Chlorophenols
2-chlorophenol; 2,4-dichlorophenol; 2,4,6-trichlorophenol (endorsed 1996)
Guideline
Based on aesthetic considerations, the concentration of chlorophenols in drinking water should not exceed the following values.
Chlorophenols would not be a health concern unless concentrations exceeded the health-based guideline values listed.
2-chlorophenol
0.3 mg/L
0.0001 mg/L
2,4-dichlorophenol
0.2 mg/L
0.0003 mg/L
2,4,6-trichlorophenol
0.02 mg/L
0.002 mg/L
General description
Chlorophenols may be present in drinking water as a result of chlorination of water that contains phenol or lower chlorophenols, or from contamination of water sources. Chlorination of water containing natural organic compounds can produce very low concentrations of chlorophenols. Degradation of phenoxy herbicides such as 2,4,5-T and 2,4-D also generates chlorophenols. The limited data available from overseas studies indicate that concentrations in drinking water are very low.
Chlorophenols have taste and odour thresholds in the range 0.0001 mg/L to 0.002 mg/L, with a characteristic antiseptic smell.
Chlorophenols are used commercially as preservatives, moth-proofing agents, germicides and anti-mildew agents. Exposure to chlorophenols via tap water has been estimated to be less than 10% of total dietary exposure.
Typical values in Australian drinking water
No data are available on concentrations of chlorophenols in Australian drinking waters. If present at all, it is likely that concentrations would be extremely low.
Treatment of drinking water
In pilot studies, granular activated carbon has successfully removed over 90% of 2-chlorophenol from water. It would probably be similarly effective in removing the other chlorophenols.
Measurement
Sensitive and isomer-specific procedures for the analysis of chlorophenols are available (USEPA Method 604 1986). The chlorophenols are derivatised with pentafluorobenzyl ether, and analysed using gas chromatography with electron capture detection. Limits of determination are 0.01 mg/L for monochlorophenol, 0.0005 mg/L for dichlorophenol and 0.00001 mg/L (10 ng/L) for trichlorophenol.
Health considerations
Chlorophenols are known to be efficiently absorbed and metabolised when administered orally to laboratory animals. Highest concentrations occur in the liver, brain and fat.
An extensive review and summary of the human and animal toxicity data for chlorophenols is available (IPCS 1989).
People occupationally exposed to chlorophenols often complain of irritation to the skin, mucous membranes and respiratory tract as a result of direct airborne contact. In addition, chronic ailments, skin lesions and ulcerations (particularly chloracne), and clinical indications of liver damage and neurological effects have also been reported, particularly in association with high exposures.
There have been a number of studies on the toxic effects of chlorophenols in rats and mice. Short-term exposure to high doses results in an increased respiration rate, motor weakness, tremors, convulsion, coma and death. Long-term studies over 2 years could not determine any specific dose-related effects using either 2-chlorophenol or 2,4-dichlorophenol, but 2,4,6-trichlorophenol induced leukaemia and lymphomas in male rats, and liver cancer in male and female mice.
No information is available on the mutagenic effects of 2-chlorophenol. Mutagenic tests on bacteria were negative for 2,4-dichlorophenol. Separate tests gave weakly positive and negative results for 2,4,6-trichlorophenol.
The International Agency for Research on Cancer has concluded that 2,4,6-trichlorophenol is possibly carcinogenic to humans (group 2B, sufficient evidence in animals) (IARC 1987).
Derivation of guideline
The guideline values for the chlorophenols in drinking water, based on health considerations, were determined as follows:
i) 2-chlorophenol:
where:
7.5 mg/kg body weight per day is the no-effect level based on a 2-year drinking water study using rats (Exon and Koller 1985).
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.
100 is the safety factor in using the results of an animal study as a basis for human. exposure (10 for interspecies variations and 10 for intraspecies variations). The use of this safety factor was recommended by the NHMRC Standing Committee on Toxicity.
The World Health Organization (WHO) Guidelines do not have a health-based guideline for 2-chlorophenol.
ii) 2,4-dichlorophenol:
where:
4.5 mg/kg body weight per day is the no-effect level based on a 2-year drinking water study using rats (Exon and Koller 1985). The use of this value was recommended by the NHMRC Standing Committee on Toxicity following a review of the available toxicity data for the chlorophenols.
Other factors are as above.
The WHO Guidelines do not have a health-based guideline for 2,4-dichlorophenol.
iii) 2,4,6-trichlorophenol:
where:
4.5 mg/kg body weight per day is the no-effect level based on a 2-year drinking water study using rats (Exon and Koller 1985). The use of this value was recommended by the NHMRC Standing Committee on Toxicity following a review of the available toxicity data for the chlorophenols.
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 carcinogenic effects).
Other factors are as above.
The WHO guideline value of 0.2 mg/L for 2,4,6-trichlorophenol was based on a calculation that estimated an additional lifetime risk of one fatal cancer per hundred thousand people (WHO 2006).
As the guideline values based on health considerations are greater than the taste thresholds for these compounds, the taste thresholds should be used as the guideline values.
References
Exon JH, Koller LD (1985). Toxicity of 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol. Water Chlorination: Chemistry, Environmental Impact and Health Effects. Proceedings of the 5th Conference on Water Chlorination: Environmental Impact and Health Effects, Williamsburg, Virginia, June 3-8, 1984. Jolly RL et al. (editors), Chelsea, Michigan, Lewis Publisher Inc., 5, 307–330.
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.
IPCS (International Programme on Chemical Safety) (1989). Chlorophenols other than Pentachlorophenol. Environmental Health Criteria, 93. World Health Organization, IPCS.
USEPA Method 604 (1986). Phenols. United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory (EMSL), Cincinnati, Ohio.
WHO (World Health Organization) (2006). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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