Toxicity Of PAHs Research Articles

Evaluation of bioaccumulation and photo-induced toxicity of fluoranthene in larval and adult life-stages of Chironomus tentans.

Laboratory sediment tests were conducted to evaluate the bioaccumulation and photo-induced toxicity of fluoranthene in larval and adult life-stages of the midge, Chironomus tentans. In the first of 2 experiments, fourth-instar and adult C. tentans exposed to spiked sediments (204 microg fluoranthene/g dry weight) were collected for determination of fluoranthene tissue concentrations and toxicity after ultraviolet (UV) radiation treatment in the absence of sediment (water-only). Fluoranthene tissue concentrations in larvae collected after a 72-hour exposure period were 7 times greater than concentrations in adults collected on emergence from the same spiked sediments. Fluoranthene-exposed adults were tolerant of UV exposure (100% survival after 7 hours), whereas larvae were sensitive (0% survival after 1 hour). In the second experiment, C. tentans larvae were exposed for 96 hours to 2 sediment treatments (170 and 54 microg fluoranthene/g dry weight), after which fluoranthene tissue concentrations were determined and UV exposures conducted under water-only versus sediment conditions. Exposure to UV radiation, in conjunction with sediment, provided larvae with significant protection from photo-induced toxicity compared with the water-only exposure. Adults that emerged from the 2 sediment treatments were also analyzed for fluoranthene tissue residues and exposed to UV radiation. Fluoranthene tissue residues were higher in adult female than in adult male midges, but exuviae from both sexes contained higher fluoranthene concentrations than whole-body tissue, thus demonstrating that the molting process is a possible detoxification mechanism. Consistent with the greater tissue residue concentrations, female midges demonstrated a significant decrease in survival under UV exposure compared with male midges. These studies indicated that both the burrowing behavior of the larvae and the elimination of fluoranthene in molted exuviae are protective mechanisms against photo-enhanced PAH toxicity in this species.

Enhancement in the sensitivity of an immobilized cell-based soil biosensor for monitoring PAH toxicity

A soil biosensor was developed in our previous study using both a recombinant bioluminescent bacterium, GC2 ( lac:: luxCDABE), immobilized with transparent glass beads within an agar matrix and rhamnolipids, a biosurfactant employed to increase the bioavailability of phenanthrene from contaminated soil. To improve the sensitivity of this biosensor, glass beads of various sizes were tested. The results showed that the detection limit of the biosensor was lowered when smaller-sized glass beads were employed. Further tests showed that the use of glass beads with smaller diameters enhanced the sensitivity of the biosensor, allowing for a more conclusive study on the phenanthrene toxicity present within soils.

Assessment of the bioavailability and toxicity of sediment-associated polycyclic aromatic hydrocarbons and heavy metals applied to Crassostrea gigas embryos and larvae

Sediments represent a vast sink for contaminants in aquatic systems, and may pose a threat to pelagic and benthic organisms. The objective of this research was to determine the bioavailability and toxicity of sediment-associated PAHs and heavy metals, using embryos and larvae of the oyster Crassostrea gigas, exposed to two sediment fractions: the whole sediment and the elutriate. The percentages of abnormal larvae, the contaminant accumulation and, (in the case of metal contamination), the induction of metallothionein in the larvae, were investigated. Sediment-associated PAHs and heavy metals were available for exposure, as indicated by their accumulation in C. gigas larvae and by the abnormalities induced during larval development. The critical body burden of PAHs (Fluo, Pyr, BaA, Triph, Chrys, BbF, BkF, BjK, BeP, BaP, Per, IP, BPer and the DahA) in the larvae was 0.3 μg g −1, above which abnormalities were observed. This value corresponds to concentrations observed for most vertebrate and invertebrate species. The bioavailability of PAHs is determined by their solubility; only the soluble fraction of PAHs is accumulated by the embryos. The bioavailability of metals for the larvae is substantiated by MT induction, correlated with cytosolic metal concentrations. MT induction provided a better early-warning response than the embryotoxicity test currently used for evaluating environmental contamination by metals. This study recommends choosing oyster embryos as a particularly sensitive tool for evaluating sediment quality.

Toxicokinetics and time-dependent PAH toxicity in the amphipod Hyalella azteca.

The relationship between toxicokinetics and time-dependent PAH toxicity to Hyalella azteca was examined to test the constant critical body residue (CBR) model. A constant CBR model is based on the assumption that the body residue for 50% mortality is constant for each PAH across exposure times. With a constant CBR, kinetic parameters determined through kinetic experiments would be similar to those estimated from time series toxicity data. Time-dependent toxicity was investigated using three types of data: time series LCW data, LT50(c), and CBR values measured at multiple exposure times for live and dead animals. Kinetic parameters were measured independently. The constant CBR model did not predict the PAH toxicity time course for H. azteca. Since a first-order kinetic model predicted the bioaccumulation of the parent PAH except for naphthalene, this result is not due to a failure to predict the internal dose (body residue). The influence of metabolites on toxicity was negligible except for naphthalene. The LC50 values at multiple exposure times decreased to an incipient lethal concentration after H. azteca reached steady state. Measured CBR values also decreased with increasing exposure time. Thus, the time course of PAH toxicity is determined not only by the bioconcentration kinetics but also by the cumulative toxicity with increasing exposure time. Therefore, time-to-death or hazard models must be developed as a complement to toxicokinetic models to describe and predict the toxicity time course.

Soil ecotoxicity of polycyclic aromatic hydrocarbons in relation to soil sorption, lipophilicity, and water solubility.

A data set was generated aiming to predict the toxicity of PAHs to soil organisms. Toxicity data include the effects of 16 PAHs on the survival and reproduction of the soil-dwelling springtail Folsomia fimetaria. The results show that only PAHs with reported log Kow values < or = 5.2 (i.e., naphthalene, acenaphthene, acenaphthylene, anthracene, phenanthrene, fluorene, pyrene, and fluoranthene) significantly affected the survival or reproduction of the test organisms. Threshold values for the toxicity of the individual PAHs could be expressed as pore-water concentrations by the use of reported organic carbon-normalized soil-pore-water partitioning coefficients (Koc values). For the PAHs with a log Kow < or = 5.2, toxicity significantly increased with increasing lipophilicity of the substances (r2 = 0.67; p = 0.012; n = 8), suggesting a narcotic mode of toxic action for most substances. However, the position of anthracene in the regression plot indicated a more specific mode of toxic action than narcosis, and removing this data point yielded the following regression equation: log EC10 (micromol/L) = -0.97 log Kow + 4.0 (r2 = 0.80; p = 0.006; n = 7). Using this quantitative structure-activity relationship (QSAR) to calculate threshold values for the toxicity of the remaining nontoxic substances (benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene, benzo[a]pyrene, perylene, and indeno[1,2,3-cd]pyrene), the absence of toxicity could, in most cases, be explained by a limited water solubility, indicating that these substances do act by narcosis as the mode of toxic action and that their toxicity is governed by concentrations in the pore-water. The results provide important input to future model predictions of the ecological risk posed by PAH contaminated sites.

Comparative (Photoenhanced) Toxicity of Homocyclic and Heterocyclic PACs

Azaarenes are a group of heterocyclic PACs in which one carbon atom has been replaced by one nitrogen atom. Heterocyclic PACs commonly occur in the environment, but risk assessment for PACs is solely based on (a small number of) homocyclic compounds. In order to examine whether the present risk assessment accurately protects against a broader range of PACs, the aim of this study was to compare the toxicity of an analogue series of homocyclic and heterocyclic PACs to a representative benthic invertebrate, the midge Chironomus riparius . The present study focused on generating toxicity data (96 h LC 50 ) for naphthalene, anthracene, phenanthrene, and pyrene to allow a comparison with previously obtained results for azaarenes. Since photoenhanced toxicity was expected for some of the compounds tested, experiments were carried out with and without a UV filter in order to obtain a complete assessment of the toxic mechanisms involved. Toxicity of homocyclic PAHs and azaarenes increased with increasing number of rings. In general, homocyclic PAHs were more toxic than their N-heterocyclic analogues, but homocyclic PAHs also are more lipophilic than their heterocyclic analogues. Consequently, this difference in toxicity between both groups of compounds disappeared when the comparison was based on log K ow . Higher than predicted toxicities of both azaarenes and homocyclic PAHs were clearly related to photoenhanced toxicity. Especially anthracene and acridine showed strong increases in toxicity in the presence of UV radiation. This photoenhanced toxicity can accurately be predicted by the HOMO-LUMO gap values of the compounds. Therefore, it is concluded that extension of the present log K ow based QSARs with a descriptor for photoenhanced toxicity (such as the overlap between the absorption spectrum of the chemicals and the irradiance emitted by the light source used) appears to be a necessity for predicting toxicity of PACs in the environment.

Comparative Studies on PAH in Pitch by Liquid Chromatography/Fluorescence and Other Methods

In order to evaluate the PAH toxicity potential of our Söderberg cell emissions, a first PAH HPLC/F1 method was developed in the early 1990′s. A quality control of PAH measurements, based on the B[a]P Eq. Index of homogeneous, stable reference materials, was implemented to follow the pitches used in the fabrication of anode pastes. This technique employed megabore columns (4.6-mm o.d.) with twin fluorescence detectors. In the mid-1990′s, this method was upgraded to minibore columns in order to increase the accuracy. Data for the same pitches was accumulated over a three-year period. This communication compares the results from the two HPLC/F1 approaches including the extraction procedures, the stability of the PAH extracts, the stability of the equipment, the temporal resolution, the wavelengths used, etc., which can affect the apparent PAH values. This new method has also been compared with the results from other laboratories using different protocols and techniques including the presence of instrument specific interferences.

Application of a Σpolycyclic aromatic hydrocarbon model and a logistic regression model to sediment toxicity data based on a species‐specific, water‐only LC50 toxic unit for Hyalella azteca

Two models, a sigmapolycyclic aromatic hydrocarbon (PAH) model based on equilibrium partitioning theory and a logistic-regression model, were developed and evaluated to predict sediment-associated PAH toxicity to Hyalella azteca. A sigmaPAH model was applied to freshwater sediments. This study is the first attempt to use a sigmaPAH model based on water-only, median lethal concentration (LC50) toxic unit (TU) values for sediment-associated PAH mixtures and its application to freshwater sediments. To predict the toxicity (i.e., mortality) from contaminated sediments to H. azteca, an interstitial water TU, calculated as the ambient interstitial water concentration divided by the water-only LC50 in which the interstitial water concentrations were predicted by equilibrium partitioning theory, was used. Assuming additive toxicity for PAH, the sum of TUs was calculated to predict the total toxicity of PAH mixtures in sediments. The sigmaPAH model was developed from 10- and 14-d H. azteca water-only LC50 values. To obtain estimates of LC50 values for a wide range of PAHs, a quantitative structure-activity relationship (QSAR) model (log LC50 - log Kow) with a constant slope was derived using the time-variable LC50 values for four PAH congeners. The logistic-regression model was derived to assess the concentration-response relationship for field sediments, which showed that 1.3 (0.6-3.9) TU were required for a 50% probability that a sediment was toxic. The logistic-regression model reflects both the effects of co-occurring contaminants (i.e., nonmeasured PAH and unknown pollutants) and the overestimation of exposure to sediment-associated PAH. An apparent site-specific bioavailability limitation of sediment-associated PAH was found for a site contaminated by creosote. At this site, no toxic samples were less than 3.9 TU. Finally, the predictability of the sigmaPAH model can be affected by species-specific responses (Hyalella vs Rhepoxynius); chemical specific (PAH vs DDT in H. azteca) biases, which are not incorporated in the equilibrium partitioning model; and the uncertainty from site-specific effects (creosote vs other sources of PAH contamination) on the bioavailability of sediment-associated PAH mixtures.

Toxicity of Sediment Associated PAHs to the Estuarine Crustaceans, Palaemonetes pugio and Amphiascus tenuiremis

Toxicity of Sediment Associated PAHs to the Estuarine Crustaceans, Palaemonetes pugio and Amphiascus tenuiremis E. F. Wirth, M. H. Fulton, G. T. Chandler, P. B. Key, G. I, Scott 1 USDC, NOAA, National Ocean Service, Center for Coastal Environmental Health and Biomolecular Research at Charleston, 219 Fort Johnson Road, Charleston, SC 29412, USA 2 Department of Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia, SC 29208, USA

Metals, acid-volatile sulfides, organics, and particle distributions of contaminated sediments

An overview of key physical/chemical parameters for contaminated sediments is presented. While sediment cores from remote lakes show little or no enrichment with heavy metals (Pb, Hg, Cd, Zn, Cu) and PAHs in top layers, the contamination near industrial areas is more significant. Cd in more bioavailable geochemical phases can occur in response to Cu inputs to sediments, and aeration during dredging operations of anaerobic sediments can reduce the pH causing release of heavy metals. The toxicity of anaerobic sediments to benthos can be effectively predicted based on interstitial water concentrations and the molar ratio between simultaneously extracted metals and acid-volatile sulfides (SEM/AVS). The toxicity of PAHs and other organics can be predicted based on equilibrium partitioning. Principal component analysis indicates that PAHs are associated with organic carbon and silt, and PCBs with inorganic clay. Finally, formulated reference sediments appear to be useful in toxicity testing by creating uniform parameters matching field conditions, and by isolating the effects of specific contaminants.

Metals, acid-volatile sulfides, organics, and particle distributions of contaminated sediments

An overview of key physical/chemical parameters for contaminated sediments is presented. While sediment cores from remote lakes show little or no enrichment with heavy metals (Pb, Hg, Cd, Zn, Cu) and PAHs in top layers, the contamination near industrial areas is more significant. Cd in more bioavailable geochemical phases can occur in response to Cu inputs to sediments, and aeration during dredging operations of anaerobic sediments can reduce the pH causing release of heavy metals. The toxicity of anaerobic sediments to benthos can be effectively predicted based on interstitial water concentrations and the molar ratio between simultaneously extracted metals and acid-volatile sulfides (SEM/AVS). The toxicity of PAHs and other organics can be predicted based on equilibrium partitioning. Principal component analysis indicates that PAHs are associated with organic carbon and silt, and PCBs with inorganic clay. Finally, formulated reference sediments appear to be useful in toxicity testing by creating uniform parameters matching field conditions, and by isolating the effects of specific contaminants.

Toxicity of sediment-associated PAHs to an estuarine copepod: Effects on survival, feeding, reproduction and behavior

The toxicities of sediment-associated phenanthrene, fluoranthene and diesel fuel to the estuarine copepod Schizopera knabeni Lang were investigated. The 4-d LC 50 was lowest for diesel fuel (194 μg/dry g), followed by phenanthrene (473 μg/dry g) and fluoranthene (> 2,100 μg/dry g). Sublethal effects on grazing rate were assessed in 30 h exposures using 14C-labeled microalgae. Feeding was inhibited at concentrations well below the 96 h LC 50 values (50% decrease at concentrations ranging from 48 to 94 μg/dry g), probably due to the narcotizing effect of PAH. PAH effects on offspring production were examined by exposing individual copulating pairs to sediment treatments for 14 d. No significant effect on clutch size was observed; however, PAHs decreased nauplii and copepodite production at sublethal sediment concentrations (50% decrease at concentrations ranging from 38 to 64 μg/dry g). Schizopera knabeni actively detected and avoided PAH-amended sediment, as determined in preference/avoidance experiments. Although mortality only occurs at exceedingly high concentrations, PAH sublethal effects will likely reduce fitness and alter S. knabeni distribution and abundance in heavily contaminated sites.

Mechanisms of photoinduced toxicity of photomodified anthracene to plants: Inhibition of photosynthesis in the aquatic higher plant Lemna gibba (duckweed)

AbstractPolycyclic aromatic hydrocarbon (PAH) toxicity is enhanced by light, especially ultraviolet (UV) radiation. To examine a potential mechanism(s) of photoinduced toxicity of PAHs to plants, the effects of anthracene and its photoproducts on photosynthesis were investigated using the aquatic higher plant Lemna gibba L. G‐3 (duckweed). Photosynthetic activity was monitored both in vivo and in vitro by measuring chlorophyll a (Chl a) fluorescence, carbon fixation, and electron transport. In simulated solar radiation (a light source with a visible light: UV‐A: UV‐B ratio similar to sunlight), inhibition of photosynthesis was more rapid with photomodified anthracene than with intact anthracene, and intact anthracene appeared to only inhibit photosynthesis following its photomodification. The primary site of action of photomodified anthracene was found to be electron transport at or near photosystem I (PSI). This was followed by inhibition of photosystem II (PSII), probably due to excitation pressure on PSII once the downstream electron transport through PSI was blocked. Accordingly, higher chemical concentrations and/or longer exposures were required to inhibit PSII than PSI. Net photosynthesis (carbon fixation) was also inhibited, implying that the inhibition of electron transport in PSI by photomodified anthracene can lead to diminished primary productivity. A linkage between inhibition of photosynthesis and inhibition of plant growth was established in terms of the initial site of action (PSI) and primary productivity (carbon fixation), which suggested that Chl a fluorescence can be used as a bioindicator of PAH impacts on plants.

Embryotoxicity and recurrent spontaneous abortions

Diluted bitumen (dilbit) from Alberta oil sands (Canada) is transported across major continental watersheds, yet little is known about its toxicity to fish if spilled into aquatic environments. The toxicity of Cold Lake (CLB) dilbit was assessed for medaka embryos (Oryzias latipes) exposed to water accommodated fractions (WAF) and chemically-enhanced WAF (CEWAF) using Corexit®EC9500A as dispersant. The effects of CLB toxicity were similar to conventional crude oils and Access Western Blend (AWB) dilbit. The prevalence of malformations and cyp1a mRNA synthesis in hatched fish increased monotonically with concentration during WAF and CEWAF treatments and provided a novel indicator of dilbit PAH toxicity. Apart from nfe2 (an antioxidant transcription factor), there were no statistically significant monotonic exposure-responses of ahr, arnt2, cat, sod, gpx, gst, gsr, g6pdh, p53, and hsp70 transcripts at total polycyclic aromatic hydrocarbons (TPAH) concentrations bracketing EC50s for embryotoxicity (WAF ≅ 3 μg/L; CEWAF ≅ 0.1 μg/L TPAH). Based on measured TPAH concentrations in exposure test solutions, CLB dilbit was 6–10 fold more toxic to medaka than AWB during chronic exposures. Lack of direct monotonic gene transcription responses to increasing oil concentrations during exposures that were embryotoxic suggests that the capacity of the oxidative stress response is limited in earlier lifestages or that differences exist among species in mechanisms of toxicity. This study provides a comparative framework for identifying suitable biomarkers and toxicity methods for those fish species in sensitive lifestages at highest risk of Canadian oil sands dilbit exposure following a spill in the freshwater environment.

UVb-induced toxicity of PAHs: effects of substituents and heteroatom substitution.

UVb-induced toxicity of PAHs: effects of substituents and heteroatom substitution.

Biotreatment of naphthalene by PAH-acclimated pure culture with white-rot fungus phanerochaete chrysosporium

The tolerance of PAH toxicity for a PAH-acclimated pure culture with the fungus P. chrysosporium was evaluated by growth characteristics. The result showed that PAH-acclimated culture could still maintain its microbial activity, whereas the nonacclimated culture showed a declined growth when a high concentration of naphthalene (NTL) or benzo(a)pyrene (B(a)P) was present. In the treatment of NTL, the PAH-acclimated culture was also superior to the nonacclimated one. More than 90% of NTL removal had been attained by the PAH enrichment culture in agitated vessels within 24 h. However, in this experiment, about 20% of NTL was adsorbed on the fungal mycelia. After 4 days of reaction in the vessels, some ethyl acetate-extractable metabolites of NTL with high polarity in the HPLC elution were detected. One of these polar products was identified to be catechol compound. This study also demonstrated that NTL treatment in the aerated batch bioreactor was not comparable to that the agitated vessel owing to low efficiency in oxygen transfer of the system.

In situ toxicity evaluations of turbidity and photoinduction of polycyclic aromatic hydrocarbons

AbstractPolycyclic aromatic hydrocarbons (PAHs) are prevalent pollutants in the aquatic environment that can cause a wide range of toxic effects. Earlier studies have shown that toxicity of PAHs can be enhanced by ultraviolet (UV) radiation. In situ and laboratory exposures with Ceriodaphnia dubia were used to evaluate photoinduced toxicity of PAHs in wet‐weather runoff and in turbid conditions. Exposure to UV increased the toxicity of PAH‐contaminated sediment to C. dubia. Toxicity was removed when UV wavelengths did not penetrate the water column to the exposed organisms. A significant correlation was observed between in situ C. dubia survival and turbidity when organisms were exposed to sunlight. Stormwater runoff samples exhibited an increase in chronic toxicity (reproduction) to C. dubia when exposed to UV wavelengths as compared to C. dubia not exposed to UV wavelengths. Toxicity was reduced significantly in the presence of UV radiation when the organic fraction of stormwater runoff was removed. The PAHs are bound to the sediment and resuspended into the water column once the sediment is disturbed (e.g., during a storm). The in situ and laboratory results showed that photoinduced toxicity occurred frequently during low flow conditions and wet weather runoff and was reduced in turbid conditions.

Biotreatment of naphthalene by PAH-acclimated pure culture with white-rot fungus phanerochaete chrysosporium

The tolerance of PAH toxicity for a PAH-acclimated pure culture with the fungus P. chrysosporium was evaluated by growth characteristics. The result showed that PAH-acclimated culture could still maintain its microbial activity, whereas the nonacclimated culture showed a declined growth when a high concentration of naphthalene (NTL) or benzo(a)pyrene (B(a)P) was present. In the treatment of NTL, the PAH-acclimated culture was also superior to the nonacclimated one. More than 90% of NTL removal had been attained by the PAH enrichment culture in agitated vessels within 24 h. However, in this experiment, about 20% of NTL was adsorbed on the fungal mycelia. After 4 days of reaction in the vessels, some ethyl acetate-extractable metabolites of NTL with high polarity in the HPLC elution were detected. One of these polar products was identified to be catechol compound. This study also demonstrated that NTL treatment in the aerated batch bioreactor was not comparable to that the agitated vessel owing to low efficiency in oxygen transfer of the system.

QSAR Evaluation of .alpha.-Terthienyl Phototoxicity

The concept that phototoxic chemicals can be identified in chemical risk assessments by computing the energy difference between highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap) was evaluated using two new sets of phototoxicity data from the recent literature. The original model, developed from data with unsubstituted PAH toxicity to Daphnia magna, showed that phototoxicity was observed when the HOMO-LUMO gap varied between 6.7 and 7.5 eV. All substituted α-terthienyls that were phototoxic to mosquito larvae and to brine shrimp had HOMO-LUMO gap energies within the 7.1 10.4 eV «phototoxicity window». The α-terthienyls within this range that did not exhibit phototoxicity contained carboxyl or other polar substituents, which likely prevented bioaccumulation in the organisms. Polyamino and polynitro derivatives of toluene in munitions wastes were reported to be phototoxic to sea urchins even though the HOMO-LUMO gap energies exceeded 8.0 eV. Because the same toluenes were not phototoxic to D. magna nor to Escherichia coli, we suggest that the developmental effects observed in the sea urchins were caused by electrophilic species from metabolic activation rather than the production of oxygen radicals from photo induced excited states of the molecules

Impacts of UV radiation and photomodification on the toxicity of pahs to the higher plant Lemna gibba (duckweed

AbstractThe toxicity of polycyclic aromatic hydrocarbons (PAHs) can be enhanced by both biotic and abiotic processes. This is exemplified by light, which, by virtue of the extensive π‐orbital systems of PAHs, can be a major factor in PAH toxicity. Light activation of PAHs is known to occur via photosensitization reactions (generation of singlet oxygen and superoxide) and potentially by photomodification of the chemicals (photooxidation and/or photolysis) to more toxic species. To examine the modes of PAH action in the light and determine if the photomodified compounds are hazardous, we investigated the photoinduced toxicity of anthracene, phenanthrene and benzo[a]pyrene to the aquatic higher plant Lemna gibba (a duckweed). Toxicity end points were inhibition of growth and extent of chlorosis. Light did indeed activate the phytotoxicity of PAHs, with UV radiation more effective than visible light. Dose‐response curves based on chemical concentration and light intensity revealed the order of phytotoxic strength to be anthracene &gt; phenanthrene &gt; benzo[a]pyrene. To explore whether photomodified PAHs were contributing to toxicity, the chemicals were irradiated before toxicity testing. The rates of photomodification of the three PAHs were rapid (half‐lives in hours), and the relative velocities were coincident with the order of toxic strength. Furthermore, the photomodified PAHs were more hazardous to Lemna than the intact compounds. Because interpretations of the potential impacts of PAHs in the environment are based mostly on measurements of the structurally intact chemicals, the severity of PAH hazards is possibly underestimated.