Replacing Lead Water Pipes with Plastic Could Raise New Safety Issues

Industry-related groups say plastic is a safe material to replace lead pipes, but some researchers and health advocates are not so sure

A landmark federal commitment to fund the elimination of a toxic national legacy—lead drinking water pipes—promises to improve the public health outlook for millions of people across the U.S. But it also presents communities with a thorny choice between replacement pipes made of well-studied metals such as copper, steel or iron and more affordable but less-studied pipes made of plastic.

Under a $15-billion allocation in last year's Bipartisan Infrastructure Law, dedicated funding has started flowing to U.S. states to pay for removing and replacing so-called lead service lines—pipes that connect underground water mains with buildings and their plumbing systems. The funds could cover the replacement of about a third of the nation's estimated six million to 10 million such lines.

In March the anticipated surge of lead-pipe-replacement work prompted a group of 19 health and environmental advocacy organizations headed by the nonprofit Natural Resources Defense Council (NRDC) to publish a set of guiding principles for lead-line replacement. Amid numerous recommendations related to community involvement, safety and economic justice, the document takes a stand against swapping in pipes made of plastic and calls for copper lines instead.

Although there is a consensus in the health and biomedical community that lead service lines should be replaced, many water quality and health questions about plastic drinking water pipes in the U.S. are unresolved or have yet to be addressed, a number of experts say. Some industry representatives disagree with recent findings that suggest links between plastic drinking water pipes and health issues. The situation could prove frustrating and confusing for utilities and consumers as communities receive federal funds for replacements—and must then consider the many dimensions of choosing the safest and most suitable new pipes for their region.

Service lines are commonly made of copper, iron, steel or one of several types of polyethylene or polyvinyl chloride (PVC), according to various sources. In the next decade up to 35 percent of U.S. utilities’ spending on drinking water distribution will go toward plastic pipes, says Bluefield Research, a firm that provides analyses of global water markets. Plastic materials such as PVC and high-density polyethylene (HDPE) are typically less expensive to purchase up front than more traditional materials such as copper, ductile iron and steel. So when measured in miles of distribution pipe, plastic is forecast to make up nearly 80 percent of the nation's water pipe inventory by 2030, according to Bluefield.

It is very clear that there is no safe level of lead exposure, according to the U.S. Centers for Disease Control and Prevention and many medical and public health leaders. Taking in even low levels of lead from paint and drinking water causes several types of health issues, including intellectual deficits, particularly in children, as well as neurological and reproductive problems and increased risk of cardiovascular death.

With plastic pipes, the matter of potential drinking water contamination is less clear-cut. In the NRDC-led group's lead-line-replacement principles, the copper-not-plastic item points to recent research suggesting that plastic pipes can potentially contaminate drinking water in three ways. The first is the release of chemicals into water from the pipe material, a process called leaching, which has been documented in several studies. The second route, called permeation, involves pollutants such as gasoline that can seep from groundwater or soils through the walls of plastic pipes, which has been noted in reports by the Environmental Protection Agency and the Water Research Foundation (formerly the Awwa Research Foundation). And finally, plastic pipes exposed to the high heat of wildfires are at risk for melting and other thermal damage. Plastic pipes damaged in wildfires could release toxic chemicals into drinking water, the NRDC document suggests, citing an October 2021 EPA fact sheet. The high heat of fires can degrade plastic pipes, valves and meters in drinking water distribution systems, potentially releasing volatile organic compounds (VOCs) into drinking water, the EPA document states. A 2020 study arrived at more explicit findings by revealing in lab tests that plastic pipes exposed to wildfire temperatures can release benzene, a carcinogen, and other VOCs into water.

Pipe material-related factors beyond those in the principles document can also contaminate drinking water. A July laboratory study by civil and environmental engineer Marc Edwards of Virginia Tech and his colleagues revealed that the growth of Legionella pneumophila, the water-borne bacterium that causes Legionnaires’ disease, varied with the pH of water, whether that water was in contact with cross-linked polyethylene (PEX) or copper pipes, and the presence of phosphate, which is used to control corrosion.

Some organizations associated with the plastic pipes industry are skeptical or dismissive of findings that link these pipes with potential drinking water quality and health concerns. Bruce Hollands, executive director of the Uni-Bell PVC Pipe Association, points to a 2015 environmental product declaration (EPD) that followed an assessment of seven PVC water and sewer pipe products by the International Organization of Standardization (ISO), a voluntary, nongovernmental standards organization. The declaration states, "PVC pipe and fittings are resistant to chemicals generally found in water and sewer systems, preventing any leaching or releases to ground and surface water during the use of the piping system. No known chemicals are released internally into the water system. No known toxicity effects occur in the use of the product." An update due out in a few months will contain the same statement, Hollands says.

A similar position is held by a nonprofit organization called NSF (originally founded as the National Sanitation Foundation), which is one of several organizations to offer testing that can lead to certification of manufacturers’ drinking water pipes and other system components under a standard called NSF/ANSI/CAN 61 Drinking Water System Components–Health Effects, or Standard 61. "We are not aware of credible evidence that would discourage the use of plastic pipe or other products that are certified to NSF/ANSI/CAN 61 in drinking water systems," NSF said in a statement to Scientific American.

Standard 61 is determined by a committee of manufacturers, toxicologists, water utilities and federal and state regulatory officials, said NSF (which is unrelated to the U.S. National Science Foundation). The standard is recognized by the nonprofit American National Standards Institute (ANSI) and the Standards Council of Canada (a federal "Crown corporation"). The EPA says it "has supported the development of independent third-party testing standards for plumbing materials" under Standard 61, the agency says. The EPA's only safety requirement for pipes and other plumbing materials is that they are free of lead. Nearly all U.S. states require utilities to use pipes and other water distribution system products that are certified to Standard 61.

Consumers with questions about the safety of pipes that are in contact with drinking water should focus on individual products that are certified to appropriate standards rather than the materials that pipes are made of, NSF wrote in its statement to Scientific American. Some material-related trends have emerged in examinations of specific contamination routes, however.

Permeation of metal pipes is "extremely rare," says Edwards, who in 2015 pinned down the cause of high lead levels amid Flint, Mich.'s water crisis. In contrast, gasoline and solvents can permeate polyethylene pipes, and pure benzene and other dangerous organic compounds also permeate PVC pipe without rubber gaskets (although gasoline does not), a Water Research Foundation report states. In a 2009 document, the Plastics Pipe Institute, a trade organization, called the conclusions of the report "inconclusive and perhaps misleading."

All pipes can leach their constituent materials to some extent, according to a 2006 National Research Council report. Corrosion control can help to manage copper that leaches from pipes made of that metal, Edwards says. Various types of plastic pipes can release compounds that are potentially toxic or carcinogenic, studies have found. Yet the EPA has set no legally enforceable federal standards for many of these contaminants if they turn up in drinking water (under the Safe Drinking Water Act, state standards for contaminants must be at least as stringent as federal ones). The current questions that need to be answered are which pipe-related contaminants get into drinking water, the extent to which they might affect water quality and human health, and whether any industry-independent researchers or government regulators are looking for specific concerning contaminants at all, especially in the case of plastic pipes.

Rather than advocating for one material over another for these service lines, many U.S. environmental engineers say the choice of material for any given underground water pipe should depend on factors such as whether a pipe will be flushed before use; how regularly the pipe will be used; whether the pipe is going in near an underground tank storing gasoline, sewage or other harmful material; and conditions such as the water pH and temperature.

For example, in a 2020 study funded by the EPA, environmental engineer Patrick Gurian of Drexel University and his colleagues found statistically significant higher concentrations of total organic carbon (TOC), a nonspecific water quality measure, in some PEX pipes than in copper ones. Organic carbon in a water supply can come from decaying leaves and other natural sources and can leach from synthetic sources such as a plastic pipe.

But the characteristics of the study's two individual water systems (in Philadelphia and Boulder, Colo.) varied by water source, disinfectant used and average pH, among other factors. Such variations are unavoidable across water systems. "Plastic pipe can leach TOC, but this can be addressed through quality control measures such as proper testing and certification," Gurian says. "Engineering is about managing risks and making tradeoffs. I am not aware of information that would justify banning all plastics from use as pipe materials." The Plastic Pipe and Fittings Association, a trade association, wrote in a statement to Scientific American that "plastic pipe has been extensively studied for all sorts of supposed maladies since the early 1980s."

Some researchers say plastic pipes in the U.S. have not yet undergone the same degree of water quality and health scrutiny as pipes made of copper, iron, steel and cement. With these so-called legacy materials, methods to prevent or remedy leaching, permeation and other issues are well known, says environmental engineer Andrew Whelton of Purdue University. But that is not the case with plastic pipes. Colleges and graduate schools that train civil engineers and public health researchers have historically ignored the chemistry and manufacturing of plastic in their curricula on water quality issues, Whelton says.

Scott Coffin, a research scientist at California's State Water Resources Control Board, studies the impacts of microplastics in drinking water on human health, as well as the potential health impacts of endocrine-disrupting additives in water distribution systems. He agrees that more research is needed on water quality and plastic drinking water pipes. "Drinking-water-distribution-system contaminants resulting from plastic pipes are not explored very often," Coffin says. "It's sort of forgotten about, honestly, in the water industry."

Whelton and his colleagues have actively pursued questions about potential contaminants in the water carried in plastic and other types of drinking water pipes. In a 2014 study, the team identified 11 PEX-related organic compounds, including toluene—one of 90 or so contaminants for which the EPA has set legal limits in drinking water—in the water that was in contact with PEX pipes installed in a six-month-old "net-zero energy" building. The compounds were not found in water entering the building. Two years later the team published a study that compared contaminants released by copper pipes and by 11 brands of a total of four types of plastic pipes. Microbial growth thresholds were exceeded in water in contact for the first three days of exposure with three of the brands of PEX pipe. Then, in a 2017 study, Whelton and other colleagues found that heavy metals, including copper, iron, lead and zinc accumulated as sediment and formed scales inside PEX drinking water pipes in a home's one-year-old plumbing system.

None of these three studies, all funded by the U.S.'s NSF (the National Science Foundation) and performed with pipes marked as certified to Standard 61, was designed to make direct health claims, Whelton says. Instead they were meant to reveal potential contaminants—some of which could hold implications for water quality and health—that could be produced by interactions between drinking water and plastic pipes.

Each of the studies, however, drew the pointed attention of the other NSF (the nonprofit testing and certifying organization), which reported $123 million in revenue in 2020. On a voluntary basis, manufacturers of products ranging from water system components to microwave ovens may pay fees to NSF, or any of several other competitors, to assess whether products meet standards (which are often set in collaboration with NSF) and whether they merit certification. Such certification indicates that "an independent organization has reviewed the manufacturing process of a product and has independently determined that the final product complies with specific standards for safety, quality or performance," according to NSF's website.

In 2018 NSF released a document addressing Whelton and his colleagues’ 2014, 2016 and 2017 studies of plastic drinking water pipes, stating that the conclusions and data "have contributed to misinformation and confusion about these products."

Whelton says there is no misinformation in the studies, each of which was peer-reviewed. NSF "claimed information was not included in the studies when it actually was," he says, adding that the organization's document itself "is an example of misinformation and should be ignored."

When it comes to drinking water safety and plastic, that is largely what the organizations that signed onto the lead-service-line-replacement principles headed by NRDC have done, putting their trust elsewhere than the plastic industry and pipe testing and certification organizations. The NRDC-led group's document of principles links to studies and reports by the EPA, the Water Research Foundation and academic researchers. And the document states that its call for copper replacement pipes rather than plastic ones draws on recommendations and concerns from the Healthy Building Network, the International Association of Fire Fighters and United Association, a plumbers’ and pipe fitters’ union. As Yvette Jordan of the Newark Education Workers Caucus, an organization that signed the document, puts it, "When you have so many people—so many organizations, especially—when they agree..., shouldn't you take notice and say, ‘Okay, we should probably reexamine this ... and use copper and not plastic’?"

Journalist Robin Lloyd, a contributing editor at Scientific American, is president of the Council for the Advancement of Science Writing's board of directors. Follow Robin Lloyd on Twitter. Credit: Nick Higgins

Robin Lloyd

Angus Chen