Pentachlorophenol
(endorsed 2011)
Guideline
Based on human health concerns, pentachlorophenol in drinking water should not exceed 0.01 mg/L.
Related chemicals
Pentachlorophenol (CAS 87-86-5) belongs to the chlorinated hydrocarbon class of chemicals. Other pesticides in this class include endosulfan (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, pentachlorophenol would not be a health concern unless the concentration exceeded 0.01 mg/L. Minor excursions above this level would need to occur over a significant period to be a health concern, as the health-based guideline is based on long-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Pentachlorophenol is an insecticide and fungicide used formerly as a wood preservative. It has also been used formerly as a pre-harvest defoliant, pre-emergence herbicide and an aquatic biocide.
There are no registered products containing pentachlorophenol in Australia, but de-registered compounds may still be detected in water. When used previously, products containing pentachlorophenol or its salt variant were intended for professional use only.
Exposure sources: If used in the future, the main source of public exposure to pentachlorophenol and its metabolites would be through residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of pentachlorophenol, in the future, may potentially lead to contamination of source waters through processes such as leaching from treated wood, run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
No occurrence data in Australian water could be found. Although pentachlorophenol has been banned in most countries, it can still often be found in surface and groundwater at low µg/L concentrations and in drinking water usually in the range 0.01-0.1 µg/L (Health Canada 1987, WHO 2003).
Treatment of drinking water
Available data indicate that concentrations of chlorophenols are not reduced significantly during conventional drinking water treatment processes. Although few relevant data are available, it is likely that concentrations below 1 µg/L can commonly be achieved by packed tower aeration and granular activated carbon adsorption (Health Canada 1987).
Measurement
Pentachlorophenol can be measured by routine gas chromatography mass spectrometry analysis, with a limit of reporting of 0.25 µg/L (Queensland Health 2007).
History of the health values
No acceptable daily intake (ADI) or acute reference dose (ARfD) values have been established for pentachlorphenol in Australia.
An ADI for pentachlorophenol was set at 0.003 mg per kg of bodyweight (mg/kg bw) by the United States National Academy of Sciences. This ADI was based on a no-observed-effect level (NOEL) of 3 mg/kg bw/day from a long-term (2-year) dietary study in rats. The NOEL is based on decreased bodyweight, liver effects and liver tumours. The ADI incorporates a safety factor of 1000 and was established in 1977.
The previous health value was 0.01 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Pentachlorophenol is readily absorbed via the gastrointestinal tract and through the skin in animals and humans. After exposure, the highest tissue levels were found in the liver and kidneys. Pentachlorophenol is excreted rapidly, either unchanged or as the metabolites, tetrachlorhydroquinone and glucuronides. The half-life for elimination in humans is 17 days.
Acute effects: Pentachlorophenol has moderate to high acute oral toxicity and moderate dermal toxicity. The skin sensitisation potential of pentachlorophenol is unknown.
Short-term effects: In short-term dietary studies in mice, rats and pigs, the main effects observed were on the liver in the form of increased relative liver weight and increased enzyme activity (particularly aryl hydrocarbon hydroxylase), together with histopathological changes. In mice, these effects, as well as increased mortality, were observed from 30 mg/kg bw/day. In pigs, liver weight changes were observed at 10 mg/kg bw/day.
Long-term effects: Long-term dietary studies were conducted in mice and rats. The liver was the main organ affected, with changes in enzyme levels and liver weight commonly noted at the lower doses, and histopathological changes and in some cases tumour formation at higher dose levels. In mice, decreased bodyweight, liver lesions, hepatocellular adenomas and carcinomas and benign adrenal medulla pheochromocytomas were observed at the lowest dose, 15 mg/kg bw/day. Female mice also showed haemangiosarcomas of the spleen and liver at 30-45 mg/kg bw/day. In rats, reduced bodyweight gain and pigment accumulation in the liver were observed from 10 mg/kg bw/day.
Carcinogenicity: Studies in mice showed an increased incidence of tumours in the spleen, liver and adrenal gland from 15 mg/kg bw/day. This dose level is well in excess of the likely level of pentachlorophenol in drinking water.
Genotoxicity: Pentachlorophenol is not considered to be genotoxic, based on in vitro and in vivo short-term studies, despite some weak evidence for chromosomal effects.
Reproductive and developmental effects: In a one-generation reproduction study in rats, there was evidence of foetotoxicity at high dose levels (25 mg/kg bw/day) only.
In a developmental toxicity study in rats, delayed foetal development was observed at 4 mg/kg bw/day, and embryonic death and maternotoxicity were seen at doses of 43 mg/kg bw/day.
Poisons Schedule: Pentachlorophenol is included in Schedule 6 and 7 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.01 mg/L for pentachlorophenol was determined as follows:
where:
3 mg/kg bw/day is the NOEL based on a long-term (2-year) dietary study in rats.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
1000 is the safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation, with an additional safety factor of 10 due to the limitation of the toxicological data available at the time the ADI was set.
The World Health Organization has a health-based guideline value of 0.009 mg/L for pentachlorophenol (WHO 2004). This guideline value is considered provisional because of the variations in metabolism between experimental animals and humans.
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
Health Canada (1987). Chlorophenols. Background document for the development of the Guidelines for Canadian Drinking Water Quality. Feb 1987. Health Canada.
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
Queensland Health (2007). Organochlorine, organophosphorous and synthetic pyrethroid pesticide, urea and triazine herbicides and PCBs in water. QHFSS SOP 16315.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
WHO (World Health Organization) (2003). Pentachlorophenol in drinking water: Background document for the development of the WHO Guidelines for Drinking Water Quality. WHO.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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