁺ and CD8⁺ T cells following PM2.5 treatment. These PM2.5-stimulated CD4⁺ and CD8⁺ T cells potently induced the death of human bronchial epithelial (HBE) cells. Interestingly, the CD4⁺ and CD8⁺ T cells presented synergistic effects at inducing HBE cytotoxicity, such that CD4⁺ T cells and CD8⁺ T cells combined resulted in higher HBE cell death than the sum of the separate effects of CD4⁺ T cells and CD8⁺ T cells. While blocking cytotoxic molecule release significantly compromised the T cell-mediated cytotoxicity against HBE cells, blocking IFN-γ, but not IL-10, could also slightly but significantly reduce T cell-mediated cytotoxicity. Together, these data demonstrated that PM2.5 could promote the inflammation of cytotoxicity of T cells in a macrophage-dependent manner. In addition, PM2.5-treated macrophages presented long-lasting proinflammatory effects on T cells.     

Pro-inflammatory effects of Dunkerque city air pollution particulate matter 2.5 in human epithelial lung cells (L132) in culture

Exposure to urban airborne particulate matter (PM) has been associated with adverse health effects. The majority of research articles published on air pollution PM relate to PM10. However, increasing emphasis and stringent regulations have been placed on PM2.5. The mechanisms for PM-induced adverse health effects are not well understood, but inflammation seems to be of importance. We focused our attention also on the capacity of air pollution PM2.5 to induce cytotoxic and inflammatory responses in human epithelial lung cells (L132) in culture. Particulate matter was collected in Dunkerque, a French seaside city characterized by the proximity of industrial activity and heavy motor vehicle traffic. Size distribution results showed that the cumulative frequency of PM2.5 was 92.15% and their specific surface area was 1 m2 g(-1). Inorganic and organic chemicals usually associated with the natural environment but also so-called anthropogenic elements were found in PM, suggesting that much of the PM was derived from wind-borne dust from the industrial complex and the heavy diesel motor vehicle. We observed PM concentration-dependent cytotoxic effects in L132 cells (LC10 = 18.84 microg PM ml(-1); LC50 = 75.36 microg PM ml(-1)). We showed that exposure to Dunkerque City's PM2.5 induced significant increases (in a concentration- and time-dependent manner) in protein secretion and/or gene expression of inflammatory cytokines (i.e. TNF-alpha, IL-1beta, IL-8, GM-CSF, IL-6, TGF-beta1). We hypothesized also that the occurrence of the acute inflammatory response might rely on the capacity of such air pollutants to generate oxidative species, which have been implicated in the stringent regulation of the cytokine network. Hence, we suggest that the development of inflammatory effects that worsen over time stems from the cytotoxicity in Dunkerque City's PM2.5-exposed L132 cells in culture.     

Fine particulate matter (PM2.5) enhances airway hyperresponsiveness (AHR) by inducing necroptosis in BALB/c mice

ObjectiveTo observe the effects of prolonged exposure to high concentrations of PM_2.5 on the trachea and lungs of mice and to determine whether the damages to the trachea and lung are induced by necroptosis.MethodsSix- to eight-week-old female Balb/C mice of PM group were restrained in an animal restraining device using a nose-only “PM_2.5 online enrichment system” for 8 weeks, in Shijiazhuang, Hebei, China. Anti -Fas group was exposed to PM_2.5 inhalation and anti-Fas treatment via intranasal instillation. The mice in the control group inhaled filtered clean air. PM_2.5 sample was collected and analyzed. Airway Hyperresponsiveness (AHR) was tested. Lung tissue and bronchoalveolar lavage fluid (BALF) were analyzed for Hematoxylin and eosin (HE) staining, electron microscopy, cellular inflammation, cytokines, Tunel, Fas, RIPK3 and MLKL expression.ResultsCompared to the other two groups, PM group displayed significantly increased AHR, neutrophils in BALF, significant bronchitis and alveolar epithelial hyperplasia and inflammation and necroptosis which were indicated by increased TUNEL, Fas, RIPK3 and MLKL measure.ConclusionOur findings suggest that PM_2.5 can enhance AHR and these changes are induced by necroptosis-related inflammation.     

Traffic air pollution and risk of death from ovarian cancer in Taiwan: fine particulate matter (PM2.5) as a proxy marker

The relationship between mortality attributed to ovarian cancer and exposure to ambient air pollutants was examined using an ecological design. The study areas consisted of 61 municipalities in Taiwan. Air quality data for recorded concentrations of fine particulate matter (PM2.5) from study municipalities for 2006-2009 were obtained as a marker of traffic emissions. These were used as a proxy for polycyclic aromatic hydrocarbons (PAH) exposure. Age-standardized mortality rates for ovarian cancer were calculated for the study municipalities for the years 1999-2008. A weighted multiple regression model was employed to calculate the adjusted risk ratio (RR) in relation to PM2.5 levels. After adjusting for urbanization level and fertility rate, the adjusted RR values (95% confidence interval [CI]) for ovarian cancer were 1.2 (1.02-1.41) for the municipalities with PM2.5 levels between 30.48 μg/m3 and 39.41 μg/m3 and 1.2 (1.03-1.39) for the municipalities with PM2.5 levels between 39.48 μg/m3 and 51.1 μg/m3, compared to the municipalities with PM2.5 levels less than 30.39 μg/m3. Results showed that individuals who resided in municipalities with higher levels of PM2.5, a proxy measure of PAH, were at an increased risk of death from ovarian cancer compared to those subjects living in municipalities with the lowest PM2.5. The findings of this study warrant further investigation into the role of exposure to air pollutants in the etiology of ovarian cancer development.     

The health impact of common inorganic components of fine particulate matter (PM2.5) in ambient air: a critical review

Ambient air particulate matter (PM) originates as either primary particles emitted directly into the atmosphere from a specific source or as secondary particles produced from atmospheric chemical reactions between precursor gases or between these gases and primary particles. PM can derive from both natural and anthropogenic sources, resulting in a complex chemical mix. The "fine" size mode of ambient PM, designated as PM(2.5), is defined as comprising those particles having aerodynamic diameters below 2.5 microm. While the total mass of PM(2.5) has been associated with adverse human health outcomes, the relationship between these and specific chemical components has not been resolved. This article provides a perspective on the current state of the science concerning health effects from a major group of chemical species found within PM(2.5), namely common inorganic constituents. The specific chemical classes discussed herein are secondary inorganic species, namely, sulfate, nitrate, and acidity, and generally crustal-derived species, namely, phosphate, sodium, potassium, calcium, magnesium, silicon, and aluminum. The article discusses evidence for adverse health effects from inorganic PM(2.5) components within the framework of various caveats surrounding both epidemiology and toxicology assessments. The largest database exists for sulfate, but conclusions that attribute sulfate to health outcomes have not been consistent across all epidemiology studies, and there is a lack of coherence with toxicology studies, which show biological responses only at high levels of exposure. Limited epidemiological and toxicological data for nitrate suggests little or no adverse health effects at current levels. Epidemiological studies specifically identifying crustal components of PM(2.5) suggest that they are not likely, by themselves, to produce a significant health risk, and these components do not have unequivocal biological plausibility from toxicological studies for being significant contributors to adverse health outcomes.     

Low dose of fine particulate matter (PM2.5) can induce acute oxidative stress,inflammation and pulmonary impairment in healthy mice

Air pollution is associated with morbidity and mortality induced by respiratory diseases. However, the mechanisms therein involved are not yet fully clarified. Thus, we tested the hypothesis that a single acute exposure to low doses of fine particulate matter (PM2.5) may induce functional and histological lung changes and unchain inflammatory and oxidative stress processes. PM2.5 was collected from the urban area of São Paulo city during 24?h and underwent analysis for elements and polycyclic aromatic hydrocarbon contents. Forty-six male BALB/c mice received intranasal instillation of 30 μL of saline (CTRL) or PM2.5 at 5 or 15?μg in 30 μL of saline (P5 and P15, respectively). Twenty-four hours later, lung mechanics were determined. Lungs were then prepared for histological and biochemical analysis. P15 group showed significantly increased lung impedance and alveolar collapse, as well as lung tissue inflammation, oxidative stress and damage. P5 presented values between CTRL and P15: higher mechanical impedance and inflammation than CTRL, but lower inflammation and oxidative stress than P15. In conclusion, acute exposure to low doses of fine PM induced lung inflammation, oxidative stress and worsened lung impedance and histology in a dose-dependent pattern in mice.     

Water‐insoluble fraction of airborne particulate matter (PM10) induces oxidative stress in human lung epithelial A549 cells

Exposure to ambient airborne particulate matter (PM) with an aerodynamic diameter less than 10 μm (PM₁₀) links with public health hazards and increases risk for lung cancer and other diseases. Recent studies have suggested that oxidative stress is a key mechanism underlying the toxic effects of exposure to PM₁₀. Several components of water‐soluble fraction of PM₁₀ (sPM₁₀) have been known to be capable of inducing oxidative stress in in vitro studies. In this study, we investigated if water‐insoluble fraction of PM₁₀ (iPM₁₀) could be also capable of inducing oxidative stress and oxidative damage. Human lung epithelial A549 cells were exposed to 10 μg/mL of sPM₁₀, iPM₁₀ or total PM₁₀ (tPM₁₀) preparation for 24 h. Here, we observed that all three PM₁₀ preparations reduced cell viability and induced apoptotic cell death in A549 cells. We further found that, similar to the exposure to sPM₁₀ and tPM₁₀, the intracellular level of hydrogen peroxide (H₂O₂) in the iPM₁₀‐exposed cells was increased significantly; meanwhile the activity of catalase was decreased significantly as compared with the unexposed control cells, resulting in significant DNA damage. Our data obtained from inductively coupled plasma‐mass spectrometry (ICP‐MS) assays showed that iron is the most abundant metal in all three PM₁₀ preparations. Thus, we have demonstrated that, similar to sPM₁₀, iPM₁₀ is also capable of inducing oxidative stress by probably inducing generation of H₂O₂ and impairing enzymatic antioxidant defense, resulting in oxidative DNA damage and even apoptotic cell death through the iron‐catalyzed Fenton reaction. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 226–233, 2014.     

Role of endogenous sulfur-containing nucleophiles in an in vitro model of cis-diamminedichloroplatinum(II)-induced nephrotoxicity

Quiescent LLC-PK1 cells have been shown to be a good model of cis-diamminedichloroplatinum(II) (DDP)-induced nephrotoxicity. In these nonproliferating porcine kidney epithelial cells, DDP inhibition of protein synthesis rate is the major correlate of cytotoxicity. We report here the use of this cell line to investigate the role of endogenous sulfur-containing nucleophiles in DDP-induced nephrotoxicity. Reaction of DDP with glutathione (GSH), cysteine, or methionine for up to 24 hr led to concentration- and time-dependent loss of its toxic effects, whereas dissolution of DDP alone did not alter its reduction of viability or protein synthesis rate in LLC-PK1 cells. Treatment of these cells with differing cytotoxic concentration of DDP produced an identical transient increase in intracellular GSH, whereas compounds known to bind GSH, trans-diamminedichloroplatinum(II) (t-DDP) and diethyl maleate (DEM), rapidly depleted LLC-PK1 intracellular GSH levels. Buthionine sulfoximine (BSO) treatment decreased intracellular GSH to 10% of control without altering cell viability or protein synthesis rate. However, BSO-pretreated LLC-PK1 cells exhibited enhanced DDP-induced toxicity. CdCl2 treatment produced a 30-fold induction of metallothionein-like, cadmium-binding proteins and a 10-fold increase in metallothionein isoform I (MT-I) mRNA, but this induction had no effect on DDP-induced reduction of viability or protein synthesis rate. Protracted DDP exposure did not induce MT-I mRNA levels in LLC-PK1 cells.     

An approach to investigating the importance of high potency polycyclic aromatic hydrocarbons (PAHs) in the induction of lung cancer by air pollution.

Evidence suggests that people living in urban areas have an increased risk of lung cancer due to higher levels of air pollution in these areas. Benzo[a]pyrene (B[a]P) is currently used as the main indicator of carcinogenic polycyclic aromatic hydrocarbons (PAHs) in air pollution, but there is concern that B[a]P may not be the ideal surrogate of choice for PAH mixtures since higher potency PAHs have recently been identified which could potentially contribute more and variably to the overall carcinogenicity. Dibenzo[a,h]anthracene (DBA) and dibenzo[a,l]pyrene (DB[a,l]P) are estimated to have carcinogenic potencies 10 or more times greater than B[a]P but data on their presence and formation in the environment are limited. Several occupational and environmental PAH biomonitoring studies are reviewed here, with particular focus on the specific exposure groups, study design, sample tissue, in particular the use of nasal tissues, and biomarkers used in each study. Consideration of these data is then used to propose a novel biomonitoring approach to evaluate exposure, uptake and the role of high potency PAHs in air pollution-related lung cancer. This is based upon an occupational study examining specific DNA adducts for DBA and DB[a,l]P in nasal cells to evaluate the extent to which these high potency PAHs might contribute to the increased risk of developing lung cancer from air pollution.     

Water-soluble and organic extracts of ambient PM2.5 in Tehran air: assessment of genotoxic effects on human lung epithelial cells (A549) by the Comet assay

The main aim of the present study is to investigate the physicochemical characterization of water-soluble extract (WS) and organic extract (OE) of PM_2.5 ambient in Tehran city air in order to evaluate the genotoxicity effects and the potential attribution to these effects. The lung epithelial cells (A549) were exposed to WS and OE, while Comet assays were conducted to analyze the genotoxicity. The results show that the amount of DNA damage in WS fraction and solvent-extractable organic samples is significantly higher than the control group and the increase in concentration significantly contributes to increase in the amount of DNA damage.     

Modulation of ethoxyresorufin O-deethylase and glutathione S-transferase activities in Nile tilapia (Oreochromis niloticus) by polycyclic aromatic hydrocarbons containing two to four rings: implications in biomonitoring aquatic pollution

Despite ubiquity of polycyclic aromatic hydrocarbons (PAHs) in the tropical environments, little information is available concerning responses of tropical fish to PAHs and associated toxicity. In the present study, effects of five PAHs containing two to four aromatic rings on hepatic CYP1A dependent ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and serum sorbitol dehydrogenase (SDH) activities in Nile tilapia, a potential fish species for biomonitoring pollution in tropical waters, were evaluated. Results showed that EROD activities were induced by the PAHs containing four aromatic rings (pyrene and chrysene) in a dose dependent manner. However PAHs with two to three aromatic rings (naphthalene, phenanthrene and fluoranthene) caused no effect or inhibition of EROD activities depending on the dose and the duration. Fluoranthene was the most potent inhibitor. SDH results demonstrated that high doses of fluoranthene induced hepatic damage. GST activity was induced by the lowest dose of phenanthrene, fluoranthene and chrysene but high doses had no effect. The results indicate that induction of EROD enzyme in Nile tilapia is a useful biomarker of exposure to PAHs such as pyrene and chrysene. However EROD inhibiting PAHs such as fluoranthene in the natural environment may modulate the EROD inducing potential of other PAHs thereby influencing PAH exposure assessments.