Effects Of Polycyclic Aromatic Hydrocarbons Research Articles

The ex vivo study of synergistic effects of polycyclic aromatic hydrocarbon, benzo(a)pyrene with ovalbumin on systemic immune responses by oral route.

The present study was undertaken in order to examine whether oral administration of soluble antigen together with one of polycyclic aromatic hydrocarbons (PAHs) which is present in diesel exhaust particles (DEPs) called benzo(a)pyrene (BP), induced the systemic immune response in mice or not. Mice were orally given 1mg of ovalbumin (OA), a common food allergen, every 3 days over a period of 15 days. The results showed that oral administration of OA plus BP produced anti-OA IgE antibodies in serum, whereas either OA or BP alone failed to show the antigen-specific IgE antibody production. Production of anti-OA IgE antibody, which is dependent on Th2 CD4(+) T cells, was seen in mice fed with combined OA and BP was significantly higher than that of other groups. The anti-OA antibody production was associated with marked secretion of the Th1 cytokines, IFN-gamma and IL-12p70 as well as the Th2 cytokines IL-4, and IL-10. These results suggest that BP may act as a mucosal adjuvant in the gut enhancing systemic Th1 and Th2 immune responses and might play a role in oral immunization and food allergy.

Inhibition of gap junction intercellular communications in cell culture by polycyclic aromatic hydrocarbons (PAH) in the absence of PAH metabolism.

We have studied the effect of polycyclic aromatic hydrocarbons (PAH) on gap junction intercellular communications (GJIC) in culture of hepatoma cells Hep G2 and G27. Carcinogenic PAH inhibited GJIC in both cultures in contrast to non-carcinogenic PAH. We showed that both constitutive and inducible expressions of mRNAs of Ah receptor and cytochrome P4501A1 (the main isoform involved in PAH metabolism) were absent in hepatoma G27 cells. We concluded that the initial, non-metabolized molecules of carcinogenic PAH are responsible for changes in GJIC through interaction with an unknown factor in the cellular membrane.

Effect of polycyclic aromatic hydrocarbons on erythrocyte membranes by DSC and EPR

Differential scanning calorimetry (DSC) and electron paramagnetic resonance spectroscopy (EPR) experiments were performed on human erythrocyte membranes and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) model systems in order to study the effect the polycyclic aromatic hydrocarbons on lipid structure and dynamics. Eight different compounds among others naphthalene and pyrene were compared, which occur in significant concentrations in dust collected from the air in large cities. Experiments using spin label technique showed that the compounds induced mobility changes in the lipid region in the environment of the fatty acid probe molecules incorporated into the membranes. The effects depended on the structure and concentration of the different compounds. Similarly to EPR observations, DSC measurements reported decrease of transition temperature in comparison to control DPPC vesicles. These results suggest that polycyclic aromatic hydrocarbons were able to modify the internal dynamics of erythrocyte membranes which might lead to damage of the biological functions.

Chemoprotective effects of broccoli and other Brassica vegetables

Numerous epidemiological studies indicate that Brassica vegetables protect humans against cancer. The family Cruciferae genus Brassica consists of the species Brassica oleracea (e.g., broccoli, cabbage, cauliflower, Brussels sprouts, kale, turnips, collards), which are the most frequently consumed vegetables worldwide. Brassica vegetables are the richest sources of glucosinolates (p-thioglycoside-N-hydroxysulfates), which have considerable anticarcinogenic properties. Glucosinolates are hydrolyzed to biologically active isothiocyanates by the plant enzyme myrosinase when the cells in the plant are damaged (e.g., cut, ground or chewed). Glucoraphanin, which accounts for 35-50% of broccoli glucosinolates, is converted to sulforaphane (1-isothiocyannato-4-(methylsulfinyl)butane), a potent monofunctional phase II enzyme inducer. Several animal studies demonstrated that Brassica vegetables are protective against various classes of DNA-reactive carcinogens. They can reduce chemically induced tumor formation, attenuate the effects of polycyclic aromatic hydrocarbons and nitrosoamines and have a protective effect against heterocyclic amines. This review outlines Brassica vegetables and their metabolism, chemoprotective mechanisms of action, pharmacogenomics and adverse effects. In addition, the overview of recently conducted epidemiological studies on risk reduction of different cancers due to consumption of Brassica vegetables is provided.

Effect of Polycyclic Aromatic Hydrocarbons on Generation and Efflux of Glutathione Conjugates in Primary Cultured Alveolar Epithelial Cells

This study was initiated to functionally characterize multidrug resistance associated protein (MRP)-mediated transport across the lung epithelium. Alveolar type II cells were isolated from rabbit lung and cultured on Transwell until forming a tight monolayers. After the cell monolayer was preloaded with monochlorobimane (mBCl) that is metabolized to a fluorescent glutathione conjugate (mBCl-SG), amount of mBCl-SG exported to apical and basal compartments were measured periodically. mBCl-SG was more preferentially exported in the apical direction than in the basolateral direction. Efflux of mBCl-SG from alveolar epithelial cells was significantly inhibited by a MRP inhibitor MK-571. Pharmacokinetic analysis of efflux profiles revealed that increased efflux of mBCl-SG by B[a]P is not due to enhanced MRP activity but simply due to an elevated level of mBCl-SG in the cells. Elevation of the intracellular level of mBCl-SG corresponded well to that of reduced GSH caused by B[a]P pretreatment.

DNA damage in T- and B-lymphocytes and granulocytes in emission inspection and incineration workers exposed to polycyclic aromatic hydrocarbons

In this study, we investigated by using comet assay the effects of polycyclic aromatic hydrocarbon (PAH) as a major factor on DNA damage of workers exposed to exhaust fumes. Twenty-four workers from three automobile emission inspection companies, 28 workers from a waste incinerating company, and 43 matched, unexposed healthy subjects were enrolled in the study. The mean values of 1-hydroxypyrene (1-OHP) in automobile emission inspection and waste incineration workers were 0.27±0.19 and 0.57±0.46 μmol/mol creatinine, respectively, and the mean values of 2-naphthol in automobile emission inspectors and waste incineration workers were 4.80±4.01 and 8.30±4.79 mol/mol creatinine, respectively. Significant difference in urinary metabolites, 1-hydroxypyrene and 2-naphthol was found between smokers and non-smokers in exposed groups and it may be due to the amounts of smoking cigarettes. In T-lymphocytes, DNA damage in control subjects, emission inspection workers and incineration workers were 1.42±0.22, 1.41±0.22 and 1.76±0.27, respectively. DNA damage of B-lymphocytes in the three groups showed the most significant differences of three cell types. The tail moments of the B-lymphocytes of control subjects, emission inspection and incineration workers were 1.40±0.27, 2.44±0.32 and 2.36±0.37, respectively. In granulocytes, DNA damage was also different, the tail moments being 2.72±0.59, 3.32±0.38 and 2.85±0.49, respectively. Although 1-OHP and 2-naphthol levels were statistically increased in smokers in workers exposed to PAHs, exposed smoking and non-smoking workers did not show any significantly difference in terms of Olive tail moments. Our results suggest that PAH causes single strand DNA breakage in human T- and B-lymphocytes, and granulocytes. A comparison of DNA damage in three groups showed that B-lymphocytes are useful target in the biomonitoring of human exposure.

Effects of polycyclic aromatic hydrocarbons on liver and lung cytochrome P450s in mice.

Certain polycyclic aromatic hydrocarbons (PAHs) have been reported to induce cytochrome P450 (CYP) 1A1 and 1A2. In the present study, the effects of six well-known PAHs, such as benzo[a]pyrene, benz[a]anthracene, dibenz[a,h]anthracene, chrysene, benzo[k]fluorancene and benzo[b]fluorancene, on the activities of hepatic and pulmonary CYP enzymes were investigated in male ICR mice. When mice were treated intraperitoneally with 3, 10 and 30 mg/kg of individual PAHs for 3 consecutive days, the activities of ethoxyresorufin- and methoxyresorufin-O-dealkylases were significantly and differentially induced in both liver and lung. Moreover, other CYP isozyme-associated monooxygenase activities were also induced significantly in liver and lung with characteristic induction profiles. Our present results suggest that individual PAHs might have inductive effects on CYP isozymes, and that the characteristic inductive effects of individual PAHs on certain CYP isozymes would be developed as a marker for determining exposure to certain PAHs.

A role of aryl hydrocarbon receptor in the antiandrogenic effects of polycyclic aromatic hydrocarbons in LNCaP human prostate carcinoma cells.

The role of aryl hydrocarbon receptor (AhR) on the antiandrogenic effects of polycyclic aromatic hydrocarbons (PAHs) was studied in LNCaP cells. The PAHs used in this study were chrysene (Chr), benzo[ k]fluoranthene (BkF), benzo[ a]pyrene (BaP), anthracene (Ant) and pyrene (Pyr). Chr, BkF and BaP acted as AhR agonists in LNCaP cells, while Ant and Pyr did not. The antiandrogenic effects of the PAHs were evaluated on the basis of regulation of prostate-specific antigen (PSA) mRNA and protein levels by 5alpha-dihydrotestosterone (DHT). Chr, BkF and BaP exhibited an antiandrogenic effect, but Ant and Pyr did not. alpha-Naphthoflavone (alpha-NF), an AhR antagonist, reversed the antiandrogen action of Chr, BkF and BaP, suggesting a requirement for activated AhR. The antiandrogenic PAHs did not significantly decrease androgen receptor (AR) levels or cellular DHT concentrations. Gel mobility shift assays revealed that Chr, BkF and BaP inhibited the binding of AR in nuclear extracts to oligonucleotide probes containing the AR-responsive element (ARE), whereas Ant and Pyr had no effect. The antiandrogenic PAHs elevated mRNA levels of c-fos and c-jun. Since activator protein-1 (AP-1), a heterodimer of c-jun and c-fos proteins, is known to inhibit binding of AR to ARE by protein-protein interaction with AR, the findings in the present study suggest a possible involvement of AP-1 in the antiandrogenic effects of PAHs acting as AhR agonists. These results suggest that AhR can stimulate AP-1 expression resulting in inhibition of the binding of AR to ARE in the transcription regulatory region of target genes such as PSA.

Novel Quantitative Assessment for the Toxic Effect of Polycyclic Aromatic Hydrocarbon-Like Compounds in a Water Environment Using the Ethoxyresorufin O-Deethylase Microbioassay.

The response of environmental pollutants can be detected bioanalytically focusing on the source and matrices of concern. Cell culture bioassays are rapid and inexpensive and thus have great potential for routine monitoring of aquatic resources. Such novel in vitro assays are a new tool to investigate lipophilic and low volatile compounds and are a powerful complement to instrumental analysis. The ethoxyresorufin O-deethylase (EROD) microbioassay was conducted to determine cytochrome P4501A (CYP1A) activity in environmental samples, and the calculated 3-methylchloranthrene (3-MC) equivalent concentration (MEQ) was introduced as a new quantitative water quality parameter. The chemical MEQ was calculated by multiplying induction equivalency factor (IEF) to GC-MS analysis data. And biological (bio-) MEQ was calculated by comparing the concentration response curve of the sample with those of the 3-MC calibration curve. Therefore, chemical MEQ is an estimation of the toxic effects of polycyclic aromatic hydrocarbons (PAHs) and bio-MEQ is the total toxic effects of various CYP1A-inducing chemicals in water samples. In this study, bio-MEQ values of water samples were higher than chemical MEQ values and total PAH concentrations, indicating that there must be other compounds in the water sample effective as inducers of EROD and that the biological activities of mixture compounds are mainly due to additive effects. There was a good correlation between bio-MEQ and total PAH concentration. The difference between bio-MEQ and total PAH concentration was high in downstream areas, i.e., polluted sites. Bio-MEQ calculated based on the enzyme-inducing effect of water samples could give information about the biological potency of water samples caused by PAH-like compounds.

Polycyclic aromatic hydrocarbons present in cigarette smoke cause endothelial cell apoptosis by a phospholipase A2-dependent mechanism.

Smoking is a major risk factor for endothelial cell injury and subsequent coronary artery disease. Epidemiological studies implicate the phospholipase A2/arachidonic acid cascade in the mechanism by which smoking causes heart disease. However, specific components of cigarette smoke that activate this pathway have not been identified. The purpose of this study was to investigate the effects of polycyclic aromatic hydrocarbons contained in cigarette smoke on phospholipase A2 (PLA2) activity and apoptosis of human coronary artery endothelial cells. 1-methylanthracene (1-MA), phenanthrene (PA), and benzo(a)pyrene (B(a)P) caused significant release of 3H-arachidonate from endothelial cells. 1-MA and PA, but not B(a)P, also caused significant release of 3H-linoleic acid. Release of fatty acids from membrane phospholipids preceded the onset of apoptosis. 3H-arachidonate release and apoptosis induced by 1-MA, B(a)P, and PA were inhibited by methylarachidonoyl-fluorophosphonate, an inhibitor of Groups IV and VI PLA2s. Bromoenol lactone, an inhibitor of Group VI enzymes, inhibited both 3H-arachidonate release and apoptosis induced by 1-MA and PA, but not B(a)P. MJ33, an inhibitor of the acidic calcium-independent PLA2, attenuated 3H-arachidonate release and apoptosis by PA, but not 1-MA or B(a)P. The presence of Groups IV and VI and the acidic iPLA2 in endothelial cells was demonstrated by reverse transcriptase-polymerase chain reaction and Western analysis. These data suggest that 1-MA, B(a)P and PA induce apoptosis of endothelial cells by a mechanism that involves activation of these three distinct isoforms of PLA2.

The effect of polycyclic aromatic hydrocarbons on the degradation of benzo[a]pyrene by Mycobacterium sp. strain RJGII‐135

Mycobacterium sp. strain RJGII-135 is capable of degrading a wide range of polycyclic aromatic hydrocarbons (PAHs), including benzo[a]pyrene (BaP). In this study, critical aspects of degradation were investigated, including compound uptake, relative rates of PAH degradation, and the effects of co-occurring PAH substrates on BaP degradation and mineralization to CO2. Mycobacterium sp. strain RJGII-135 was capable of degrading phenanthrene, anthracene, and pyrene at a 10- to 20-fold greater rate than benz[a]anthracene (BaA) and BaP. A significant amount of phenanthrene and pyrene, 30% and 10%, respectively, was completely mineralized, whereas less than 4% of anthracene, BaA, and BaP was mineralized. The PAH uptake assays demonstrated that high amounts of BaP and BaA, 81% and 75% of added compound, respectively, could be recovered from bacterial cell fractions after a 4-h incubation compared with pyrene (61%), anthracene (53%), and phenanthrene (47%). The half-saturation constant (Km) for pyrene was threefold lower for pyrene over BaP, suggesting that the degradation system in Mycobacterium sp. strain RJGII-135 has a higher affinity for pyrene, reaching maximal degradative activity at lower concentrations. No hybridization to dioxygenase gene probes nahAc, bphA1, or tolC1C2 was detected. Studies to investigate competition between different PAH substrates demonstrated that the rate of BaP metabolism was influenced by the presence of a second PAH substrate. The BaP metabolism was inhibited when coincubated with BaA, pyrene, and anthracene. Phenanthrene did not inhibit but enhanced BaP metabolism sixfold. These data suggest that induction effects of components of complex mixtures may be as important as competitive metabolism when assessing the ability of bacteria to effectively degrade high-molecular-weight PAHs in the environment.

Immunosuppressive Effect of Polycyclic Aromatic Hydrocarbons by Induction of Apoptosis of pre-B Lymphocytes of Bone Marrow

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous environmental pollutants, distinguished by genotoxic, hepatotoxic, nephrotoxic and immunotoxic effects. Especially secondary toxicity after bioactivation by microsomal monooxygenases (dependent on cytochromes P450) is characteristic of them. The immunotoxic effect is the result of very global impact on immunological reactivity of an organism and immunosuppression by induction of apoptosis of pre-B lymphocytes represents one of its particular forms. It has been proved that the effect of PAH is caused mostly by the following mechanisms: enzymatic induction by the way of activation of AhR (Aromatic hydrocarbon Receptor); alteration of cellular DNA; development of oxidative stress; increase in the concentration of intercellular calcium and decline of activity of NF-kappaB (Nuclear Factor-kappa B). Most sensitive to these changes are particularly B-lymphocytic precursors and pre-B lymphocytes. Intensity of entire manifestations is also considerably dependent on the presence and intensity of mechanisms of active or passive resistance of cells.

Identification of novel Ah receptor agonists using a high-throughput green fluorescent protein-based recombinant cell bioassay.

The Ah receptor is a ligand-dependent transcription factor that mediates the biological and toxic effects of polycyclic aromatic hydrocarbons and halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin). Recent evidence also suggests a role for the AhR in normal physiology and development. Although a variety of structurally diverse chemicals are reported to bind to and activate the AhR, the full spectrum of structural chemical classes that can interact with the AhR remains to be elucidated. Large-scale analysis of the ligand binding specificity of the AhR requires the use of a high-throughput AhR bioassay system for chemical screening. We have utilized a recombinant mouse hepatoma cell line (H1G1.1c3) containing a stably integrated TCDD- and AhR-responsive enhanced green fluorescent protein (EGFP) reporter gene to screen a 1,5-dialkylamino-2,4-dinitrobenzene combinatorial chemical library consisting of 155 parental amines and up to 12 090 combinatorial products in less than 7 days for novel AhR agonists. These analyses have identified numerous parental amines as relatively potent inducers of EGFP (with EC(50)s between 8 and 1000 microM) and also have revealed several novel products of the combinatorial chemical library synthesis with EC(50)s between 10 and 100 microM. Overall, these results have not only allowed the identification of novel activators of the AhR but also demonstrate the utility of the recombinant H1G1.1c3 cell bioassay for high-throughput chemical screening.

Human Aryl Hydrocarbon Receptor Polymorphisms That Result in Loss of CYP1A1 Induction

The aryl hydrocarbon receptor (AHR) binds xenobiotic chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and regulates transcription of the P4501 subfamily that metabolizes many carcinogens. In humans, the most frequent polymorphism is R554L. We report here an additional two polymorphisms in AHR that show apparent linkage disequilibrium with the codon 554 polymorphism: the first is a previously described polymorphism, V570I; the second is a novel human AHR polymorphism, P571S. In vitro expression of these variant forms showed normal ligand binding and DNA binding activities. However, transient expression experiments revealed that the combined Ile570 + Lys554 variant failed to support TCDD-dependent induction of CYP1A1 expression. It is possible that the abrogation of CYP1A1 induction in the combined Lys554 + Ile570 variant may reduce susceptibility of the host to the carcinogenic effects of polycyclic aromatic hydrocarbons. This combination of variant genotypes is rare and appears to be confined primarily to persons of African descent.

Effects of cruciferous vegetables and their constituents on drug metabolizing enzymes involved in the bioactivation of DNA-reactive dietary carcinogens

Epidemiological studies give evidence that cruciferous vegetables (CF) protect humans against cancer, and also results from animal experiments show that they reduce chemically induced tumor formation. These properties have been attributed to alterations in the metabolism of carcinogens by breakdown products of glucosinolates, which are constituents of CF. The present article gives an overview on the present state of knowledge on the impact of CF and their constituents on enzymes that are involved in the metabolism of DNA-reactive carcinogens. The development of in vitro models with metabolically competent cell lines led to the detection of potent enzyme inducers contained in CF such as sulforaphane. Recently, we showed that Brassica juices induce glutathione- S-transferases (GST) and cytochrome P-450 1A2 in human hepatoma cells (HepG2) and protect against the genotoxic effects of B(a)P and other carcinogens. Earlier in vivo experiments with rodents indicated that indoles and isothiocyanates, two major groups of glucosinolate breakdown products, attenuate the effects of polycyclic aromatic hydrocarbons (PAHs) and nitrosamines via induction of GST and inhibition of cytochrome-P450 isoenzymes, respectively. Our own investigations showed that CF are also protective towards heterocyclic amines (HAs): Brussels sprouts- and garden cress juices attenuated IQ-induced DNA-damage and preneoplastic lesions in colon and liver of rats. These effects were paralleled by induction of uridine-di-phospho-glucuronosyl transferase (UDPGT) which is very probably the mechanism of protection against HAs by cruciferous vegetables. There is also evidence that consumption of CF might protect humans against cancer. In matched control intervention studies with these vegetables, it was shown that they induce GST-activities in humans but overall, results were inconclusive. Recently, we carried out crossover intervention studies and found pronounced GST-induction upon consumption of Brussels sprouts and red cabbage, whereas no effects were seen with white cabbage and broccoli. Furthermore, we found that the isoenzyme induced was GST-π which plays an important role in protection against breast, bladder, colon and testicular cancer. No induction of the GST-α isoform could be detected. Urinary mutagenicity experiments gave further evidence that CF affect drug metabolism in humans. Consumption of red cabbage led to changes in the pattern of meat-derived urinary mutagenicity. Overall, CF are among the most promising chemopreventive dietary constituents and further elucidation of their protective mechanisms and the identification of active constituents may contribute to the development of highly protective Brassica varieties.

Uptake and diverse effects of polycyclic aromatic hydrocarbons on the metabolic activity of Elliptio complanata measured by calorespirometry

Polycyclic aromatic hydrocarbons (PAHs) are important contaminants of world water resources, with effects on aquatic life. Metabolic responses to short-term acute toxicities of naphthalene, anthracene, and chrysene were investigated in the freshwater bivalve mollusk Elliptio complanata using differential scanning calorespirometry coupled with uptake and scanning electron microscopy. Comparing the uptakes of naphthalene, anthracene, and chrysene with that of inulin, which is known to occupy only extracellular space, showed that all compounds studied were taken up. The PAHs studied had diverse effects on the metabolic activity of E. complanata. Naphthalene and, to a lesser degree, chrysene caused stimulation of heat rates, possibly due to uncoupling of oxidative metabolism. Differential scanning calorespirometry coupled with studies of rates of oxygen consumption by the gill tissue exposed to the PAHs showed similar diverse patterns of respiratory rate stimulation and inhibition. Analysis of results of scanning electron microscopy suggested that irreversible damage to the gill tissue occurred in the presence of anthracene but not in the presence on naphthalene or chrysene. The batch calorespirometric method coupled with uptake and spectroscopy proved to be a useful technique to assess the toxicity of PAHs on the control of energy flux in gills of a freshwater bivalve mollusk.

Effects of polycyclic aromatic hydrocarbons on expression of cyp1a in salmon (Salmo salar) following experimental exposure and after the Braer oil spill

AbstractThe induction of hepatic CYP1A by selected polycyclic aromatic hydrocarbons (PAHs) was followed in Atlantic salmon (Salmo salar) by measurement of CYP1A messenger RNA (mRNA), CYP1A protein levels, and catalytically by the measurement of 7‐ethoxyresorufin‐O‐deethylase activity. There was clear correspondence between all three methods of measurement both in terms of the specificity of response to five‐ and some four‐ring PAHs and in terms of the dose‐response relationship to methyl‐cholanthrene. The level of induction was compared with that measured in salmon confined in sea pens around Shetland and exposed to crude oil spilled from the Braer in January 1993. This oil was rapidly dispersed by the extreme weather (turbulence) at the time of the spill. The time course of the hepatic CYP1A induction was followed and related to the levels of oil measured in water and the concentration of PAHs determined in the flesh of the fish. Again there was a good correspondence between the different methods of measuring CYP1A expression, and the results show a rapid induction response in fish at the most contaminated sites and small, insignificant changes occurring at the reference stations. There was a clear concentration response between CYP1A and catalytic activity and between the exposure observed.

HCN and HCO+Images of the Orion Bar Photodissociation Region

The Orion Bar is an ideal astrophysical laboratory for studying photodissociation regions because of its nearly edge-on orientation in the observer's line of sight. High angular resolution (~9'') maps of the Orion Bar in the J = 1-0 emission lines of HCO+ and HCN have been made by combining single-dish millimeter observations with interferometric data. This mapping technique provides both large-scale structural information and high resolution. The new maps show that HCO+ and HCN have globally similar spatial distributions in the Orion Bar. Both molecular species show the same clumpy NE to SW bar seen by previous observers in molecular line emission from the Orion Bar. However, our maps show HCN emission to be more confined to the bar structure and to clump cores than HCO+ emission. We do a crosscut comparison of our full-synthesis maps with previously published observations of the Orion Bar in: (1) the rotational transitions of 12CO J = 1-0, 13CO J = 1-0, CN N = 3-2, and CS J = 7-6; (2) the UV-pumped rovibrational transition of H2 at 2.122 μm; (3) 3.3 μm emission attributed to the aromatic C–H bond stretching of polycyclic aromatic hydrocarbons (PAH); and (4) the atomic fine-structure transitions of C I (609 μm), O I (63 μm), and C II (158 μm). The crosscuts show the same chemical stratification seen by previous observers as expected from an edge-on photodissociation region. In addition, we see that the HCN peak profile is relatively narrow and symmetrical compared to the broader asymmetrical HCO+ peak. We argue that this difference in peak shape supports a previously published suggestion that HCO+ production is enhanced in warm gas at the surface of the photodissociation region. We explain these observations using a nonhomogeneous photodissociation region model to which we have added nitrogen chemistry and the thermal chemical effects of polycyclic aromatic hydrocarbons. Instead of using a homogeneous model, we follow more recent models employing two components because the clumpiness seen in all the recent observations suggests at least two density components in the Orion Bar. From our model calculations, we have found that a ridge of dense clumps (3 × 106 cm-3) embedded in a lower density interclump medium (5 × 104 cm-3) explains our observations very well. Although some of the observations (e.g., emissions from H2, CO, O I, C I and C II) arise from the interclump medium, we show that HCN and HCO+ J = 1-0 emission must come from a ridge of dense clumps near the ionization front. This result agrees with the findings of previous observers, who have suggested the presence of dense clumps in the Orion Bar.

Effects of benzo(a)pyrene and size of organic matter particles on bioaccumulation and growth of Asellus aquaticus.

The effects of sediment-bound toxicants to aquatic invertebrates may vary due to differences in bioavailability, food quality, or food structure. The equilibrium partitioning theory (EPT) assumes that organic matter content of sediments and not structure of organic matter is relevant for biological effects of polycyclic aromatic hydrocarbons. To test this hypothesis effects of benzo(a)pyrene (B(a)P) and size of sediment organic matter particles on the bioaccumulation and growth of the waterlouse Asellus aquaticus were studied in laboratory microcosms. Sediments and A. aquaticus were both sampled in an unpolluted, spring-fed pond. The sampled sediment was divided into two portions. From one portion the size of the organic matter particles was mechanically reduced. One set of each sediment fraction (fine and coarse) was spiked with B(a)P and incubated for 3 weeks resulting in a concentration of 70 mg B(a)P per kg sediment. Bioassays of 32 days were performed in a 2 x 2 factorial design with four replicas of each treatment. The results showed that the growth of A. aquaticus was mainly influenced by the size of organic matter particles. Growth was significantly less (27%) on finer sediments than on coarser sediments. The increase in length was 9-14% lower in the spiked sediments, but this difference was not significant. The reduced growth of A. aquaticus on finer sediments may be due to a change in the availability and/or quality of food together with a change in feeding behavior. The coarse and fine spiked sediment types did not differ significantly with respect to the sediment water partition coefficient, the organic carbon water partition coefficient, and the bioconcentration factor. In contrast, the biota to sediment accumulation factors were significantly 15% higher in the cosms with coarse sediments than in cosms with fine sediments. However, this difference is too small to conflict with EPT.

Plasma steroid levels in female flounder ( Platichthys flesus) after chronic dietary exposure to single polycyclic aromatic hydrocarbons

The chronic effects of polycyclic aromatic hydrocarbons (PAHs) on ovary development, total hepatic lipids and plasma sex- and corticosteroid levels in female flounder ( Platichthys flesus) were examined. Sexually mature feral female flounder were exposed via the diet to phenanthrene (0.5, 2.5 or 12.5 nmol/g food) or chrysene (0.4 nmol/g food) for 12 weeks, during the previtellogenic phase of the annual reproductive cycle. PAH exposure did not directly affect germ cell development since no structural and/or developmental differences were observed between control and exposed fish. On the contrary, all treatments resulted in altered plasma steroid levels. The most pronounced effect was the significant decrease in plasma 17β-estradiol to 19±11%, 27±7%, 63±20% and 61±12% in relation to control fish, respectively, in flounders exposed to 12.5, 2.5 or 0.5 nmol phenanthrene/g food and 0.4 nmol chrysene/g food. Impaired ovarian growth was not observed, most likely because experiments were ended before the period of vitellogenesis, even though a non-significant general decline in total hepatic lipids could be observed. Moreover, all exposed flounders, except fish fed with the highest amount of phenanthrene, showed a negative correlation between plasma 17β-estradiol and 17α-hydroxyprogesterone levels ( r=−0.46). One possible explanation is that PAH action may be mediated by a specific inhibition of steroidogenic enzymes. These findings provide evidence that selected PAHs are antiestrogenic xenobiotics with the capability to impair female teleost reproductive function.