Evaluation of DNA damage induced by decabromodiphenyl ether (BDE-209) in hemocytes of Dreissena polymorpha using the comet and micronucleus assays

Toxicity of persistent organic pollutants: a theoretical study

CONTEXT

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are two families of persistent organic pollutants that are dangerous as they remain in the atmosphere for long periods and are toxic for humans and animals. They are found all over the world, including the penguins of Antarctica. One of the mechanisms that explains the toxicity of these compounds is related to oxidative stress. The main idea of this theoretical research is to use conceptual density functional theory as a theory of chemical reactivity to analyze the oxidative stress that PCBs and PBDEs can produce. The electron transfer properties as well as the interaction with DNA nitrogenous bases of nine PCBs and ten PBDEs found in Antarctic penguins are investigated. From this study, it can be concluded that compounds with more chlorine or bromine atoms are more oxidizing and produce more oxidative stress. These molecules also interact directly with the nitrogenous bases of DNA, forming hydrogen bonds, and this may be an explanation for the toxicity. Since quinone-type metabolites of PCBs and PBDEs can cause neurotoxicity, examples of quinones are also investigated. Condensed Fukui functions are included to analyze local reactivity. These results are important as the reactivity of these compounds helps to explain the toxicity of PCBs and PBDEs.

METHODS

All DFT computations were performed using Gaussian16 at M06-2x/6-311 + g(2d,p) level of theory without symmetry constraints. Electro-donating (ω-) and electro-accepting (ω +) powers were used as global response functions and condensed Fukui functions as local parameters of reactivity.

A critical review on BDE-209: Source, distribution, influencing factors, toxicity, and degradation

As the most widely used polybrominated diphenyl ether, BDE-209 is commonly used in polymer-based commercial and household products. Due to its unique physicochemical properties, BDE-209 is ubiquitous in a variety of environmental compartments and can be exposed to organisms in various ways and cause toxic effects. The present review outlines the current state of knowledge on the occurrence of BDE-209 in the environment, influencing factors, toxicity, and degradation. BDE-209 has been detected in various environmental matrices including air, soil, water, and sediment. Additionally, environmental factors such as organic matter, total suspended particulate, hydrodynamic, wind, and temperature affecting BDE-209 are specifically discussed. Toxicity studies suggest BDE-209 may cause systemic toxic effects on living organisms, reproductive toxicity, embryo-fetal toxicity, genetic toxicity, endocrine toxicity, neurotoxicity, immunotoxicity, and developmental toxicity, or even be carcinogenic. BDE-209 has toxic effects on organisms mainly through epigenetic regulation and induction of oxidative stress. Evidence regarding the degradation of BDE-209, including biodegradation, photodegradation, Fenton degradation, zero-valent iron degradation, chemical oxidative degradation, and microwave radiation degradation is summarized. This review may contribute to assessing the environmental risks of BDE-209 to help develop rational management plans.

Cellular and physiological mechanisms of halogenated and organophosphorus flame retardant toxicity

Flame retardants (FRs) are chemical substances used to inhibit the spread of fire in numerous industrial applications, and their abundance in modern manufactured products in the indoor and outdoor environment leads to extensive direct and food chain exposure of humans. Although once considered relatively non-toxic, FRs are demonstrated by recent literature to have disruptive effects on many biological processes, including signaling pathways, genome stability, reproduction, and immune system function. This review provides a summary of research investigating the impact of major groups of FRs, including halogenated and organophosphorus FRs, on animals and humans in vitro and/or in vivo. We put in focus those studies that explained or referenced the modes of FR action at the level of cells, tissues and organs. Since FRs are highly hydrophobic chemicals, their biophysical and biochemical modes of action usually involve lipophilic interactions, e.g. with biological membranes or elements of signaling pathways. We present selected toxicological information about these molecular actions to show how they can lead to damaging membrane integrity, damaging DNA and compromising its repair, changing gene expression, and cell cycle as well as accelerating cell death. Moreover, we indicate how this translates to deleterious bioactivity of FRs at the physiological level, with disruption of hormonal action, dysregulation of metabolism, adverse effects on male and female reproduction as well as alteration of normal pattern of immunity. Concentrating on these subjects, we make clear both the advances in knowledge in recent years and the remaining gaps in our understanding, especially at the mechanistic level.

Biomarkers for pollution in caged mussels from three reservoirs in Bulgaria: A pilot study

The mussel-watch concept was firstly proposed in 1975, which was later adopted by several international monitoring programs worldwide. However, for the very first time, a field experiment with caged mussels was performed in three reservoirs in Bulgaria to follow the harmful effects of sub-chronic pollution (30 days) of metals, trace, and macro-elements, as well as some organic toxicants, such as polybrominated diphenyl ethers and chlorinated paraffins. Therefore, we studied the biometric indices, histochemical lesions in the gills, biochemical changes in the digestive glands (antioxidant defense enzymes, such as catalase, glutathione reductase, and glutathione peroxidase; metabolic enzymes, such as lactate dehydrogenase, alanine aminotransferase, and aspartate aminotransferase, and the neurotransmitter cholinesterase), in addition to the DNA damage in the Chinese pond mussel, Sinanodonta woodiana (Lea, 1834) in Kardzhali, Studen Kladenets and Zhrebchevo reservoirs in Bulgaria. Significant correlation trends between the pollution levels, which we reported before, and the biomarker responses were established in the current paper. Overall, we found that both tested organs were susceptible to pollution-induced oxidative stress. The different alterations in the selected biomarkers in the caged mussels compared to the reference group were linked to the different kinds and levels of water pollution in the reservoirs, and also to the simultaneously conducted bioaccumulation studies.

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The effects of water pollution in caged mussels from three large dam reservoirs in Bulgaria were assessed.

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A cocktail of different inorganic and organic toxicants was measured both in waters and mussels for the first time.

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Different biomarker responses (cellular to individual) were also followed in gills and digestive glands of the transplants.

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Correlation trends between the pollution levels and the applied biological tools were established.

How can environmental conditions influence dicofol genotoxicity on the edible Asiatic clam, Meretrix meretrix?

Genotoxic effects of dicofol on the edible clam Meretrix meretrix were investigated through a mesocosm experiment. Individuals of M. meretrix, were exposed to environmental concentration (D1 = 50 ng/L) and supra-environmental concentration (D2 = 500 ng/L) of dicofol for 15 days, followed by the same depuration period. DNA damage (i.e., strand breaks and alkali-labile sites) was evaluated at day 1, 7 and 15, during uptake and depuration, using Comet assay (alkaline version) and nuclear abnormalities (NAs) as genotoxicity biomarkers. The protective effects of dicofol against DNA damage induced by ex vivo hydrogen peroxide (H₂O₂) exposure were also assessed. Comet assay results revealed no significant DNA damages under dicofol exposure, indicating 1) apparent lack of genotoxicity of dicofol to the tested conditions and/or 2) resistance of the animals due to optimal adaptation to stress conditions. Moreover, ex vivo H₂O₂ exposure showed an increase in the DNA damage in all the treatments without significant differences between them. However, considering only the DNA damage induced by H₂O₂ during uptake phase, D1 animals had significantly lower DNA damage than those from other treatments, revealing higher protection against a second stressor. NAs data showed a decrease in the % of cells with polymorphic, kidney shape, notched or lobbed nucleus, along the experiment. The combination of these results supports the idea that the clams used in the experiment were probably collected from a stressful environment (in this case Pearl River Delta region) which could have triggered some degree of adaptation to those environmental conditions, explaining the lack of DNA damages and highlighting the importance of organisms' origin and the conditions that they were exposed during their lives.

Aspartic acid assisted one-step synthesis of stable CsPbX3@Asp-Cs4PbX6 by in situ growth in NH2-MIL-53 for ratiometric fluorescence detection of 4-bromophenoxybenzene

A molecularly imprinted ratiometric fluorescent sensor was synthesized for the detection of 4-bromophenoxybenzene (BDE-3) based on perovskite quantum dots and metal organic framework. First, aspartic acid (Asp) was introduced during the synthesis of perovskite CsPbX₃ for the formation of a core-shell structure of CsPbX₃@Asp-Cs₄PbX₆. Due to the protection of the shell layer Cs₄PbX₆, the stability of the core CsPbX₃ was improved significantly. Compared to CsPb(BrI)₃, the ultraviolet and thermal stabilities of CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆ were increased by 26 times and 32 times, respectively, and, compared to CsPbBr₃, these stabilities of CsPbBr₃@Asp-Cs₄PbBr₆ were increased by 3 times and 13 times, respectively. The water stabilities of CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆ and CsPbBr₃@Asp-Cs₄PbBr₆ were greatly improved too. Then, a ratiometric fluorescence sensor was constructed by in situ growth of CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆ in metal organic framework (NH₂-MIL-53) for the detection of BDE-3, in which the orange fluorescence of CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆ (614 nm) was regarded as the reference signal and the cyan fluorescence of NH₂-MIL-53 (494 nm) was used as the fluorescence response signal. To improve the selectivity of the sensor, the molecular imprinting polymer (MIP) was modified on the NH₂-MIL-53 and an imprinting factor of 3.17 was obtained. Under 365 nm light excitation, the fluorescent response signal at 494 nm was quenched gradually by BDE-3 in the range 11.4 to 68.5 nmol/L, while the reference signal at 614 nm remained unchanged. The limit of detection and limit of quantification were 3.35 and 11.2 nmol/L, respectively, and the fluorescent color of the sensor changed gradually from cyan to green to orange, which illustrated that the developed sensor has an ability to recognize BDE-3 specifically, a good anti-interference ability, and a sensitively visual detection ability. Moreover, the sensor was successfully applied to the BDE-3 detection in polyethylene terephthalate plastic bottle, polyvinyl chloride plastic bag, and circuit board with satisfactory recoveries (96.3-108.1%) and low relative standard deviations (5%). The preparation processes of NH₂-MIL-53, NH₂-MIL-53-CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆, and the MIP-NH₂-MIL-53-CsPb(BrI)₃@Asp-Cs₄Pb(BrI)₆ composites.

Toxicological effects and bioaccumulation of fullerene C60 (FC60) in the marine bivalve Ruditapes philippinarum

Fullerene C₆₀ (FC₆₀), with its unique physical properties, has been used in many applications in recent decades. The increased likelihood of direct release into the environment has raised interest in understanding the biological effects of FC₆₀ to aquatic organisms. Nowadays, only few studies have analysed FC₆₀ effects and bioaccumulation in marine organisms following in vivo exposure. To provide new data about FC₆₀ toxicity, Ruditapes philippinarum was selected as target species to assess potential adverse effects of the contaminant. Clams were exposed for 1, 3 and 7 days to predicted environmental concentrations of FC₆₀ (1 and 10 μg/L) and cellular and biochemical responses were evaluated in clams' gills, digestive gland and haemolymph. The FC₆₀ content in gills and digestive gland was determined in all experimental conditions after 7 days of exposure. Results showed an increase in oxidative stress. In particular, a significant modulation in antioxidant enzyme activities, and changes in glutathione S-transferase activity were observed in gills. Moreover, damage to lipids and proteins was detected in FC₆₀-treated (10 µg/L) clams. In digestive gland, slighter variations in antioxidant enzyme activities and damage to molecules were detected. CAT activity was significantly affected throughout the exposure, whereas damage to lipids was evident only at the end of exposure. FC₆₀ accumulation was revealed in both gills and digestive gland, with values up to twelve-fold higher in the latter. Interestingly, haemolymph parameters were slightly affected by FC₆₀ compared to the other tissues investigated. Indeed, only Single Cell Gel Electrophoresis and Neutral Red uptake assays showed increased values in FC₆₀-exposed clams. Moreover, volume and diameter of haemocytes, haemocyte proliferation, and micronucleus assay highlighted significant variations in treated clams, but only in the first phases of exposure, and no changes were detected after 7 days. Our results suggested clam gills as the target tissue for FC₆₀ toxicity under the exposure conditions tested: the high damage detected to lipids and proteins could contribute to long-term problems for the organism.

BDE-47 exposure modulates cellular responses, oxidative stress and biotransformation related-genes in Mytilus galloprovincialis

Polybrominated diphenyl ethers (PBDEs) are flame retardants, characterized by elevated stability in the marine environment, where are accumulated by organisms, inducing a wide panel of negative effects. In this study, some biochemical patterns related to toxicity, biotransformation and oxidative stress, were studied in the marine model system, Mytilus galloprovincialis, exposed to BDE-47. Mussels were fed with microalgae, previously treated with increasing concentrations of PBDEs (maximum dose 100 ng L-1 of BDE-47 per day). After 15 days of treatment, mussels were fed with the same diet without BDE-47, for additional 15 days. Gills and digestive glands were analyzed at T 0, at 15 and 30 days. Histopathological lesions were assessed in digestive glands of contaminated mussels, while expression of genes, related to cell cycle, multidrug resistance, oxidative stress and detoxification was evaluated on both gills and digestive glands. After 15 days, BDE-47 exposure significantly affected the cell activity in digestive gland and, at 30 days, only mussels exposed to the lower doses showed a certain recovery. Regarding the gene expression, both gills and digestive glands showed a significant down-regulation of the target genes at 15 days, although most of them were up-regulated at 30 days in digestive gland. The results on BDE-47 accumulation in mussels revealed a dose-dependent concentration in tissues, which remained elevated after further 15 days of depuration. This trend supports the responses of the biomarkers, indicating that exposure, at environmentally realistic concentrations of BDE-47, strongly modulates oxidative stress and related patterns of gene expression, suggesting concerns for long-term effect in the biota.

Effects of BDE-47 exposure on immune-related parameters of Mytilus galloprovincialis

The persistent pollutants polybrominated diphenyl ethers (PBDEs) have been demonstrated to produce several negative effects on marine organisms. Although Mytilus galloprovincialis was extensively studied as model system, the effects of PBDEs on the innate immune system of mussels remains unclear. In this study, except for the control treatment, specimens of M. galloprovincialis were fed with microalgae treated with increasing concentrations of PBDEs (maximum level 100 ng L^-1 of BDE-47 per day). BDE-47 treatment was maintained for 15 days and then the animals were fed with the same control diet, without contaminants, for 15 days. Samples of haemolymph (HL) were obtained at T0, T15 and T30 days of the experiment to evaluate different parameters related to immunity, such as neutral red retention time, and peroxidase, protease, antiprotease, lysozyme and bactericidal activities. BDE-47 exposure for 15 days affected both the stability of haemocytes and humoral parameters. In addition, the obtained results indicated that, at 30 days, after 15 days of culture without contaminant, the immune parameters were still affected, as some of them did not return to the basal levels, and others remained stimulated. Overall the results indicate that BDE-47 exposures at environmentally realistic levels may affect various aspects of immune function in M. galloprovincialis, acting as stressor that can compromise the general welfare.

Dechlorane Plus induces oxidative stress and decreases cyclooxygenase activity in the blue mussel

Dechlorane Plus (DP) is a chlorinated flame retardant used mainly in electrical wire and cable coating, computer connectors, and plastic roofing materials. Concentrations of DP (syn and anti isomers) are increasingly being reported in aquatic ecosystems worldwide. However, there is exceedingly little information on the exposure-related toxicity of DP in aquatic organisms, especially in bivalves. The objective of this study was to investigate the in vivo and in vitro effects of DP exposure on histopathology, lipid peroxidation (LPO) levels, cyclooxygenase (COX) activity, phagocytosis capacity and efficiency, and DNA strand breakage in the blue mussel (Mytilus edulis) following a 29days exposure (0.001, 0.01, 0.1 and 1.0μg DP/L). Blue mussels accumulated DP in muscle and digestive gland in a dose-dependent manner. LPO levels in gills were found to increase by 82% and 67% at the 0.01 and 1.0μg DP/L doses, respectively, while COX activity in gills decreased by 44% at the 1μg/L dose. No histopathological lesion was found in gonads following DP exposure. Moreover, no change in hemocyte DNA strand breakage, phagocytosis rate, and viability was observed following DP exposure. Present study showed that toxicity of DP may occur primarily via oxidative stress in the blue mussel and potentially other bivalves, and that gills represent the most responsive tissue to this exposure.

BDE-47 exposure changed the immune function of haemocytes in Mytilus edulis: An explanation based on ROS-mediated pathway

Brominated Tetra-BDE (BDE-47), is suggested to be widely distributed in marine environments and highly accumulated in marine organisms. Blue mussel Mytilus edulis is a sentinel organism that is commonly used for monitoring chemical contaminants in coastal ecosystems, and its haemocytes play an essential role in immune function. Therefore, we estimated the effects of BDE-47 exposure on the M. edulis haemocytes' immune function under controlled laboratory conditions. The study found the following results: (1) BDE-47 exposure increased the mortality of the haemocytes and decreased the total haemocyte counts. The ultrastructure and microstructure in the haemocytes were significantly changed, and the micronucleus frequency was increased steadily in a concentration-dependent manner, inferring that cellular and molecular damages occur during the exposure. (2) The immune function of the haemocytes was estimated from lysosomal and phagocytic changes. The lysosomal membrane stability was significantly disrupted compared to the control according to neutral red retention time changes, and the phagocytic ability was reduced significantly. Two lysosomal enzymes, acid phosphatases and alkaline phosphatases, presented similar increasing trends during the treatment. (3) BDE-47 exposure significantly induced the overproduction of reactive oxygen species and malondialdehyde in a clear time- and concentration-dependent manner, suggesting the occurrence of oxidative stress. We thus presumed that BDE-47 exposure affected the immune function of the mussel's haemocytes, and an ROS-mediated pathway might be one of the possible explanations for the observation.

Genotoxic effects of cadmium in human head and neck cell line SQ20B

As cadmium may be involved in the etiology of head and neck cancers, we investigated in the present work, the cytotoxic and genotoxic effects of Cd on human larynx cells. SQ20B cells were exposed to 25 and 50 μM Cd for 48 and 72 h. Results showed a dose-dependent decrease in cell viability, especially after 48 h, associated with mitochondria alterations as showed by transmission electronic microscopy. Surprisingly, the flow cytometry shows that the cells treated with Cd have a normal proliferative cycle like the untreated cell especially in G1 or G2 phase of cell cycle. DNA damages were investigated by comet assay and immunofluorescence for gamma layer of the H2AX (g-H2AX) foci formation. Results show a strong induction of DNA double-strand breaks after Cd exposure. Overall, our results demonstrate the cytotoxicity and genotoxicity of Cd in human larynx cells and support the view that Cd could be an etiologic factor of head and neck cancers.

Exposure to2,2',4,4'-tetrabromodiphenyl ether (BDE-47) alters thyroid hormone levels and thyroid hormone-regulated gene transcription in manila clam Ruditapes philippinarum

Polybrominated diphenyl ethers (PBDEs) have the potential to disturb the thyroid endocrine system in vertebrates, but little is known about the disruptive effects of PBDEs on marine bivalves. In this study, we first examined the effects of BDE-47 exposure on growth of juvenile manila clams Ruditapes philippinarum. The result showed that 1.0 and 10 μg L(-1) BDE-47 had adverse effects on 14-d shell-length growth of juvenile clams. Then, one-year-old adult clams were exposed to 0, 0.1 and 1 μg L(-1) BDE-47 for 15 d. BDE-47 (1 μg L(-1)) exposure caused significant decreases of total T4 (thyroxine) by 40% and T3 (3,5,3'-triiodothyronine) by 75% concentrations in haemolymph of the clams. Transcription of genes involved in thyroid hormone synthesis and metabolism were also studied by quantitative RT-PCR. Gene expression levels of sodium iodide symporter (rp-NIS), iodothyronine deiodinase (rp-Deio) and thyroid peroxidase (rp-TPO) were increased in a dose-dependent manner at day 5 and day 10, while monocarboxylate transporter 8 (rp-Mct8) was downregulated at day 5, day 10 and day 15. The effect and preliminary mechanism observed in the present study were consistent with the results from previous studies on rodent and fish, implying that exposure to BDE-47 may pose threat to thyroid hormone homeostasis in bivalves through thyroid synthesis and metabolism pathways. This study may provide a first step towards understanding of the thyroid function disruptive effects of PBDEs on marine bivalves and the underlying mechanism across taxonomic groups and phyla.

Evaluation of the Genotoxic and Physiological Effects of Decabromodiphenyl Ether (BDE-209) and Dechlorane Plus (DP) Flame Retardants in Marine Mussels (Mytilus galloprovincialis)

Dechlorane Plus (DP) is a proposed alternative to the legacy flame retardant decabromodiphenyl ether (BDE-209), a major component of Deca-BDE formulations. In contrast to BDE-209, toxicity data for DP are scarce and often focused on mice. Validated dietary in vivo exposure of the marine bivalve (Mytilus galloprovincialis) to both flame retardants did not induce effects at the physiological level (algal clearance rate), but induced DNA damage, as determined by the comet assay, at all concentrations tested. Micronuclei formation was induced by both DP and BDE-209 at the highest exposure concentrations (100 and 200 μg/L, respectively, at 18% above controls). DP caused effects similar to those by BDE-209 but at lower exposure concentrations (5.6, 56, and 100 μg/L for DP and 56, 100, and 200 μg/L for BDE-209). Moreover, bioaccumulation of DP was shown to be concentration dependent, in contrast to BDE-209. The results described suggest that DP poses a greater genotoxic potential than BDE-209.

Distribution of polybrominated diphenyl ethers and HBCD in sediments of the Hunhe River in Northeast China

Forty surface sediment samples from the Hunhe River in Northeast China were evaluated for contamination by polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD). The results showed that decabromodiphenyl ether (BDE-209) was the predominant congener, accounting for >98 % of PBDEs in all sediment. The concentrations of BDE-209 and HBCD ranged from 3.96 to 327 ng/g dry weight and 0.05 to 25.8 ng/g dry weight, respectively, suggesting that BDE-209 was more widely applied in the study area. The mean concentrations of BDE-209 and HBCD in the downstream portion of the Hunhe River (BDE-209 148 ng/g dry weight and HBCD 3.74 ng/g dry weight) were found to be relatively higher than those in the upstream portion of the Hunhe River and the Dahuofang Reservoir, revealing an association with municipal sewage and industrial effluent received from the cities of Fushun and Shenyang. γ-HBCD was the most abundant diastereoisomer of all three analyzed HBCD isomers; however, marked elevations of α-HBCD were also found in most sediment samples. Surprisingly, the relative abundance (mean 38%) of α-HBCD in sediment from the upstream portion of the Hunhe River was significantly higher (p < 0.006, t test) than those in Dahuofang Reservoir (mean 24%). Moreover, the severe heavy metal contamination associated with the frequent mining activities in this region was tentatively suggested as being responsible for the increased levels of α-HBCD.

Genotoxicity of cadmium chloride in the marine gastropod Nerita chamaeleon using comet assay and alkaline unwinding assay

This paper presents an evaluation of the genotoxic effects of cadmium chloride (CdCl2 ) on marine gastropod, Nerita chamaeleon following the technique of comet assay and the DNA alkaline unwinding assay (DAUA). In this study, the extent of DNA damage in gill cells of N. chamaeleon was measured after in vivo exposure to four different concentrations (10, 25, 50, and 75 µg/L) of CdCl2 . In vitro exposure of hydrogen peroxide (H2 O2 ; 1, 10, 25, and 50 µM) of the gill cells showed a significant increase in the percentage tail DNA, Olive tail moment, and tail length (TL). Significant changes in percentage tail DNA by CdCl2 exposure were observed in all exposed groups of snails with respect to those in control. Exposure to 75 µg/L of CdCl2 produced significant decrease in DNA integrity as measured by DAUA at all duration with respect to control. In vivo exposure to different concentrations of CdCl2 (10, 25, 50, and 75 µg/L) to N. chamaeleon showed considerable increase in DNA damage as observed by both alkaline comet assay and the DAUA. The extent of DNA damage in marine gastropods determined by the application of alkaline comet assay and DAUA clearly indicated the genotoxic responses of marine gastropod, N. chamaeleon to a wide range of cadmium concentration in the marine environment.

Does zebra mussel (Dreissena polymorpha) represent the freshwater counterpart of Mytilus in ecotoxicological studies? A critical review

One of the fundamentals in the ecotoxicological studies is the need of data comparison, which can be easily reached with the help of a standardized biological model. In this context, any biological model has been still proposed for the biomonitoring and risk evaluation of freshwaters until now. The aim of this review is to illustrate the ecotoxicological studies carried out with the zebra mussel Dreissena polymorpha in order to suggest this bivalve species as possible reference organism for inland waters. In detail,we showed its application in biomonitoring, as well as for the evaluation of adverse effects induced by several pollutants, using both in vitro and in vivo experiments. We discussed the advantages by the use of D. polymorpha for ecotoxicological studies, but also the possible limitations due to its invasive nature.

Cadmium and decabrominated diphenyl ether mixture: In vitro evaluation of cytotoxic, prooxidative and genotoxic effects

In order to look into the combined effects of Cd and BDE-209 in vitro, this study was aimed at examining cytotoxic and genotoxic effects using the human colon carcinoma cell line (SW 480) as a biological test system as well as to determine if ROS production was one of the possible mechanisms of their mixture action. This cell line was chosen since ingestion of contaminated food/water represents an important route of exposure to both Cd and BDE-209, which is why intestinal cells are a common target for the contaminants present in food and water. Cells were treated with single Cd in concentrations of 2.5, 7.5 or 15μg Cd/mL (corresponding to 22, 67 or 134μM), single BDE-209 in concentrations of 2.5, 5 or 10μg BDE209/mL (corresponding to 2.5, 5 or 10μM), and their mixtures (design 3×3). Mixture of Cd and BDE-209 has shown clear potential to reduce the viability of SW 480 cells, as evidenced by cytotoxicity associated with ROS generation. Factorial regression models used to identify type of interaction revealed synergism related to mixture citotoxicity and additive interaction for the effect on ROS production. The results from this introductory study could contribute to the issue of possible adverse effects associated with co-exposure and body burden with two persistent environmental pollutants, Cd and BDE-209.

Evaluation of impairment of DNA in marine gastropod, Morula granulata as a biomarker of marine pollution

The impairment of DNA in marine gastropod Morula granulata was evaluated in terms of the loss of DNA integrity in the species as a measure of the impact of genotoxic contaminants prevalent in the marine environment along the coast of Goa, India. The extent of DNA damage occurred in the marine gastropods collected from different sampling sites such as Arambol, Anjuna, Sinquerim, Dona Paula, Bogmalo, Hollant, Velsao, Betul and Palolem along the coast of Goa was measured following the technique of partial alkaline unwinding as well as comet assays. The highest DNA integrity was observed at Arambol (F, 0.75), identified as the reference site, whereas the lowest DNA integrity at Hollant (F, 0.33) situated between the two most contaminated sites at Bogmalo and Velsao. The impact of genotoxic contaminants on marine gastropods was pronounced by their low DNA integrity at Sinquerim (F, 0.40) followed by Betul (F, 0.47), Velsao (F, 0.51), Anjuna (F, 0.54), Bogmalo (F, 0.55), Dona Paula (F, 0.67) and Palolem (F, 0.70). The extent of DNA damage occurred in M. granulata due to ecotoxicological impact of the prevailing marine pollutants along the coast of Goa was further substantiated by comet assay and expressed in terms of %head-DNA, %tail DNA, tail length and Olive tail moment. The single cell gel electrophoresis of M. granulata clearly showed relatively higher olive tail moment in the marine gastropod from the contaminated sites, Anjuna, Hollant, Velsao and Betul. The variation in the mean %head DNA at different sampling sites clearly indicated that the extent of DNA damage in marine gastropod increases with the increase in the levels of contamination at different sampling sites along the coast. The stepwise multiple regression analysis of the water quality parameters showed significant correlation between the variation in DNA integrity and PAH in combination with NO3, salinity and PO4 (R¯(2), 0.90). The measurement of DNA integrity in M. granulata thus provides an early warning signal of contamination of the coastal ecosystem of Goa by genotoxic contaminants.

Identification of differentially expressed genes in the digestive gland of manila clam Ruditapes philippinarum exposed to BDE-47

Suppression subtractive hybridization (SSH) was used to identify alterations in gene transcription of the manila clam Ruditapes philippinarum after exposure to 5μg/L 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) for 15days. The ability to accumulate BDE-47 in digestive gland and gill was also evaluated in order to provide information for food safety. Analysis of tissue extracts indicated that digestive gland had the higher BDE-47 levels (12,463.1±1334.8 ng/g d.w.) compared to gill (6368.6±738.7ng/g d.w.) after a 15-day exposure period. Forward and reverse SSH libraries were made from pooled digestive glands of R. philippinarum, from which 75 high quality sequences were obtained by BLAST analysis. The expression of 39 genes with significant homology (E-value<10(-5)) out of the 75 sequences was investigated by quantitative RT-PCR. Among the 39 genes, 27 genes were found up-regulated while 12 genes were found down-regulated after the BDE-47 exposure. The 39 genes were involved in cellular cycle, cytoskeleton, substance and energy metabolism, stress response, innate immunity and cell signaling and transport which were extensively discussed. This study provides a preliminary basis for studying the response of marine bivalves upon exposure to PBDEs in terms of regulated gene expression.

Analysis of the Dreissena polymorpha gill proteome following exposure to dioxin-like PCBs: mechanism of action and the role of gender

PCBs are a persistent environmental problem due to their high stability and lipophilicity. The non-ortho- and the mono-ortho-substituted PCBs (dioxin-like-PCBs) share a common and well-described toxicity mechanism in vertebrates, initially involving binding to cytosolic AhRs. Invertebrate AhRs, however, show a lack of dioxin binding, and little information is available regarding the mechanism of toxicity of dl-PCBs in invertebrates. In this study, a proteomic approach was applied to analyse the variations in the pattern of the gill proteome of the freshwater mussel Dreissena polymorpha. Mussels were exposed to a mixture of dl-PCBs, and to perform a more in-depth evaluation, we chose to investigate the role of gender in the proteome response by analysing male and female mussels separately. The results revealed significant modulation of the gill tissue proteome: glycolysis and Ca(2+) homeostasis appear to be the main pathways targeted by dl-PCBs. In light of the differences between the male and female gill proteome profiles following exposure to dl-PCBs, further in-depth investigations of the role of gender in the protein expression profiles of a selected biological model are required.

Prenatal exposure to decabrominated diphenyl ether impairs learning ability by altering neural stem cell viability, apoptosis, and differentiation in rat hippocampus

Background:Polybrominated diphenyl ether (PBDE) levels in children and teenagers were higher than those of the adults and the highest levels were found in infants and toddlers. 2,2',3,3',4,4',5,5',6,6'-Decabrominated diphenyl ether (BDE-209) readily crosses the placental barrier and produces toxicity in the developing fetus, particularly to the developing brain.Objectives:This present study aims to investigate the potential effects of prenatal BDE-209 exposure on regulation of neurogenesis and learning function in an experimental rat model.Methods:Pregnant rats received BDE-209 (10, 30, or 50 mg kg-1 day-1) or vehicle (arachis oil) through gastric gavage from gestation day 1 to 14 (n = 10 per group). The embryonic hippocampal neural stem cells (NSCs) from five pregnant rats in each group were collected on day 14 and cultured in vitro to determine the cell viability, apoptosis, and differentiation of NSCs using cell counting kit 8 assay, flow cytometry, and immunofluorescence staining, respectively. In total, 20 male offspring on postnatal day 25 from each group were chosen to evaluate learning ability using a Morris water navigation task assay.Results:The data showed that prenatal exposure to BDE-209 decreased cell viability and differentiation of NSCs but promoted apoptosis in a dose-dependent manner. Prenatal BDE-209 exposure also impaired rat-learning acquisition in a dose-dependent manner.Conclusions:Prenatal BDE-209 exposure impairs rat-learning acquisition, possibly by affecting neurogenesis in the hippocampus during embryonic development.

Effects of decabromodiphenyl ether (BDE-209) on the avoidance response, survival, growth and reproduction of earthworms (Eisenia fetida)

The effects of decabromodiphenyl ether (BDE-209) on avoidance response, survival, growth, and reproduction of earthworms (Eisenia fetida) were investigated under laboratory conditions using natural and artificial soils as substrate. Results showed that no significant avoidance response was observed when earthworms were exposed to 0.1-1000 mg/kg of BDE-209 for 48 h. After 28-days exposure, no significant effects on survival and growth of adult earthworms was induced by 0.1-1000 mg/kg of BDE-209 indicating the Lowest Observed Effect Level (LOEL) of BDE-209 on their survival and body weight was more than 1000 mg/kg. Except for a significant decrease in the number of juveniles per hatched cocoon in artificial soils at 1000 mg/kg of BDE-209, no significant effects on reproductive parameters (e.g. cocoon production per earthworms, weight per cocoon and cocoon hatchability) were observed. These results suggest that adult earthworms have a strong tolerance for BDE-209 exposure in soils, but a potential toxicity does exist for earthworm embryos or juveniles.

Effects of triclosan in the freshwater mussel Dreissena polymorpha: a proteomic investigation

Triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy)phenol) is commonly used in several personal care products, textiles, and children's toys. Because the removal of TCS by wastewater treatment plants is incomplete, its environmental fate is to be discharged into freshwater ecosystems, where its ecotoxicological impact is still largely unexplored. Previously, we began a structured multi-tiered approach in order to evaluate TCS toxicity in the freshwater mussel Dreissena polymorpha. The results of our previous studies, based on in vitro and in vivo experiments, highlighted a pronounced cytogenotoxic effect exerted by TCS, and showed that an increase in oxidative stress was likely to be one of its main toxic mechanisms. In this work, in order to investigate TCS toxicity mechanisms in aquatic non-target species in greater depth, we decided to use a proteomic approach, analysing changes in protein expression profiles in gills of D. polymorpha exposed for seven days to TCS. Moreover, thiobarbituric acid reactive substances (TBARS) were measured to investigate further the role played by TCS in inducing oxidative stress. Finally, TCS bioaccumulation in mussel tissues was also assessed, to ensure an effective accumulation of the toxicant. Our results not only confirmed the role played by TCS in inducing oxidative stress, but furthered knowledge about the mechanism exerted by TCS in inducing toxicity in an aquatic non-target organisms. TCS induced significant alterations in protein expression profiles in gills of D. polymorpha. The wide range of proteins affected suggested that this chemical has marked effects on various biological processes, especially those involved in calcium binding or stress response. We also confirmed that the proteomic analysis, using 2-DE and de novo sequencing, is a reliable and powerful approach to investigate cellular responses to pollutants in a non-model organism with few genomic sequences available in databases.

Evaluation of DNA damage induced by 2 polybrominated diphenyl ether flame retardants (BDE-47 and BDE-209) in SK-N-MC cells

Polybrominated diphenyl ethers (PBDEs) are a class of flame retardants whose levels have increased in the environment and in human tissues in the past decades. Exposure to PBDEs has been associated with developmental neurotoxicity, endocrine dysfunction, and reproductive disorders. In spite of their widespread distribution and potential adverse health effects, only few studies have addressed the potential neurotoxicity of PBDEs. In the present study, we evaluated the cyto- and genotoxicity of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209) in human neuroblastoma cells (SK-N-MC). The DNA damage was measured using the alkaline version of the Comet assay, while specific oxidative-generated DNA damage was evaluated by a modified version of the Comet assay with the repair enzyme formamidopyrimidine glycosylase (FPG). The results show that BDE-47 and BDE-209 (5-20 μmol/L) are able to induce DNA damage in human SK-N-MC cells. Pretreatment with the antioxidant melatonin significantly reduced the DNA damage induced by both congeners. The Comet assay carried out in the presence of FPG suggests that both congeners increase purine oxidation. In all cases, BDE-47 was more potent than BDE-209. The results indicate that 2 environmentally relevant PBDEs cause DNA damage which is primarily mediated by the induction of oxidative stress and may contribute to adverse health effects.

Comparison of bioaccumulation and biomarker responses in Dreissena polymorpha and D. bugensis after exposure to resuspended sediments

The zebra mussel Dreissena polymorpha is widely used as sentinel organism for the assessment of environmental contamination in freshwater environments. However, in the River Rhine (Germany), the D. polymorpha population is declining, whereas the closely related quagga mussel D. bugensis is found in high numbers at some sites. In the present laboratory study, D. polymorpha and D. bugensis were exposed to resuspended native sediments for ≤2 weeks. Wet sediments (<63 μm, 100 mg l(-1) dry weight) were used as surrogate suspended particulate matter to mimic one of the mussels' main uptake route for chemicals. The sediments were sampled in (1) the River Elbe in Dessau, a site known to be highly polluted with, e.g., organochlorine (OC) pesticides and (2) at a relatively unpolluted site in Havelberg in the River Havel, one of the Elbe's tributaries. Chemical analysis of persistent OC compounds (seven polychlorinated biphenyls [PCBs], DDT and its metabolites (DDX), hexachlorocylohexanes [HCHs], and hexachlorobenzene [HCB]) in soft tissue of mussels showed significantly greater values of PCBs 101, 118, 153, 138, 180, the sum of seven PCBs, and p,p'-DDD in D. bugensis compared with D. polymorpha. Fourteen days of exposure to Dessau sediment increased the concentration of p,p'-DDE and p,p'-DDD, as well as the sum of DDX, in both species compared with Havelberg sediment. Interspecific differences were less pronounced when regarding chemical concentrations with lipid content instead of dry-weight of tissue because D. bugensis had greater levels of total lipid than D. polymorpha. DNA damage in gills, as measured with the comet assay, was greater in D. bugensis compared with D. polymorpha. Simultaneously, the content of heat-shock protein (hsp70) in gills was greater in D. polymorpha than in D. bugensis. DNA damage and hsp70 were not induced by exposure time or sediment type. This study shows that D. bugensis and D. polymorpha may differ in their bioaccumulation potential of OC pesticides as well as their levels of DNA damage and hsp70. Therefore, more investigations are needed before quagga mussel can be used as alternative test organism for the zebra mussel.

Cyto-genotoxic effects induced by three brominated diphenyl ether congeners on the freshwater mussel Dreissena polymorpha

Polybrominated diphenyl ethers (PBDEs) are a group of highly hydrophobic and persistent chemicals that has been used as flame retardants in several industrial applications. They have been detected in various environmental matrices worldwide and an increasing number of studies have recently been carried out to investigate their potential toxicity on ecosystem communities. Although a variety of biological damage has been documented in vertebrates, the effects on invertebrates are largely unknown. The objective of the present study was to determine the cyto-genotoxic effects induced by single exposure to three concentrations of 2,4,2',4'-tetra BDE (BDE 47), 2,2',4,4',6-penta BDE (BDE-100) and 2,2',4,4',5,6'-hexa BDE (BDE-154) on the freshwater mussel Dreissena polymorpha by a multi-biomarker approach. We performed on bivalve hemocytes the Single Cell Gel Electrophoresis (SCGE) assay, the DNA Diffusion assay and the Micronucleus test (MN test) to assess genotoxicity, while the Neutral Red Retention Assay (NRRA) was used to evaluate cytotoxic effects. Results showed that BDE-47 did not produce any genetic damage at the tested concentrations (0.1 μg/L, 0.5 μg/L and 1 μg/L), while BDE-100 and BDE-154 can be considered moderately genotoxic, since both primary and fixed DNA injuries were induced. The NRRA indicated a moderate increase in cellular stress in BDEs-treated bivalves. Thus, our data seems to suggest that investigated BDEs may pose a low risk to freshwater mussels at environmental concentrations.

Sub-lethal effects induced by a mixture of three non-steroidal anti-inflammatory drugs (NSAIDs) on the freshwater bivalve Dreissena polymorpha

Non-steroidal anti-inflammatory drugs (NSAIDs) are the sixth top-selling drugs worldwide and are commonly found in freshwater ecosystems in the high ng/l to low μg/l range. Recent studies have investigated both the acute and the chronic toxicity of single NSAIDs on different biological models, but these studies have completely neglected the fact that, in the environment, non-target organisms are exposed to mixtures of drugs that have unforeseeable toxicological behavior. This work investigated the sub-lethal effects induced by a mixture of three common NSAIDs, namely, diclofenac, ibuprofen and paracetamol, on the freshwater bivalve, the zebra mussel (Dreissena polymorpha). The mussels were exposed to three different environmental concentrations of the mixture (Low, Mid and High). A multi-biomarker approach was used to highlight cyto-genotoxic effects and the imbalance of the oxidative status of the treated specimens. The Neutral Red Retention Assay (NRRA) was used as a biomarker of cytotoxicity, whereas the activities of catalase, superoxide dismutase, glutathione peroxidase and glutathione S-transferase were measured to assess the role played by the oxidative stress enzymes. In addition, the single cell gel electrophoresis assay, the DNA Diffusion assay and the micronucleus test were used to investigate possible genotoxic effects. According to our NRRA results, each treatment was able to induce a significant cellular stress in bivalves, probably due to the raise of oxidative stress, as indicated by the alteration of enzyme activities measured in treated specimens. Moreover, the mixture induced significant enhancements of DNA fragmentation, which preluded fixed genetic damage, as highlighted by the increase of both apoptotic and micronucleated cells.

Illicit drugs as new environmental pollutants: cyto-genotoxic effects of cocaine on the biological model Dreissena polymorpha

The increase in global consumption of illicit drugs has produced not only social and medical problems but also a potential new environmental danger. Indeed, it has been established that drugs consumed by humans end up in surface waters, after being carried through the sewage system. Although many studies to measure concentrations of several drugs of abuse in freshwater worldwide have been conducted, no data have been available to evaluate their potentially harmful effects on non-target organisms until now. The present study represents the first attempt to investigate the cyto-genotoxic effects of cocaine, one of the primary drugs consumed in Western Countries, in the biological model Dreissena polymorpha by the use of a biomarker battery. We performed the following tests on Zebra mussel hemocytes: the single cell gel electrophoresis (SCGE) assay, the apoptosis frequency evaluation and the micronucleus assay (MN test) for the evaluation of genotoxicity and the lysosomal membranes stability test (neutral red retention assay; NRRA) to identify the cocaine cytotoxicity. We exposed the molluscs for 96 h to three different nominal concentrations in water (40 ng L(-1); 220 ng L(-1); and 10 μg L(-1)). Cocaine caused significant (p<0.05) primary DNA damage in this short-term experiment, but it also caused a clear increase in micronucleated cells and a marked rise in apoptosis, which was evident in samples from even the lowest environmental cocaine concentration. Because cocaine decreased the stability of lysosomal membranes, we also highlighted its cytotoxicity and the possible implications of oxidative stress for the observed genotoxic effects.

A proteomic study using zebra mussels (D. polymorpha) exposed to benzo(α)pyrene: the role of gender and exposure concentrations

It has recently been established that the use of proteomics can be a useful tool in the field of ecotoxicology. Despite the fact that the mussel Dreissena polymorpha is a valuable bioindicator for freshwater ecosystems, the application of a proteomic approach with this organism has not been deeply investigated. To this end, several zebra mussel specimens were subjected to a 7-day exposure of two different concentrations (0.1 and 2 μg L⁻¹) of the model pollutant benzo[α]pyrene (B[α]P). Changes in protein expression profiles were investigated in gill cytosolic fractions from control/exposed male and female mussels using 2-DE electrophoresis. B[α]P bioaccumulation in mussel soft tissue was also assessed to validate exposure to the selected chemical. We evaluated overall changes in expression profiles for 28 proteins in exposed mussels, 16 and 12 of which were, respectively, over- and under-expressed. Surprisingly, the comparative analysis of protein data sets showed no proteins that varied commonly between the two different B[α]P concentrations. Spots of interest were manually excised and analysed by MALDI-TOF/TOF mass spectrometry. The most significant proteins that were identified as altered were related to oxidative stress, signal transduction, cellular structure and metabolism. This preliminary study indicates the feasibility of a proteomic approach with the freshwater mussel D. polymorpha and provides a starting point for similar investigations. Our results confirm the need to increase the number of invertebrate proteomic studies in order to increase the following: their representation in databases and the successful identification of their most relevant proteins. Finally, additional studies investigating the role of gender and protein modulation are warranted.

Evaluation of 4-nonylphenol in vivo exposure in Dreissena polymorpha: Bioaccumulation, steroid levels and oxidative stress

Nonylphenol (NP) represents the most critical metabolite of alkylphenols (APs) and alkylphenol ethoxylates (APEs), non-ionic surfactants widely used in the formulation of domestic and industrial products. On the basis of in vitro and in vivo animal studies 4-nonylphenol (4-NP) is considered an endocrine disrupting chemical (EDC). The evidence to date indicates that mollusks are able to synthesize sex steroids from the precursor cholesterol and their endocrine pathways are theoretically susceptible to disruption. The aim of this study was to investigate the endocrine modulating potency of 4-NP in the freshwater mussel Dreissena polymorpha by looking at endogenous steroid levels in control and exposed individuals. 4-NP bioaccumulation in mussels tissues and alterations in the activity of enzymes related both to oxidative stress (catalase - CAT- and glutathione peroxidase - GPX-) and phase II metabolism (glutathione-S-transferase - GST-) were also assessed. The results highlighted a build-up of 4-NP in exposed mussels and an overall decrease of 17-beta-estradiol and testosterone levels. On the other hand this chemical at the tested concentrations does not interfere with the antioxidant defense mechanisms in D. polymorpha. The mechanisms by which 4-NP alter steroids levels are unknown and require more in-depth investigations.

Multi-biomarker approach for the evaluation of the cyto-genotoxicity of paracetamol on the zebra mussel (Dreissena polymorpha)

Paracetamol (PCM; N-(4-hydroxyphenyl)acetamide) is a widely used analgesic and antipyretic agent that is utilized in human medicine. Its use is so widespread that it is constantly being introduced into global water bodies where it reaches concentrations up to several microgL(-1). A battery of eight biomarkers was applied in the freshwater bivalve Dreissena polymorpha in order to evaluate its potential sub-lethal effect. Mussels were exposed for 96h to increasing environmental concentrations (1, 5, 10nM) of PCM. Cyto-genotoxicity was determined in mussel hemocytes by the lysosomal membrane stability (Neutral Red Retention Assay), the single cell gel electrophoresis (SCGE) assay, the micronucleus test (MN test) and assessments of the apoptotic frequency (DNA diffusion assay). Moreover, in order to evaluate the probable alterations to the mussels' oxidative status, measurements of the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and the detoxifying enzyme glutathione S-transferase (GST) were performed using the cytosolic fraction extracted from a pool of entire mussels. The biomarker battery demonstrated moderate cyto-genotoxicity in zebra mussel hemocytes since no primary DNA fragmentation was measured by the SCGE assay and only a slight increase in fixed DNA damage was registered by apoptotic and MN frequencies. Significant destabilization of the lysosomal membrane from baseline levels was evident at 5 and 10nM at the end of the exposures, as was a high induction capacity of the activities of CAT and GST.

Accumulation and DNA damage in fathead minnows (Pimephales promelas) exposed to 2 brominated flame-retardant mixtures, Firemaster 550 and Firemaster BZ-54

Firemaster 550 and Firemaster BZ-54 are two brominated formulations that are in use as replacements for polybrominated diphenyl ether (PBDE) flame retardants. Two major components of these mixtures are 2,3,4,5-tetrabromo-ethylhexylbenzoate (TBB) and 2,3,4,5-tetrabromo-bis(2-ethylhexyl) phthalate (TBPH). Both have been measured in environmental matrices; however, scant toxicological information exists. The present study aimed to determine if these brominated flame-retardant formulations are bioavailable and adversely affect DNA integrity in fish. Fathead minnows (Pimephales promelas) were orally exposed to either FM 550, FM BZ54, or the nonbrominated form of TBPH, di-(2-ethylhexyl) phthalate (DEHP) for 56 d and depurated (e.g., fed clean food) for 22 d. At several time points, liver and blood cells were collected and assessed for DNA damage. Homogenized fish tissues were extracted and analyzed on day 0 and day 56 to determine the residue of TBB and TBPH and the appearance of any metabolites using gas chromatography-electron-capture negative ion mass spectrometry (GC/ECNI-MS). Significant increases (p < 0.05) in DNA strand breaks from liver cells (but not blood cells) were observed during the exposure period compared with controls, although during depuration these levels returned to control. Both parent compounds, TBB and TBPH, were detected in tissues at approximately 1% of daily dosage along with brominated metabolites. The present study provides evidence for accumulation, metabolism, and genotoxicity of these new formulation flame retardants in fish and highlights the potential adverse effects of TBB- and TBPH-formulated fire retardants to aquatic species.

A multi-biomarker assessment of the impact of the antibacterial trimethoprim on the non-target organism Zebra mussel (Dreissena polymorpha)

A battery of eight biomarkers was applied in the freshwater mussel Dreissena polymorpha to evaluate potential sub-lethal effects of the antimicrobial trimethoprim (TMP, 5-[3,4,5-trimethoxybenzyl]pyrimidine-2,4-diamine). Mussels were exposed for 96 h to increasing concentrations (1, 3, 10 nM) of TMP in in vivo experiments. We determined the single cell gel electrophoresis (SCGE) assay, the micronucleus test (MN test), the apoptotic frequency (Halo assay) and the lysosomal membrane stability (Neutral Red Retention Assay) in mussel hemocytes. Moreover, to reveal whether the oxidative status was altered, measurements of the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and the phase II detoxifying enzyme glutathione S-transferase (GST) were performed using the cytosolic fraction extracted from a pool of entire mussels. The biomarker battery pointed out only a moderate cyto- and genotoxicity on Zebra mussel hemocytes since only a slight increase in DNA damage was registered by apoptosis induction and MN frequency, while significant differences of lysosomal membrane stability from baseline levels were measured at 3 and 10 nM at the end of exposures only. Finally, TMP seems to have a very low induction capability or even an inhibitory effect on the activities of antioxidant enzymes, but a clear significant induction on GST.

Genotoxic effects of p,p'-DDT (1,1,1-trichloro-2,2-bis-(chlorophenyl)ethane) and its metabolites in Zebra mussel (D. polymorpha) by SCGE assay and micronucleus test

This is the first study to evaluate the potential genotoxicity of p,p'-DDT (1,1,1-trichloro-2,2-bis-(chlorophenyl)ethane) and its metabolites (p,p'-DDD and p,p'-DDE) in the sentinel mollusc Zebra mussel (Dreissena polymorpha). DNA damage was measured using the single cell gel electrophoresis (SCGE) assay and the micronucleus test (MN test), which represent two of the more sensitive biomarkers for genotoxicity evaluation. Three different concentrations (0.1, 2, and 10 mug/L) of each compound were administered in water for 168 hr, maintaining mussels at constant laboratory conditions and collecting several specimens every 48 hr for biochemical analyses. At the same time, the bioaccumulation process and the concentration/effect relationship were checked by GC-MS/MS analyses of mussel soft tissues. The SCGE assay results showed a clear and significant (P < 0.05) relationship between DNA injuries and tested doses for all the homologues throughout the 7-day exposure period. The final DNA damage due to p,p'-DDE was almost double that of the other two homologues that showed the same toxicity pattern. The micronucleus frequency analysis confirmed the genotoxicity potential of the three homologues and p,p'-DDE showed the highest irreversible DNA damage. The capability of Zebra mussels to biotransform the administered compound in the other homologues was demonstrated by multiple regression analyses carried out between the MN frequencies and the concentrations of the different homologues in the mussel soft tissues. A greater genotoxic potential of the p,p'-DDE with respect to the other two chemicals was revealed.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.