Specifying piping materials for water infrastructure systems

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copper-pipe
A recently installed underground copper service line. Copper has been used for piping purposes for over 75 years. Photo: John Galloway

By Daniella M. Pizzurro, David Mayfield, and Ifeoluwa A. Bamgbose

There are two main material options to consider when looking to replace drinking water systems: plastic or copper. Concerns have been raised about both materials. Do plastic pipes leach harmful chemicals into drinking water? Does exposure to elevated copper have health implications?

In an attempt to clarify potential hazards associated with indoor potable water pipes, a survey was conducted of publicly available, peer-reviewed studies containing information about chemicals leaching from seven common piping materials: copper, polyethylene (PE), cross-linked polyethylene (PEX), high-density polyethylene (HDPE), polypropylene (PP), chlorinated polyvinyl chloride (CPVC), and polyvinyl chloride (PVC). Click here to read the full survey summarized by this article.

Due to the complex and varied composition of plastics, numerous studies have been conducted to assess the myriad substances leaching from these materials. The composition of copper piping is much less complex, consisting of 99.9% copper and a small amount of phosphorus as the only intentional components. Therefore, studies on leaching from copper focus less on leachable substances and more on the factors contributing to corrosion and leaching.

Copper pipes

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Copper has been used for piping purposes for over 75 years, typically because of its durability, reliability, corrosion resistance, safety and longevity. The majority of copper tubing produced is manufactured with a specific copper alloy, C12200, which is comprised of a minimum of 99.9% copper and less than 0.04% phosphorus.

While lead has historically been identified as a corrosion byproduct in drinking water systems that use copper pipes, there is no lead in copper piping. Any lead leaching is likely from older lead pipes, solders and fluxes used to connect copper pipes in the same system, and/or alloys containing lead (e.g., brass), and not from the copper material.

Regulations and research on copper pipes are mainly focused on corrosion control and monitoring rather than on leaching, because the scaling and oxidation of copper contributes to the amount and types of byproducts, ions and/or particles that leach into the water. Among the contributing factors to corrosion are pH, hardness, temperature, dissolved oxygen, oxidizing and complexing agents, other ion concentration, the duration of water stagnation, and age of the pipes. These various factors affect the rate and extent of scaling, oxidation, and leaching in the copper pipes.

Copper piping is primarily composed of one substance and is tightly constrained by alloy specifications. As a result, the byproducts reported to form on, and leach from, copper piping are mainly soluble and insoluble copper compounds.

The most common compounds formed in pure water are substances that contain the cupric ion (an ionic form of copper, missing two ions). Substances such as copper sulfate or phosphate compounds are formed to a lesser degree, depending on the quality of the water conveyed and the use of water treatment agents (e.g., orthophosphate).

These affect copper solubility and the form of the copper compound(s) that grow on the inner pipe wall and can leach into the water. In any case, studies indicate that these copper compounds and their potential health effects are established, well-known, and regulated.

Plastic pipes

To understand the phenomena of leaching from plastic pipes, the published literature was first surveyed for studies on substances potentially leaching from commonly used drinking water system piping materials. The analysis focused on the six plastic piping materials, PE, PEX, HDPE, PP, CPVC and PVC, from which 163 leachable substances were identified.

Next, to assess the extent to which the identified leachable substances are currently understood well enough to be regulated, drinking water quality criteria or standards from a variety of sources were reviewed. It was found that criteria or standards exist for 89 of the 163 substances, but none are available for the remaining 74. Moreover, no guidelines exist for 17 of the 37 substances most frequently reported to have leached from various plastic piping materials.

When sorted by piping material, the substances identified as having leached from PEX are the most common, followed by PVC and HDPE materials. The substances were also sorted into 38 separate chemical groups. This categorization revealed the following patterns:

  • Halogenated compounds and hydrocarbons represent a sizable fraction of all the substances identified and are reported as leaching predominantly from CPVC and PVC materials.
  • Organotins are reported as having leached from PVC and CPVC only, and not from HDPE, PP, PE or PEX.
  • Alkyl phenols (including alkyl phenol esters, acids, ester amides, aldehydes, and ketones) and quinones are all reported as having leached from HDPE, PE, PEX and/or PP materials, but not from PVC or CPVC.
  • For other chemicals, clear patterns are not as easily discernable. Aromatic hydrocarbons, phthalates, and vinyl compounds, for example, are reported as having leached from a variety of material types.

Some of the key factors that affect substances leaching from plastic piping materials include water quality, pH, sampling duration, the age of the materials, temperature, and exposure to UV radiation or other gross manipulations. Different substance profiles have been measured in water from pipe segments of the same polymeric materials from different manufacturers.

Thus, such observations appear to depend not only on material type and the aforementioned factors (e.g., pH, water quality, use conditions), but also on the processes by which they are manufactured. This point requires further investigation into manufacturing processes and standards in place that may result in different formulations and the ultimate reactivity of the materials.

The literature survey confirmed that, under certain environmental conditions, many substances can leach from commonly-used plastic piping materials into drinking water. Importantly, the mere presence of such substances in drinking water does not necessarily present a health risk. A detailed review and understanding of each water quality criterion is needed before any conclusions can be drawn about the significance of the measured substance concentrations in drinking water. Future research could build upon this analysis to prioritize substances or chemical groups for additional data collection.

Pipe fittings

Pipes themselves are not the only materials that come into contact with drinking water. Plastic piping materials often contain plastic fittings and solvent cement joints, which may be comprised of substances and materials that are different from that of the actual piping and may also contribute substances that could leach into drinking water.

In the case of copper, they are manufactured from the same alloy as copper piping, and are 99.9% copper. In some cases, specialty fittings require the use of other copper alloys, with primary alloying elements being tin and zinc. Solders used to join copper are primarily tin-based (approximately 95% tin), with small amounts of antimony, copper, silver, selenium or other minor alloying metals added. Fluxes used to make the solder joint are designed to be lead free, and are also designed to flush free of the system after the joints are made.

In either case, fittings and joining methods must also be evaluated separately when assessing health and environmental consequences. In both copper and plastic systems, the growing use of mechanical joints greatly limits the additional materials that are introduced to the system in joining.

Daniella M. Pizzurro, Ph.D., David Mayfield, M.S., DABT, BCES, and Ifeoluwa A. Bamgbose, M.S., are with Gradient. For more information visit www.gradientcorp.com. This article appears in ES&E Magazine’s June 2018 issue.

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