Micronucleated lymphocytes in people occupationally exposed to potential environmental contaminants: the age effect

Mutagenicity monitoring in humans: Global versus specific origin of mutations

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.e., traditional analyses of aberrations, translocation studies involving chromosome painting and fluorescence in situ hybridization (FISH) and determinations of micronuclei (MN). Other T-cell assays measure gene mutations. i.e., hypoxanthine-guanine phosphoriboslytransferase (HPRT) and phosphoribosylinositol glycan class A (PIGA). In addition to the T-cell assays, also reviewed are those assays that measure events in peripheral blood cells that necessarily arose in BM cells, i.e., MN in reticulocytes; glycophorin A (GPA) gene mutations in red blood cells (RBCs), and PIGA gene mutations in RBC or granulocytes. This review considers only cell culture- or cytometry-based assays to describe endpoints measured, methods, optimal sampling times, and sample summaries of typical quantitative and qualitative results. However, to achieve its intended focus on the target cells where events occur, kinetics of the cells of peripheral blood that derive at some point from precursor cells are reviewed to identify body sites and tissues where the genotoxic events originate. Kinetics indicate that in normal adults, measured events in T-cells afford global assessments of in vivo mutagenicity but are not specific for BM effects. Therefore, an agent's capacity for inducing mutations in BM cells cannot be reliably inferred from T-cell assays as the magnitude of effect in BM, if any, is unknown. By contrast, chromosome or gene level mutations measured in RBCs/reticulocytes or granulocytes must originate in BM cells, i.e. in RBC or granulocyte precursors, thereby making them specific indicators for effects in BM. Assays of mutations arising directly in BM cells may quantitatively reflect the mutagenicity of potential leukemogenic agents.

Chronic low dose exposure of hospital workers to ionizing radiation leads to increased micronuclei frequency and reduced antioxidants in their peripheral blood lymphocytes

Purpose: The regular low dose occupational exposure to ionizing radiation may induce deleterious health effects, which may be of particular interest to medical radiation workers who daily handle X-ray machines. Human peripheral blood lymphocytes are able to retain the signature of radiation-induced DNA damage, therefore, the present study was undertaken to investigate the DNA damage and antioxidants status in hospital workers occupationally exposed to low doses of X-rays. Materials and methods: The peripheral blood lymphocytes of the occupationally exposed and control groups matched for age, gender, tobacco usage, and alcohol consumption were cultured and micronuclei frequency was determined. Activities of antioxidant enzymes and lipid peroxidation were also estimated in their plasma. Results: The micronuclei frequency in the occupationally exposed group (n = 33), increased significantly (p < .0001) followed by reduced glutathione-s-transferase (p < .01) and catalase (p < .001) activities, and increased lipid peroxidation (p < .05) when compared to the control group (n = 33). Occupational exposure resulted in an effective dose ranging between 3.14 to 144.5 mSv (40.88 ± 39.86mSv) depending on the employment duration of 3-29 years (10.33 ± 7.05 years). A correlation between the micronuclei frequency (p < .05) and catalase activity (p < .05) existed in the occupationally exposed individuals depending on the smoking habit, age, duration of employment, cumulative exposure dose and number of patients handled per day. Conclusions: We have observed that protracted low dose exposure to ionizing radiation is an inevitable occupational hazard leading to persistence of oxidative stress and increased genomic instability in the radiological technicians depending on the time spent with X-rays, cumulative dose received and the number of patients handled daily raising the risk of cancer development.

Assessment of the genotoxicity and cytotoxicity in environmentally exposed human populations to heavy metals using the cytokinesis-block micronucleus cytome assay

The cytokinesis-block micronucleus cytome (CBMN-Cyt) assay was developed as a system for evaluating DNA damage, cytostasis, and cytotoxicity. The aim of the present study was to estimate levels of micronuclei (MNi), nucleoplasmic bridges (NPBs), nuclear buds (NBUDs), cell death (apoptosis/necrosis), nuclear division index, and nuclear division cytotoxicity index values in the peripheral blood lymphocytes of environmentally exposed subjects to heavy metals from five Bosnian regions, characterized by different exposure to heavy metals. The study was performed using CBMN-Cyt assay, considering factors, such as age, gender and smoking habits and their possible effects on analyzed parameters. In total, 104 healthy subjects were selected (49.04% females and 50.96% males; average age, 35.41 years; 51.92% smokers and 48.08% nonsmokers). There was significant difference between the frequency of NBUDs in Tuzla as compared to the control group. Furthermore, there was observed a statistically significant difference for the frequency of NPBs between Zenica, Olovo, and Kakanj when compared with the controls. Males showed a significantly higher number of apoptotic cells than females in controls. There were significant differences between smokers and nonsmokers in the frequency of NPBs in controls (higher in nonsmokers) and necrotic cells in Olovo (higher in nonsmokers). The pack years of smoking significantly influenced the number of necrotic cells in controls and the frequency of NBUDs in the overall sample. The results of the present study provide evidence of significantly increased frequency of NPBs and NBUDs in exposed subjects, suggesting that these endpoints are highly sensitive markers for measuring genotoxicity.

Inter-individual variability in the response of human peripheral blood lymphocytes to ionizing radiation: comparison of the dicentric and micronucleus assays

Ionizing radiation can induce a wide range of DNA damage that leads to chromosomal aberrations. Some of those aberrations (dicentrics and micronuclei) are applied in biodosimetry. Biological dosimetry assumes similar radiosensitivity of each donor, but it does not exclude inter-individual variations in radiation susceptibility. Therefore, for biological reasons, it is always challenging to investigate inter-individual variability in response to radiation. For mechanistic reasons, it is also interesting to investigate the correlation between dicentric and micronuclei formation in response to radiation. In this experiment, irradiated blood specimens from 14 healthy male and female donors have been used to evaluate inter-individual variability in response to the genotoxic effects of X-ray radiation, as well as the dose-response relationship and test sensitivity using two endpoints (dicentrics and micronuclei). The results showed similar patterns of cytogenetic biomarker distribution between donors, but differences in the response of some donors at some doses. Data also showed that responses of male donors were better detected using the dicentric test, while for females, micronucleus frequencies were higher in response to the same dose of radiation. No influence of smoking status or age on specific responses was observed. Group variability in response to radiation was evaluated using coefficient of variation for each group of individuals irradiated with the same doses; as the dose increases, group variability becomes substantially lower. Despite sporadic inter-individual variability, trend of radiation-induced changes was similar. Produced calibration curves for both types of damage revealed dicentrics as genetic damage more typical for radiation than micronuclei.

Metallic ion content and damage to the DNA in oral mucosa cells patients treated dental implants

The aim of this study was to assess the potential genotoxicity of dental implants, evaluating biomarkers of DNA damage (micronuclei and/or nuclear buds), cytokinetic defects (binucleated cells) and the presence of trace metals in gingival cells of patients with implants, comparing these with a control group. A total of 60 healthy adults (30 patients with dental implants and 30 control patients without) were included in the study. Medical and dental histories were made for each including life-style factors. Genotoxicity effects were assessed by micronucleus assays in the gingival epithelial cells of each patient; 1,000 epithelial cells were analyzed, evaluating the frequency of micronucleated cells and other nuclear anomalies. The concentration of metals (Al(27), Ag(107), Co (59), Cr (52), Cu(63), Fe(56), Sn(118), Mn(55), Mo(92), Ni(60), Pb(208), Ti(47)) were assayed by means of coupled plasma-mass spectrophotometry (ICP-MS). The frequency of micronuclei in the patient group with implants was higher than in the control group but without statistically significant differences (P > 0.05). Similar results were found for binucleated cells and nuclear buds (P > 0.05). For metals assayed by ICP-MS, significant differences were found for Ti(47) (P ≤ 0.045). Univariate analysis identified a significant association between the presence of micronuclei and age. Dental implants do not induce DNA damage in gingival cells, the slight effects observed cannot be indicated as biologically relevant.

Genotoxic damage in hospital workers exposed to ionizing radiation and metabolic gene polymorphisms

Of all workers exposed globally to synthetic sources of radiation, medical personnel represent the largest group, but receive relatively low doses. Accidental or therapeutic acute radiation exposure of humans was observed to induce various forms of cytogenetic damage, including the possibility of increasing the incidence of micronuclei (MN) and chromosomal aberrations (CA). The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation (IR). The cytokinesis-block MN and comet assays were used to examine peripheral blood lymphocytes (PBL) of 31 exposed workers to IR and 33 control subjects corresponding in gender, age, and smoking. Glutathione S-transferases (GSTM1, GSTT1, and GSTP1) are postulated to be involved in the detoxification of endogenous and exogenous genotoxicants. The association between these biomarkers and polymorphic genes of xenobiotic metabolizing enzymes was thus also assessed. MN frequency was significantly higher in the exposed subjects compared controls. Comet assay results showed a significant increase of tail length in workers exposed to IR. Data obtained suggest that GSTM1, GSTT1, and GSTP1 polymorphism do not modify significantly the genotoxic potential of IR. Therefore, the exposed medical personnel need to carefully apply radiation protection procedures and minimize, as low as possible, IR exposure to avoid possible genotoxic effects.

Normal and Cut-Off Values of the Cytokinesis-Block Micronucleus Assay on Peripheral Blood Lymphocytes in the Croatian General Population

Mikronukleus (MN) test na limfocitima periferne krvi jedna je od najvažnijih metoda koje se primjenjuju u citogenetičkom nadzoru. Osnovni preduvjet za primjenu nekog testa u svrhu nadzora profesionalno izloženih populacija jest poznavanje normalnih vrijednosti promatranoga biološkog pokazatelja (biomarkera) u kontrolnoj populaciji. Baze podataka na razini opće populacije moraju se redovito obnavljati novim podacima. Cilj ovog istraživanja bio je utvrditi normalne i granične vrijednosti MN-testa na limfocitima periferne krvi 200 zdravih ispitanika obaju spolova iz opće populacije Republike Hrvatske te ispitati koji čimbenici pridonose spontanom nastanku MN. Na razini istražene populacije utvrđeno je prosječno (6,90±3,32) MN (medijan 7 MN), dok je raspon pojedinačnih vrijednosti iznosio 0 do 18 MN u 1000 binuklearnih stanica. Gornja granična vrijednost dobivena izračunavanjem 95. percentila za cjelokupnu promatranu populaciju iznosi 12,5 MN na 1000 limfocita. Utvrđeno je da na spontani nastanak MN utječu spol, dob i navika pušenja. Žene u prosjeku imaju više vrijednosti svih parametara MN-testa od muškaraca, a u njih je bio i naglašeniji porast vrijednosti citogenetičkog nalaza zbog navike pušenja. Kako su literaturni podaci o utjecaju pušenja cigareta na nastanak MN kontradiktorni, planiran je nastavak istraživanja radi razjašnjavanja utjecaja dnevno utrošenog broja cigareta i ukupnog trajanja pušačkog staža na vrijednosti parametara MN-testa. Usporedba rezultata s literaturnim podacima potvrdila je da su dobivene vrijednosti u skladu s vrijednostima MN-testa zabilježenim na općoj populaciji u drugim svjetskim laboratorijima. Normalne i granične vrijednosti MN-testa utvrđene u ovome istraživanju poslužit će kao osnova za usporedbu i tumačenje nalaza MN-testa u ispitanika izloženih populacija te daljnju nadogradnju laboratorijske baze podataka.

Cytogenetic analysis of tannery workers in Morocco

This study investigated the possible genetic effects in blood lymphocytes of tannery workers from Morocco being professionally exposed to multiple chemical agents. It was shown that the frequencies of cells with chromosome aberrations and micronuclei were significantly increased in the lymphocytes of the workers compared with the frequencies found in an unexposed control population.

Cytogenetic damage in female Pakistani agricultural workers exposed to pesticides

Bhawalpur is a major cotton-growing area in Pakistan. Cotton picking in Pakistan is carried out by females and as a result of the intensive use of pesticides during the growing season these females are exposed to pesticide residues in the picking season. In the present study, peripheral blood was obtained from 69 cotton pickers and 69 unexposed females and used to assess the effect of pesticide exposure on genetic damage as well as on hepatic enzymes and serum cholinesterase. The subjects were of similar average age in workers and control groups (37.55 +/- 12.75 vs. 37.52 +/- 13.47, P > 0.05). Average exposure time of the picker females was 10.26 +/- 6.14 years. Subjects from the exposed group did not use any protective measures during their work activities. Levels of serum cholinesterase were lower, and levels of alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase were higher in the exposed workers as compared with the control group (P < 0.001). The exposed group exhibited significantly increased frequencies of binucleated cells with micronuclei (12.72 +/- 3.48 vs. 4.35 +/- 2.44, P < 0.001) and total number of micronuclei in binucleated lymphocytes (16.51 +/- 4.27 vs. 5.86 +/- 3.09, P < 0.001) in comparison with subjects of the control group. The binucleated cells with micronuclei frequency also seemed to increase with age in both the groups, however, the magnitude of increase was greater in exposed group than the control. Results from the present study indicate that occupational exposure to pesticide mixtures results in cytogenetic damage in exposed females.

Polymorphisms in folate and homocysteine metabolizing genes and chromosome damage in mothers of Down syndrome children

We recently observed an association between combinations of polymorphisms in the methylenetetrahydrofolate reductase (MTHFR 677C > T or 1298A > C) and reduced folate carrier (RFC-1 80G > A) genes and the risk of a Down syndrome (DS) pregnancy in young Italian women. Others have observed an association between a methionine synthase (MTR 2756A > G) gene polymorphism and the risk of a DS offspring in Italy. Moreover, in a separate study, we observed an increased frequency of both binucleated micronucleated cells (BNMN) and chromosome malsegregation events in peripheral lymphocytes of mothers of DS individuals aged less than 35 years at conception (MDS) in respect to controls. The aim of the present study was to evaluate chromosome damage, measured by means of the micronucleus assay, in peripheral lymphocytes of a group of women (n = 34) who had a DS child in young age (<35 years) and in a control group (n = 35), and to correlate them with MTHFR 677C > T and 1298A > C, RFC-1 80G > A and MTR 2756A > G polymorphisms. We observed an increased frequency of BNMN in the MDS group compared to the control group (17.13 +/- 8.31 per thousand vs. 10.28 +/- 4.53 per thousand; P < 0.001), and, in the general population, a correlation between years of age and BNMN frequency (P = 0.05). A significant correlation between the frequency of BNMN and the MTHFR 677C > T polymorphism (P = 0.038) was also found. Present results indicate that MDS are more prone to chromosome damage than control mothers; moreover the contribution of folate and homocysteine metabolizing gene polymorphisms seems to have an effect on the baseline frequency of BNMN lymphocytes.

Genotoxicity of hydrochlorothiazide in cultured human lymphocytes. I. Evaluation of chromosome delay and chromosome breakage

Hypertension is often treated with diuretics, like hydrochlorothiazide (HCTZ). Previous results on the in vitro genotoxicity of HCTZ are equivocal. In the present study, we have evaluated the genotoxicity of HCTZ in cultured human lymphocytes using the Cytokinesis Blocked Micronucleus (CBMN) assay. In addition, micronucleus (MN) induction was analyzed by Fluorescence In Situ Hybridization (FISH) with an alpha-satellite DNA centromeric probe to distinguish between clastogenic and aneugenic effects. Lymphocyte cultures from 32 healthy adults were exposed to 5 and 40 microg/ml HCTZ. Age, gender, and smoking were evaluated as factors affecting the MN analysis. We found that HCTZ increased MN frequencies. FISH analysis revealed that HCTZ exerts its genotoxicity more strongly at the 40 microg/ml concentration, and principally through chromosome delay (aneugenicity). Multiregression analysis of our results confirmed the known effect of age and gender on MN induction in human lymphocytes. Smoking was also a confounding factor for MN induction, especially for centromere-negative MN frequencies. Under the experimental conditions used, only age had a clear positive effect on the response of lymphocytes to HCTZ. These data indicate that HCTZ produces micronuclei in cultured human lymphocytes by a mechanism that involves chromosome delay and to a lesser extent through chromosome breakage.

Cytogenetic biomarkers, urinary metabolites and metabolic gene polymorphisms in workers exposed to styrene

The present study comprised a biomonitoring study in 95 workers occupationally exposed to styrene and 98 unexposed controls, employing an integrated approach involving biomarkers of exposure, effect, and susceptibility. Airborne styrene was evaluated at workplace, and urinary styrene metabolites, mandelic acid (MA), phenylglyoxylic acid (PGA), vinylphenols (VPTs) and phenylhydroxyethylmercapturic acids (PHEMAs), were measured as biomarkers of internal dose. Cytogenetic alterations were evaluated by analysing the frequency of chromosomal aberrations (CAs) and micronucleated binucleated cells (MNBN) in peripheral blood lymphocytes. The micronucleus assay was coupled with centromeric fluorescence in situ hybridization to distinguish micronuclei (MN) arising from chromosomal breakage (C- MN) from those harboring whole chromosomes (C+ MN). The possible influence of genetic polymorphisms of xenobiotic-metabolizing enzymes involved in styrene biotransformation (EPHX1, GSTT1, GSTM1, GSTP1) and NAT2 on the cytogenetic endpoints was investigated. The exposed workers showed a significantly higher frequency of MNBN (13.8+/-0.5% versus 9.2+/-0.4%; P<0.001) compared to control subjects. The effect appeared to concern both C- and C+ MN. A positive correlation was seen between the frequency of C+ MN and urinary level of MA+PGA (P<0.05) and VPTs (P<0.001). Chromosome-type CAs positively correlated with airborne styrene level and VPTs (P<0.05), whereas chromatid-type CAs correlated with PHEMAs (P<0.05). Workers bearing GSTM1 null genotype showed lowered levels of PHEMAs (P<0.001). The GSTT1 null genotype was associated with increased MNBN frequencies in the exposed workers (P<0.05) and the fast activity EPHX genotype with a moderate decrease in both MNBN and CAs in the controls. Our results suggest that occupational exposure to styrene has genotoxic effects that are potentiated by the GSTT1 gene deletion. These observations may have relevance considering the risk of lymphatic and haematopoietic malignancies tentatively associated with styrene exposure.

Susceptibility to chromosome malsegregation in lymphocytes of women who had a Down syndrome child in young age

Recent findings seem to converge towards a unified hypothesis trying to relate Down's syndrome (DS), trisomy 21 and Alzheimer's disease (AD). The majority of DS individuals develop neuropathological characteristics of AD by the age of 40. Previous cytogenetic studies performed by us showed an increased frequency of aneuploidy in peripheral lymphocytes and fibroblasts of AD patients and a preferential occurrence of chromosome 21 in malsegregation events. An increased frequency of AD among young mothers of individuals with DS (MDS) is reported. This study investigates the cytogenetic characteristics and the predisposition to chromosome malsegregation of peripheral blood lymphocytes in a group of women (n = 35) who had a Down syndrome child in young age (<35 years) and in a control group (n = 30). We applied the micronucleus assay and the dual-color FISH in order to assess the susceptibility to malsegregation events. The results indicate a higher frequency of binucleated micronucleated cells in MDS in respect to the control group (16.1+/-9.1 per thousand versus 8.7+/-5.4 per thousand). Moreover, our data reveal that peripheral lymphocytes of MDS are more prone to chromosome non-disjunction with both chromosomes, 13 and 21, equally involved.

Cytogenetic damage in female Chilean agricultural workers exposed to mixtures of pesticides

The VIII Region of Bio-Bio is a major fruit-growing area of Chile that makes intensive use of agricultural pesticides. The cytogenetic damage associated with exposure to mixtures of pesticides was evaluated by comparing peripheral blood lymphocyte micronucleus (MN) frequencies in a group of 64 female agricultural workers and 30 female controls. The exposed subjects worked during the spring and summer in thinning and pruning fruit trees and in harvesting and packing different fruits, such as raspberries, grapes, apples, and kiwis. They did not use any protective measures during their work activities. A significant increase in the frequency of binucleated cells with micronuclei (BNMN) was found in the exposed women as compared with the controls (36.94 +/- 14.47 vs. 9.93 +/- 6.17 BNMN/1000 BN cells; P < 0.001). The frequency of BNMN varied as a function of age in both the exposed and control groups, but no correlation was found between BNMN frequency and the duration of exposure. Also, smoking and other habits had no effect on MN frequency. Our study confirms that occupational exposure to pesticide mixtures results in cytogenetic damage.

Frequency of micronuclei in peripheral blood lymphocytes from subjects occupationally exposed to low levels of ionizing radiation

The aim of this study was to evaluate the genotoxic effect of low dose of occupational radiation exposure in Nuclear Medicine Department employees, by using cytokinesis-blocked micronucleus assay in peripheral blood lymphocytes. The study included 46 exposed individuals together with 27 from the same area without occupational exposure to radiation which served as controls. The results obtained were evaluated with respect to age, gender, smoking habits, pathological condition and the occupational exposure to radiation of the individuals. The frequency of micronuclei increased significantly with the age of the subjects (P = 0.007). However there were no significant differences in micronucleus frequency with gender, smoking habits and occupational exposure. The frequency of micronuclei was significantly higher in individuals with presence of pathological condition (P < 0.0001) in comparison to healthy population irrespective of their exposure status.

Monitoring DNA damage following radiation exposure using cytokinesis–block micronucleus method and alkaline single-cell gel electrophoresis

The structure of DNA can be damaged as a result of exposure to ionizing radiation. Determining the frequency of chromosome aberrations is a well-known method to estimate the dose of radiation received in acute and chronic exposures. In the past few years, cytogenetic analysis has benefited from the development of new techniques, such as the micronucleus (MN) and comet assays, which provide additional information concerning repair capacity after exposure. The present article discusses the use of peripheral blood lymphocytes for the assessment of populations exposed to ionizing radiation. Also discussed are individual factors that interfere with the frequency of mutations and their impact in the selection of control individuals for the monitoring of radiation exposure and in the interpretation of results.

Biomonitoring results and cytogenetic markers among harbour workers with potential exposure to river silt aerosols

BACKGROUND

Workers on dredgers and lighters on rivers are potentially exposed to a variety of substances.

AIMS

To determine the internal load of heavy metals and arsenic as well as levels of cytogenetic markers in workers exposed to river silt aerosols.

METHODS

One hundred exposed workers were examined up to eight times within three years. Additionally, 100 control workers were studied once. Blood samples were analysed for lead, mercury, and cadmium. Additionally, micronuclei frequency and sister chromatid exchange (SCE) rates were determined. Urinary samples were analysed for cadmium, mercury, nickel, chromium, and arsenic. Information on potential confounders, such as smoking habits and consumption of fish were assessed.

RESULTS

Apart from some increased concentrations of mercury in blood (maximum 14.6 microg/l) and arsenic in urine (maximum 356.5 microg/l) all measurements were within reference values. None of the exposure and effect markers were found to be significantly increased in exposed workers compared to non-exposed controls. In multiple linear regression models, mercury levels in blood as well as the concentration of arsenic in urine were strongly related to fish consumption. Cadmium levels in blood as well as urinary cadmium concentrations were strongly related to smoking habits. After adjusting for smoking habits, SCE rates were associated with cadmium levels in blood.

CONCLUSION

Increased exposure levels or enhanced levels of cytogenetic markers were not found in workers exposed to river silt aerosols. However, cadmium exposure in blood was related to SCE frequency.

Chromosome aberration and sister chromatid exchange in workers of the iron and steel factory of Iskenderun, Turkey

The aim of this study was to investigate, by using chromosome aberration (CA) and sister chromatid exchange (SCE) tests, whether or not the workers employed in the Iskenderun (Turkey) iron and steel factory have any genotoxic risk. The CA and the SCE were investigated in 48 males employed in a coke ovens unit and 8 males employed in a product side unit of the factory and in control groups. The frequency of CA was higher while the frequency of the SCE was not in all the smoker-nonsmoker workers than in smoker-nonsmoker control groups. In addition, there was no significant decrease in the RI, while the MI was significantly lower than in the controls. .

Effect of smoking habit on the frequency of micronuclei in human lymphocytes: results from the Human MicroNucleus project

The effect of tobacco smoking on the frequency of micronuclei (MN) in human lymphocytes has been the object of many population studies. In most reports, the results were unexpectedly negative, and in many instances smokers had lower frequencies of MN than non-smokers. A pooled re-analysis of 24 databases from the HUMN international collaborative project has been performed with the aim of understanding the impact of smoking habits on MN frequency. The complete database included 5710 subjects, with 3501 non-smokers, 1409 current smokers, and 800 former smokers, among subjects in occupational and environmental surveys. The overall result of the re-analysis confirmed the small decrease of MN frequencies in current smokers (frequency ratio (FR) = 0.97, 95% confidence interval (CI) = 0.93-1.01) and in former smokers (FR = 0.96, 95% CI = 0.91-1.01), when compared to non-smokers. MN frequency was not influenced by the number of cigarettes smoked per day among subjects occupationally exposed to genotoxic agents, whereas a typical U-shaped curve is observed for non-exposed smokers, showing a significant increase of MN frequency in individuals smoking 30 cigarettes or more per day (FR = 1.59, 95% CI = 1.35-1.88). This analysis confirmed that smokers do not experience an overall increase in MN frequency, although when the interaction with occupational exposure is taken into account, heavy smokers were the only group showing a significant increase in genotoxic damage as measured by the micronucleus assay in lymphocytes. From these results some general recommendations for the design of biomonitoring studies involving smokers can be formulated. Quantitative data about smoking habit should always be collected because, in the absence of such data, the simple comparison of smokers versus non-smokers could be misleading. The sub-group of heavy smokers (> or =30 cigarettes per day) should be specifically evaluated whenever it is large enough to satisfy statistical requirements. The presence of an interaction between smoking habit and occupational exposure to genotoxic agents should be always tested.

Biomarkers to assess the genetic damage induced by alcohol abuse in human lymphocytes

Alcohol abuse is a major risk factor for cancer of the upper alimentary tract, the upper respiratory tract, and liver. Chromosome damage is used as early effect biomarker in the surveillance of human exposure to genotoxic carcinogens. In the present study, two genetic markers, namely chromosome aberrations (CAs) and micronuclei (MN), were used to evaluate genetic damage in peripheral lymphocytes from 20 alcoholics, 20 abstinent alcoholics, and 20 controls. Composition of the three groups was fairly similar as regards sex, age and smoking habits. A highly significant increase was observed in the frequencies of CA and MN in lymphocytes of alcoholics as compared both with controls and abstinent alcoholics. However, no correlation was found between the length of alcohol abuse and the frequencies of either biomarkers in alcoholics. CA and MN frequencies in abstinent alcoholics were similar than those in controls. Our data indicate that CA and MN can be two useful biomarkers to assess genetic damage associated with alcohol abuse. They could be included in programs for cancer prevention in alcoholics. Abstinence appears to normalize the frequency of both MN and CA. This could offer therapists another tool to help alcoholics change their lifestyle.

The genotoxic risk of hospital, pharmacy and medical personnel occupationally exposed to cytostatic drugs--evaluation by the micronucleus assay

The aim of this study was to evaluate the genotoxicity of cytostatic drugs in hospital and pharmacy employees (n=100), occupationally exposed. The micronucleus assay was used to study lymphocytes in 247 peripheral blood samples. Samples were collected at "baseline level" without any cytostatic drugs exposure before recruiting or after at least 3 weeks without cytostatic drugs contact and at three times (cycle 1-3) post-exposure. Samples from 60 office employees served as controls. Furthermore, our results were compared to urinary analyses of cytostatic drugs (oxazaphosporines, anthracyclines, platinum) which were collected in parallel to the cytogenetic investigation. Statistical analyses were performed under consideration of age, gender and X-ray exposure. The frequency of micronuclei was significantly related to the age of the subjects (r(Spearman)=0.16; P<0.05). However, there were no significant differences in micronucleus rates between controls and exposed hospital workers. Similarly, micronucleus rates were not significantly different at the various sampling time points and there was no correlation between duration of employment and micronucleus rates. Furthermore, no correlation between current biomonitoring data of exposure (urine tests) and micronuclei frequency was found. Therefore, significantly increased genotoxic damage of the lymphocytes investigated in this study could not be demonstrated.

Mutagenic and cytotoxic effectiveness of zinc dimethyl and zinc diisononyldithiocarbamate in human lymphocyte cultures

The mutagenic and cytotoxic effectiveness of the vulcanisation accelerators zinc dimethyldithiocarbamate (ZDMC; ziram) and zinc diisononyldithiocarbamate (ZDINDC; arbestab Z) was tested in lymphocyte cultures of five healthy probands. ZDMC and ZDINDC (c=0.1, 1.0 and 10.0microg/ml) were studied in lymphocyte cultures without external metabolic activation. Additionally, incubation of the compounds (c=10.0microg/ml) was performed in the presence of liver microsomes from aroclor-induced rats (1 and 2h, 1 and 2mg microsomal protein). Genotoxicity testing was performed by analysis of chromosomal aberrations (CA), sister chromatid exchanges (SCEs) and micronuclei (MN). For evaluation of antiproliferative effects, mitotic index (MI) and cell cycle kinetics (CCK) were determined. In contrast to earlier investigations we found no significantly increased mutagenic or cytotoxic activity of ZDMC; ZDINDC also was inactive under these conditions.

Extended exposure of adult and fetal mice to 50 Hz magnetic field does not increase the incidence of micronuclei in erythrocytes

The flow cytometer-based micronucleus assay was used to study the effects on chromosomes in erythroid cells of CBA/Ca mice after extended exposure to 50 Hz magnetic field (MF), 14 microT, peak-to-peak (p-p). The study included two different experiments: (a) mice exposed in utero during 18 days of their prenatal stage, and (b) adult mice exposed for 18 days. In experiment (a) 35 days after exposure was terminated, peripheral blood was drawn from the mice exposed in utero to determine whether the exposure had a genotoxic effect on the pluripotent erythroid stem cells. About 200000 polychromatic erythrocytes (PCE) and 200000 normochromatic erythrocytes (NCE) were analysed from each of 20 exposed mice. The EMF exposure did not significantly change the frequency of micronucleated PCE or NCE in comparison with 20 sham-irradiated mice. There was no difference in the proportion of PCE between exposed and unexposed animals. Similarly, in experiment (b) no differences were seen between EMF exposed and unexposed adult mice when samples of peripheral blood were taken at the end of exposure and analyzed for micronuclei in PCE and NCE. The proportion of PCE was the same in both groups. The results indicate that exposure to EMF does not induce direct or indirect effects on chromosomes in erythroid cells expressed as increased levels of micronucleated erythrocytes of mice. No indications of delayed genetic effects were found.

HUman MicroNucleus project: international database comparison for results with the cytokinesis-block micronucleus assay in human lymphocytes: I. Effect of laboratory protocol, scoring criteria, and host factors on the frequency of micronuclei

Micronucleus (MN) expression in peripheral blood lymphocytes is well established as a standard method for monitoring chromosome damage in human populations. The first results of an analysis of pooled data from laboratories using the cytokinesis-block micronucleus (CBMN) assay and participating in the HUMN (HUman MicroNucleus project) international collaborative study are presented. The effects of laboratory protocol, scoring criteria, and host factors on baseline micronucleated binucleate cell (MNC) frequency are evaluated, and a reference range of "normal" values against which future studies may be compared is provided. Primary data from historical records were submitted by 25 laboratories distributed in 16 countries. This resulted in a database of nearly 7000 subjects. Potentially significant differences were present in the methods used by participating laboratories, such as in the type of culture medium, the concentration of cytochalasin-B, the percentage of fetal calf serum, and in the culture method. Differences in criteria for scoring micronuclei were also evident. The overall median MNC frequency in nonexposed (i.e., normal) subjects was 6.5 per thousand and the interquartile range was between 3 and 12 per thousand. An increase in MNC frequency with age was evident in all but two laboratories. The effect of gender, although not so evident in all databases, was also present, with females having a 19% higher level of MNC frequency (95% confidence interval: 14-24%). Statistical analyses were performed using random-effects models for correlated data. Our best model, which included exposure to genotoxic factors, host factors, methods, and scoring criteria, explained 75% of the total variance, with the largest contribution attributable to laboratory methods.

Assessment of DNA damage in lymphocytes of workers exposed to X-radiation using the micronucleus test and the comet assay

The mutagenic and carcinogenic effects of genotoxic agents on exposed people have constituted an increasing concern. Therefore, the objective of this work was to assess DNA damage in lymphocytes of workers exposed to X-radiation using the cytokinesis-blocked micronucleus test and the comet assay (single-cell gel electrophoresis), and to compare these two techniques in the monitoring of exposed populations. The cytokinesis-blocked micronucleus test and the comet assay were employed in the monitoring of 22 workers occupationally exposed to X-radiation in a hospital in southern Brazil. The frequency of dicentric bridges was also measured. The results of both assays and the frequency of dicentric bridges revealed a significant increase in genetic effects on the cells of exposed individuals. Age was significantly correlated with micronucleus frequency and damage index in the comet assay. The concomitant analysis of dicentric bridges when determining micronucleus frequency does not require much extra work, and may serve as a reference to the type of mutagenic effect (clastogenic or aneugenic). The combination of the alkaline comet assay with the cytokinesis-blocked micronucleus test appears to be very informative for the monitoring of populations chronically exposed to genotoxic agents.

Comparison of micronuclei frequencies in mono-, bi- and poly-nucleated lymphocytes from subjects of a residential suburb and subjects living near a metallurgical plant

Spontaneous baseline frequencies of micronuclei in mono-, bi- and poly-nucleated lymphocytes were analyzed, using the cytokinesis-block technique, in 103 subjects living in a residential suburb (Genova-Nervi), and in 203 subjects living in an urban industrialized area near a metallurgical plant and a coke factory (Genova-Cornigliano). Statistical analysis showed that the average frequency of micronucleated binucleated lymphocytes (MnBNL) was significantly higher (1.42-fold) in donors of Nervi than in donors of Cornigliano living in a contaminated environment. In contrast, the average frequency of micronucleated polynucleated lymphocytes (MnPNL) was significantly higher (1.66-fold) in donors of Cornigliano than in donors of Nervi. The existence in the whole population examined of a positive correlation between frequency of MnBNL and frequency of MnPNL and the absence of a positive correlation between frequency of bi- and poly-nucleated lymphocytes and frequency of MnPNL suggest that the formation of MnPNL is a consequence of genetic damage and not of mitotic errors arising during the division of bi- and poly-nucleated cells. In agreement with previous findings the frequency of MnBNL increased with age and was significantly higher in females than in males; unexpectedly it was higher in non-smokers/non-drinkers than in smokers/drinkers.

Increased nondisjunction of chromosome 21 with age in human peripheral lymphocytes

Fluorescence in situ hybridization (FISH) on binucleated cells with chromosome-specific DNA probes provides a convenient way to visualize reciprocal segregation patterns in daughter nuclei, and overcomes most problems related to the artefactual loss or gain of chromosomes that flaw chromosome preparations. In this study, FISH was employed to evaluate age- and sex-effects on spontaneous malsegregation, nondisjunction and loss of chromosome 21 in human lymphocytes after the first division in culture. A total of 68 healthy nonsmokers and nondrinkers of alcohol (37 males and 31 females) were grouped by age as Group I (0-10 years), Group II (20-30 years), Group III (40-50 years) and Group IV (60-70 years), with at least seven subjects per group and sex. FISH with a pericentric chromosome 21 specific DNA probe was carried out on binucleated lymphocytes, cytokinesis-blocked by cytochalasin B (6 microg/ml for 26 h) at 44 h after initiation of cultures. Linear regression analyses demonstrated a significant age-related increase in the frequency of micronuclei without chromosome 21 (MN-21)(r=0.73, p<0.001 in females; r=0.69, p<0.001 in males) in all binucleated cells, with a steeper slope in females (0.1758) than in males (0. 1241). Analysis using the 2x2 chi-square (chi(2)) test on the frequencies of MN-21 showed significant age-related differences in both males and females, except males in Group III and Group IV (p>0. 05). A significant sex-related difference was found only in subjects over 60 years (p<0.05), with females having more MN-21 (12.57 per thousand vs. 8.43 per thousand) than males. Loss of chromosome 21, occurring at mean levels of 0.38 per thousand in all binucleated cells and 0.24 per thousand in binucleated cells containing four FISH signals, was shown not to be age- or sex-related. A positive age-related increase in nondisjunction of chromosome 21 was shown in males (r=0.50, p<0.01), females (r=0.61, p<0.001) and all subjects (r=0.55, p<0.001) by linear regression analysis. An age effect was found only between children and adults (p<0.01 for females, p<0.05

Increased micronuclei frequencies in couples with reproductive failure

A higher incidence of chromosomal instability in the infertile population is widely recognized. An increased level of micronuclei has been shown to be a marker of chromosome damage. Therefore, micronuclei frequencies were assessed in cytokinesis-blocked lymphocytes of 130 patients (65 couples) with idiopathic infertility or with two or more spontaneous abortions, and 30 healthy fertile donors (15 couples). The frequency of micronucleated cells in the cohort with reproductive failure and healthy controls averaged 14.95+/-6.04 per 1000 and 10.60 +/-2.57 per 1000 (P<0.0001), respectively. When micronuclei frequency sums in particular couples (male + female) were analyzed in the same order, identical statistical significance was reached (P<0.0001). We found no effect of age or sex on micronuclei frequency. In summary, the cytokinesis-blocked micronuclei assay revealed increased micronucleus frequency in couples with infertility or two or more spontaneous abortions, suggesting a possible role of chromosomal instability in reproductive failure.

Human cytogenetic biomonitoring using flow-cytometric analysis of micronuclei in transferrin-positive immature peripheral blood reticulocytes

We have developed a method to isolate and analyze nascent human reticulocytes in peripheral blood for the presence of micronuclei (MN). For a very short time peripheral reticulocytes show residual expression of the transferrin receptor. Using immunomagnetic separation of cells expressing the transferrin receptor, a population of immature reticulocytes (Trf-Ret) was isolated from peripheral blood. In humans, the spleen actively removes micronucleated erythrocytes but during the short lifetime of the isolated Trf-Ret only a fraction (less than about 20%) of the MN-containing reticulocytes will have been eliminated. Cells were stained with the fluorescent dyes Thiazole Orange for RNA and Hoechst 33342 for DNA and analyzed by flow cytometry and fluorescence microscopy. Baseline frequencies of MN-Trf-Ret on a group of healthy donors were found to be 1.1% for males and 1.4% for females; however, the gender difference was not significant. The frequency of MN-Trf-Ret in the studied group increased with age, and was dependent on blood group. In three donors studied over 4 months, the baseline level remained stable. In cancer patients treated with radiation or chemotherapy, the frequency of MN-Trf-Ret increased 10- to 20-fold after 1-4 days, depending on the treatment. A high correlation between flow and manual analysis of MN-Trf-Ret was seen. We believe the method has a high potential as a sensitive and rapid method for biological monitoring in presumed exposed groups and individuals.

Biomarkers of carcinogenesis in humans exposed to polycyclic aromatic hydrocarbons

The frequencies of micronuclei (MN) in cytokinesis-blocked lymphocytes of 91 steel foundry workers were analysed. On the basis of ambient PAH levels at the work stands and 1-hydroxypyrene concentrations in the urine, the coke-oven workers were the most exposed as compared to the rollers reference group. The difference in results for the two groups studied was not statistically significant, although MN were slightly higher for coke-oven workers. The frequency of MN did not increase with exposure: after some increase in 1-10 years, a decreasing tendency was observed.

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.

Examination of various biomarkers measuring genotoxic endpoints from Barcelona airport personnel

Three different biomarkers: sister-chromatid exchanges (SCE), micronuclei (MN), and the Comet assay, were used to evaluate different kinds of genetic damage in peripheral blood lymphocytes from 34 male workers at Barcelona airport, exposed to low levels of hydrocarbons and jet fuel derivatives. The control group consisted of 11 unexposed men. We also investigated the ras p21 protein levels in plasma, in order to evaluate whether the ras gene could serve as a suitable potential marker of carcinogenic pollution in occupationally exposed cohorts. SCE and MN analyses failed to detect any statistically significant increase in the airport workers when compared with the controls, and in fact, the frequency of binucleated cells with MN in the exposed group was significantly lower than that obtained in the control. However, slight but significant differences in the mean comet length and genetic damage index were observed between the exposed and control groups when using the Comet assay. There were no statistically significant differences between both groups in p21 plasma levels. Smoking was shown to affect significantly both SCE and high frequency cells (HFC) in the exposed group.

DNA damage in lymphocytes of elderly patients in relation with total antioxidant levels

DNA damage may occur as a result of an imbalance between the production and removal of free radicals, a process in which age plays an outstanding role. The purpose of this study was to analyze the relationship between total antioxidants and DNA damage in a sample of old age people in Mexico City. The sample included a total of 88 subjects, 15 males and 69 females, with a mean age of 65.5 years old (range between 60 and 79 years old), all of whom had lived in Mexico City during the last 10 years and had been diagnosed as clinically healthy. Results showed that 52% of the subjects presented DNA damage in peripheral blood lymphocytes which was assessed through an alkaline unicellular electrophoresis procedure (Comet Test), regardless of total antioxidant serum levels quantified through a colorimetric method (Randox Kit). Higher non-damage occurrences were observed in subjects with low antioxidant levels, a difference that was statistically significant (P < 0.05). Furthermore, the highest incidence of damaged cells was observed in subjects belonging to the 70-years-old-and-above group (P < 0.05). As to the magnitude and intensity of the damage associated to total antioxidant concentrations, a trend toward greater DNA damage in subjects with low serum levels was observed. It is concluded that low antioxidant levels are not always indicative of oxidative strain and therefore should not be considered as predictors of DNA damage in this population.

Micronucleated lymphocyte rates from head-and-neck cancer patients

We investigated whether head-and-neck cancers are associated with an increased micronucleated cell rates (MN cell rates) and whether risk factors for these cancers are associated with alterations in micronucleated lymphocytes. MN cell rates were assessed in cytokinesis-blocked lymphocytes of 57 head-and-neck cancer patients (CP) before any anticancer treatment and of 198 male and female healthy subjects (HS). In the HS group, only smoking status significantly affect MN cell rates. In CP group age, sex, tobacco status, alcohol status, tumor stage, family history of cancer had no significant effect. For the non-smokers, the comparison between MN cell rates in HS and CP adjusted for age and sex showed a significant difference. The increase of MN cell rates in non-smokers patients may be attributable to cancer status. For the smokers, the comparison of MN cell rates in HS and CP matched for age and sex showed no significant difference. Pathological status could mask the smoking effect on peripheral blood lymphocytes in patients. Moreover, it probably could partly explain why MN cell rates in matched-CP smokers and HS smokers were similar. The authors do not recommend the CBMN assay in this present form to study smoking DNA-damage effects in peripheral blood lymphocytes of cancer patients, especially for patients with upper aero-digestive tract cancers or lung cancers for which tobacco is the major risk factor.

Application of the comet assay for monitoring DNA damage in workers exposed to chronic low-dose irradiation. I. Strand breakage

We examined a group of people professionally at risk of exposure to low doses of ionizing radiation (altogether 49 individuals). Age, use of therapeutic drugs, work-related exposure to hazardous agents, previous exposures to diagnostic X-rays, such as patient and nuclear medical examination, were registered. For each individual, the occupational radiation burden received over the past period of 5 years was taken from the official personal records based on film dosimetry controlled every month. A matched group of controls was chosen among the administrative employees (40 individuals). The mean age of the studied population at the time of blood sampling was 49 years (range 24-69). The individuals were divided into groups according to risk of exposure and sex. The alkaline comet assay was used to measure DNA breaks and alkali-labile sites. We compared the mean tail moments, tail length and percentage of DNA in the tail. There was a significant difference between the control and hazard groups in DNA damage. Higher DNA damage was also found for men than for women in the control group. There was no relation of DNA damage to age either in control or hazard group. Additionally, analysis of distributions of tail moment values pointed to a considerable individual diversity even in the control group. Therefore, further investigations were necessary into the suitability of the comet assay as a biological dosimetry method; the results obtained so far warrant such investigations.

Sister chromatid exchange and micronucleus frequency in human lymphocytes of 1,650 subjects in an Italian population: II. Contribution of sex, age, and lifestyle

Sister chromatid exchange (SCE) and micronuclei (MN) analysis was carried out on 1,650 healthy individuals living in Pisa and in two nearby small cities, Cascina and Navacchio (Ca-Na). The effect of smoking on SCEs was linearly correlated with the number of cigarettes per day, and an increase of 7.3% SCEs was detectable for as few cigarettes as 1-10/day. Ex-smokers showed intermediate mean values of SCEs (8.09 +/- 1.88) in comparison with never smokers (7.54 +/- 1.61) and current smokers (8.45 +/- 1.94). Mean values of SCEs of ex-smokers decreased linearly with time of smoking cessation, reaching the mean values of never smokers within 8 years. The extent of SCE decrease was inversely proportional to the number of cigarettes previously smoked. No interaction between smoking habits and coffee or alcohol drinking on SCEs was observed. A borderline (P = 0.053) increase in mean SCE values in coffee drinkers (more than 3 cups/day) was found. The age effect on SCEs was remarkable in Ca-Na, but not in Pisa donors. Job type was not associated with significant modification of mean values of SCEs. Multiple logistic regression analysis revealed a statistically significant association between the proportion of high frequency cells (HCF) outliers and coffee consumption. Age and sex appeared to be by far the most important variables associated with modifications in MN frequency, which increased by 0.04 per thousand and 0.02 per thousand per year in males and females, respectively. Children and young donors (age < or = 40 years) showed lower MN frequency regardless of sex, whereas sex appeared to determine a significantly higher increase of MN only in females older than 40 years. In contrast, in males the MN rate by age tended to level off after the age of 30-50. MN frequencies of Pisa blue- and white-collar workers were statistically significantly higher than in students (+0.71 and +0.55 per thousand, respectively). Smoking did not determine any increase of MN frequency. A total lack of correlation (P = 0.913) between MN and SCEs was observed.

Increased spontaneous formation of micronuclei in cultured fibroblasts of first-degree relatives of familial melanoma patients

The phenomenon of spontaneous increased micronuclei and enhanced UV-sensitivity, which is known for familial cutaneous malignant melanoma (CMM) patients, could be demonstrated again in fibroblasts of 17 familial CMM patients. In order to determine if close relatives of familial CMM patients show both a comparable spontaneous chromosomal instability and enhanced UV-sensitivity, cultured fibroblasts of 24 healthy, first-degree relatives of patients with familial malignant melanoma were investigated. The cytokinesis-block micronucleous technique was used to detect enhanced chromosomal instability. Fibroblasts of the investigated relatives showed a significantly increased spontaneous formation of micronuclei, in comparison to 19 healthy controls, but no enhanced UV-sensitivity was evident. We conclude that chromosomal instability might be a hereditary trait and a causative factor in developing familial malignant melanoma. This supports the concept of a genetic predisposition to familial CMM and may help to identify high-risk family members at a cytogenetic level in addition to the common clinicopathological traits.

Evaluation of genotoxic potential of styrene in furniture workers using unsaturated polyester resins

Styrene is a widely used chemical, mostly in making synthetic rubber, resins, polyesters, plastics and insulators. Increasing attention has been focused on this compound since experiments using cytogenetic end-points have implicated styrene as a potential carcinogen and mutagen. In order to perform biological monitoring of genotoxic exposure to styrene monomer, we evaluated the urinary thioether (UT) excretion, and sister chromatid exchanges (SCEs) and micronuclei (MN) in peripheral lymphocytes from 53 furniture workers employed in small workplaces where polyester resin lamination processings were done and from 41 matched control subjects. The mean air concentration of styrene in the breathing zone of workers was 30.3 ppm. As a metabolic marker for styrene exposure, mandelic acid + phenylglyoxylic acid was measured in the urine and the mean value was 207 mg/g creatinine. The mean +/- SD value of UT excretions of workers was 4.43 +/- 3.42 mmol SH-/mol creatinine and also mean UT for controls was found to be a 2.75 +/- 1.78 mmol SH-/mol creatinine. The mean +/- SD/cell values of SCE frequency in peripheral lymphocytes from the workers and controls were 6.20 +/- 1.56 and 5.23 +/- 1.23, respectively. The mean +/- SD frequencies (%o) of MN in the exposed and control groups were 1.98 +/- 0.50 and 2.09 +/- 0.35, respectively. Significant effects of work-related exposure were detected in the UT excretion and SCEs analyzed in peripheral blood lymphocytes (p < 0.05 and p < 0.01, respectively). The MN frequency in lymphocytes from the styrene-exposed group did not differ from that in the controls (p > 0.05). Effect of smoking, age and duration of exposure on the genotoxicity parameters analyzed were also evaluated. In conclusion, although our data do not demonstrate a dose-response relationship, they do suggest that styrene exposure was evident and that this styrene exposure may contribute to the observed genotoxic damage in furniture workers.