Phototoxicity Of Polycyclic Aromatic Hydrocarbons Research Articles

Application of toxicity‐based fractionation techniques and structure‐activity relationship models for the identification of phototoxic polycyclic aromatic hydrocarbons in sediment pore water

AbstractRecent studies conducted at our laboratory have shown that sediments contaminated with complex mixtures of polycyclic aromatic hydrocarbons (PAHs) can exhibit enhanced toxicity (lethality) to a variety of aquatic species when the samples are tested under ultraviolet (UV) light designed to mimic the wavelengths present in sunlight. However, because these contaminated sediments can contain literally thousands of chemicals, it is difficult to use conventional analytical techniques to identify those compounds responsible for photo‐induced toxicity. The purpose of this study was to adapt existing toxicity identification evaluation methods to attempt to identify those compounds contributing to the phototoxicity observed in our sediment samples. Pore water obtained from sediments collected near an oil refinery discharge was toxic to Lumbriculus variegatus following exposure to UV light, while organisms exposed to the same pore water, but without subsequent UV treatment, showed no toxic effect. Solid‐phase extraction disks and high‐performance liquid chromatography were used, in conjunction with toxicity tests with L. variegatus, to extract and fractionate phototoxic chemicals from the pore water. Phototoxic fractions analyzed by gas chromatography–mass spectrometry revealed the presence of a number of aliphatic hydrocarbons, substituted PAHs, and PAHs containing heteroatoms. Chemicals were screened for their phototoxic potential based on empirical data and predictive models. A refined list of PAHs was then evaluated on the basis of their phototoxic potency as defined by a recently developed quantitative structure–activity relationship model and estimates of their bioaccumulation potential. Based on the model predictions of potency and bioaccumulation, nine likely phototoxic chemicals were identified.

Behavioral and histopathological effects of fluoranthene on bullfrog larvae (Rana catesbeiana)

AbstractThe goals of this study were to use behavioral and histopathological endpoints to examine the sublethal effects of fluoranthene exposure in conjunction with solar ultraviolet radiation on bullfrog larvae. Exposure to fluoranthene and simulated solar ultraviolet radiation for 48 h caused a significant effect on locomotor behavior at 60 μg fluoranthene/L. At 96 h, however, hyperactivity was noted in the 40‐μg fluoranthene/L exposure. The skin of bullfrog larvae was sensitive to the phototoxic effects of fluoranthene. Following exposure to sublethal levels of fluoranthene (10 μg fluoranthene/L) there were signs of necrosis as well as structural alterations in the skin when examined using light microscopy. Based on these results, the photoinduced toxicity of fluoranthene, and hence other phototoxic polycyclic aromatic hydrocarbons, pose a potential hazard to ranid larvae well within the water solubility limits of the compound.

Evaluation of models for predicting the phototoxic potency of polycyclic aromatic hydrocarbons

The objective of this study was to evaluate the validity of two previously developed models to predict: (a) the relative phototoxic potency of polycyclic aromatic hydrocarbons (PAHs) through structure activity relationships (SARs), and (b) the interactive effects of variable light intensity and PAH dose on phototoxicity. The oligochaete Lumbriculus variegatus was exposed to multiple concentrations of the PAHs anthracene, pyrene, fluorene and fluoranthene for 96 h, followed by a 96 h holding period in clean water at three different ultraviolet (UV) light intensities. Based upon measured tissue residue concentrations, anthracene and pyrene were approximately equitoxic, and both were four-fold more potent than fluoranthene. Fluorene was not phototoxic to the oligochaete. These results were in good quantitative agreement with the toxicity predictions of the SAR model. Time-dependent lethality of the three phototoxic PAHs to the oligochaete was accurately modeled by plotting mortality as a function of the product of initial tissue residue of the PAH and UV light intensity to which the organisms were exposed, which also was in good agreement with the interactive toxicity model. These studies contribute to the technical basis for developing an integrated modeling approach to predicting the ecological risk of mixtures of phototoxic PAHs.

Effect of water temperature and dissolved oxygen concentration on the photo-induced toxicity of anthracene to juvenile bluegill sunfish ( Lepomis macrochirus)

Polycyclic aromatic hydrocarbons (PAHs) are widespread pollutants in the aquatic environment and demonstrate a wide variety of toxic effects in freshwater and marine organisms. We have previously documented photo-induced toxic effects of a model PAH (i.e. anthracene) in fish. The goal of our ongoing studies is to examine environmental factors which may enhance or mitigate this toxicity in order to better estimate the risks of phototoxic PAHs to aquatic organisms. The purpose of the present study was to determine the effect of water temperature and oxygen concentration on the photo-induced toxicity of anthracene to juvenile bluegill sunfish ( Lepomis macrochirus). Bluegill sunfish were exposed to anthracene (<0.01, 6.20, 11.62 and 20.88 μg l ) and solar ultraviolet radiation (SUVR) at different water temperatures (20 and 30°C) and oxygen concentrations (5.0, 6.9 and 8.1 mg O 2/1 for 120 h in a laboratory flow-through system. A trend toward an inverse relationship was found between water temperature and LC 50 values, although no significant temperature effect was observed. A nonlinear relationship was found between oxygen concentration and LC 50 values, with significantly increased toxicity at the middle oxygen concentration. Opercular ventilation rates were inversely related to oxygen concentration and directly related to anthracene concentration. A statistical relationship was developed on the basis of oxygen concentration to predict LC 50 values. We conclude that dissolved oxygen concentration is an important environmental factor in the assessment of photo-induced toxicity of anthracene to fish.

The toxicity of benzo[a]pyrene and pyrene in the mosquito [formula omitted], in the dark and in the presence of ultraviolet light

The phototoxicity of benzo[a]pyrene constitutes a much greater risk to immature forms of the mosquito Aedes aegypti than its mutagenicity or carcinogenicity. First instar larvae, fourth instar larvae, and pupae of the mosquito Aedes aegypti were treated with benzo[a]pyrene at concentrations up to 6.7 ppm, either in the dark or in the presence of long wavelength ultraviolet light (for only 30 min). The irradiations had a profound effect on the fate of first instar larvae. Their LC 50 value for 24 h survival was about 0.002 ppm. When the adult emergence was determined, the LC 50 value was about 0.0015 ppm. The development of fourth instar larvae was also modified by the photochemical treatments, with an LC 50 value for adult emergence of 0.12 ppm. The treatment of pupae had no effect on adult emergence. The LC 50 values for the highly carcinogenic BAP are very similar to those determined for pyrene, its non-carcinogenic parent molecule. This provides one additional proof that the carcinogenicity and the phototoxicity of polycyclic aromatic hydrocarbons are not necessarily related.