Comparative carcinogenic and mutagenic activity of coal tar and petroleum asphalt paints used in potable water supply systems.

Coal tar and petroleum asphalt paints are among the products used as coatings for water pipes and storage tanks to retard corrosion. Formulations of these coatings were tested in the Ames mutagenesis and the mouse skin carcinogenesis bioassays. To test the mutagenicity of the paints, six doses ranging from 0.005 to 10 microliters per plate were assayed. In the mouse skin bioassay, doses of the coal tar paints ranging from 0.2 to 200 microliters were administered topically to 30 SENCAR mice per group. These initiating doses were followed by applications of 1.0 micrograms of 12-o-tetradecanoyl-phorbol-13-acetate (TPA) in 0.2 ml acetone topically, three times weekly for 20 weeks. Petroleum asphalt paints were tested in groups of 40 animals at 200 and 600 microliters doses. All coal tar paints showed mutagenic activity after metabolic activation with S-9, with the highest response being in strains TA 98 and TA 100. None of the petroleum asphalt paints gave mutagenic responses. Both types of coatings resulted in positive responses in the initiation/promotion study. The coal tar paints gave rise to 1000-1800 times the tumor response observed with petroleum asphalt products. One coal tar product was positive when tested as a complete carcinogen in the mouse at 2 microliters per application once weekly for 30 weeks, whereas the asphalt paint was negative at 100 times the dose. The biological responses to the products were greater than expected from their polycyclic aromatic hydrocarbon (PAH) content. These findings suggest that the hazard posed by these coatings may not be fully explained by their PAH contents.