Cohort and case-control analyses of workers exposed to vinyl chloride: an update

Microplastic and plastic pollution: impact on respiratory disease and health

Throughout their lifecycle, from production to use and upon disposal, plastics release chemicals and particles known as micro- and nanoplastics (MNPs) that can accumulate in the environment. MNPs have been detected in different locations of the human body, including in our lungs. This is likely a consequence of MNP exposure through the air we breathe. Yet, we still lack a comprehensive understanding of the impact that MNP exposure may have on respiratory disease and health. In this review, we have collated the current body of evidence on the implications of MNP inhalation on human lung health from in vitro, in vivo and occupational exposure studies. We focused on interactions between MNP pollution and different specific lung-resident cells and respiratory diseases. We conclude that it is evident that MNPs possess the capacity to affect lung tissue in disease and health. Yet, it remains unclear to which extent this occurs upon exposure to ambient levels of MNPs, emphasising the need for a more comprehensive evaluation of environmental MNP exposure levels in everyday life.

Worker studies suggest unique liver carcinogenicity potential of polyvinyl chloride microplastics

BACKGROUND

Plastic debris pervades our environment. Some breaks down into microplastics (MPs) that can enter and distribute in living organisms causing effects in multiple target organs. MPs have been demonstrated to harm animals through environmental exposure. Laboratory animal studies are still insufficient to evaluate human impact. And while MPs have been found in human tissues, the health effects at environmental exposure levels are unclear.

AIM

We reviewed and summarized existing evidence on health effects from occupational exposure to MPs. Additionally, the diverse effects documented for workers were organized by MP type and associated co-contaminants. Evidence of the unique effects of polyvinyl chloride (PVC) on liver was then highlighted.

METHODS

We conducted two stepwise online literature reviews of publications focused on the health risks associated with occupational MP exposures. This information was supplemented with findings from animal studies.

RESULTS

Our analysis focused on 34 published studies on occupational health effects from MP exposure with half involving exposure to PVC and the other half a variety of other MPs to compare. Liver effects following PVC exposure were reported for workers. While PVC exposure causes liver toxicity and increases the risk of liver cancers, including angiosarcomas and hepatocellular carcinomas, the carcinogenic effects of work-related exposure to other MPs, such as polystyrene and polyethylene, are not well understood.

CONCLUSION

The data supporting liver toxicity are strongest for PVC exposure. Overall, the evidence of liver toxicity from occupational exposure to MPs other than PVC is lacking. The PVC worker data summarized here can be useful in assisting clinicians evaluating exposure histories from PVC exposure and designing future cell, animal, and population exposure-effect research studies.

A vinyl chloride-exposed worker with an adrenal gland angiosarcoma: a case report

Adrenal epithelioidangiosarcoma (AEA) is a rare neoplasm that accounts for less than 1% of sarcomas. Due to its rarity, it can easily be misdiagnosed, both by the clinician and the pathologist. Data on the patient's occupational history was collected and analyzed. The bibliographic data was found on the PUBMED bibliographic search site after entering the word "extrahepaticangiosarcoma". We report a case of adrenal epithelioidangiosarcoma (AEA) in a 68 yr-old Caucasian male factory worker exposed to Vinyl Chloride (VC) for 15 yr. He underwent surgery, chemotherapy and radiotherapy. Hepatic angiosarcoma is a known consequence of VC exposure, but occupational causality of extra-hepatic angiosarcoma is controversial. Extra-hepatic angiosarcomas have been reported in VC workers, but never AEA. Cancerogenic effects of VC involve all endothelial areas of the body and extra-hepatic endothelial tumors may also be caused by this substance. This is the first published report of AEA diagnosed in a worker exposed to VC.

Update of the NIOSH life table analysis system: a person-years analysis program for the windows computing environment

BACKGROUND

Person-years analysis is a fundamental tool of occupational epidemiology. A life table analysis system (LTAS), previously developed by the National Institute for Occupational Safety and Health, was limited by its platform and analysis and reporting capabilities. We describe the updating of LTAS for the Windows operating system (LTAS.NET) with improved properties.

SOFTWARE DEVELOPMENT PROCESS

A group of epidemiologists, programmers, and statisticians developed software, platform, and computing requirements. Statistical methods include the use of (indirectly) standardized mortality ratios, (directly) standardized rate ratios, confidence intervals, and P values based on the normal approximation and exact Poisson methods, and a trend estimator for linear exposure-response associations.

SOFTWARE FEATURES

We show examples using LTAS.NET to stratify and analyze multiple fixed and time-dependent variables. Data import, stratification, and reporting options are highly flexible. Users may export stratified data for Poisson regression modeling.

CONCLUSIONS

LTAS.NET incorporates improvements that will facilitate more complex person-years analysis of occupational cohort data.

Model selection in logistic joinpoint regression with applications to analyzing cohort mortality patterns

We consider a general model for anomaly detection in a longitudinal cohort mortality pattern based on logistic joinpoint regression with unknown joinpoints. We discuss backward and forward sequential procedures for selecting both the locations and the number of joinpoints. Estimation of the model parameters and the selection algorithms are illustrated with longitudinal data on cancer mortality in a cohort of chemical workers.

Vinyl chloride: a case study of data suppression and misrepresentation

When the U.S. Environmental Protection Agency (EPA) finalized its 2000 update of the toxicological effects of vinyl chloride (VC), it was concerned with two issues: the classification of VC as a carcinogen and the numerical estimate of its potency. In this commentary we describe how the U.S. EPA review of VC toxicology, which was drafted with substantial input from the chemical industry, weakened safeguards on both points. First, the assessment down-plays risks from all cancer sites other than the liver. Second, the estimate of cancer potency was reduced 10-fold from values previously used for environmental decision making, a finding that reduces the cost and extent of pollution reduction and cleanup measures. We suggest that this assessment reflects discredited scientific practices and recommend that the U.S. EPA reverse its trend toward ever-increasing collaborations with the regulated industries when generating scientific reviews and risk assessments.

Intracranial Neoplasms

This chapter begins with a discussion of the taxonomy of primary brain tumors, with a focus on gliomas, meningiomas, and grading systems for these tumors. It discusses methodological challenges for studies of brain tumor incidence including variations in diagnostic practices. It summarizes descriptive epidemiology studies of brain tumor incidence and mortality by age, sex, histologic type, and ethnicity. Factors associated with survival are discussed including histologic grade, tumor location, and extent of surgical resection. Much work remains to discover the causes of the majority of human brain tumors, as established risk factors account for only a small proportion of these tumors. The chapter critiques evidence regarding possible risk factors for brain tumors, including genetic predisposition, ionizing radiation, chemical carcinogen exposure, electromagnetic fields, infections, head trauma, smoking, and diet.

Lung cancer risk in workers exposed to poly(vinyl chloride) dust: a nested case-referent study

BACKGROUND

There have been few investigations of an association between poly(vinyl chloride) (PVC) dust exposure and an increase in lung cancer incidence, and their conclusions have been inconsistent.

AIMS

To determine whether PVC and/or vinyl chloride monomer (VCM) is the associated risk factor(s), by means of a nested case-referent study, in order to estimate lung cancer risk, avoiding selection, information, or confounding biases.

METHODS

Thirty eight cases of histologically verified lung cancer and 224 control subjects without a history of cancer were selected from an Italian cohort of 1658 vinyl chloride workers. Information sources included clinical records (diagnosis, smoking habits) and plant records (occupational history). The risk of lung cancer was estimated by odds ratios (OR) with 95% confidence intervals (CI), calculated using logistic regression models.

RESULTS

In PVC baggers exposed to high levels of respirable PVC particles in the workplace, the lung cancer OR increases by 20% for each extra year of work (OR = 1.2003; 95% CI 1.0772 to 1.3469; p = 0.0010), when the influence of age and smoking habits is controlled. No relation was found between lung cancer and cumulative VCM exposure.

CONCLUSION

This nested case-control study showed, in the VCM/PVC industry, an increased risk of lung cancer associated with exposure to PVC dust; previous cohort studies failed to recognise such excess, probably because they used VCM exposure as the risk indicator.

Vinyl chloride and liver and brain cancer at a polymer production plant in Louisville, Kentucky

Studies of overlapping cohorts in the United States have shown an excess mortality from brain cancer in vinyl chloride (VC)-exposed workers. One plant located in Louisville, Kentucky, is included in many of these studies. We separated this plant from the large US cohort and re-analyzed the mortality experience. Louisville experienced significantly elevated liver (standardized mortality analyses [SMR] = 400) and brain cancer (SMR = 229) mortality. Liver cancer mortality remained significantly elevated (SMR = 344) in the remaining cohort; however, brain cancer mortality was markedly reduced (SMR = 112) when Louisville was removed. In contrast with liver cancer, a preliminary review of work assignments did not suggest that the brain cancer excess was related to VC exposure. The Louisville brain cancer cluster has had a significant impact on the reported literature. Although unrelated to VC, the cause of this cluster remains uncertain.

A case-cohort study of angiosarcoma of the liver and brain cancer at a polymer production plant

Past studies have reported an excess of angiosarcoma of the liver and brain cancer at a polymer production plant in Louisville, Kentucky. Although angiosarcoma has clearly been linked to vinyl chloride exposure, the cause of the brain cancer excess has been uncertain. We conducted case-cohort and case-control studies of both conditions in relation to chemicals used in polyvinyl chloride and nitrile rubber production. Angiosarcoma was strongly associated with vinyl chloride exposure but not with other chemicals used in production. Brain cancer was highest in workers hired prior to 1950 but was not associated with vinyl chloride or other specific exposures or production processes. This brain cancer cluster is similar to those reported in other industries in this generation of workers, the specific cause remaining unknown.

Periportal fibrosis and other liver ultrasonography findings in vinyl chloride workers

AIMS

To investigate the presence of liver lesions and their relation with vinyl chloride monomer (VCM) exposure or other personal risk factors, in workers involved in the production of VCM and polyvinyl chloride (PVC).

METHODS

A liver ultrasonography examination was conducted in 757 workers, some of whom had long standing service in the production of VCM and PVC. The study involved: assessment of individual past and present VCM exposure of each worker; collection of past personal health history, lifestyle and personal data; routine liver function tests; and liver ultrasonography.

RESULTS

No cases of liver malignancies were detected. Angiomas and liver cysts were found with a frequency of occurrence within the expected range of the general population. The main findings consisted of hepatomegaly (34.7%), steatosis (31.8%), and periportal fibrosis (16.0%). A logistic regression analysis indicated that hepatomegaly and steatosis were associated with obesity and lipid metabolism disturbances and not with VCM exposure. Periportal fibrosis, in addition to constitutional or dietary factors, was shown to be associated with VCM exposure, but only when maximum exposure in the subject's history had been at least 200 ppm as a yearly average; no effects were observed at 50 ppm or below.

CONCLUSIONS

Workers exposed to 200 ppm VCM for at least one year have a fourfold increased risk of developing periportal liver fibrosis. Liver ultrasonography is a suitable and important diagnostic test for the medical surveillance of vinyl chloride workers.

An increased standardised mortality ratio for liver cancer among polyvinyl chloride workers in Taiwan

AIMS

To determine the standardised mortality ratio (SMR) corresponding to different causes of death in workers from polyvinyl chloride polymerisation factories in Taiwan.

METHODS

Retrospective cohort study of workers from six polyvinyl chloride polymerisation factories in Taiwan. A total of 3293 male workers who had been employed for at least one year during the period 1 January 1950 to 31 December 1992, and were alive on 1 January 1985 were included for analysis. Using data acquired from Taiwan's National Mortality Registry, it was found that 144 of these workers died during the period 1985-97. The follow up rate was 99% with a total number of person-years at risk of 40 557.

RESULTS

SMR for all causes of death was 0.78, indicating a possible "healthy worker" effect. The SMR for liver cancer decreased with increasing age of first exposure to vinyl chloride monomer. This association was more prominent for workers who were first employed in the industry prior to 1970 (SMR 4.82). Medical records indicated that most liver cancers in this study were hepatocellular carcinoma.

CONCLUSIONS

Polyvinyl chloride workers may experience a higher risk of developing liver cancer, particularly hepatocelluar carcinoma.

Comparison of cancer risk estimates for vinyl chloride using animal and human data with a PBPK model

Vinyl chloride (VC) is a trans-species carcinogen, producing tumors in a variety of tissues, from both inhalation and oral exposures, across a number of species. In particular, exposure to VC has been associated with a rare tumor, liver angiosarcoma, in a large number of studies in mice, rats, and humans. The mode of action for the carcinogenicity of VC appears to be a relatively straightforward example of DNA adduct formation by a reactive metabolite, leading to mutation, mistranscription, and neoplasia. The objective of the present analysis was to investigate the comparative potency of a classic genotoxic carcinogen across species, by performing a quantitative comparison of the carcinogenic potency of VC using data from inhalation and oral rodent bioassays as well as from human epidemiological studies. A physiologically-based pharmacokinetic (PBPK) model for VC was developed to support the target tissue dosimetry for the cancer risk assessment. Unlike previous models, the initial metabolism of VC was described as occurring via two saturable pathways, one representing low capacity-high affinity oxidation by CYP2E1 and the other (in the rodent) representing higher capacity-lower affinity oxidation by other isozymes of P450, producing in both cases chloroethylene oxide (CEO) and chloroacetaldehyde (CAA) as intermediate reactive products. Depletion of glutathione by reaction with CEO and CAA was also described. Animal-based risk estimates for human inhalation exposure to VC using total metabolism estimates from the PBPK model were consistent with risk estimates based on human epidemiological data, and were lower than those currently used in environmental decision-making by a factor of 80.

Historical cohort study of 10 109 men in the North American vinyl chloride industry, 1942-72: update of cancer mortality to 31 December 1995

OBJECTIVES

To update and assess mortality from neoplasms to 31 December 1995 among 10 109 men employed in a job exposed to vinyl chloride for at least 1 year between 1942 and 1972 at any of 37 North American factories. Previous analyses indicated associations between employment in vinyl production and increased mortality risk from cancers of the liver and biliary tract, due to increased mortality from angiosarcoma of the liver, and brain cancer.

METHODS

Standardised mortality ratio (SMR) analyses, overall and stratified by several work related variables, were conducted with United States and state reference rates. Cox's proportional hazards models and stratified log rank tests were used to further assess occupational factors.

RESULTS

895 of 3191 deaths (28%) were from malignant neoplasms, 505 since the previous update to the end of 1982. Mortality from all causes showed a deficit (SMR 83, 95% confidence interval (95% CI) 80 to 86), whereas mortality from all cancers combined was similar to state referent rates. Mortality from cancers of the liver and biliary tract was clearly increased (SMR 359, 95% CI 284 to 446). Modest excesses of brain cancer (SMR 142, 95% CI 100 to 197) and cancer of connective and soft tissue (SMR 270, 95% CI 139 to 472) were found. Stratified SMR and Cox's proportional hazard analyses supported associations with age at first exposure, duration of exposure, and year of first exposure for cancers of the liver and soft tissues, but not the brain.

CONCLUSIONS

Excess mortality risk from cancer of the liver and biliary tract, largely due to angiosarcoma, continues. Risk of mortality from brain cancer has attenuated, but its relation with exposure to vinyl chloride remains unclear. A potentially work related excess of deaths from cancer of connective and soft tissue was found for the first time, but was based on few cancers of assorted histology.

Angiosarcoma of the liver in Great Britain in proximity to vinyl chloride sites

OBJECTIVES

To study the incidence of angiosarcoma of the liver in England and Wales 1979-86 and Scotland 1975-87. To investigate whether any non-occupational neighbourhood cases occurred near a vinyl chloride site.

METHODS

This is a geographical study of incident cases among the general population of Great Britain. Diagnosis of angiosarcoma of the liver was based mainly on the national cancer registry, the world register of cases among vinyl chloride workers, and the register of cases (including histological review) maintained by the Health and Safety Executive. Proximity (< 10 km) of residence to a vinyl chloride site was based on postcode of address at the time of diagnosis.

RESULTS

55 cases were ascribed to angiosarcoma of the liver in England and Wales with a further six cases in Scotland (annual incidence in Great Britain from all sources of around 1.4 cases per 10 million population). There were two cases with documented exposure to Thorotrast, and 10 cases among vinyl chloride workers. There were no vinyl chloride sites in Scotland. Among the 25 cases in England and Wales with histological diagnosis after review by a panel of pathologists, only 15 were confirmed as angiosarcoma, and one of the two Scottish cases after histological review was also confirmed. Overall, 11 cases ascribed to angiosarcoma were resident within 10 km of a vinyl chloride site; nine were vinyl chloride workers, one further case on histological review was not considered to have been correctly diagnosed as angiosarcoma, and the remaining case, confirmed as angiosarcoma, was employed at a vinyl chloride factory during the late 1950s, although not as a vinyl chloride worker.

CONCLUSION

The incidence of angiosarcoma of the liver in Great Britain remains extremely rare. The one confirmed case in a non-vinyl chloride worker within 10 km of a site must nevertheless be presumed to have been exposed to vinyl chloride in the workplace. In the period of study, there were no confirmed non-occupationally exposed cases of angiosarcoma among residents living near a vinyl chloride site in Great Britain.

Fatal work-related injuries in the U.S. chemical industry 1984-89

Several mortality studies of the chemical industry have examined fatal injuries, but most of these studies have been of employees of large chemical firms and have not separated work-related from non-work-related injuries. We examined all U.S. Occupational Safety and Health Administration (OSHA) investigation files in 1984-89 in 47 U.S. states of fatal injuries in the chemical industry, Standard Industrial Classification (SIC) 2800-2899. OSHA investigates all reported deaths over which it has jurisdiction; this includes most causes of work-related death except for homicide and motor vehicle crashes. For the 6 year period, there were 234 fatalities in the chemical industry, for a work-related fatality rate of 0.55 per 10,000 workers/year. The largest category of deaths was from explosions, with 99 (42%), followed by fire & burns, with 32 (14%), poisoning, with 31 (13%), and falls, with 18 (8%). Of the 99 deaths from explosions, 45 (45%) involved manufacture or handling of fireworks or other explosives. The fatality rate at firms with fewer than 50 employees was more than twice that of larger firms (P < 0.05) and employees at small firms were less likely to have been covered by a union contract (P < 0.05). OSHA issued citations for safety violations in 73% of the deaths. While regulatory authorities and the media often focus attention on large, multinational chemical corporations, the highest worker fatality rates are found at the smallest chemical firms.

Changes in lymphocyte single strand breakage and liver function of workers exposed to vinyl chloride monomer

Vinyl chloride monomer (VCM) is a suspected human carcinogen. Its metabolite, chloroethylene epoxide, is able to alkylate the DNA molecule and to produce single strand breakage (SSB). A total of 244 workers from 4 polyvinyl chloride (PVC) manufacturing factories were recruited to assess the SSB of their peripheral lymphocyte DNA. The method of alkaline unwinding and hydroxyapatite chromatography was used to detect and calculate frequencies of SSB. In addition, hepatitis B and C markers and the liver function of the workers were also examined. The worker's cumulative exposures to VCM were retrospectively constructed from the current monitoring data and each worker's job history. Multiple linear regression models were constructed to predict the worker's level of SSB and liver functions based on various exposure indices and variables, such as age, sex, smoking, drinking, and hepatitis markers. The results showed that current smoking and drinking status, and the presence of VCM exposures on the previous day were 3 major determinants of the level of SSB. Among the liver function tests, only gamma-glutamyl transpeptidase (GGT) was associated with current VCM exposures. In contrast, aspartate aminotransferase (AST), alkaline phosphatase (ALP) and alanine aminotransferase (ALT) were mainly affected by the presence of hepatitis B surface antigen (HBsAg) or anti-hepatitis C virus (anti-HCV). We conclude that GGT should be considered to be included in the regular health screening of VCM workers, and that the SSB method may not be suitable for long-term monitoring of cumulative exposure because of the quick DNA repair mechanism in humans.

The role of chemical, physical, or viral exposures and health factors in neurocarcinogenesis: implications for epidemiologic studies of brain tumors

This review highlights some future prospects and implications for epidemiologic research on the etiology of nervous system tumors. It reviews some points regarding physiology of the nervous system, in connection with mechanisms of neurocarcinogenesis, and experimental studies in animals. The results of epidemiologic studies are summarized in the light of the biological and experimental observations. The following aspects are particularly emphasized: (i) higher susceptibility of the developing nervous system to neurocarcinogenic agents (in the fetus and after birth); (ii) possible implications of knowledge about mechanisms of neurocarcinogenesis regarding crossing of the blood-brain barrier, activation of oncogenes and inactivation of anti-oncogenes, relationship between chemical structure and neurocarcinogenic action; (iii) necessity of further investigation concerning the occurrence of nitrosoureas and their precursors in the environment, and the potential role of nitroso compounds in the development of human brain tumors; (iv) lack of information about promoting or inhibiting neurocarcinogenic effects, and co-carcinogenesis--among others, interaction between X-irradiation and exposure to neurocarcinogenic nitrosoureas; (v) need for studying the potential neurocarcinogenic risk of polyomaviruses BKV, JCV, and SV40 to humans.

Mortality and cancer incidence among PVC-processing workers in Sweden

The mortality pattern and the cancer incidence were investigated among 717 men who had been employed for at least 3 months during 1964-1974 in three Swedish PVC-processing plants. The mortality was followed 1964-1986 and the cancer incidence 1964-1984. Expected figures were calculated from Swedish national rates. Among Swedish citizens, the observed mortality and cancer incidence was close to the expected in most diagnoses. Among immigrants, mostly from Finland, there was a marked excess of circulatory deaths. This finding was probably due to the higher incidence of coronary mortality in Finland compared to Sweden. In the whole cohort, five cases of malignant melanoma had occurred as compared to 1.5 expected (SMR = 3.4, 95% confidence limit 1.1-7.9). This may be due to chance but merits further investigation since an increased incidence of malignant melanoma has previously been found among Norwegian PVC-manufacturing workers.

Exposure to vinyl chloride monomer: results of a cohort study after a seven year follow up. The French VCM Group

In 1980 a prospective cohort study of exposed and non-exposed subjects was initiated in France by the Institut National de la Santé et de la Recherche Médicale (INSERM U287) in collaboration with occupational physicians from the companies involved. The aim was to evaluate the association between mortality and cancer morbidity and occupational exposure to vinyl chloride monomer (VCM). A total of 1100 subjects exposed to VCM and 1100 non-exposed controls matched for age (to two years), plant, and physician were followed up for seven years (8299 and 8202 person years for exposed subjects and controls respectively) for vital status and health and occupational state. Forty deaths occurred among exposed and 43 among non-exposed subjects (relative risk (RR) = 1.0; 95% confidence interval (95% CI) 0.6-1.5). Forty eight and 32 cases of cancer were reported among exposed and non-exposed subjects, respectively (RR = 1.3; 95% CI 0.8-2.1). Three cases of angiosarcoma of the liver occurred in the exposed group. Eight cases of lung cancer occurred among exposed subjects and six among non-exposed subjects. Fourteen cases of Raynaud's disease were found among exposed and one among non-exposed subjects and the difference was significant. One hundred and twenty three and 93 cases of cardiovascular disease (Raynaud's disease excluded) occurred in the exposed and non-exposed groups respectively (RR = 1.4; 95% CI 1.0-1.8); this difference was mainly due to hypertension. The test for an increasing risk with increased exposure was significant. The percentages of diseases of the respiratory system did not differ between the two groups (RR = 1.1; 95% CI 0.7-1.8).

Role of the physician in environmental medicine

This article describes the role of the medical history and of laboratory findings in diagnosing diseases caused by environmental chemicals. An understanding of routes of exposure is crucial in appropriate diagnosis and in preventing further harm. A listing of potential sources of information is also included.