by Brianna Crandall — November 5, 2014—Several types of plastic pipes in eco-friendly “green” buildings in the United States have been found to leach chemicals into drinking water that can cause odors and sometimes exist at levels that may exceed health standards, according to a new collaborative study. The odors can cause residents and workers to question the safety of their drinking water.
Buildings are being plumbed with many types of plastic drinking water pipes. These include crosslinked polyethylene (PEX), high-density polyethylene (HDPE), polyvinylchloride (PVC), chlorinated PVC (cPVC) and polypropylene (PP) pipes, observes Andrew Whelton, an assistant professor in Purdue University’s Lyles School of Civil Engineering and Division of Environmental and Ecological Engineering.
Plastic pipes are generally seen as less expensive, lighter and easier to install than metal pipes. A 2012 comparison showed PEX pipe was the least expensive among plastic pipes, costing 43 cents per foot compared to the most expensive metal, copper pipe, at $2.55 per foot. Thousands of dollars can be saved during construction by installing plastic instead of metal plumbing systems, and proponents assert plastic pipes require less energy to manufacture—generating less carbon dioxide compared to metal pipes—ostensibly making them a good fit for green buildings.
“Little is known about the degree to which plastic pipes sold in the U.S. affect drinking water quality,” comments Whelton.
The research
Whelton detailed the research findings in a presentation during the 2014 U.S. Green Building Council’s Greenbuild International Conference and Exposition recently concluded in New Orleans with Rebecca Bryant, managing principal of Watershed LLC of Fairhope, Alabama. Some testing results were published online in September in the journal Water Research. There, the researchers describe drinking water impacts caused by six brands of PEX pipes available in the United States.
In the September study, drinking water was tested from a PEX plumbing system in a “net-zero energy” building in Maryland six months after the system had been installed. The testing revealed the presence of 11 chemicals that were PEX pipe ingredients and ingredient degradation products. Research with PEX pipes in the laboratory also showed that six brands caused drinking water to exceed the U.S. Environmental Protection Agency’s (EPA) maximum recommended drinking water odor limit.
The U.S. EPA’s maximum drinking water odor limit is a “threshold odor number” of 3, or 3 TON. Compliance is voluntary because the standard is based on aesthetic—not health—considerations.
Chemical treatment of water
Odor and chemical levels were monitored with and without chlorine treatment over a 30-day period for the six pipe brands. Chlorine, the most popular disinfectant chemical used in the United States, protects drinking water from disease-causing organisms as it travels to the tap. When chlorine reacted with chemicals leached by the plastic pipes, odor levels for one brand of PEX pipe tripled. While the total mass of chemicals leached by PEX pipes was found to decline after 30 days of testing, the study found that odors generally continued as the pipes aged.
Odor-causing chemicals with regulated limits: ETBE
A general assumption in the United States is that chemicals responsible for drinking water odors pose no health dangers. However, several chemicals found in the plumbing research have regulated health limits, and one PEX pipe brand caused drinking water to exceed the ethyl-tert-butyl ether (ETBE) drinking water health standard. ETBE is a PEX pipe manufacturing byproduct listed in drinking water standards in New Hampshire and New York state. When establishing the ETBE limit in New Hampshire, public health officials specifically added a tenfold reduction to allow for its suspected carcinogenic potential. However, no federal drinking water standard exists for ETBE.
The researchers found ETBE drinking water levels as high as 175 parts per billion (ppb) during the first three days of PEX pipe use and then 74 ppb after 30 days of use when the testing ended. New Hampshire has the most stringent drinking water health standard of 40 ppb. Michigan also has an ETBE standard, but it is based on limiting drinking water odor caused by ETBE.
Varieties of PEX products
The research, funded by the National Science Foundation, also is showing that there are differences in the quality of PEX products on the market, and different brands cause different odor and chemical-leaching impacts.
Continuing research into carcinogens, bacterial growth, cleaning practices
The Water Research paper was authored by University of South Alabama graduate student Keven M. Kelley; associate professor Alexandra C. Stenson and assistant professor Rajarashi Dey at the University of South Alabama; and Whelton, a former faculty member at the University of South Alabama.
The team plans to continue the work and release additional results from the study over the next several months. Findings show some chemicals released by plumbing pipes can be transformed into carcinogenic chemicals regulated by the EPA; chemicals leached by certain plastics are conducive to bacterial growth; and plumbing system cleaning practices described in some, but not all, plumbing codes can cause PEX pipe chemical leaching to worsen.
The “Release of Drinking Water Contaminants and Odor Impacts Caused by Green Building Cross-linked Polyethylene (PEX) Plumbing Systems” article is available for purchase or free to qualified readers online.
