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

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.

Associations of urinary carbon disulfide metabolite with oxidative stress, plasma glucose and risk of diabetes among urban adults in China

Carbon disulfide (CS₂) has been reported to induce disorder of glucose metabolism. However, the associations of CS₂ exposure with plasma glucose levels and risk of diabetes have not been explored in general population, and the underlying mechanisms remain unclear. We aim to examine the relationships between CS₂ exposure and fasting plasma glucose (FPG) levels, as well as diabetes, and assess the potential role of oxidative stress among the abovementioned relationships in Chinese general adults. The concentrations of urinary biomarkers of CS₂ exposure (2-thiothiazolidin-4-carboxylic acid, TTCA), and biomarkers for lipid peroxidation (8-isoprostane, 8-iso-PGF_2α) and DNA oxidative damage (8-oxo-7,8-dihydro-20-deoxyguanosine, 8-OHdG) were measured among 3338 urban adults from the Wuhan-Zhuhai cohort. Additionally, FPG levels were tested promptly. Generalized linear models and logistic regression models were used to quantify the associations among urinary TTCA, oxidative damage markers, FPG levels and diabetes risk. Mediation analysis was employed to estimate the role of oxidative damage markers in the association between urinary TTCA and FPG levels. We discovered a significant relationship between urinary TTCA and FPG levels with regression coefficient of 0.080 (95% CI: 0.002,0.157). Besides, the risk of diabetes was positively related to urinary TTCA (OR:1.282, 95% CI: 1.055,1.558), particularly among those who did not exercise regularly. Each 1% increase of urinary TTCA concentration was associated with a 0.096% and 0.037% increase in urinary 8-iso-PGF_2α and 8-OHdG, respectively. Moreover, we found an upward trend of FPG level as urinary 8-iso-PGF_2α gradually increased (P_trend<0.05), and urinary 8-iso-PGF_2α mediated 21.12% of the urinary TTCA-associated FPG increment. Our findings indicated that urinary CS₂ metabolite was associated with increased FPG levels and diabetes risk in general population. Lipid peroxidation partly mediated the association of urinary CS₂ metabolite with FPG levels.

Changes of median nerve conduction velocity in rayon manufacturing workers: A 6-year cohort study

Objectives:

We conducted a 6-year cohort study to evaluate the relationship between carbon disulfide (CS₂) exposure and reductions in the motor and sensory nerve conduction velocity (MCV and SCV) of the median nerve.

Methods:

Study subjects at baseline included 432 exposed workers and 402 unexposed workers. Among the exposed workers, 145 workers terminated CS₂ exposure during the follow-up period (ex-exposed workers). MCV and SCV were measured at baseline and followed up. CS₂ personal exposure concentration was measured two times a year during a 6-year follow-up period and mean (range) CS₂ exposure concentrations (ppm) were 5.96 (0.8-16.0) and 3.93 (0.6-9.9) in the exposed and ex-exposed workers, respectively.

Results:

Reductions in MCV during the follow-up period did not differ among the exposed, ex-exposed, and unexposed workers. Reduction in SCV (m/s) of the exposed workers (-4.47±3.94) was significantly larger than that of the unexposed (-3.38±3.97) and ex-exposed workers (-3.26±3.79). For SCV reduction, a partial multiple regression coefficient of (ex-exposed workers) / (unexposed workers) was significantly positive (+0.915, p < 0.01) after adjustment for confounding variables.

Conclusions:

This cohort study showed that 6-year CS₂ exposure around a mean level of 6 ppm did not affect MCV reduction but induced significant SCV reduction beyond the influence of aging. The effect of CS₂ on SCV around a mean exposure level of 4 ppm may be reversible, since it disappeared in the ex-exposed workers after CS₂ exposure cessation for a mean period of 4.1 years.

Carbon disulfide. Just toxic or also bioregulatory and/or therapeutic?

The overview presented here has the goal of examining whether carbon disulfide (CS₂) may play a role as an endogenously generated bioregulator and/or has therapeutic value.

Occupational chemical exposure and diabetes mellitus risk

Diabetes mellitus (DM) is a group of metabolic diseases that may originate from an interaction between genetic and lifestyle risk factors. However, the possible role of occupational chemical exposures in the disease development and progression remains unclear. Therefore, this review aimed to provide a comprehensive evaluation of the relationship between occupational exposure to specific chemical substances or industrial activities and DM morbidity and mortality outcomes. Although some positive findings may support the diabetogenic role of certain pesticides and dioxins in different workplaces, the variable conditions of exposure, the lack of quantitative environmental or biological monitoring data and the different outcomes evaluated do not allow defining a specific exposure-disease causality. Therefore, further epidemiological studies will be necessary to adequately assess modes of action for different substances, dose–response relationships as well as individual susceptibility factors potentially affecting the exposure-disease continuum. Overall, this appears important to adequately assess, communicate and manage risks in occupational chemical exposure settings with the aim to protect workers and build healthier job conditions for diabetic employees.

Six year observational cohort study of the effect of carbon disulphide on brain MRI in rayon manufacturing workers

AIMS

To clarify whether the current occupational exposure limit (OEL) for carbon disulphide (CS2) is low enough to prevent the occurrence of adverse effects on the cerebrovascular system.

METHODS

A total of 432 male workers exposed to CS2 and 402 male referent workers in 11 Japanese viscose rayon factories were studied at baseline; 750 of these were followed up. Brain MRI was performed at both baseline and follow up surveys. Changes in the number of hyperintense spots in T2 weighted images (HIS), which point to so-called "silent cerebral infarctions", were evaluated over six years. A total of 666 subjects (217 exposed, 125 ex-exposed, and 324 referent subjects) who twice received brain MRI were subjected to analysis. Mean duration of exposure to the end of the study was 19.6 years for the exposed workers. The geometric mean CS2 (ppm) and TTCA (mg/g creatinine) concentrations for the past six years were 4.9 and 1.6 for all exposed workers, 5.8 and 1.9 for spinning/refining workers, and 2.7 and 0.9 for other exposed workers, respectively.

RESULTS

Exposed subjects showed a significantly higher risk for an increase in the number of HIS over six years. Odds ratios adjusted for possible confounders in the exposed and ex-exposed workers were 2.27 (95% CI 1.37 to 3.76) and 1.33 (95% CI 0.70 to 2.54), respectively. No exposure-response relations were observed in a number of analyses among the exposed workers.

CONCLUSIONS

Exposure to CS2 under the current Japanese OEL, 10 ppm, might increase the number of HIS in brain MRI. However, results should be interpreted with caution.

A six year follow up study of the subclinical effects of carbon disulphide exposure on the cardiovascular system

AIMS

A six year prospective cohort study was conducted to clarify whether the current carbon disulphide (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 effects on the cardiovascular systems.

METHODS

The study subjects were 432 male workers exposed to CS2 and 402 non-exposed workers in Japan, all of whom were examined in 1992-93. A total of 251 CS2 exposed, 140 formerly exposed, and 359 non-exposed workers participated in the follow up survey (follow up rate 89.9%) in 1998-99. Mean duration of exposure was 19.3 years at the end the study. Mean CS2 and 2-thiothiazolidine-4-carboxylic acid (TTCA) concentrations were 5.0 ppm and 1.6 mg/g creatinine. Health items examined were serum biochemical indices including lipids and coagulation-fibrinolysis factors, blood pressure, aortic stiffness, ophthalmography, and electrocardiography at rest and after Master's double 2 step test. Potential confounding factors were adjusted for.

RESULTS

Incidence of ischaemic findings, defined as Minnesota codes I, IV(1-3), V(1-3) (at rest and after the load), or receiving treatment for ischaemia, was significantly higher in the exposed workers, especially for the spinning/refining workers (adjusted OR 2.1; 95% CI 1.1 to 4.0) or the highest quartile of six year mean TTCA (adjusted OR 3.9; 95% CI 1.8 to 8.7), although the observed increase in risk was diminished when rigorous ECG criteria were applied. Incidence of retinal microaneurysm was increased with marginal significance. Among cardiovascular risk factors we examined, only blood pressure values were significantly increased in the exposed workers.

CONCLUSIONS

Increased risk of ischaemic electrocardiogram findings among Japanese viscose rayon workers was observed. Although its clinical significance is to be discussed, the current Japanese occupational exposure limit for CS2, 10 ppm, would be high to prevent subclinical cardiovascular effects in this study population.