State of the Science Report for Ethylbenzene

Exposure Assessment, Hazard Characterization and Risk Evaluation

The upper-bounding estimates of exposure to ethylbenzene for the general population of Canada range from 95 µg/ kg-bw per day for the 60+ years age group to 287 µg/ kg-bw per day for the 0.5-4 years age group (Table 1). Based on the available data, inhalation of indoor air is the primary source of exposure. These estimates are based on data from Canadian surveys of ambient air, indoor air, drinking water and soil (Otson et al., 1982; Dann and Wang, 1989; Fellin et al., 1992; OMEE, 1993). Canadian data on the concentration of ethylbenzene in whitefish muscle (Lockhart et al., 1992) were selected to represent levels in fish and combined with data from the U.S. Food and Drug Administration's Market Basket Survey (U.S. FDA, 2000) as a basis for estimating intake in Canadian foodstuffs. Confidence in the database on exposure to ethylbenzene through environmental media is considered high, as representative surveys are available for all media.

Based on the available information on use patterns of ethylbenzene in Canada, consumer products represent another source of exposure. Smoking may also contribute to overall exposure. To assess the potential increased exposure to ethylbenzene from use of consumer products, estimates of resulting airborne concentrations and daily intake for the Canadian adult population (20-59 years old) were made for exposure from paints (spray paint and latex paint) and gasoline (see Appendix A). These products were selected because they represent important product uses of ethylbenzene and principal consumer products from which exposure to ethylbenzene may occur. The Canadian adult population is expected to be the principal user of these products. Exposure to an aerosol spray paint was considered to be representative of an acute exposure for paint products, whereas exposure to a latex paint was considered to be representative of a chronic exposure, based on the nature of the exposures, event duration and event frequency. Exposure to gasoline was considered most likely to occur while refuelling a vehicle . Based on these screening estimates, inhalation intake from latex paint could contribute substantially to exposure (85 µg/ kg-bw per day), while dermal intake is negligible and exposure through gasoline is limited. Smoking may contribute to the overall exposure to ethylbenzene through environmental and mainstream tobacco smoke (see Appendix A); however, the indoor air study used in deriving upper-bounding estimates of exposure did not distinguish between smoking and non-smoking homes. Confidence in the intake estimates of ethylbenzene from consumer products is moderate. The intake estimates were calculated for the most commonly used products with the highest potential for exposure. These estimates are based on modelled exposure scenarios and on use pattern assumptions that may not be valid for all users of the products. Estimated exposures may be higher when averaged over shorter periods of time. Emissions of ethylbenzene from consumer products are expected to contribute significantly to indoor air levels; however, the contributions have not been characterized fully and cannot be quantified at this time.

An assessment by the International Agency for Research on Cancer (IARC, 2000) concluded that ethylbenzene was possibly carcinogenic to humans (Group 2B), based on sufficient evidence in experimental animals and inadequate evidence in humans. In a carcinogenicity bioassay, male and female mice and rats were exposed to concentrations up to 750 ppm (0, 326, 1090 or 3260 mg/m³) ethylbenzene for 103 and 104 weeks, respectively (Chan et al., 1998; NTP, 1999). In male mice, there were concentration-related increases in the incidence of both alveolar/bronchiolar adenomas and combined alveolar/bronchiolar adenomas and carcinomas of the lung, which were significant at the highest concentration. In females, there were concentration-related increases in the incidence of both hepatocellular adenomas and combined adenomas and carcinomas, which were significant at the highest concentration. These incidences were within the ranges of historical controls. In rats, significant increases in the incidences of renal tubular adenomas and combined adenomas and carcinomas were observed in males at the highest concentration. Significant increases in incidences of renal adenomas were observed in females at the highest concentration. In both groups, there was also a significant increase in the incidence of focal renal tubular hyperplasia at the highest concentration, which was considered to be a precursor stage of adenoma by the authors of the study.

Ethylbenzene has not been mutagenic or clastogenic in in vivo assays, with results of well-conducted studies being negative for chromosome aberrations in rat bone marrow and mouse micronuclei. It has also been negative in well-conducted assays for mutations in bacteria and yeast in vitro and in insects, as well as for chromosomal aberrations in mammalian cells. However, there have been a limited number of positive results in well-conducted assays in vitro in mammalian cells, including cell transformation and micronuclei in Syrian hamster embryo cells, a cell line noted for its metabolic capacity. In addition, there was an unequivocal positive response at a single elevated dose in the mouse lymphoma assay. With the exception of a positive in vivo micronucleus prediction, results predicted using quantitative structure-activity relationships (QSARs) within the domains of the models for a range of genotoxicity endpoints were all negative, including the subset of models for which ethylbenzene was not included in the training set. Therefore, while the weight of evidence for direct interaction of ethylbenzene with DNA is limited, it cannot be precluded.

Overall, the confidence in the database on the toxicity of ethylbenzene is considered to be moderate to high, as a wide range of study type s is available (Table 2). However, there is some uncertainty concerning whether the tumours observed in the long-term bioassays could be associated with a genotoxic mode of action, since the genotoxic potential of ethylbenzene is unclear. It was noted that significant increases in tumours were observed only at the higher concentrations and were within the range observed in historical controls.

The lowest identified effect level for inhalation of ethylbenzene in air, the principal route of human exposure, is a lowest-observed-effect concentration (LOEC) of 326 mg/m³, at which there was an increased severity of nephropathy in female rats exposed for 104 weeks (NTP, 1999). Reductions in liver pentoxyresorufin O-dealkylase (PROD) and ethoxyfluorocoumarin-O-dealkylase (EFCOD) and lung ethoxyresorufin O-dealkylase (EROD) and PROD activities were observed in male and female mice exposed to 326 mg/m³ for 5 days (Stott et al., 2003).

Comparison of the lowest inhalation effect level (326 mg/m³) with the highest concentration in indoor air (539.31 µg/m³) results in a margin of exposure of 600. In addition, exposures when using consumer products such as paints may reach or exceed concentrations reported to have adverse effects in laboratory animals exposed for similarly short durations. The likely significant contribution of consumer products to total exposure is supported by the large variation between mean and maximum concentrations reported in indoor air (e.g., 50-fold).

In light of the possible carcinogenicity of ethylbenzene in humans, for which a mode of induction involving direct interaction with DNA cannot be precluded , and potentially significant exposures from use of consumer products, the outcome of this evaluation is that it is suspected that the margins between levels causing health effects in experimental animals and exposure may not be adequate to account for the uncertainties in the database. Information addressing the mode of action for tumour induction and potential genotoxicity would permit a more definitive conclusion. In addition, data on measured human exposure from use of products containing ethylbenzene, such as acrylic enamel spray paint and latex paint is desirable.

Table 1: Upper-bounding estimates of daily intake of ethylbenzene by the general population in Canada

Route of exposure	Estimated intake (µg/kg-bw per day) of ethylbenzene by various age groups
	0-6 months1,2,3		0.5-4 years4	5-11 years5	12-19 years6	20-59 years7	60+ years8
	Formula fed	Not formula fed
Ambient air9	0.6		1.3	1	0.6	0.5	0.4
Indoor air10	132		283	221	126	107.8	93.7
Drinking water11	1.1	0.4	0.4	0.4	0.2	0.2	0.2
Food and beverages12		1.7	2.4	1.8	1.1	1	0.7
Soil13	2.0 × 10-4		3.3 × 10-4	1.1 × 10-4	2.6 × 10-5	2.2 × 10-5	2.1 × 10-5
Total intake	134	135	287	224	128	110	95

¹ Data for concentrations of ethylbenzene in breast milk were not identified.
² Assumed to weigh 7.5 kg, to breathe 2.1 m³ of air per day, to drink 0.8 L of water per day (formula fed) or 0.3 L/day (not formula fed) and to ingest 30 mg of soil per day (EHD, 1998).
³ For exclusively formula-fed infants, intake from water is synonymous with intake from food. The concentration of ethylbenzene in water used to reconstitute formula was based on a study of water taken from water treatment plants across Canada (Otson et al., 1982). Data on concentrations of ethylbenzene in formula were not identified. Approximately 50% of not-formula-fed infants are introduced to solid foods by 4 months of age and 90% by 6 months of age (NHW, 1990).
⁴ Assumed to weigh 15.5 kg, to breathe 9.3 m³ of air per day, to drink 0.7 L of water per day and to ingest 100 mg of soil per day (EHD, 1998).
⁵ Assumed to weigh 31.0 kg, to breathe 14.5 m³ of air per day, to drink 1.1 L of water per day and to ingest 65 mg of soil per day (EHD, 1998).
⁶ Assumed to weigh 59.4 kg, to breathe 15.8 m³ of air per day, to drink 1.2 L of water per day and to ingest 30 mg of soil per day (EHD, 1998).
⁷ Assumed to weigh 70.9 kg, to breathe 16.2 m³ of air per day, to drink 1.5 L of water per day and to ingest 30 mg of soil per day (EHD, 1998).
⁸ Assumed to weigh 72.0 kg, to breathe 14.3 m³ of air per day, to drink 1.6 L of water per day and to ingest 30 mg of soil per day (EHD, 1998).
⁹ Dann and Wang (1989) monitored ambient air at 11 sites in the Greater Vancouver Regional District. The maximum concentration observed (17.9 µg/m³) was used to calculate the upper-bounding estimate of exposure. Canadians are assumed to spend 3 hours outdoors each day (EHD, 1998). Data considered in the selection of critical data also included Health Canada (2003), Gagnon (2001), OMEE (2000), Bell et al. (1991), Chan et al. (1990) and Environment Canada (1989, 1990). Concentrations as high as 1163 µg/m³ have been observed (PACE, 1989) in the areas surrounding service stations but were not included in the calculation for upper-bounding estimate of exposure due to the transient nature of exposure. Other exposure sources such as smoking and vehicle operation were not included in the upper-bounding estimate of exposure due to the variability in exposure within the general population.
¹⁰ Fellin et al. (1992) conducted a study in which volatile organic chemicals, including ethylbenzene, were monitored for 3-24 hours in 754 homes across Canada. A maximum concentration of 539.31 µg/m³ was observed in a family dwelling and has been used to calculate the upper-bounding estimate of exposure. Canadians are assumed to spend 21 hours indoors each day (EHD, 1998). Fellin et al. (1992) did not appear to distinguish between smoking and non-smoking homes. Data considered in the selection of critical data also included Health Canada (2003), Otson et al. (1994), Bell et al. (1991), Chan et al. (1990) and CH2M Hill Engineering Ltd. (1989).
¹¹ A concentration of 10 µg/L was detected in 1 of 35 samples taken from various water treatment plants across Canada between August and December 1979 (Otson et al., 1982). This concentration has been used to calculate the upper-bounding estimate of exposure. Data considered in the selection of critical data also included City of Toronto (1990, 2002), Goss et al. (1998), OME (1989), Environment Canada (1988) and Otson (1987).
¹² Lockhart et al. (1992) analyzed fish samples from northern Manitoba and the Northwest Territories, observing a maximum concentration of 273 µg/kg in whitefish muscle. This value was used to estimate the "fish" component of the calculation of intake due to the ingestion of food. The other 11 categories represented by the foodstuffs with the highest concentration following analysis in the U.S. Food and Drug Administration's Total Diet Study (U.S. FDA, 2000) were as follows: dairy products: cheese, 12 µg/kg; fats: olive or safflower oil, 23 µg/kg; fruits and fruit products: 34 products, not detected; vegetables: potato chips, 19 µg/kg; cereal products: pumpkin pie, 29 µg/kg; meat and poultry: hamburger, 38 µg/kg; eggs: three different preparations, not detected; foods -- primarily sugar: chocolate bar, 13 µg/kg; mixed dishes and soups: eight products, not detected; nuts and seeds: mixed nuts, 21 µg/kg; soft drinks and alcohol: coffee, 17 µg/kg. No detection limit was identified, and a value of zero was used in the calculation of upper-bounding estimate of exposure where applicable. This calculation includes exposure due to beverages other than drinking water. Amounts of foods consumed on a daily basis by each age group are described by Health Canada (EHD, 1998). Data considered in the selection of critical data also included Enviro-Test Laboratories (1991, 1992, 1993).
¹³ The highest concentration of ethylbenzene detected (0.51 ng/kg) in 122 soil samples collected from typical urban residential and parkland locations in Ontario was used to calculate the upper-bounding estimate of exposure (OMEE, 1993). No other data were identified.

Table 2: Summary of health effects information for ethylbenzene

Endpoint	Lowest effect levels1/Results
Acute toxicity	Lowest oral LD50 = 3500 mg/kg-bw in rats (Wolf et al., 1956) [Additional studies: Smyth et al., 1962; NTP, 1986] Lowest dermal LD50 = 15 354 mg/kg-bw in rabbits (Smyth et al., 1962) [Additional studies: Harton and Rawl, 1976] Lowest inhalation LC50 = 17 200 mg/m3 in rats (4 hours) (Smyth et al., 1962) [Additional studies: Ivanov, 1962]
Short-term repeated-dose toxicity	Lowest inhalation LOEC = 75 ppm (326 mg/m3): reductions in liver pentoxyresorufin O-dealkylase (PROD) and ethoxyfluorocoumarin-O-dealkylase (EFCOD) activities in male and female mice exposed to 75 ppm ethylbenzene after a 5-day exposure. For the same exposure period, concentration-related reductions in lung ethoxyresorufin O-dealkylase (EROD) and PROD activities were observed in male and female mice exposed to all tested concentrations (i.e., 75 and 750 ppm) of ethylbenzene (Stott et al., 2003). [Additional studies: Andersson et al., 1981; Toftgård and Nilsen, 1982; Romanelli et al., 1986; Mutti et al., 1988; Cragg et al., 1989; Cappaert et al., 1999; Stott et al., 2003 (rats)]
Subchronic toxicity	Lowest inhalation LOEC = 100 ppm (434 mg/m3): increased blood alkaline phosphatase levels in female rats exposed for 6 hours/day, 5 days/week for 13 weeks (NTP, 1992) [Additional studies: Wolf et al., 1956; Elovaara et al., 1985] Lowest oral LOEL = 408 mg/kg-bw per day via stomach tube to female Wistar rats 5 days/week for 6 months: increase in absolute liver and kidney weights and cloudy swelling of the parenchymal cells of the liver and the tubular epithelium of the kidney (Wolf et al., 1956)
Chronic toxicity/ Carcinogenicity	Lowest inhalation LOEC = 75 ppm (326 mg/m3): increased severity of nephropathy in female rats (104-week study) (NTP, 1999) Neoplastic endpoints: F344 rats and B6C3F1 mice were exposed to concentrations of 0, 75, 250 or 750 ppm ( 0, 326, 1090 or 3260 mg/m3) for 104 and 103 weeks, respectively. At the highest concentration, there were significantly increased incidences of renal tubule neoplasms (3/50, 5/50, 8/50, 21/50; historical control range 0-4%) and testicular adenomas (36/50, 33/50, 40/50, 44/50; historical control range 54-83%) in male F344 rats and renal tubule neoplasms (0/50, 0/50, 1/50, 8/50; no historical control range provided) in female F344 rats. There were significantly increased incidences of alveolar/bronchiolar neoplasms in male B6C3F1 mice (7/50, 10/50, 15/50, 19/50; historical control range 10-42%) and hepatocellular neoplasms in female B6C3F1 mice (13/50, 12/50, 15/50, 25/50; historical control range 3-54%) (Chan et al., 1998; NTP, 1999). [Additional studies: Maltoni et al., 1985, 1997]
Genotoxicity and related endpoints: in vivo	Chromosomal aberrations Negative: Rat bone marrow cells [note that substance tested was a xylene mixture with 18.3% ethylbenzene] (Donner et al., 1980) Micronuclei test Negative: Mouse peripheral lymphocytes (NTP, 1992), mouse bone marrow (Mohtashamipur et al., 1985), mouse peripheral erythrocytes (NTP, 1999) Non-mammalian sex-linked recessive lethal assay Negative: Drosophila (Donner et al., 1980)
Genotoxicity and related endpoints: in vitro	Cell transformation assay Positive: Syrian hamster embryo (Kerckaert et al., 1996) Negative: Syrian hamster embryo (Heidelberger et al., 1983) Chromosomal aberrations Negative: Chinese hamster ovary (NTP, 1992); Chinese hamster ovary, with and without activation (NTP, 1999) Gene conversion Negative: Pseudomonas putida (Leddy et al., 1995) Micronuclei test Positive: Syrian hamster embryo cell (Gibson et al., 1997) Mutagenicity Positive: Mouse lymphoma cells, without activation (McGregor et al., 1988; NTP, 1992, 1999) Negative: Salmonella typhimurium strains TA97, TA98, TA100, TA1535 with and without activation (NTP, 1992, 1999); Escherichia coli WP2, Wp2uvrA and Saccharomyces cerevisiae JD1 (Dean et al., 1985) Sister chromatid exchange Positive: Human lymphocytes, with activation (Norppa and Vainio, 1983) Negative: Chinese hamster ovary cells (NTP, 1992); Chinese hamster ovary, with and without activation (NTP, 1999)
Developmental / reproductive toxicity	Lowest inhalation LOAEC = 100 ppm (435 mg/m3): extra ribs (rat), reduced litter size (rabbit) (Hardin et al., 1981) [Additional studies: Ungvary and Tatrai, 1985; Saillenfait et al., 2003]

¹ LC₅₀ = median lethal concentration; LD₅₀ = median lethal dose; LOAEC = lowest-observed-adverse-effect concentration; LOEC = lowest-observed-effect concentration; LOEL = lowest-observed-effect level.