Mortality experience of arsenic-exposed workers

More evidence of unpublished industry studies of lead smelter/refinery workers

BACKGROUND

Lead smelter/refinery workers in the US have had significant exposure to lead and are an important occupational group to study to understand the health effects of chronic lead exposure in adults. Recent research found evidence that studies of lead smelter/refinery workers have been conducted but not published. This paper presents further evidence for this contention.

OBJECTIVES

To present further evidence of industry conducted, unpublished epidemiologic studies of lead smelter/refinery workers and health outcomes.

METHODS

Historical research relying on primary sources such as internal industry documents and published studies.

RESULTS

ASARCO smelter/refinery workers were studied in the early 1980s and found to have increased risk of lung cancer and stroke in one study, but not in another.

CONCLUSIONS

Because occupational lead exposure is an on-going concern for US and overseas workers, all epidemiologic studies should be made available to evaluate and update occupational health and safety standards.

Putative mechanisms responsible for the decline in cancer prevalence during organism senescence

Most scientific literature reports that aging favors the development of cancers. Each type of cancer, however, initiates and evolves differently, and their natural history can start much earlier in life before their clinical manifestations. The incidence of cancers is spread throughout human life span, and is the result of pre- and post-natal aggressions, individual susceptibility, developmental changes that evolve continuously throughout an individual's life, and time of exposure to carcinogens. Finally, during human senescence, the incidence declines for all cancers. Frequently, the progression of cancers is also slower in aged individuals. There are several possible explanations for this decline at the tissue, cell, and molecular levels, which are described here in. It is time to ask why some tumors are characteristic of either the young, the aged, or during the time of a decline in the reproductive period, and finally, why the incidence of cancers declines late during senescence of human beings. These questions need to be addressed before the origin of cancers can be understood.

An update of respiratory cancer and occupational exposure to arsenicals

Mortality was updated through 1982 for 611 arsenic-exposed employees originally studied through 1973. In the earlier report, total mortality was observed to have been below the comparable U.S. population; however, mortality was significantly elevated for respiratory cancer. The focus of the update was on respiratory cancer and of special interest was whether the risk of respiratory cancer remained in excess for individuals alive as of the end of the last study. In the update, 9 additional respiratory cancers were observed subsequent to 1973, the end of the follow-up in the original study, versus 7.8 expected. The risk ratio for the time-interval 1974-1982 (standardized mortality ratio SMR = 116) was diminished compared to that reported in the original study (SMR = 330). When the entire study period was analyzed, the risk of respiratory cancer did not appear to decline with interval since exposure cessation. Analyses by duration of arsenic exposure and interval since first exposure did not reveal any obvious dose-response relationships.

Lung cancer in never smokers: clinical epidemiology and environmental risk factors

More than 161,000 lung cancer deaths are projected to occur in the United States in 2008. Of these, an estimated 10 to 15% will be caused by factors other than active smoking, corresponding to 16,000 to 24,000 deaths annually. Thus lung cancer in never smokers would rank among the most common causes of cancer mortality in the United States if considered as a separate category. Slightly more than half of the lung cancers caused by factors other than active smoking occur in never smokers. As summarized in the accompanying article, lung cancers that occur in never smokers differ from those that occur in smokers in their molecular profile and response to targeted therapy. These recent laboratory and clinical observations highlight the importance of defining the genetic and environmental factors responsible for the development of lung cancer in never smokers. This article summarizes available data on the clinical epidemiology of lung cancer in never smokers, and several environmental risk factors that population-based research has implicated in the etiology of these cancers. Primary factors closely tied to lung cancer in never smokers include exposure to known and suspected carcinogens including radon, second-hand tobacco smoke, and other indoor air pollutants. Several other exposures have been implicated. However, a large fraction of lung cancers occurring in never smokers cannot be definitively associated with established environmental risk factors, highlighting the need for additional epidemiologic research in this area.

Antagonistic combinations of occupational carcinogens

Several epidemiological and experimental studies demonstrate that combinations of carcinogens may interact in a synergistic way. This has prompted speculations that modulating interactions of individual chemical carcinogens are synergistic as a rule. However, various combinations of chemical carcinogens have been described which interact not even additively but in an antagonistic way. The aim of this review is to collect information of antagonistic interactions of occupational carcinogens obtained by epidemiologic and animal studies. In addition, appropriate in vitro studies with the genotoxic endpoints DNA-adducts and micronuclei are included. The toxicological mechanisms of antagonistic interactions, although speculative in some cases, are discussed.

Mortality among Children Residing near the American Smelting and Refining Company (ASARCO) Copper Smelter in Ruston, Washington

A retrospective cohort study was undertaken to determine whether childhood exposure to ambient arsenic was associated with increased mortality rates. Cohort members comprised children who had lived within 4.0 km (2.5 mi) of the American Smelting and Refining Company (ASARCO) copper smelter and arsenic refinery in Ruston, Washington, for at least 2 yr during the time period from 1907 to 1932. The cohort included 1,827 boys and 1,305 girls identified from school census records. Exposure intensity was computed as the total number of years a child had lived at a residence less than 1.6 km (1.0 mi) from the smelter stack during the study period. In only one exposure intensity group (i.e., residence > or = 10.0 yr less than 1.6 km [1.0 mi] from the smelter) for boys were Cox proportional hazards ratios significantly higher than 1.00: for all causes of death (1.52), ischemic heart disease (1.77), and external causes (1.93). For girls, hazard ratios were not elevated significantly for any cause of death in any exposure intensity group.

Epidemiology of lung cancer

In the United States, lung cancer remains the leading cause of cancer death in both men and women even though an extensive list of risk factors has been well-characterized. Far and away the most important cause of lung cancer is exposure to tobacco smoke through active or passive smoking. The reductions in smoking prevalence in men that occurred in the late 1960s through the 1980s will continue to drive the lung cancer mortality rates downward in men during the first portion of this century. This favorable trend will not persist unless further reductions in smoking prevalence are achieved.

Reduction of the ex vivo production of tumor necrosis factor alpha by alveolar phagocytes after administration of coal fly ash and copper smelter dust

We investigated the effect of intratracheally instilled coal fly ash (FA) and copper smelter dust (CU) on the lung integrity and on the ex vivo release of tumor necrosis factor alpha (TNF-alpha) by alveolar phagocytes. Groups of female NMRI mice received a single intratracheal administration of different particles normalized for the arsenic content (20 micrograms/kg body weight, i.e., 600 ng arsenic/mouse) and the particle load (100 mg/kg body weight, i.e., 3 mg/mouse). Mice received tungsten carbide (WC) alone (100 mg/kg), FA alone (100 mg/kg, i.e., 20 micrograms arsenic/kg), CU mixed with WC (CU, 13.6 mg/kg, i.e., 20 micrograms arsenic/kg; WC, 86.4 mg/kg) and Ca3(AsO4)2 mixed with WC (20 micrograms arsenic/kg; WC, 100 mg/kg). Animals were sacrificed at 1, 6, or 30 d posttreatment and analyzed by bronchoalveolar lavage for total protein (TP) content, inflammatory cell number and type, and TNF-alpha production. Additional mice were studied to evaluate particle retention by measuring total arsenic retention in the lung at appropriate times. Instillation of WC induced a mild and transient (d 1) inflammatory reaction characterized by an increase of TP and an influx of polymorphonuclear leukocytes in the alveolar compartment. Compared to WC, Ca3(AsO4)2 produced a significant increase of TP content in BALF. CU particles caused a severe but transient inflammatory reaction, while a persisting alveolitis (30 d) was observed after treatment with FA. Compared to control saline, a marked inhibition of TNF-alpha release was observed in response to LPS in all groups at d 1. Cytokine production was upregulated in WC- and Ca3(AsO4)1-treated animals after 6 and 30 d, respectively. However, a 90% inhibition of TNF-alpha production was still observed at d 30 after administration of CU and FA. Although arsenic was cleared from the lung tissue 6 d after Ca3(AsO4)2 administration, a significant fraction persisted (10-15% of the arsenic administered) in the lung of CU- and FA-treated mice at d 30. We hypothetize that suppression of TNF-alpha production is dependent upon the slow elimination of the particles and their metal content from the lung.

Lung retention and bioavailability of arsenic after single intratracheal administration of sodium arsenite, sodium arsenate, fly ash and copper smelter dust in the hamster

Arsenic is present in airborne particulate material released by coal-fired power plants and non-ferrous metal smelters. We have assessed whether the physico-chemical properties of arsenic in such particles play a role in its lung retention and uptake by the body. Female hamsters were given a single intratracheal instillation of fly ash or copper smelter dust suspensions (at doses of 50 or 100 μg As kg(-1)) or identical amounts of soluble tri- and pentavalent arsenic, in the presence or absence of an inert dust material (tungsten carbide). The concentration of the element was measured in a 24 hour urine sample collected on the 1st, 2nd and 6th day after treatment and arsenic remaining in lung tissue was determined at the end of the same time periods. Both lung retention and urinary As excretion indicate a prolonged contact of the lung tissue with particulate As in contrast to soluble As salts. In addition to the effect of solubility described here, more research is needed to determine the effect of particle size and lung loading on retention, as well as the potential differences in the lung inflammatory response using arsenic-rich particulates from various sources.

Mortality in a cohort of orchard workers exposed to lead arsenate pesticide spray

During the period from 1890 to 1940, lead arsenate was the major pesticide used in apple orchards to control the coddling moth. In the Wenatchee area of Washington State, lead arsenate spray was used for longer periods and in larger quantities than in other areas of the United States. In 1938, a cohort of 1,231 people who lived in this area was selected for a study to determine the effects of exposure to lead arsenate spray and residue. This same cohort was re-examined to determine whether there was excess mortality that could be attributed to the lead arsenate exposure. Three levels of exposure (i.e., orchardist, intermediate, consumer) were defined, based upon the use of lead arsenate pesticide spray before and during the 1938 apple growing season. Age-adjusted hazard ratios for all causes of mortality were elevated for both male orchardists and male intermediates. The only significantly increased age-adjusted hazard ratio (1.94) was heart disease in male intermediates. No significantly elevated age-adjusted hazard ratios were observed for women in any exposure group. The lack of evidence that supported an increase in mortality from respiratory cancer in this cohort may have resulted from the lower cumulative concentration of arsenic exposure, the type of arsenical compound, and the small number of study subjects.

Survey of antimony workers: mortality 1961-1992

The mortality of a census population and a prospective cohort of men employed on an antimony smelter in the north east of England was followed up from 1961-1992. The workers studied were exposed to a variety of agents including antimony and its oxides, arsenic and arsenic oxides, sulphur dioxide, and polycyclic aromatic hydrocarbons. The regional mortality rates were used to calculate expected deaths and a group of zircon sand workers employed on the site were used as a comparison group. For the census population of men working on the smelter before 1961 a significant increase in deaths from lung cancer was found (32 observed v 14.7 expected, P < 0.001). A similar excess was seen among maintenance men (12 observed v 5.3 expected P = 0.016). No such excess was found in the cohort recruited after 1960 (5 observed v 9.2 expected, maintenance workers 3 observed v 2.8 expected). There was evidence of a minimum latency period of around 20 years between first exposure and death from lung cancer. No evidence was found for a correlation between length of time worked and mortality from lung cancer. The results show that an increased risk of lung cancer existed in the workers employed before 1961, but it was not possible to attribute this excess to any particular agent. Mortality analysed by five year calendar periods of first exposure show a lessening of effect after 1955. Although the power of the study is clearly less for more recent periods of exposure the absence of any excess in the population after 1960 is encouraging.

A review of the carcinogenicity of chemicals most frequently found at National Priorities List sites

Several studies have shown that numerous National Priorities List (NPL) sites have been contaminated with arsenic (747), cadmium (791), chloroform (596), or nickel (664). The National Toxicology Program (NTP, 1991) has classified these substances as known human carcinogens (arsenic and certain arsenic compounds) or as substances that may reasonably be anticipated to be carcinogens (cadmium and certain cadmium compounds, chloroform, and nickel and certain nickel compounds). The general population is probably exposed to low levels of these hazardous substances through drinking water, eating food, or inhaling contaminated air. People working or living near industries and facilities that manufacture and use chloroform, nickel, arsenic, or cadmium may be exposed to higher than background levels of these hazardous substances. Multiple pathways of exposure may exist for populations near hazardous waste sites. For example, high levels of chloroform (1,890 ppb) were found in well water near a waste site; high levels of cadmium exposure may exist for individuals living near cadmium-contaminated waste sites.

Do quantitative exposure assessments improve risk estimates in occupational studies of cancer?

Quantitative assessment of exposure intensity is a difficult process, particularly for jobs held long ago. Despite difficulties, the use of this approach is growing in occupational epidemiology because it is hoped that the estimates will more closely approximate delivered dose than more traditional measures such as duration of exposure. If this assumption is correct, development and use of quantitative exposure estimates should reduce nondifferential exposure misclassification, sharpen exposure-response gradients, and enhance interpretation of study results. In this report, we used two methods to assess the value of quantitative exposure assessments in cancer epidemiology. In one, we surveyed the literature for investigations on occupational cancer that included assessments of both duration and intensity of exposure. The results of this survey indicated that exposure measures based on some measure of intensity of exposure yielded monotonically increasing exposure-response gradients and larger relative risks more often than those based on duration of exposure. Duration of exposure, however, occasionally provided the larger relative risks. In another approach, we found that different measures of exposure to formaldehyde classified subjects quite differently. For example, duration of exposure was unrelated to average exposure and was only weakly associated with exposure intensity or peak exposure. Because different measures of exposure may classify subjects quite differently and because quantitative estimates usually, but not always, yield larger relative risks and sharper exposure-response gradients than other measures of exposure, we believe that the prudent approach in epidemiologic investigations would be to develop quantitative estimates of exposure and to conduct analyses using several different measures of exposure, or combinations such as duration by intensity. Multiple comparisons would, however, increase chance findings. The value of such an approach is twofold. When a true association exists, use of several different measures decreases the chances of an unfortunate selection of an exposure measure that is poorly related to delivered dose, which would tend to produce negative results, and increases the chances of uncovering sharper exposure-response gradients. Use of several exposure measures in investigations that fail to exhibit an association between exposure and disease would be of value because such an approach would provide greater confidence that negative findings were not simply due to exposure misclassification.

Continued surveillance of cancer incidence among Swedish smelter workers

A cohort study of workers at a smeltery in northern Sweden showed an excess mortality, mostly due to deaths in cancer (especially in the respiratory organs) and circulatory diseases. Further follow-up of the cohort showed a decreasing trend in lung cancer incidence and mortality. The cohort studied has now been expanded and comprises 6,334 blue-collar workers first employed 1928-1979. They were followed in the cancer register up to 1987-01-01 and in the cause-of-death register up to 1988-01-01. The decreasing trend in lung cancer incidence and mortality continued but there was still an elevated lung cancer incidence among the workers when compared with Swedish males. The cumulative occurrence of lung cancer since time of first employment was analyzed by different employment cohorts and a higher occurrence of lung cancer was found among those earlier employed.

Metal carcinogenesis: mechanistic implications

Cancer epidemiology has identified several metal compounds as human carcinogens. Recent evidence suggests that carcinogenic metals induce genotoxicity in a multiplicity of ways, either alone or by enhancing the effects of other agents. This review summarizes current information on the genotoxicity of arsenic, chromium, nickel, beryllium and cadmium compounds and their possible roles in carcinogenesis. Each of these metals is distinct in its primary modes of action; yet there are several mechanisms induced by more than one metal, including: the induction of cellular immunity and oxidative stress, the inhibition of DNA metabolism and repair and the formation of DNA- and/or protein-crosslinks.

Inorganic arsenic compounds: are they carcinogenic, mutagenic, teratogenic?

This review examines and evaluates the literature on the ability of inorganic arsenic compounds to cause cancer in humans and laboratory animals. The epidemiological data that supports the position that inorganic arsenical derivatives are carcinogenic in humans is convincing and difficult to deny because of their consistency. These data are from studies of different occupational exposures such as smelter and pesticide workers, as well as from studies of drinking water, wines and medicinal tonics that contained or were contaminated with inorganic compounds of arsenic. Indeed, positive dose-response relationships between cancer incidence or mortality with many inorganic arsenical substances have been shown. Despite the presence of data which confuse the interpretation and evaluation of epidemiological data, associated neoplasms of the lungs, skin and gastrointestinal systems have been observed as a result of exposure to inorganic arsenic compounds.The mechanism of carcinogenicity of inorganic arsenical substances in humans is unknown. Inorganic arsenic compounds are not carcinogenic in laboratory animals by most routes of administration. However, further studies (subchronic, chronic, carcinogenic) using intratracheal and other conventional routes in other animal species would appear to be warranted. Moreso, especially since there is no evidence that organic arsenic compounds are carcinogenic in numerous mammalian species. Inorganic derivatives of arsenic are not mutagenic but may be teraiogenic. This latter conclusion is dependent on the method of administration and size of the dose, as well as on the species of animal used for the study.

International Commission for Protection Against Environmental Mutagens and Carcinogens. ICPEMC Working Paper 7/1/2. Shared risk factors for cancer and atherosclerosis--a review of the epidemiological evidence

This paper reviews the epidemiological literature of relevance for the hypothesis that somatic mutation is involved in the formation of the atherosclerotic plaque. Assuming that somatic mutations are involved in atherogenesis, one would expect at least some of the risk factors for cancer and for atherosclerosis to be identical. Therefore, the review covers the correlated occurrence of cancer and atherosclerotic disease. Special interest is given to populations at high risk of cancer, including subpopulations with certain genetic diseases, and populations exposed to certain carcinogenic environmental agents including ionizing radiation, vinyl chloride monomer (VCM), arsenic, tobacco, and various industrial combustion effluents containing polycyclic aromatic hydrocarbons (PAHs). Exposure to combustion effluents from burning of tobacco or fuel is associated with an increased risk of cancer and atherosclerotic disease. Combustion effluents constitute a complex mixture of potentially hazardous agents, however, and the observed correlation of cancer and atherosclerosis among exposed persons cannot be unambiguously interpreted as evidence of a common etiology of the two groups of diseases. For ionizing radiation, arsenic, and VCM there is suggestive evidence that these agents possess an atherogenic effect beside their well-known carcinogenic properties. Both arsenic and VCM seem to have a specific affinity to the vascular bed causing various lesions including angiosarcomas and atherosclerotic plaques. Regarding ionizing radiation, the atherogenic effects seem to be localized to heavily irradiated fields. Beside the carcinogenic and atherogenic effects, exposure to arsenic, VCM, and ionizing radiation brings about an increase in the incidence of mutations and chromosomal aberrations. A theory involving somatic mutation in the pathogenesis of the atherosclerotic plaque could be consistent with the observed biological effects of ionizing radiation, arsenic, and VCM. The scant data from families with certain inherited diseases may also be consistent with an involvement of the genome in the pathogenesis of atherosclerosis. In conclusion, there is strong epidemiological evidence that several factors associated with an increased risk of cancer are also associated with an increased risk of atherosclerosis.

The confounding of occupation and smoking and its consequences

A strong pattern in smoking behavior can be demonstrated, in which smoking is much more prevalent among those occupational groups (and social strata) that are also more exposed to hazards in the workplace and much less prevalent among those groups less exposed to such hazards. As a consequence, comparing individuals with greater to those with lesser exposure to tobacco also compares groups that differ with respect to occupational exposure to dust, fumes and toxic substances and with respect to occupationally related lifestyle factors. Analyses of the U.S. National Health Interview Survey show that smoking and occupation are substantially confounded among individuals differing by (1) amount of smoking; (2) smoking cessation; (3) types of cigarettes smoked; (4) age of starting to smoke; and (5) exposure to more or less environmental tobacco smoke at home. This confounding between types of work and proximity to tobacco smoke may have masked relationships between type of employment and disease. But it is difficult to disentangle the effects of occupation and of smoking from each other without well planned further studies because (1) of the difficulty of estimating occupational effects and simultaneously adjusting for healthy worker effects, (2) satisfactory techniques for estimating relative effects of intertwined variables make demands on the quality and quantity of data that are not met by presently available data, and (3) there may be deeply rooted social and psychological attitudes toward effects of work versus effects of lifestyles that tend to bias investigative work.

Relation of arsenic exposure to lung cancer among tin miners in Yunnan Province, China

The relation of mining and smelting exposure to arsenic and lung cancer was studied among tin miners in Yunnan Province in the People's Republic of China. Interviews were conducted in 1985 with 107 living tin miners who had lung cancer and an equal number of age matched controls from among tin miners without lung cancer to obtain information on risk factors for lung cancer including detailed history of employment and tobacco use. Occupational history was combined with industrial hygiene data to estimate cumulative arsenic exposure. Similar methods were also used to estimate radon exposure for simultaneous evaluation in this analysis. The results indicate that subjects in the highest quarter of cumulative arsenic exposure have a relative risk of 22.6 compared with subjects without exposure after adjusting for tobacco and radon exposure, and a positive dose response relation was observed. Simultaneous evaluation of arsenic and tobacco exposure indicates a greater risk for arsenic, whereas simultaneous assessment of arsenic and radon exposure suggests radon to be the greater risk. There is no evidence of synergism between arsenic and tobacco exposure. Among arsenic exposed individuals, cases of lung cancer have longer duration but lower average intensity of arsenic exposure than controls, indicating that duration of exposure to arsenic may be more important than intensity in the aetiology of lung cancer. Finally, risk of lung cancer among workers exposed to arsenic only in mining is only slightly less than for miners whose exposure to arsenic was limited to smelting, although risks are highest when workers were exposed to both mining and smelting.

Methods for testing interactions, with applications to occupational exposures, smoking, and lung cancer

Various approaches to assessing the interaction between smoking and occupational exposures are described. The definition of interaction depends on the measure of association under consideration and can be expressed in terms of disease risk, time, or dose. Simple descriptive methods and maximum likelihood model fitting methods are presented for analyzing interactions in terms of joint effects on disease risk. Methods for assessing the influence of exposures on times to disease, using appropriate denominators, are also described. The various approaches are illustrated with published data on lung cancer in relation to asbestos, radon daughters, chloromethyl ethers, and arsenic. Some of the mechanisms that can be invoked to explain the observed patterns include initiation and promotion, lung clearance, transport across cell membranes, and mucous secretion.

Clinical and environmental aspects of arsenic toxicity

Arsenic is widely distributed throughout the animal and plant kingdoms and our environment where sources can be natural or anthropogenic. Agricultural uses of arsenic have declined recently, but it still has well-defined roles in industry. Small amounts of arsenic are metabolized in a variety of ways and are largely rapidly methylated and excreted by man and animals. Poisoning can occur and may follow an acute or chronic course. Toxic manifestations in man occur at the cellular level and may appear in many organ systems. Specific effects can often be demonstrated in the skin and in the vascular and nervous systems. Other toxic effects appear to include carcinogenesis, mutagenesis, and teratogenesis.

Cancer and aging

It is widely accepted that the incidence of cancer increases with aging and many hypotheses have been put forward to explain this association. A review of the literature, however, shows that the relationship between cancer and aging has to be reappraised. Although the incidence of most cancers increases during the second half of the animal life span, only with a few does it increase progressively with senescence in humans as well as in animals. As a matter of fact in many cases the incidence does not vary, levels off or even decreases in old individuals. Late developing tumors also seem in many instances to progress more slowly. Thus it seems that the incidence of cancer is related to age rather than to aging and that some conditions may be created during senescence which oppose the development of some cancers.

On the pulmonary tumorigenicity of arsenic trisulfide and calcium arsenate in hamsters

The pulmonary tumorigenicity of arsenic trisulfide and calcium arsenate was explored following 15 intratracheal instillations in male Syrian golden hamsters at weekly doses of about 3 mg/kg body weight (as arsenic). One lung adenoma appeared in 28 animals examined in the arsenic trisulfide group and 4 adenomas in 35 animals surviving the treatment with calcium arsenate. No adenomas were seen in 26 animals instilled with the vehicle (0.9% saline solution). The results show that calcium arsenate is tumorigenic (P less than 0.05), while the evidence is inconclusive for arsenic trisulfide.

Effects of chronic exposure to arsenate on the cardiovascular function of rats

Cardiovascular function was studied in anaesthetised male rats which received 50 micrograms/ml of arsenic (as sodium arsenate) in deionised drinking water for 320 days. High urinary excretion of arsenic was found at the end of treatment and the metal accumulated considerably in the kidneys and liver, which both presented slight alterations. No histopathological modifications were evident in other organs. Base line blood pressure, cardiac inotropism, and chronotropism and cardiovascular reactivity to noradrenaline, acetylcholine, angiotensin II, bradykinin, histamine, and serotonin did not differ in exposed or in control animals. In the exposed group, however, there was potentiation of the effects of vascular beta-adrenoceptor stimulation and a reduction in the vascular responsiveness to angiotensin I. Chronic arsenic exposure did not affect the baroreflex sensitivity but was able to induce sympathetic hyperactivity or hypersensitivity, or both, possibly associated with an antivagal action. Our results might help to explain the cardiovascular alterations seen in people chronically exposed to high concentrations of arsenic.

Urinary arsenic, chromium, and copper levels in workers exposed to arsenic-based wood preservatives

Urinary excretion of arsenic, chromium, and copper in workers exposed to arsenic-based wood preservatives was examined to evaluate occupational exposure to these chemicals. Spot urine samples were collected from 89 wood treaters and a comparison group of 232 individuals with no known exposure to arsenicals. The results of urinalysis revealed that the wood treaters averaged 103 micrograms arsenic/L while the comparison group averaged 74 micrograms arsenic/L. The mean urinary chromium and copper levels of the wood treaters were 41 micrograms chromium/L and 191 micrograms copper/L compared with 63 micrograms chromium/L and 221 micrograms copper/L for the comparison group. Covariance analysis of urinary arsenic level between the exposed and comparison groups revealed that the adjusted mean arsenic levels of the exposed population (78 to 122 micrograms arsenic/L) were significantly higher than that of the comparison group (72 micrograms arsenic/L). The adjusted mean urinary arsenic levels of these wood treaters, however, were within published normal limits. Analysis of covariance allowed comparison of group means after statistical adjustments for possible confounding variables such as seafood intake and age. The results indicate that urinary arsenic values can provide a useful index of occupational exposure to chromated copper arsenate wood preservatives, when the effects of dietary arsenic are controlled statistically.

A new method for the analysis of cohort studies: implications of the multistage theory of carcinogenesis applied to occupational arsenic exposure

Implications of the multistage theory of carcinogenesis for evaluating the effect of exposure to carcinogens in the workplace are described. This theory predicts different patterns of excess risk related to duration of exposure, age at initial exposure, and follow-up time since exposure stopped, depending upon which stage of the carcinogenic process is affected by the carcinogen, i.e., action at an early stage or a late stage. New statistical methodologies are proposed to examine these patterns and are applied to the lung cancer mortality experience from a cohort study of smelter workers exposed to arsenic. Under this multistage hypothesis, the results indicate that arsenic exerts a definite late stage effect though an additional effect at the initial stage cannot be ruled out. The possibilities of biased conclusions resulting from incomplete exposure histories and lack of smoking information are also discussed as well as implications of these results to experimental animal studies.

Possible effects on occupational lung cancer from smoking related changes in the mucus content of the lung

A number of recent epidemiological studies of lung cancer among occupations that expose workers to dusts or toxic aerosols have reported a larger prevalence of lung cancer among non-smoking than among smoking workers. One recent study using Beagle dogs has also reported significantly fewer respiratory tumors among animals exposed to radon, radon daughters, uranium dust and tobacco smoke than among animals exposed similarly except for tobacco smoke. The evidence is summarized here that the increased mucus in the lungs of smokers may help in the elimination of dust and toxic substances by facilitating migration of particles and aerosols and possibly also adding protection by thickening of the mucus layer. Recent developments in use of in vivo magnetometric measurements of dust content of workers' lungs in fact indicate that lungs of chronically exposed miners and millers contain less dust if they smoke than if they do not. The hypothesis that increasing mucus in the lung of exposed workers may protect them against lung disease now needs experimental verification in appropriate animal studies. If protective qualities of lung mucus are verified, means need to be explored that will increase mucus flow in non-smoking (and smoking) workers exposed to respiratory hazards.

Arsenic exposure, smoking, and respiratory cancer in copper smelter workers

A report by Lee and Fraumeni in 1969 linked exposure to arsenic and other contaminants to a threefold excess of respiratory cancer among 8,047 employees at the Anaconda copper smelter. We established vital status through December 1977 for a sample of 1,800 men from the original cohort. Average arsenic concentrations were estimated for each smelter department based on industrial hygiene measurements made from 1943 to 1965. Departments with similar concentrations were combined into four categories of exposure: 1) low (less than 100 micrograms/m3), 2) medium (100-499 micrograms/m3), 3) high (500-4,999 micrograms/m3) and 4) very high (greater than or equal to 5,000 micrograms/m3). Three indices of individual arsenic exposure were developed: time-weighted average, 30-day ceiling, and cumulative. Exposures to sulfur dioxide and asbestos were also examined. Smoking habits were obtained by questionnaire. Mortality was compared to that of men in the State of Montana using the modified lifetable method. A clear dose-response relationship between arsenic exposure and respiratory cancer was demonstrated. Men in the highest exposure category had a sevenfold excess. Those in the low and medium categories had a risk close to that expected. Ceiling arsenic exposure appeared to be more important than did time-weighted average exposure. Sulfur dioxide and asbestos did not appear to be important in the excess of respiratory cancer, although sulfur dioxide and arsenic exposures could not be separated completely. Smoking did not appear to be as important as arsenic exposure. Our findings suggest that had men worked only in departments with low or medium arsenic exposures (i.e., less than 500 micrograms/m3) there would have been little excess respiratory cancer. Since the estimates of arsenic exposure were based on department averages rather than on concentrations for individual jobs, these results must be interpreted with caution.

Studies of cytogenetic effects of sodium arsenicals on mammalian cells in vitro

The cytotoxic and cytogenetic effect of sodium arsenite and sodium arsenate on Chinese hamster ovary (CHO) cells is reported. Chromosome aberrations were induced with both arsenic compounds. Trivalent arsenic was more clastogenic than pentavalent arsenic. Sodium arsenite was also shown to produce increased sister chromatid exchange in CHO cells and increased chromosome breakage in human lymphocytes.

Health of workmen in the chromate-producing industry in Britain

In a follow-up study of 2715 men who had worked for at least one year at the three chromate-producing factories in Britain between 1948 and 1977 only 298 were lost to follow-up, and the average number of person-years in the study was 16.3. One hundred and sixteen deaths from lung cancer occurred in these men, with only 48.0 expected (O/E = 2.4; p less than 0.001). For men employed at the factory, which is still in operation, the relative risk of lung cancer has decreased from over 3.0 before plant modification to about 1.8 in those who have worked only since plant modification. A multivariate analysis was used in an attempt to unravel the overlapping influence of duration of employment, length of follow-up, plant modification, factory, age at entry to work, and estimated degree of chromate exposure. The major dependent factor appeared to be duration of employment; in addition the analysis suggested that modifications in the plant and work environment had been associated with an appreciable reduction of the excess risk from lung cancer.

Arsenic compounds and cancer

Exposure to arsenic compounds has been epidemiologically associated with various types of cancers, particularly cancer of the lung among copper smelters and pesticide workers, whereas skin cancers and liver angiosarcomas have been associated with ingestion of arsenic for treatment of skin disorders, especially psoriasis. Attempts to reproduce cancer in animals have been mainly unsuccessful, however. Experimental evidence suggests that arsenic inhibits DNA repair; this might help to explain the somewhat conflicting observations from epidemiologic studies and animal experiments with regard to carcinogenicity, and perhaps also cardiovascular morbidity related to arsenic exposure.

Mortality studies of smelter workers

In view of the historic importance of smelter workers in the field of occupational medicine, it is surprising that until very recently little data was available on the mortality experience of these workers. The problem in most studies lies in identifying the smelter workers, because smelting, strictly speaking, refers to the melting of ores for the purposes of recovering metals, whereas smelters sometimes perform the operations of roasting, calcining, sintering, converting, and refining. These distinctions are not made in most mortality studies. Most mortality studies of smelter workers conducted to date have shown some excess in lung cancer. For lead, copper, cadmium, and nickel smelters a different etiologic agent has been proposed for each. These different explanations arise partly from different initial perspectives in conducting the studies. In this paper, data are presented on a current historical-prospective study of males who worked a year or more during the period January 1, 1940 to December 31, 1964 at a copper smelter in Tacoma, Washington. This smelter (and refinery) handled a copper ore with a relatively high arsenic content and produced arsenic trioxide as a by-product. Overall 97.2% of the original study population was traced through 1976. Of the 1,061 who were found to have died, death certificates were obtained for 1,018, or 96%. For all causes of death, the mortality rates in this cohort, expressed as a Standardized Mortality Ratio (SMR), were 3.5% higher than that expected based on the United States white male mortality experience. A total of 104 respiratory system cancers were observed compared to 54.6 expected (SMR = 190.5, p less than .05). Respiratory cancer rates were found to be elevated in both smokers and nonsmokers. Overall, a gradual rise in SMR's for respiratory cancer was observed with increasing duration of exposure but not with an increasing interval from onset of exposure. This observation is consistent with the notion that the effects of arsenic on cancer incidence disappear with time. This phenomenon has also been observed for cigarette smokers and chromate workers. Additional analyses are planned for the Tacoma cohort, which will examine mortality according to process as well as by exposure to arsenic and other contaminants. The importance of studies of workers at other kinds of smelters and refineries is stressed.