Patterns of genotoxicity and contaminant exposure: evidence of genomic instability in the marsh frogs (Rana ridibunda) of Sumgayit, Azerbaijan

Micronucleus test on Triturus carnifex as a tool for environmental biomonitoring

The amphibian micronucleus test has been widely used during the last 30 years to test the genotoxic properties of several chemicals and as a tool for ecogenotoxic monitoring. The vast majority of these studies were performed on peripheral blood of urodelan larvae and anuran tadpoles and to a lesser extent adults were also used. In this study, we developed protocols for measuring micronuclei in adult shed skin cells and larval gill cells of the Italian crested newt (Triturus carnifex). Amphibians were collected from ponds in two protected areas in Italy that differed in their radon content. Twenty-three adult newts and 31 larvae were captured from the radon-rich pond, while 20 adults and 27 larvae were taken from the radon-free site. The animals were brought to the laboratory and the micronucleus test was performed on peripheral blood and shed skins taken from the adults and on larval gills. Samples from the radon-rich site showed micronucleus frequencies higher than those from the radon-free site and the difference was statistically significant in gill cells (P < 0.00001). Moreover, the larval gills seem to be more sensitive than the adult tissues. This method represents an easy (and noninvasive in the case of the shed skin) application of the micronucleus assay that can be useful for environmental studies in situ.

Environmental contaminants and chromosomal damage associated with beak deformities in a resident North American passerine

A large cluster of beak abnormalities among black-capped chickadees (Poecile atricapillus) in Alaska raised concern about underlying environmental factors in this region. Metals and trace elements, organochlorine pesticides, polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans (PCDD-Fs) were analyzed in adults, nestlings, and eggs of the affected population; local bird seed was also tested for organochlorine pesticides. The results offered no support for the hypothesis that selenium or any other inorganic element was responsible for beak deformities among chickadees, but some evidence that organochlorine compounds may be contributing factors. Adults with beak deformities had an elevated level of chromosomal damage, which was correlated with lipid level and concentrations of several organochlorine compounds. Multivariate analyses of pesticides and PCBs did not distinguish abnormal from normal adults, but subsequent univariate analysis demonstrated higher concentrations of heptachlor epoxide and PCB-123 in abnormal adults. Concentrations of all organochlorine compounds were low, and none is known to cause beak or keratin abnormalities. Patterns of PCB congener concentrations differed between nestlings with normal and abnormal parents. Eggs from clutches with low hatchability had higher concentrations of hexachlorobenzene and PCDD-Fs than those with high hatching success, and hexachlorobenzene was found in seeds. Additional testing for PCDD-Fs, polycyclic aromatic hydrocarbons, and other emerging contaminants, including brominated compounds, is needed to rule out environmental contaminants as a cause of beak deformities in chickadees in Alaska.

Impaired liver function in Xenopus tropicalis exposed to benzo[a]pyrene: transcriptomic and metabolic evidence

Background

Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role pollutants play in the decline of amphibian populations remains unclear. Amongst the most common aquatic contaminants, polycyclic aromatic hydrocarbons (PAHs) have been shown to induce several adverse effects on amphibian species in the larval stages. Conversely, adults exposed to high concentrations of the ubiquitous PAH, benzo[a]pyrene (BaP), tolerate the compound thanks to their highly efficient hepatic detoxification mechanisms. Due to this apparent lack of toxic effect on adults, no studies have examined in depth the potential toxicological impact of PAH on the physiology of adult amphibian livers. This study sheds light on the hepatic responses of Xenopus tropicalis when exposed to high environmentally relevant concentrations of BaP, by combining a high throughput transcriptomic approach (mRNA deep sequencing) and a characterization of cellular and physiological modifications to the amphibian liver.

Results

Transcriptomic changes observed in BaP-exposed Xenopus were further characterized using a time-dependent enrichment analysis, which revealed the pollutant-dependent gene regulation of important biochemical pathways, such as cholesterol biosynthesis, insulin signaling, adipocytokines signaling, glycolysis/gluconeogenesis and MAPK signaling. These results were substantiated at the physiological level with the detection of a pronounced metabolic disorder resulting in a possible insulin resistance-like syndrome phenotype. Hepatotoxicity induced by lipid and cholesterol metabolism impairments was clearly identified in BaP-exposed individuals.

Conclusions

Our data suggested that BaP may disrupt overall liver physiology, and carbohydrate and cholesterol metabolism in particular, even after short-term exposure. These results are further discussed in terms of how this deregulation of liver physiology can lead to general metabolic impairment in amphibians chronically exposed to contaminants, thereby illustrating the role xenobiotics might play in the global decline in amphibian populations.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-666) contains supplementary material, which is available to authorized users.

The legacy of persistent organic pollutants in Azerbaijan: an assessment of past use and current contamination

Azerbaijan has a history of production and heavy use of organochlorine pesticides (OCPs) with use focused in the main agricultural lowland region centred on the Kur River. Using a number of data sources, including archived reports from several government ministries, we attempt to construct production and use inventories for dichlorodiphenyltrichloroethane (DDT) and HCHs and compare these to scientific estimates of production and use of these chemicals in the 1960s to the 1980s. Notable discrepancies are evident particularly for DDT, with Azeri government records indicating much higher use (147-fold) than that estimated by the international scientific community. Soil and river sediment data from the 1980s and 2000s are also presented. While it is recognised that analytical uncertainties remain high for these older data (generated by GC-ECD), there is some evidence to show a decline in concentrations for some OCPs over this period. Extremely high concentrations of OCPs are evident for soils sampled in the vicinity of obsolete pesticide storage sites (found in numerous locations around the agricultural lowlands) and these levels may pose a health risk to wildlife and humans. River sediment data indicate high levels of both OCPs and polychlorinated biphenyls (PCBs), particularly downstream of the confluence of the two main rivers, the Kur and Araz. Particle-bound annual fluxes from the Kur River into the Caspian Sea are estimated for PCBs and OCPs and these are likely to influence levels observed in local coastal sediments, with agreement between river sediment data generated in the early 2000s and coastal marine sediment data generated from separate studies. We recommend that monitoring efforts should focus on soils in agricultural areas and around pesticide storage and production facilities as these soils will continue to provide a source of POPs to the regional environment.

Effect of mercury ions on cysteine metabolism in Xenopus laevis tissues

The effect of mercury ions on the level of cysteine, glutathione, sulfane sulfur, and on the activity of rhodanese, 3-mercaptopyruvate sulfurtransferase (MPST) and γ-cystathionase in brain, heart muscle, liver, kidneys, testes and skeletal muscle of adult Xenopus laevis was investigated. Frogs of both sexes were exposed for 7 or 14 days to 1.353mgL(-1) (ppm) of mercury chloride (HgCl(2)) dissolved in water. The activity of the investigated enzymes participating in cysteine metabolism depends on cysteine in their active sites. Mercury ions can bind to -SH groups and, therefore, lower the activity of enzymes and change the level of sulfane sulfur, a product of l-cysteine desulfuration. The effect of mercury was found to depend on the time of exposure and the kind of tissue. In the liver, the main site of glutathione biosynthesis, the ratio of GSH to GSSG was essentially unchanged. The total glutathione level was decreased after 7 days of exposure to mercury, similarly as the activity of rhodanese. Sulfane sulfur levels were significantly increased after a shorter duration, while they decreased after a longer time of exposure. The kidney, brain and testes were able to enhance the level of GSH, probably thanks to high γ-glutamyltranspeptidase activity. These tissues showed an increased value of GSH/GSSG ratio during the shorter exposure to mercury. The activity of sulfurtransferases was decreased, especially after the longer exposure to mercury. In the heart and skeletal muscle, the level of GSH, sulfane sulfur, and the activity of the investigated sulfurtransferases was diminished after 14 days of exposure to Hg. It can be concluded that the main mechanism of toxic Hg activity is generation of reactive oxygen species in cells due to depleted GSH level, and a decreased sulfurtransferases activity either by blocking or oxidation of their -SH groups, what in consequence results in a diminished sulfane sulfur levels in tissues, especially the heart and testes.

Evolutionary toxicology: contaminant-induced genetic mutations in mosquitofish from Sumgayit, Azerbaijan

This study builds on a long-term program that has shown Sumgayit, Azerbaijan to contain wetlands with high levels of a diversity of chemical contaminants. Previous contaminant and biomarker studies of turtles and frogs showed a correlation between somatic chromosomal damage and chemical contaminants at Sumgayit. The objective of this study was to determine if a recently arrived species (mosquitofish) has genetic impacts similar to native species (marsh frogs) thus confirming the pattern is not the result of historical events such as glacial cycles, but is associated with recent chemical contamination. Nucleotide sequences of the mtDNA control region of invasive mosquitofish (Gambusia holbrooki) from Sumgayit were compared to mosquitofish from pristine sites in Europe and Azerbaijan and to native North American populations. Persistent heteroplasmy for a hyper-mutable simple sequence repeat and low haplotype and nucleotide diversities were observed in all invasive populations. However, Sumgayit possessed four de novo haplotypes and heteroplasmic conditions. All of the observed variable nucleotide positions were within or adjacent to a cytosine mononucleotide repeat. This repeat was within a conserved secondary structure; the region likely undergoes expansion and contraction at a rate sufficient to prevent fixation of the common 1/3 heteroplasmy. Whereas the 1/3 heteroplasmy appeared coincident with the establishment of mosquitofish in Europe, other forms of heteroplasmy resulted from contaminant-induced de novo mutations in Sumgayit. We conclude that Sumgayit is a mutational hotspot caused by legacy contaminants from chemical factories from the era of the Soviet Union.

Are endocrine disruptors among the causes of the deterioration of aquatic biodiversity?

Exposure to environmental pollutants such as endocrine-disrupting compounds (EDCs) is now taken into account to explain partially the biodiversity decline of aquatic ecosystems. Much research has demonstrated that EDCs can adversely affect the endocrine system, reproductive health, and immune function in aquatic species. These toxicological effects include 1) interference with normal hormonal synthesis, release, and transport, 2) impairment of growth, development, and gonadal maturation, and 3) increased sensitivity to environmental stressors. Recent studies also have confirmed that EDCs have carcinogenic and mutagenic potential. In essence, these changes in physiological and biochemical parameters reflect, to some extent, some phenotypic characteristics of the deterioration of aquatic biodiversity. At present, evidence at the molecular level shows that exposure to EDCs can trigger genotoxicity, such as DNA damage, and can reduce genetic diversity. Field studies have also provided more direct evidence that EDCs contribute to the population decrease and biodiversity decline. Evolutionary toxicology and multigenerational toxicity tests have further demonstrated that EDCs can damage an organism's offspring and eventually likely lead to loss of evolutionary potential. Taken together, these results provide some basis for understanding the relationship between variety deterioration and EDC exposure. It is conceivable that there is a causal association between EDC exposure and variety deterioration of aquatic organisms.

Sublethal and lethal effects on Rhinella arenarum (Anura, Bufonidae) tadpoles exerted by the pirimicarb-containing technical formulation insecticide Aficida

Acute toxicity, genotoxicity, and cytotoxicity of the pirimicarb-containing commercial-formulation carbamate insecticide Aficida(R) (50% pirimicarb) were evaluated on Rhinella arenarum (Anura, Bufonidae) tadpoles exposed under laboratory conditions. Lethal and sublethal effects were employed as bioassays for acute toxicity, whereas micronuclei (MNi) induction and alterations in the ratio erythrocytes:erythroblasts were employed as end-points for genotoxicity and cytotoxicity, respectively. Cr(VI) (23 mg L(-1)) and cyclophosphamide (40 mg L(-1)) were employed as positive controls for toxicity and geno-cytotoxicity assays, respectively. In Gosner stage 25 (STD25), the results revealed mean values of 402.0 and 223.6 mg Aficida L(-1) for LC-50(24)(h) and LC-50(96)(h), respectively. When STD37-39 tadpoles were exposed, the LC-50(24)(h) and LC-50(96)(h) reached values of 239.4 and 181.7 mg Aficida L(-1), respectively. Sublethal effects revealed a mean EC-50(96)(h) of 133.85 and 104.2mg Aficida in those STD25 and STD37-39 treated tadpoles, respectively. The results demonstrated that in 48-h-exposed tadpoles, a MNi increase was found only in those 80.0 mg L(-1) Aficida-treated individuals. When tadpoles were exposed to Aficida for 96h, only the 160 mg L(-1)-treated individuals showed a significant increase in MNi frequency. Concentrations ranging from 80.0 to 250.0mg Aficida L(-1) resulted in cellular cytotoxicity, revealed by a decreased proportion of circulating erythrocytes and an enhancement of erythroblasts. Accordingly, this species could provide a suitable and useful experimental model for biomonitoring aquatic ecosystems.

Wildlife toxicology: biomarkers of genotoxic exposures at a hazardous waste site

A large number of hazardous waste sites in the United States have undergone the initial stages of remediation or containment. At many of the remaining sites, the potential for exposure to ecological receptors is a primary concern. This manuscript reports on studies to investigate the impact on ecological receptors exposed to complex mixtures at a former creosote facility. Currently there are isolated areas on-site that were not addressed in the initial removal action that appear to be releasing polycyclic aromatic hydrocarbons (PAHs) to the surrounding environment. The U.S. EPA collected environmental samples and performed ex situ sediment bioassays to measure chronic toxicity; whereas, this study describes an in situ study to measure biomarkers of effect in two ecological receptors. Mosquitofish (Gambusia affinis) and cricket frogs (Acris crepitans) were collected from a small intermittent creek adjacent to the site, and reference stations. A weight-of-evidence ecological risk assessment was completed for the amphibian and fish communities. The ecological risk assessment was developed using analysis of media chemistry, body burden of specific PAHs, bioassay results, community surveys, and cellular genome size variation as a biomarker of genotoxicity. Flow cytometric estimates of chromosomal damage were significantly elevated for both mosquitofish and cricket frogs inhabiting the contaminated site, relative to at least one reference site. Surface water screening values for fish and amphibians exceeded screening values for PAHs by more than one order of magnitude in the on-site creek, and sediment PAH concentrations were extremely high (up to 1,549 microg/dry g). Tissue concentrations of PAHs were below screening values. Media chemistry, bioassay and genotoxicity data all support the same conclusion that on-site PAHs continue to impact aquatic receptors. The genotoxicity findings are consistent with and contribute to results of the weight-of-evidence ecological risk assessment. The results support continuing efforts to incorporate biomarkers as valuable lines of evidence within ecological risk assessment.

An evaluation of the health status of the Lavaca Bay, Texas ecosystem using Crassostrea virginica as the sentinel species

Locational risks for compromised ecosystem health for the eastern oysters (Crassostrea virginica) harvested from Lavaca Bay, Texas were estimated. Flow cytometric evaluation of variations in DNA content and the lysosomal destabilization assay were used for evaluation of genotoxicity and stress, respectively. Bayesian geo-statistical methods were utilized to estimate and evaluate spatial effects. For models with spatial risks, continuous surface maps of predicted parameter values were created to evaluate risk location. Lysosomal destabilization assay results were spatially oriented whereas flow cytometry results were fit best with the random effects model. While not spatially oriented, the highest levels of variations in DNA content were also present near industrial facilities. Locational risks of increased biomarkers of genotoxicity and stress in the eastern oyster (Crassostrea virginica) were increased with proximity to industrial facilities.

Potential effects of environmental contaminants on P450 aromatase activity and DNA damage in swallows from the Rio Grande and Somerville, Texas

Cliff swallows (Petrochelidon pyrrhonota) and cave swallows (P. fulva) were sampled during the breeding season at several locations in the Rio Grande, Texas, to evaluate the potential effects of environmental contaminants on P450 aromatase activity in brain and gonads and DNA damage in blood cells. The tritiated water-release aromatase assay was used to measure aromatase activity and flow cytometry was used to measure DNA damage in nucleated blood cells. There were no significant differences in brain and gonadal aromatase activities or in estimates of DNA damage (HPCV values) among cave swallow colonies from the Lower Rio Grande Valley (LRGV) and Somerville. However, both brain and gonadal aromatase activities were significantly higher (P < 0.05) in male cliff swallows from Laredo than in those from Somerville. Also, DNA damage estimates were significantly higher (P < 0.05) in cliff swallows (males and females combined) from Laredo than in those from Somerville. Contaminants of current high use in the LRGV, such as atrazine, and some of the highly persistent organochlorines, such as toxaphene and DDE, could be potentially associated with modulation of aromatase activity in avian tissues. Previous studies have indicated possible DNA damage in cliff swallows. We did not observe any differences in aromatase activity or DNA damage in cave swallows that could be associated with contaminant exposure. Also, the differences in aromatase activity and DNA damage between male cliff swallows from Laredo and Somerville could not be explained by contaminants measured at each site in previous studies. Our study provides baseline information on brain and gonadal aromatase activity in swallows that could be useful in future studies.

Geostatistical analysis of biomarkers of genotoxicity in cattle, Bos taurus and Bos taurus x Bos indicus, sentinels near industrial facilities

This study, performed at the behest of ranchers living and working down-prevailing wind from industrial facilities located in Calhoun County, Texas investigated locational risks to ecosystem health associated with proximity to specific industrial complexes. Concerns expressed were for potential genotoxicity in cattle resulting from the release of complex chemical mixtures. The Comet Assay and flow cytometric evaluation of variations in DNA content were utilized to evaluate DNA damage. Bayesian geo-statistical analysis revealed the presence of important spatial processes. The Comet assay's optical density provided a strong indication of increased damage down-prevailing wind from the industrial complexes. Results indicated that proximity to and location down-prevailing winds from industrial facilities increased the locational risk of genotoxicity in this sentinel species.

In situ biomonitoring of PAH-contaminated sediments using juvenile coho salmon (Oncorhynchus kisutch)

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous marine and freshwater sediment contaminants. Extensive data exist to confirm that PAHs are toxic to aquatic receptors. However, limited information is available regarding the bioavailability and genotoxicity of sediment PAHs to aquatic organisms. This study investigated an integrated biomonitoring approach using chemical analyses and biomarkers to characterize the bioavailability and genotoxicity of a complex PAH mixture in freshwater lake sediments associated with a former manufactured gas plant (MGP). Sediment PAH genotoxicity was assessed by flow cytometry (FCM), DNA adduct (32)P-postlabeling, and erythrocyte micronuclei in juvenile coho salmon (Oncorhynchus kisutch) caged in the water column. Significant PAH-induced genotoxicity was observed with FCM and (32)P-postlabeling, but not with erythrocyte micronuclei. Chromosome damage in peripheral blood and hepatic DNA adducts correlated with sediment, but not water column PAH concentrations. Total hepatic DNA adducts in salmon caged nearest the former MGP facility was 39+/-6.5 (RALx10(9)), while salmon caged in a reference lake had 28+/-2.3 total hepatic DNA adducts per 10(9) nucleotides. These results indicate that in situ biomonitoring using biomarkers and caged fish can be a sensitive indicator of genotoxic PAHs in sediments.

Comparison of metal bioavailability in frogs from urban and rural sites of Western Ukraine

The seasonal and spatial fluctuations of heavy metals in the liver of the frog Rana ridibunda from a river in Western Ukraine were investigated. Liver weight was seen to increase from spring to summer/autumn, most probably as a result of accumulation of metabolites, especially fat and glycogen. The concentrations of the metals found in the liver of the frog was in the order: Fe>Cu approximately Zn>Mn>Cd. For most metals, the highest concentration was recorded in the frogs inhabiting the urban site. The highest level of Cu in the liver was observed in the spring, in the agricultural site, while the highest level of other metals was observed in the summer. The most probable explanation for the high concentration of Cu in the rural site was that in this wetland there were discharge effluents from fungicides with Cu in their formula. Compared to other metals, the bioavailability of Cu was approximately 1000 times higher. The high concentration of Fe rather reflects its fluctuation in the water. Despite its very low concentration in the water (below the limit of detection), Cd was detected in the liver of frogs inhabiting both sites. This is an indication that tissues accumulate Cd, despite the very low concentration detected in the water. This may be an indication of intermittent exposure of frogs to Cd and possibly of other heavy metals.

Evolutionary toxicology: population-level effects of chronic contaminant exposure on the marsh frogs (Rana ridibunda) of Azerbaijan

We used molecular methods and population genetic analyses to study the effects of chronic contaminant exposure in marsh frogs from Sumgayit, Azerbaijan. Marsh frogs inhabiting wetlands in Sumgayit are exposed to complex mixtures of chemical contaminants, including petroleum products, pesticides, heavy metals, and many other industrial chemicals. Previous results documented elevated estimates of genetic damage in marsh frogs from the two most heavily contaminated sites. Based on mitochondrial DNA (mtDNA) control region sequence data, the Sumgayit region has reduced levels of genetic diversity, likely due to environmental degradation. The Sumgayit region also acts as an ecological sink, with levels of gene flow into the region exceeding gene flow out of the region. Additionally, localized mtDNA heteroplasmy and diversity patterns suggest that one of the most severely contaminated sites in Sumgayit is acting as a source of new mutations resulting from an increased mutation rate. This study provides an integrated method for assessing the cumulative population impacts of chronic contaminant exposure by studying both population genetic and evolutionary effects.