HDPE Water Pipes: A Reliable Barrier Against PFAS Permeation

Researchers investigated if per- and polyfluoroalkyl substances (PFAS) can permeate polyethylene (PE) and polyvinyl chloride (PVC) water pipes.

Drinking water is commonly distributed using plastic pipes due to their durability and ease of installation and handling. However, contaminants can sometimes permeate the material if the pipe runs through contaminated soil. This is a known issue with hydrocarbons, but does PFAS pose the same threat?

You can also read: PFAS in Food Contact: Applications and Regulatory Actions

Permeation: A Known Issue with Hydrocarbons

Permeation of piping material refers to the passage of external contaminants into the drinking water through the pipe’s material. This permeation process typically occurs through:

1. Sorption between the outer surface of the pipe and the contaminated medium
2. Diffusion through the material of the pipe
3. Desorption from the inner surface of the pipe into the water

A 2002 report from the US EPA found that permeation incidents almost always involved plastic pipes. Hydrocarbon contaminants originated from various sources, including the leaking of petrol, oil, and paint thinners. Urban areas typically face less threat from PFAS contamination than that of hydrocarbons. Nevertheless, manufacturing facilities, wastewater treatment sites, landfills, and firefighting training sites are associated with environmental PFAS contamination. Since PFASs have different physical and chemical properties than hydrocarbons, the question remains whether permeability is an issue.

A comparison of the physical and chemical properties of select PFAS and hydrocarbons. Courtesy of Are PFAS an Issue for Permeation of Plastic Water Pipes?

Based on the characteristics of PFAS, it is unlikely that permeation would be an issue for PE and PVC pipes. Nevertheless, there are over 6,000 PFAS chemicals, and their characteristics vary.

Testing if PFAS Poses Similar Problems

In a 2018 study, researchers investigated the possibility of PFAS permeation in plastic water pipes. Researchers immersed new HDPE in PFAS-containing material comprised of a 3% (by weight) Aqueous Film Forming Foam (AFFF) solution. They exposed the pipe sections to the PFAS-containing material for six months, periodically analyzing the pipe’s water contents.

The configuration of one of the sets of immersed pipe sections used in the study. Researchers immersed the top three pictured pipes in 3% AFFF and kept the bottom three adjacent to the AFFF solution. Courtesy of Are PFAS an Issue for Permeation of Plastic Water Pipes?

The study’s results showed that, with two exceptions, PFAS concentrations remained below detection levels. Researchers considered it likely that an analytical issue led to these detections since there was no detection in duplicates. Additionally, perfluorohexane sulfonic acid was the sole PFAS detected. If permeation did occur, researchers would also expect to detect smaller molecules.

Promising Results for the Safety of Plastic Water Pipes

The researchers believe that permeation did not occur during this study. These results suggest that it is unlikely that PFAS permeation affects undamaged PE and PVC pipes. Researchers did not evaluate PVC pipes in this study, so this conclusion is an assumption. Additionally, PFASs with chain lengths shorter than C₄ were out of the scope of this study. Though this investigation shows promising results for the safety of plastic water pipes, avenues for future research remain.