MATERIALS | PEX


Right: PEX pipe is widely used in building and construction applications


“Despite many advantages, [PEX] materials


release a significant number of contaminants into drinking water because of the high mechanical stress involved in manufacturing, together with the chemical transformation responsible for chain scission in polymers, and due to the degradation of additives,” said the researchers, in a paper pub- lished in Water Research. “As substances leaching from pipes in contact with drinking water may cause a health risk for consumers – or impair water quality – it became important to identify them.” One substance of interest – which is “repeatedly


present in considerable concentrations” – is believed to be a leachable substance from the commercial anti-oxidant Irganox 1010, say the researchers. In their paper, they refer to the substance as [1]. It is assessed and measured using gas chromatography-mass spectrometry (GC-MS). The substance is partially converted to a second substance – called [2] in the paper. This is difficult to detect using GC-MS, so the researchers used HPLC-MS/MS. Comparative measurements of migration waters


from PEX pipes using both methods showed that the concentrations of [1] – detected with GC-MS – corresponded to the sum of [1] and [2] measured with HPLC-MS/MS. The highest concentration of [1], using GC-MS, was > 300 μg/L. The longer the materials are stored without contact with water, the more [1] was measured in the migration waters. Stability assessment showed that [1] developed an equilibrium with [2] under acidic conditions and was completely converted to [2] at pH 10. At pH 7, it takes more than 50 days for the two to reach an equilibrium. However, at 60°C, [1] is rapidly transformed into [2]. In addition, other – currently unknown – degradation products are also formed, said the researchers. “As there is no comprehensive toxicological assessment for both substances available today, our findings underline the need for regulatory consequences,” they concluded.


Toxic assessment US-based researchers at Purdue University have also investigated leaching from PEX pipe – to assess the effect on microbial growth, and potential toxicity.


During periods of plumbing stagnation, drinking


water chemistry and microbiology changes can occur, said the researchers in a paper published in Environmental Advances. The study’s objectives were: to characterise drinking water total organic carbon (TOC) concen- tration changes caused by PEX and cell growth; to


40 PIPE & PROFILE EXTRUSION | September 2023


identify compounds leached, using two extraction approaches; and to directly measure acute and developmental toxicity effects of the PEX contact waters. They carried out a series of short- and long-term


stagnation experiments. For three different PEX pipe brands, the PEX-b brand showed the highest organic carbon migration. Total cell counts in- creased for all three PEX types and conditions over the 120-hour exposure period at 55°C. The simulated 60-day exposure period showed that TOC levels were greater at 55°C than at 23°C. Zebrafish exposed to PEX contact waters


exhibited changes in body and brain length – but no impact on survival or behaviour patterns was detected. Exposure to PEX-b and PEX-c waters at 23°C caused a decrease in animal total body length and brain length compared to larvae in the control group. An increased ratio of head-to-body length was seen for those exposed to room temperature PEX-a, indicating abnormal develop- ment compared to the control group. “Additional studies are recommended to


characterise the type and magnitude of contami- nants leached and directly measure the toxicity of the resulting waters,” said the researchers.


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