Multiple myeloma and benzene exposure in a multinational cohort of more than 250,000 petroleum workers

Long-term occupational exposures on disability-free survival and mortality in older adults

BACKGROUND

The impact of long-term occupational exposures on health in older adults is increasingly relevant as populations age. To date, no studies have reported their impact on survival free of disability in older adults.

AIMS

We aimed to investigate the association between long-term occupational exposure and disability-free survival (DFS), all-cause mortality and cause-specific mortality in initially healthy older adults.

METHODS

We analysed data from 12 215 healthy participants in the ASPirin in Reducing Events in the Elderly (ASPREE) study whose mean age was 75 years. Their work history was collated with the 'ALOHA-plus JEM' (Job Exposure Matrix) to assign occupational exposures. The primary endpoint, DFS, was a composite measure of death, dementia or persistent physical disability. The secondary endpoint, mortality, was classified according to the underlying cause. Cox proportional hazard models were used to calculate hazard ratios and 95% confidence intervals, adjusted for confounders.

RESULTS

A total of 1835 individuals reached the DFS endpoint during the median 4.7 years follow-up period. Both ever-high and cumulative exposure to all dusts and all pesticides during a person's working years were associated with reduced DFS. Compared to no exposure, men with high exposure to dusts and pesticides had a reduced DFS. Neither of these exposures were significantly associated with all-cause mortality. Men with high occupational exposure to solvents and women exposed to dusts experienced higher all-cause and cancer-related mortality.

CONCLUSIONS

Long-term occupational exposure to all dusts and pesticides was associated with a reduced DFS and increased mortality in community-dwelling healthy older adults.

Systematic Review and Meta-Analysis of Selected Cancers in Petroleum Refinery Workers

OBJECTIVE

We studied the risk of 11 cancers of a priori interest in petroleum refinery workers.

METHODS

Iterative searches identified 36 studies for the 11 cancer sites. Statistical heterogeneity and publication bias were assessed to enhance interpretation of meta-relative risks.

RESULTS

Statistical heterogeneity was marked for mesothelioma, but was largely due to study quality. Higher quality studies showed a meta-relative risk (RR) of 3.22, (95% prediction interval 1.45 to 7.23). Melanoma (meta-RR = 1.23) and acute lymphoid leukemia (meta-RR = 1.51), showed results consistent with higher risk, but both were driven by one or two studies. Eight other cancer outcomes showed summary meta-RR's consistent with unity.

CONCLUSIONS

Most cancer outcomes are consistent with background risk in refinery workers. This work has clarified an excess mesothelioma risk, conditional on study quality stratification. Continued surveillance is warranted for melanoma and ALL.

Abnormal Plasma Cell Disorders in Refinery Waste Workers

A monoclonal gammopathy of undetermined significance (MGUS) may develop into a multiple myeloma or a correlated lymphoproliferative malignancy with a progress rate of 1% per year. The immune status, occupational-environmental risk factors, and hereditary factors may influence the risk of developing MGUS. We investigated the prevalence of MGUS in 77 refinery waste workers. They were all males, averagely aged 36, with a mean working history of 18.5 years and working in the dump for about 4.2 years. After analyzing the results of standard serum electrophoresis migrations, 16% of cases (n = 12) showed levels beyond the normal ranges. In all 12 samples we observed an increase of gamma component: 67%, IgG; 17%, IgM; 8%, IgA; 8%, oligoclonal. Workers were exposed to hazardous refinery waste. After the biological monitoring of urine samples for metals and t,t-muconic acid, no extra-range values were observed. The multivariate analysis shows, however, that cigarette smoking and residence near industrial sites are significantly (p < 0.001) associated with a high risk of MGUS development; while no association was found with occupational exposure. Additional attention might be paid in particular to these conditions in epidemiological studies and further larger, prospective, population-based researches appear warranted to evaluate the strength of any positive association.

Contamination by oil crude extraction - Refinement and their effects on human health

The harmful effects of oil on various species of flora and fauna have been studied extensively; however, few studies have studied the effects of oil exposure on human health. The objective of this research was to collect information on the acute health effects and serious psychological symptoms of the possible consequences of such exposure to crude oil. Some studies focused on the composition of different chemicals used in the extraction process, and wastes generated proved to be highly harmful to human health. Thus, studies have shown that individuals who live near oil fields or wells - or who take part in activities of cleaning oil spills - have presented health conditions, such as irritation to the skin, eyes, mucous membranes, kidney damage, liver, reproductive, among others. In Ecuador, this reality is not different from other countries, and some studies have shown increased diseases related with oil crude and oil spills, like skin irritation, throat, liver, lung, infertility, and abortions, and it has been linked to childhood leukemia. Other studies suggest a direct relationship between DNA damage because of oil resulting in a genetic instability of the main enzymes of cellular metabolism as well as a relationship with some cancers, such as leukemia.

Risk Factors for Multiple Myeloma: A Systematic Review of Meta-Analyses

The epidemiology of multiple myeloma (MM) is an increasingly investigated field, with many controversies. This systematic review aims to synthesize meta-analyses examining risk factors for MM so as to provide a comprehensive, parsimonious summary of the current evidence. Eligible meta-analyses were sought in PubMed adopting a predefined algorithm, without any restriction of publication language; end-of-search date was October 10, 2014. The selection of eligible studies and data extraction were performed by working in pairs, independently and blindly to each other; in case of disagreement, consensus with the whole team was reached. Among the 22 ultimately included meta-analyses, 9 examined occupational factors, 4 assessed aspects of lifestyle (smoking, alcohol, body mass index), 5 evaluated the presence of other diseases, and 4 addressed genetic factors as potential risk factors of MM. A vast compendium of significant associations arose, including farming, occupation as a firefighter, occupation as a hairdresser, exposures to chemicals or pesticides, overweight and obesity, patterns of alcohol intake, pernicious anemia, ankylosing spondylitis, gene promoter methylation, and polymorphisms. In conclusion, MM is a multifactorial disease, encompassing a wide variety of risk factors that span numerous life aspects. Further accumulation of evidence through meta-analyses is anticipated in this rapidly growing field.

An evidence-based analysis of epidemiologic associations between lymphatic and hematopoietic cancers and occupational exposure to gasoline

The presence of benzene in motor gasoline has been a health concern for potential increased risk of acute myelogenous leukemia and perhaps other lymphatic/hematopoietic cancers for approximately 40 years. Because of the widespread and increasing use of gasoline by consumers and the high exposure potential of occupational cohorts, a thorough understanding of this issue is important. The current study utilizes an evidence-based approach to examine whether or not the available epidemiologic studies demonstrate a strong and consistent association between occupational exposure to gasoline and lymphatic/hematopoietic cancers. Among 67 epidemiologic studies initially identified, 54 were ranked according to specific criteria relating to the relevance and robustness of each study for answering the research question. The 30 highest-ranked studies were sorted into three tiers of evidence and were analyzed for strength, specificity, consistency, temporality, dose-response trends and coherence. Meta statistics were also calculated for each general and specific lymphatic/hematopoietic cancer category with adequate data. The evidence-based analysis did not confirm any strong and consistent association between occupational exposure to gasoline and lymphatic/hematopoietic cancers based on the epidemiologic studies available to date. These epidemiologic findings, combined with the evidence showing relatively low occupational benzene vapor exposures associated with gasoline formulations during the last three decades, suggest that current motor gasoline formulations are not associated with increased lymphatic/hematopoietic cancer risks related to benzene.

Occupational benzene exposure and the risk of lymphoma subtypes: a meta-analysis of cohort studies incorporating three study quality dimensions

BACKGROUND

The use of occupational cohort studies to assess the association of benzene and lymphoma is complicated by problems with exposure misclassification, outcome classification, and low statistical power.

OBJECTIVE

We performed meta-analyses of occupational cohort studies for five different lymphoma categories: Hodgkin lymphoma (HL), non-Hodgkin lymphoma (NHL), multiple myeloma (MM), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL).

DATA EXTRACTION

We assessed three study quality dimensions to evaluate the impact of study quality variations on meta-relative risks (mRRs): stratification by the year of start of follow-up, stratification by the strength of the reported acute myelogenous leukemia association, and stratification by the quality of benzene exposure assessment.

DATA SYNTHESIS

mRRs for MM, ALL, and CLL increased with increasing study quality, regardless of the study quality dimension. mRRs for NHL also increased with increasing study quality, although this effect was less pronounced. We observed no association between occupational benzene exposure and HL.

CONCLUSIONS

Our meta-analysis provides support for an association between occupational benzene exposure and risk of MM, ALL, and CLL. The evidence for an association with NHL is less clear, but this is likely complicated by the etiologic heterogeneity of this group of diseases. Further consideration of the association between benzene and NHL will require delineation of risks by NHL subtype.

ATSDR evaluation of health effects of benzene and relevance to public health

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.

Risk of leukemia and multiple myeloma associated with exposure to benzene and other organic solvents: evidence from the Italian Multicenter Case-control study

BACKGROUND

While there is a general consensus about the ability of benzene to induce acute myeloid leukemia (AML), its effects on chronic lymphoid leukemia and multiple myeloma (MM) are still under debate. We conducted a population-based case-control study to evaluate the association between exposure to organic solvents and risk of myeloid and lymphoid leukemia and MM.

METHODS

Five hundred eighty-six cases of leukemia (and 1,278 population controls), 263 cases of MM (and 1,100 population controls) were collected. Experts assessed exposure at individual level to a range of chemicals.

RESULTS

We found no association between exposure to any solvent and AML. There were elevated point estimates for the associations between medium/high benzene exposure and chronic lymphatic leukemia (OR = 1.8, 95% CI = 0.9-3.9) and MM (OR = 1.9, 95% CI = 0.9-3.9). Risks of chronic lymphatic leukemia were somewhat elevated, albeit with wide confidence intervals, from medium/high exposure to xylene and toluene as well.

CONCLUSIONS

We did not confirm the known association between benzene and AML, though this is likely explained by the strict regulation of benzene in Italy nearly three decades prior to study initiation. Our results support the association between benzene, xylene, and toluene and chronic lymphatic leukemia and between benzene and MM with longer latencies than have been observed for AML in other studies.

Epidemiology of the plasma-cell disorders

This review of the plasma-cell disorders begins with the definition of monoclonal gammopathy of undetermined significance (MGUS). The prevalence of MGUS in white and black populations is described. MGUS is a common finding in the medical practice of all physicians, and thus it is important to both the patient and the physician to determine whether the monoclonal protein remains stable or progresses to multiple myeloma (MM), Waldenström's macroglobulinemia (WM), primary systemic amyloidosis (AL), or a related disorder. The long-term (almost 40 years) follow-up data of 241 patients in the Mayo Clinic population is provided. In a large study of 1384 patients with MGUS from southeastern Minnesota, the risk of progression to MM, WM, AL, or other disorders was approximately 1% per year. Risk factors for progression are provided. The incidence of MM in Olmsted County, Minnesota, remained stable for the 56-year span 1945-2001. The apparent increase in incidence and mortality rates among patients with MM in many studies is due to improved case ascertainment, especially among the elderly. The incidence and mortality rates of MM in the United States and other countries are presented. The major emphasis is on the cause of MM, which is unclear. Exposure to radiation from atomic bombs, therapeutic and diagnostic radiation, and in workers in the nuclear industry field are addressed. Many studies involving agricultural occupations, exposure to benzene, petroleum products, and engine exhaust and other industrial exposures are discussed. Tobacco use, obesity, diet, and alcohol ingestion are all possible causes of MM. Clusters of MM have been noted. Multiple cases of MM have been found in first-degree relatives.

Increased risk of acute myelogenous leukemia and multiple myeloma in a historical cohort of upstream petroleum workers exposed to crude oil

Benzene exposure has been shown to be related to acute myelogenous leukemia, while the association with multiple myeloma and non-Hodgkin lymphoma has been a much-debated issue. We performed a historical cohort study to investigate whether workers employed in Norway's upstream petroleum industry exposed to crude oil and other products containing benzene have an increased risk of developing various subtypes of hematologic neoplasms. Using the Norwegian Registry of Employers and Employees we included all 27,919 offshore workers registered from 1981 to 2003 and 366,114 referents from the general working population matched by gender, age, and community of residence. The cohort was linked to the Cancer Registry of Norway. Workers in the job category "upstream operator offshore", having the most extensive contact with crude oil, had an excess risk of hematologic neoplasms (blood and bone marrow) (rate ratio (RR) 1.90, 95% confidence interval (95% CI): 1.19-3.02). This was ascribed to an increased risk of acute myelogenous leukemia (RR 2.89, 95% CI: 1.25-6.67) and multiple myeloma (RR 2.49, 95% CI: 1.21-5.13). There were no statistical differences between the groups in respect to non-Hodgkin lymphoma. The results suggest that benzene exposure, which most probably caused the increased risk of acute myelogenous leukemia, also resulted in an increased risk of multiple myeloma.

Multiple myeloma: A review of the epidemiologic literature

Multiple myeloma, a neoplasm of plasma cells, accounts for approximately approximately 15% of lymphatohematopoietic cancers (LHC) and 2% of all cancers in the US. Incidence rates increase with age, particularly after age 40, and are higher in men, particularly African American men. The etiology is unknown with no established lifestyle, occupational or environmental risk factors. Although several factors have been implicated as potentially etiologic, findings are inconsistent. We reviewed epidemiologic studies that evaluated lifestyle, dietary, occupational and environmental factors; immune function, family history and genetic factors; and the hypothesized precursor, monoclonal gammopathies of undetermined significance (MGUS). Because multiple myeloma is an uncommon disease, etiologic assessments can be difficult because of small numbers of cases in occupational cohort studies, and few subjects reporting exposure to specific agents in case-control studies. Elevated risks have been reported consistently among persons with a positive family history of LHC. A few studies have reported a relationship between obesity and multiple myeloma, and this may be a promising area of research. Factors underlying higher incidence rates of multiple myeloma in African Americans are not understood. The progression from MGUS to multiple myeloma has been reported in several studies; however, there are no established risk factors for MGUS. To improve our understanding of the causes of multiple myeloma, future research efforts should seek the causes of MGUS. More research is also needed on the genetic factors of multiple myeloma, given the strong familial clustering of the disease.

Risk of multiple myeloma following medication use and medical conditions: a case-control study in Connecticut women

BACKGROUND

Certain commonly used drugs and medical conditions characterized by chronic immune dysfunction and/or antigen stimulation have been suggested to affect important pathways in multiple myeloma tumor cell growth and survival. We conducted a population-based case-control study to investigate the role of medical history in the etiology of multiple myeloma among Connecticut women.

METHODS

A total of 179 incident multiple myeloma cases (21-84 years, diagnosed 1996-2002) and 691 population-based controls was included in this study. Information on medical conditions, medications, and medical radiation was obtained by in-person interviews. We calculated odds ratios (OR) as measures of relative risks using logistic regression models.

RESULTS

A reduced multiple myeloma risk was found among women who had used antilipid statin therapy [OR, 0.4; 95% confidence interval (95% CI), 0.2-0.8] or estrogen replacement therapy (OR, 0.6; 95% CI, 0.4-0.99) or who had a medical history of allergy (OR, 0.4; 95% CI, 0.3-0.7), scarlet fever (OR, 0.5; 95% CI, 0.2-0.9), or bursitis (OR, 0.4; 95% CI, 0.2-0.7). An increased risk of multiple myeloma was found among women who used prednisone (OR, 5.1; 95% CI, 1.8-14.4), insulin (OR, 3.1; 95% CI, 1.1-9.0), or gout medication (OR, 6.7; 95% CI, 1.2-38.0).

CONCLUSIONS

If our results are confirmed, mechanistic studies examining how prior use of insulin, prednisone, and, perhaps, gout medication might promote increased occurrence of multiple myeloma and how antilipid statins, estrogen replacement therapy, and certain medical conditions might protect against multiple myeloma may provide insights to the as yet unknown etiology of multiple myeloma.

Benzene Exposure and Multiple Myeloma: A Detailed Meta-analysis of Benzene Cohort Studies

Case reports and epidemiological studies of workers exposed to benzene have demonstrated associations with a number of lymphohematopoietic diseases, but the association with multiple myeloma (MM) has been less apparent. Data from all of the "benzene cohort studies" conducted to date have been selected and evaluated for inclusion in a meta-analysis. The analysis demonstrates a significant excess in the relative risk (RR) of MM in relation to benzene exposure. Pooling the data from seven cohort studies, a meta-analysis yields a statistically significant weighted RR estimate of 2.13 (95% CI = 1.31-3.46). In the analysis of cohort data, an understanding of the cohort follow-up period in relation to benzene exposure and RR of MM is important. Exposure-related RRs of disease decline after the median latency periods are exceeded, particularly when exposure has terminated decades earlier. The positive epidemiological evidence for benzene as a cause of MM is supported by biological plausibility for such an effect from benzene exposure. Studies of refinery workers are difficult to interpret in relation to benzene exposure and risk of MM, but are limited in the study design and analysis. Nonetheless, they provide some support for an association between refinery work and MM.

Occupational exposures and haematological malignancies: overview on human recent data

OBJECTIVE

Occupational causes of haematological malignancies are relatively uncommon, under-studied and under-identified. They are also often unrecognized by clinicians. This review summarizes the principal epidemiologic studies on this topic.

METHODS

We analyzed the recent relevant human data found in the Medline, the Pascal and the BDSP databases.

RESULTS

Benzene and ionizing radiation are the only agents conclusively demonstrated to be carcinogenic to the haematopoietic system. In particular, both exposures are strongly associated with acute myeloid leukaemia. Low doses of both may also be related to myeloid malignancies. Infectious agents and pesticides are also thought to induce lymphoproliferative cancers. Some studies show an association between haematological malignancies and low-frequency electromagnetic fields and organic solvents. All of these suspected occupational causes must be confirmed by further studies.

CONCLUSIONS

Better knowledge and understanding of occupational causes of haematological malignancies are necessary to improve their prevention and compensation.

Familial characteristics of autoimmune and hematologic disorders in 8,406 multiple myeloma patients: A population-based case-control study

A population-based case-control study was conducted to evaluate risk of developing multiple myeloma (MM) associated with personal history of autoimmune diseases and occurrence of autoimmune and selected hematologic disorders in first-degree relatives. Data were obtained for all (n = 8,406) MM cases diagnosed in Sweden (1958-1998), with linkable relatives, 16,543 matched controls and first-degree relatives of cases (n = 22,490) and controls (n = 44,436). Odds ratios (ORs) were calculated to quantify the risk of MM in relation to personal/family history of 32 autoimmune disorders. Familial aggregation of malignancies was evaluated in a marginal survival model using relatives as the cohort. The risk for MM was significantly elevated among subjects with a personal history of pernicious anemia (OR = 3.27; 2.22-4.83) and individuals with a family history of systemic lupus erythematosus (OR = 2.66; 1.12-6.32). Compared with controls, relative risk (RR) of MM was significantly increased (RR = 1.67; 1.02-2.73) in relatives of cases, particularly relatives of probands aged > or =65 at diagnosis (RR = 2.50; 1.19-5.27). Risks were nearly 4-fold elevated among female relatives (RR = 3.97; 1.54-10.2) and among relatives of female probands (RR = 3.74; 1.58-8.83). MM cases had more cases of monoclonal gammopathy of undetermined significance (MGUS) among their relatives than controls, but the numbers were too small to be conclusive. There was generally no increase in risk of MM in probands whose relatives had hematologic malignancies other than MM. These findings do not support a strong association between personal/familial autoimmune diseases and MM. However, MM itself shows significant familial aggregation, implicating the etiologic importance of this type of hematological neoplasm and perhaps MGUS in germ line genes.

Retrospective Cohort Mortality Study and Nested Case???Control Study of Workers Exposed to Creosote at 11 Wood-Treating Plants in the United States

OBJECTIVE

The objective of this study was to assess both malignant and nonmalignant mortality risks of workers exposed to creosote. For background, a literature review is also presented.

MATERIALS AND METHODS

The retrospective cohort study consisted of 2179 employees at 11 plants in the United States where wood (primarily railroad ties and utility poles) is treated with creosote-based preservatives. The observation period covered 1979-2001. Mortality data in the cohort study were analyzed in terms of cause-specific standardized mortality ratios (SMRs) and 95% confidence intervals (95% CIs), with expected deaths based on U.S. national cause-, gender-, race-, year-, age-specific mortality rates. In addition to the cohort investigation, a nested case-control study of lung cancer and multiple myeloma was conducted. Information on tobacco consumption and detailed employment (job titles) was obtained for cases and matched controls. Jobs were classified into 5 categories according to potential for exposure to creosote. Odds ratios (ORs) and 95% CIs were calculated for job categories and length of exposure.

RESULTS

Overall mortality for the entire cohort was lower than expected (293 observed deaths vs. 325.37 expected, SMR = 90.1, 95% CI = 80.0-101.0). Close to 90% employees were hourly, whose potential for exposure was generally much higher than that of salaried employees. Among hourly employees, except for multiple myeloma, none of the specific cancer sites showed any significant increase. Furthermore, detailed analysis by length of employment did not reveal any significant mortality excess or upward trend. Six deaths were from multiple myeloma, whereas 1.50 deaths were expected (SMR = 401.1, 95% CI = 147.2-873.1). However, analysis by length of employment did not show any upward trend for multiple myeloma. No significant mortality increase was reported for any nonmalignant disease, and analysis by length of employment did not reveal any upward trend. In the case-control study, an increased risk of lung cancer was associated with tobacco consumption (OR = 4.92) but not with any job/exposure category. For example, the lung cancer odds ratio for routine exposure to creosote-based wood preservatives was 0.58 (95% CI = 0.11-3.03). Similarly, case-control analyses of multiple myeloma did not reveal any association with employment at the plants or with exposure to creosote-based wood preservatives or to creosote-treated products.

CONCLUSION

Based on the present investigation and other studies, there was no evidence that employment at the 11 wood-treating plants or exposure to creosote-based wood preservatives was associated with any significant mortality increase from site-specific cancers or nonmalignant diseases. Some results should be interpreted with caution because they were based on small numbers.

Myeloma aetiology and epidemiology

Recently there have been substantial improvements in our understanding of the biology of myeloma. These findings have important implications for aetiological studies aimed at defining the causative factors for myeloma. Myeloma is closely related to monoclonal gammopathy of unknown significance (MGUS), which is now recognized to be very common in the older population. The epidemiology of these conditions is presented and discussed in the context of the genetic factors governing both the risk of developing MGUS or of transformation to myeloma. Biological studies support a role for aberrant class switch recombination early in the natural history of myeloma suggesting that factors in the environment may interact with this mechanism to increase myeloma risk. Case-control and cohort studies have identified several known and suspected environmental exposures. These exposures include high doses of ionizing radiation, and occupational exposure in the farming and petrochemical industries. The data supporting these associations are presented and discussed in the context of the molecular mechanisms underlying these exposures. In particular DNA damage occurring as a consequence could readily interact with the class switch recombination process to increase the risk of chromosomal translocations, oncogene deregulation and malignant transformation. A further hypothesis, which has been extensively investigated, is the role of chronic immune/antigenic stimulation and the risk of myeloma. This concept is difficult to explain in the context of our current immunological concepts. The data supporting the association and how molecular epidemiological studies using genetic variants in cytokine genes are allowing us to revisit this concept are discussed in detail.

Updated epidemiological study of workers at two California petroleum refineries, 1950-95

OBJECTIVES

To further assess the potential role of occupational exposures on mortality, a second update of a cohort study of workers at two petroleum refineries in California was undertaken.

METHODS

Mortality analyses were based on standardised mortality ratios (SMRs) and 95% confidence intervals (95% CIs) using the general population of California as a reference. Additional analyses of lymphatic and haematopoietic cancer deaths and diseases related to asbestos were undertaken.

RESULTS

The update consisted of 18,512 employees, who contributed 456,425 person-years of observation between 1950 and 1995. Both overall mortality and total cancer mortality were significantly lower than expected, as were several site specific cancers and non-malignant diseases. In particular, no significant increases were reported for leukaemia cell types or non-Hodgkin's lymphoma. Mortality excess from multiple myeloma was marginally significant. The excess was confined to employees enrolled before 1949. Furthermore, there was no significant upward trend based on duration of employment, which argues against a causal interpretation relative to employment or exposures at the refineries. No increase was found for diseases related to asbestos: pulmonary fibrosis; lung cancer; or malignant mesothelioma. There was no significant increase in mortality from any other cancers or non-malignant diseases.

CONCLUSION

This second update provides additional reassurance that employment at these two refineries is not associated with increased risk of mortality.

Health findings from a mortality and morbidity surveillance of refinery employees

PURPOSE

To present results from a prospective mortality (1973-1998) and morbidity (1990-1998) surveillance of a refinery population in California.

METHODS

Mortality and illness-absence data were extracted from the Shell Oil Company's Health Surveillance System (HSS). Mortality data were compared to the United States, the state of California, and Contra Costa County, where the refinery is located. Morbidity data were compared to other company manufacturing employees. The standardized mortality/morbidity ratio (SMR/SMbR) was used as a measure of risk. Morbidity frequency and duration of absence were calculated by age, sex, and four health risk factors (smoking, high blood pressure, hypercholesterolemia, and obesity).

RESULTS

With the United States as a comparison, the all causes combined SMR was 0.84 [95% confidence interval (CI) = 0.78-0.90], and the SMR for all cancer was 0.75 (95% CI = 0.64-0.88). Statistically significant deficits in mortality were found for lung cancer (SMR = 0.60) and leukemia (SMR = 0.26). Morbidity frequency and duration of absence among smokers were substantially higher than those of nonsmokers. Similar results were also noted for obese employees when compared to those of normal weight.

CONCLUSIONS

Regardless of the comparison population, significantly fewer deaths were seen for all causes combined, all cancer, lung cancer, and leukemia. The study also showed no increased mortality from cancer of the stomach, kidney, skin, prostate, and brain. The increased morbidity frequency and duration of absence were associated with the presence of known health risk factors. These study findings are useful in setting priorities for medical programs and directing efforts such as health promotion and disease prevention strategies.

Updated mortality among diverse operating segments of a petroleum company

OBJECTIVES

To update mortality for 34 560 employees from diverse operating segments of a Canadian petroleum company; and to investigate potential relations with occupational factors.

METHODS

Employees from 1964-83 were linked to the Canadian mortality data base to provide 11 years additional follow up. There were 6760 deaths and 750 683 person-years of follow up compared with 3909 and 428 190, respectively, in the earlier study. Analyses used standardised mortality ratios (SMRs) to compare worker cause specific mortality with the Canadian general population. Duration of employment and latency analyses were performed for causes previously found to be increased in this and other petroleum cohorts, as well as any findings of interest.

RESULTS

For the period 1964-94, employees experienced significantly low overall mortality (SMR=0.86 men, SMR=0.80 women). Kidney cancer, which has been increased in some studies of petroleum workers, was not increased. Acute non-lymphocytic leukaemia in exposed operating segments was consistent with the expected or only slightly, non-significantly increased. The most notable finding was increased deaths from mesothelioma among refinery and petrochemical workers (SMR 8.68; 95% confidence interval (95% CI) 5.51 to 13.03), most of whom were long term employees in jobs with presumed exposure to asbestos (mechanical and pipefitters). Deaths from multiple myeloma among marketing and distribution workers, which were previously increased, remained increased (SMR 2.08; 95% CI 0.95 to 3.95) in the update period 1984-94; however, there was no clear pattern by duration of employment or latency. Aortic aneurysms, which also were previously significantly increased among marketing and distribution workers approached the expected in the update period (SMR 1.18; 95% CI 0. 65-1.98). Analyses by duration of employment showed suggestive trends for aortic aneurysms, but earlier studies of this cohort have not found a relation between aortic aneurysms and exposure to hydrocarbons.

CONCLUSION

The additional 2851 deaths and 322 493 person-years of follow up strengthened the assessment of mortality patterns relative to occupational factors. With the exception of mesothelioma, no clear work related increases in disease were identified.

A critical review of cancer epidemiology in the petroleum industry, with a meta-analysis of a combined database of more than 350,000 workers

In 1989 we published a critical review of cancer epidemiology in petroleum workers, which included as a component of the review a meta-analysis by cancer site. Subsequently we have completed three additional reviews and meta-analyses on cell-type-specific leukemias (1995), multiple myeloma (1997), and non-Hodgkin's lymphoma (2000). The objective of the present investigation was to update our 1989 review and meta-analysis of nonlymphohematopoietic cancers in cohort studies of petroleum workers. Included in the present investigation were cohort studies of petroleum workers from the United States, the United Kingdom, Canada, Australia, Finland, Sweden, and Italy. Individual studies were reviewed with regard to specific cancer sites. For each cancer of interest, risk ratios from the individual studies were presented. In some studies, subcohort analyses stratified by exposure parameters such as length of employment, job category, and hire year were also reported. These subcohort or stratified analyses were reviewed and the results of these analyses were taken into consideration in our interpretation. In addition to the qualitative review of individual studies, a meta-analysis was performed to combine data from individual cohort studies of petroleum workers. The primary purpose of the meta-analysis was to provide a summary measure of risk for each cancer site. Based on a review and meta-analyses of cohort studies of more than 350,000 petroleum workers in the United States, the United Kingdom, Canada, Australia, Finland, Sweden, and Italy, we concluded that there was no increased mortality from digestive cancers (stomach, large intestine, liver, or pancreas), lung cancer, bladder cancer, kidney cancer, or brain cancer. The summary standardized mortality ratios for these cancer sites were all below unity. Significant increases of melanoma mortality were reported in some small groups of refinery workers in the United Kingdom and upstream operation workers in Canada, but no responsible agent(s) had been identified. The observed mortality from skin cancer in all other studies was similar to the expected. In particular, no significant increase of skin cancer mortality was reported in any of the U.S. studies. Elevated mortality from prostate cancer was noted in short-term workers at a U.S. refinery and in short-term workers employed in certain crafts at U.S. crude oil operations. However, the absence of an upward trend by length of employment in these workers argued against an association between exposure to petroleum products and prostate cancer. For all petroleum workers as a whole, mortality from prostate cancer was as expected.

Non-Hodgkin's lymphoma and exposure to benzene in a multinational cohort of more than 308,000 petroleum workers, 1937 to 1996

Petroleum workers are exposed to benzene or benzene-containing petroleum products. As such, studies of these workers provide an opportunity for investigating the relationship between benzene and non-Hodgkin's lymphoma (NHL). However, few cohort studies of petroleum workers report results of NHL separately. One reason is that NHL is usually grouped with other lymphopoietic cancers in the analysis. Another reason is the relatively small number of NHL cases in some studies. To determine the risk of NHL in petroleum workers, we identified 26 cohorts of petroleum workers in the United States, the United Kingdom, Canada, Australia, Italy, and Finland. Authors of the original studies were contacted, and data on the number of observed deaths and person-years of observation were requested. Data from these studies were reviewed individually as well as combined in a pooled analysis (meta-analysis). In particular, results for individual cohorts, most of which had never been reported before, were presented. The combined multinational cohort consisted of more than 308,000 petroleum workers (6.6 million person-years), and the observation period covered an interval of 60 years from 1937 to 1996. A total of 506 NHL deaths were observed, compared with 561.68 expected. The standardized mortality ratio was 0.90 and the 95% confidence interval was 0.82 to 0.98. Analyses were performed by type of facility and industrial process. Stratum-specific standardized mortality ratios (95% confidence intervals) were 0.96 (0.86 to 1.07) for US refinery workers, 1.12 (0.90 to 1.37) for non-US refinery workers, 0.64 (0.50 to 0.82) for product (gasoline) distribution workers, and 0.68 (0.47 to 0.95) for crude oil workers. When individual cohorts were stratified by length of observation, no pattern was detected. In general, exposure levels before 1950 were much higher than thereafter. However, analysis of workers by hire date (< 1950, > or = 1950) revealed no difference in NHL mortality. Furthermore, none of the individual studies showed significant exposure-response relations. In summary, results from individual studies, as well as from the pooled analysis, indicated that petroleum workers were not at an increased risk of NHL as a result of their exposure to benzene or other benzene-containing petroleum products in their work environment. This conclusion was supported by cohort studies of workers in other industries who were exposed to benzene as well as by population-based case-control studies of NHL and occupational exposures.

Nested case-control study of leukaemia, multiple myeloma, and kidney cancer in a cohort of petroleum workers exposed to gasoline

OBJECTIVES

This nested case-control study was based on data in a cohort study of more than 18,000 petroleum distribution workers exposed to gasoline, which contains about 2%-3% benzene. Risks of leukaemia, acute myeloid leukaemia, multiple myeloma, and kidney cancer were examined relative to exposure to gasoline.

METHODS

For each case, up to five individually matched controls were selected. Analyses based on the Mantel-Haenszel procedure as well as univariate and multivariate conditional logistic regression were performed for each disease category. Jobs with similar exposures were grouped into homogeneous categories for analysis. Several quantitative indices of exposure to gasoline were used in the analyses: duration of exposure, cumulative exposure, frequency of peak exposure, and time of first exposure.

RESULTS

No increased risks for the four cancers were found for any job category. Analyses with logistic regression models based on duration of exposure, cumulative exposure, and frequency of peak exposure did not show any increased risk or exposure-effect relation. Time of first exposure to gasoline was also found to be unrelated to the four diseases under investigation.

CONCLUSION

Exposure to gasoline or benzene at the concentrations experienced by this cohort of distribution workers is not a risk factor for leukaemia (all cell types), acute myeloid leukaemia, multiple myeloma, or kidney cancer.

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.

Update of the Texaco mortality study 1947-93: Part II. Analyses of specific causes of death for white men employed in refining, research, and petrochemicals

OBJECTIVE

To examine patterns of mortality for specific causes of death with increases in the Texaco mortality study to determine if the patterns are related to employment in the petroleum industry.

METHODS

Mortality patterns by duration of employment in various job groups were examined for mesothelioma, non-Hodgkin's lymphoma, multiple myeloma, cell type specific leukaemia, and brain tumours.

RESULTS

Mortality from mesothelioma was examined for the total cohort and for two maintenance groups with the greatest potential for exposure to asbestos. The insulator group had a standardised mortality ratio (SMR) of 3029, and a larger group consisting of insulators, carpenters, labourers, electricians, pipefitters, boiler-makers, and welders had an SMR of 411. The mortalities from mesothelioma increased with increasing duration of employment. Mortality was lower for those first employed after 1950. An analysis of all brain tumours for the total cohort and some job and unit subgroups resulted in an SMR of 178 for those employed on the units related to motor oil and 166 for those employed as laboratory workers. Mortality from brain tumours in both of these job groups was higher for those employed > or = 5 years in the group. An analysis of non-Hodgkin's lymphoma showed no consistent patterns among the various employment groups. Mortality from multiple myeloma was non-significantly increased among people employed on the crude (SMR = 155) and fluid catalytic cracking units (SMR = 198). Leukaemia mortality was not increased for the total cohort, and a cell type analysis of leukaemia mortality for the total cohort showed no significant increases for the major cell types. However, there were significant increases for acute unspecified leukaemia (SMR = 276) and leukaemia of unknown cell type (SMR = 231).

CONCLUSIONS

Analyses of specific causes of death by duration of employment in various job and process units did not show any patterns which suggest that, other than for mesothelioma, any of these increases in mortalities were likely to have resulted from workplace exposures or from employment at one of the places included in the Texaco mortality study.

Potential health effects of gasoline and its constituents: A review of current literature (1990-1997) on toxicological data

We reviewed toxicological studies, both experimental and epidemiological, that appeared in international literature in the period 1990-1997 and included both leaded and unleaded gasolines as well as their components and additives. The aim of this overview was to select, arrange, and present references of scientific papers published during the period under consideration and to summarize the data in order to give a comprehensive picture of the results of toxicological studies performed in laboratory animals (including carcinogenic, teratogenic, or embryotoxic activity), mutagenicity and genotoxic aspects in mammalian and bacterial systems, and epidemiological results obtained in humans in relation to gasoline exposure. This paper draws attention to the inherent difficulties in assessing with precision any potential adverse effects on health, that is, the risk of possible damage to man and his environment from gasoline. The difficulty of risk assessment still exists despite the fact that the studies examined are definitely more technically valid than those of earlier years. The uncertainty in overall risk determination from gasoline exposure also derives from the conflicting results of different studies, from the lack of a correct scientific approach in some studies, from the variable characteristics of the different gasoline mixtures, and from the difficulties of correctly handling potentially confounding variables related to lifestyle (e.g., cigarette smoking, drug use) or to preexisting pathological conditions. In this respect, this paper highlights the need for accurately assessing the conclusive explanations reported in scientific papers so as to avoid the spread of inaccurate or misleading information on gasoline toxicity in nonscientific papers and in mass-media messages.