Critical review of the epidemiological literature on the potential cardiovascular effects of occupational carbon disulfide exposure

A framework for integrating evidence to assess hazards and risk

To accurately characterize human health hazards, human, animal, and mechanistic data must be integrated and the relevance to the research question of all three lines of evidence must be considered. Mechanistic data are often critical to the full integration of animal and human data and to characterizing relevance and uncertainty. This novel evidence integration framework (EIF) provides a method for synthesizing data from comprehensive, systematic, quality-based assessments of the epidemiological and toxicological literature, including in vivo and in vitro mechanistic studies. It organizes data according to both the observed human health effects and the mechanism of action of the chemical, providing a method to support evidence synthesis. The disease-based component uses the evidence of human health outcomes studied in the best quality epidemiological literature to organize the toxicological data according to authors' stated purpose, with the pathophysiology of the disease determining the potential relevance of the toxicological data. The mechanism-based component organizes the data based on the proposed mechanisms of effect and data supporting events leading to each endpoint, with the epidemiological data potentially providing corroborating information. The EIF includes a method to cross-classify and describe the concordance of the data, and to characterize its uncertainty. At times, the two methods of organizing the data may lead to different conclusions. This facilitates identification of knowledge gaps and shows the impact of uncertainties on the strength of causal inference.

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.

Absorption lines measurements of carbon disulfide at 4.6 μm with quantum cascade laser absorption spectroscopy

We report measured line intensities and air- and self-broadening coefficients for fifty-one carbon disulfide transitions in the ν1 + ν3 band near 4.6 μm. This spectral region was chosen due to the strong carbon disulfide absorption strength and in the range of the mid-infrared atmospheric window for laser-based sensing applications. Spectroscopic parameters were determined by spectra measuring with quantum cascade laser direct absorption spectroscopy and multi-line fitting with Voigt lineshape. These measured results would facilitate the development of calibrated-free mid-infrared carbon disulfide sensors.

Continuous exposure to low-frequency noise and carbon disulfide: Combined effects on hearing

Carbon disulfide (CS₂) is used in industry; it has been shown to have neurotoxic effects, causing central and distal axonopathies.However, it is not considered cochleotoxic as it does not affect hair cells in the organ of Corti, and the only auditory effects reported in the literature were confined to the low-frequency region. No reports on the effects of combined exposure to low-frequency noise and CS₂ have been published to date. This article focuses on the effects on rat hearing of combined exposure to noise with increasing concentrations of CS₂ (0, 63,250, and 500ppm, 6h per day, 5 days per week, for 4 weeks). The noise used was a low-frequency noise ranging from 0.5 to 2kHz at an intensity of 106dB SPL. Auditory function was tested using distortion product oto-acoustic emissions, which mainly reflects the cochlear performances. Exposure to noise alone caused an auditory deficit in a frequency area ranging from 3.6 to 6 kHz. The damaged area was approximately one octave (6kHz) above the highest frequency of the exposure noise (2.8kHz); it was a little wider than expected based on the noise spectrum.Consequently, since maximum hearing sensitivity is located around 8kHz in rats, low-frequency noise exposure can affect the cochlear regions detecting mid-range frequencies. Co-exposure to CS₂ (250-ppm and over) and noise increased the extent of the damaged frequency window since a significant auditory deficit was measured at 9.6kHz in these conditions.Moreover, the significance at 9.6kHz increased with the solvent concentrations. Histological data showed that neither hair cells nor ganglion cells were damaged by CS₂. This discrepancy between functional and histological data is discussed. Like most aromatic solvents, carbon disulfide should be considered as a key parameter in hearing conservation régulations.

Coronary artery disease and cancer mortality in a cohort of workers exposed to vinyl chloride, carbon disulfide, rotating shift work, and o-toluidine at a chemical manufacturing plant

BACKGROUND

We updated through 2007 the mortality experience of 1,874 workers employed at a New York State chemical manufacturing plant between 1946 and 2006.

METHODS

Reassessed exposures to vinyl chloride, carbon disulfide, and shift work and categories of o-toluidine exposure were based on year, department and job title. Standardized mortality ratios (SMR) compared mortality to that of the US population. Internal comparisons used directly standardized rate ratios.

RESULTS

Hepatobiliary cancer mortality was elevated among workers ever exposed to vinyl chloride (SMR = 3.80, 95% confidence interval 1.89-6.80); directly standardized rates increased with increasing vinyl chloride exposure duration. No increase in non-Hodgkin lymphoma mortality was observed with vinyl chloride and shift work exposures. Internal comparisons showed increased coronary artery disease mortality among long-term workers exposed to carbon disulfide and shift work for 4 years or more.

CONCLUSIONS

Excess coronary artery disease mortality confirms earlier results; further investigation is needed to understand risk factors.

[Epidemiologic review of long-term, low-level exposure to environmental chemicals and cardiovascular disease: an exposure-response relationship]

The effects of exposure to environmental chemicals, such as heavy metals and fine particulates, on cardiovascular diseases have been reported. To set a permissible exposure standard, an exposure-response relationship should be elucidated. Thus, epidemiologic evidence in relation to long-term, low-level exposure to environmental chemicals (i.e., lead, cadmium, mercury, arsenic, PM(2.5), carbon disulfide) was reviewed. As a result, there exists a clear exposure-response relationship between exposure to lead or PM(2.5) and cardiovascular diseases, but those cohort studies were carried out in the US only. From epidemiologic viewpoint, "consistency" of the observed relationship must be clarified, especially findings of a study in the Japanese population. It is well known that the distribution pattern of cardiovascular risk factors are quite different between two countries, which could modify the true relationship. This will require studies of large samples from the general Japanese population with control for potential confouders. Moreover, to detect a small effect of exposure within low-level range, random misclassification of exposure as well as that of effect must be minimized. Thus, for studies of heavy metals, sensitive biomarkers identified in toxicological studies would be applied. For PM(2.5), a wide range of population samples should be covered by a national sampling network in the near future. Finally, the integration of epidemiologic and toxicological evidence would be more important for risk assessment of environmental chemicals at low exposure levels, because an exposure-response relationship from only epidemiologic observation may be unstable with a wide confidence interval around the threshold.

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.

Accumulation of urinary 2-thiothiazolidine-4-carboxylic acid (TTCA) among workers occupationally exposed to carbon disulfide for 1 week

OBJECTIVES

To investigate if carbon disulfide (CS(2)) accumulates after a 1-week exposure period, and how the work-shift duration and exposure magnitude affects this accumulation for the workers in viscose rayon industry.

METHODS

Six 8-h and seven 12-h workers in the spinning department historically known to be exposed to high air CS(2) were recruited as the exposed groups. Seven workers from other non-CS(2)-exposed departments were recruited as non-exposure controls. Exposure monitoring covered a full work shift with personal breathing zone monitoring. Urine was collected pre- and post-shift every day throughout the 5 consecutive days. 2-Thiothiazolidine-4-carboxylic acid levels in the urine (U-TTCA) were determined.

RESULTS

No detectable values were found for airborne (<0.6 ppm) and urinary (<35 ng/ml) monitoring for the control groups. The exposure levels for a 12-h shift (11.3+/-1.47) (AM+/-S.D.) were significantly greater than for an 8-h shift (6.3+/-0.64). The linear accumulation trend for daily U-TTCA across the workdays was only significant for the 12-h shift at pre-shift. Statistical significance was found in the regression of the ratios for pre-shift U-TTCA to airborne CS(2) levels on the preceding day to the day of the exposure at pre-shift for a 12-h shift (r=0.98, P=0.02).

CONCLUSIONS

The U-TTCA accumulation for occupational exposure to CS(2) was exposure-magnitude-dependent. The linear equations derived in this study indicated that the U-TTCA increment at pre-shift for each additional daily 12-h exposure, after an adjustment for the CS(2) exposure level, was 0.02 mg/g creatinine/ppm of CS(2). The long-term exposure response under such repeated and intermittent conditions should be noteworthy.