Epidemiological study of endocrinological effects of carbon disulfide

How to Differentiate General Toxicity-Related Endocrine Effects from Endocrine Disruption: Systematic Review of Carbon Disulfide Data

This review provides an overview of the assessment of the endocrine disrupting (ED) properties of carbon disulfide (CS₂), following the methodology used at the European level to identify endocrine disruptors. Relevant in vitro, in vivo studies and human data are analyzed. The assessment presented here focuses on one endocrine activity, i.e., thyroid disruption, and two main adverse effects, neurotoxicity and cardiotoxicity. The data available on the different ED or non-ED modes of action (MoA), known to trigger these adverse effects, are described and the strength of evidence of the different MoA is weighted. We conclude that the adverse effects could be due to systemic toxicity rather than endocrine-mediated toxicity. This assessment illustrates the scientific and regulatory challenges in differentiating a specific endocrine disruption from an indirect endocrine effect resulting from a non-ED mediated systemic toxicity. This issue of evaluating the ED properties of highly toxic and reactive substances has been insufficiently developed by European guidance so far and needs to be further addressed. Finally, this example also raises questions about the capacity of the technics available in toxicology to address such a complex issue with certainty.

Occupational hazards to male fecundity

Research methods and knowledge in the field of male reproductive toxicology have gradually improved since reports in the late 1970s on severe impairment of spermatogenesis in workers with occupational exposure to certain chlorinated hydrocarbon pesticides (the nematocide 1,2-dibromochloropropan and the insecticide and fungicide chlordecone, but still we have only vague answers to basic questions about the overall significance of the environmental and occupational impact of these compounds on male reproductive capability.

Lack of Relationship between Occupational Exposure to Carbon Disulfide and Endocrine Dysfunction: A Six‐year Cohort Study of the Japanese Rayon Workers

OBJECTIVES

A six-year prospective cohort study was conducted to clarify whether the current carbon disulfide (CS2) exposure level is low enough to prevent subclinical health impairment and/or to ameliorate health effects due to previous high exposure. This paper describes the follow-up results, exposure assessment, and effects on the endocrine system.

METHODS

The study subjects were 432 male workers exposed to CS2 at one of the 11 rayon factories in Japan and 402 referent workers from the same factories, all of whom were examined in 1992-93. 251 CS2-exposed, 140 former-exposed and 359 referent workers participated in the follow-up survey (follow-up rate 89.9%) in 1998-99. Urinary 2-thiothiazolidine-4-carboxylic acid (TTCA) at the end of a shift as internal exposure index and the time-weighted average CS2 concentration as external exposure index were measured twice a year from 1992-1993. By using various blood indices, we evaluated effects on thyroid, hypophysis, and gonad function, as well as effects on glucose metabolism. Information on potential confounding factors, such as age, smoking and alcohol drinking, were collected and adjusted for.

RESULTS

When the individual exposure level was represented by arithmetic mean for TTCA and CS2 concentration, geometric means (SD) of CS2 workers were 1.61 (1.91) mg/g.crea and 5.02 (1.84) ppm, respectively. There were no exposure-related differences in glucose metabolism or any of the endocrinological indices.

CONCLUSIONS

No biologically significant effects of CS2 were found on endocrine function in Japanese rayon manufacturing workers when the average internal and external exposure levels were maintained below the current occupational exposure limit.

How work-place conditions, environmental toxicants and lifestyle affect male reproductive function

Major temporal and geographical shifts in male reproductive function is presently an issue worldwide. The hormonal disruption hypothesis has achieved considerable attention but epidemiological evidence in support of the theory is lacking. Several occupational hazards to male reproductive function are known but exposure prevalences are hardly sufficient to play a role for reduced sperm count in the general male population. Sedentary work may be an exception. Perhaps prolonged time in the sedentary position exhausts the testicular heat regulation. But so far studies addressing implications of the heat hypothesis in the general population are few. Neither change of sexual behaviour nor reduced period of sexual continence seems to be a likely explanation. Tobacco smoking and consumption of caffeine and alcoholic beverages in adulthood have a rather marginal impact on spermatogenesis and can hardly explain major shifts or regional differences in male reproductive health. However, prenatal effects following smoking during pregnancy might play a role because we have witnessed a smoking epidemic among fertile women in some countries during the second half of the twentieth century. Moreover, if genetic factors play more than a marginal role for testicular function and sperm count, pregnancy planning resulting in reduced family size during the past 100 years could possibly explain a decline in semen quality because the most fertile part of the population reproduce less while the subfertile probably continue to get a limited number of children.

Cross-sectional study of the ophthalmological effects of carbon disulfide in Chinese viscose workers

This article presents cross-sectional investigation results of ophthalmological effects for the occupational exposure to carbon disulfide of workers at a large viscose fibre factory in the middle part of China. The total of 271 exposed subjects (191 males, 80 females) and 133 workers (93 males, 40 females) not exposed to any toxic agent in the working environment underwent ophthalmological examination. The self-administered questionnaire collected data on the medical history and ophthalmological complaints during the past three months. The ophthalmologic examination included routine examination for retinal capillary anomalies and and color vision with the FM 100-Hue test method. Nearly all subjects did not use respirators, smocks or aprons, gloves or other personal protective devices during work time. The average personal CS2 exposure level in the present study was 13.7-20.05 mg/m3. The FM 100-Hue test results showed that the total error scores of the exposed group, whether male or female, were higher than that of the control, the discrimination of the green and blue zones was also impaired significantly. A fundus examination showed no retinal capillary anomalies or other serious ophthalmological symptoms that may be related to effects of CS2. In conclusion, color vision was disturbed in workers exposed to CS2, at levels below the present threshold value. Reduced color discrimination may be attributed to long-term carbon disulfide exposure and suggests that health surveillance of workers exposed to carbon disulfide should include the FM 100-Hue Test as a sensitive and easy method.

Comparison of occupational exposure to carbon disulphide in a viscose rayon factory before and after technical adjustments

The objective of this follow-up study was to verify the efficacy of the technical adjustments gradually introduced in departments of a viscose rayon factory from 1989 onward. Personal exposure to carbon disulphide was assessed by means of personal monitoring through active sampling. Six job titles in three departments of the factory were sampled. Geometric means were calculated and used as estimates of time-weighted average (TWA) concentrations. The results from the present study were compared with similar measurements from a previous study in the same factory. Due to organizational changes, only three job titles (spinner, first spinner, and viscose preparator) could be compared directly. Two new job titles were identified, although tasks performed in these two job titles already existed. The measurements from one job title could not be compared, due to a substantial reorganization and automation of the tasks carried out in the department. The comparison before and after technical improvements shows that personal exposure of spinner and first spinner has been substantially reduced. Even the geometric means of measurements outside the fresh air mask are below the TWA-TLV (Threshold Limit Value). Despite the difficulties in comparing the results from the two studies, it is concluded that the technical measures reduced up to tenfold personal exposure to carbon disulphide and personal protection reduced it further by a factor two.

Candidate EPA, NIOSH method for determining carbon disulfide in air with capillary gas chromatography by orthogonal design

This paper describes a candidate NIOSH EPA method for the determination of carbon disulfide in the air of workplaces with capillary gas chromatography using an orthogonal design. This method is designed to replace the packed column of the NIOSH method with a capillary column. The first part of this work concerned the setup of the method, particularly the choice of chromatographic parameters and finding their main favorable working ranges. The second part, using the statistical method orthogonal design, focused on optimizing the GC conditions, which were: column temperature, T(c) = 90 degrees C; injector temperature, T(i) = 140 degrees C; U section detector temperature, FPDU = 160 degrees C; L section detector temperature, FPDL = 210 degrees C; flow rate of carrier gas, F(c) = 20 cm/s; split ratio = 1/70; and injection volume = 1 microL. The quality control test showed that the coefficient of intra-day variation (CV) was 2.21%. A good logarithm linear correlation between the standard solutions and their peak areas was obtained. In general, the method reported here seems a valid candidate for a NIOSH EPA method due to its high precision and accuracy.

Cross sectional observation of the effects of carbon disulphide on the nervous system, endocrine system, and subjective symptoms in rayon manufacturing workers

OBJECTIVES

A prospective cohort study was initiated to clarify whether the current level of exposure to carbon disulphide (CS2) is low enough to prevent occurrence of subclinical health impairments or to ameliorate health effects due to past high exposure. This paper describes the effects of exposure to CS2 on the nervous and endocrine systems, and the subjective symptoms in a baseline observation.

METHODS

The effects were evaluated of CS2 on the median nerve conduction velocity, neurobehavioural and psychological tests, and subjective symptoms related to solvents in 432 male workers exposed to CS2 and 402 reference workers from 11 rayon factories in Japan. Adjustment was made for potential confounding factors such as age or alcohol drinking. Exposure to CS2 was either dichotomised or categorised into three groups by job type.

RESULTS

Reductions were observed in motor (-1.9 m/s) and sensory (-0.91 m/s for orthodromic and -1.1 m/s for antidromic) nerve conduction velocities in the workers exposed to CS2 at the spinning and refining processes. Small but significant increases were found in self rated depression scale score and decrease in digit span (backward) in the workers exposed to CS2. Of 54 subjective symptoms many were increased--namely, heavy feeling in the head, light headedness, fainting after suddenly standing up, tremor, dullness, and increased sensitivity of skin in the extremities, reduced grasping power, reduced sexual desire, and increased rough skin. The endocrinological indicator--the concentration of glycosylated haemoglobin--was also increased in the workers exposed to CS2.

CONCLUSIONS

Subclinical effects on the nervous system and on glucose metabolism were found in the workers exposed to CS2. One interpretation is that relatively higher exposure to CS2 in the past may induce these, but the effects are still not entirely ameliorated under the current exposure to CS2. Another possibility is that the current exposure to CS2 may cause these positive findings. A follow up observation is necessary to clarify these questions.

Toxicology of male reproduction in animals and humans

Environmental contaminants can interfere with the male reproduction function. A review is presented of those pollutants with adverse effects on human reproduction. The possible effects of occupational and environmental exposure to various substances on male reproductive health are evaluated. This analysis considers studies showing damage of men exposed to halogenated hydrocarbons, other organic compounds, heavy metals and some physical agents, and some lifestyles, such as continuous stress, alcohol consumption, cigarette and marijuana smoking, and other addictions. Possible influences of these agents on the neuroendocrine system with the decrease of male fertility during the last decades are also discussed.

Identifying environmental risk to male reproductive function by occupational sperm studies: logistics and design options

Malfunction of the male reproductive system might be a sensitive marker of environmental hazards, the effects of which may extend beyond reproductive function. The testis is more vulnerable to heat and ionising radiation than any other organ of the body and several xenobiotics are known to disrupt spermatogenesis after low level exposure. Studies of environmental impact on human health are often most informative and accurate when carried out in the workplace where exposures can be high and easy to document. Semen analysis provides readily obtainable information on testicular function. The main advantages in comparison with functional measures such as fertility rates and time taken to conceive are the possibilities to examine men independently of marriage and pregnancy, to find changes of fecundity with different exposures within the same person and to detect adverse effects when no alteration of fertility is yet taking place. In the implementation of an occupational sperm study considerable attention must be paid to logistic issues. A mobile laboratory unit for initial semen preparation and processing may in some situations increase worker compliance and the quality of sperm cell motility. The cross sectional design which has been used in almost all male reproductive studies so far has several severe limitations including selection bias because of differential participation, difficulties in defining a suitable reference group, and lack of information about the time dimension of the cause-effect relation. The longitudinal design deals adequately with most of these constraints. Semen samples are collected before, during, and possibly after exposure to the risk factor of interest and causal inferences are based upon change of semen variables within a man over time rather than upon differences between men. The logistics of the longitudinal study may benefit from pre-employment health examinations to enrol newly hired workers and require fewer participants to obtain comparable statistical power. In conclusion, andrological methods and epidemiological designs are available for the implementation of valid studies concerned with environmental impact on human testicular function. Occupational sperm studies should probably not be the first choice when the objective is initial screening of environmental impact on fertility but should be implemented when their is a need to corroborate or refuse earlier evidence that specific exposures have impact on testicular function.

Epidemiological study of the systemic ophthalmological effects of carbon disulfide

A total of 123 male viscose rayon workers who were exposed to carbon disulfide, and an additional 67 workers who were not exposed to any toxic agent in the working environment, underwent a thorough ophthalmological examination. The relationship between exposure and ophthalmological results was analyzed with univariate and multivariate methods. The most striking findings were strong associations between exposure and the 100-HUE color vision score and excess of microaneurysms in the exposed group. The current threshold limit value appeared to protect against these effects.

Occupational hazards for the male reproductive system

The etiology of male infertilities is largely undetermined, and our knowledge of exogenous factors affecting the male reproductive system is still limited. In particular, the role of specific environmental and occupational factors is incompletely elucidated. Various occupational (physical and chemical) agents have been shown to affect male reproductive functions in animals, but large differences in reproductive function and/or xenobiotic handling between species limit extrapolation to humans. When available, human data are often conflicting and, except in a few instances, usually refer to broad and heterogenous occupational categories or to groups of agents (e.g., solvents). It is often difficult to elucidate the role of a single agent because occupational exposure conditions are often complex and various confounding factors related to lifestyle (smoking, alcohol, and diet) or socioeconomic state may also affect sperm quality, fertility, or pregnancy outcomes. The objective of this work is to summarize the main epidemiological and, where relevant, experimental findings pertaining to agents (physical and chemical) encountered in the occupational environment that might affect the male reproductive system (sperm count, motility and morphology, libido, and fertility) and/or related pregnancy outcomes (spontaneous abortion, stillbirth, low birth weight, and birth defects and childhood malignancy in offspring). Some methodological issues related to research on the reproductive effects of toxicants are also discussed briefly.

An Epidemiologic Study of the Effects of Carbon Disulfide on the Peripheral Nerves

Although the labor inspection had disclosed considerable exposure to carbon disulfide (CS&inf2;) in a Belgian viscose rayon factory, the company medical officer had not diagnosed any case of polyneuropathy in association with CS&inf2; exposure, although this finding had been extensively reported in the literature. Personal monitoring of CS&inf2; exposure was performed in 17 jobs. Because the working conditions in the factory had not changed since 1932, a CS&inf2; cumulative exposure index (CS&inf2; index) could be calculated for each individual. Examination of the exposed subjects (n = 111) included a self-administered questionnaire, a clinical neurologic examination, and electroneuromyography. Seventy-four workers from other plants, not exposed to CS&inf2; or to any other neurotoxic agent, served as referents. The average CS&inf2; exposures of the study group ranged from 4 to 112 mg/m(3). The data were analyzed with multiple regression methods, adjusting the effect of exposure for a number of possible confounders. Significant associations were found between the cumulative CS&inf2; index and symptoms consistent with polyneuropathy in the legs and with abnormal recruitment pattern and decrease of motor conduction velocities of the peroneal nerves. Exposures to CS&inf2; at levels below the present threshold limit value (31 mg/m(3)) were associated with significant decreases of motor conduction velocity.

A Mailed-questionnaire Survey of Ex-workers: A Tool to Evaluate the Healthy-worker Effect in Cross-sectional Studies

In order to evaluate a possible healthy-worker effect in a cross-sectional study in a viscose rayon plant, a survey of ex-workers was conducted. From the personnel records of this factory, 475 male, Caucasian, Dutch-speaking, carbon disulfide (CS&inf2;)-exposed workers who had been employed ten years prior to the cross-sectional study were selected for study. Of these, 142 were still employed in the same plant, and 64 were deceased. Retrieval of the causes of death proved impossible. A questionnaire was mailed to the remaining 269 men, of whom 149 completed and returned it. Eighty-nine subjects reported having left the plant for health reasons. Among the health reasons specified, eye-irritation complaints were most often mentioned (53.7%), followed by gastrointestinal complaints (32.8%), complaints concerning the central nervous system (19.4%) and the peripheral nerves (11.9%), heart or lung problems (14.9%), and problems affecting the skin (9.0%). The average duration of employment decreased significantly with the intensity of the exposure to CS&inf2;. The results suggest that the findings of a cross-sectional study of current workers in the same viscose rayon plant may represent underestimates of some conditions, in particular the acute eye-irritation complaints. Other complaints with high prevalences in the cross-sectional study, such as complaints consistent with polyneuropathy, seemed less, while others, such as impotence, seemed not at all, subject to underestimation.

Epidemiological study of the effects of carbon disulfide on male sexuality and reproduction

One hundred sixteen male viscose rayon workers exposed to carbon disulfide and 79 other workers, who were not exposed to any toxic agent in the working environment, were asked about their sexual behavior and reproductive record. Forty-three exposed and 35 nonexposed men provided a semen sample. The relationship with occupational exposure was analyzed with univariate and multivariate methods. The results indicate a significant effect of carbon disulfide exposure on libido and potency, but no effects were noted on fertility nor on semen quality.