Impact of the surface aging of potable water plastic pipes on their lead deposition characteristics

Abstract

The use of plastic potable water pipes to replace corroded metallic plumbing and construct new potable water plumbing systems is rapidly increasing due to the low cost, noncorrosive characteristics, and easy installation of plastic water pipes. However, unlike for metallic pipes, the understanding of the fate of heavy metals within plastic potable water pipes is limited. This study elucidates the effect of plastic pipe surface aging on lead (Pb) deposition under stagnant conditions. Accelerated aging of crosslinked polyethylene-A (PEX-A) and high-density polyethylene (HDPE) pipes was conducted through exposure to a concentrated chlorine solution at an elevated temperature. Variations in the surface chemistry of the plastic pipes due to aging were examined via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The kinetics of Pb deposition onto new and aged pipes were studied through 5 day Pb exposure experiments. Moreover, the influence of the initial Pb concentration [50–1000 μg L⁻¹] on the rate of Pb deposition onto the plastic pipes was investigated. The ATR-FTIR and XPS analysis revealed the formation of several oxidized carbon functional groups [>C–O, >CO, >O–CO] on the PEX-A pipe and HDPE pipe surfaces after 14 days of accelerated aging. Zeta potential measurements conducted on the HDPE pipes showed a slightly more negative surface charge for the aged pipes than for the new pipes. Kinetics experiments showed that the aged PEX-A (387 μg m⁻²) and HDPE (418 μg m⁻²) pipes deposited significantly greater levels of Pb compared to the new PEX-A (288 μg m⁻²) and HDPE (335 μg m⁻²) pipes at equilibrium. Pb deposition onto the new and aged PEX-A and HDPE pipes followed a first-order kinetics model implying surface confinement of the Pb species. As the initial Pb concentration was increased, a significantly greater rate of Pb deposition (p-value < 0.05) was found for aged PEX-A compared to new PEX-A. However, for new and aged HDPE pipes this rate was not significantly different (p-value > 0.05). This study provides the groundwork for future investigations into the fate of heavy metals in potable water infrastructure.