Antioxidant and biotransformation responses in Liza aurata under environmental mercury exposure - relationship with mercury accumulation and implications for public health

This study was carried out in the Laranjo basin (Ria de Aveiro, Portugal), an area impacted by mercury discharges. Liza aurata oxidative stress and biotransformation responses were assessed in the liver and related to total mercury (Hgt) concentrations. A seasonal fish survey revealed a sporadic increase in total glutathione (GSHt) and elevated muscle Hgt levels, although Hg levels did not exceed the EU regulatory limit. As a complement study, fish were caged for three days both close to the bottom and on the water surface at three locations, and displayed higher Hgt levels accompanied by increased GSHt content and catalase activity as well as EROD activity inhibition. The bottom group displayed higher hepatic Hgt and GSHt contents compared with the surface group. Globally, both wild and caged fish revealed that the liver accumulates higher Hgt concentrations than muscle and, thus, better reflects environmental contamination levels. The absence of peroxidative damage in the liver can be attributed to effective detoxification and antioxidant defense.

Transport properties of graphene nanoribbons with side-attached organic molecules

In this work we address the effects on the conductance of graphene nanoribbons (GNRs) of organic molecules adsorbed at the ribbon edge. We studied the case of armchair and zigzag GNRs with quasi-one-dimensional side-attached molecules, such as linear poly-aromatic hydrocarbons and poly(para-phenylene). These nanostructures are described using a single-band tight-binding Hamiltonian and their electronic conductance and density of states are calculated within the Green's function formalism based on real-space renormalization techniques. We found that the conductance exhibits an even-odd parity effect as a function of the length of the attached molecules. Furthermore, the corresponding energy spectrum of the molecules can be obtained as a series of Fano antiresonances in the conductance of the system. The latter result suggests that GNRs can be used as a spectrograph sensor device.

Endocrine and metabolic responses of Anguilla anguilla L. caged in a freshwater-wetland (Pateira de Fermentelos--Portugal)

The present short-term in situ study was carried out in a freshwater-wetland--Pateira de Fermentelos--considered an enlargement of Cértima River, in the centre of Portugal. This ecosystem is an important fishing and recreation place, receiving effluents from different origins namely, electroplating industrial effluents containing heavy metals, domestic wastes, as well as pesticides and fertilizers resulting from agriculture activities. The aim of the present research work was to monitor the effects induced by the contaminants present in Pateira de Fermentelos water, using Anguilla anguilla L. (European eel) as a bioindicator. The eels were caged for 48 h at four Pateira de Fermentelos sites, differing in their distances to the main known pollution source (Cértima River): A (close to the lagoon entrance), B, C and D (the farthest from the Cértima River). A reference site was selected near the Cértima river spring. The following parameters were measured: liver ethoxyresorufin-O-deethylase (EROD) and alanine transaminase (ALT) activities, plasma levels of cortisol, 17beta-estradiol (E2), thyroid-stimulating-hormone (TSH), free thyroxine (T4), free triiodothyronine (T3), as well as glucose and lactate. The erythrocytic nuclear abnormalities (ENA) frequency was also scored as a genotoxicity indicator. The results revealed increased plasma cortisol and glucose concentrations at all exposure sites, displaying a similar response pattern. Plasma T3 showed a significant decrease only at site A when compared to reference site, whereas plasma E2 increased at sites B and D when compared to all the other sites, including reference site. The present results indicate the Pateira de Fermentelos water contamination, demonstrating the usefulness of the adopted strategy.

Cytochrome P4501A, genotoxic and stress responses in golden grey mullet (Liza aurata) following short-term exposure to phenanthrene

This study represents a first approach to short-term effects of phenanthrene (Phe) in fish. The teleost Liza aurata was exposed to 0.1-2.7microM Phe during 16h. CYP1A induction was assessed as liver ethoxyresorufin-O-deethylase (EROD) activity. Genotoxicity was evaluated in gill and liver as DNA integrity (by alkaline unwinding), whereas in blood the erythrocytic nuclear abnormalities (ENA) frequency was determined. Stress responses were determined as cortisol, glucose and lactate plasma levels. Liver EROD activity was significantly increased by Phe 0.3-2.7microM. Phe genotoxicity in gill was not found, whereas liver DNA integrity significantly decreased after exposure to Phe 0.1 and 0.9microM demonstrating its genotoxicity which did not correlate with liver CYP1A induction. Phe genotoxicity in blood was demonstrated by a significant ENA increase from 0.1 up to 2.7microM. In terms of stress responses, plasma cortisol was significantly increased by Phe 0.3-2.7microM, though plasma glucose was only significantly increased by Phe 0.9 and 2.7microM. The Phe observed effects on L. aurata detected at different levels demonstrate a physiological unbalance and a probable ecological risk to ichthyofauna.

Oxidative stress and genotoxic effects in gill and kidney of Anguilla anguilla L. exposed to chromium with or without pre-exposure to beta-naphthoflavone

Fish in the aquatic environment can be subjected to a multipollution state and the occurrence of sequential exposures is an important aspect of eco-toxicological research. In this context, a preceding exposure can affect a toxic response to a subsequent exposure. Therefore, the current study was based on sequential exposures, viz. to a PAH-like compound (beta-naphthoflavone, BNF) followed by a heavy metal (chromium, Cr), focusing on the assessment of oxidative stress responses and their role in induction of genotoxicity. Oxidative stress responses in gill and kidney were investigated in European eel (Anguilla anguilla L.), and measured as lipid peroxidation (LPO), glutathione peroxidase (GPX), catalase (CAT) and glutathione S-transferase (GST) activity, and reduced glutathione (GSH) concentration, whereas genotoxicity was measured as DNA strand breakage. Fish were exposed for 24 h to two Cr concentrations (100 microM, 1 mM), with or without pre-exposure to BNF (2.7 microM, 24 h). In gill, a GSH decrease was observed along with loss of DNA integrity at all exposure conditions except at the lowest Cr concentration, showing a crucial role of GSH over genotoxicity. Moreover, sporadic induction of antioxidant enzymes was not effective in the protection against genotoxicity. However, a different mechanism seems to occur in kidney, since the loss of DNA integrity detected for all exposed groups was not accompanied by alterations in antioxidant levels. With regards to peroxidative damage, both organs showed an LPO increase after sequential exposure to BNF and 100 microM Cr. However, no association between LPO induction and antioxidant responses could be established, showing that LPO is not predictable solely on the basis of antioxidant depletion. The interference of BNF pre-exposure with the response of organs to Cr showed a marked dependence on the Cr concentration. Gill showed synergistic effects on LPO and GPX increase, as well as on CAT and GSH decrease for the lowest Cr concentration. However, for the highest concentration an additive effect on decrease of DNA integrity and an antagonistic effect on the increase of GPX were observed. In kidney, synergistic effects were evident on LPO increase and GSH decrease for the lowest Cr concentration, as well as on CAT and GST decrease for the highest concentration. In contrast, an antagonistic action was observed on DNA integrity loss for both Cr concentrations. The current results are relevant in assessing the interactions of PAHs and metals and contribute to a better knowledge about oxidative stress and mechanisms of genotoxicity in fish.

Biotransformation, stress and genotoxic effects of 17beta-estradiol in juvenile sea bass (Dicentrarchus labrax L.)

The effects of 17beta-estradiol (E(2)) on fish became a matter of concern, since significant levels of this hormone were detected in the aquatic environment released mainly by domestic sewage treatment plants. In this perspective, the current study was focused on E(2) effects upon biotransformation, stress and genotoxic responses of juvenile Dicentrarchus labrax L. (sea bass). Fish were exposed to E(2) during 10 days in two different ways: water diluted (200 ng/L or 2,000 ng/L) and i.p. injected (0.5 mg/kg or 5 mg/kg). A battery of biological responses was evaluated: liver ethoxyresorufin-O-deethylase (EROD) and alanine transaminase (ALT) activities, liver somatic index (LSI), plasma cortisol, glucose and lactate concentrations, as well as erythrocytic nuclear abnormalities (ENA). All the exposure conditions induced endocrine disruption, measured as plasma cortisol decrease, and genotoxicity, measured as ENA increase. Thus, no differences were detected either between different exposure routes or tested concentrations. Concerning liver EROD and ALT activities, as well as plasma glucose and lactate concentrations no differences were found between treated and control groups. LSI was the only parameter to respond differently in the two exposure routes, as only E(2) water diluted induced a significant increase in this hepatic indicator.

Anguilla anguilla L. Genotoxic responses after in situ exposure to freshwater wetland (Pateira de Fermentelos, Portugal)

Pateira de Fermentelos is a Cértima River enlargement, close to its river mouth (by the Agueda River), where the introduction of agricultural chemicals such as fertilisers and pesticides, domestic sewage, as well as heavy metals from electroplating industries, results in increased water pollution. The present research work concerns a 48 h in situ exposure of caged eels (Anguilla anguilla L.) at the Pateira de Fermentelos. Five exposure sites were selected, i.e., site A, site B, site C, site D and site E in order to study its water genotoxicity potential, measured in gill, blood, liver and kidney as DNA strand breaks. Eels were also exposed at a reference site by the Cértima River spring. Bottom water samples were collected for further physical-chemical analysis. Site A exposure, significantly decreased gill, blood and liver DNA integrity. Gill and liver DNA integrity was also significantly decreased at site B. At site C only blood DNA integrity was significantly decreased. The present field in situ study demonstrated that the three exposure sites close to the Pateira initial part, such as A, B and C are polluted by pro and/or genotoxic compounds. The genotoxic effects induced in A. anguilla L. suggest a different contamination of the exposure sites A, B and C, in genotoxic chemicals. Thus, according to its genotoxic potential the exposure sites A, B and C, may be ordered as follows site A>site B>site C. No genotoxic effects on A. anguilla L. were observed at site E as DNA strand breaks increase.

Responses of European eel (Anguilla anguilla L.) circulating phagocytes to an in situ closed pulp mill effluent exposure and its association with organ-specific peroxidative damage

The effect of bleached kraft pulp mill effluent (BKPME) persistent compounds on phagocyte activities and its organ-specific influence in gill, kidney and liver was studied in European eel (Anguilla anguilla L.). Eels were caged and plunged at 3 different sites-50 m (site 1), 100 m (site 2) and 2,000 m (site 3) away from the end of the closed BKPME discharging channel for 8 and 48 h. Gill, head kidney and peritoneum phagocytes oxidative burst activity (OBA) was measured by the nitroblue tetrazolium reduction assay whereas lipid peroxidation (LPO) in eel gill, kidney and liver was measured by thiobarbituric acid reaction. A significant gill OBA induction was found at 8h on site 2, and on sites 1, 2 and 3 at 48 h exposure. However, in head kidney and peritoneal exudate phagocytes, OBA induction was significant only at sites 2 and 3 after 48 h exposure. In those particular sites, a significant increase in gill, kidney and liver LPO was measured that is assumed to result from OBA induction. Considering OBA and LPO, gill is the most affected tissue compared to kidney and liver. Gill vulnerability towards peroxidative damage was demonstrated at 8h on site 2 and at 48 h on sites 1, 2 and 3, whereas in kidney was observed at sites 2 and 3 only at 48 h. Liver LPO increased at site 2 only after 48 h exposure. Our results demonstrate that the OBA activation pattern in gill and kidney is associated with the induced peroxidative damage extent in those organ, together with water pollution the exposure route, resulting from previous BKPME effluent sediment contamination which may affect the activation pattern of circulating fish phagocytes.

Effects of applied magnetic fields and hydrostatic pressure on the optical transitions in self-assembled InAs/GaAs quantum dots

A theoretical study of the photoluminescence peak energies in InAs self-assembled quantum dots embedded in a GaAs matrix in the presence of magnetic fields applied perpendicular to the sample plane is performed. The effective mass approximation and a parabolic potential cylinder-shaped model for the InAs quantum dots are used to describe the effects of magnetic field and hydrostatic pressure on the correlated electron-hole transition energies. Theoretical results are found in quite good agreement with available experimental measurements for InAs/GaAs self-assembled quantum dots.

Effects of applied magnetic fields and hydrostatic pressure on the optical transitions in self-assembled InAs/GaAs quantum dots

A theoretical study of the photoluminescence peak energies in InAs self-assembled quantum dots embedded in a GaAs matrix in the presence of magnetic fields applied perpendicular to the sample plane is performed. The effective mass approximation and a parabolic potential cylinder-shaped model for the InAs quantum dots are used to describe the effects of magnetic field and hydrostatic pressure on the correlated electron-hole transition energies. Theoretical results are found in quite good agreement with available experimental measurements for InAs/GaAs self-assembled quantum dots.

Electric field effects on the energy spectrum of carbon nanotubes

Electronic properties of straight carbon nanotubes under an external electric are investigated, following a single-π-orbital tight binding approximation. Metal-insulator transitions in metallic tubes and energy gap modulations in semiconducting ones were found due to the action of the electric field. Reductions in the tube symmetry operations induced by the field are manifested in the energy spectrum as a function of the angle determined by the field direction and equivalent in-plane atomic positions along the circumferential direction. We find that particular energies in the spectra exhibit a periodic oscillation with this dephasing angle. The range and position of those energies, as well the amplitude of the oscillation, can be properly manipulated by changing the strength and direction of the applied electric field.

The impact on rural New Mexico of a family medicine residency

PURPOSE

To determine the impact on rural New Mexico of the large, decentralized University of New Mexico (UNM) family medicine residency.

METHOD

A cross-sectional study was conducted of all 317 residency's graduates from 1974 to 2004. Location of current practice was correlated with the residents' gender, ethnicity, medical school of origin, and whether most training took place in the urban program or one of three rural programs. The residency's impact on rural communities was assessed.

RESULTS

There was no significant gender difference between graduates who went into urban or rural practice. Compared with non-minority graduates, a significantly greater percentage of ethnic minority graduates were in rural and urban New Mexico practices and fewer in out-of-state practices. A greater percentage of graduates who had been medical students in New Mexico practiced in both rural and urban New Mexico areas compared with graduates of out of state medical schools. Finally, a greater percentage of graduates from the three rural family medicine residencies remained in the state and practiced in rural areas compared with graduates from the urban program. The graduates' contributions to the school of medicine and to rural New Mexico are described.

CONCLUSIONS

Graduates of UNM's family medicine residency have contributed significantly to the state's rural health workforce. Ethnic minority status, graduation from New Mexico's medical school, and training in one of the three rurally based residencies favored in-state and rural retention, while gender had no significant effect. The rural orientation of the residencies offered rural communities economic benefits.

Biotransformation and genotoxic biomarkers in mullet species (Liza sp.) from a contaminated coastal lagoon (Ria de Aveiro, Portugal)

The aim of the present study was to assess liver ethoxyresorufin-O-deethylase (EROD) activity and erythrocytic nuclear abnormalities (ENA) frequency in three mullet species, as biotransformation and genotoxicity biomarkers, respectively, for monitoring aquatic ecosystems. Specimens of Liza aurata, Liza ramada and Liza saliens were caught bimonthly, between May 2000 and March 2001, at nine stations in the Ria de Aveiro (Portugal), a polluted coastal lagoon. The survey revealed two critical areas (Vagos and Carregal) where it was observed elevated EROD activity and ENA frequency, comparing to the reference sites. The results often reflect a contamination by a mixture of pollutants, from point and non-point sources. Nevertheless, the responses observed at Vagos are probably attributable to high polycyclic aromatic hydrocarbon (PAH) water levels measured at that station. All species were able to detect inter-site differences; however L. aurata seems to be the most appropriate bio-indicator due to its larger geographical distribution and abundance during the whole year. The adopted biomarkers, applied to mullet species, can be successfully employed for biomonitoring anthropogenic contamination in both Atlantic and Mediterranean European coastal waters.

Stress-induced expression in wheat of the Arabidopsis thaliana DREB1A gene delays water stress symptoms under greenhouse conditions

One of the major environmental factors limiting plant productivity is lack of water. This is especially true for the major cereals maize, rice, and wheat, which demonstrate a range of susceptibility to moisture deficit. Although conventional breeding and marker-assisted selection are being used to develop varieties more tolerant to water stress, these methods are time and resource consuming and germplasm dependent. Genetic engineering is attractive because of its potential to improve abiotic stress tolerance more rapidly. Transcription factors have been shown to produce multiple phenotypic alterations, many of which are involved in stress responses. DREB1A, a transcription factor that recognizes dehydration response elements, has been shown in Arabidopsis thaliana to play a crucial role in promoting the expression of drought-tolerance genes. In our efforts to enhance drought tolerance in wheat, the A. thaliana DREB1A gene was placed under control of a stress-inducible promoter from the rd29A gene and transferred via biolistic transformation into bread wheat. Plants expressing the DREB1A gene demonstrated substantial resistance to water stress in comparison with checks under experimental greenhouse conditions, manifested by a 10-day delay in wilting when water was withheld.

Physiological and genetic responses of European eel (Anguilla anguilla L.) to short-term chromium or copper exposure-Influence of preexposure to a PAH-like compound

Anguilla anguilla L. (European eel) was exposed for 24 h to chromium (Cr-100 microM and 1 mM) or copper (Cu-1 and 2.5 microM), with or without a 24-h preexposure to beta-naphthoflavone (BNF-2.7 microM), a polycyclic aromatic hydrocarbon (PAH)-like compound, simulating sequential exposure to PAHs and heavy metals. Plasma cortisol, thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) were determined in order to assess the effects on endocrine function. Plasma glucose and lactate also were measured. The frequency of erythrocytic nuclear abnormalities (ENA) was scored as a genotoxicity indicator. Plasma T4 decreased in eels when exposed to Cr only. The interference of BNF preexposure on Cr effects was observed as a significant plasma glucose increase. Single exposures to Cu elevated plasma cortisol and glucose (2.5 microM), as well as plasma lactate (1 microM), whereas a T4 decrease was found for both concentrations. BNF preexposure prevented plasma cortisol and lactate increases; however, a greater T4 decrease was observed in eels exposed to 2.5 microM Cu. Moreover, this pretreatment was crucial for genotoxicity expression because only BNF+2.5 microM Cu-exposed fish exhibited significant ENA induction. In general, plasma T4 was the most affected hormone, as it responded to all Cr and Cu exposure conditions.

Sparus aurata L. liver EROD and GST activities, plasma cortisol, lactate, glucose and erythrocytic nuclear anomalies following short-term exposure either to 17beta-estradiol (E2) or E2 combined with 4-nonylphenol

Immature Sparus aurata L. (gilthead seabream) were exposed to 17beta-estradiol (E(2)) 4000 ng/l and to the same E(2) concentration mixed with 50,000 ng/l 4-nonylphenol (E(2) + NP) during 4, 8, 12 and 16 h. E(2) availability and E(2) plasma level variations were assessed. Liver biotransformation capacity was measured as ethoxyresorufin-O-deethylase (EROD) and glutathione-S-transferase (GST) activities. Plasma cortisol, lactate and glucose were also determined. Genotoxicity was assessed through erythrocytic nuclear anomalies (ENA) frequency. Liver EROD activity significantly decreased during the whole experiment for both treatments, with the exception of 16 h exposure to E(2). Liver GST activity was significantly increased after 8 and 12 h of exposure either to E(2) or E(2) + NP. An endocrine disruption expressed as plasma cortisol decrease was observed after 16 h exposure under both tested conditions, concomitantly with a plasma lactate increase. No genotoxic responses, measured as ENA frequency, were detected. Analyzing the E(2) water concentration in aquaria without fish it was demonstrated an intense and fast E(2) loss, considerably reducing its availability to fish. In the presence of fish, E(2) water levels were drastically reduced after 4 h exposure, being this reduction more pronounced in E(2) aquarium when compared to E(2) + NP aquarium. In addition, it was demonstrated a rapid E(2) uptake from the water since the highest E(2) plasma concentrations were observed after 4 h exposure, followed by a continuous decrease, which became more pronounced between 8 and 12 h of exposure. Furthermore, during the first 8 h exposure to E(2) and E(2) + NP, seabream plasma E(2) concentrations were higher than the initial water exposure concentration. Comparing the E(2) plasma levels in both seabream-exposed groups, it was clear that its concentration is always higher in E(2) + NP-treated fish. Despite the previous results, no significant differences were found in the measured responses between E(2) and E(2) + NP.

Morphological criteria to distinguish cell death induced by apoptotic and necrotic treatments

We present a comparative study of apoptotic and necrotic morphology (light and scanning electron microscopy), induced by well known experimental conditions (photodynamic treatments, etoposide, hydrogen peroxide, freezing-thawing and serum deprivation) on cell cultures. Our results indicate that morphological criteria (apoptotic cell rounding and shrinkage, and appearance of membrane bubbles in early necrosis) allow to distinguish these cell death mechanisms, and also show that, independently of the damaging agents, the necrotic process occurs in a characteristic sequence (coalescence of membrane bubbles in a single big one that detaches from cells remaining on the substrate).

Endocrine and metabolic changes in Anguilla anguilla L. following exposure to beta-naphthoflavone--a microsomal enzyme inducer

Anguilla anguilla L. were exposed during 24 and 48 h to 2.7 muM beta-naphthoflavone (BNF), a known microsomal enzyme inducer. The BNF effects on thyroid-stimulating hormone (TSH), free triiodothyronine (T3), free thyroxine (T4) and cortisol plasma levels were investigated. Alterations on plasma glucose and lactate levels were also measured as an indication of energy-mobilizing hormones alterations. BNF showed to be able to decrease significantly A. anguilla plasma T4 levels, whereas TSH, T3 and cortisol plasma remained constant. However, plasma glucose levels were significantly increased, demonstrating that intermediary metabolism has been affected. These results demonstrate that BNF a PAH-like compound alters the normal functioning of the hypothalamo-pituitary-thyroid (HPT) axis in A. anguilla.

Juvenile sea bass biotransformation, genotoxic and endocrine responses to beta-naphthoflavone, 4-nonylphenol and 17 beta-estradiol individual and combined exposures

Juvenile sea bass, Dicentrarchus labrax L., were exposed during 2, 4, 8, and 24 h to 0.9 microM beta-naphthoflavone (BNF), 131 nM 17 beta-estradiol (E(2)), 4.05 microM 4-nonylphenol (NP), as well as to BNF combined either to E(2) or NP (maintaining the previous concentrations). Liver cytochrome P450 content (P450), ethoxyresorufin-O-deethylase (EROD), and glutathione S-transferase (GST) activities were measured in order to evaluate biotransformation responses. Genotoxicity was assessed as erythrocytic nuclear abnormalities (ENA) frequency. The effects on endocrine function were evaluated as plasma cortisol and glucose. Cortisol was not affected by xeno/estrogens tested, either in single exposure or mixed with BNF. Nevertheless, the intermediary metabolism was affected since glucose concentration increased after 4 h exposure to E(2), and after all BNF+NP exposure lengths. Moreover, a synergism between BNF and NP was thoroughly demonstrated, whereas a sporadic antagonistic interaction was found at 4 h BNF + E(2) exposure. Liver EROD and GST activities were not significantly altered by single E(2) or NP exposure. However, both compounds were able to induce EROD activity in the presence of BNF. NP single exposure was able to significantly increase liver P450 content, while its mixture with BNF displayed an antagonistic interference. Considering the xeno/estrogens single exposures, only NP induced an ENA increase; however, both mixtures (BNF + E(2) and BNF + NP) displayed genotoxic effects. Fish responses to mixtures of xenobiotics are complex and the type of interaction (synergism/potentiation or antagonism) in a particular mixture can vary with the evaluated biological response.

Glutathione protects heavy metal-induced inhibition of hepatic microsomal ethoxyresorufin O-deethylase activity in Dicentrarchus labrax L

The in vitro effects of chromium (Cr(VI)), copper (Cu2+), iron (Fe2+), mercury (Hg2+), and zinc (Zn2+) were assessed on liver microsomal ethoxyresorufin O-deethylase (EROD) activity from a sea bass (Dicentrarchus labrax L.) preexposed under laboratory conditions to 2.7 microM beta-naphthoflavone. The reduced glutathione (GSH) protection potential against heavy metal effects was also studied. The heavy metal concentration ranges used for this study were as follows: 10 pM-5 mM Cr(VI), 10 pM-100 microM Cu2+, 10 pM-1 mM Fe2+, 10 pM-10 microM Hg2+, and 10 pM-100 microM Zn2+. Liver microsomal EROD activity was significantly inhibited after in vitro exposure to Cr(VI) (500 microM), Cu2+ (1 microM), Fe2+ (100 microM), Hg2+ (100 pM), and Zn2+ (10 microM). Heavy metals inhibitory effect on liver EROD activity was ordered as follows: Hg2+ > Cu2+ > Zn2+ > Fe2+ > Cr(VI). Protective effects against Hg2+ (1 and 10 microM), Cu2+ (1, 10, and 100 microM), and Zn2+ (10, 50, and 100 microM) were observed in the presence of 0.5 mM GSH by a decrease in liver microsomal EROD activity inhibition. However, 0.5 mM GSH did not protect liver microsomal EROD activity from Cr(VI), and Fe2+-induced inhibition. The effect of metal mixtures (Cu(2+) + Zn(2+), Zn(2+) + Fe(2+), Zn(2+) + Cr(VI), and Cr(VI) + Fe(2+)) (100 microM) on liver microsomal EROD activity was also assessed, revealing a synergistic interaction.