Cytogenetic abnormalities of the descendants of permanent residents of heavily contaminated East Kazakhstan

More than 400 nuclear explosion tests were conducted at the Semipalatinsk Nuclear Test Site (SNTS) and significant radioactive substances were released. The long-term consequences of the activities at the SNTS and the appearance of any hereditary effects remain insufficiently studied about 25 years after the test site was closed. The population living in villages near the SNTS are considered to have been heavily exposed to external and internal radiation. This study aims to perform an assessment and comprehensive cytogenetic analysis of the inhabitants living near the SNTS, and their first-(F1) and second-(F2) generation children. Residents of the East Kazakhstan region living in the area covered by the former SNTS were included in the study. To evaluate the hereditary effects of nuclear testing, comprehensive chromosome analyses were performed in lymphocytes using conventional Giemsa and fluorescent in situ hybridization methods in 115 F1 and F2 descendants in the villages of Dolon and Sarzhal, which were heavily contaminated. The parents of the subjects had permanently lived in the villages. A higher number of stable-type chromosome aberrations such as translocations was found in these residents than in 80 residents of the control area, Kokpecty, which indicates the possibility that radiation had biological effects on the exposed subjects.     

Iodine-129 measurements in soil samples from Dolon village near the Semipalatinsk nuclear test site

Dolon village, located about 60 km from the border of the Semipalatinsk nuclear test site, is known to be heavily contaminated by the first USSR atomic bomb test in August 1949. Soil samples around Dolon were taken in October 2005 in an attempt to evaluate internal thyroid dose arising from incorporation of radioiodine isotopes (mainly (131)I). Iodine-129 in soil was measured by using the technique of accelerator mass spectrometry. The (129)I/(127)I atom ratios measured were in the range from 3.3 x 10(-9) to 3.3 x 10(-7). These values were within the range of the current background level ( approximately 10(-9) to 10(-7)) in the environment, including contributions from the global fallout of atmospheric nuclear tests and local fallout of nuclear facilities. The (129)I atom accumulated level in soil ranged from 1.28 x 10(13) to 1.59 x 10(14) atoms m(-2), the average (8.0 x 10(13)) of which was higher than the background level of (2-5) x 10(13). From the relationship between (129)I and( 137)Cs (corrected for background and decay from 1949 to 2005) accumulated levels, the background level of (129)I and the (129)I/(137)Cs ratio around Dolon were estimated to be (6.4 +/- 0.4) x 10(13) atoms m(-2) and 0.25 +/- 0.16, respectively. This (129)I/(137)Cs ratio is almost similar to the fission yield ratio for (239)Pu fast fission (0.24).     

Reconstruction of local fallout composition and gamma-ray exposure in a village contaminated by the first USSR nuclear test in the Semipalatinsk nuclear test site in Kazakhstan

After the disintegration of the USSR in end of 1991, it became possible for foreign scientists to visit Kazakhstan, in order to investigate the radiological consequences of nuclear explosions that had been conducted at the Semipalatinsk nuclear test site (SNTS). Since the first visit in 1994, our group has been continuing expeditions for soil sampling at various areas around SNTS. The current level of local fallout at SNTS was studied through γ-spectrometry for ¹³⁷Cs as well as α-spectrometry for ^239,240Pu. Average values of soil inventory from wide areas around SNTS were 3,500 and 3,700 Bq m^?2 for ¹³⁷Cs and ^239,240Pu, respectively, as of January 1, 2000. The average level of ¹³⁷Cs is comparable to that in Japan due to global fallout, while the level of ^239,240Pu is several tens of times larger than that in Japan. Areas of strong contamination were found along the trajectories of radioactive fallout, information on which was declassified after the collapse of the USSR. Our recent efforts of soil sampling were concentrated on the area around the Dolon village heavily affected by the radioactive plume from the first USSR atomic bomb test in 1949 and located 110 km east from ground zero of the explosion. Using soil inventory data, retrospective dosimetry was attempted by reconstructing γ-ray exposure from fission product nuclides deposited on the ground. Adopting representative parameters for the initial ¹³⁷Cs deposition (13 kBq m^?2), the refractory/volatile deposition ratio (3.8) and the plume arrival time after explosion (2.5 h), an absorbed dose in air of 600 mGy was obtained for the 1-year cumulative dose in Dolon village, due to the first bomb test in 1949. Considering possible ranges of the parameters, 350 and 910 mGy were estimated for high and low cases of γ-ray dose in air, respectively. It was encouraging that the deduced value was consistent with other estimations using thermal luminescence and archived monitoring data. The present method can be applied to other settlements affected by local fallout from SNTS.     

Study of the cytogenetic effects of occupational exposure to pesticides on sanitation workers in Belo Horizonte, Brazil

Sanitation workers handling pesticides in the control of disease vectors constitute an occupationally exposed population to genotoxic substances. The aim of the present study was to investigate the relation between the occupational exposure to various pesticides and the presence of cytogenetic damage. Fifty-nine men were selected (29 sanitation workers and 30 control individuals) with ages varying between 18-57 years who lived and worked in the same area in Belo Horizonte (Brazil). The following parameters were determined for all individuals using the cytokinesis-block micronucleus (MN) assay in peripheral blood lymphocytes: MN/1000 binucleated cells (BC), BC with MN (BCMN)/1000 BC, nucleoplasmic bridges (NB)/1000 BC, apoptotic and necrotic cells/500 cells and nuclear division index. The analysis of covariance showed significantly higher (p < 0.05) mean frequencies of MN (15.81 +/- 1.31 vs 4.71 +/- 0.42), BCMN (15.10 +/- 1.22 vs 4.62 +/- 0.44), NB (4.59 +/- 0.76 vs 1.00 +/- 0.34), and necrotic cells (12.07 +/- 1.45 vs 5.17 +/- 0.70) in the exposed group when compared to the control group. There was no significant difference in the apoptotic cell frequency between the two groups, while the nuclear division index was significantly lower (1.49 +/- 0.02 vs 1.61 +/- 0.02) in the control group. Neither the time of exposure nor the smoking or alcohol drinking habit influenced the cytogenetic parameters examined. According to these results, occupational exposure to pesticides induced genotoxic and cytotoxic effects in sanitation workers.     

The problem of the transgeneration phenomenon of genome instability in sick children of different age groups after the accident at the Chernobyl Nuclear Power Plant

A complex genetic examination of children which belong to two cohorts and their parents were carried out. The first cohort included children and constantly living on territories contaminated with radionuclides (Novozybkov district, Bryansk region). They were subdivided in groups according to the ontogenetic age periods of development of their parents at the time of the Chernobyl accident. In the children born in 1986-1995 the level of aberrant genomes is significantly higher as compared to the control (p < 0.001). In children born in 1998-2002 the differences are insignificant (p > 0.05). The frequency of aberrant genomes had a tendency to decrease with the period of time between the birth date of a child and the moment of the accident. Analysis of the results of cytogenetic investigation for the same living on territories with different densities of radioactive contamination (zone I-- 627-688 kBq/m2, 137Cs and zone II-- 135-402 kBq/m2, 137Cs) revealed insignificant differences in the spectrum and average frequencies of chromosome aberrations. The second cohort included children born in 1987-1991 and 1993-2002 from irradiated fathers (Chernobyl clean-up workers) and unirradiated mothers living on territories without radionuclide contamination. These children also displayed increased frequencies of aberrant genomes as compared to the control (p < 0.001). The analysis of the dynamics years of birth of cytogenetic disturbances in the same cohorts of children showed the average frequencies of aberrant genomes remain higher than the control level. In most of the children of both cohorts the repair synthesis of genome DNA by gamma- and UV-radiation is reduced as compared to one in the children from the control group.     

Polymix breeding with parental analysis of progeny: an alternative to full-sib breeding and testing

Implementation of most traditional full-sib crossing and testing designs is logistically difficult, costly, and genetic gain is constrained by resource availability. An alternative to full-sib crossing and testing can ameliorate all these constraints. The alternative solution is to apply a pollen mix (PMX) of many male parents rather than a single pollen for each cross. PMX breeding is easy to implement, ensures good estimates of breeding values of the parent being pollinated, and provides for increased genetic gain opportunity because of the significantly increased number of effective parental combinations tested. However, PMX breeding has found limited use because inbreeding and pedigree control is lost. The development of relatively inexpensive molecular markers allows for the paternity analysis of progeny, thus allowing full pedigree control. We call this system PMX breeding with parental analysis (PMX/WPA). The feasibility of PMX/WPA was evaluated in a loblolly pine (Pinus taeda) third-generation population of 45 select individuals, among which there was considerable relatedness. All parental trees were genotyped at seven chloroplast and three nuclear microsatellite loci. Unique fingerprints were obtained for all 45 individuals, but unambiguous paternal determinations for progeny from a complete pollen mix would not be possible due largely to relatedness in the breeding population. The inclusion of more markers and/or the creation of polmixes and breeding groups that avoid relatedness would resolve this problem. Three PMX/WPA scenarios are described and compared with conventional full-sib breeding and testing systems: (1) paternity analysis of only the forward (next generation) selection candidates in each generation, (2) paternal genotyping of all progeny test individuals in PMX crosses and using those data to construct the effective full-sib crosses for statistical analysis, and (3) like #2 except mixing seed of the several PMX crosses for ease of greenhouse rearing and progeny testing and then doing maternal and paternal analysis. Received: 27 October 2000 / Accepted: 5 March 2001     

A registry for exposure and population health in the Altai region affected by fallout from the Semipalatinsk nuclear test site

A registry of the rural population in the Altai region exposed to fallout from nuclear tests at the Semipalatinsk test site (STS) was established more than four decades after the first Soviet nuclear explosion on August 29, 1949. Information about individuals living in an exposed and a control area was collected using all available local sources, such as kolkhoz documentation, school registries, medical treatment records and interviews with residents. As a result, a database comprising an exposed group of 39 179 individuals from 53 Altai region villages, 6769 external and 3303 internal controls was compiled. For several settlements, effective dose estimates reached the level of 1.5 Sv, while the average effective dose estimate in the exposed group was 340 mSv. Dosimetric data, vital status information and health records gathered at rayon and village medical facilities are held in the registry. Cause-of-death information for deceased residents is obtained from death registration forms archived at the Altai region vital statistics office. At present, a follow-up of approximately 40% of the population exposed in 1949 has been done. More will be added by searching for migrants to the larger towns of the Altai region, i.e. Barnaul, Rubtsovsk and Biisk. In order to assess the influence of radiation exposure, analytical studies with a case-control design for stomach and lung cancer are currently being prepared. The number of known cases is sufficient to detect an odds ratio of 1.5 at the 95% confidence level. Epidemiological studies in populations affected by fallout from STS may be equally important to the atomic bomb survivors’ study for the direct quantification of radiation effects. The range of exposure rates experienced will extend the acute high-dose-rate findings from Hiroshima/Nagasaki towards acute and protracted lower exposures, which are more relevant for radiation protection issues. Received: 3 March 1999 / Accepted in revised form: 8 June 1999     

Ecological and Social Determinants of Group Cohesiveness and Within‐Group Spatial Position in Wild Assamese Macaques

Individual spatial positioning plays an important role in mediating the costs and benefits of group living and, as such, shapes different aspects of animal social systems including group structure and cohesiveness. Here, we aim to quantify variation in individual spacing behaviour and its correlates in a group of wild Assamese macaques (Macaca assamensis) in north‐eastern Thailand, which experiences both predation pressure and within‐group feeding competition. Data on individual spatial positions were collected during group scans using GPS devices and results suggest that both group cohesiveness and individual spatial positions within a group can be adjusted to mediate the costs and benefits of group living. Individuals had greater nearest neighbour distances and lower numbers of close neighbours when the group was feeding, compared to when the main group activity was resting/social or moving. This is likely due to the high costs of proximity associated with feeding competition. Immature individuals and females with young infants which are more vulnerable to predation were located closer to the centre of the group than both adult males and females without infants. This indicates the importance of predation risk in driving individual spatial position. Among adults, higher ranking individuals occupied more central positions within the group while lower ranking individuals were more peripheral. It appears that low ranking individuals trade reduced feeding interference and improved feeding success for increased predation risk. This could help explain why females in the study population do not display a rank related skew in energy intake.     

The effect of supplementary feeding upon the sizes of the home ranges of woodmice Apodemus sylvaticus living on a system of maritime sand-dunes

The woodmouse is primarily a woodland species but it also occurs on maritime sand-dunes. The home ranges of mice living on the sand-dunes are much larger than those of animals living in woodlands. Here we test the hypothesis that this difference is due to the fact that woodland provides substantially more food than do sand-dunes. Our experimental approach was to provide supplementary food in the form of wheatgrain to a sand-dune population and to compare range sizes with a control population. Range sizes on the supplemented area were significantly smaller than the controls and essentially similar to those of woodmice living in deciduous woodland.     

Chromosome aberrations and urinary thioethers in smokers

Chromosome aberrations, classified as chromosome- and chromatid-type aberrations, were evaluated in 94 individuals. The concentration of thioethers in the urine was also determined. The sample consisted of 41 non-smokers (control group) and 53 smokers, 25 smoked 10-20 cigarettes/day (subgroup IIA) and 28 smoked more than 20 cigarettes/day (subgroup IIB). Our aim was to perform internal dosimetry on smokers using a cytogenetic test, and a test for urinary excretion of thioethers, in order to determine the relation between these 2 methods of dosimetry. Our results show a higher frequency of chromosome aberrations (p less than 0.0001) and a higher excretion of urinary thioethers (p less than 0.0001) in smokers as compared to non-smokers. However, linear regression between these parameters was not statistically significant. In view of the variation between different individuals with regard to the amount of urinary thioethers, it seems more accurate to perform the biomonitoring of smoking by analyzing chromosome aberrations.     

Mortality in the offspring of individuals living along the radioactively contaminated Techa River: a descriptive analysis

From 1949 onwards, radioactive waste was released into the Techa River in the southern Urals and the population living along the river was exposed to ionising radiation. Relocation of these people did not start until several years later, causing many individuals to be exposed to substantial doses from internal and external radiation. The identification and follow-up of the exposed individuals started more than 40 years ago and is still continuing. The Techa River offspring cohort (TROC) that has recently been established, comprises 10,459 children born to at least one parent living along the Techa River during the period 1950-1992. Of these children, 3,897 were born during the period of highest release, i.e. between 1950 and 1956 and might thus have been exposed in utero. A total of 1,103 individuals have since died mainly due to infectious and respiratory diseases, injury and poisoning. Only 25 cases were identified as having died of a malignant condition. The radioactive contamination of the Techa River in the southern Urals gives a unique possibility to study the adverse effects of protracted exposure to ionising radiation in a large well-described cohort. The Techa River offspring cohort will make it possible to study the effects on those exposed in utero or early in life and the follow-up of the cohort in the future is, therefore, of great importance. Comparisons with other cohorts of humans exposed early in life, will increase our knowledge in this field of research.     

Stable chromosome aberrations in the lymphocytes of a population living in the vicinity of the Semipalatinsk nuclear test site

SalomaTranslocation analysis using FISH (fluorescence in situ hybridization) chromosome painting was performed to evaluate the magnitude of exposure to ionizing radiation among the human population living close to the Semipalatinsk nuclear test site in Kazakhstan. We studied two generations of people living in villages that were in the path of the radioactive cloud from the first Soviet surface nuclear test performed in August 1949 and from later tests. The older generation (P(0)) lived in the area at the time of testing, and the younger generation (F(1)) was exposed to smaller doses from the residual fallout and later tests. In both P(0) and F(1) generations, similar translocation frequencies were observed in persons living in either the Semipalatinsk area or a noncontaminated area. Assuming translocation stability in peripheral blood lymphocytes over several decades, these findings suggest that on average, the magnitude of exposure of this cohort in the Semipalatinsk area has been considerably smaller than that reported in the literature. Previously reported doses of the order of 1-4.5 Gy (mean 2.9 Gy in the P(0) generation) cannot be confirmed by the present data.     

粤北和粤东北若干珍稀濒危野生植物的种群特征

在2000～2007年间野外调查的基础上,用核实法或样方法研究了粤北和粤东北部分山区15个县市的珍稀濒危保护野生植物,计31科40属48种.重点介绍了有新分布区或呈群落状分布的7种植物的种群大小、植株高度、年龄结构等主要特征.其中在平远新发现10株仙湖苏铁野生植株;伯乐树在连州的种群数量达160株,以幼苗为主;在仁化篦子三尖杉达300株;平远半枫荷有100株;任豆新见于清新和始兴,数量1000株以上;和平、河源和蕉岭发现苏铁蕨种群,合计数百株;始兴新发现57株银鹊树.最后分析了这些珍稀濒危植物的濒危等级和致危因素,提出了相应的保护管理策略.     

Comparative study of the prevalence of maxillary sinusitis in later Medieval urban and rural populations in Northern England

Six hundred sixty-three Medieval individuals from Wharram Percy, a rural settlement in the Yorkshire Wolds, and 1,042 individuals from St. Helen-on-the-Walls, a poor parish in the Medieval city of York, were examined in order to test the hypothesis that maxillary sinusitis would be more prevalent in an urban population due to social and environmental conditions characteristic of an industrialized settlement. The results showed that the individuals from St. Helen-on-the-Walls, living in the urban environment, had a greater prevalence of maxillary sinusitis than the rural population; 39% (106) of the individuals from Wharram Percy had evidence of sinusitis compared to 55% (134) of the individuals from St. Helen-on-the-Walls. It is suggested that this pattern may be attributed to occupation and industrial air pollution in the Medieval city of York. © 1995 Wiley-Liss, Inc.     

Population monitoring: experience with residents exposed to uranium mining/milling waste

More emphasis should be placed upon using biomarkers to address potential health risk among populations exposed to high concentrations of environmental toxicants. Among these studies, those which integrate exposure measurements with analyses of validated biomarkers may provide more reliable information for risk assessment and disease prevention. We have used a multidisciplinary approach to elucidate potential health hazards in a population living around uranium mining/milling facilities. The study included 24 target and 24 control residents who were matched for age and gender and selected based on time of residence in the study areas and proximity to mining/milling sites. Environmental samples were analyzed for uranium-238 concentrations and lead isotope ratios using inductively coupled plasma-mass spectrometry (ICP-MS) procedures, and blood samples were collected for cytogenetic analysis. We found that the concentrations in soil samples were significantly higher than those in the control areas. In addition, the concentrations in the surface soil were significantly higher than in the subsurface soil (p<0.05) from target areas indicating environmental contamination by the mining/milling activities. Lead isotope data from soil samples taken near a railroad transfer location was significantly different from those of other sites, indicating contamination by non-native ore transported from sources outside of the region to local milling facilities for processing. Therefore, local residents have been exposed to low levels of radioactive contamination from the mining/milling activities on a daily basis for many years. From our cytogenetic analysis, the target population had more chromosome aberrations than the controls, although the differences were not significant (p<0.05). However, using our challenge assay, cells from the target population had a significantly abnormal DNA repair response, compared to cells from the same control population. In conclusion, the observed environmental contamination by uranium is consistent with the observed genotoxic effects in the target residents. Therefore, the residents have increased health risk and some of the health problems will most likely be related to exposure to the radioactive contaminants. Since the chromosome aberration frequency revealed increased, but not significant differences between the exposed and the control populations, we conclude that the health risk among the exposed residents is similar to those among nuclear workers.     

Complex cytogenetic characteristic of people suffered from Chernobyl accident

A cytogenetic study was performed on Chernobyl cleanup workers, on their children, on persons evacuated from contaminated aeria (adult and children), on so named "veterans of particular risk" irradiated due to the accidents on the nuclear plant, testing of nuclear weapons etc. and on control donors. The yield of stable (FISH analysis) and of unstable chromosome aberrations, micronuclei in both lymphocytes and erythrocytes, HPRT mutations was found to be increased in exposed groups as compared to control ones. In children of liquidators and in evacuated children we observed genomic instability and increased in vitro chromosomal radiosensitivity. Acceleration of age accumulation of translocations characterized the exposed population in comparison with control group. People with the highest level of routine chromosome aberrations had cardiovascular and digestive diseases more often likely than those with the lowest level. In frame of International Project ECP-6--"Biological dosimetry" the dose-responses for dicentrics and translocations were constructed in dose range 0-100 cGy of gamma-irradiation on the base of data of 8 laboratories. On cancer patients undergone whole-body gamma-irradiation (every day at the dose 11.5 cGy to a total of dose 57.5 cGy) we constructed the dose-responses for the dicentrics and translocations and compared them with the dose-responses for these aberrations after the in vitro irradiation of lymphocytes of the same patients. For the dicentrics the effectiveness of the in vivo irradiation was less than of the in vitro one. No differences were found for translocations.     

Kinship ecology of competition: size hierarchies in kin and nonkin laboratory cohorts of tadpoles

Summary This study provides an experimental test of the ecological significance of kinship in competitive interactions among individuals. Tadpoles of the fire-bellied toad, Bombina variegata (Anura, Discoglossidae) reared in the laboratory in a high density of siblings grew better and developed faster than when they were reared with similar densities of nonrelatives. Kinship-based genotypic uniformity may therefore be advantageous: it can lead to faster and more uniform growth. In nature it may well be kin recognition that permits such advantage to be realised. The largest tadpoles from pure-sibship cohorts accounted, on average, for the smaller fraction of the cohort total biomass than the largest tadpoles reared with cohorts of nonrelatives, although they attained the same absolute weight and developmental stage. The smallest individuals from pure-sibship cohorts had a much larger absolute body weight than the smallest tadpoles from mixed-sibship cohorts, and were also much more advanced developmentally. The results could be an effect of an altruistic restraint in growth rate on the part of the largest tadpoles in sibling cohorts and certainly not of the smallest ones. However, the results could also be due to the altruism-independent facilitation of living conditions in pure-sibship groups, resulting solely from potential advantages of homogeneous water conditioning.     

When a Duck Initiates Movement,Do Others Follow? Testing Preference in Groups

Choice tests have been widely used to assess animal preferences. In the case of group‐living species, these tests are commonly presented to animals in groups, because isolation can have strong effects on behaviour and motivation. However, assessing preference at the group level could be misleading if strong control of movement, through influential individuals, and group cohesion were present. The needs of majority of the population might not be properly represented by the test results. The current study investigated whether or not groups of ducks (four ducklings per group) have individuals that consistently initiate movement and considered the implications for group cohesion, synchronisation and a measure of preference during a choice test. In all groups included in the analyses, there were ducks that initiated more movements than the rest, and this trend was stronger when leading towards areas providing resources such as pools. Also, more ducks preferentially followed the first initiator (birds initiating most movements within a group) into the bathing area. Group cohesion was higher in groups that frequently had the same individual initiating movement. The number of followers following the ducks that initiated most movements was associated with the measure of preference (time spent at preferred area, as a proportion of total time spent at any area) but the number of movements initiated by these individuals was not. These results highlight the need to consider the effects of initiators and group‐cohesive forces when conducting choice tests in groups of animals.     

Socioeconomic predictors of suicide risk among cancer patients in the United States: A population-based study

ObjectiveTo assess the socioeconomic predictors of suicide risk among cancer patients in the United States.MethodsCancer patients available within Surveillance, Epidemiology and End Results (SEER) database who were diagnosed between 2000–2010 have been reviewed. Linkage analysis to Census 2000 SF files was conducted to determine area-based socioeconomic attributes. Observed/ Expected ratios were calculated for the overall cohort as well as for clinically and socioeconomically defined subgroups. “Observed” is the number of observed completed suicide cases in the studied cohort; while “Expected” is the number of completed suicide cases in a demographically similar cohort within the United States and within the same period of time.ResultsThe current study reviews a total of 3,149,235 cancer patients (diagnosed 2000–2010) within the SEER database. Regarding socioeconomic county attributes, higher risk of suicide seems to be associated with lower educational attainment (O/E for counties with > 20% individuals with less than high school education: 1.41; 95% CI: 1.35–1.47), poverty rates (O/E for counties with > 5% individuals below poverty line: 1.39; 95% CI: 1.34–1.43), unemployment rates (O/E for counties with >5% families below poverty line: 1.36; 95% CI: 1.31–1.41) and less people living in urban areas (O/E for counties with < 50% individuals living in urban areas: 1.63; 95% CI: 1.50–1.77). On the other hand, risk of suicide seems to be inversely related to a higher representation of foreign-born individuals (O/E for counties with < 5% foreign-born individuals: 1.56; 95% CI: 1.47–1.65); and inversely related to a higher representation with recent immigrants to the US (O/E for counties with < 5% recent immigrants: 1.33; 95% CI: 1.29–1.38).ConclusionsCancer patients living in a socioeconomically vulnerable environment (lower educational status, poverty, and unemployment) seem to have higher suicide risk compared to other cancer patients.     

Cytogenetic analysis of peripheral blood lymphocytes in workers exposed to benzene

In the present study, the method of cytogenetic analysis of peripheral blood lymphocytes was used to investigate 66 workers exposed to benzene, and 20 individuals selected from general population from the same locality, not exposed to particular mutagenic or carcinogenic agents (control group). Altogether, 8,600 metaphases were analysed. Frequencies of aberrant cells, including chromatide and chromosomal breaks, and chromatide and chromosomal exchanges, were scored in both groups. A very slight increase in aberrant cell frequencies (2.152% aberrant cells) was observed in the professional exposure group as compared to the control group (1.6% aberrant cells). Increased frequencies of aberrant cells were found in smokers of both the benzene-exposed and the control group. The differences were however not significant. In addition to cytogenetic examination, the workers underwent a general examination of their health condition (preventive examination). Benzene exposure seemed to have no injurious effect on the state of health of exposed workers. Biochemical and haematological tests gave normal values.