Toluene
CASRN 108-88-3 (endorsed 2013)
Guideline
Based on aesthetic considerations (taste and odour), the concentration of toluene in drinking water should not exceed 0.025 mg/L.
Based on health considerations the concentration of toluene should not exceed 0.8 mg/L.
General description
Toluene is a colourless liquid, which occurs naturally as a component of crude oil and is present in petrol. It constitutes approximately 5-8% of unleaded gasoline by volume. It can enter water sources through atmospheric deposition, by leaching from synthetic coatings used to protect storage tanks, and by point-source pollution.
Toluene, also known as methylbenzene is produced in large quantities during petroleum refining and is a byproduct in the manufacture of styrene and coke-oven preparations. Toluene is also used as solvent in paints adhesives and nail polish. It also occurs in natural gas and emissions from volcanoes, forest fires, and cigarettes.
Toluene has a taste and odour threshold at 0.025 mg/L.
Typical values in Australian drinking water
Toluene has only rarely been identified in Australian drinking waters. Natural concentrations in most water sources are usually very low. Toluene can occur naturally in groundwater as a result of proximity to, or contact with, coal seams, petroleum and gas deposits, and shales. It may be mobilised by extraction activities (Lesage et al., 1997; Leusch and Bartkow, 2011; Volk et al, 2011). However, contamination can occur, usually via exposure to petrochemicals in surface waters or groundwaters. Known sources of groundwater contamination include leakage from sub-surface fuel storage tanks (do Rego & Netto, 2007). Emissions of fuel components from boating use is a known source of contamination of multiple-use lakes and reservoirs (Schmidt et al., 2004). Toluene was reported in 19% of samples from an extensive groundwater survey undertaken in Denmark with the highest concentration being 0.002 mg/L (Juhler & Felding, 2003). Toluene has been detected in well water at 0.005 to 0.1 mg/L in the USA (IPCS, 1985). Groundwater from contaminated wells in the USA contained up to 3.5 mg/L of toluene (ATSDR, 2000). Toluene has been reported at up to 0.001 mg/L in municipal drinking water in Croatia (Karaconji et al., 2006), up to 0.027 mg/L in Canada (average 0.002 mg/L; IPCS, 1985), up to 0.063 mg/L in municipal drinking water in Taiwan (Kuo et al., 1997) and is occasionally detected in drinking waters in the USA (Williams et al., 2004) up to 0.011 mg/L (IPCS, 1985).
Treatment of drinking water
Volatile organic chemicals such as toluene are most commonly treated in drinking water by aeration stripping and/or adsorption to granular activated carbon (GAC). A conventional biologically active sand filter has been shown to be highly effective for the removal of toluene from contaminated water, under suitable conditions (Arvin et al., 2004). Effective bioremediation of highly contaminated groundwaters has also been demonstrated (Sedran et al., 2004; Zein et al., 2006).
Measurement
A purge and trap gas chromatographic procedure can be used for the analysis of toluene (APHA, AWWA & WEF, 2012). An inert gas is bubbled through the sample and toluene is trapped on an adsorbent. The adsorbent is then heated and toluene analysed using gas chromatography with mass spectrometric (GC-MS) detection (Method 6200 B) or photoionisation (PI) detection (Method 6200 C) (APHA, AWWA & WEF, 2012). The method detection limit is 47 ng/L for GC-MS and 23 ng/L for GC-PI (APHA, AWWA & WEF, 2012).
Health considerations
In humans, toluene is readily absorbed from the gastrointestinal tract after ingestion, and is distributed preferentially in adipose tissue, then the kidneys, liver and brain. It is rapidly metabolised by the liver to benzyl alcohol, benzoic acid, and to a lesser extent, phenols.
Data on human health effects come mainly from inhalation studies. The predominant effects of acute exposure were impairment of the central nervous system and irritation of the mucous membranes, with fatigue and drowsiness being the most obvious symptoms (ATSDR, 2000).
Rats exposed to toluene vapour for 2 years exhibited decreased blood haematocrit values at high toluene concentrations (380 ppm in air). No data are available on long term oral toxicity; however, a 13 week gavage study using rats and mice reported increased liver weights at doses from 625 mg/kg body weight per day (NTP 1990).
Toluene generally did not exhibit genotoxic activity in tests on bacteria, yeast cells, and mammalian cells in vitro.
The International Agency for Research on Cancer has concluded that toluene is not classifiable as to its carcinogenicity in humans (Group 3, inadequate evidence in humans and in animals) (IARC, 1989).
Derivation of guideline
The USEPA (2009) has set a drinking water guideline of 1.0 mg/L for toluene, while the WHO (2011) proposes a guideline of 0.7 mg/L.
The health-based guideline value of 0.8 mg/L for toluene in drinking water was determined as follows:
where:
312 mg/kg body weight per day is the no effect level based on a 13-week oral study using rats (NTP 1990)
70 kg is the average weight of an adult
0.1 is the proportion of total daily intake attributable to the consumption of water
2 L/day is the average amount of water consumed by an adult
1000 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations, 10 for intraspecies variations and 10 because a less than lifetime study was used)
5/7 is used to convert data based on a 5 day per week gavage study to a 7-day week equivalent.
This health-based guideline value exceeds the taste threshold of toluene in water of 0.025 mg/L.
The WHO guideline value of 0.7 mg/L is based on an adult body weight of 60 kg. The difference in guideline values is not significant.
References
American Public Health Association (APHA), American Water Works Association (AWWA) and Water Environment Federation (WEF) (2012). Standard Methods for the Examination of Water and Wastewater, 22nd Edition. Eds. Rice EW, Baird RB, Eaton AD and Clesceri LS.
Arvin, E., Engelsen, P. and Sebber, U. (2004) Biodegradation of gasoline compounds (BTEX) in a water works sand filter. Water Science & Technology: Water Supply, 4(5-6), 29-33.
ATSDR (2000). Toxicological profile for toluene.US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, USA.
do Rego, E. C. P. and Netto, A. D. P. (2007) PAHs and BTEX in groundwater of gasoline stations from Rio de Janeiro City, Brazil. B. Environ. Contam. Tox., 79(6), 660-664.
IARC (International Agency for Research on Cancer) (1989) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: some organic solvents, resin monomers and related compounds, pigments and occupational exposures in paint manufacture and painting., Lyon.
IPCS (1985). Environmental Health Criteria 52: Toluene. International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland.
Juhler, R. K. and Felding, G. (2003) Monitoring methyl tertiary butyl ether (MTBE) and other organic micropollutants in groundwater: Results from the Danish National Monitoring Program. Water Air Soil Poll., 149(1-4), 145-161.
Karaconji, B., Skender, L. and Karacic, V. (2006) Benzene, toluene, ethylbenzene, and isomeric xylenes in various water samples in Croatia. B. Environ. Contam. Tox., 76(3), 458-462.
Kuo, H. W., Chiang, T. F., Lo, L. I., Lai, J. S., Chan, C. C. and Wang, J. D. (1997) VOC concentration in Taiwan’s household drinking water. Sci. Total Environ., 208(1-2), 41-47.
Lesage, S., Hao, X., and Kent, S. (1997) Distinguishing Natural Hydrocarbons from Anthropogenic Contamination in Ground Water. Groundwater, 35(1), 149-160
NTP (National Toxicology Program) United States Department of Health and Human Services (1990) Toxicology and carcinogenesis studies of toluene in F344/N rats and B6C3F1 mice. NTP Report No 371. NIH Publication No. 90 2826.
Schmidt, T. C., Haderlein, S. B., Pfister, R. and Forster, R. (2004) Occurrence and fate modeling of MTBE and BTEX compounds in a Swiss Lake used as drinking water supply. Water Res., 38(6), 1520-1529.
Sedran, M. A., Pruden, A., Wilson, G. J., Suidan, M. T. and Venosa, A. D. (2004) Biodegradation of methyl tert-butyl ether and BTEX at varying hydraulic retention times. Water Environ. Res., 76(1), 47-55.
Volk, H., Pinetown, C., Johnston,W. (2011) A desktop study of the occurrence of total petroleum hydrocarbon (TPH) and partially water-soluble organic compounds in Permian coals and associated coal seam groundwater. CSIRO Petroleum and Geothermal Research Portfolio Report EP-13-09-11-11 2011 (Bentley, WA, Australia).
Williams, P. R. D., Benton, L. and Sheehan, P. J. (2004) The risk of MTBE relative to other VOCs in public drinking water in California. Risk Anal., 24(3), 621-634.
Zein, M. M., Suidan, M. T. and Venosa, A. D. (2006) Bioremediation of groundwater contaminated with gasoline hydrocarbons and oxygenates using a membrane-based reactor. Environ. Sci. Technol., 40(6), 1997-2003.
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