Proposed Notification Levels for sec-Butylbenzene and tert-Butylbenzene

TO: David P. Spath, Ph.D., Chief
Division of Drinking Water and
Environmental Management Branch
Department of Health Services

VIA: George V. Alexeeff, Ph.D., D.A.B.T.
Deputy Director for Scientific Affairs

VIA: Anna M. Fan, Ph.D., Chief
Pesticide and Environmental Toxicology Section

FROM: Robert A. Howd, Ph.D., Chief
Water Toxicology Unit
Pesticide and Environmental Toxicology Section

Staff of the Office of Environmental Health Hazard Assessment (OEHHA) have reviewed your Department's proposed Notification Levels of 80 ug/L for sec-butylbenzene and tert-butylbenzene. OEHHA recommends action levels of 260 ug/L for sec-butylbenzene and tert-butylbenzene. The toxicological basis is the same, except for the use of an uncertainty factor of three (3) instead of ten (10) for the subchronic to chronic toxicity study extrapolation.

Sec-butylbenzene and tert-butylbenzene are flammable liquids used in United States commerce for synthetic organic chemistry, as solvents, and tert-butylbenzene is used as a polymer linking agent. Sec-butylbenzene is a component of crude oil (Wang and Fingas, 1995), vehicle emissions (Schroder and Dannecker, 1994; Sigsby et al., 1987), ambient air (Juttner, 1986), and is a possible migrant from microwave heating of thermoset polyester plastics (Gramshaw et al., 1995). Tert-butylbenzene has been identified in landfill gas (Eklund et al., 1998). Both compounds are on the U.S. Environmental Protection Agency (U.S. EPA) Method 524.2 analyte list for monitoring in groundwater, surface water, and drinking water and, in California, are considered unregulated chemicals requiring monitoring (Title 22, California Code of Regulations §64450).

The routes of exposure to sec-butylbenzene and tert-butylbenzene are ingestion, inhalation, and dermal. These chemicals are known to cause eye and skin irritation, can cause irritation to mucous membranes, and are considered aspiration hazards to the lung. However, their prevalence in the environment is apparently rare, with only one detection of tert-butylbenzene in California water supplies among 9635 tests and no detections of sec-butylbenzene in 9637 tests (California Department of Health Services, 2000). This compilation covered the years 1984-1998. On the other hand, Wisconsin detected sec-butylbenzene 110 times out of 2207 tests of wells (January-December 1997), with a high measurement of 60 ug/L. They also found 66 occurrences of tert-butylbenzene out of 2168 tests, with a high value of 9 ug/L (Wisconsin Department of Natural Resources, 2000).

The toxicology of these isomers has not been thoroughly characterized. Acute oral data have been reported. Eight out of ten rats died after administration of approximately 4.3 g/kg sec-butylbenzene and 7/10 died after the same dose of tert-butylbenzene in olive oil (Gerarde, 1959). Dow Chemical (1954) reported that no deaths occurred among four rats treated orally with 2 g/kg sec-butylbenzene and Sandmeyer (1981) reported an LD₅₀ of 2.24 g/kg for this isomer. LD₅₀s in rats for tert-butylbenzene ranged from 2.5 to 5.0 g/kg (U.S. EPA, 1997). These oral toxicity data indicate low acute oral toxicity but are inadequate to derive a no-adverse-effect-level (NOAEL) for either sec-butylbenzene or tert-butylbenzene for long-term exposures.

The U.S. EPA National Center for Environmental Assessment (NCEA) has recommended that a provisional reference dose (RfD) for these compounds be derived from the toxicity data for a closely-related branched-chain alkylbenzene, cumene (isopropylbenzene). NCEA states that "confidence in this provisional RfD is very low, reflecting low confidence in the RfD for cumene and the lack of suitable data for the branched-chain butylbenzenes"(U.S. EPA, 1997). Confidence can be enhanced somewhat by comparing cumene toxicity with other saturated short chain alkylbenzenes which are structurally similar. These are summarized below:

(Adapted from U.S. EPA, 1977)

Cumene (isopropylbenzene) has a dose-schedule-adjusted NOAEL of 110 mg/kg-day based on 139 gavage doses to female rats in a 194-day period (Wolf et al., 1956). Other data on cumene and similar alkylbenzenes support this as an approximate NOAEL for the chemicals. OEHHA therefore agrees that this NOAEL is appropriate to be used for sec-butylbenzene and tert-butylbenzene. However, the lack of specific data justifies a large uncertainty factor. An uncertainty factor of 3,000 is recommended (three for subchronic to chronic extrapolation, ten for interspecies extrapolation, ten for human variability, and ten for database deficiencies).

A public health protective concentration (C) for sec-butylbenzene and tert-butylbenzene in drinking water can be derived from the equation:

C = NOAEL x BW x RSC / UF x DWC =
(110 mg/kg-day)(70 kg)(0.2) / (3,000)(2 L/day) =
0.257 mg/L =(rounded) 260 ug/L

where:

NOAEL = no-observed-adverse-effect-level,
BW = body weight (adult),
RSC = relative source contribution,
UF = uncertainty factor, and
DWC = drinking water consumption (adult).

Based on the health protective concentration calculated, OEHHA recommends and supports an Notification Level of 260 ppb (ug/L) for sec-butylbenzene and an Notification Level of 260 ppb (ug/L) for tert-butylbenzene in drinking water.

Should you have any questions about this review, please contact me at (510) 622-3170 or Dr. Robert Haas at (510) 622-3172.

References

California Department of Health Services (2000). Detections of Unregulated Chemicals Requiring Monitoring, https://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chemicalcontaminants.aspx

Dow Chemical (1954). Results of range find toxicological test on sec-butylbenzene. U.S. EPA/OTS Public Files, 8D submission. Microfiche # OTS0515962 (as cited by U.S. EPA, 1997).

Eklund B, Anderson EP, Walker BL, and Burrows DB (1998). Characterization of landfill gas composition at the Fresh Kills municipal solid-waste landfill. Environ Sci Technol 32:2233?2237.

Gerarde HW (1959). Toxicological studies on hydrocarbons. III. The biochemorphology of the phenylalkanes and phenylalkenes. AMA Arch Ind Health 19:403-418 (as cited by U.S. EPA, 1997).

Gramshaw JW, Vandenburg HJ, and Lakin RA (1995). Identification of potential migrants from samples of dual-ovenable plastics. Food Add Contam 12:211-222.

Juttner F (1986). Analysis of organic compounds (VOC) in the forest air of the southern Black Forest. Chemosphere 15:985-922.

Sandmeyer EE (1981). Aromatic Hydrocarbons. In: Patty's Industrial Hygiene and Toxicology, Vol. IIB, 3rd Ed., GD Clayton, Ed. New York, New York: John Wiley and Sons, p. 3253-3451 (as cited by U.S. EPA, 1997).

Schroder B and Dannecker W (1994). Vehicle emissions as the major source of gaseous aromatic hydrocarbons at different locations in Germany. Sci Tot Environ 146/147: 275-279.

Sigsby JE, Tejada S, Ray W, Lang JM, and Duncan JW (1987). Volatile organic compound emissions from 46 in-use passenger cars. Environ Sci Technol 21:466-475.

U.S. EPA (1997). Risk Assessment Issue Paper for: Derivation of Provisional Chronic RfDs for n-Butylbenzene (CASRN 104-51-8), sec-Butylbenzene (CASRN 135-98-8), tert-Butylbenzene (CASRN 98-06-6), and n-Propylbenzene (CASRN 103-65-1). National Center for Environmental Assessment, U.S. Environmental Protection Agency (97-009/6-5-97).

Wisconsin Department of Natural Resources (2000). Wisconsin Groundwater Sampling Data - Top 100 Parameters from Jan-Dec 1997. http://dnr.wi.gov/topic/drinkingwater/quality.html

Wang Z and Fingas M (1995). Differentiation of the source of spilled oil and monitoring of the oil weathering process using gas chromatography-mass spectrometry. J Chromat A712:321-343.

Wolf MA, Rowe VK, McCollister DD, Hollingsworth RL and Oyen F (1956). Toxicological studies of certain alkylated benzenes and benzene. Arch Ind Health 14:387-398.

Chemical Reference

• sec-butylbenzene
• tert-Butylbenzene