Effects of light on the cytotoxicity and genotoxicity of benzo(a)pyrene and an oil refinery effluent in the newt

Micronucleus Assays in Amphibians

Induction of micronucleus (MN) expression is a well-validated biomarker of genotoxic exposure in eukaryotic cells and is widely used in biomonitoring programs. The presence of permeable skin, which facilitates toxicant exposure and local abundance, is among the characteristics that make amphibians good indicators of ecosystem health. The presence of large nucleated erythrocytes, which divide in the circulation, makes amphibian erythrocytes an ideal target tissue to detect genotoxin exposure using the MN assay. Published literature have highlighted the promising prospects of using the amphibian MN assay as a sensitive biomonitoring tool for water quality assessment to detect potential genotoxins. The present chapter provides the basic outline of the amphibian MN assay and highlights its use in genotoxicity testing in experimental and biomonitoring studies.

Cytochrome P450 1A transcript is a suitable biomarker of both exposure and response to diluted bitumen in developing frog embryos

In order for Alberta's thick bitumen to be transported through pipelines, condensates are added creating a diluted bitumen (dilbit) mixture. Recent pipeline expansion projects have generated concern about potential dilbit spills on aquatic wildlife health. Studies have suggested that polycyclic aromatic compounds (PACs) are toxic to aquatic vertebrates and could potentially also interfere with their endocrine system. The research objectives of this study were to investigate the toxicity of dilbit to developing frog embryos and to identify the molecular mechanisms of action involved. Fertilized embryos of Western clawed frog (Silurana tropicalis) were exposed for 72 h to water accommodated fractions (WAF; 0.7-8.9 μg/L TPACs) and chemically-enhanced WAFs (CEWAF; 0.09-56.7 μg/L TPACs) of Access Western Blend (AWB) and Cold Lake Blend (CLB) dilbits. Both dilbit's CEWAFs significantly increased embryonic mortality and malformation incidence in the highest treatments tested, while WAF treatments led to no visible toxic effects. Increases of the cytochrome P450 1A (cyp1a) mRNA levels were observed for all WAF and CEWAF dilbit treatments suggesting that phase I detoxification is activated in the dilbit-exposed larvae. When exposed to PAC concentrations ranging from 0.09 to 8.9 μg/L, the frogs displayed no observable malformations, but expressed significant increases of cyp1a mRNA levels (2- to 25-fold; indicating a suitable biomarker of exposure); however, when concentrations were of 46.6 μg/L or higher, both malformed frog phenotype and induction of cyp1a mRNA level (>250-fold) were measured (indicating a suitable biomarker of response). The expression of several genes related to cellular detoxification and endocrine disruption were also measured, but were not significantly altered by the treatments. In sum, cyp1a mRNA level is a highly sensitive endpoint to measure subtle molecular changes induced by PAC exposure in the frog embryos and larvae, and data suggest that PAC concentration higher than 46 μg/L would be toxic to the developing S. tropicalis.

The Genotoxicity of Priority Polycyclic Aromatic Hydrocarbons (PAHs) Containing Sludge Samples

ABSTRACT In this research work we developed in vitro tests utilizing mammalian cell cultures, which can rapidly assess effect of exposure of oily sludge-derived chemicals on human and ecological health. Many of these are hazardous to health and environment due to their toxicity and/or accumulation potential in sediments as well as in organisms. Petroleum refinery and petrochemical industry-derived oily sludges contain toxic polycyclic aromatic hydrocarbons (PAHs), some of which are lipophilic in nature. Risk assessment of environmental samples suffers from inadequate availability of toxicity data, lack of knowledge about behavior of genotoxic substances in complex matrices, paucity of information on synergistic and antagonistic interactions of mixture of components, etc.; the literature describing the behavior of genotoxic substances in complex mixtures is sparse and sometimes contradictory. The present study aims at assessing the genotoxic potential of oily sludges collected from an integrated petroleum refinery and petrochemical industry located in the southwestern part of India and a petrochemical industry located in the western part of India using a battery of genotoxicity assays such as DNA damage/strand break, chromosomal aberration, p(53) protein induction, and apoptosis in CHO-K1 cell culture system. Exposure with different dose levels of sludge extracts (25, 50, 100 muL) in CHO-K1 cells could cause statistically significant level of (P < 0.001) DNA damage, chromosomal aberration, p(53) protein induction, and apoptosis in comparison to negative control treatment groups, and the genotoxicity was attributed to PAHs present in the sludge as identified by GC-MS. This implies that the sludges are genotoxic in nature in mammalian cells tested, and the exposure to these may pose a potential genotoxic risk to human beings.

Linking embryo toxicity with genotoxic responses in the freshwater snail Physa acuta: single exposure to benzo(a)pyrene, fluoxetine, bisphenol A, vinclozolin and exposure to binary mixtures with benzo(a)pyrene

Genotoxic effects on fauna after waterborne pollutant exposure have been demonstrated by numerous research programmes. Less effort has been focused on establishing relationship between genotoxicity and long-term responses at higher levels of biological organization. Taking into account that embryos may be more sensitive indicators of reproductive impairment than alterations in fertility, we have developed two assays in multiwell plates to address correlations between embryo toxicity and genotoxicity. The potential teratogenicity was assessed by analyzing abnormal development and mortality of Physa acuta at embryonic stage. Genotoxicity was measured by the micronucleus (MN) test using embryonic cells. Our results showed that linkage between genotoxicity and embryo toxicity depends on mechanisms of action of compounds under study. Embryo toxic responses showed a clear dose-related tendency whereas no clear dose-dependent effect was observed in micronucleus induction. The higher embryo toxicity was produced by benzo(a)pyrene exposure followed by fluoxetine and bisphenol A. Vinclozolin was the lower embryo toxic compound. Binary mixtures with BaP always resulted in higher embryo toxicity than single exposures but antagonistic effects were observed for MN induction. Benzo(a)pyrene produced the higher MN induction at 0.04 mg/L, which also produced clear embryo toxic effects. Fluoxetine did not induce cytogenetic effects but 0.25mg/L altered embryonic development. Bisphenol A significantly reduced hatchability at 0.5mg/L while MN induction appeared with higher treatments than those that start causing teratogenicity. Much higher concentration of vinclozolin (5mg/L) reduced hatchability and induced maximum MN formation. In conclusion, while validating one biomarker of genotoxicity and employing one ecologically relevant effect, we have evaluated the relative sensitivity of a freshwater mollusc for a range of chemicals. The embryo toxicity test is a starting point for the development of a life cycle test with freshwater snails even for undertaking multigeneration studies focused on transgenerational effects.

Toxicity of coal-tar and asphalt sealants to eastern newts, Notophthalmus viridescens

Between 1970 and 2000 the concentration of total polycyclic aromatic hydrocarbons (TPAH) in several lakes across the country increased whereas those of other persistent organic pollutants (POPs) tended to remain stable or declined. Urbanized watersheds experienced greater rises in TPAH concentration compared to non-urban lakes. Sources for urban PAHs include industrial wastes, vehicular exhausts and oil leaks and sealants from pavement surfaces. Both coal-tar and asphalt sealants are used to protect surfaces but runoff from surfaces coated with coal-tar can have mean concentrations of 3500 mg TPAHs kg(-1), much higher than runoff from asphalt-sealed or cement surfaces. Unaltered parent compounds of PAHs can have many lethal and sublethal toxic effects, but oxidation and UV radiation can alter the toxicity of these compounds, sometimes creating degradates that are many times more toxic than parent compounds. The purposes of this study were to determine if coal-tar sealants can be toxic to adult eastern newts (Notophthalmus viridescens) and to compare the toxicity of coal-tar sealant to that of asphalt sealant. Newts were exposed to sediments containing dried sealants ranging from 0 mg kg(-1) to 1500 mg kg(-1) under simultaneous exposure to UV radiation and visible light to determine concentration/response relationships. No significant mortality occurred with any treatment. Significant effects due to sealants included decreased righting ability and diminished liver enzyme activities. Coal-tar sealant was more effective in inducing these changes than was asphalt sealant.

Toxicity of coal-tar pavement sealants and ultraviolet radiation to Ambystoma Maculatum

Polycyclic aromatic hydrocarbons (PAHs) can affect amphibians in lethal and many sublethal ways. There are many natural and anthropogenic sources of PAHs in aquatic environments. One potentially significant source is run off from surfaces of parking lots and roads that are protected with coal tar sealants. Coal tar is 50% or more PAH by wet weight and is used in emulsions to treat these surfaces. Break down of sealants can result in contamination of nearby waters. The toxicity of PAHs can be greatly altered by simultaneous exposure to ultraviolet radiation. This study exposes larvae of the spotted salamander (Ambystoma maculatum) to determine if coal tar sealant can have negative effects on aquatic amphibians and if coal tar toxicity is influenced by ultraviolet radiation. Spotted salamanders were exposed to 0, 60, 280 and 1500 mg coal tar sealant/kg sediment for 28 days. Half of the animals were exposed to conventional fluorescent lighting only and half were exposed to fluorescent lighting plus ultraviolet radiation. No significant mortality occurred during the experiment. Exposure to sealants resulted in slower rates of growth, and diminished ability to swim in a dose-dependent fashion. Exposure to ultraviolet radiation affected the frequencies of leukocytes and increased the incidence of micronucleated erythrocytes. There was an interactive effect of sealant and radiation on swimming behavior. We conclude that coal-tar sealant and ultraviolet radiation increased sublethal effects in salamanders, and may be a risk to salamanders under field conditions.

Variation in genotoxic stress tolerance among frog populations exposed to UV and pollutant gradients

Populations of widely distributed species can be subjected to unequal selection pressures, producing differences in rates of local adaptation. We report a laboratory experiment testing tolerance variation to UV-B and polycyclic aromatic hydrocarbons (PAHs) among common frog (Rana temporaria) populations according to their natural exposure level in the field. Studied populations were naturally distributed along two gradients, i.e. UV-B radiation with altitude and level of contamination by PAHs with the distance to emitting sources (road traffic). Tadpoles from eight populations were subjected to (1) no or high level of artificial UV-B; (2) four concentrations of benzo[a]pyrene (BaP) (0, 50, 250, 500microgL(-1)); (3) simultaneously to UV-B and BaP. Since both stressors are genotoxic, the number of micronucleated erythrocytes (MNE) in circulating red blood cells was used as a bioindicator of tadpole sensitivity. High-altitude populations appear to be locally adapted to better resist UV-B genotoxicity, as they showed the lowest MNE numbers. Conversely, no correlation was observed between levels of PAH contamination in the field and tadpole tolerance to BaP in the laboratory, indicating the absence of local adaptation for BaP tolerance in these populations. Nevertheless, the decrease of MNE formation due to BaP exposure with altitude suggests that high-altitude populations were intrinsically more resistant to BaP genotoxicity. We propose the hypothesis of a co-tolerance between UV-B and BaP in high-altitude common frog populations: local adaptation to prevent and/or repair DNA damage induced by UV-B could also protect these highland populations against DNA damage induced by BaP. The results of this study highlight the role of local adaptation along pollutant gradients leading to tolerance variation, which implies that is it necessary to take into account the history of exposure of each population and the existence of co-tolerance that can hide toxic effects of a new pollutant.

The effects of coal tar based pavement sealer on amphibian development and metamorphosis

Coal tar based pavement sealers are applied regularly to parking lots and contain significant levels of polycyclic aromatic hydrocarbons (PAHs). Recently a connection between elevated levels of PAHs in streams and storm water runoff from parking lots has been identified. We tested the hypothesis that coal tar based pavement sealers could alter the survival, growth, and development of amphibians using a model species, Xenopus laevis. Ten fertilized individuals were placed singly into containers containing one of four treatment groups: control, low, medium, and high (respective nominal concentrations 0, 3, 30, and 300 ppm TPAH). All of the individuals in the high exposure group died by the sixth day of exposure. By day 14 there were significant patterns of stunted growth (p<0.0001) and slower development (p=0.006) in the medium and high exposure groups relative to the control and low treatment groups. When the experiment ended on day 52 the control and low-dose individuals had achieved more advanced developmental stages than the medium group (p=0.0007). These data indicate that these commonly used coal tar based pavement sealers may potentially affect the amphibian taxa living in areas that receive storm water runoff.

Induction of micronuclei and nuclear abnormalities in Oreochromis niloticus following exposure to petroleum refinery and chromium processing plant effluents

The genotoxic effects of effluents from a petroleum refinery and a chromium processing plant were evaluated in Oreochromis niloticus (Pisces: Perciformes) using the micronucleus test. Fish were exposed to different concentrations (5, 10 and 20%, v/v) of the effluents for 3, 6 and 9 days. Micronucleus analyses were carried out on gill epithelial cells and peripheral blood erythrocytes. Nuclear abnormalities other than micronuclei, considered as genetic damage indicators, were also evaluated on erythrocytes. Cyclophosphamide at a single dose of 4 mg/L was used as a positive control. The results of this study showed that both effluents had genotoxic potential. On the other hand, the level of genetic damage induced by petroleum refinery effluent was considerably higher than that of chromium processing plant effluent. Our results further indicate that nuclear abnormalities other than micronuclei, such as blebbed and lobed nuclei, may also be used as indicators of genotoxic damage.

Induction of micronucleated cells in the shed skin of salamanders (Ambystoma sp.) treated with colchicine or cyclophosphamide

The micronucleus (MN) assay can be used to detect the genotoxic effects of chemical agents in virtually any cell that divides frequently. Salamanders (Ambystoma sp.) are amphibians that can be easily maintained and bred in the laboratory and spontaneously shed their skin every 2.5-4 days. In this present study, we have evaluated the usefulness of this shed skin for the MN assay. We exposed salamanders to different concentrations of both the aneugen colchicine (COL) and the clastogen cyclophosphamide (CP) and we determined the frequency of micronucleated cells (MNCs) in their sheds. Fragments of shed skin were placed on clean slides, fixed, stained, observed with a light microscope, and the number of MNCs was counted. The MNC frequency was increased significantly by all doses of COL and CP tested, administered either as single or repeated exposures. The presence of MNCs in the shed skin and the speed of sloughing lead us to propose that the sheds of Ambystoma sp., or other amphibians that slough their skin, are suitable alternative models for detecting genotoxic exposures relevant to aquatic environments.

The combination of benzo[a]pyrene and ultraviolet A causes an in vivo time-related accumulation of DNA damage in mouse skin

Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are ubiquitous environmental carcinogens. BaP is metabolized in vivo to reactive intermediates that become covalently bound to DNA and form BaP-DNA adducts, an initial event in carcinogenesis. Ultraviolet A (UVA) synergizes with BaP to significantly enhance genetic damage and accelerate carcinogenic processes. This study was initiated to investigate in vivo cellular changes related to carcinogenesis induced by repeated exposures to BaP plus UVA. Simulated chronic exposure to an environmental carcinogen and sunlight was conducted through biweekly topical application of BaP followed 2 h later by UVA exposure over a 10 week period. BaP diol epoxide (BPDE)-DNA adducts were measured in vivo by immunohistochemistry using an anti-BPDE-DNA monoclonal antibody. Oxidative DNA damage was measured by the detection of 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation using high-performance liquid chromatography. Alterations in the cell cycle that were relevant to carcinogenesis were revealed by changes in p53, as identified in vivo using a polyclonal anti-p53 antibody. We found that cells containing BPDE-DNA adducts and nuclear p53 expression significantly increased between 2 and 10 weeks of BaP-UVA treatment, whereas neither BPDE-DNA adducts nor significant changes in p53 were observed in untreated skin. Using regression analysis, oxidative 8-OHdG damage also showed a parallel increase over 2-10 weeks (r = 0.80). These results indicate that genetic damage caused by exposures to BaP plus UVA accumulates with time and increases the potential for inductive events leading to carcinogenesis and tumor formation.