[DNA methylation analysis in environmental and occupational cancer research]

The present paper reviews recent laboratory methods and experimental evidence concerning epigenetic biomarkers involved in carcinogenesis mechanisms. We introduce DNA methylation and its role in gene expression control. DNA methylation analysis may allow to identify early changes leading to cancer and other chronic diseases. We describe here strategies for laboratory analyses and their possible applications. We examine results from recent experimental studies suggesting that the effects of certain occupational agents are mediated by alterations in DNA methylation. Planning and conducting investigations on exposed human subjects will allow to verify whether DNA methylation changes identified in animal and in-vitro studies may be used as early-effect and susceptibility biomarkers. DNA methylation analysis has the potential for future applications in risk assessment and prevention programs conducted on subjects exposed to human carcinogens.

Descriptive epidemiology of malignant mesothelioma

BACKGROUND

Malignant mesothelioma (MM) is a rare cancer associated with exposure to asbestos, whose occurrence is increasing in industrialized countries.

OBJECTIVES

Describe and discuss: determinant factors, natural history, epidemic pattern, burden of MM to society at large, where interventions should be directed to change MM occurrence, gaps in knowledge.

METHODS

Review of the literature. Description of MM epidemiological features, with emphasis on risk, prognosis, control measures.

RESULTS

MM may be associated with low level asbestos exposure. Natural fibres other than asbestos possess the same carcinogenic potency. The estimated mean induction period is 25 years, and can be as long as 60 or more years. Survival is poor; current rates of MM in industrialized countries mirror past use of asbestos. In the USA, MM incidence increased steeply from the 1970's, peaked in 2000-2004, then levelled off and is expected to return to background levels by 2055. In the same period, the time-pattern for females was constant. Questions remain unanswered about the contribution of environmental asbestos exposure to MM occurrence. A gender effect has been described. The role of genetic and familial susceptibility is suggested by studies in Turkey. Sv40 has been proposed as co-factor in the asbestos-MM association. Controversy about the different hazards of different asbestos forms is still strong.

CONCLUSIONS

World production of asbestos has been declining dramatically in recent years, however increases have occurred in Asia. The decrease in asbestos use and a ban in several industrialized countries have proved effective in reducing the societal burden of MM.

Urinary t,t-muconic acid, S-phenylmercapturic acid and benzene as biomarkers of low benzene exposure

This research compared the capability of urinary trans,trans-muconic acid (t,t-MA), S-phenylmercapturic acid (S-PMA) and benzene excreted in urine (U-benzene) to monitor low benzene exposure and evaluated the influence of smoking habit on these indices. Gasoline attendants, urban policemen, bus drivers and two groups of referents working in two large Italian cities (415 people) were studied. Median benzene exposure was 61, 22, 21, 9 and 6 microg/m3, respectively, with higher levels in workers than in referents. U-benzene, but not t,t-MA and S-PMA, showed an exposure-related increase. All the biomarkers were strongly influenced by cigarette smoking, with values up to five-fold higher in smokers compared to non-smokers. In conclusion, in the range of investigated benzene exposure (<478 microg/m3 or <0.15 ppm), the smoking habit may be regarded as a major source of benzene intake; among the study indices, U-benzene is the marker of choice for the biological monitoring of occupational and environmental exposure.

[New effect biomarkers]

The major research goals for researchers developing biomarkers of effect are the development and validation of biomarkers that permit the prediction of the risk of disease in individuals and groups. One important objective is to prevent human cancer. This article reviews the most recent analytical methodologies, validation studies and field trials together with auditing and quality assessment of the necessary data based on scientific grounds. Consideration is given to new developments in the relatively young field of toxicogenomics, possibly leading to the identification of early changes that may lead to both cancer and non-cancer end points. Although the creation and development of reliable databases integrating information from genomic and proteomic research programmes should offer a contribution to the prediction of risks and prevention of diseases related to chemical exposure, the most promising future application of these technologies lies in the molecular diagnosis of diseases whose nosography will probably be redefined.

[The role of biological monitoring in health and epidemiological surveillance: the epidemiological approach]

A fundamental pre-requisite for the realization of biological monitoring programs for health surveillance is the availability of sufficiently accurate tests and adequate knowledge of the relationship between biomarkers and health effects. In this respect, epidemiology plays an essential role: in conjunction with other disciplines (industrial hygiene, toxicology, occupational medicine), it provides a conceptual and methodological framework for many biological monitoring activities. Compared to biomarkers of dose and effect, susceptibility markers (for example, metabolic polymorphisms), for which we have seen an explosion of research in recent years, need a specific consideration in that they pose (or may pose in a non-remote future) special problems. For different reasons, the use of genetic tests for predictive aims at the individual level should now be avoided; their use should be restricted to the research field for a better understanding of etiopathogenetic mechanisms.

[Intention to leave the nursing profession]

BACKGROUND

The NEXT Study (Nurses' Exit Study) was initiated in 10 European countries in order to shed light on nurses' working conditions and reasons of shortage.

OBJECTIVES

The study objective was to determine organisation and psychosocial conditions that lead to premature departure from the nursing profession.

METHODS

The questionnaire we used took into account aspects such as work history, work demands and organisation, career prospectives and individual resources. This article describes steps related to the construction and validation of the questionnaire and sampling methods. Preliminary results are also reported. Data analysis, performed in relation to the intention to leave the nursing profession, showed the distinctiveness of the situation in Italy compared to other European countries.

RESULTS

Conditions related to intention to leave are multifaceted, but they can be summarized as inadequacy of facilities to support the family needs of staff low level of trust in official structures, together with poor support by colleagues and superiors, work overload, and lack of independence at work--although the latter is foreseen in current legislation--and scant career and development possibilities.

CONCLUSIONS

These results confirm the existence of a difficult situation, although certain legislative changes are aimed at solving these problems.

[A simple method for risk assessment and its application to 1,3-butadiene]

BACKGROUND

This paper presents a risk assessment exercise applied to 1,3-butadiene, a probable carcinogenic agent, in the context of the activity of the Scientific Committee on Occupational Exposure Limits (SCOEL) of the European Commission. Data on cumulative exposures and relative risks for leukaemia in humans were derived from the open literature.

METHODS

A variety of excess relative risk models were applied taking into consideration, in a life-table fashion, mortality from leukaemia by age.

RESULTS

As an example of the outcome of the method, results are presented for a 1 ppm exposure (each year) lasting for a working lifetime. They show that in a population of 1,000 adult males experiencing mortality rates similar to those of the 1981 male population of England and Wales, occupational exposure to 1 ppm of 1,3-butadiene for each year of a working life (40 years between the age of 20 and 65) will cause from 0 to 7.1 extra leukaemia deaths between the age 20-85 years, in addition to the 5.1 leukaemia deaths expected to occur in the absence of exposure to 1,3-butadiene. A summary of the estimates, in terms of excess leukaemia deaths, obtained for 0.1 ppm, 0.2 ppm, 0.5 ppm, 1.0 ppm, 2.0 ppm, 5.0 ppm, and 10 ppm of exposure (each year) is also presented.

CONCLUSIONS

The method can be applied to predict the risk of carcinogenic agents for which dose-response data exist and no health-based limit value can be established. Results are consistent with those of previous risk assessments based on similar assumptions

[European multicenter cross-sectional study on exposure to low doses of benzene]

A cross-sectional multicenter european study has been carried out to evacuate the relations between exposure to low level of benzene and biological markers of internal dose (t,t-MA, S-PMA) and early biological effect (DNA-SSB). The research has shown significantly increased levels (adjusted for smoking habits) of the urinary excretion of t,t-MA, S-PMA and DNA-SSB in petrochemical workers (mean benzene level = 5,694 micrograms/m3) but not in filling station attendants, traffic police officers, and bus drivers compared to referent workers. Dose-response relations were detected between benzene air levels, t,t-MA, S-PMA and DNA-SSB in petrochemical workers, with significantly increased levels of DNA-SSB detected for benzene exposure levels in the range 391-1,800 micrograms/m3 (0.12-0.58 ppm).

[Molecular epidemiology for the study of the environment-genome interaction]

The study of the gene-environment interaction considered initially genes involved in the biotransformation of carcinogenic agents. Genetic polymorphisms are useful markers of individual susceptibility, provided that their association with the exposure and the outcome of interest are clearly understood. The availability of biochemical and molecular markers in epidemiology research has been greeted as a major step forward from the traditional "black box" epidemiology, and certainly represents a real advancement in knowledge. Yet, the advancement in research made possible by the adoption of molecular biomarkers in epidemiological studies still needs to be evaluated as a relevant and effective tool for a more adequate prevention of the adverse effects caused by environmental agents.

[Occupational epidemiology: contributions and prospects]

Occupational epidemiology (OE) played a major role in the development of modern occupational medicine from a practice concerned with individual disease cases to a practice concerned with populations and their working environment. One of the greatest contribution was the identification of occupational carcinogenic agents. OE also represented the foundation for the development of environmental epidemiology which represents today a major research and public health activity. OE has, in perspective, still several contributions to provide to the development of occupational health, including the systematic description of the present burden of work-related disease on our society; the investigation of the mechanistic steps linking exposure to disease onset, in order to identify, in parallel, more adequate and effective prevention measures; the validation of health surveillance and screening programs at work; the study of the "causative" link between exposures and effects; and the risk assessment for an evidence based management of the health risks at work.

[The role of the "Clinica del Lavoro Luigi Devoto" in international research]

During its long history, the Clinica del Lavoro Luigi Devoto has produced numerous internationally recognized scientific contributions in the specific field of occupational medicine and health, and in other broader areas as, for example, immunology, toxicology, cytogenetics. Pivotal in this activity was the figure of Enrico C. Vigliani, director of the Clinica for over 35 years. We mention here, in particular, the results of the study of "early" markers of lead intoxication; the research on the carcinogenicity of benzene and aromatic amines; the study of the pathogenesis of silicosis and byssinosis; the study of cytogenetic damage after exposure to industrial toxic chemicals; the technical research for dust abatement in mines. Such research also played a major role in the development of pulmonary medicine, toxicology and immunology in Italy, and conferred scientific dignity on the newborn "industrial hygiene" discipline thanks to the work of Nicola Zurlo. Today, the Clinica's research is maintained at international standards especially by the work of thematic Research Centers recently established within the Clinica, covering fields such as occupational and environmental toxicology, occupational oncology, ergonomics, respiratory disease and allergy, psycho-social risk factors. These Centers are also devoted to the development of innovative methods in epidemiology, toxicology, psychology, molecular biology, and ergonomic measurement for the identification and evaluation of health risks at work.

Health effects of dioxin exposure: a 20-year mortality study

Follow-up of the population exposed to dioxin after the 1976 accident in Seveso, Italy, was extended to 1996. During the entire observation period, all-cause and all-cancer mortality did not increase. Fifteen years after the accident, mortality among men in high-exposure zones A (804 inhabitants) and B (5,941 inhabitants) increased from all cancers (rate ratio (RR) = 1.3, 95% confidence interval (CI): 1.0, 1.7), rectal cancer (RR = 2.4, 95% CI: 1.2, 4.6), and lung cancer (RR = 1.3, 95% CI: 1.0, 1.7), with no latency-related pattern for rectal or lung cancer. An excess of lymphohemopoietic neoplasms was found in both genders (RR = 1.7, 95% CI: 1.2, 2.5). Hodgkin's disease risk was elevated in the first 10-year observation period (RR = 4.9, 95% CI: 1.5, 16.4), whereas the highest increase for non-Hodgkin's lymphoma (RR = 2.8, 95% CI: 1.1, 7.0) and myeloid leukemia (RR = 3.8, 95% CI: 1.2, 12.5) occurred after 15 years. No soft tissue sarcoma cases were found in these zones (0.8 expected). An overall increase in diabetes was reported, notably among women (RR = 2.4, 95% CI: 1.2, 4.6). Chronic circulatory and respiratory diseases were moderately increased, suggesting a link with accident-related stressors and chemical exposure. Results support evaluation of dioxin as carcinogenic to humans and corroborate the hypotheses of its association with other health outcomes, including cardiovascular- and endocrine-related effects.

Occupational and environmental agents as endocrine disruptors: experimental and human evidence

In the last few years great concern has arisen from the description of adverse endocrine effects of several occupational and environmental chemical agents on human and/or wildlife health. Such agents may exert their effects directly, specifically binding to hormone receptors, and/or indirectly, by altering the structure of endocrine glands and/or synthesis, release, transport, metabolism or action of endogenous hormones. Many studies have been focused on the outcomes of the exposure to those chemicals mimicking estrogenic or androgenic actions. Nonetheless, the disruption of other hormonal pathways is not negligible. This paper reviews the experimental and human evidence of the effects of occupational and environmental chemical agents on hypothalamus-pituitary unit, pineal gland, parathyroid and calcium metabolism and adrenal glands.

Future prevention and handling of environmental accidents

According to the 1995 World Disaster Report, accidents are second only to floods in frequency. Chemical accidents leading to a serious danger to the general public and to the environment rank 10th, just after epidemics and followed by landslides. Can the occurrence of these environmental accidents be reduced in the future and their consequences minimized? The answer is yes, provided that decisions are made and actions implemented now. Future management of environmental accidents requires that the same effort so far devoted to relief measures in the postimpact phase be devoted to advance planning in the preaccident period. International cooperation should be activated to predispose risk reduction measures, including a hazard-oriented approach to prevention, preparedness plans for possible incidents in major hazardous installations, and collaborative programs and resource sharing for response to accidents and the follow-up of their consequences. Clear and unequivocal communication with the public, with other professionals, decision makers, and the media play a key role in each step.

[Occupational epidemiology and new challenges in occupational medicine]

Epidemiology has greatly contributed in the past to the recognition of work-related ill health. Working life, work organisation and labour markets are now rapidly changing. Does epidemiology still have a relevant role in this evolving context? New exposures at the workplace and related health and behavioural changes currently prevailing in industrialized countries are reviewed. It appears that epidemiology might in the future play an even greater role than in the past, when the mere observation of a few subjects could sometimes lead to the identification of occupation-related risks. In order to examine the relations between complex and low-level exposures and subtle and long-term risks in working populations, epidemiology appears essential. Controlled, longitudinal population studies are especially needed to clarify, for prevention purposes, the meaning and the predictive role of the increasing number of markers of exposure, of effect and of individual susceptibility; to describe and model in quantitative terms exposure-response relations; to assist with risk assessment and evaluation. Although occupational health research has a long tradition of inter-disciplinary co-operation, this remains a major challenge for the future.

Mortality study in an Italian oil refinery: extension of the follow-up

This article present the results of the extension of the follow-up of a cohort of workers employed in an Italian oil refinery. 1,583 workers employed in 1949-1982 in a northern Italy oil refinery plant were followed-up for mortality as of May 31, 1991. Environmental measurements documented potential exposure to benzene. Standardized mortality ratios (SMR) and their 95% confidence intervals (95% CI) were calculated using as references national (1949-1968) and regional mortality rates (1969-1991). Elevated mortality from lymphoma (seven deaths, SMR 190, 95% CI 76-391) and leukemia (eight deaths, SMR 225, 95% CI 97-443) was observed. No consistent trends by length of employment or time since first exposure were apparent. Nonetheless, the excess risk was particularly and significantly increased among workers with 15 or more years of employment, and 30 or more years since first employment. The findings of elevated mortality from leukemia and lymphoma are in agreement with those of other oil refinery studies. Chance, confounding, or other biases might have played a marginal, if any, role in determining the results. Exposure to benzene is a biologically plausible explanation.

[IARC multicenter study on neoplastic disease caused by man-made vitreous mineral fibers (MMVF)]

Man-made vitreous fibres (MMVF) showed carcinogenic potential in experimental animals. Epidemiological data suggested an increased mortality from lung cancer among production workers, but the interpretation is still a matter of controversy. A European study encompassing 13 plants in 7 countries pointed towards a moderate excess of lung cancer among workers employed longer than 1 year in the production of rock/slag wool (SMR = 1.34, 95% CI = 1.08-1.63) and glass wool (SMR = 1.27, 95% CI = 1.07-1.50); the latter increase was not confirmed after applying local rates to calculate expected deaths. The elevated risk among rock/slag wool producers was present even in comparison with local rates, and was associated with increasing time from first exposure, and duration of exposure. Glass wool results exhibited a less definite pattern. Smoking was excluded, although indirectly, as a sufficient alternative explanation of the increased lung cancer risk. In a few plants, exposure to asbestos had occurred in limited periods for some workers, and might have contributed to the findings. Case-control studies are under way to thoroughly investigate the relative and possibly combined role of the different exposures, either occupational or not. Cohort studies in the USA produced results closely consistent with those of the European study.

[Seveso. Dioxin: an example of environmental medicine. Epidemiologic data as guidelines for health programming]

The 1976 dioxin accident in Seveso, Italy, represented a major environmental health problem for the population of the surrounding territory and a challenge for the entire regional area and the health and scientific institutions. The role of occupational health and of epidemiology in the incident investigation and management is discussed. Of major relevance was the consideration of all the different component factors of the interested environment, from chemical pollution to cultural attitudes and psycho-social stressors. Scientific research was helpful in elucidating the incompletely known toxic effects of dioxin and the complex mechanism of cancer induction by this widespread pollutant of our industrialized environments. The experience gained in Seveso was also useful in prompting national and international legislation concerning major industrial accidents, and the lessons learned contributed to the content of this legislation. Preparedness to these events requires mapping of the potential sources of these accidental occurrences and the monitoring of the social and health characteristics of the possibly affected populations. In the Lombardy Region, the numerous epidemiological investigations performed and the expertise implemented for the study and the control of the accident consequences, formed the basis on which the Regional Epidemiology Surveillance System established.

2,3,7,8-Tetrachlorodibenzo-p-dioxin plasma levels in Seveso 20 years after the accident

In 1976, near Seveso, Italy, an industrial accident caused the release of large quantities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) into the atmosphere, resulting in the highest levels of the toxicant ever recorded in humans. The contaminated area was divided into three zones (A, B, R) corresponding to decreasing TCDD levels in soil, and cohort including all residents was enumerated. The population of the surrounding noncontaminated area (non-ABR) was chosen as referent population. Two decades after the accident. plasma TCDD levels were measured in 62 subjects randomly sampled from the highest exposed zones (A and B) and 59 subjects from non-ABR, frequency matched for age, gender, and cigarette smoking status. Subjects living in the exposed areas have persistently elevated plasma TCDD levels (range = 1.2-89.9 ppt; geometric mean = 53.2 and 11.0 ppt for Zone A and Zone B, respectively). Levels significantly decrease by distance from the accident site (p = 0.0001), down to general population values (4.9 ppt) in non-ABR, thus validating the original zone classification based on environmental measurements. Women have higher TCDD levels than men in the entire study area (p = 0.0003 in Zone B; p = 0.007 in non-ABR). This gender difference persists after adjustment for location within the zone, consumption of meat derived from locally raised animals, age, body mass index, and smoking. There is no evidence for a gender difference in exposure, so variation in metabolism or elimination due to body fat or hormone-related factors may explain this finding. Elevated TCDD levels in women may contribute to adverse reproductive, developmental, and cancer outcomes.

The Seveso studies on early and long-term effects of dioxin exposure: a review

The industrial accident that occurred in the town of Seveso, Italy, in 1976 exposed a large population to substantial amounts of relatively pure 2,3,7,8-tetrachlorodibenzo-p-dioxin. Extensive monitoring of soil levels and measurements of a limited number of human blood samples allowed classification of the exposed population into three categories, A (highest exposure), B (median exposure), and R (lowest exposure). Early health investigations including liver function, immune function, neurologic impairment, and reproductive effects yielded inconclusive results. Chloracne (nearly 200 cases with a definite exposure dependence) was the only effect established with certainty. Long-term studies were conducted using the large population living in the surrounding noncontaminated territory as reference. An excess mortality from cardiovascular and respiratory diseases was uncovered, possibly related to the psychosocial consequences of the accident in addition to the chemical contamination. An excess of diabetes cases was also found. Results of cancer incidence and mortality follow-up showed an increased occurrence of cancer of the gastrointestinal sites and of the lymphatic and hematopoietic tissue. Experimental and epidemiologic data as well as mechanistic knowledge support the hypothesis that the observed cancer excesses are associated with dioxin exposure. Results cannot be viewed as conclusive. The study is continuing in an attempt to overcome the existing limitations (few individual exposure data, short latency period, and small population size for certain cancer types) and to explore new research paths (e.g., differences in individual susceptibility).

Dioxin exposure and non-malignant health effects: a mortality study

OBJECTIVE

To investigate, in a population heavily exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the possible unusual occurrence of diseases other than cancer.

METHODS

Five year extension of the follow up of the cohort involved in the Seveso accident. Soil measurements identified three exposure zones: (A) highest contamination, (B) substantial, and (R) low but higher than background contamination. Blood TCDD measurements, although limited in number, confirmed zone exposure ranking. The 15 year mortality in the exposed cohort was compared with that of a large population in the surrounding non-contaminated territory. Relative risks (RRs) and 95% confidence intervals (95% CIs) were estimated with Poisson regression techniques.

RESULTS

The already noted increased occurrence of cardiovascular deaths was confirmed, in particular in zone A, among males for chronic ischaemic heart disease (five deaths, RR 3.0, 95% CI 1.2 to 7.3), and among females for hypertensive disease (three deaths, RR 3.6, 95% CI 1.2 to 11.4) and chronic rheumatic heart disease. Novel findings were the increase of chronic obstructive pulmonary disease, most notably among males in zone A (four deaths, RR 3.7, 95% CI 1.4 to 9.9) and females in zone B (seven deaths, RR 2.4, 95% CI 1.1 to 5.1); and from diabetes, which was significantly increased in females in zone B (13 deaths, RR 1.9, 95% CI 1.1 to 3.2). In zone R, chronic ischaemic heart disease (males and females), hypertension (females), and diabetes (females) showed less pronounced, although significant excesses.

CONCLUSIONS

As well as high TCDD exposure, the accident caused a severe burden of strain in the population. Both these factors might have contributed to the noted increased risks (in particular, circulatory and respiratory). The cardiovascular and immune toxicity of TCDD, as well as its complex interaction with the endocrine system, might be relevant to the explanations of these findings. These results, although not conclusive, concur with previous data in suggesting cardiopulmonary and endocrine effects in humans highly exposed to TCDD.

Why and how to control for age in occupational epidemiology

In occupational epidemiology, the need to consider the age factor properly influences the choice of study design and analytical techniques. In most studies, age is viewed as a potential confounder. Age is strongly associated with end points of interest in occupational epidemiology (diseases, physiological characteristics, doses of xenobiotics, etc), but to measure age as a confounder it must be associated with the exposure under study. When the exposure of interest is time related-for example, duration of employment, time since first exposure, cumulative exposure-a strong intrinsic association with age can be anticipated, and age will behave as a (usually strong) confounder. When occupational exposures without a direct relation with age-for example, job, department, type of exposure-are evaluated, the degree and direction of confounding bias cannot be anticipated. Control of the confounding effect of age can be accomplished in the design phase of a study by way of randomisation, restriction, and matching. Randomisation is seldom viable in occupational settings. Restriction is rarely used in the case of age. Matching is often used in a case-control study as a method to increase the study efficiency, but it must be followed by proper matched or stratified analysis. Options for age adjustment in the analysis phase involve stratification and regression methods. In longitudinal studies the modified life table analysis is used to take into account the fact that subjects cross categories of age as the study proceeds. Stability of relative measures of effect over age strata favoured the greater use of relative risks than risk differences. In the presence of effect modification the influence of age should not be eliminated; its interaction with exposure should be explicitly considered.

Dioxin exposure and cancer risk: a 15-year mortality study after the "Seveso accident"

Dioxin (2,3,7,8-tetrachlorodibenzo-para-dioxin, or TCDD) is a powerful carcinogen in experimental animals, whereas the evidence in humans is limited. We examined cancer mortality from 1976 to 1991 among residents of Seveso, Italy, which was highly contaminated after an industrial accident. The area was divided into zones with decreasing exposure to dioxin (A = highest, B = lower, R = lowest). The population of a surrounding noncontaminated area was used as a reference group. Zone A was small (11,516 person-years); in that zone, we saw a moderate increase in mortality from digestive cancer among women [relative risk (RR) = 1.5; 95% confidence interval (CI) = 0.5-3.5]. In zone B, we also saw excesses at digestive sites (83,610 person-years), 10 years after the accident. Women had an increased mortality from stomach cancer (RR = 2.4; 95% CI = 0.8-5.7), and men had increased mortality from rectal cancer (RR = 6.2; 95% CI = 1.7-15.9). Hematologic neoplasms were increased. The highest risks were seen in zone B for leukemia in men (RR = 3.1; 95% CI = 1.3-6.4), multiple myeloma in women (RR = 6.6; 95% CI = 1.8-16.8), and Hodgkin's disease in both genders (RR = 3.3; 95% CI = 0.4-11.9 in men; and RR = 6.5; 95% CI = 0.7-23.5 in women). Soft tissue sarcoma was elevated only among zone R males (256,408 person-years; RR = 2.1; 95% CI = 0.6-5.4). We found no increase for all-cancer mortality or major specific sites (for example, respiratory among males, breast among females). The specific excesses that we observed were not explained by bias or confounding, and their association with dioxin exposure is plausible. The follow-up is continuing.

Cancer mortality in workers exposed to phenoxy herbicides, chlorophenols, and dioxins. An expanded and updated international cohort study

The authors examined cancer mortality in a historical cohort study of 21,863 male and female workers in 36 cohorts exposed to phenoxy herbicides, chlorophenols, and dioxins in 12 countries. Subjects in this updated and expanded multinational study coordinated by the International Agency for Research on Cancer were followed from 1939 to 1992. Exposure was reconstructed using job records, company exposure questionnaires, and serum and adipose tissue dioxin levels. Among workers exposed to phenoxy herbicides contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or higher chlorinated dioxins, mortality from soft-tissue sarcoma (6 deaths; standardized mortality ratio (SMR) = 2.03, 95% confidence interval (CI) 0.75-4.43) was higher than expected from national mortality rates. Mortality from all malignant neoplasms (710 deaths; SMR = 1.12, 95% CI 1.04-1.21), non-Hodgkin's lymphoma (24 deaths; SMR = 1.39, 95% CI 0.89-2.06), and lung cancer (225 deaths; SMR = 1.12, 95% CI 0.98-1.28) was slightly elevated. Risks for all neoplasms, for sarcomas, and for lymphomas increased with time since first exposure. In workers exposed to phenoxy herbicides with minimal or no contamination by TCDD and higher chlorinated dioxins, mortality from all neoplasms (398 deaths; SMR = 0.96, 95% CI 0.87-1.06), non-Hodgkin's lymphoma (9 deaths; SMR = 1.00), and lung cancer (148 deaths; SMR = 1.03) was similar to that expected, and mortality from soft-tissue sarcoma was slightly elevated (2 deaths; SMR = 1.35). In a Poisson regression analysis, workers exposed to TCDD or higher chlorinated dioxins had an increased risk for all neoplasms (rate ratio = 1.29, 95% CI 0.94-1.76) compared with workers from the same cohort exposed to phenoxy herbicides and chlorophenols but with minimal or no exposure to TCDD and higher chlorinated dioxins. These findings indicate that exposure to herbicides contaminated with TCDD and higher chlorinated dioxins may be associated with a small increase in overall cancer risk and in risk for specific cancers.

Cancer mortality among man-made vitreous fiber production workers

We have updated the follow-up of cancer mortality for a cohort study of man-made vitreous fiber production workers from Denmark, Finland, Norway, Sweden, United Kingdom, Germany, and Italy, from 1982 to 1990. In the mortality analysis, 22,002 production workers contributed 489,551 person-years, during which there were 4,521 deaths. Workers with less than 1 year of employment had an increased mortality [standardized mortality ratio (SMR) = 1.45; 95% confidence interval (CI) = 1.37-1.53]. Workers with 1 year or more of employment, contributing 65% of person-years, had an SMR of 1.05 (95% CI = 1.02-1.09). The SMR for lung cancer was 1.34 (95% CI = 1.08-1.63, 97 deaths) among rock/slag wool workers and 1.27 (95% CI = 1.07-1.50, 140 deaths) among glass wool workers. In the latter group, no increase was present when local mortality rates were used. Among rock/slag wool workers, the risk of lung cancer increased with time-since-first-employment and duration of employment. The trend in lung cancer mortality according to technologic phase at first employment was less marked than in the previous follow-up. We obtained similar results from a Poisson regression analysis limited to rock/slag wool workers. Five deaths from pleural mesothelioma were reported, which may not represent an excess. There was no apparent excess for other categories of neoplasm. Tobacco smoking and other factors linked to social class, as well as exposures in other industries, appear unlikely to explain the whole increase in lung cancer mortality among rock/slag wool workers. Limited data on other agents do not indicate an important role of asbestos, slag, or bitumen. These results are not sufficient to conclude that the increased lung cancer risk is the result of exposure to rock/slag wool; however, insofar as respirable fibers were an important component of the ambient pollution of the working environment, they may have contributed to the increased risk.

Relationship between prevalence rate ratios and odds ratios in cross-sectional studies

BACKGROUND

Cross-sectional data are frequently encountered in epidemiology and published results are predominantly presented in terms of prevalence odds ratios (POR). A recent debate suggested a switch from POR, which is easily obtained via logistic regression analysis available in many statistical packages, to prevalence rate ratios (PRR). We thought it useful to explore the mathematical relationship between PRR and POR and to evaluate the degree of divergence of the two measures as a function of the prevalence of disease and exposure.

METHODS

With the use of some algebra and the common definitions of prevalence of the disease (Pr(D)), prevalence of the exposure (Pr(E)), PRR, and POR in a 2 x 2 table, we have identified a useful formula that represents the mathematical relationship between these four quantities. Plots of POR versus PRR for selected values of Pr(D) and Pr(E) are reported.

RESULTS

Mathematically speaking the general relationship takes the form of a second order curve which can change curvature and/or rotate around the point POR = PRR = 1 according to the values of Pr(D) and Pr(E), with POR being always further from the null value than is PRR. The discrepancies are much more influenced by variations in Pr(D) than in Pr(E).

CONCLUSIONS

We think that the choice between POR or PRR in a cross-sectional study ought to be based on epidemiological grounds and not on the availability of software tools. The paper offers a formula and some-examples for a better understanding of the relationship between PRR and POR as a function of the prevalence of the disease and the prevalence of the exposure.

Soft tissue sarcoma and non-Hodgkin's lymphoma in workers exposed to phenoxy herbicides, chlorophenols, and dioxins: two nested case-control studies

We examined the effect of exposure to chemicals present in the production and spraying of phenoxy herbicides or chlorophenols in two nested case-control studies of soft tissue sarcoma and non-Hodgkin's lymphoma. Eleven sarcoma and 32 lymphoma cases occurring within an international cohort were matched for age, sex, and country of residence with 55 and 158 controls, respectively. Exposures to 21 chemicals or mixtures were estimated by three industrial hygienists who were blind to the subject's case-control status. Excess risk of soft tissue sarcoma was associated with exposure to any phenoxy herbicide [odds ratio (OR) = 10.3; 95% confidence interval (CI) = 1.2-91] and to each of the three major classes of phenoxy herbicides (2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, and 4-chloro-2-methylphenoxyacetic acid), to any polychlorinated dibenzodioxin or furan (OR = 5.6; 95% CI = 1.1-28), and to 2,3,7,8-tetrachlorodibenzo-p-dioxin (OR = 5.2; 95% CI = 0.85-32). Sarcoma risk was not associated with exposure to raw materials or other process chemicals. In the non-Hodgkin's lymphoma study, associations were generally weaker than those found in the study on sarcoma. These findings indicate that workers exposed to phenoxy herbicides and their contaminants are at a higher risk of soft tissue sarcoma.

Association between CYP1A1 genotype, mRNA expression and enzymatic activity in humans

Genetic susceptibility factors may play a role in determining adverse effects of exposure to environmental toxins. As a preliminary step to a molecular epidemiological study in a population exposed to 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD), we investigated 20 healthy Caucasian volunteers with a set of putative susceptibility markers including a CYP1A1 Msp I restriction fragment length genetic polymorphism (RFLP), CYP1A1 mRNA expression, and ethoxyresorufin-O-deethylase (EROD) activity in cultured and mitogen-activated blood lymphocytes. Both basal (p = 0.008) and induced (p = 0.0001) EROD activity was significantly higher among persons with a mutation in one or both alleles of the CYP1A1 gene (variant CYP1A1 genotype). Induction in vitro by TCDD significantly increased EROD activity in both variant and wild-type CYP1A1 subjects; however, the absolute increase was greater in subjects with variant genotypes. An additive interaction between genotype and TCDD induction was suggested. Expression of CYP1A1 mRNA, both basal and induced, did not vary significantly across the genotypes.

Cancer in a young population in a dioxin-contaminated area

An industrial accident in Seveso, Italy, in 1976, caused contamination of the residential community with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We investigated cancer occurrence in the first post-accident decade (1977-1986) among nearly 20,000 subjects aged 0-19 years. People who left the area were actively followed with a 99% follow-up rate. For reported cancer cases confirmation was obtained through consultation with original medical records. Two ovarian cancers were observed versus none expected. A suggestive increase was seen for Hodgkin's lymphoma (relative risk [RR] = 2.0; 95% confidence interval [CI] = 0.5-7.6). Myeloid leukaemia showed a clear, but not statistically significant increase (RR = 2.7; 95% CI = 0.7-11.4). The most prominent result concerned thyroid cancer, not just for the magnitude of the increase (two cases, RR = 4.6; 95% CI = 0.6-32.7), but also for its consistency with experimental findings and previous observations in humans. Any conclusive interpretation would be premature because of the short time since initial exposure, ecological definition of exposure status, and limited number of events.

Cancer incidence and mortality in women occupationally exposed to chlorophenoxy herbicides, chlorophenols, and dioxins

The association between exposure to chlorophenoxy herbicides contaminated with dioxins and occurrence of cancer has been studied mainly in male populations. In animal experiments, gender differences have been recorded in the cancer response to administered 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Mortality and cancer incidence in an international cohort of 701 women from an International Register of Workers occupationally exposed to chlorophenoxy herbicides, chlorophenols, and dioxins is examined. Cause-specific, national death rates and cancer incidence rates were used as referents. Cancer risk was not increased overall, with a standardized incidence ratio (SIR) of 96 and 95 percent confidence interval (CI) of 64-137, based on 29 cases. Among workers exposed to those chlorophenoxy herbicides contaminated with TCDD, excess cancer incidence (for all sites) was observed (SIR = 222, CI = 102-422, 9 cases); this was highest in the first 10 years after exposure. No excess was observed for breast cancer, the most common cancer in this cohort. Results on cancer mortality were consistent with those on incidence.

Chemical exposure in manufacture of phenoxy herbicides and chlorophenols and in spraying of phenoxy herbicides

Exposure patterns are reported for manufacturing and sprayer cohorts incorporated in the "IARC International Register of Workers exposed to Phenoxy Herbicides and Contaminants." Information was based on company questionnaires, company reports, plant visits, and serum 2, 3, 7, 8-TCDD measurements. In addition to phenoxy herbicides and chlorophenols, workers in manufacturing plants may have been exposed to raw materials, process chemicals, other agents synthesized or formulated, and impurities of all these agents. Sprayers also had a complex exposure pattern, including phenoxy herbicides and some other pesticides, their carriers and additives, and residues of chemicals formed during manufacture. Occurrence of agents, including dioxins, varied between countries. Biological monitoring and industrial hygiene data were rarely available, most since the late 1970s. Exposure of workers depended mainly on the jobs they performed, but several factors influenced level of exposure. A quantitative exposure classification is not feasible in this study. Semiquantitative exposure estimates may be derived through a critical interpretation of biological monitoring and industrial hygiene data together with individual work histories.

Lung cancer mortality among workers in the European production of man-made mineral fibers--a Poisson regression analysis

One hundred and eighty-one lung cancer deaths among workers during 301,085 person-years in European man-made mineral fiber production between 1930-1955 and 1982 were analyzed according to Poisson regression models including age, calendar period, country, and exposure variables. Time since first employment was the variable most strongly associated with lung cancer risk in both the rock-slag wool and glass wool subcohorts. Workers in the early technological phase were at higher risk than those in other categories, particularly in rock-slag wool production. No clear trend with duration of employment was suggested. No major changes occurred in the interpretation of the results when workers with less than one year of employment or less than 20 years since first exposure were excluded. The original results, based on analyses for standardized mortality ratios, were confirmed, and workers with a short duration of employment or a short time since first employment did not need to be excluded from the analysis.

Mortality of a young population after accidental exposure to 2,3,7,8-tetrachlorodibenzodioxin

The mortality experience of 19,637 people aged 1-19 years living in an area around Seveso, Italy, contaminated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) after an accidental explosion in a chemical plant was examined for the period 1976-1986. For comparison, the mortality of the population of nearly 100,000 people living in the surrounding districts was examined. People who left the study area were followed up. Vital status ascertainment was successful in over 99% of the cases. A group of 186 children who contracted chloracne, a reversible marker of TCDD intoxication, shortly after the accident were in the study: none of them died during the observation period. Among the exposed, mortality owing to all causes, to all accidents and to all cancers failed to show major departure from expectations. Five leukaemia deaths were observed, four among males and one among females; the corresponding relative risks were 2.1 (95% confidence interval (CI): 0.7-6.9), and 2.5 (95% CI: 0.2-27.0), respectively. Two lymphatic leukaemias among males yielded a RR = 9.6 (95% CI: 0.9-106.0). Mortality owing to congenital anomalies showed a nearly twofold increase in the contaminated area; however, five out of seven observed cases were born before the accident. Interpretation is limited by the small number of deaths, short latency period and low validity of death certificate information for certain causes, and by the definition of exposure which was based merely on residence. The follow-up is continuing. A cancer morbidity study is in progress.

Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols

Epidemiological studies have revealed an increased risk of cancer, notably soft-tissue sarcomas and non-Hodgkin's lymphomas, in people occupationally exposed to chlorophenoxy herbicides, including those contaminated by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). We report here a historical cohort study of mortality in an international register of 18,910 production workers or sprayers from ten countries. Exposure was reconstructed through questionnaires, factory or spraying records, and job histories. Cause-specific national death rates were used as reference. No excess was observed in all-cause mortality, for all neoplasms, for the most common epithelial cancers, or for lymphomas. A statistically non-significant two-fold excess risk, based on 4 observed deaths, was noted for soft-tissue sarcoma with a standardised mortality ratio (SMR) of 196 and 95% confidence interval (Cl) 53-502; this was concentrated as a six-fold statistically significant excess, occurring 10-19 years from first exposure in the cohort as a whole (SMR = 606 [165-1552]) and, for the same time period, as a nine-fold excess among sprayers (SMR = 882 [182-2579]). Risks appeared to be increased for cancers of the testicle, thyroid, other endocrine glands, and nose and nasal cavity, based on small numbers of deaths. The excess of soft-tissue sarcomas among sprayers is compatible with a causal role of chlorophenoxy herbicides but the excess does not seem to be specifically associated with those herbicides probably contaminated by TCDD.

[How to identify an aspecific association? Epidemiological considerations on the study of health of office workers]

An epidemiological approach to the study of health conditions of office workers. Nowadays the work-relatedness of the majority of diseases occurring at the workplace is by no means obvious. The relationship to work environment and performance of work is one of several causative factors. However, the multifactorial origin of diseases is not at all a new concept since principles and methods for the study of the numerous factors playing a role in any association between exposure and disease are already available. The model of causal constellations developed by Rothman can be particularly useful for the investigation of "non-specific" associations, like those commonly occurring in office work. The study of the health conditions of office workers is faced with many difficulties, including the identification, measurement and classification of exposure variables and health outcomes. In designing these studies, particular attention should be devoted to aspects regarding sample size, length of observation and referent population.

[Problems and perspectives of occupational carcinogenesis]

Epidemiologic research has played an important role in identifying and confirming the carcinogenicity of chemicals. This was facilitated in the past by the high levels of exposure and by the simple correspondence between one exposure and one or few job titles. Today we are faced with a different picture: workers are exposed to complex mixtures, exposure levels have decreased while mobility of the work-force has increased. In this changing context, epidemiology needs new methodological tools to improve the validity of risk assessment. The most promising of these seem to be the new techniques of biochemical epidemiology and the development of job-exposure matrices. Among the more traditional tools, record-linkage studies may be relevant in identifying long-term occupational hazards. The methodological problems and the ethical and operative implications of these trends in research are discussed.

[A follow-up study of 304 cases of suspected pathology caused by benzene seen in 1950-71]

A group of 304 subjects admitted to the Institutes of Occupational Health of Milan and Pavia (Italy) between 1951 and 1970 for suspected benzene intoxication were retrieved from hospital records and their mortality experience was examined up to 31 December, 1986. The aims of the study were: 1) to estimate, in quantitative terms, the risk associated with benzene exposure in that area in the time period considered (these risks had already been reported, but merely as case reports); 2) to investigate the possibility of an increased frequency of neoplasms other than leukaemia; and 3) to further investigate the exposure history of these subjects. In the absence of data on the population at risk, mortality was analysed via the mortality odds ratio (MOR) method. A local population mortality experience was used as reference. Twenty-eight malignant neoplasms were observed (MOR = 2.2; 95% confidence interval = 1.3-3.7), 15 of which were haematologic neoplasms (MOR = 13.3; 95% confidence interval = 8.0-22.2). No odds ratio increases were observed for any of the other tumour sites or types. Eleven observed blood diseases represented a large numerical increase in the odds ratio. For all the haematologic neoplasms there had been an estimated exposure to airborne benzene concentrations above 20 ppm. However, no conclusions on dose-response relationships can be drawn from these data because of the approximate evaluation of individual exposure and, especially, because the study group most probably consisted of a highly selected sample of the exposed population.(ABSTRACT TRUNCATED AT 250 WORDS)

Mortality in an area contaminated by TCDD following an industrial incident

The mortality experience of the population, aged 20-74 years, living in an area contaminated by TCDD after an industrial accident in 1976, was examined in the period 1976-1986 and compared with the mortality of the population of the surrounding noncontaminated territory. People who left the area during the study period were followed up, and vital status was successfully ascertained for over 99% of the cohort members. An increased mortality, from chronic ischemic heart disease (males) and hypertensive disease (females), which could not be explained in terms of chance, confounding, or bias, was noted in the exposed population. The stressful experience of the population in the aftermath of the disaster was deemed relevant to the interpretation of these findings. Overall, cancer mortality was not increased. Suggestive increases, however, were seen for melanoma, brain cancer, soft tissue sarcomas and certain hematologic neoplasms, whereas mortality from breast cancer and cancer of the liver was noticeably decreased. Further research is in progress in order to thoroughly investigate the association, if any, of cancer occurrence with TCDD contamination.

Ten-year mortality study of the population involved in the Seveso incident in 1976

In 1976, an accidental explosion in a plant near Seveso, Italy, caused the contamination of a populated area by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The area was subdivided into three zones (A, B, and R) having decreasing mean levels of TCDD soil contamination. This study examines the mortality between 1976 and 1986 among the subjects, aged 20-74 years, who were resident in the area since the accident (n = 556 in zone A, n = 3,920 in zone B, n = 26,227 in zone R). Subjects' exposure was classified by residence. A referent cohort of 167,391 subjects who lived in the immediate surroundings was concurrently examined. Vital status ascertainment was successful for over 99% of the subjects. Increased mortality from cardiovascular causes was found; incident-related stressors were considered more relevant to increased mortality than was TCDD exposure. Mortality from several cancers was elevated. The increases in biliary cancer (females), brain cancer, and lymphatic and hemopoietic neoplasms (particularly leukemia in males) did not appear to result from chance, confounding, or information/comparison bias. However, no definite patterns related to exposure classification were apparent. Merely suggestive increases in soft tissue tumors and melanoma were also noted. Liver and breast cancer mortality tended to be below expectations. Interpretation is hampered by the short observation period, small number of deaths from certain causes, and poor exposure definition. Further research is in progress.

Industrial disasters and epidemiology. A review of recent experiences

Disasters of industrial origin are usually overt, but sometimes their source is silent and their occurrence diluted in time. Thus, the ascertainment of the health impact is not the sole epidemiologic task; epidemiology is often needed to identify the disaster source; in addition, a postdisaster scenario may represent an unfortunate, unplanned experimental setting from which scientific knowledge and public health achievements can be drawn. In the aftermath of a disaster, three sets of illness determinants ought to be considered: the relevant exposure; the stressful experience of the population; the response measures. Ecological, geographic, and personal indicators might be used to ascertain individuals' exposure. Relevant health outcomes (early and long-term) are either exposure-related or stress-related (mental and physical). A cohort approach should be sought to avoid major selection/information biases and facilitate later studies. Early planning is of paramount importance to identify study goals, problems, and resource requirements.

[Mortality caused by pleural mesothelioma in the 1979-1983 lustre in Italy regarding provinces and single local health districts]

The geographic distribution of deaths from pleural mesothelioma in Italian provinces was analysed over the five-year period 1979-1983. In the provinces where the mortality rates were markedly higher than the national average, a further analysis was made on the data referred to the local health districts (USSL) of each province. It was thus possible, in some cases, to identify small, high risk areas which corresponded, as expected, to the location of large factories or shipyards using asbestos.

[Carcinogenic risk for resin producers exposed to formaldehyde: extension of follow-up]

A significant increase in lung cancer was observed in a previous study on the mortality experience of a cohort of 1332 male workers employed between 1959 and 1980 in a resin manufacturing plant. Due to the limited exposure and an inadequate follow-up, it was not possible to make a thorough analysis of the potential association of this elevated risk with exposure to formaldehyde. The study was therefore continued and extended for a further six years (1980-1986), in order to overcome the limitations. Despite these attempts, however, there were still 219 workers whose specific exposure could not be identified. Lung cancer risk in the whole cohort (27,202 person-years) was equal to that of the local population (observed = 24; expected = 23.9). Among those definitely exposed to formaldehyde, 6 lung cancer cases were observed and 8.7 were expected, while those with non-specified exposure exhibited an increase risk (observed = 9; SMR = 211); they were mainly short-term workers employed at the beginning of operations. The previously suggested increase in haematologic neoplasms was confirmed (observed = 7; SMR = 143); the risk was highest among formaldehyde-exposed workers (observed = 3; SMR = 173). Five deaths due to primary liver cancer were observed, while 2.0 would have been expected from the local population rates (SMR = 244); the increased risk was fairly evenly distributed across the exposure categories (exposed to formaldehyde, SMR = 244; non-exposed to formaldehyde, SMR = 227; non-specified exposure = 287); however, all cases were first exposed at the age of 45 years or older. A noteworthy finding was a 50% increase in mortality from respiratory diseases. The increase was mainly apparent among those with longest and earliest exposure, employed in operations classified as involving exposures other than formaldehyde (observed = 9; SMR = 224). Overall, the results of this extended study do not provide sufficient grounds for associating work in formaldehyde resin production in this plant with increased carcinogenic risk; however, limitations in the individual exposure classification and suggestions of an increased risk for certain tumours preclude considering the study as negative. The numerous airborne irritative agents present in the plant environment appeared to have increased the risk of respiratory disease.(ABSTRACT TRUNCATED AT 250 WORDS)