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Carbon disulfide exposure estimate and prevalence of chronic diseases after carbon disulfide poisoning-related occupational diseases
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Research Article Carbon disulfide exposure estimate and prevalence of chronic diseases after carbon disulfide poisoning-related occupational diseases
Hweemin Chung1, Kanwoo Youn1, Kyuyeon Kim1, Kyunggeun Park2
Annals of Occupational and Environmental Medicine 2017;29:52.
DOI: https://doi.org/10.1186/s40557-017-0208-6
Published online: October 26, 2017

1Department of Occupational & Environmental Medicine, Wonjin Green Hospital (Seoul), Sagajeong-ro 49-gil 53, Jungrang-gu, Seoul, South Korea

2Department of Internal Medicine, Wonjin Green Hospital (Guri), Dongguneung-ro 65-gil, Guri Si, Gyeonggi-do, South Korea

• Received: April 20, 2017   • Accepted: October 17, 2017

© The Author(s). 2017

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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  • Background
    In Korea, Carbon disulfide (CS2) toxicity was an important social problem from the late 1980s to the early 1990s but there have been few large-scale studies examining the prevalence of diseases after CS2 exposure discontinuance. So we investigated past working exposure to CS2 characteristics from surviving ex-workers of a rayon manufacturing plant including cumulative CS2 exposure index. Furthermore, we studied the prevalence of their chronic diseases recently after many years.
  • Methods
    We interviewed 633 ex-workers identified as CS2 poisoning-related occupational diseases to determine demographic and occupational characteristics and reviewed their medical records. The work environment measurement data from 1992 was used as a reference. Based on the interviews and foreign measurement documents, weights were assigned to the reference concentrations followed by calculation of individual exposure index, the sum of the portion of each time period multiplied by the concentrations of CS2 during that period.
  • Results
    The cumulative exposure index was 128.2 ppm on average. Workers from the spinning, electrical equipment repair, and motor repair departments were exposed to high concentrations of ≥10 ppm. Workers from the maintenance of the ejector, manufacturing of CS2, post-process, refining, maintenance and manufacturing of viscose departments were exposed to low concentrations below 10 ppm. The prevalence for hypertension, coronary artery disease, cerebrovascular disease, diabetes, arrhythmia, psychoneurotic disorder, disorders of the nervous system and sensory organ were 69.2%, 13.9%, 24.8%, 24.5%, 1.3%, 65.7%, 72.4% respectively.
  • Conclusions
    We estimated the individual cumulative CS2 exposure based on interviews and foreign measurement documents, and work environment measurement data. Comparing the work environment measurement data from 1992, these values were similar to them. After identified as CS2 poisoning, there are subjects over 70 years of average age with disorders of the nervous system and sensory organs, hypertension, psychoneurotic disorder, cerebrovascular disease, diabetes, coronary artery disease, and arrhythmia. Because among ex-workers of the rayon manufacturing plant, only 633 survivors recognized as CS2 poisoning were studied, the others not identified as CS2 poisoning should also be investigated in the future.
Carbon disulfide (CS2) is a substance in which two sulfur atoms are bonded to one carbon molecule. It is colorless and has high volatility and flammability. CS2 has been an important industrial chemical since the 1800s because of its many useful properties, including its ability to solubilize fats, rubbers, phosphorus, sulfur, and other elements. In the early 1900s, CS2 was used in large quantities during the synthesis of viscose rayon. CS2 is absorbed mainly by inhalation of steam whereupon it enters the bloodstream and is distributed throughout the body. CS2 can also be absorbed via other mucous membranes such as those of the eyes and skin. The target organs include the central nervous system, cardiovascular system, peripheral nervous system, reproductive system, eyes, and skin [13].
Among the health effects of CS2, the most commonly known is the increase in the incidence of cerebral cardiovascular diseases due to sclerotic changes in blood vessels cause by impaired lipid metabolism. One of the specific vascular effects of CS2 is the development of retinal lesions characterized by petechiae of the retina [4] or microalbuminuria. Cerebral cardiovascular disease as well as central nervous system disorders are among the major health effects of CS2 poisoning. In addition, polyneuropathy may occur after chronic exposure to low doses [5]. Parkinson’s symptoms such as cogwheel rigidity, resting tremor, action tremor, bradykinesia, cerebellar ataxia, and vertebral symptoms may occur [6]. Diffuse encephalopathy has been observed in clinical studies, psychiatric studies, and neuroradiologic studies for decades [7]. In addition, reports claim that CS2 exposure is associated with the development of endocrine disease associated with impaired lipid metabolism. Also, owing to its effects on mental health, CS2 poisoning results in excessive nervousness, uncontrolled anger, rapid mood changes, paranoia, and suicidal tendencies [8].
Thus, CS2 poisoning affects the cardiovascular system [911], the cerebrovascular system [1214], the endocrine system [15, 16], mental health [8], and the nervous system [57, 15].
In Korea, CS2 toxicity was an important social problem from the late 1980s to the early 1990s, but paradoxically, it contributed to the development of the industrial safety and health system in Korea. Wonjin Rayon Co., Ltd. imported mechanical equipment from Japan, and since 1962 has manufactured viscose rayon and used CS2 as the main raw material in the process. In 1966 about 15 tons of viscose rayon was produced per day, which increased to 50 tons per day in 1976. Since then, a deficit has accumulated owing to changes in the industrial environment, and CS2 toxicity became a social problem. Wonjin Rayon Co., Ltd. was closed in 1993. Until the mid-1970s when production was high, about 3000 employees worked in the manufacturing plant annually, but the number of employees at the time of the closure was about 1000.
The cases of CS2 poisoning of Wonjin Rayon Co., Ltd. were reported around 1988. Accordingly, the Graduate School of Public Health of Seoul National University carried out an epidemiological survey in 1992, and since then, the number of patients with CS2 poisoning has increased drastically. The procedure for recognizing occupational diseases was as follows. As a first step, a person with a career in carbon disulfide working at Wonjin Rayon confirmed his working career at the Wonjin workers’ occupational medicine committee and completed a medical treatment application. As a second step, he examined a primary care from Seongsoo’s clinic and received a medical report on CS2 poisoning. As a third step, he was examined at a university hospital. As a final step, he was judged to have an occupational disease according to the standard of occupational accidents recognized by the Ministry of Labor (Industrial Accident Compensation Insurance Act, Article 39, Ministry of Labor). In this way, a total of 910 persons were recognized as CS2 poisoning-related occupational diseases, among whom 208 persons died and 702 persons survived by November 2016.
However, despite the number of studies reporting CS2 poisoning in Korea, the social significance of this issue was underreported. In addition to the epidemiologic survey [16], a few case reports and studies on the clinical symptoms and distribution of a single disease among a small number of workers exposed to CS2 have been reported [7, 17]. There have been few large-scale studies examining the prevalence of diseases after CS2 exposure discontinuance.
The purpose of this study was to investigate past working exposure to CS2 characteristics from investigable 633 ex-workers identified as CS2 poisoning-related occupational diseases including cumulative CS2 exposure index. Furthermore, we studied the prevalence of their major chronic diseases associated with CS2 poisoning recently after many years. We approached ex-workers of Wonjin Rayon Co., Ltd., who were identified as CS2 poisoning-related occupational diseases, via the Wonjin Industrial Accident Society.
Study population
From 1962 to 1993, there were about 12,000 employees at Wonjin Rayon Co., Ltd., but all of their information is not available. Only 910 persons were recognized as having occupational diseases. The standard of occupational accidents about CS2 poisoning or its secondary diseases is shown in Table 1. Initially, the approval name of industrial accidents was carbon disulfide poisoning, and further details are not available. Of these, 208 persons died and 702 persons survived until November 2016. Finally, 633 persons, excluding 69 who refused to participate in the survey or were unable to express their opinions, were selected for the study. This study was approved by the ethics reviews board of Wonjin Institute for Occupational and Environmental Health.
Table 1
Standards of occupational accidents about CS2 poisoning or its secondary diseasesa
20. CS2 poisoning or its secondary diseases
Ga. A worker who has worked for more than two years on work exposed to CS2 vapor of around 10 ppm shall be considered as a work-related disease if any of the following symptoms or symptoms appear.
(1) When there is one of retinal microvessels, multiple cerebral infarction, capillary glomerulosclerosis on renal biopsy.
However, it excludes diseases caused by causes other than CS2, such as diabetes, hypertension and vascular disorders.
(2) Retinal lesions other than microvascular lesions, multiple peripheral nerve lesions, optic neuritis, coronary heart disease, central nervous system disorders or psychiatric disorders.
However, it excludes diseases caused by causes other than CS2, such as diabetes, hypertension and vascular disorders.
(3) There is one of (2) and there is at least one of kidney disorder, liver disorder, hematopoietic system disorder, reproductive system disorder, sensory nerve impairment disorder, and hypertension.
Na. A worker who is exposed to more than 20 ppm of CS2 vapor for more than two weeks shall be considered as a work-related disease if they present with sudden manifestations of mental disorders such as confusion, delirium, schizophrenia and bipolar disorder.
Da. When exposed to a large or high concentration of CS2 vapor, symptoms of acute intoxication such as consciousness disorder are regarded as occupational diseases.
aIndustrial Accident Compensation Insurance Act, Article 39, Ministry of Labor, 1997
Through the medical records of the 6 hospitals that manage the health of the subjects, the results of the medical examinations conducted over the past 1 year, prescriptions, and clinical history were reviewed. The name of the disease listed in data for the 295 diseases classified by the Health Insurance Statistical Yearbook of 2015 is composed of several diagnostic codes corresponding to the International Classification of Disease (ICD) codes as shown in Table 2. In addition, the Wonjin Industrial Accident Society, for 2 months since September 19, 2016, individually contacted the research subjects and conducted a one-on-one interview using a questionnaire to determine working history, demographic characteristics, health behavior, and habits. Information regarding working history included items such as year of employment, department of work, contents of work, move within/across departments, and period of work.
Table 2
ICD-10 code of target disease
Disease Classification of 298 Diseasesa ICD-10 codeb
Hypertension
Essential(primary) hypertention
Other hypertensive diseases
I10 Essential (primary) hypertension
I11 Hypertensive heart disease
I12 Hypertensive renal disease
I13 Hypertensive heart and renal disease
I15 Secondary hypertension
Coronary artery disease
Acute myocardial infarction
Other ischaemic heart diseases
I20 Angina pectoris
I21 Acute myocardial infarction
I22 Subsequent myocardial infarction
I23 Certain current complications following acute myocardial infarction
I24 Other acute ischaemic heart diseases
I25 Chronic ischemic heart disease
Cerebrovascular disease
Transient cerebral ischaemic attacks and related syndromes
Cerebral palsy and other paralytic syndromes
G45 Transient cerebral ischaemic attacks and related syndromes
G50 Disorders of trigeminal nerve
G51 Facial nerve disorders
G52 Disorders of other cranial nerves
G53 Cranial nerve disorders in diseases classified elsewhere
G80 Cerebral palsy
G81 Hemiplegia
G82 Paraplegia and tetraplegia
G83 Other paralytic syndromes
Diabetes mellitus
Diabetes mellitus E10 Type 1 diabetes mellitus
E11 Type 2 diabetes mellitus
E12 Malnutrition-related diabetes mellitus
E13 Other specified diabetes mellitus
E14 Unspecified diabetes mellitus
Arrhythmia
Conduction disorders and cardiac arrhythmias I44 Atrioventricular and left bundle-branch block
I45 Other conduction disorders
I46 Cardiac arrest
I47 Paroxysmal tachycardia
I48 Atrial fibrillation and flutter
I49 Other cardiac arrhythmias
Psychoneurotic disorder
Schizophrenia schizotypal and delusional disorders
Mood [affective] disorders
Neurotic,stress-related and somatoform disorders
F20 Schizophrenia
F21 Schizotypal disorder
F22 Persistent delusional disorders
F23 Acute and transient psychotic disorders
F24 Induced delusional disorder
F25 Schizoaffective disorders
F28 Other nonorganic psychotic disorders
F29 Unspecified nonorganic psychosis
F40 Phobic anxiety disorders
F41 Other anxiety disorders
F42 Obsessive-compulsive disorder
F43 Reaction to severe stress, and adjustment disorders
F44 Dissociative [conversion] disorders
F45 Somatoform disorders
F48 Other neurotic disorders
Disorders of the nervous system and sensory organs
Nerve, nerve root and plexus disorders
Other diseases of the nervous system
G12 Spinal muscular atrophy and related syndromes
G13 Systemic atrophies primarily affecting central nervous system in diseases classified elsewhere
G21 Secondary parkinsonism
G22 Parkinsonism in diseases classified elsewhere
G24 Dystonia
G25 Other extrapyramidal and movement disorders
G26 Extrapyramidal and movement disorders in diseases classified elsewhere
G37 Other demyelinating diseases of central nervous system
G56 Mononeuropathies of the upper limb
G57 Mononeuropathies of the lower limb
G58 Other mononeuropathies
G59 Mononeuropathy in diseases classified elsewhere
G62 Other polyneuropathies
G64 Other disorders of the peripheral nervous system
G70 Myasthenia gravis and other myoneural disorders
G72 Other myopathies
G73 Disorders of the myoneural junction and muscle in diseases classified elsewhere
G90 Disorders of the autonomic nervous system
G92 Toxic encephalopathy
G93 Other disorders of the brain
G94 Other disorders of the brain in diseases classified elsewhere
G95 Other diseases of the spinal cord
G96 Other disorders of the central nervous system
G98 Other disorders of the nervous system not elsewhere classified
G99 Other disorders of the nervous system in diseases classified elsewhere
a2015 National Health Insurance Statistical Yearbook
bInternational Classification of Disease-10
Estimation of CS2 exposure
To estimate past exposure to CS2 without actual measurement data, the work environment measurement data from 1992 used by the Seoul National University Graduate School of Public Health [18] were analyzed by 15 departments and used as the reference concentration. Based on the interviews of the study subjects, facility-related weights were assigned to the baseline concentrations according to the change in the equipment repair time and production amount. Exposure index in the absence of measurement data were weighted with reference to foreign measurement documents.

CS2 exposure by job department

The results of the Ministry of Labor’s environment survey of Wonjin Rayon Co., Ltd. conducted in 1991 and the average of the work environment measurement data estimated by the Seoul National University Graduate School of Public Health in 1992 were applied as standard concentrations. The Maintenance Department, Chemical Engineering Department, and General Affairs Department, which do not have measurement data, applied estimates by referring to the contents of the work. Table 3 shows the results of the workers’ working areas and the environmental characteristics of CS2 exposure (Table 3). Based on studies conducted in the EU a time-weighted average (TWA) of 5 ppm for departments exposed to CS2 concentrations of ≥5 ppm was classified as high exposure. Based on studies conducted in the National Institute for Occupational Safety and Health a TWA of 1 ppm for departments exposed to CS2 concentrations of <1 ppm was classified as low exposure. Departments exposed to concentrations of ≥1 ppm and <5 ppm were classified as involving moderate exposure.
Table 3
Establishing criteria for CS2 exposure concentration by department
Department CS2 -exposed Concentration (ppm) Job Contents
High exposure concentration department
Spinning
  Doping 6.53 Threading up a spinning machinery and taking out the cake, As CS2 is released during rayon regeneration, exposure concentration is highest with direct exposure.
  Circuit 6.58 In the spinning room having a tangled or broken thread, As CS2 is released during rayon regeneration, exposure concentration is highest with direct exposure.
  Motor Repair 3.79 Repairing motors of a spinning machinery
Moderate exposure concentration department
 Electrical Equipment Repair 4.33 High amount of spinning room work while repairing electrical equipment due to mechanical corrosion problems.
 Maitenance of Ejector 3.03 It is intermittent for reasons such as machine maintenance, but working within the spinning department
 Collection of Sulfuric acid 3.79 CS2 mixed in the recovered solution.
 Manufacturing of CS2 2.77 Exposure to high concentrations of CS2 for a short time while manufacturing, but protective gear is used.
Post-Process
  Packing 3.6 Restricted to the spinning room
  Carrying 1.96 Working in a spinning room for a long time to transport rayon.
  Refining 2 Exposure to remaining CS2 while processing semi-finished cake
 Maintenance 2.16 Estimated at 50% of that in the electrical equipment repair department
 Manufacturing of Viscose 1.35
Low exposure concentration department
 Water Treatment 0.45 Sewage inspection and cleaning in the spinning room
 Manufacturing of Chemicals 0.23 Estimated at 50% of that in the water treatment department, production of caustic soda and liquid chlorine, lower possibility of direct exposure.
 General Affairs 0.12 Estimated at 50% of that in the manufacturing department

Weights by work period

Through interviews of 30 workers conducted to identify objective facts about past CS2 exposure and the 1991 Wonjin Rayon Co., Ltd. Status report, the cost of investing in work environment management was found to gradually increase over time. By taking into account the average concentration for each period identified in foreign literature and the changes in the work environment, facilities, and production volume of Wonjin Rayon Co., Ltd., we divided work period into three stages and weighed them according to the timing (Table 4).
Table 4
Setting weight by operating period
Operating Period (year) Weight by period Evidence
1966 (Initial operation)-1974 3.5 The average concentration of CS2 in the spinning division in the 1960s (20 ppm) was about 3.5 times the average concentration of the total spinning division measured in 1991 (5.6 ppm).
1975–1989 2.75 The average concentration in the spinning division measured in the 70s and 80s (10–15 ppm) was about 2.25 times the average concentration in the total spinning division measured in 1991 (5.6 ppm).
Since 1975, the production of rayon has increased. According to the operator interview, the exhaust system has changed, and the screen breaks down due to the age of the equipment. Thus, an additional weight of 0.5 was included.
1990–1993 (Upon closure) 0.5 The compliance towards wearing personal protective gear was relatively good.
The highest CS2 exposure concentration measured in protective equipment (3.2 ppm) was about 0.5 times that measured in 1991 (5.6 ppm).
In 1973, the National Institute for Occupational Safety and Health in the US showed that the 8-h TWA of airborne exposure in the workplace, such as during spinning and cutting in the rayon plant, exceeded 200 ppm in 12 of 36 cases; in 7 cases, the 8-h TWA exceeded 100 ppm. In another factory, in more than 50% of the 196 cases analyzed, the concentration of CS2 exceeded 100 ppm, and the time weighted average was 11.2 ppm (range: 0.9–127 ppm) [19]. Analysis of the measurement data of a rayon factory in Finland from 1945 to 1967 showed that the concentration of CS2 was generally estimated to be more than >40 ppm before 1950, 20–40 ppm between 1950 and 1960, and 10–30 ppm in the 1960s [20]. The average concentration of CS2 in the spinning division in the 1960s (20 ppm), which was identified in previous foreign literature, was about 3.5 times the average concentration of the total spinning division measured in 1991 (5.6 ppm). As a result, the weight of the period from early 1966 to 1974 was 3.5. The average concentration in the spinning division measured in the 70s and 80s (10–15 ppm) was about 2.25 times the average concentration in the total spinning division measured in 1991 (5.6 ppm).The weight of the period from 1975 to 1989 was estimated as 2.75 by adding 0.5 in consideration of the working environment at that time. From 1990 to 1993, the compliance towards wearing personal protective gear was relatively good and the highest CS2 concentration in the protective area was 3.2 ppm. Since the concentration was 0.5 times the reference concentration, the weight assigned was 0.5.
Based on these data, the individual cumulative exposure index and the individual average exposure concentration were calculated as shown in Table 5.
Table 5
Calculation of the cumulative exposure index and time-weighted average concentration of CS2
• cumulative exposure index (CEI) = Σ (working years x reference concentration x weight)
• time weighted average CS2 concentration = Σ (the hours in the workday x reference concentration x weight) / the hours in the workday of exposure to CS2
Characteristics of the study population
Characteristics of the workers included in this study are shown in Table 6. The subjects of this study were mainly male, accounting for 86.3% of the population; the mean age was 70.7 years (70.7 ± 7.5 years) and the mean age at the time of study entry was 27.9 years (27.9 ± 5.3 years). Of the subjects, 41.1% consumed alcohol more than once a week and 60.8% were current smokers.
Table 6
Demographic and employment characteristics of the study subjects
Number of the subjects Mean SD
N %
Demographic characteristics
Total 633 100.0
Sex Male 546 86.3
Female 87 13.7
Age distribution (year) 50–59 57 52.6
60–69 196 69.4
≥ 70 380 71.6
Smoking No 212 33.5
Yes 385 60.8
No answer 36 5.7
Alcohol consumption (days/week) <1 336 53.1
≥1 260 41.1
No answer 37 5.9
Employment characteristics
Age at first employment (years) 27.9 5.3
Age at date last observed among survivors (years) 70.7 7.5
Year in the first employment (year) 1974.2 6.2
<1975 339 53.6
1975–1993 294 46.4
Duration of employment (years) 12.8 5.6
<10 204 29.7
10–<20 379 59.9
≥20 66 10.4
Cumulative CS2 exposure index (ppm·yr) 128.2 82.2
0–<67a 169 26.7
67–<134 206 32.5
≥134b 258 40.8
Time-weighted average CS2 concentration (ppm) 10.1 4.9
0- < 5c 112 17.7
5–<10d 199 31.4
≥10 322 50.9
Department distribution by CS2 exposure concentration
Low (<5 ppm)e 340 53.7
High (≥5 ppm) 293 46.3
alower one third defined by distribution of metric among all the study subject
bupper one third defined by distribution of metric among all the study subject
cEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values
dIndustrial Safety and Health Act enforcement regulations separate Table 3 of 11 Amendment of allowable standard of exposure concentration by harmful factor, IRE - 2010 Code of Practice for the Safety, Health and Welfare at Work (Chemical Agents) Regulations 2001. Published by the Health and Safety Authority
eEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values
CS2 exposure
According to working department, 53.7% of the subjects were working in departments with low exposure, with a TWA CS2 concentration of <5 ppm, and 46.3% of subjects were in departments with high exposure, with a TWA CS2 concentration of ≥5 ppm. The average employment duration was 12.8 years (12.8 ± 5.6 years). To estimate the cumulative CS2 exposure index, we calculated the cumulative exposure index as 128.2 ppm (128.2 ± 82.2 ppm) considering all the departments they moved to. The TWA concentration was 10.1 ppm (10.1 ± 4.9 ppm) (Table 6). Furthermore, 93.2%, 76.9%, and 61.5% of workers from the spinning, electrical equipment repair, and motor repair departments, respectively, were exposed to high concentrations of ≥10 ppm on average. During the maintenance of the ejector, manufacturing of CS2, post-process, refining, maintenance and manufacturing of viscose departments, 80.0%, 91.7%, 99.3%, 100.0%, 100.0% and 98.2% workers, respectively, were exposed to concentrations below 10 ppm on average. These values are similar to those reported in the 1991–1992 work environment measurement data (Table 7).
Table 7
CS2 exposure concentrations by department
Workers Exposed to CS2 (%)
Department (N = 633)
Spinning Electrical Equipment Repair Motor Repair Collection of Sulfuric acid Maintenance of ejector Manufacturing of CS2 Post-Process Refining Maintenance Manufacturing of Viscose Water Treatment General Affairs
CS2 exposure concentrationa (ppm)
0- < 5b N 10 1 0 0 1 0 37 2 9 52 0 0
% 3.6 7.7 0.0 0.0 2.5 0.0 25.5 25.0 56.3 96.3 0.0 0.0
5- < 10c N 9 2 10 12 31 11 107 6 7 1 2 1
% 3.2 15.4 38.5 34.3 77.5 91.7 73.8 75.0 43.7 1.9 100.0 50.0
≥10 N 261 10 16 23 8 1 1 0 0 1 0 1
% 93.2 76.9 61.5 65.7 20.0 8.3 0.7 0.0 0.0 1.8 0.0 50.0
total (N) 280 13 26 35 40 12 145 8 16 54 2 2
aTime-weighted average CS2 concentration
bEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values
cIndustrial Safety and Health Act enforcement regulations separate Table 3 of 11 Amendment of allowable standard of exposure concentration by harmful factor, IRE - 2010 Code of Practice for the Safety, Health and Welfare at Work (Chemical Agents) Regulations 2001. Published by the Health and Safety Authority
The prevalence of chronic diseases for the subjects
Table 8 presents the prevalence of diseases for subjects [21]. The prevalence for hypertension, coronary artery disease, cerebrovascular disease, diabetes, arrhythmia, psychoneurotic disorder, disorders of the nervous system and sensory organ were 69.2%, 13.9%, 24.8%, 24.5%, 1.3%, 65.7%, 72.4% respectively.
Table 8
Disease prevalence for the study subjects
Observed Events Study population Disease Prevalence
N N %
Disease
 Hypertension 438 633 69.2
 Coronary artery disease 88 633 13.9
 Cerebrovascular disease 157 633 24.8
 Diabetes mellitus 155 633 24.5
 Arrhythmia 8 633 1.3
 Psychoneurotic disorder 416 633 65.7
 Disorders of the nervous system and sensory organs 458 633 72.4
We investigated past working exposure to CS2 characteristics from investigable 633 ex-workers identified as CS2 poisoning-related occupational diseases including cumulative CS2 exposure index. Furthermore, we studied the prevalence of their major chronic diseases associated with CS2 poisoning recently after many years. Comparing work environment measurement data reported in the 1991–1992, these values were similar to them. After the subjects were identified as CS2 poisoning-related occupational diseases, there are subjects over 70 years of average age with chronic diseases. Disorders of the nervous system and sensory organs, hypertension, psychoneurotic disorder, cerebrovascular disease, diabetes, coronary artery disease, and arrhythmia are the descending order of the prevalence for their chronic diseases.
In our study, there were several advantages to the survey method. We used an evidence-based approach to estimate past exposure to CS2 and to examine the presence or absence of chronic diseases. In the study of Nishiwaki et al. [22], 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 magnetic resonance imaging was performed at both baseline and follow-up surveys. They found that the CS2 concentrations in the workers’ breathing zones and the level of 2-thiothiazolidine-4-carboxylic acid (TTCA), a metabolite of CS2, were measured twice a year since the spring of 1993 during the study period. Individual exposure level was represented by the arithmetic mean of the concentrations of TTCA and CS2 for 6 years. Similarly, our study also used the TWA concentration in the workers’ breathing zone as a means of assessing CS2 exposure. However, the data could be used only to estimate past exposures. On the other hand, restriction of TTCA estimation to urine samples as a means of biomonitoring could be a limitation. Kotseva et al. [23] also conducted a similar CS2 exposure assessment method. Concentrations of CS2 were assessed using stationary measurements and personal sampling methods. A preliminary estimate of CS2 concentrations in the manufacturing area was achieved by short-term sampling. To estimate the CS2 exposure at the time of the study, 8-h weighted average personal breathing zone samples were collected from some workers in each job category. A cumulative exposure index was calculated for each worker by multiplying the number of years he had held a particular job with the CS2 concentrations in that job. According to the degree of personal exposure, the study population was allocated to three groups: highly exposed, moderately exposed, and non-exposed.
In contrast with our approach (review of prescription and medical records and medical examination results), Nishiwaki et al. [22] used the medical records of the company via interview when examining the medical history of the subjects. Thus, our study has an advantage in that the prevalence estimated is more accurate [15, 2326], because it relies on past history by self-filling or one-on-one interview questionnaires.
To estimate CS2 exposure index prior to 1986, exposure index was estimated by applying baseline and weights according to work period in 1991 and 1992, where the data were available. Because the departmental exposure index recorded in existing work environment measurement results (Table 3) and that of the present study (Table 7) showed a similar distribution, the exposure assessment can be deemed appropriate. There was an exception to this distribution. For example, the department with high CS2 exposure contained workers with moderate or low exposure because of the short working period in the high-exposure department since the 1990s. The presence of workers with high CS2 exposure in the department with low exposure indicates that these workers in the production department moved to the low-exposure department.
The average age of the subjects was 70.7, and most diseases that they have are chronic. The prevalence for hypertension, coronary artery disease, cerebrovascular disease, diabetes, arrhythmia, psychoneurotic disorder, disorders of the nervous system and sensory organ were 69.2%, 13.9%, 24.8%, 24.5%, 1.3%, 65.7%, 72.4% respectively. Vanhoorne et al. showed significant effects of the CS2 cumulative exposure index on systolic BP, diastolic BP [11]. Hyung-Joon Jhun et al. suggested that CS2 poisoned subjects have an increased risk of ECG abnormalities even after the exposure to CS2 is no longer present [27]. Several cross-sectional epidemiological studies have demonstrated that exposure to CS2 can result in increased cardiovascular risk factors and thus mortality [911, 28]. Recently, long-term exposure to CS2 was found to be an independent risk factor for changes in intima-media thickness in a German rayon manufacturing plant [9]. Long-term CS2 exposure has also been associated with increased cardiovascular mortality [11]. The abnormalities of cerebrovascular system were evaluated in CS2 poisoning cases [1214]. Eunil Lee et al. [12] suggested that CS2 exposure could lead to a decrease of cerebral vasoreactivities by the atherosclerotic change of cerebral vessels. In a study of the health effects of CS2 on metabolic syndrome, the CS2-poisoned group showed an increased risk for abdominal obesity and high fasting glucose levels after adjusting for covariates [16]. Krstev et al. [29] reported neuropsychiatric effects in workers with occupational exposure to CS2. In a study of the effects of CS2 on the peripheral nervous system using nervous conduction, the number of cases with abnormal nerve conduction results increased according to age and duration of exposure [5]. Also in this study, after ex-workers of the rayon manufacturing plant were identified as CS2 poisoning-related occupational diseases, there are subjects with chronic diseases as mentioned earlier. Disorders of the nervous system and sensory organs, hypertension, psychoneurotic disorder, cerebrovascular disease, diabetes, coronary artery disease, and arrhythmia are the descending order of the prevalence for their chronic diseases.
This study has the following limitations. First, concurrent exposure to other chemicals as well as failure to control for other disease risk factors, such as aging, is a limitation of this study. Second, diseases involving high mortality rates and severity, such as cerebrovascular diseases, involve a relatively large number of deaths and intensive care unit admission, making follow-up observations difficult. Third, a prevalence-incidence bias could occur [30]. Fourth, because demographic and work-related factors were investigated using a one-on-one interview survey approach, the intention of researchers and responders could be reflected. Fifth, the research subjects were very selective and could not be compared with the general population. Finally, there is a problem with the reliability of the reference data, and it is impossible to calculate the accurate exposure amount according to the change in the work environment during the period. The date regarding the working environment at Wonjin Rayon Co., Ltd. and medical examination results prior to 1986 were not available. There is no measurement data except for the very limited measurement results from 1986 to 1990, and these results also have many limitations in terms of the reliability of the results owing to the lack of samples, lack of cooperation of the company, and method of analysis. In order to overcome these limitations, exposure index was estimated by applying periodic weights with reference to foreign documents.
Because among ex-workers of the rayon manufacturing plant, only 633 survivors recognized as CS2 poisoning-related occupational were studied, the others not identified as CS2 poisoning occupational diseases should also be investigated. A patient-control study will be needed in the future.
We investigated past working exposure to CS2 characteristics from investigable 633 ex-workers of the rayon manufacturing plant who were identified as CS2 poisoning-related occupational diseases including cumulative CS2 exposure index based on the interviews, foreign measurement documents, and work environment measurement data reported in the 1991–1992. Comparing work environment measurement data reported in the 1991–1992, these values were similar to them. It is known that CS2 poisoning affects the cardiovascular system, the cerebrovascular system, the endocrine system, mental health, and the nervous system. Thus, we studied the prevalence of their major chronic diseases associated with CS2 poisoning recently after many years. Also in this study, after the subjects were identified as CS2 poisoning-related occupational diseases, there are subjects over 70 years of average age with disorders of the nervous system and sensory organs, hypertension, psychoneurotic disorder, cerebrovascular disease, diabetes, coronary artery disease, and arrhythmia. Because among ex-workers of the rayon manufacturing plant, only 633 survivors recognized as CS2 poisoning-related occupational were studied, the others not identified as CS2 poisoning occupational diseases should also be investigated. A patient-control study will be needed in the future.
This study was supported by Wonjin Industrial Accident Society (WIAS).
Funding
Not applicable.
Availability of data and materials
The datasets generated and analysed during the current study are not publicly available due to reasons why data are not public.

CI

Confidence interval

CS2

Carbon disulfide

ICD

International classification of disease

OR

Odds ratio

SPR

Standardized prevalence ratio

TTCA

2-thiothiazolidine-4-carboxylic acid

TWA

Time weighted average
HMC drafted this manuscript. KWY designed this study and corrected final manuscript as corresponding author. HMC and KWY developed questionnaire and revised it. HMC, KGP and KYK conducted the survey and contributed to the data collection. HMC analyzed the data. All authors read and approved the final manuscript.
Ethics approval and consent to participate
All study subjects were informed of the purpose of this study. The subjects were consented to participate under the ‘Ethics, consent & permissions’ heading and to publish to report individual patient data. This study was approved by the Ethics Committee of Wonjin Institute for Occupational and Environmental Health. The reference number is IRB-2016-003.
Consent for publication
The subjects were consented to publish to report individual patient data.
Competing interests
The authors declare that they have no competing interests.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Figure & Data

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      Carbon disulfide exposure estimate and prevalence of chronic diseases after carbon disulfide poisoning-related occupational diseases
      Ann Occup Environ Med. 2017;29:52  Published online October 26, 2017
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    Carbon disulfide exposure estimate and prevalence of chronic diseases after carbon disulfide poisoning-related occupational diseases
    Carbon disulfide exposure estimate and prevalence of chronic diseases after carbon disulfide poisoning-related occupational diseases
    20. CS2 poisoning or its secondary diseases
    Ga. A worker who has worked for more than two years on work exposed to CS2 vapor of around 10 ppm shall be considered as a work-related disease if any of the following symptoms or symptoms appear.
    (1) When there is one of retinal microvessels, multiple cerebral infarction, capillary glomerulosclerosis on renal biopsy.
    However, it excludes diseases caused by causes other than CS2, such as diabetes, hypertension and vascular disorders.
    (2) Retinal lesions other than microvascular lesions, multiple peripheral nerve lesions, optic neuritis, coronary heart disease, central nervous system disorders or psychiatric disorders.
    However, it excludes diseases caused by causes other than CS2, such as diabetes, hypertension and vascular disorders.
    (3) There is one of (2) and there is at least one of kidney disorder, liver disorder, hematopoietic system disorder, reproductive system disorder, sensory nerve impairment disorder, and hypertension.
    Na. A worker who is exposed to more than 20 ppm of CS2 vapor for more than two weeks shall be considered as a work-related disease if they present with sudden manifestations of mental disorders such as confusion, delirium, schizophrenia and bipolar disorder.
    Da. When exposed to a large or high concentration of CS2 vapor, symptoms of acute intoxication such as consciousness disorder are regarded as occupational diseases.
    DiseaseClassification of 298 Diseasesa ICD-10 codeb
    Hypertension
    Essential(primary) hypertention
    Other hypertensive diseases
    I10 Essential (primary) hypertension
    I11 Hypertensive heart disease
    I12 Hypertensive renal disease
    I13 Hypertensive heart and renal disease
    I15 Secondary hypertension
    Coronary artery disease
    Acute myocardial infarction
    Other ischaemic heart diseases
    I20Angina pectoris
    I21Acute myocardial infarction
    I22 Subsequent myocardial infarction
    I23 Certain current complications following acute myocardial infarction
    I24 Other acute ischaemic heart diseases
    I25Chronic ischemic heart disease
    Cerebrovascular disease
    Transient cerebral ischaemic attacks and related syndromes
    Cerebral palsy and other paralytic syndromes
    G45 Transient cerebral ischaemic attacks and related syndromes
    G50 Disorders of trigeminal nerve
    G51 Facial nerve disorders
    G52 Disorders of other cranial nerves
    G53 Cranial nerve disorders in diseases classified elsewhere
    G80 Cerebral palsy
    G81 Hemiplegia
    G82 Paraplegia and tetraplegia
    G83 Other paralytic syndromes
    Diabetes mellitus
    Diabetes mellitusE10 Type 1 diabetes mellitus
    E11 Type 2 diabetes mellitus
    E12 Malnutrition-related diabetes mellitus
    E13 Other specified diabetes mellitus
    E14 Unspecified diabetes mellitus
    Arrhythmia
    Conduction disorders and cardiac arrhythmiasI44 Atrioventricular and left bundle-branch block
    I45 Other conduction disorders
    I46 Cardiac arrest
    I47 Paroxysmal tachycardia
    I48 Atrial fibrillation and flutter
    I49 Other cardiac arrhythmias
    Psychoneurotic disorder
    Schizophrenia schizotypal and delusional disorders
    Mood [affective] disorders
    Neurotic,stress-related and somatoform disorders
    F20 Schizophrenia
    F21 Schizotypal disorder
    F22 Persistent delusional disorders
    F23 Acute and transient psychotic disorders
    F24 Induced delusional disorder
    F25 Schizoaffective disorders
    F28 Other nonorganic psychotic disorders
    F29 Unspecified nonorganic psychosis
    F40 Phobic anxiety disorders
    F41 Other anxiety disorders
    F42 Obsessive-compulsive disorder
    F43 Reaction to severe stress, and adjustment disorders
    F44 Dissociative [conversion] disorders
    F45 Somatoform disorders
    F48 Other neurotic disorders
    Disorders of the nervous system and sensory organs
    Nerve, nerve root and plexus disorders
    Other diseases of the nervous system
    G12 Spinal muscular atrophy and related syndromes
    G13 Systemic atrophies primarily affecting central nervous system in diseases classified elsewhere
    G21 Secondary parkinsonism
    G22 Parkinsonism in diseases classified elsewhere
    G24 Dystonia
    G25 Other extrapyramidal and movement disorders
    G26 Extrapyramidal and movement disorders in diseases classified elsewhere
    G37 Other demyelinating diseases of central nervous system
    G56 Mononeuropathies of the upper limb
    G57 Mononeuropathies of the lower limb
    G58 Other mononeuropathies
    G59 Mononeuropathy in diseases classified elsewhere
    G62 Other polyneuropathies
    G64 Other disorders of the peripheral nervous system
    G70 Myasthenia gravis and other myoneural disorders
    G72 Other myopathies
    G73 Disorders of the myoneural junction and muscle in diseases classified elsewhere
    G90 Disorders of the autonomic nervous system
    G92 Toxic encephalopathy
    G93 Other disorders of the brain
    G94 Other disorders of the brain in diseases classified elsewhere
    G95 Other diseases of the spinal cord
    G96 Other disorders of the central nervous system
    G98 Other disorders of the nervous system not elsewhere classified
    G99 Other disorders of the nervous system in diseases classified elsewhere
    DepartmentCS2 -exposed Concentration (ppm)Job Contents
    High exposure concentration department
    Spinning
      Doping6.53Threading up a spinning machinery and taking out the cake, As CS2 is released during rayon regeneration, exposure concentration is highest with direct exposure.
      Circuit6.58In the spinning room having a tangled or broken thread, As CS2 is released during rayon regeneration, exposure concentration is highest with direct exposure.
      Motor Repair3.79Repairing motors of a spinning machinery
    Moderate exposure concentration department
     Electrical Equipment Repair4.33High amount of spinning room work while repairing electrical equipment due to mechanical corrosion problems.
     Maitenance of Ejector3.03It is intermittent for reasons such as machine maintenance, but working within the spinning department
     Collection of Sulfuric acid3.79CS2 mixed in the recovered solution.
     Manufacturing of CS2 2.77Exposure to high concentrations of CS2 for a short time while manufacturing, but protective gear is used.
    Post-Process
      Packing3.6Restricted to the spinning room
      Carrying1.96Working in a spinning room for a long time to transport rayon.
      Refining2Exposure to remaining CS2 while processing semi-finished cake
     Maintenance2.16Estimated at 50% of that in the electrical equipment repair department
     Manufacturing of Viscose1.35
    Low exposure concentration department
     Water Treatment0.45Sewage inspection and cleaning in the spinning room
     Manufacturing of Chemicals0.23Estimated at 50% of that in the water treatment department, production of caustic soda and liquid chlorine, lower possibility of direct exposure.
     General Affairs0.12Estimated at 50% of that in the manufacturing department
    Operating Period (year)Weight by periodEvidence
    1966 (Initial operation)-19743.5The average concentration of CS2 in the spinning division in the 1960s (20 ppm) was about 3.5 times the average concentration of the total spinning division measured in 1991 (5.6 ppm).
    1975–19892.75The average concentration in the spinning division measured in the 70s and 80s (10–15 ppm) was about 2.25 times the average concentration in the total spinning division measured in 1991 (5.6 ppm).
    Since 1975, the production of rayon has increased. According to the operator interview, the exhaust system has changed, and the screen breaks down due to the age of the equipment. Thus, an additional weight of 0.5 was included.
    1990–1993 (Upon closure)0.5The compliance towards wearing personal protective gear was relatively good.
    The highest CS2 exposure concentration measured in protective equipment (3.2 ppm) was about 0.5 times that measured in 1991 (5.6 ppm).
    • cumulative exposure index (CEI) = Σ (working years x reference concentration x weight)
    • time weighted average CS2 concentration = Σ (the hours in the workday x reference concentration x weight) / the hours in the workday of exposure to CS2
    Number of the subjectsMeanSD
    N%
    Demographic characteristics
    Total633100.0
    SexMale54686.3
    Female8713.7
    Age distribution (year)50–595752.6
    60–6919669.4
    ≥ 7038071.6
    SmokingNo21233.5
    Yes38560.8
    No answer365.7
    Alcohol consumption (days/week)<133653.1
    ≥126041.1
    No answer375.9
    Employment characteristics
    Age at first employment (years)27.95.3
    Age at date last observed among survivors (years)70.77.5
    Year in the first employment (year)1974.26.2
    <197533953.6
    1975–199329446.4
    Duration of employment (years)12.85.6
    <1020429.7
    10–<2037959.9
    ≥206610.4
    Cumulative CS2 exposure index (ppm·yr)128.282.2
    0–<67a 16926.7
    67–<13420632.5
    ≥134b 25840.8
    Time-weighted average CS2 concentration (ppm)10.14.9
    0- < 5c 11217.7
    5–<10d 19931.4
    ≥1032250.9
    Department distribution by CS2 exposure concentration
    Low (<5 ppm)e 34053.7
    High (≥5 ppm)29346.3
    Workers Exposed to CS2 (%)
    Department (N = 633)
    SpinningElectrical Equipment RepairMotor RepairCollection of Sulfuric acidMaintenance of ejectorManufacturing of CS2 Post-ProcessRefiningMaintenanceManufacturing of ViscoseWater TreatmentGeneral Affairs
    CS2 exposure concentrationa (ppm)
    0- < 5b N101001037295200
    %3.67.70.00.02.50.025.525.056.396.30.00.0
    5- < 10c N921012311110767121
    %3.215.438.534.377.591.773.875.043.71.9100.050.0
    ≥10N26110162381100101
    %93.276.961.565.720.08.30.70.00.01.80.050.0
    total (N)28013263540121458165422
    Observed EventsStudy populationDisease Prevalence
    NN%
    Disease
     Hypertension43863369.2
     Coronary artery disease8863313.9
     Cerebrovascular disease15763324.8
     Diabetes mellitus15563324.5
     Arrhythmia86331.3
     Psychoneurotic disorder41663365.7
     Disorders of the nervous system and sensory organs45863372.4
    Table 1 Standards of occupational accidents about CS2 poisoning or its secondary diseasesa

    aIndustrial Accident Compensation Insurance Act, Article 39, Ministry of Labor, 1997

    Table 2 ICD-10 code of target disease

    a2015 National Health Insurance Statistical Yearbook

    bInternational Classification of Disease-10

    Table 3 Establishing criteria for CS2 exposure concentration by department

    Table 4 Setting weight by operating period

    Table 5 Calculation of the cumulative exposure index and time-weighted average concentration of CS2

    Table 6 Demographic and employment characteristics of the study subjects

    alower one third defined by distribution of metric among all the study subject

    bupper one third defined by distribution of metric among all the study subject

    cEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values

    dIndustrial Safety and Health Act enforcement regulations separate Table 3 of 11 Amendment of allowable standard of exposure concentration by harmful factor, IRE - 2010 Code of Practice for the Safety, Health and Welfare at Work (Chemical Agents) Regulations 2001. Published by the Health and Safety Authority

    eEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values

    Table 7 CS2 exposure concentrations by department

    aTime-weighted average CS2 concentration

    bEU - Commission Directive 2006/15/EC of 7 February 2006 establishing a second list of indicative occupational exposure limit values

    cIndustrial Safety and Health Act enforcement regulations separate Table 3 of 11 Amendment of allowable standard of exposure concentration by harmful factor, IRE - 2010 Code of Practice for the Safety, Health and Welfare at Work (Chemical Agents) Regulations 2001. Published by the Health and Safety Authority

    Table 8 Disease prevalence for the study subjects


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