Report No FR0425


MARCH 1994



Understanding the health significance of polycyclic aromatic hydrocarbons (PAHs) commonly found in some drinking water supplies, will better enable the water industry to prioritise improvement programmes in relation to potential health-related problems. Understanding their significance to health will also aid in the derivation of a scientifically justifiable basis for regulating PAH in drinking water.


To review the occurrence and toxicity of the six regulated PAHs and any others likely to be present in water and prioritise these according to their toxicological risk.


Trace concentrations of PAH are commonly detected in some drinking waters due to the historical use of internal coal-tar pitch linings in cast iron distribution pipes. Some supplies can exceed the UK PAH standard of 200 ng l-1 which is specified for the sum of six named PAHs. However, this value as well as the six 'representative ' PAHs are not based on toxicological considerations. Affected water suppliers, therefore, need to be aware of the health effects of PAHs in order to understand the significance, if any, when the standard for total PAH is exceeded.


  1. The occurrence of the six regulated PAHs in some drinking water supplies at concentrations exceeding the standard is an increasing problem, particularly in those of groundwater origin. Where breaches occur, this is almost invariably due to fluoranthene.

  2. The health effect of primary concern for PAHs is the ability that some, but not all, can cause cancer in laboratory animals following long-term exposure.

  3. Fluoranthene, which is the PAH most commonly detected at elevated levels, does not appear to be carcinogenic.

    Based on the available evidence, it would appear that the concentrations of PAH which are commonly detected in drinking water are unlikely to be of significant risk to human health.

  4. Benzo(a)pyrene is the only PAH with sufficient toxicity data on which to derive a drinking water guideline value for long-term exposure. It has been shown to cause cancer in laboratory animals following ingestion. Of the twenty PAHs studied, this PAH, along with dibenz(a,h)anthracene, appears to be of most toxicological concern. The World Health Organization (WHO) has recently published a drinking water guideline value of 700 ng l-1 for benzo(a)pyrene. This is a considerable increase in comparison to the guideline value of 10 ng l-1 previously recommended in 1984.

  5. The standard of 200 ng l-1 for total PAH in the EC Directive is not based on toxicological considerations. The revision of the WHO drinking water guideline for benzo(a)pyrene to a value above the present total PAH standard would suggest that the Directive may also need revision. However, due to the lack of suitable toxicity data to derive health-based standards for individual PAHs, it would seem unlikely that a health-based approach will be adopted by the European Commission.

  6. Until the Drinking Water Directive is amended, PAH will continue to be an issue for the water industry.

  7. Further toxicological data, particularly concerning mixtures of PAHs, are required in order to establish the significance, if any, of PAH at the low concentrations found in drinking water.


This report is presented as an extended summary with a discussion of the legislation, occurrence and health concerns of PAH commonly found in drinking water, with emphasis on the implications for the water industry. More detailed technical information to support these findings is given in the appendices.

Copies of the Report are available from FWR, price 25.00 less 20% to FWR Members