Miljøprojekt, 1167 – Undersøgelse af PEX rør til drikkevandsbrug

Undersøgelse af PEX rør til drikkevandsbrug

Summary and conclusions

In 2005, the Danish Environmental Protection Agency performed a field investigation of actual leaching of contaminants from the existing water supply system made of PE and PVC pipes, and compared the results with leaching tests on new pipes. This investigation was reported in “Field investigation of the plastic drinking water supply pipes”, Environmental project No. 1049/2005.

In parallel to the above investigations, a preliminary lab investigation of 2 types of PEX pipes used as internal distribution pipes in buildings was carried out. On the basis of the results of this preliminary investigation, it was decided to carry out larger scale lab and field investigations of PEX pipes in order to achieve more thorough knowledge of these.

The investigation comprised water sampling at six different sites (residential and institutions) at which PEX pipes of different types and from different manufacturers were installed and used as distribution pipes for the cold-water supply.

In order to relate the above field investigations of actual contaminant leaching to results of investigations of leaching from new pipes, lab-tests (migration tests) on new pipes of the type used in the residential installations and on another new type of pipe, Alupex, were performed.

Laboratory test

In the lab test, the PEX pipes were filled with test water at 23 degrees C for three days and then replaced twice after a period of three days, so that the leaching test comprises three repeats called 1st, 2nd and 3rd extraction. Hereafter, a test with an eight-hour retention time, called the 4th extraction, was performed.

The results of the lab tests (migration tests) of the seven types of pipes demonstrated leaching of the degradation products from the antioxidants added to the PEX pipes. Out of ten possible degradation products, six were found in concentrations above the detection level. Generally, concentrations are lower in the 3rd extract than in the 1st extract.

Concentrations above 1 μg/l in the 3rd extraction were found for the following components:

2,6-di-tert-butyl-p-benzoquinone (III) found in the leachate from five pipes in concentrations between 0.5 and 12 μg/l.
2,4-di-tert-butylphenol (lV) found in the leachate from two pipes in concentrations between 0.07 and 1.2 μg/l.
3,5-di-tert-butyl-4-hydroxybenzaldehyde (VI) found in the leachate from all seven pipes in concentrations between 0.05 and 1.5 μg/l.
7,9-di-tert-butyl-1-oxaspiro[4,5]-deca-6,9 dien-2,8-dione (VIII) found in the leachate from five pipes in concentrations between 1.7 and 33 μg/l.
3-(3,5-di-tert-butyl-4-hydroxyphenyl) methylpropanoate (IX) found in the leachate from two pipes in concentrations between 1.1 and 1.6 μg/l.

In six out of seven pipes, MTBE concentrations from between 0.042 and 0.37 μg/l were measured in the 3rd extract. However, in the leachate from one of the pipe types, concentrations of 47 μg/l in 1st extraction, 12 μg/l in the 3rd extraction, and 5.1 μg/l in the 4th extraction were measured.

During the lab test, the level of NVOC in the leachates ranged from below the detection level of 0.1 mg/l up to 5.1 mg/l. In accordance with “Den danske VA-godkendelsesordning for plastrør” (The Danish approval standard for plastic pipes), the release of NVOC must not exceed 0.3 mg/l in the 3rd extraction in leaching tests. Two types of PEX pipes exceed this limit in that the release of NVOC in the 3rd extraction was 0.4 and 3.5 mg/l, respectively.

Field investigation

To examine the actual leaching from residential installations, sampling and analysis of water samples were carried out at six sites. The field investigation showed that at four of the six sites, there were low concentrations of degradation products from antioxidants (concentrations from 0.05 to 2.9 μg/l) in water samples. These water samples were taken in the morning after a minimum eight--hour period with no consumption the previous evening and night.

The water analyses demonstrated the presence of three out of ten degradation products from antioxidants as follows:

2,6-di-tert-butyl-p-benzoquinone (III) found at four sites in concentrations between 0.28 and 2.9 μg/l.
2,4-di-tert-butylphenol (lV) found at only one site in a concentration of 0.06 μg/l, which is close to the detection level.
7,9-di-tert-butyl-1-oxaspiro[4,5]-deca-6,9 dien-2,8-dione (VIII) found at two sites in concentrations of 0.05 and 0.09 μg/l, which is equal to and very close to the detection level.

The above degradation products were also found in the lab tests as noted above.

The field investigation also demonstrated that in water samples from three out of six sites, low concentrations of MTBE of 0.02 – 0.33 μg/l could be measured. In all field measurements, the concentrations were, however, below the drinking water criteria for MTBE at 5 μg/l.

In two out of six sites in the field investigation, the NVOC concentration in water samples at the tapping cock were slightly higher than for water samples entering the property (reference sample). It is uncertain if the difference in the NVOC content is due to contamination from the PEX pipes or variation in the quality of the water from the waterworks.

Conclusion

The investigation shows that the contamination from the PEX pipes is much less in the field investigation than found in the lab test.

The comparatively large release of degradation products from the antioxidants found in the lab test was not confirmed in the water samples from the existing residential installations.

The same tendency was seen for the other analytical parameters of interest – MTBE and NVOC. For MTBE, the lab-test showed a general content of MTBE above detection level, but below the drinking water criteria. For NVOC, the lab-test showed a larger release of NVOC than permitted by the approval standards for plastic pipes. However, on basis of the field investigation, there is no basis for concluding that the release of NVOC is above the permitted level.

The samples taken in the field investigation had a retention time of approx. eight hours. This is approximately the retention time used for the last extraction (4th extraction) in the lab-test. The release should therefore be the same magnitude, but in fact it was considerably lower in the field investigation.

This difference might be due to the difference in the pipes’ age. In the lab test, the pipes tested were completely new PEX pipes, while the pipes tested in the field investigation had been in use for 1-3 years, and therefore the release from these pipes is likely to be less.

The investigation also shows a difference in the release of antioxidant degradation products from different pipes. However, the investigation is too limited to be able to conclude whether the difference can be related to the individual pipe type. There are, however, indications that the release from the PEX-a pipes is in general less than the release from the PEX-c pipes tested in the lab-tests.

Generally, the PEX pipes (between 9 and 16 metres) tested in the field investigation are assessed to be longer than the lengths of pipes normally used in residential housing. In the planning of the field investigation, it was difficult to find sites with PEX pipes of the lengths required for the tests, and therefore the field investigations should be regarded as conservative.