Treatment and storage conditions influence migration of material monomers from PE-pipe

Key messages
PE-pipes release material monomers that are undesirable in drinking water due to health concerns. We
investigated how monomer released to drinking water from PE-pipes can be minimized by different
treatment and storage methods.
Storage conditions such as duration of storage time, caps, temperature, microbial biofilms, and
surrounding environment influenced monomer release in subsequent migration tests.
Storage of PE-pipe outside for 28 days, short-term exposure to pressurized steam, or heating to 75ᵒC for
3h without caps appeared to be attractive pretreatment methods to minimize subsequemt monomer
migration from PE-pipes to drinking water

Abstract text
PE-pipes are the predominant material applied when distribution networks are renewed and currently
constitute approximately 32-46% in Denmark. PE-pipes release material monomers that are undesirable
in drinking water as some are suspected hormone disruptors. We investigated how monomer release to
drinking water from PE-pipes can be minimized by different treatments and storage methods.
Pipes were stored under different conditions or exposed to different treatments e.g. heating or
microorganisms (figure). Following treatment or storage a migration test was conducted after Standard
DS/EN 12873-1. Migration was analyzed after 72h with stagnant water to achieve a worst-case scenario.
Selected organic substances and phenols in the migration water were analyzed by GC-MS or LC-QTOF
(figure).
Concentration of monomers ranged from <0,05 to 26 μg/L (33 ng per cm2). 5-methyl-2-hexanone
release peaked after 3-14 days storage, while the pattern for the remaining monomers was more
influenced by treatment. During migration testing PE-pipes stored or heated without caps released lower
concentrations of monomers as compared to PE-pipes stored with caps. More phenoles (30-66%)
migrated from PE-pipes after storage in a storage facility as compared to PE-pipes stored outside.
Storage of PE-pipe 6 months outside in the shadow led to least migration of monomers during migration
testing. However, despite being equipped with caps, earwigs had inhabited the pipe. Minimizing risk of
water contamination vs. release of monomers to the consumers therefore need to be carefully
considered.
An alternative solution to prolonged storage is to actively reduce migration after installation by advanced
procedures. Heating of PE-pipes to 75ᵒC for 3h without caps accelerated migration during storage, and
release of components in the following migration test was for most components comparable to PE-pipes
stored for a month. Rinsing with pressurized steam also resulted in decreased subsequent migration
compared to a new pipe. Surprisingly, preincubation with a microbial enrichment lead to a 18% increase
in migration of 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-dien-2,8 to water as compared to a new pipe.
Based on current observations, storage outside for 28 days, pressurized steam, or heating to 75ᵒC for
3h without caps appear to be attractive