Report No DWI0023

Jun 1988


The objective of the work outlined in this report was to determine the extent to which drinking water supplies are contaminated with particles of coal-tar pitch derived from pipe linings. The work carried out stemmed from a WRc survey of polycyclic aromatic hydrocarbon levels in British waters in which the possibility emerged that drinking water may be contaminated with particles of coal-tar pitch arising from the linings of iron distribution pipes.

In Great Britain about 60% by length of the distribution pipes laid for the Water Industry are of ductile iron and the majority of these have been coated internally with coal-tar pitch according to BS 4164. Since 1978 there has been no further use of coal-tar pitch for this purpose.

Such linings, and any derived particles, can contain up to 50D polycyclic aromatic hydrocarbons (PAH), some of which (eg benzo[a]pyrene) are carcinogenic.

The subject was discussed with appropriate bodies in late 1975 and there was general concern about the possibility of particles of lining material, containing substantial proportions of carcinogens, lodging in the digestive tract. It was decided that information was needed on the exposure of people to such particles.

The result was that a contract was placed by the Department of the Environment with WRc for studies on the occurrence of coal-tar pitch particles in drinking water This work was reported to the Department in 1983.

The experimental approach adopted was to examine mains deposits and particles collected from tapwater. Attempts were made to develop methods designed to characterise (size, number, chemical composition) individual particles. One such method showed promise (laser microprobe mass analyser) but would require considerable effort and expense to produce a routine method suitable for use in a survey. As a back-up technique particles were extracted with an organic solvent and the extracts analysed by gas chromatography for the presence of PAH indicative of coal-tar pitch.

Due to the time needed to develop and test suitable techniques and the slowness of the methods that emerged, a wide survey of drinking waters was not feasible. However, in the limited number of tapwaters examined one sample exhibited high levels of coal-tar pitch. To obtain information on detailed exposure to coal-tar pitch particles via tapwater, on a large scale, will be technically very difficult and extremely expensive.

Mains deposits frequently contained relatively massive levels of PAH due to the presence of coal-tar pitch particles. Coal-tar pitch particles down to at least 3 śm diameter were detected in these deposits and one would expect such particles to be 'mobile'. Any situation that disturbs the deposits, such as mains renovations and flow reversals, could release coal-tar pitch particles in the water. Such situations need to be examined.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.