Miljøprojekt, 1049 – Feltundersøgelse af vandforsyningernes plastrør

Feltundersøgelse af vandforsyningernes plastrør

Summary

The overall purpose of this project is to investigate the leaching from plastic pipes used for the supply of drinking water to the Danish consumers.

The project comprises analyses of water samples from existing pipelines at three representative water supply companies. The samples were taken from a total of 10 pipe sections; seven PE pipes, and three PVC pipes. The dimensions of the pipes of the sections examined are from 63 to 110 mm. The age of the PE pipes is one and three years, and the age of the PVC pipes is approximately 15 years.

From the selected pipe sections, a piece of the pipeline was removed after water sampling, and the potential leaching from these old pipes was measured in the laboratory. The method applied is the standard method used for approval of new pipes (migration test), supplemented by analyses for organics including 10 specific components, which are degradation products from antioxidants, included in the formulation of PE pipes.

To be able to relate these measurements to the quality of the pipe used today, similar migration tests were made on new pipes from three manufacturers of pipes to the Danish market.

The results of the laboratory tests of PE pipes show that release of degradation products from the antioxidants added to PE pipes can be detected in new as well as old pipes after leaching for three days. Only one out of seven old pipes shows no leaching. In the rest of the pipes, between one and seven degradation products were identified in the eluant. Concentrations up to 3.6 µg/l were measured, and the total concentration for the sum of components was 10 µg/l.

In the seven field water samples from the PE pipes, degradation products were found in only two sections, and only in the first of two replicates. One and three components were identified in these two sections, and the total concentration was 3 µg/l. Less leaching was measured in the field water samples compared to the laboratory tests due to the fact that the retention time in the field is shorter (from 7 hours to 2.5 days), and the temperature lower.

The investigation shows that the pipes examined comply with the demands of the existing DS system for plastic pipes for drinking water. Furthermore, the investigation shows differences in the leaching of degradation products of added antioxidants from the individual pipes. However, the investigation is too limited to allow any conclusion whether these differences can be attributed to different types of pipe.

There is only very limited knowledge on the toxicological effect of the measured degradation products from the antioxidants added. The Danish Environmental Protection Agency has made a provisional assessment of one of the degradation products identified. This assessment points at a limit value – based on a health assessment – for drinking water at 20µg/l for 2,4 di-tert-buthylphenol.

On the basis of the present results, the leaching can be calculated for other pipe dimensions and retention times. Results which are based on the total leaching measured in the laboratory indicate that the leaching of degradation products will not - under normal conditions - present a health problem. For consumers with very long service lines (several hundred meters), and therefore a long retention time, the leaching of degradation products from antioxidants in PE pipes will be below 20 µg/l.

The laboratory investigation of PVC pipes does not show any leaching of organic components. Investigations of the old pipe sections showed leaching from lead in all three sections, and in concentrations up to 0.82 µg/l. At the inlet to a property, the limit value for lead is 5µg/l. Since 2001, addition of lead to PVC pipes for drinking water has been forbidden.

Field investigations of water samples from PVC pipes did not show any leaching of organic components or of lead. Leaching of organotin compounds was found in one of the three sections examined. At the inlet to a property, the concentration of dibuthyltin was up to 0.031µg/l. There are no limit values for this compound.