A biomonitoring study on the workers from textile dyeing plants

We evaluated the genotoxic risk of workers from textile dyeing plants in Kahramanmaras, Turkey. Sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) were investigated in peripheral blood lymphocyte cultures of 40 workers and compared to those of 32 age-sex- and habit-matched healthy controls. Groups were selected after a questionnaire administration. Use of Maras powder (a kind of smokeless tobacco) was considered as modulating factor. The SCEs level did not show significant differences between workers and controls. The frequency of CA was significantly higher in workers than in controls. Use of Maras powder was a significant factor to increase the frequencies of SCE and CA in control group. The level of SCE and CA did not correlate with the age whereas there was a significant correlation between years of exposure and CA frequency. The results of this study revealed the genotoxic risk of textile dyers. Protective measures such as masks and gloves are desirable for preventing or minimizing the occupational exposure.     

The genotoxic risk of underground coal miners from Turkey

A cytogenetic monitoring study was carried out on a group of workers from a bituminous coal mine in Zonguldak province of Turkey, to investigate the genotoxic risk of occupational exposure to coal mine dust. Cytogenetic analysis, namely sister chromatid exchanges (SCEs), chromosomal aberrations (CAs) and micronucleus (MN) tests were performed on a strictly selected group of 39 workers and compared to 34 controls matched for gender, age, and habit. Smoking and age were considered as modulating factors. Both SCE and CA frequencies in coal miners appeared significantly higher than in controls. Similarly, there was a significant increase in the frequency of total micronuclei in exposed group as compared to control group. The effect of smoking on the level of SCE and MN was significant in the control group. A positive correlation between the age and the level of SCE was also found in controls. The frequencies of both SCE and CA were significantly enhanced with the years of exposure. The results of this study demonstrated that occupational exposure to coal mine dust leads to a significant induction of cytogenetic damage in peripheral lymphocytes of workers engaged in underground coal mining.     

The genotoxic risk of underground coal miners from Turkey

A cytogenetic monitoring study was carried out on a group of workers from a bituminous coal mine in Zonguldak province of Turkey, to investigate the genotoxic risk of occupational exposure to coal mine dust. Cytogenetic analysis, namely sister chromatid exchanges (SCEs), chromosomal aberrations (CAs) and micronucleus (MN) tests were performed on a strictly selected group of 39 workers and compared to 34 controls matched for gender, age, and habit. Smoking and age were considered as modulating factors. Both SCE and CA frequencies in coal miners appeared significantly higher than in controls. Similarly, there was a significant increase in the frequency of total micronuclei in exposed group as compared to control group. The effect of smoking on the level of SCE and MN was significant in the control group. A positive correlation between the age and the level of SCE was also found in controls. The frequencies of both SCE and CA were significantly enhanced with the years of exposure. The results of this study demonstrated that occupational exposure to coal mine dust leads to a significant induction of cytogenetic damage in peripheral lymphocytes of workers engaged in underground coal mining.     

Genotoxic damage in Maras powder consumers from Kahramanmaras province of Turkey

In the present study, chromosomal aberrations (CAs) and micronucleus (MN) levels in the lymphocytes from 60 male individuals consisting of 40 habitues of Maras powder (a kind of smokeless tobacco) and 20 unexposed subjects were determined to investigate the possible inducing effect of Maras powder. The consumers of Maras powder had no exposure to any other known mutagens or toxicants. The mean exposure period to Maras powder was 12.25 + 0.93 years (range 3-22). Data obtained from microscopic examination of the slides was analyzed by SPSS (10.0) package programme. Mean frequency of CA and MN was found to be significantly higher in Maras powder consumers as compared to controls. Similarly, there was a significant elevation in the level of aberrant cells (Ab.Cells) with CAs and binucleated cells with MN (BNMN) in habitues. Spearman's rho correlation analysis indicated a significant increase in the frequency of CA and MN with increase in both age and years of exposure in consumers. Our finding of a significant elevation of CA and MN frequencies in peripheral lymphocytes from smokeless tobacco consumers demonstrated a potential cytogenetic hazard associated with Maras powder exposure.     

Genotoxic damage in Maras powder consumers from Kahramanmaras province of Turkey

In the present study, chromosomal aberrations (CAs) and micronucleus (MN) levels in the lymphocytes from 60 male individuals consisting of 40 habitues of Maras powder (a kind of smokeless tobacco) and 20 unexposed subjects were determined to investigate the possible inducing effect of Maras powder. The consumers of Maras powder had no exposure to any other known mutagens or toxicants. The mean exposure period to Maras powder was 12.25 ± 0.93 years (range 3–22). Data obtained from microscopic examination of the slides was analyzed using SPSS (10.0) software package. Mean frequency of CA and MN was found to be significantly higher in Maras powder consumers as compared to controls. Similarly, there was a significant elevation in the level of aberrant cells (Ab.Cells) with CAs and binucleated cells with MN (BNMN) in habitues. Spearman’s rho correlation analysis indicated a significant increase in the frequency of CA and MN with increase in both age and years of exposure in consumers. Our finding of a significant elevation of CA and MN frequencies in peripheral lymphocytes from smokeless tobacco consumers demonstrated a potential cytogenetic hazard associated with Maras powder exposure. The text was submitted by the authors in English.     

Cytogenetic damage in workers exposed to ethylene oxide

Sister-chromatid exchanges (SECs) and chromosomal aberrations (CAs) were detected in the peripheral lymphocytes of 41 sanitary workers exposed to ethylene oxide (EO) in the sterilizing units of 8 hospitals in the Venice Region. The first group (19 workers) was exposed to 10.7 +/- 4.9 ppm EO, expressed as the time-weighted average concentration for an 8-h working day (TWA/8 h conc.), and the second group (22 workers) to 0.35 +/- 0.12 ppm. Each exposed worker was paired with a control of similar age and smoking habits. A highly significant (P less than 0.001) increase in the mean frequency of SCEs was found in the higher exposure group, 14 (74%) exposed subjects having significantly increased levels of SCEs compared to their matched controls. In the lower exposure group, the increase in mean frequency of SCEs was lower, though still significant (P less than 0.05): 7 (33%) exposed subjects had higher and 1 (5%) had a lower SCE level than the matched controls. From the first group, 10 subjects, 7 of whom had increased SCE levels, were reanalysed 12-18 months after their exposure had been lowered or interrupted: in only 2 of them the SCE level was significantly decreased. A statistically significant correlation between SCE frequency and level of EO exposure (TWA/8 h conc.), as well as a multiple correlation between SCE level and EO exposure, smoking and age were found. However, no interaction could be detected between EO exposure and smoking in the induction of SCEs. In controls, SCE frequency was correlated with smoking and age. In the higher exposure group, the number of both chromatid- and chromosome-type aberrations, independent of gaps, was significantly increased, whereas in the lower exposure group only the frequency of chromosome-type aberrations, excluding gaps, was statistically higher than in controls. The level of CAs remained to a great extent unchanged in the 10 subjects re-examined at a later stage after lowering or halting exposure. Taking the group as a whole, the frequency of cells with total CAs was found to be weakly (P = 0.05) correlated with EO exposure, and was not correlated with smoking, age or SCE frequency.     

Sister chromatid exchanges in patients with precancerous and cancerous lesions of cervix uteri

Summary The frequency of sister chromatid exchanges (SCEs) was studied in leucocytes from 46 patients with cervical carcinoma, 89 precancerous lesions, and 43 age-matched control women. The frequency of SCEs was found to be 10.15 ±2.49 in cancer, 8.83±2.15 in precancerous lesions, and 7.55±2.24 in controls. The analyses of SCE data revealed a highly significant (P<0.001) increase in precancerous and cancerous lesions compared to controls. The intra-chromosomal distribution of SCEs revealed a random increase in various chromosomal groups in patients with cancer and dysplasia compared to controls. The mean SCE level among various groups of precancerous lesions according to severity of pathological condition did not show significant differences. However, 70.8% of dysplasia cases revealed SCE levels higher than the average in controls. The increased frequencies of SCEs in the majority of cancer patients and a few, precancerous lesions indicate that individuals with high SCE levels may be at a high risk of developing cancer. Thus the usefulness of SCE levels as a preclinical marker to identify the high risk group of dysplasias needs to be ascertained by follow-up studies; these are in progress.     

Cytogenetic damage in workers from a coal-fired power plant

The aim of this study was to investigate the genotoxic risk to workers occupationally exposed to coal combustion products in Afsin-Elbistan A power plant, located in south-eastern Turkey. We analysed chromosomal aberrations (CAs), polyploidy, sister-chromatid exchanges (SCEs), and micronuclei (MN) in 48 male workers without a history of smoking, tobacco chewing, or alcohol consumption. The results were compared with a control group of 30 healthy male individuals without exposure to any known genotoxic agents. The mean frequencies of CA, polyploidy, SCEs (P<0.01), and MN (P<0.05) were significantly higher in workers than in the control group, by the Mann-Whitney U-test. Spearman's rho correlation analysis revealed a significant increase in the frequency of CA and MN with increasing years of exposure (P<0.05). However, there was no significant effect of age on the cytogenetic markers analysed in both groups (P>0.05). The data obtained from this study clearly showed chromosomal hazard in the peripheral lymphocytes of workers exposed to coal combustion products in Afsin-Elbistan A power plant for several years. This cytogenetic damage might be attributed to the cumulative effects of several substances due to chemical complexity of the coal ash and gaseous emissions rather than a specific substance.     

Effect of sulphur dioxide exposure on human chromosomes

The genotoxic effects of an average concentration of 41.7 mg/m³ of SO₂ exposure on 42 workers of a fertilizer factory were investigated. Mitotic index (MI), chromosomal aberrations (CAs), sister-chromatid exchanges (SCEs) and satellite associations (SA) were observed. In SO₂-exposed workers, a higher mitotic index (7.09) was recorded in comparison to controls (4.34). The MI, however, declined with duration of exposure. Satellite associations showed a two-fold increase (17.1) as compared to controls (8.11). Among chromosomes, D-G group associations were the highest (7.43%), while 3D type associations were the lowest (0.4%). There was a significant difference (p < 0.05) in the mean frequency of CAs per cell in the exposed workers (3.262%) and the controls (0.833%). The mean frequency of SCEs per cell increased from 3.32 ± 0.1 in controls to 7.72 ± 0.19 in the exposed group. The difference was significant (p < 0.05). In smokers, alcoholics and smoker-alcoholics, the frequency of CAs and SCEs per cell was significantly higher than the non-smokers and non-alcoholics, both in the controls and the SO₂-exposed workers and showed a correlation with the duration of exposure. SO₂ is therefore a clastogenic and genotoxic agent for which necessary precautions must be taken.     

Clastogenicity of selective serotonin-reuptake inhibitors

OBJECTIVE: Selective serotonin-reuptake inhibitors (SSRIs) are used in the treatment of various forms of psychiatric disorders. Preclinical studies in laboratory animals have indicated that SSRIs were not genotoxic, but clear results from in vitro testing of SSRIs in a human cell system are currently scarce. The purpose of this study was to investigate whether SSRIs might be genotoxic. Sertraline was chosen as model SSRI, since it appears to be at least as well-tolerated as other SSRIs and may even have a more favourable side-effect profile. Unlike fluoxetine, fluvoxamine and paroxetine, sertraline has low potential for pharmacokinetic drug interactions. So, sertraline would be considered first in the treatment of psychiatric disorders requiring SSRI therapy in the future. We therefore examined peripheral lymphocytes from sertraline-treated patients for both sister chromatid exchanges (SCEs), cells with a high frequency of SCEs (HFC) and chromosome aberrations (CA) to evaluate the clastogenicity of SSRIs. METHOD: Ten sertraline-treated patients meeting 'Structured Clinical Interview for DSM-IV' criteria for both generalized anxiety disorder and major depression were compared with 18 healthy volunteers and 18 non-treated patients with similar psychopathology. Sertraline hydrochloride was administered orally at 50 mg daily for 10 months to 1 year. The participants were selected on the basis of similar responses to a questionnaire assessing risk of genotoxicity related to other aspects of life. All participants had very similar lifestyles, medical histories, biological and dietary factors. All subjects were non-smokers. RESULT: A statistically significant difference between patients with both generalized anxiety disorder and major depression (sertraline-treated or non-treated) and healthy volunteer groups was found by both SCE frequencies and HFC percentages. Both patient groups showed higher frequencies of SCEs than the healthy controls. No statistically significant difference was found between SCE frequencies or HFC percentages observed in sertraline-treated and non-treated patient groups. No statistical difference was found between groups with respect to the frequency of CA. CONCLUSION: There are no adequate studies analysing the clastogenicity of SSRIs, in particular of sertraline. The SCE frequency, the percentage HFC and the frequency of CA in patients with both generalized anxiety disorder and major depression exposed to daily doses of sertraline do not indicate a possible clastogenic hazard. The increased SCE frequencies in patients with both generalized anxiety disorder and major depression in our study-irrespective of sertraline treatment-indicate a possible genotoxic effect. However, our observations were based on a limited number of patients; the results may be explained by psychogenic stress.     

Genotoxic effects of occupational exposure to lead and cadmium

This study was designed to assess genotoxic damage in somatic cells of workers in a Polish battery plant after high-level occupational exposure to lead (Pb) and cadmium (Cd), by use of the following techniques: the micronucleus (MN) assay, combined with in situ fluorescence hybridization (FISH) with pan-centromeric probes, analysis of sister chromatid exchanges (SCEs), and the comet assay. Blood samples from 44 workers exposed to lead, 22 exposed to cadmium, and 52 unexposed persons were used for SCE and MN analysis with 5'-bromodeoxyuridine (BrdU) or cytokinesis block, respectively. In parallel, the comet assay was performed with blood samples from the same persons for detection of DNA damage, including single-strand breaks (SSB) and alkali-labile sites (ALS). In workers exposed mostly to lead, blood Pb concentrations ranged from 282 to 655 microg/l, while the range in the controls was from 17 to 180 microg/l. Cd concentration in lead-exposed workers fell in the same range as for the controls. In workers exposed mainly to cadmium, blood Cd levels varied from 5.4 to 30.8 microg/l, with respective values for controls within the range of 0.2-5.7 microg/l. Pb concentrations were similar as for the controls. The incidence of MN in peripheral lymphocytes from workers exposed to Pb and Cd was over twice as high as in the controls (P<0.01). Using a combination of conventional scoring of MN and FISH with pan-centromeric probes, we assessed that this increase may have been due to clastogenic as well as aneugenic effects. In Cd- and Pb-exposed workers, the frequency of SCEs as well as the incidence of leukocytes with DNA fragmentation in lymphocytes were slightly, but significantly increased ( P<0.05) as compared with controls. After a 3h incubation of the cells to allow for DNA repair, a clear decrease was found in the level of DNA damage in the controls as well as in the exposed workers. No significant influence of smoking on genotoxic damage could be detected in metal-exposed cohorts. Our findings indicate that lead and cadmium induce clastogenic as well as aneugenic effects in peripheral lymphocytes, indicating a potential health risk for working populations with significant exposures to these heavy metals.     

Chromosomal aberrations and SCEs as biomarkers of cancer risk

Previous studies have suggested that the frequency of chromosomal aberrations (CAs), but not of sister chromatid exchanges (SCEs), predicts cancer risk. We have further examined this relationship in European cohorts comprising altogether almost 22,000 subjects, in the framework of a European collaborative project (CancerRiskBiomarkers). The present paper gives an overview of some of the results of the project, especially as regards CAs and SCEs. The results confirm that a high level of CAs is associated with an increased risk of cancer and indicate that this association does not depend on the time between CA analysis and cancer detection, i.e., is obviously not explained by undetected cancer. The present evidence indicates that both chromatid-type and chromosome-type CAs predict cancer, even though some data suggest that chromosome-type CAs may have a more pronounced predictive value than chromatid-type CAs. CA frequency appears to predict cancers at various sites, although there seems to be a particular association with gastrointestinal cancers. SCE frequency does not appear to have cancer predictive value, at least partly due to uncontrollable technical variation. A number of genetic polymorphisms of xenobiotic metabolism, DNA repair, and folate metabolism affect the level of CAs and might collectively contribute to the cancer predictivity of CAs. Other factors that may influence the association between CAs and cancer include, e.g., exposure to genotoxic carcinogens and internal generation of genotoxic species. Although the association between CA level and cancer is seen at the group level, an association probably also exists for the individual, although it is not known if an individual approach could be feasible. However, group level evidence should be enough to support the use of CA analysis as a tool in screening programs and prevention policies in occupational and environmental health.     

Cytogenetic analysis of nasal mucosa cells and lymphocytes from high-level long-term formaldehyde exposed workers and low-level short-term exposed waiters

The evidence for genotoxic potential of formaldehyde (FA) in humans is insufficient and conflicting. We previously reported a higher frequency of micronuclei in nasal and oral exfoliative cells from students exposed to formaldehyde vapor for short-term. To further evaluate the genetic effects of long-term occupational exposure to FA and short-term exposure to FA of indoor sources, the frequencies of micronuclei (MN) in nasal mucosa cells, sister chromatid exchanges (SCEs) of peripheral lymphocytes, and the lymphocyte subsets were evaluated in 18 non-smoking workers (mean exposure duration was 8.6 years) in an FA factory and 16 non-smoking waiters exposed to FA for 12 weeks in a ballroom. A non-smoking student group without occupational exposure (n=23) to FA was used as control. The 8h time-weighted average (TWA) concentrations of formaldehyde was 0.985+/-0.286 mg/m3 with the ceiling exposure concentration of 1.694 mg/m3 in the workshop, and 0.107+/-0.067 mg/m3 in the ballroom (5 h TWA). Higher frequencies of micronuclei per thousand cells in nasal mucosa cells of workers versus control (2.70+/-1.50 versus 1.25+/-0.65, p<0.05) and higher frequency of SCEs in peripheral lymphocytes of workers group (8.24+/-0.89 versus 6.38+/-0.41, p<0.05) were observed. Increased frequency of micronuclei in nasal mucosa cells or SCE in peripheral lymphocytes was not found among waiters group. The results suggest that the genotoxic potential of high level FA exposure may have occupational risks in long-term exposure groups.     

Paradoxical changes in SCE frequencies persistently elevated in vivo, on exposure to a mutagen in vitro

Lymphocyte cultures from 4 individuals with persistently significantly elevated frequencies of sister-chromatid exchange (SCE) were examined with no treatment, and with 2 concentrations of mitomycin C. In each of the 4 cases, the mean level of SCEs in the untreated lymphocytes exhibited a paradoxical reduction in SCE frequency when exposed to the lower (0.005 microgram/ml) of the two doses of mitomycin C. At the second higher dose of mitomycin C (0.025 microgram/ml) the mean level of SCE/cell exceeded the untreated mean. When the distributions of SCE/cell were examined it appeared that the untreated cultures had two or more populations of cells; one was in the normal SCE frequency range, while the second population was in an elevated SCE frequency range. The paradoxical reduction in SCE frequency was apparently due to elimination of, or mitotic inhibition of cells in the highest range of SCE frequency, while a small elevation in SCEs was initiated in the cells with a normal SCE frequency. Thus, mean levels of SCE/cell can be misleading. This data suggests that new exposure to the same or a different genotoxic agent might possibly result in a misleading lowering of the mean SCE frequency.     

Genotoxic effects of malathion: an organophosphorus insecticide, using three mammalian bioassays in vivo

The genotoxic effects of malathion was evaluated using chromosome aberration, sister chromatid exchange (SCE) and sperm abnormality assays in mice. All the three acute doses (2.5, 5 and 10mg/kg) of malathion tested in the present study, induced significant dose-dependent increase in the frequency of chromosome aberrations and sperm abnormalities, but did not affect the total sperm count. The highest acute dose induced a >12-fold increase in the frequency of chromosome aberrations, two-fold increase in the frequency of SCEs and four-fold increase in the frequency of sperms with abnormal head morphology following intraperitoneal (i.p.) exposure. Further, a significant increase in the frequency of SCEs was observed, but the increase was not dose-dependent. At higher doses, malathion induced a moderate delay in cell cycle as evident from the increase in average generation time (AGT). The present findings suggest that technical grade malathion is a potent genotoxic agent and may be regarded as a potential germ cell mutagen also.     

Metabolite ratio of toluene-exposed rotogravure printing plant workers reflects individual mutagenic risk by sister chromatid exchanges

The study involved a group of 42 printing plant workers and a control group of 45 blood donors. At the working places, the ambient air-toluene concentration amounted from 141 to 328 mg/m(3). Sister chromatid exchanges (SCEs) were significantly elevated by three units in the exposed group. In this group, the concentration of urinary toluene metabolites was also considerably increased-hippuric acid was four times higher and the o-cresol and p-cresol fractions were twice as high. Results of toluene monitoring of ambient air- or blood-toluene concentrations did not show any relationships with individual SCE. While these SCE values revealed only a weak relationship with the corresponding hippuric acid data, a significant correlation with the cresols, which are known to be more genotoxic than hippuric acid, appeared in highly exposed workers. An attempt was made to consider the individual metabolic balance of toluene excretion products. For that reason individual cresol to hippuric acid ratios were calculated and related to corresponding SCE values. In all investigated subpopulations of the exposed group, this ratio correlated with SCE at a level of high significance. This strong interrelationship is a powerful argument for the genotoxic behavior of toluene. Furthermore, the individual metabolic balance, as a consequence of genetic polymorphism, should be considered in the discussion about genetic risk of toluene.     

Cytogenetic study of workers exposed to chromium compounds

The frequency of sister chromatid exchanges (SCEs), high SCE frequency cells (HFCs), and genetic polymorphism of genotypes glutathione S-transferase (GST) M1 and T1 were analyzed in peripheral lymphocytes of 35 workers occupationally exposed to chromium (Cr) and 35 matched control group. Results showed that workers exposed to Cr showed 6.07 SCE/cell, as compared to 4.76 SCE/cell for the control group (p<0.01). Smokers showed a statistically significant higher frequency of SCE than non-smokers in both groups. The work duration of Cr workers was an important factor. Workers exposed for more than 5 years showed a significantly higher level of SCEs (p<0.05). Workers exposed to Cr for 5 or more years had higher HFC rates (51.4%) than those exposed for less than 5 years (22.9%), with an odds ratio of 4.5 times than those exposed for less than 5 years. In HFC analysis, Cr workers who smoked showed a higher level of HFC (60%) than the control group (5.7%) and also had a higher odds ratio (60.4) compared with the control group. Among non-smokers, the odds ratio was 9.0. Another objective of this study is to investigate the relationship between SCE and genetic polymorphisms of GST M1 and T1 in Cr workers. The results showed that the incidence of GSTM1 null genotype was 60% in the control group and 77.1% in Cr workers, and percentages of GSTT1 deletion were 42.9% and 62.9% in control and exposed individuals, respectively. There was a slightly increased frequency of SCE among Cr workers with GSTM1 null genotype as opposed to non-null genotype individuals. A similar result was seen among the control group; however, there were no statistically significant differences. In conclusion, the current study found the positive induction of SCE in workers who smoked or/and were exposed to Cr. However, different GST genotypes did not influence the level of cytogenetic damage between groups. Despite slight variation in numbers, they all appear to be not different.     

Increased levels of sister chromatid exchanges in military aircraft pilots

Sister chromatid exchanges (SCEs) were scored in lymphocytes of nine high-performance pilots of alphajet aircrafts and of ten control individuals from the same air base. Statistical analysis of the mean SCE count per cell in the total number of cells analyzed as well as in those having 12 or more SCEs (high-frequency cells, HFCs) revealed a significant difference between pilots and controls, after adjusting for the effect of smoking. Analysis of the cell cycle kinetic data (replication and mitotic indices) revealed no significant differences either between pilots and controls or between smokers and nonsmokers. Previously, we reported an increase in the SCE levels in workers of the aeronautical industry exposed to noise and whole-body vibration. The present results corroborate those findings and indicate that noise and whole-body vibration may cause genotoxic effects in man.     

Variation in the frequency of sister chromatid exchanges in repeated human lymphocyte cultures

Summary Repeated blood samples from two healthy donors were taken over a period of about one year to determine the temporal variation in human lymphocyte baseline sister chromatid exchange (SCE)-frequencies. The investigations were performed on whole blood cultures and purified lymphocyte cultures using a standardized protocol for blood collection and cultures. Significant differences in the frequencies of SCEs were found between the two cultivation systems and the two blood donors but also between repeated cultures of the same individual. There was no systematic relationship between the proliferation of the cultures and the basal SCE values. The results indicate the necessity of concurrent controls and repeated blood samples whenever SCEs are used as a test for monitoring human exposure to potential mutagens. Temporal variation in human lymphocyte baseline SCE frequencies is a limiting factor for the detection of minor effects of genotoxic agents.     

Sister chromatid exchange in pathology staff occupationally exposed to formaldehyde

Sister chromatid exchange (SCE) was measured in peripheral lymphocytes of 90 workers from 14 hospital pathology departments in Israel who were occupationally exposed to formaldehyde (FA) and of 52 unexposed workers from the administrative section of the same hospitals. The mean exposure period to FA was 15.4 years (range 1-39). The results of SCEs are expressed in two variables: (a) mean number of SCEs per chromosome and (b) proportion of high frequency cells (cells with more than eight SCEs). A high correlation was found between these two variables. The adjusted means of both SCEs variables were significantly higher among the exposed compared with that of the unexposed group (P<0.01). Adjustment was made for age, sex, smoking habits, education workers and origin. Evaluation of the influence of years of exposure on the frequency of SCEs showed that the two variables of SCEs were higher among those who were exposed to FA for 15 or more than among those with less than 15 years of exposure. Concerning levels of exposure, both variables of SCEs were the same in the low and in the high levels of exposure sub-groups. However, among the smokers, both variables of SCEs were higher in the high exposure sub-group than in the low exposure sub-group.Our finding of a significant increase of SCEs frequency in peripheral lymphocytes in pathology staff indicates a potential cytogenetic hazard due to FA exposure. We conclude that our data indicate that FA is mutagenic to humans.