A cohort study on trichloroethylene exposure and cancer mortality

Mortality in a combined cohort of uranium enrichment workers

OBJECTIVE

To examine the patterns of cause-specific mortality and relationship between internal exposure to uranium and specific causes in a pooled cohort of 29,303 workers employed at three former uranium enrichment facilities in the United States with follow-up through 2011.

METHODS

Cause-specific standardized mortality ratios (SMRs) for the full cohort were calculated with the U.S. population as referent. Internal comparison of the dose-response relation between selected outcomes and estimated organ doses was evaluated using regression models.

RESULTS

External comparison with the U.S. population showed significantly lower SMRs in most diseases in the pooled cohort. Internal comparison showed positive associations of absorbed organ doses with multiple myeloma, and to a lesser degree with kidney cancer.

CONCLUSION

In general, these gaseous diffusion plant workers had significantly lower SMRs than the U.S.

POPULATION

The internal comparison however, showed associations between internal organ doses and diseases associated with uranium exposure in previous studies. Am. J. Ind. Med. 60:96-108, 2017. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Risk of cancer among workers exposed to trichloroethylene: analysis of three Nordic cohort studies

BACKGROUND

Trichloroethylene (TCE) is a widely used chlorinated solvent with demonstrated carcinogenicity in animal assays. Some epidemiologic studies have reported increased risk of cancer of the kidney, cervix, liver and biliary passages, non-Hodgkin lymphoma, and esophageal adenocarcinoma.

METHODS

We established a pooled cohort, including 5553 workers with individual documented exposure to TCE in Finland, Sweden, and Denmark. Study participants were monitored for the urinary TCE metabolite trichloroacetic acid from 1947 to 1989 and followed for cancer. Standardized incidence ratios (SIRs) were calculated based on cancer incidence rates in the three national populations. Cox proportionate hazard analyses were used for internal comparisons. Tests of statistical significance are two-sided.

RESULTS

Overall, 997 cases of cancer (n = 683 in men; n = 314 in women) were identified during 154 778 person-years of follow-up. We observed statistically significant elevated standardized incidence ratios for primary liver cancer (1.93; 95% confidence interval [CI] = 1.19 to 2.95) and cervical cancer (2.31; 95% CI = 1.32 to 3.75). The standardized incidence ratio for kidney cancer was 1.01 (95% CI = 0.70 to 1.42) based on 32 cases; we did not observe a statistically significant increased risk of non-Hodgkin's lymphoma (SIR = 1.26; 95% CI = 0.89 to 1.73) or esophageal adenocarcinoma (SIR = 1.84; 95% CI = 0.65 to 4.65). Tobacco- and alcohol-associated cancers were not statistically significantly increased.

CONCLUSIONS

Our results suggest TCE exposure is possibly associated with an increased risk for liver cancer. The relationship between TCE exposure and risks of cancers of low incidence and those with confounding by lifestyle and other factors not known in our cohort require further study.

Environmental factors in cancer: trichloroethylene and related solvents: science, regulation, and cancer prevention

In summary, I have used the case of TCE exposure as an example of: (1) The importance of population-based research to identify and characterize possible environmental risk factors for cancer, and the need for a greater emphasis and proportional increase in public funding of research on prevention as compared to treatment. We need to understand these risks better, and use this information to drive effective public health prevention actions. (2) The imposition of strong restrictions on requests by bona fide researchers for access to data as a barrier to research that could be used to help resolve some of the most controversial issues in TCE epidemiology, in particular, and environmental risks in general, especially access to individual level data including data of event and location of residence. Researchers need ready access these data to more accurately characterize environmental exposures, diseases and their possible associations, and to help develop more effective public health preventive actions, although they should also protect confidentiality. (3) The need for more accurate and comprehensive biomarkers of exposure and disease to better assess possible associations between environmental and occupational exposures and disease; (4) The role of non-scientific concerns in limiting regulatory and advisory agencies in the reevaluation of their positions relative to preventing or lowering allowable exposures to TCE, in light of the growing body of evidence on the possible carcinogenicity of a compound still widely in use, to which many workers, and substantial segments of the general public, are exposed.

Scrutinizing ACGIH risk assessments: the trichloroethylene case

BACKGROUND

The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs) for occupational exposure to chemicals and physical agents have been very influential in the setting of occupational exposure limits in many countries.

METHODS

Three ACGIH risk assessments of the chlorinated solvent trichloroethylene (TCE) [ACGIH (1989): 5th edition; ACGIH (1992): 5th edition. Revised Vol II; ACGIH (1996): Suppl. 6th edition] are compared to 26 other risk assessments made of the same chemical substance. The documents are compared in terms of their overall conclusions and the data selected for assessment.

RESULTS

It is shown that these ACGIH risk assessment documents were based on incomplete and biased data sets.

CONCLUSIONS

The data on which the ACGIH [ACGIH (1996): Suppl. 6th edition] base their TCE risk assessment do not adequately reflect the available scientific knowledge about TCE toxicity and carcinogenicity. This may have influenced their conclusion that TCE is not carcinogenic in either animals or humans which stand out compared to contemporary risk assessments.

Interpretations of primary carcinogenicity data in 29 trichloroethylene risk assessments

This paper explores to what extent interpretations of individual primary carcinogenicity data differ between different risk assessors, and discusses possible reasons for such differences as well as their impact on the overall risk assessment conclusions. For this purpose 29 different TCE carcinogenicity risk assessments are used as examples. It is concluded that the TCE risk assessors surprisingly often interpret and evaluate primary data differently. Two particular reasons for differences in data interpretation are discussed: different assessments of statistics, and different assessments of whether the results obtained in bioassays have toxicological relevance. Differences in the interpretation and evaluation of epidemiological data are also explored and discussed.

The use and evaluation of primary data in 29 trichloroethylene carcinogen risk assessments

This paper reports the results from a detailed study on how risk assessments of chemicals are actually made. The study is performed by comparing 29 cancer risk assessments made of one and the same chemical substance, namely, trichloroethylene. In this paper, the conclusions that are drawn in these risk assessment documents are described, and differences between the conclusions are explored. This is made within the framework of a proposed cancer risk assessment index. The selection of scientific data for risk assessment purposes is analyzed and the different risk assessors' interpretations and evaluations of individual primary data are compared. It is concluded that the data sets utilized by the trichloroethylene risk assessors are surprisingly incomplete and that biased data selection may have influenced some of the risk assessors' conclusions. Different risk assessors often interpret and evaluate one and the same study in different ways. There are also indications of both interpretation bias and evaluation bias for some of the risk assessors.

Trichloroethylene and cancer: epidemiologic evidence

Trichloroethylene is an organic chemical that has been used in dry cleaning, for metal degreasing, and as a solvent for oils and resins. It has been shown to cause liver and kidney cancer in experimental animals. This article reviews over 80 published papers and letters on the cancer epidemiology of people exposed to trichloroethylene. Evidence of excess cancer incidence among occupational cohorts with the most rigorous exposure assessment is found for kidney cancer (relative risk [RR] = 1.7, 95% confidence interval [CI] 1.1-2.7), liver cancer (RR = 1.9, 95% CI(1.0-3.4), and non-Hodgkin's lymphoma (RR = 1.5, 95% CI 0.9-2.3) as well as for cervical cancer, Hodgkin's disease, and multiple myeloma. However, since few studies isolate trichloroethylene exposure, results are likely confounded by exposure to other solvents and other risk factors. Although we believe that solvent exposure causes cancer in humans and that trichloroethylene likely is one of the active agents, we recommend further study to better specify the specific agents that confer this risk and to estimate the magnitude of that risk.

Agency for Toxic Substances and Disease Registry's 1997 priority list of hazardous substances. Latent effects--carcinogenesis, neurotoxicology, and developmental deficits in humans and animals

In support of Superfund re-authorization legislation, the Division of Toxicology of the Agency for Toxic Substances and Disease Registry (ATSDR) prepared a chemical-specific consultation document for Congress that identified those chemicals with carcinogenic, neurological, or developmental adverse effects having a latency period longer than 6 years. The review was limited to the top 50 substances listed on ATSDR's 1997 Priority List of Hazardous Substances (Priority List). Among the top 50 chemicals, a review of the technical literature indicated that 38 (76%) were classified as "reasonably anticipated," "possibly," or "probably" capable of causing cancer in humans, based either on human and animal data. Eight chemicals (16%) had well-established cancer latency periods in humans of 6 years or more following exposure. Three substances (6%)--arsenic, creosote, and benzidine--had data indicating latency periods longer than 6 years. The technical literature review likewise confirmed the potential for neurological and developmental effects with a latency of 6 years. Twenty-seven (54%) of the top 50 substances caused acute and/or chronic neurotoxic effects; a number of these also caused neurological effects that persisted beyond 6 years (or the equivalent in animal studies) such as: behavioral problems, neurological deficiencies, reduced psychomotor development, cognitive deficiencies, and reduced IQ. Twenty-eight substances (56%) caused adverse developmental effects in offspring of exposed individuals or animals including increased fetal and infant mortality, decreased birth weights and litter sizes, and growth delays. Latency periods for related chemicals are expected to be similar due to structural and toxicological similarities.

To what extent are biomonitoring data available in chemical risk assessment?

1. Chemical risk assessment integrates the identification of hazards and the human exposure levels which can be established from external and/or internal exposure data. 2. The availability of biomonitoring and metabolism animal data, the skin penetration ability, and the existence of atmospheric threshold limit values were examined for twelve substances of the European first list of priority existing substances. This investigation was focused on workplace exposures and on urinary biomarkers of exposure. Appropriate biomonitoring data appeared to be available for two substances: styrene and trichloroethylene. Some biomonitoring research has been conducted on acrylonitrile, buta-1,3-diene, cyclohexane, 1,4-dichlorobenzene, hydrogen fluoride, 2-(2-methoxyethoxy)ethanol, however additional studies could be usefully carried out. No biomonitoring data are available for alkanes, C10-13, chloro; benzene, C10-13-alkyl derivatives; bis(pentabromophenyl)ether; diphenylether, octabromo-derivative. 3. It was concluded that in some cases, biomonitoring data are either lacking or scarce. This is rather surprising since the selection of the substances of the priority list was based on high tonnage, widespread use, extent of human exposure, and toxicological concern. The development of biomonitoring information could be helpful in assessing individual or population chemical exposure whatever the source and route, and would result in both more realistic and more accurate risk assessments.

Mortality and cancer incidence of aircraft maintenance workers exposed to trichloroethylene and other organic solvents and chemicals: extended follow up

OBJECTIVES

To extend the follow up of a cohort of 14,457 aircraft maintenance workers to the end of 1990 to evaluate cancer risks from potential exposure to trichloroethylene and other chemicals.

METHODS

The cohort comprised civilians employed for at least one year between 1952 and 1956, of whom 5727 had died by 31 December 1990. Analyses compared the mortality of the cohort with the general population of Utah and the mortality and cancer incidence of exposed workers with those unexposed to chemicals, while adjusting for age, sex and calendar time.

RESULTS

In the combined follow up period (1952-90), mortality from all causes and all cancer was close to expected (standardised mortality ratios (SMRs) 97 and 96, respectively). Significant excesses occurred for ischaemic heart disease (SMR 108), asthma (SMR 160), and cancer of the bone (SMR 227), whereas significant deficits occurred for cerebrovascular disease (SMR 88), accidents (SMR 70), and cancer of the central nervous system (SMR 64). Workers exposed to trichloroethylene showed non-significant excesses for non-Hodgkin's lymphoma (relative risk (RR) 2.0), and cancers of the oesophagus (RR 5.6), colon (RR 1.4), primary liver (RR 1.7), breast (RR 1.8), cervix (RR 1.8), kidney (RR 1.6), and bone (RR 2.1). None of these cancers showed an exposure-response gradient and RRs among workers exposed to other chemicals but not trichloroethylene often had RRs as large as workers exposed to trichloroethylene. Workers exposed to solvents other than trichloroethylene had slightly increased mortality from asthma, non-Hodgkin's lymphoma, multiple myeloma, and breast cancer.

CONCLUSION

These findings do not strongly support a causal link with trichloroethylene because the associations were not significant, not clearly dose-related, and inconsistent between men and women. Because findings from experimental investigations and other epidemiological studies on solvents other than trichloroethylene provide some biological plausibility, the suggested links between these chemicals and non-Hodgkin's lymphoma, multiple myeloma, and breast cancer found here deserve further attention. Although this extended follow up cannot rule out a connection between exposures to solvents and some diseases, it seems clear that these workers have not experienced a major increase in cancer mortality or cancer incidence.

Occupational risk factors for female breast cancer: a review

OBJECTIVES

Although progress has been made in identifying personal risk factors and in improving treatment for female breast cancer, incidence rates continue to increase. With women now occupying a sizable fraction of the workforce, it is worth inquiring whether there are occupational risk factors for breast cancer. This is a review of occupational studies on female breast cancer.

METHODS

Suitable reports and published articles with associations of female breast cancer and occupation were identified from technical reports, by searching the MEDLINE bibliographic data base, and by reviewing each paper on cancer that was published in 20 major journals during the period from about 1971-94.

RESULTS

A total of 115 studies were identified; 19 studies relied exclusively on data collected for administrative purposes, and there were four incident case-control studies and 92 cohort studies. Although data for individual industries, occupations, and exposures were sparse, there was limited evidence of an association with employment in the pharmaceutical industry and among cosmetologists and beauticians. Associations were also found for chemists and occupations with possible exposure to extremely low frequency electromagnetic fields, but potential methodological weaknesses preclude drawing any definite conclusions. There was little support for increased risks among textiles workers, dry cleaning workers, and nuclear industry workers.

CONCLUSIONS

Few high quality occupational studies directed specifically toward women have been carried out to allow the unambiguous identification of occupational risk factors for breast cancer. It is suggested that investigations that account for non-occupational risk factors and that assess exposure in a more detailed way be carried out. One strategy already suggested is to conduct population based, case-control studies in which subjects are interviewed about their occupational histories and exposure to chemical and physical agents which are then attributed from the job descriptions by a team of experts. These studies can then be supplemented when necessary with cohort studies of specific populations.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

Increased incidence of renal cell tumors in a cohort of cardboard workers exposed to trichloroethene

A retrospective cohort study was carried out in a cardboard factory in Germany to investigate the association between exposure to trichloroethene (TRI) and renal cell cancer. The study group consisted of 169 men who had been exposed to TRI for at least 1 year between 1956 and 1975. The average observation period was 34 years. By the closing day of the study (December 31, 1992) 50 members of the cohort had died, 16 from malignant neoplasms. In 2 out of these 16 cases, kidney cancer was the cause of death, which leads to a standard mortality ratio of 3.28 compared with the local population. Five workers had been diagnosed with kidney cancer: four with renal cell cancers and one with a urothelial cancer of the renal pelvis. The standardized incidence ratio compared with the data of the Danish cancer registry was 7.97 (95% CI: 2.59-18.59). After the end of the observation period, two additional kidney tumors (one renal cell and one urothelial cancer) were diagnosed in the study group. The control group consisted of 190 unexposed workers in the same plant. By the closing day of the study 52 members of this cohort had died, 16 from malignant neoplasms, but none from kidney cancer. No case of kidney cancer was diagnosed in the control group. The direct comparison of the incidence on renal cell cancer shows a statistically significant increased risk in the cohort of exposed workers. Hence, in all types of analysis the incidence of kidney cancer is statistically elevated among workers exposed to TRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlorinated hydrocarbon solvents: substituting our way toward human carcinogenicity

A discussion of the history of substitutions in industrial solvent use is presented, and animal carcinogenicity studies with certain chlorinated hydrocarbon solvents are reviewed. The present knowledge on the association between occupational exposure to chlorinated hydrocarbon solvents and human carcinogenicity is summarized, including a critical review of 23 studies pertaining to human carcinogenicity. Several deficiencies are identified in these studies that make interpretation of the results uncertain, including poor characterization of exposures in qualitative and quantitative terms, the small numbers of deaths or cases, and short follow-up periods. Despite these weaknesses, we conclude that, when viewed collectively, the evidence strongly suggests that occupational exposures to chlorinated hydrocarbon solvents are associated with an excess human cancer risk. The literature supports an association between occupational exposures to chlorinated hydrocarbons and elevated risks of leukemia, lymphoma, and urinary tract cancer. Parental occupational exposures are consistently associated with an elevated childhood cancer risk in the offspring.

Subclinical and reversible hepatic effects of occupational exposure to trichloroethylene

To detect early hepatic effects of chronic exposure to low-level trichloroethylene (TCE), serum total cholesterol (T-C), high-density-lipoprotein cholesterol (HDL-C) and activities of three serum enzymes [aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyl transpeptidase (GGT)] were determined in 148 workers (a cross-sectional study) and in 13 workers (a 2-year follow-up study) occupationally exposed to TCE in air. In the cross-sectional study, three exposure groups were defined by urinary total trichloro-compounds (U-TTC) levels of the workers [low-exposure group (n = 49): U-TTC < 10 mg/g creatinine; moderate-exposure group (n = 56): U-TTC 10- < 100; high-exposure group (n = 43): U-TTC > or = 100]. With increasing exposure levels, T-C (P = 0.143 by ANOVA) and HDL-C (P = 0.080 by ANOVA) slightly increased. The exposure, however, had no effect on the activities of the three serum enzymes. In the follow-up study, the fluctuations in U-TTC were well reflected in subclinical changes in HDL-C, AST, and GGT, but not in T-C or ALT. These results suggest that exposure to low-level TCE influences hepatic functions, affecting cholesterol metabolism rather than causing hepatic cell damage, and that these influences are subclinical and reversible. The increases in HDL-C caused by exposure to low-level TCE may be an example of "chemical hormesis" in humans.

Quantitative prediction of human cancer risk from rodent carcinogenic potencies: a closer look at the epidemiological evidence for some chemicals not definitively carcinogenic in humans

The existence of rodent carcinogens for which at least one epidemiological study found no evidence of human carcinogenicity has been claimed to provide evidence of the poor predictivity of rodent bioassays (F. K. Ennever, T. J. Noonan, and H. S. Rosenkranz (1987). Mutagenesis 2, 73-78). We have performed quantitative comparisons of the rodent and human carcinogenic potencies for these same chemicals. Starting with the rodent TD50 at the most sensitive site, we derived a predicted human incidence for the degree of exposure and duration of follow-up corresponding to the most comprehensive epidemiological study available, and then we compared the predicted incidence with the observed incidence. If a chemical produced no statistically significant increase in cancer at any site in the exposed population, consistency with rodent results is inferred if the minimum rodent TD50 is sufficiently high that no attributable cases would have been expected under the actual conditions of human exposure and follow-up. For 18 of the 22 chemicals examined, the human evidence is consistent with the predictions based on the rodent bioassay results. For two chemicals, dichlorobenzidine and ethylene thiourea, there is not enough epidemiological information to make a useful comparison with rodent bioassay data. For the two remaining chemicals, actinomycin D and vinylidene chloride, the human evidence is inconsistent with the predictions. But the conditions of the rodent bioassay of actinomycin D were inappropriate for the comparison, and for vinylidene chloride the human exposure dose and duration were uncertain; either chemical might yet demonstrate consistency with the rodent results in future epidemiological studies.

Retrospective cohort mortality study of workers at an aircraft maintenance facility. I. Epidemiological results

A retrospective cohort study of 14,457 workers at an aircraft maintenance facility was undertaken to evaluate mortality associated with exposures in their workplace. The purpose was to determine whether working with solvents, particularly trichloroethylene, posed any excess risk of mortality. The study group consisted of all civilian employees who worked for at least one year at Hill Air Force Base, Utah, between 1 January 1952 and 31 December 1956. Work histories were obtained from records at the National Personnel Records Centre, St. Louis, Missouri, and the cohort was followed up for ascertainment of vital state until 31 December 1982. Observed deaths among white people were compared with the expected number of deaths, based on the Utah white population, and adjusted for age, sex, and calendar period. Significant deficits occurred for mortality from all causes (SMR 92, 95% confidence interval (95% CI) 90-95), all malignant neoplasms (SMR 90, 95% CI 83-97), ischaemic heart disease (SMR 93, 95% CI 88-98), non-malignant respiratory disease (SMR 87, 95% CI 76-98), and accidents (SMR 61, 95% CI 52-70). Mortality was raised for multiple myeloma (MM) in white women (SMR 236, 95% CI 87-514), non-Hodgkin's lymphoma (NHL) in white women (SMR 212, 95% CI 102-390), and cancer of the biliary passages and liver in white men dying after 1980 (SMR 358, 95% CI 116-836). Detailed analysis of the 6929 employees occupationally exposed to trichloroethylene, the most widely used solvent at the base during the 1950s and 1960s, did not show any significant or persuasive association between several measures of exposure to trichloroethylene and any excess of cancer. Women employed in departments in which fabric cleaning and parachute repair operations were performed had more deaths than expected from MM and NHL. The inconsistent mortality patterns by sex, multiple and overlapping exposures, and small numbers made it difficult to ascribe these excesses to any particular substance. Hypothesis generating results are presented by a variety of exposures for causes of death not showing excesses in the overall cohort.

Consideration of the target organ toxicity of trichloroethylene in terms of metabolite toxicity and pharmacokinetics

Trichloroethylene (TRI) is readily absorbed into the body through the lungs and gastrointestinal mucosa. Exposure to TRI can occur from contamination of air, water, and food; and this contamination may be sufficient to produce adverse effects in the exposed populations. Elimination of TRI involves two major processes: pulmonary excretion of unchanged TRI and relatively rapid hepatic biotransformation to urinary metabolites. The principal site of metabolism of TRI is the liver, but the lung and possibly other tissues also metabolize TRI, and dichlorovinyl-cysteine (DCVC) is formed in the kidney. Humans appear to metabolize TRI extensively. Both rats and mice also have a considerable capacity to metabolize TRI, and the maximal capacities of the rat versus the mouse appear to be more closely related to relative body surface areas than to body weights. Metabolism is almost linearly related to dose at lower doses, becoming dose dependent at higher doses, and is probably best described overall by Michaelis-Menten kinetics. Major end metabolites are trichloroethanol (TCE), trichloroethanol-glucuronide, and trichloroacetic acid (TCA). Metabolism also produces several possibly reactive intermediate metabolites, including chloral, TRI-epoxide, dichlorovinyl-cysteine (DCVC), dichloroacetyl chloride, dichloroacetic acid (DCA), and chloroform, which is further metabolized to phosgene that may covalently bind extensively to cellular lipids and proteins, and, to a much lesser degree, to DNA. The toxicities associated with TRI exposure are considered to reside in its reactive metabolites. The mutagenic and carcinogenic potential of TRI is also generally thought to be due to reactive intermediate biotransformation products rather than the parent molecule itself, although the biological mechanisms by which specific TRI metabolites exert their toxic activity observed in experimental animals and, in some cases, humans are not known. The binding intensity of TRI metabolites is greater in the liver than in the kidney. Comparative studies of biotransformation of TRI in rats and mice failed to detect any major species or strain differences in metabolism. Quantitative differences in metabolism across species probably result from differences in metabolic rate and enterohepatic recirculation of metabolites. Aging rats have less capacity for microsomal metabolism, as reflected by covalent binding of TRI, than either adult or young rats. This is likely to be the same in other species, including humans. The experimental evidence is consistent with the metabolic pathways for TRI being qualitatively similar in mice, rats, and humans. The formation of the major metabolites--TCE, TCE-glucuronide, and TCA--may be explained by the production of chloral as an intermediate after the initial oxidation of TRI to TRI-epoxide.(ABSTRACT TRUNCATED AT 400 WORDS)

An association of human congenital cardiac malformations and drinking water contaminants

During an informal study in 1973 it was noted that approximately one third of patients with congenital heart disease lived in a small area in the Tucson Valley. In 1981 groundwater for a nearly identical area was found to be contaminated with trichloroethylene and to a lesser extent with dichloroethylene and chromium. Contamination probably began during the 1950s. Affected wells were closed after discovery of contamination. This sequence of events allowed investigation of the prevalence of congenital heart disease in children whose parents were exposed to the contaminated water area as compared with children whose parents were never exposed to the contaminated water area. The contaminated water area contained 8.8% of the Tucson Valley population and 4.5% of the labor force. Using their case registry, the authors interviewed parents of 707 children with congenital heart disease who, between 1969 and 1987, 1) conceived their child in the Tucson Valley, and 2) spent the month before the first trimester and the first trimester of the case pregnancy in the Tucson Valley. Two random dialing surveys showed that only 10.5% of the Tucson Valley population had ever had work or residence contact, or both, with the contaminated water area, whereas 35% of parents of children with congenital heart disease had had such contact (p less than 0.005). The prevalence of congenital cardiac disease (excluding syndromes, children with atrial tachycardia or premature infants with patent ductus arteriosus) in the Tucson Valley was 0.7% of live births and with syndromes was calculated to be 0.82%. The odds ratio for congenital heart disease for children of parents with contaminated water area contact during the period of active contamination was three times that for those without contact (p less than 0.005) and decreased to near unity for new arrivals in the contaminated water area after well closure. The proportion of infants with congenital heart disease as compared with the number of live births was significantly higher for resident mothers in the contaminated water area than for mothers with no exposure. No other environmental agent could be identified that was localized to the contaminated water area, but one could have been missed. The data show a significant association but not a cause and effect relation between parental exposure to the contaminated water area and an increased proportion of congenital heart disease among live births as compared with the proportion of congenital heart disease among live births for parents without contaminated water area contact.

Health risk assessment of environmental exposure to trichloroethylene

A review of the animal data showed trichloroethylene (TRI) to be of low acute toxicity. Repeated exposure showed that the target organs were the liver, and to a lesser extent, the kidney. TRI is not mutagenic or only marginally mutagenic. There is no evidence of fetotoxicity or teratogenicity. TRI is judged not to exhibit chronic neurotoxicity. Lifetime bioassays resulted in tumors in both the mouse and the rat. However, because of qualitative and quantitative metabolic differences between rodent and human, no one suitable tumor site can be chosen for human health risk assessment. In addition, of the several epidemiology studies, none has demonstrated a positive association for increased tumor incidence. A review of the health effects in humans shows TRI to be of low acute toxicity and, following chronic high doses, to be hepatotoxic. Environmental exposure to TRI is mainly via the atmosphere, while the contribution from exposure to drinking water and foodstuffs is negligible. The total body burden was calculated as 22 micrograms/day. The safety margin approach based on human health effects showed that TRI levels are well within the safety margin for the human no-observable-effect level (10,000 times lower). The total body burden represents a risk of 1.4 X 10(-5) by linearized multistage modeling. Therefore, by either methodological approach to risk assessment, the environmental occurrence of TRI does not represent a significant health risk to the general population or to the population in areas close to industrial activities.

Genetic toxicology of 1,1,2-trichloroethylene

1,1,2-Trichloroethylene (TCE) is a widely used halogenated solvent, produced in hundreds of millions of kg each year for industrial purposes. Occupational and environmental exposure of human populations to TCE has been reported in industrialized areas. Long-term carcinogenicity studies in rodents demonstrate that exposure to high doses of TCE results in the induction of liver and lung tumors in the mouse, and tumors of the kidney and the testis in the rat. An indirect mechanism, based on the stimulation of liver peroxisome proliferation by TCE metabolites, was proposed to explain species differences in TCE hepatocarcinogenicity. Mutagenicity studies indicate that TCE is weakly active both in vitro, where liver microsomes produce electrophilic TCE metabolites, and also in vivo in mouse bone marrow, where high rates of micronuclei, but no structural chromosome aberrations, are found. Among TCE metabolites, trichloroacetic acid was reported to be carcinogenic to mouse liver. Furthermore, both trichloroacetic acid and chloral hydrate were found to be genotoxic in vivo, inducing structural and numerical chromosome abnormalities, respectively.

Mortality among United States Coast Guard marine inspectors

Work history records and fitness reports were obtained for 1,767 marine inspectors of the U.S. Coast Guard between 1942 and 1970 and for a comparison group of 1,914 officers who had never been marine inspectors. Potential exposure to chemicals was assessed by one of the authors (RP), who is knowledgeable about marine inspection duties. Marine inspectors and noninspectors had a deficit in overall mortality compared to that expected from the general U.S. population (standardized mortality ratios [SMRs = 79 and 63, respectively]). Deficits occurred for most major causes of death, including infectious and parasitic diseases, digestive and urinary systems, and accidents. Marine inspectors had excesses of cirrhosis of the liver (SMR = 136) and motor vehicle accidents (SMR = 107), and cancers of the lymphatic and hematopoietic system (SMR = 157), whereas noninspectors had deficits for these causes of death. Comparison of mortality rates directly adjusted to the age distribution of the inspectors and noninspectors combined also demonstrated that mortality for these causes of death was greater among inspectors than noninspectors (directly adjusted ratio ratios of 190, 145, and 198) for cirrhosis of the liver, motor vehicle accidents, and lymphatic and hematopoietic system cancer, respectively. The SMRs rose with increasing probability of exposure to chemicals for motor vehicle accidents, cirrhosis of the liver, liver cancer, and leukemia, which suggests that contact with chemicals during inspection of merchant vessels may be involved in the development of these diseases among marine inspectors.

Sister-chromatid exchanges in lymphocytes of workers exposed to trichloroethylene

To detect mutagenic effects of trichloroethylene (TCE) on humans, sister-chromatid exchanges (SCEs) were analyzed in lymphocytes of 22 workers occupationally exposed to TCE and 22 matched controls. Although urinalysis in the workers revealed their obvious exposure to TCE, no increase in SCE frequencies was found in lymphocytes of the workers. SCE analysis in lymphocytes could not detect mutagenic effects by occupational exposure to TCE on humans.

Metabolic activity of antipyrine in workers occupationally exposed to trichloroethylene

In order to investigate possible effects of occupational exposure to trichloroethylene (TRI) on the liver cytochrome P-450 dependent monooxygenases, the metabolic activity of salivary antipyrine was determined in workers (I; N = 32) employed in dry-cleaning shops (I-1; N = 17) and in an industrial metal degreasing process (I-2; N = 15). The studies were performed twice: (a) during the working period, (b) and after at least three weeks free of exposure. The control group (II) consisted of 29 subjects with no known exposure to chemicals. Analyses of the solvents used (TRI) showed them to be mixtures. Statistically significant differences were found (P less than 0.01) in antipyrine t1/2 and clearance within the exposed group (Ia:Ib), but not between the exposed (I) and control (II) group. A breakdown of antipyrine pharmacokinetic data by I-1 and I-2 subgroups demonstrated a statistically significant difference in t1/2 (P less than 0.02) and clearance (P less than 0.05) within I-1 subgroup (a:b), in contrast to the I-2 subgroup (a:b). The difference in antipyrine t1/2 between I-1,a and the control group (II) was also statistically significant (P less than 0.05). Although there was no difference in TRI exposure between I-1 and I-2 based on the biological parameters of TRI absorption, the TRI used in I-2 was of higher grade of purity. It can therefore be concluded that TRI itself is not an inducer of liver monooxygenases and that the monooxygenase induction in subgroup I-1 of TRI exposed workers could be due to TRI impurities.

A genotoxic study of metal workers exposed to trichloroethylene. Sperm parameters and chromosome aberrations in lymphocytes

Metal workers exposed to trichloroethylene for the degreasing of metals were studied to evaluate the genotoxicity of this exposure. For 15 workers presently exposed to high doses of trichloroethylene there was no difference from unexposed persons with respect to sperm count and morphology, and a small increase of two fluorescent bodies (YFF%) in spermatozoa. In contrast, there was a highly significant increase in frequency of structural aberrations (breaks, gaps, translocation, deletions, inversions) and hyperdiploid cells in cultured lymphocytes from trichloroethylene degreasers. As control groups, physicians from chemically non-exposed surroundings and a concurrently sampled reference from cytogenetic investigations were used. This study indicates positive correlations between exposure to trichloroethylene and somatic chromosome aberrations, whereas no effect on male germ cells could be demonstrated.

Biological markers of solvent exposure

The important limitation of many epidemiologic studies is the relative inaccuracy of the assessment of the magnitude of exposure. For some solvents, the concentration in biological media is an indication of the internal exposure and is an indirect indication of the health risk, at least for acute effects. For long-term effects, e.g., carcinogenicity, biological monitoring data can also be used as showed with the individual occupational data on the level of trichloroacetic acid (TCA) in urine. Occupational epidemiology can improve the methods for the assessment of the actual total exposure and health risk in environmental epidemiology by providing higher dose cohort data.

Cause-specific mortality among Rhode Island jewelry workers

Cause-specific mortality patterns among Rhode Island jewelry manufacturing workers, as identified on death certificates from 1968 to 1978, were examined using the proportionate mortality ratio (PMR) method. Among males, elevated PMRs were observed for nonmalignant kidney disease (PMR = 163; Observed deaths [Obs] = 19; p less than or equal to .05), liver cancer (PMR = 297; Obs = 6; p less than or equal to .05), drug dependence (PMR = 379; Obs = 5; p less than or equal to .05), and accidental poisonings (PMR = 274; Obs = 8; p less than or equal to .05). All but one of the deaths from accidental poisonings involved drugs or drugs and alcohol. Among females, elevated PMRs were observed for stomach cancer (PMR = 174; Obs = 20; p less than or equal to .01), peptic ulcer (PMR = 235; Obs = 8; p less than or equal to .05), diseases of the skin and subcutaneous tissue (PMR = 383; Obs = 5; p less than or equal to .05), and drug dependence (PMR = 674; Obs = 3; p less than or equal to .05). Exposure to known renal toxins (heavy metals and solvents) used in the jewelry industry may account for the excess deaths from kidney disease. The elevated PMR for liver cancer may be due to exposure to solvents (trichloroethylene, perchloroethylene, carbon tetrachloride) that cause liver cancer in animals. The elevated PMRs for drug dependence and accidental poisonings may be due to the socioeconomic status of jewelry workers, or to the interaction between solvents used in jewelry manufacturing and drugs, or drugs and alcohol. Because of the lack of information about the specific occupational exposures of the decedents, this should be viewed as an exploratory investigation requiring further follow-up.

Dealing with the exposure variable in occupational and environmental epidemiology

Whereas the outcome variable in epidemiologic research is usually well-defined, the exposure is more diffuse, complex and variable, involving components of both intensity and duration. Usually, the time integral of the intensity has been used as a measure of exposure, e.g. working level months, fibre-years, etc. Toxicological models have suggested, however, that greater importance should be accorded to early exposure in cancer epidemiology, while the recent exposure may be more important as regards the development of some other types of disorders. A simplified approach in cancer epidemiology would be to consider the exposure within a time-window or otherwise allow for induction-latency time. For the practical assessment of exposure, so-called job exposure matrices might be of value, especially if recall bias is suspected, but on the other hand, there is rather little objective indication in the literature that serious recall bias is a major problem in case-referent studies.

[The liver and environmental poisons]

For almost a century now numerous examples of acute and subacute hepatic injury from exposure to toxic agents in the occupational or non-occupational environment have been extensively studied and are well documented, but such events are comparatively rare. In contrast, epidemiological data associating exposure to environmental chemicals with chronic liver disease or primary hepatic malignancies in the human is scarce as compared with the vast body of literature concerning chronic pulmonary disease as a consequence of exposure at the workplace. Large-scale industrial production of many newly synthesized organic chemicals began during the period 1930-1940 but it was not until the 1960s that the output increased exponentially. Consequently, the spectrum of environmental influences is gaining increasing complexity since simultaneous or sequential exposure to a variety of pollutants is becoming the rule rather than the exception. Possible interaction or synergism of environmental agents--even of those which in themselves or for their low dosage level may be considered "harmless" - and particularly latency periods of more than one decade further complicate preventive strategies. The liver, as the central site for the biotransformation of xenobiotics, deserves special attention when new chemicals which are to be introduced into the environment are being tested for their potential toxicity, especially since many hepatotoxic agents have been shown to undergo bioactivation in the liver. Currently available information on hepatic injury due to environmental agents is briefly reviewed and comprises solvents and degreasing agents, pesticides, polyhalogenated biphenyls, dioxins and dibenzofuranes, epoxy resin hardeners, vinyl chloride, naturally occurring hepatotoxins in plants and fungi, herbal medicines and traditional remedies and a side-light on the Reye syndrome and the Spanish "toxic oil syndrome".

Biochemical, histological, and ultrastructural changes in rat and mouse liver following the administration of trichloroethylene: possible relevance to species differences in hepatocarcinogenicity

Trichloroethylene (TRI), administered by gavage for 10 consecutive days, at doses of 500 to 1500 mg/kg body wt increased liver weight (175% of control), decreased hepatic DNA concentration (66% of control), and increased the synthesis of DNA (500% of control; as measured by [3H]dT incorporation) in B6C3F1 mice and Alderley Park mice. Similar treatment of Osborne-Mendel rats or Alderley Park rats resulted in smaller increases in liver weight (130% of control) and decreases in DNA concentration (83% of control). No effect of TRI on DNA synthesis was seen in rats. The increased DNA synthesis in the mouse was not apparently due to regenerative hyperplasia since no signs of necrosis were seen. Furthermore the increased [3H]dT incorporation probably represented semiconservative replication of DNA and not repair, since a parallel increase of mitotic figures was observed. Hence, the liver growth noted after TRI administration appears to be due to liver cell enlargement (hypertrophy) in the rat, but both hypertrophy and hyperplasia (cell proliferation) in the mouse. An important observation has been that TRI induced the peroxisomal enzyme activities, catalase, and cyanide-insensitive palmitoyl-CoA oxidation (147 and 786% of control, respectively), in mice but not in rats. Furthermore, increases in peroxisome volume density (up to 1110% of control) were observed in mice receiving TRI. These observations lead us to suggest that the species difference in hepatocarcinogenicity of TRI, seen between the rat and mouse, is possibly due to a species difference in peroxisome proliferation and cell proliferation, the peroxisome proliferation leading to increased reactive oxygen species and DNA damage, and the cell proliferation then acting to promote this lesion.

Trichloroethylene: an update

The toxicity of tricholoroethylene (TCE) has been summarized in a number of reviews. In this particular update, only the more recent studies that deal with metabolism and carcinogenicity have been examined. In reviewing the more recent publications on metabolism of TCE, we determined that differences exist in its metabolism if low doses are compared with high doses in animals. There may also be a difference in the metabolism of TCE between different species--namely mice, rats, and humans. TCE has not been shown to be a potent carcinogen in rats and it only seems to be a potent carcinogen in one specific strain of mice, namely the B6C3F1 mouse. Epidemiology studies have been rather limited. The number of persons examined so far for chronic toxic effects is small, compared with the enormous size of the work force that is exposed to TCE over prolonged periods. On an empirical basis, the occupational experience with TCE does not suggest that this compound is a potent carcinogen. The risk associated with exposure to trace amount (ppb) concentrations of TCE in water appear to be minimal or perhaps negligible. Because there are differences in metabolism of TCE, it is important that theoretical risks attributed to TCE in the past be reexamined. It is highly possible that in humans, the metabolic pathway leading to the formation of the proximate carcinogen is not activated at low doses, where TCE is excreted by first-order kinetics.

Interactions of trichloroethylene with DNA in vitro and with RNA and DNA of various mouse tissues in vivo

The covalent binding of 14C-1,1,2-trichloroethylene (14C-TRI) metabolites to calf thymus DNA in vitro and to RNA and DNA of mouse brain, lung, liver, kidney, spleen, pancreas, and testis after repeated i.p. injections has been studied. Hydrolysates of DNA reacted with 14C-TRI in vitro and hydrolysates of RNA and DNA from selected organs were separated on Aminex A6 for quantitation of alkylation products. The presence of 3,N4-etheno(deoxy)cytidine, 1,N6-etheno(deoxy)adenosine and 1,N6-ethenoadenine was investigated. No radioactivity could be registered in DNA incubated with 14C-TRI in the absence of liver microsomes. Covalent binding of 14C-TRI to DNA took place in the presence of liver microsomes from control mice. The binding was enhanced by 50% if liver microsomes from phenobarbital pretreated mice were used. The radioactivity in DNA reacted with 14C-TRI and microsomes from control mice was eluted in early fractions and together with thymidine. The same two peaks appeared on chromatography of DNA incubated with 14C-TRI and liver microsomes from phenobarbital pretreated mice. In addition, radioactivity was eluted together with 1,N6-ethenoadenine. Radioactivity was registered in RNA and DNA from all of the studied organs after i.p. injections of 14C-TRI. The radioactivity in RNA increased in the order brain less than testis less than pancreas less than kidney less than liver less than lung less than spleen. The radioactivity in DNA increased in the order brain less than kidney less than testis less than lung less than pancreas less than liver less than spleen. Aminex A6 chromatography revealed that the entire radioactivity in RNA from liver and kidney and in DNA from kidney, testis, lung, pancreas, and spleen was due to metabolic incorporation, particularly into guanine and adenine. This finding indicates that the C-C bond in TRI is split, with the formation of C1-fragments, during biotransformation in vivo. In liver DNA, the metabolic incorporation of radioactivity was insignificant. Instead, the dominant part of the radioactivity in liver DNA was eluted in early fractions. The elution profile of radioactivity in liver DNA gave no direct evidence of the formation of TRI-DNA adducts in vivo. No etheno-derivatives were identified as alkylation products of TRI in vivo, which is consistent with current theories of the metabolic fate of TRI.

Application and results of whole-body autoradiography in distribution studies of organic solvents

With the growing concern for the health hazards of occupational exposure to toxic substances attention has been focused on the organic solvents, which are associated with both deleterious nervous system effects and specific tissue injuries. Relatively little is known about the distribution of organic solvents and their metabolites in the living organism. Knowledge of the specific tissue localizations and retention of solvents and solvent metabolites is of great value in revealing and understanding the sites and mechanisms of organic solvent toxicity. Whole-body autoradiography has been modified and applied to distribution studies of benzene, toluene, m-xylene, styrene, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene and carbon disulfide. The high volatility of these substances has led to the development of cryo-techniques. Whole-body autoradiographic techniques applicable to the study of volatile substances are reviewed. The localizations of nonvolatile solvent metabolites and firmly bound metabolites have also been examined. The obtained results are discussed in relation to toxic effects and evaluated by comparison with other techniques used in distribution studies of organic solvents and their metabolites.

Epoxides--is there a human health problem?

The purpose of this review is to consider whether epoxides represent a hazard to human health. Possible means of occupational and non-occupational exposure are discussed with reference to the production and uses of industrially important compounds and other epoxides, such as naturally occurring plant and fungal products. In addition to epoxides themselves, unsaturated compounds that may be metabolised in vivo to epoxides are included, since this appears to be a further important means of exposure. The toxicology, in particular carcinogenicity and mutagenicity, is discussed, along with a brief outline of the biochemistry such as metabolism, binding to cell constituents, and DNA repair mechanisms. The question of interactions between different epoxides in vivo is also raised.

Toxicological aspects of chemical hazards in the rubber industry

Only three recognized strong carcinogens are used in the Swedish rubber industry: mineral oil, ethylene thiourea, and trichloroethylene. Besides, many curing agents, accelerators, antioxidants/antiozonants, and retarders may possess mutagenic and/or carcinogenic activity and may thus contribute to the total cancer risk in the rubber industry. Irritating compounds as well as modifiers of biotransformation further contribute to the complex exposure panorama of the rubber industry. Cancer risks in the work environment of the rubber industry can probably be more effectively reduced by general sanitary measures aimed at reduction of total exposure than by specific regulation of only a few established carcinogenic chemicals.

Chlorinated hydrocarbons and cancer: epidemiologic aspects

Available epidemiologic information related to halogenated hydrocarbons and cancer is reviewed. Many chlorinated hydrocarbons, both pesticides and solvents, have been shown to possess mutagenic or carcinogenic properties in bacterial test systems and animal experiments. Rather few substances have been associated with human cancer, but relatively few studies have been conducted.

Trichloroethylene vapours do not produce dominant lethal mutations in male mice

Exposure of male mice to trichloroethylene vapours during 24 h at levels or 50, 202 and 450 ppm did not reveal mutagenic effects in the dominant lethal assay. The following parameters were registered and evaluated: Fertilization rate, post-implantation loss, preemplantation loss and dominant lethal mutations.