Health effects from chronic low-level exposure to hydrogen sulfide.

The acute toxic effects of hydrogen sulfide have been known for decades. However, studies investigating the adverse health effects from chronic, low-level exposure to this chemical are limited. In this study, the authors compared symptoms of adverse health effects, reported by residents of two communities exposed mainly to chronic, low-levels of industrial sources of hydrogen sulfide, to health effects reported by residents in three reference communities in which there were no known industrial sources of hydrogen sulfide. Trained interviewers used a specially created, menu-driven computer questionnaire to conduct a multi-symptom health survey. The data-collection process and questions were essentially the same in the reference and exposed communities. The two exposed communities responded very similarly to questions about the major categories. When the authors compared responses of the exposed communities with those of the reference communities, 9 of the 12 symptom categories had iterated odds ratios greater than 3.0. The symptoms related to the central nervous system had the highest iterated odds ratio (i.e., 12.7; 95% confidence interval = 7.59, 22.09), followed by the respiratory category (odds ratio = 11.92; 95% confidence interval = 6.03, 25.72), and the blood category (odds ratio = 8.07; 95% confidence interval = 3.64, 21.18). Within the broader health categories, individual symptoms were also elevated significantly. This study, like all community-based studies, had several inherent limitations. Limitations, and the procedures the authors used to minimize their effects on the study outcomes, are discussed. The results of this study emphasize the need for further studies on the adverse health effects related to long-term, chronic exposure to hydrogen sulfide.

Cytogenetic effects from exposure to mixed pesticides and the influence from genetic susceptibility.

Exposure to pesticides remains a major environmental health problem. Health risk from such exposure needs to be more precisely understood. We conducted three different cytogenetic assays to elucidate the biological effects of exposure to mixed pesticides in 20 Costa Rica farmers (all nonsmokers) compared with 20 matched controls. The farmers were also exposed to dibromochloropropane during the early employment years, and most of them experienced sterility/fertility problems. Our data show that the farmers had consistently higher frequencies of chromosome aberrations, as determined by the standard chromosome aberration assay, and significantly abnormal DNA repair responses (p < 0.05), as determined by the challenge assay, but no statistically significant differences in the tandem-probe fluorescence in situ hybridization (FISH) assay (p > 0.05). Genotype analysis indicates that farmers with certain "unfavorable" versions of polymorphic metabolizing genes (cytochrome P4502E1, the glutathione S-transferases mu and theta, and the paraoxonase genes) had significantly more biological effects, as determined by all three cytogenetic assays, than both the farmers with the "favorable" alleles and the matched controls. A unique observation is that, in individuals who had inherited any of the mentioned "unfavorable" alleles, farmers were consistently underrepresented. In conclusion, the Costa Rican farmers were exposed to genotoxic agents, most likely pesticides, which expressed the induction of biological and adverse health effects. The farmers who had inherited "unfavorable" metabolizing alleles were more susceptible to genotoxic effects than those with "favorable" alleles. Our genotype data suggest that the well-recognized "healthy worker effect" may be influenced by unrecognized occupational selection pressure against genetically susceptible individuals.

The health effects of living near cement kilns; a symptom survey in Midlothian, Texas.

Cement kilns are major sources of toxic air emissions. Regulations based on demonstrated concentrations of specific chemicals, and risk assessments with inherent limitations and uncertainties, are the current methods of preventing exposure to 'unsafe' emission levels. Monitoring data are frequently incomplete. These limitations mandate that residents residing near cement kilns be evaluated for adverse health effects. This study reports findings from a symptom survey conducted in Midlothian, Texas, which adds to the limited but growing body of knowledge showing that persons living near cement kilns are experiencing increased respiratory effects. This cross-sectional study uses randomized sampling and an extensive health questionnaire, covering 12 physiological systems, to determine differences in reported health symptoms between the study community (Midlothian, Texas, n = 58) and the reference community (Waxahachie, Texas, n = 54). Findings indicate significant elevations in reported respiratory symptoms in the study community (p-value 0.002). Although the comparatively small sample size is a limitation, the fact that only 'respiratory effects' were highly significant supports the efficacy of this investigation. Respiratory effects would be the major anticipated outcome from the known exposures under investigation. This specificity of response (i.e., elevation in respiratory symptoms only), indicates that 'response bias' was not a significant factor in this study.

Abnormal DNA repair activities in lymphocytes of workers exposed to 1,3-butadiene.

Exposure to high concentrations of butadiene has been shown to cause cancer among exposed workers. We have conducted a biomarker study to elucidate whether current butadiene exposure conditions are hazardous to workers. Twenty-four workers exposed consistently to butadiene were matched with 19 co-workers who had much less contact with butadiene and who served as our controls. In the standard cytogenetic assay, there was no difference in chromosome aberration frequencies between the exposed and control groups. In the challenge assay, the exposed group shows a consistent, but non-significant, increase in chromosome aberrations indicating some abnormality in DNA repair response. The observed dicentric frequency in the challenge assay (indicative of abnormal repair of damaged chromosomes) is significantly correlated with a butadiene metabolite, 1,2-dihydroxy-4-(N-acetylcysteinyl)butane, in urine (r = 0.52; p = 0.04). Furthermore, cigarette smokers had consistently abnormal repair response compared with non-smokers for both the control and exposed groups. A small subset of the studied workers were evaluated for toxicant-induced DNA repair deficiency using an independent cat-host cell reactivation (CAT-HCR) assay. When cigarette smokers and non-smokers were combined in our analysis, we observed that the exposed group (n = 9) had a significant reduction of DNA repair activities (p = 0.009) compared with the control group (n = 6). Cigarette smoking contributed significantly to the effect as exposed smokers (n = 4) had a significant reduction in DNA repair activities (p = 0.04) compared with exposed non-smokers. The results from the two independently conducted assays support each other and confirm the previously reported abnormal DNA repair response in another group of butadiene workers. In conclusion, our data indicates that exposure to environmental toxicants, such as butadiene, can cause DNA repair defects. Therefore, the current butadiene exposure conditions are still hazardous to workers. However, our data indicates that butadiene is not a potent genotoxic agent. Furthermore, the butadiene-induced effect is significantly enhanced by the cigarette smoking habit.

Two-color ratio-coding of chromosome targets in fluorescence in situ hybridization: quantitative analysis and reproducibility.

Ratio coding in fluorescence in situ hybridizations has the potential to identify more DNA and RNA targets simultaneously using fewer fluorescent labels than other multi-color techniques. Ratio coding uses hybridization probes containing different proportions of two or more distinguishable labels to stain each target. In order to better define the limits of ratio coding applied to chromosome detection, we have 1) examined methods of processing electronic images of ratio-coded hybridizations to increase our ability to visually and quantitatively distinguish different stained targets and 2) examined the reproducibility of target identification. A number of hybridizations were performed using eight ratios of two fluorescent labels to identify whole chromosomes in metaphase spreads, and using five ratios of two labels on repetitive sequence probes to identify chromosomes in metaphase spreads and interphase nuclei. Greater visual discrimination was afforded by color composite images which expanded the color range across the entire visual spectrum. Quantitative ratio measurements on 25 metaphase spreads predicted that eight different chromosomes can be identified simultaneously with 96% accuracy using whole chromosome probes. Analysis of a smaller data set predicted that six different chromosomes can be identified with 97% accuracy using repetitive sequence probes.

Biological monitoring for mutagenic effects of occupational exposure to butadiene.

The use of biological markers in the evaluation of human exposure to hazardous agents has increased rapidly in recent years. Because 1,3-butadiene is a mutagenic carcinogen, existing occupational levels of exposure may be appropriately evaluated using somatic cell mutation as a biomarker. Previously, we have described a biomarker study of workers in a butadiene monomer plant (Ward et al., 1994). We now report results from a second study of the same group of workers, conducted after plant modernization, and present preliminary results from a study of exposures in a styrene butadiene rubber (SBR) plant. Air levels of butadiene were determined using either charcoal tubes with air pumps or passive badge dosimeters. The quantity of a butadiene metabolite in the urine was used as a biomarker of exposure and the mutagenic effects of exposure were measured using the autoradiographic hprt mutant lymphocyte assay. In all three studies, the frequencies of hprt mutants were significantly elevated in workers from the areas of highest exposure when compared to workers from lower exposure areas or non-exposed subjects. The concentration of the urinary metabolite was significantly increased in high-exposed workers in the first study of monomer plant workers but not in the second. In the first monomer plant study, historical air concentrations of butadiene were higher in the production units than in the central control unit. While concurrent determined air concentrations were not elevated in the second monomer plant study, they were elevated in high exposure areas in the SBR plant study. Mutant frequencies in the lower-exposure and the non-exposed groups were consistent with historical values for non-smoking individuals who were not exposed to known mutagens. The use of biomarkers, including the hprt mutant lymphocyte assay, may be of great value in determining an appropriate occupational exposure limit for butadiene.

Chromosome damage and DNA repair response in lymphocytes of women who had children with neural tube defects.

Mothers who resided in Brownsville, Texas and who had children with neural tube defects (NTD) were studied to determine whether exposure to environmental mutagens may be a cause of abnormal reproductive outcomes. Peripheral blood lymphocytes from 19 of the mothers who had children with NTD and from 14 matched mothers who had normal children and who resided in Corpus Christ. Texas were investigated using the standard cytogenetic assay and a challenge assay to determine the existence of chromosome aberrations and abnormal DNA repair response. No differences were observed when the spontaneous and the challenged chromosome aberration frequencies were compared between the core and the control groups. Our data suggests that the core group was not exposed to mutagens at levels to cause significant increases of chromosome aberrations or to cause abnormal DNA repair response as determined by our assays. However, exposure to non-mutagenic environmental teratogens cannot be ruled out.

Monitoring populations for DNA repair deficiency and for cancer susceptibility.

The induction of a mutator phenotype has been hypothesized to cause the accumulation of multiple mutations in the development of cancer. Recent evidence suggests that the mutator phenotype is associated with DNA repair deficiencies. We have been using a challenge assay to study exposed populations to test our hypothesis that exposure to environmental toxicants induce DNA repair deficiency in somatic cells. In this assay, lymphocytes were irradiated in vitro to challenge cells to repair the radiation-induction DNA strand breaks. An increase of chromosome aberrations in the challenged cells from toxicant-exposed populations compared to nonexposed populations is used to indicate abnormal DNA repair response. From studies of cigarette smokers, butadiene-exposed workers, and uranium-exposed residents, the assay showed that these exposed populations had mutagen-induced abnormal DNA repair response. The phenomenon was also demonstrated using experimental animals. Mice were exposed in vivo to two different doses of N-methyl-N'-nitro-N-nitroso-guanidine (MNNG) and their lymphocytes were challenged with one dose of a radiomimetic chemical, bleomycin, in vitro. These challenged lymphocytes showed an MNNG dose-dependent increase of abnormal DNA repair response. In a population that was potentially exposed to teratogens--mothers having children with neural tube defects--lymphocytes from these mothers did not have the abnormal response in our assay. In studies with patients, we reported that lymphocytes from Down's syndrome patients have the abnormal DNA repair response. Lymphocytes from skin cancer-prone patients (epidermodysplasia verruciformis) have normal response to gamma-ray challenge but abnormal response to UV-light challenge. These patient studies also indicate that the challenge assay is useful in documenting the radiosensitivity of Down's syndrome and the UV sensitivity in EV patients. In most cases, the challenge assay is more sensitive in detecting biological effects than the standard chromosome aberration assay. Our series of studies indicates that the challenge assay can be used to document biological effects from exposure to mutagens and that the effect is an abnormal DNA repair response. This abnormality can increase the risk for development of cancer. The repair deficiency is currently being validated using a plasmid transfection (host-reactivation) assay. The need to integrate chromosome aberration and the challenge assays with other relevant assays for better documentation of biological effects and for more precise prediction of health risk will be presented. Our experience in using genetic polymorphism and host-reactivation assays will be discussed.

Fluorescence in situ hybridization: powerful molecular tool for cancer prognosis.

We review several aspects of fluorescence in situ hybridization (FISH) technology that demonstrate its breadth and power in detecting and monitoring genetic abnormalities associated with cancers. The clinical utility of FISH in disease management is demonstrated in several examples, including trisomy 8 detection with high specificity and sensitivity in patients with myeloid leukemias; trisomy 12 detection with higher efficiency than conventional cytogenetics in patients with chronic lymphocytic leukemia; assessment of engraftment success, chimerism, and relapse in opposite sex bone marrow transplantation; and correlation of trisomy 7 with survival time in patients with prostate tumors. Advances in FISH technology include multicolor analyses, which permit the simultaneous detection of several genetic abnormalities by using cohybridization of probes labeled with several fluorescent labels or label combinations, and comparative genomic hybridization, a relatively new method whereby a single hybridization can reveal aberrations across the entire genome.

Biomarker monitoring of a population residing near uranium mining activities.

We investigated whether residents residing near uranium mining operations (target population), who are potentially exposed to toxicants from mining waste, have increased genotoxic effects compared with people residing elsewhere (reference population). Population surveys were conducted, and 24 target and 24 reference residents were selected. The selected subjects and controls were matched on age and gender and they were nonsmokers. Blood samples were collected for laboratory studies. The standard cytogenetic assay was used to determine chromosome aberration frequencies, and the challenge assay was used to investigate DNA repair responses. We found that individuals who resided near uranium mining operations had a higher mean frequency of cells with chromosome aberrations and higher deletion frequency but lower dicentric frequency than the reference group, although the difference was not statistically significant. After cells were challenged by exposure to gamma-rays, the target population had a significantly higher frequency of cells with chromosome aberrations and deletion frequency than the reference group. The latter observation is indicative of abnormal DNA repair response in the target population.

Chromosome aberrations and response to gamma-ray challenge in lymphocytes of workers exposed to 1,3-butadiene.

An integrated population monitoring study was initiated to investigate whether occupational exposure to current low levels of butadiene is mutagenic to workers. Ten exposed workers (mean production area concentration of 3.5 ppm) and 10 matched plant controls (mean exposure to 0.03 ppm) were selected and blood samples were collected for our study. The standard cytogenetic assay was used to determine chromosome aberration frequencies. In addition, a challenge assay was used to determine response to gamma-rays as an indication of DNA repair deficiencies. In the latter assay, cells were exposed to gamma-rays at the G1 phase of the cell cycle in vitro and the frequencies of chromosome aberrations in the first post-irradiation metaphase cells were quantitated. Based on results of the cytogenetic assay, the exposed group had a higher frequency of cells with chromosome aberrations and higher chromatid breaks per 100 cells compared with the control. However, the difference was not significant (p > 0.1). With the challenge assay, the exposed group had a higher frequency of aberrant cells (p < 0.04), chromatid breaks (p < 0.05), deletions (p < 0.07), and dicentrics (p < 0.02) than the controls. In addition, the dicentric frequencies from workers were significantly correlated with the presence of a butadiene metabolite [1,2-dihydroxy-4-(N-acetylcysteinyl-S)butane] in urine with a correlation of coefficient of 0.6 (p < 0.01). Two outliers were identified and our interpretation of their responses will be discussed. This study indicates that the workers had exposure-induced mutagenic effects. Together with the observation of gene mutation in a subset of the present population, this study indicates that the current occupational exposure to butadiene may not be safe to workers.

Application of integrated genetic monitoring: the optimal approach for detecting environmental carcinogens.

Short-term in vitro genetic toxicity assays have not fulfilled their anticipated role in predicting the carcinogenicity of environmental agents reliably and economically. A reduction in emphasis from nonanimal systems to relevant animal assays and population monitoring will help to reestablish the credibility of this field. An analysis of the various steps in the carcinogenic process indicates the biological responses occurring during these stages can be utilized for early detection of environmental carcinogens. Emphasis should be placed on using the earliest significant response that indicates genetic damage (e.g., gene mutations and chromosome alterations). Assays that detect pregenomic damage (e.g., adduct formation), without evidence of subsequent heritable genetic alterations, may produce misleading results for risk assessment and should not be considered as stand-alone monitoring procedures. Late biological responses may occur in tissues or organs where genetic damage may be difficult to measure, and the opportunity for intervention diminishes as we approach the clinical outcome. For example, analyzing localized cells that contain activated protooncogenes and inactivated tumor suppressor genes, although they further document adverse response from exposure to carcinogens, may be of greater value for indicating clinical outcome than for genetic monitoring. With few notable exceptions, the window of opportunity for genetic monitoring is the period after exposure where genetic damage is evident and where circulating lymphocytes can faithfully record this damage. An ongoing study of butadiene-exposed workers illustrates an optimum protocol, where multiple assays can be carried out and correlated with both external and internal measurements of exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

hprt mutant lymphocyte frequencies in workers at a 1,3-butadiene production plant.

1,3-Butadiene is a major industrial chemical that has been shown to be a carcinogen at multiple sites in mice and rats at concentrations as low as 6.25 ppm. Occupational exposures have been reduced in response to these findings, but it may not be possible to determine by using traditional epidemiological methods, whether current exposure levels are adequate for protection of worker health. However, it is possible to evaluate the biological significance of exposure to genotoxic chemicals at the time of exposure by measuring levels of genetic damage in exposed populations. We have conducted a pilot study to evaluate the effects of butadiene exposure on the frequencies of lymphocytes containing mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in workers in a butadiene production plant. At the same time, urine specimens from the same individuals were collected and evaluated for the presence of butadiene-specific metabolites. Eight workers from areas of the plant where the highest exposures to butadiene occur were compared to five workers from plant areas where butadiene exposures were low. In addition, six subjects with no occupational exposure to butadiene were also studied as outside controls. All of the subjects were nonsmokers. An air sampling survey conducted for 6 months, and ending about 3 months before the study, indicated that average butadiene levels in the air of the high-exposure areas were about 3.5 +/- 7.5 ppm. They were 0.03 +/- 0.03 ppm in the low-exposure areas. Peripheral blood lymphocytes from the subjects were assayed using an autoradiographic test for hprt mutations.(ABSTRACT TRUNCATED AT 250 WORDS)