Health Watch exposure estimates: do they underestimate benzene exposure?

Characterizing methane and total non-methane hydrocarbon levels in Los Angeles communities with oil and gas facilities using air quality monitors

Over the past decade, sensor networks have been proven valuable to assess air quality on highly localized scales. Here we leverage innovative sensors to characterize gaseous pollutants in a complex urban environment and evaluate differences in air quality in three different Los Angeles neighborhoods where oil and gas activity is present. We deployed monitors across urban neighborhoods in South Los Angles adjacent to oil and gas facilities with varying levels of production. Using low-cost sensors built in-house, we measured methane, total non-methane hydrocarbons (TNMHCs), carbon monoxide, and carbon dioxide during three deployment campaigns over four years. The multi-sensor linear regression calibration model developed to quantify methane and TNMHCs offers up to 16% improvement in coefficient of determination and up to a 22% reduction in root mean square error for the most recent dataset as compared to previous models. The deployment results demonstrate that airborne methane concentrations are higher within a 500 m radius of three urban oil and gas facilities, as well as near a natural gas distribution pipeline, likely a result of proximity to sources. While there are numerous additional sources of TNMHCs in complex urban environments, some sites appear to be larger emitters than others. Significant methane emissions were also measured at an idle site, suggesting that fugitive emissions may still occur even if production is ceased. Episodic spikes of both compounds suggested an association with oil and gas activities, demonstrating how sensor networks can be used to elucidate community-scale sources and differences in air quality moving forward.

An Assessment on Ethanol-Blended Gasoline/Diesel Fuels on Cancer Risk and Mortality

Although cancer is traditionally considered a genetic disease, the epigenetic abnormalities, including DNA hypermethylation, histone deacetylation, and/or microRNA dysregulation, have been demonstrated as a hallmark of cancer. Compared with gene mutations, aberrant epigenetic changes occur more frequently, and cellular epigenome is more susceptible to change by environmental factors. Excess cancer risks are positively associated with exposure to occupational and environmental chemical carcinogens, including those from gasoline combustion exhausted in vehicles. Of note, previous studies proposed particulate matter index (PMI) as a measure for gasoline sooting tendency, and showed that, compared with the other molecules in gasoline, 1,2,4-Trimethylbenzene, 2-methylnaphthalene and toluene significantly contribute to PMI of the gasoline blends. Mechanistically, both epigenome and genome are important in carcinogenicity, and the genotoxicity of chemical agents has been thoroughly studied. However, less effort has been put into studying the epigenotoxicity. Moreover, as the blending of ethanol into gasoline substitutes for carcinogens, like benzene, toluene, xylene, butadiene, and polycyclic aromatic hydrocarbons, etc., a reduction of secondary aromatics has been achieved in the atmosphere. This may lead to diminished cancer initiation and progression through altered cellular epigenetic landscape. The present review summarizes the most important findings in the literature on the association between exposures to carcinogens from gasoline combustion, cancer epigenetics and the potential epigenetic impacts of biofuels.

Epigenetic Effects of Benzene in Hematologic Neoplasms: The Altered Gene Expression

Simple Summary

Benzene is produced by diverse petroleum transformation processes and it is widely employed in industry despite its oncogenic effects. In fact, occupational exposure to benzene may cause hematopoietic malignancy. The leukemogenic action of benzene is particularly complex. Possible processes of onset of hematological malignancies have been recognized as a genotoxic action and the provocation of immunosuppression. However, benzene can induce modifications that do not involve alterations in the DNA sequence, the so-called epigenetics changes. Acquired epigenetic modification may also induce leukemogenesis, as benzene may alter nuclear receptors, and cause changes at the protein level, thereby modifying the function of regulatory proteins, including oncoproteins and tumor suppressor proteins.

Abstract

Benzene carcinogenic ability has been reported, and chronic exposure to benzene can be one of the risk elements for solid cancers and hematological neoplasms. Benzene is acknowledged as a myelotoxin, and it is able to augment the risk for the onset of acute myeloid leukemia, myelodysplastic syndromes, aplastic anemia, and lymphomas. Possible mechanisms of benzene initiation of hematological tumors have been identified, as a genotoxic effect, an action on oxidative stress and inflammation and the provocation of immunosuppression. However, it is becoming evident that genetic alterations and the other causes are insufficient to fully justify several phenomena that influence the onset of hematologic malignancies. Acquired epigenetic alterations may participate with benzene leukemogenesis, as benzene may affect nuclear receptors, and provoke post-translational alterations at the protein level, thereby touching the function of regulatory proteins, comprising oncoproteins and tumor suppressor proteins. DNA hypomethylation correlates with stimulation of oncogenes, while the hypermethylation of CpG islands in promoter regions of specific tumor suppressor genes inhibits their transcription and stimulates the onset of tumors. The discovery of the systems of epigenetic induction of benzene-caused hematological tumors has allowed the possibility to operate with pharmacological interventions able of stopping or overturning the negative effects of benzene.

Key event-informed risk models for benzene-induced acute myeloid leukaemia

Occupational exposure to benzene at levels of 10 ppm or more has been associated with increased risk of acute myeloid leukaemia (AML). The mode of action (MOA) for AML development leading to mortality is anticipated to include multiple earlier key events, which can be observed in hematotoxicity and genetic toxicity in peripheral blood of exposed workers. Prevention of these early events would lead to prevention of the apical, adverse outcomes, the morbidity and mortality caused by the myelodysplastic syndromes (MDS) and AML. Incorporation of key event information should modify the risk model, but few modification approaches have been suggested. To that end, two approaches to risk model modification are described that use sub-linear and segmented linear increases in risk below key events, while maintaining a linear increase in AML mortality risk beginning at 2 ppm, the lowest observed adverse effect concentration (LOAEC) identified for hemato- and geno- toxicity in high quality studies of human occupational exposure. Below 2 ppm two different modification approaches to quantitative risk models were applied: a continuously decreasing slope model and a segmented modification in slope. These two approaches provide greater flexibility to incorporate MOA information in risk model development and selection.

A brief review of relationship between occupational benzene exposure and hematopoietic cancer

We reviewed articles to clarify the current evidence status for 1) types of cancer which related to benzene exposure, and 2) certain benzene exposure level which might cause the hematopoietic cancers. Hematopoietic function of the bone marrow is involved in the production of all blood cells types. The benzene metabolites including benzoquinone and mucoaldehyde affect hematopoietic stem cells as well as differentiation steps of progenitor cells for each blood cell. Hence, we concluded that benzene was associated with all lymphohematic carcinogenesis. First, it is supported by biological plausibility. Second, it is supported by meta-analysis although sing study did not show relationship due to lack of sample size or statistical power. More recent studies show lesser exposed level related to risk of cancer, compare to past studies did. Actually, early studies show the risk of malignancies in workers who exposed more than 200 ppm-years. However, only 0.5 to 1 ppm-year benzene exposed show significant linking to risk of malignancies in recent study. As reviewed research articles, we concluded that the relatively lower exposure level, such as 0.5–1 ppm-year, will be considering at risk of hematopoietic cancer. However, more research needs to be done on dose-response analysis.

Combined analysis of job and task benzene air exposures among workers at four US refinery operations

Workplace air samples analyzed for benzene at four US refineries from 1976 to 2007 were pooled into a single dataset to characterize similarities and differences between job titles, tasks and refineries, and to provide a robust dataset for exposure reconstruction. Approximately 12,000 non-task (>180 min) personal samples associated with 50 job titles and 4000 task (<180 min) samples characterizing 24 tasks were evaluated. Personal air sample data from four individual refineries were pooled based on a number of factors including (1) the consistent sampling approach used by refinery industrial hygienists over time, (2) the use of similar exposure controls, (3) the comparability of benzene content of process streams and end products, (4) the ability to assign uniform job titles and task codes across all four refineries, and (5) our analysis of variance (ANOVA) of the distribution of benzene air concentrations for select jobs/tasks across all four refineries. The jobs and tasks most frequently sampled included those with highest potential contact with refinery product streams containing benzene, which reflected the targeted sampling approach utilized by the facility industrial hygienists. Task and non-task data were analyzed to identify and account for significant differences within job-area, task-job, and task-area categories. This analysis demonstrated that in general, areas with benzene containing process streams were associated with greater benzene air concentrations compared to areas with process streams containing little to no benzene. For several job titles and tasks analyzed, there was a statistically significant decrease in benzene air concentration after 1990. This study provides a job and task-focused analysis of occupational exposure to benzene during refinery operations, and it should be useful for reconstructing refinery workers' exposures to benzene over the past 30 years.

Proposal on limits for chemical exposure in saturation divers' working atmosphere: the case of benzene

Saturation diving is performed under extreme environmental conditions. The divers are confined to a limited space for several weeks under high environmental pressure and elevated oxygen partial pressure. At present, divers are protected against chemical exposure by standard exposure limits only adjusted for the increased exposure length, i.e. from 8 to 24 hours a day and from 5 to 7 days a week. The objective of the present study was to indicate a procedure for derivation of occupational exposure limits for saturation diving, termed hyperbaric exposure limits (HEL). Using benzene as an example, a procedure is described that includes identification of the latest key documents, extensive literature search with defined exclusion criteria for the literature retrieved. Hematotoxicity and leukemia were defined as the critical effects, and exposure limits based upon concentration and cumulative exposure data and corresponding risks of leukemia were calculated. Possible interactions of high pressure, elevated pO₂, and continuous exposure have been assessed, and incorporated in a final suggestion of a HEL for benzene. The procedure should be applicable for other relevant chemicals in the divers' breathing atmosphere. It is emphasized that the lack of interactions from pressure and oxygen indicated for benzene may be completely different for other chemicals.

Advances in understanding benzene health effects and susceptibility

Benzene is a ubiquitous chemical in our environment that causes acute leukemia and probably other hematological cancers. Evidence for an association with childhood leukemia is growing. Exposure to benzene can lead to multiple alterations that contribute to the leukemogenic process, indicating a multimodal mechanism of action. Research is needed to elucidate the different roles of multiple metabolites in benzene toxicity and the pathways that lead to their formation. Studies to date have identified a number of polymorphisms in candidate genes that confer susceptibility to benzene hematotoxicity. However, a genome-wide study is needed to truly assess the role of genetic variation in susceptibility. Benzene affects the blood-forming system at low levels of occupational exposure, and there is no evidence of a threshold. There is probably no safe level of exposure to benzene, and all exposures constitute some risk in a linear, if not supralinear, and additive fashion.

Ensuring comparability of benzene exposure estimates across three nested case-control studies in the petroleum industry in support of a pooled epidemiological analysis

BACKGROUND

Three case-control studies each nested within a cohort of petroleum workers assessed exposure to benzene in relation to risk of haematopoietic cancers. These studies have each been updated and the cases will be pooled to derive a more powerful study. The benzene exposure of new leukemia cases and controls was estimated in accordance with each respective study's original methods. An essential component of the process of pooling the data was comparison and rationalisation of the exposure estimates to ensure accuracy and consistency of approach. This paper describes this process and presents comparative estimates before and after appropriate revision took place. The original petroleum industry studies, in Canada, the UK and Australia, were conducted at different points in time by different study teams, but the industry used similar technology in similar eras in each of these countries.

METHODS

A job history for each subject giving job title, dates of starting and leaving the job and location of work, was assembled. For each job or task, the average benzene exposure (Base Estimate (BE) in ppm) was derived from measurements collected at applicable worksites. Estimates of exposure intensity (workplace exposure estimates (WE)) were then calculated for each line of work history by adjusting the BEs for site- and era-specific exposure-related variables such as loading technology and percentage benzene in the product. To ensure that the exposure estimates were comparable among the studies, the WEs were allocated to generic Job Categories, e.g. Tanker Driver (by technology used e.g. bottom loading), Motor Mechanic. The WEs were stratified into eras, reflecting technological changes in the industry. The arithmetic mean (AM), geometric mean (GM) and range of the stratified WEs were calculated, by study, for each generic Job Category. These were then compared. The AMs of the WEs were regarded as substantially similar if they were within 20% in all three studies in one era or for at least two studies in two eras. If the AM of the WE group differed by more than 20%, the data were examined to see whether the difference was justified by differences in local exposure conditions, such as an enclosure versus open work area. Estimates were adjusted in the absence of justification for the difference.

RESULTS

Reconciliation of differences resulted in changes to a small number of underlying BEs, particularly the background values, also the BEs attributed to some individuals and changes to the allocation of jobs between Job Categories. Although the studies covered some differing sectors of the industry and different time periods, for 22 Job Categories there was sufficient overlap, particularly in the downstream distribution sector, to make comparisons possible. After adjustment 12 Job Categories were judged to be similar and 10 were judged to be justifiably different. Job-based peak and skin exposure estimates were applied in a uniform way across the studies and a single approach to scoring the certainty of the exposure estimates was identified.

CONCLUSIONS

The revised exposure estimates will be used in the pooled analysis to examine the risk of haematopoietic cancers and benzene exposure. This exercise provided an important quality control check on the exposure estimates and identified similarly exposed Job Categories that could be grouped for risk assessment analyses.

Occupational exposure to benzene at the ExxonMobil refinery at Baton Rouge, Louisiana (1977-2005)

Because crude oil contains up to 3% benzene and there is an association between high chronic exposure to appreciable concentrations of benzene and acute myelogenous leukemia, exposure of refinery workers has been studied for many years. To date, no extensive industrial hygiene exposure analyses for historical benzene exposure have been performed, and none have focused on the airborne concentrations in the workplace at specific refineries or for specific tasks. In this study, the authors evaluated the airborne concentrations of benzene and their variability over time at the ExxonMobil refinery in Baton Rouge between 1977 and 2005. Refinery workers were categorized into 117 worker groups using company job descriptions. These 117 groups were further collapsed into 25 job categories based on similarity of measured exposure results. Results of 5289 personal air samples are included in this analysis; 3403 were considered nontask (>or= 180 min) personal samples, and 830 were considered task-related (< 180 min) personal samples; the remainder did not fit in either category. In general, nontask personal air samples indicated that exposures of the past 30 years were generally below the occupational exposure limit of 1 ppm, but there was only a small, decreasing temporal trend in the concentrations. The job sampled most frequently during routine operations was process technician and, as broken down by area, resulted in the following mean benzene concentrations: analyzers (mean = 0.12 ppm), coker (mean = 0.013 ppm), hydrofiner (mean = 0.0054 ppm), lube blending and storage (mean = 0.010 ppm), waste treatment (mean = 0.092 ppm), and all other areas (mean = 0.055 ppm). Task-based samples indicated that the highest exposures resulted from the sampling tasks, specifically from those performed on process materials; in general, though, even these tasks had concentrations well below the STEL of 5 ppm. The most frequently sampled task was gauging (mean = 0.12 ppm). Task-related exposures were also similar across job categories for a given task, with a few exceptions. This study thus provides a task-focused analysis for occupational exposure to benzene during refinery operations, which can be insightful for understanding exposures at this refinery and perhaps others operated since about 1975.

Guidelines to evaluate human observational studies for quantitative risk assessment

BACKGROUND

Careful evaluation of the quality of human observational studies (HOS) is required to assess the suitability of HOS for quantitative risk assessment (QRA). In particular, the quality of quantitative exposure assessment is a crucial aspect of HOS to be considered for QRA.

OBJECTIVE

We aimed to develop guidelines for the evaluation of HOS for QRA and to apply these guidelines to case-control and cohort studies on the relation between exposure to benzene and acute myeloid leukemia (AML).

METHODS

We developed a three-tiered framework specific for the evaluation of HOS for QRA and used it to evaluate HOS on the relation between exposure to benzene and AML.

RESULTS

The developed framework consists of 20 evaluation criteria. A specific focus of the framework was on the quality of exposure assessment applied in HOS. Seven HOS on the relation of benzene and AML were eligible for evaluation. Of these studies, five were suitable for QRA and were ranked based on the quality of the study design, conduct, and reporting on the study.

CONCLUSION

The developed guidelines facilitate a structured evaluation that is transparent in its application and harmonizes the evaluation of HOS for QRA. With the application of the guidelines, it was possible to identify studies suitable for QRA of benzene and AML and rank these studies based on their quality. Application of the guidelines in QRA will be a valuable addition to the assessment of the weight of evidence of HOS for QRA.

Benzene-induced cancers: abridged history and occupational health impact

Benzene-induced cancer in humans was first reported in the late 1920s. Carcinogenesis findings in animals were not reported conclusively until 1979. Industry exploited this "discrepancy" to discredit the use of animal bioassays as surrogates for human exposure experience. The cardinal reason for the delay between first recognizing leukemia in humans and sought-after neoplasia in animals centers on poor design and conduct of experimental studies. The first evidence of carcinogenicity in animals manifested as malignant tumors of the zymbal glands (sebaceous glands in the ear canal) of rats, and industry attempted to discount this as being irrelevant to humans, as this organ is vestigial and not present per se in humans. Nonetheless, shortly thereafter benzene was shown to be carcinogenic to multiple organ sites in both sexes of multiple strains and multiple species of laboratory animals exposed via various routes. This paper presents a condensed history of the benzene bioassay story with mention of benzene-associated human cancers.

The health watch case-control study of leukemia and benzene: the story so far

A case-control study nested in the Health Watch cohort of petroleum industry workers, investigated whether the excess of lymphohematopoetic cancers, identified among male members of the Health Watch cohort, was associated with benzene exposure. Cases of non-Hodgkin's lymphoma (n = 31), multiple myeloma (n = 15), and leukemia (n = 33) were identified between 1981 and 1999. Cases were age-matched to five controls. Exposure was retrospectively estimated for each occupational history using an algorithm in a relational database. Benzene exposure measurements, supplied by Australian petroleum companies, were used to estimate exposure for specific tasks. The tasks carried out within the job, the products handled, and the technology used, were identified from interviews with contemporary colleagues. More than half of the subjects started work after 1965 and had an average exposure period of 20 years. Exposure was low, 85% of the cumulative exposure estimates were <10 ppm years. Matched analyses showed that non-Hodgkin's lymphoma and multiple myeloma were not associated with benzene exposure. Leukemia risk, however, was significantly increased for the subjects with greater than 16 ppm years cumulative exposure, odds ratio (OR) 51.9 (5.6-477) or with greater than 0.8 ppm intensity of highest exposed job. Cumulative exposures were similar to those found in comparable studies. The inclusion of occasional high exposures, for example, as a result of spillages, reduced the ORs, when the exposure was treated as either a continuous or a categorical variable. Our data demonstrate a strong association between leukemia and modest benzene exposure. The choice of cut-point and reference group has a marked effect on the ORs, but does not change the overall conclusions.