Occupational Exposure to Benzene

by

Melvyn Kopstein

• LAST REVIEWED: 26 April 2018
• LAST MODIFIED: 26 April 2018
• DOI: 10.1093/obo/9780199756797-0180

Introduction

Millions of workers around the world are routinely exposed to benzene from product mixtures formulated with benzene-containing petrochemicals (e.g., toluene, VM&P naphtha) that are classified as Group 3 carcinogens by the International Agency for Research on Cancer (IARC). Exposure regulations do not differentiate between benzene exposures arising from untested mixtures (in terms of carcinogenicity) and those arising from the use of pure benzene. Petrochemicals containing less than 0.1 percent benzene, such as severely hydrotreated mineral spirits, are sometimes referred to as “trace” benzene products. As will be discussed, products containing less than 0.1 percent benzene may cause benzene exposures that are hardly “trace.” Benzene exposures are generally expressed in parts per billion (ppb) and parts per million (ppm), with single digit ppb measurements roughly corresponding to urban background levels. On the other hand, some published articles report occupational exposures to benzene that are are tens of thousands-fold higher than outdoor background levels. The magnitude of any benzene exposure depends on exposure factors such as (a) the benzene content of the product, (b) ventilation, (c) liquid and air temperatures, (d) activity coefficient of benzene in the product, (e) pattern of product usage (e.g., volume used and time spent performing a task), (f) distance between a worker’s breathing zone and evaporating product, and (g) personal protective equipment. Because an unlimited combination of workplace exposure factors are possible, benzene exposures are known to vary by orders of magnitude in different occupational settings. The Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) and short-term exposure limit (STEL) for benzene are 1 ppm and 5 ppm, respectively. The American Conference of Governmental Industrial Hygienists (ACGIH) STEL for benzene is 2.5 ppm and its threshold limit value (TLV) is 0.5 ppm. PELs and TLVs reflect long-term exposures averaged over eight-hour sample periods, while an STEL reflects short-term exposures averaged over a continuous 15-minute period. The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) for benzene is only 0.1 ppm. Peak exposures, as well as short-term exposures averaged over less than 15-minutes, may be orders of magnitude higher than long-term exposures averaged over eight hgours. Because long-term exposures effectively smooth out high and low (or no) benzene exposures within sampling periods, it is important to understand that short-term exposures could easily exceed an STEL within any given long-term sampling period in which the time-averaged long-term benzene exposure is well below the PEL and TLV. Since published benzene exposure data are scarce relative to the known extent of the benzene exposure problem, published exposure data must be carefully evaluated before extrapolating them to workplaces having no exposure monitoring data, and for which relevant information about exposure factors is lacking. Anticipating and estimating benzene exposures requires a proper understanding of the amount of benzene in a product under consideration. Product benzene contents reported in published articles should be based upon peer-reviewed analytical testing methods (e.g., those issued by ASTM International) or generally accepted secondary sources. Moreover, benzene contents should comport with the chemical and physical properties of commodity petrochemical ingredients such as nitration-grade toluene and how they were manufactured.

General Overviews

Working conditions around the world are known to be highly variable (International Agency for Research on Cancer (IARC) 2012). Countless commercial products used by workers are formulated with toluene, VM&P naphtha, mixed hexanes, regular mineral spirits, severely hydrotreated mineral spirits, mixed xylenes, and other benzene-containing commodity petrochemicals. Some products are mixtures of different hydrocarbons, while others include hydrocarbon solvents along with chemicals such as methyl alcohol, methyl ethyl ketone (MEK), and acetone. Millions of workers are exposed to benzene arising from their use of benzene-containing products (Goldstein and Infante 2016; Kauppinen, et al. 2000; ATSDR 2000). Benzene exposures occur in thousands of workplaces around the world, all with their own (and variable) ventilation characteristics, environmental conditions, administrative controls, and patterns in which benzene-containing products are used. The amount of published benzene exposure data in occupational settings is extremely limited and/or difficult to assess (van Wijngaarden and Stewart 2003, cited under Occupational Exposures to Benzene; Verma, et al. 2000; Verma and Rana 2001; Caldwell, et al. 2000). Given the paucity of published exposure information and the existence of highly variable exposure conditions—and the fact that the amount of benzene in products is also highly variable—it is not advisable to statistically analyze limited published exposure data (frequently presented with incomplete monitoring conditions) and extrapolate them to workplaces for which information about ventilation and other exposure factors is unavailable. It is essential to have an understanding of the concentration of benzene in a product in order to control exposures and to retrospectively estimate past exposures. The amount of benzene in a petrochemical matrix such as mineral spirits can be measured using gold standard testing methods offered by ASTM International (Grob and Barry 2004, cited under Benzene Content of Petrochemicals). ASTM International and US Environmental Protection Agency (EPA) testing methods have been peer reviewed, and their precision, detection limits, and other performance metrics are known.

• ATSDR. 2000. Stoddard solvent toxicity. Publication ATSDR-HE-CS-2001–004.

  The report discusses 2 million workers (excluding those employed by the military) experiencing exposure to Stoddard solvent between 1981 and 1983.

• Caldwell, D., T. Armstrong, N. J. Barone, J. A. Suder, and M. J. Evans. 2000. Hydrocarbon solvent exposure data: Compilation and analysis of the literature. American Industrial Hygiene Association Journal 61:881–894.

  The article discusses benzene exposures in the period 1978 to 1997. According to the authors, while hydrocarbon solvents are used in a very wide range of industries and processes, historic exposure data are rare. Also see Occupational Exposures to Benzene and Examples of High Benzene Exposures.

• Goldstein, B., and P. Infante. 2016, May. Benzene as a cause of hematological cancers: A recurring example of the importance of mechanistic understanding and animal studies. Poster session at IARC 50th Anniversary meeting. Lyon, France.

  Millions of workers remained exposed to benzene in 2016 according to the authors. They urge IARC to reevaluate the relation between benzene exposure and non-Hodgkins lymphoma.

• International Agency for Research on Cancer (IARC). 2012. Chemical agents and related occupations. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 100F.

  The monograph reports wide variability in working conditions in places of employment around the world. Since table 1.2 in the 100F Benzene Monograph pertains to only twenty-two settings where products containing very low levels of benzene were used (under conditions that are not specified), the tabulated measurements should not be viewed as predictive of exposures at other workplaces in which different conditions of exposure (e.g., product benzene content, temperatures, ventilation, product type) apply. Also see Material Safety Data Sheets and Benzene-Containing Mixtures.

• Kauppinen, T., J. Toikkanen, D. Pedersen, et al. 2000. Occupational exposure to carcinogens in the European Union. Occupational and Environmental Medicine 57:10–18.

  According to Table 3, 1.4 million workers in the European Union were exposed to benzene between 1990 and 1993.

• Verma, D., M. Johnson, and J. McLean. March/April 2000. Benzene and total hydrocarbons exposures in the downstream petroleum industries. American Industrial Hygiene Association Journal 61:255–263.

  The authors cite the need for more exposure monitoring. Their recommendation is (page 262), “Task-based sampling should be carried out in addition to traditional long-term full-shift personal sampling.” Table 3 includes 124 sampling results showing short-term exposures between 10 ppb and 50 ppm. Of that number, forty-nine samples were between 1.1 and 50 ppm. Also see Occupational Exposures to Benzene, Short-Term (Task-Specific) Exposures, and Examples of High Benzene Exposures.

• Verma, Y., and S. Rana. 2001. Biological monitoring of exposure to benzene in petrol pump workers and dry cleaners. Industrial Health 39:320–333.

  The authors discuss shortages of published benzene exposure data and present two important conclusions. First, reporting benzene exposure data statistically (e.g., arithmetic means) without individual data from which the means were calculated could lead to misinterpretation because high exposures are “lost in such averaging.” Second, short-term (task-specific) exposure monitoring is needed to capture high exposures that are lost in long-term sampling. Also see Occupational Exposures to Benzene, Short-Term (Task-Specific) Exposures, and Examples of High Benzene Exposures.