Hexachlorobutadiene
(endorsed 1996)
Guideline
Based on health considerations, the concentration of hexachlorobutadiene in drinking water should not exceed 0.0007 mg/L.
General description
Hexachlorobutadiene has occasionally been detected in drinking water supplies in the United States and some European countries at concentrations less than 0.005 mg/L.
Hexachlorobutadiene is used as a solvent in chlorine gas production, an intermediate in the manufacture of rubber compounds, a lubricant, a pesticide and a fumigant.
Typical values in Australian drinking water
Hexachlorobutadiene has not been found in Australian drinking waters. It is included here to provide guidance in the unlikely event of contamination, and because it has been detected occasionally in drinking water supplies overseas.
Treatment of drinking water
Granular activated carbon has proved effective in trials for the removal of hexachlorobutadiene from drinking water.
Measurement
A purge and trap gas chromatographic procedure can be used for analysis (USEPA Draft Method 502.1 1986). An inert gas is bubbled through the sample and hexachlorobutadiene trapped on an adsorbent. The adsorbent is then heated and hexachlorobutadiene analysed using gas chromatography with electron capture detection. The limit of determination is approximately 0.0004 mg/L.
Health considerations
Experiments in laboratory animals have revealed that approximately 95% of the ingested dose of hexachlorobutadiene is absorbed. It has been found in the blood, liver, brain, spleen, kidney and mesentery. Hexachlorobutadiene is metabolised in the gastrointestinal tract and kidney to a number of water soluble metabolites, and excreted in the urine.
Long-term intermittent human exposure has been reported to cause higher incidences of hypotension, myocardial dystrophy, nervous system and liver disorders, and respiratory tract lesions.
In studies using rats, hexachlorobutadiene caused multiple toxicologic effects, with the kidney being the organ most affected. Kidney tumours have been induced at doses of 20 mg/kg body weight per day.
Tests for mutagenicity with different strains of bacteria have reported both positive and negative results. Some metabolites have given positive results.
The International Agency for Research on Cancer has concluded that hexachlorobutadiene is not classifiable as to its carcinogenicity to humans (Group 3, no adequate evidence in humans and limited evidence in animals) (IARC 1987).
Derivation of guideline
The assessment of the toxicological data for hexachlorobutadiene by the World Health Organization (WHO) has been used without review. The guideline value of 0.0007 mg/L was determined as follows:
where:
0.2 mg/kg body weight per day is the no-effect level based on a 2-year feeding study using rats (Kociba 1977).
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 for possible carcinogenic effects and genotoxicity of some metabolites).
The WHO guideline value of 0.0006 mg/L was based on an adult body weight of 60 kg. The difference in guideline values is not significant.
References
IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.
Kociba RJ, Keyes DG, Jersey GC, Ballard JJ, Dittenber DA, Quast JF, Wade CE, Humiston CG, Schwetz BA (1977). Results of a two-year toxicity study with hexachlorobutadiene in rats. American Industrial Hygiene Association Journal, 38:589–602.
USEPA Draft Method 502.1 (1986). Volatile halogenated organic compounds in water by purge and trap gas chromatography. United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory (EMSL), Cincinnati, Ohio.
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