Pioneering Tests on Odors from Plastic Water Pipe

Released: 8/13/2007 4:00 PM EDT
Embargo expired: 8/23/2007 2:00 PM EDT
Source Newsroom: American Chemical Society (ACS)
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Citations 234th American Chemical Society National Meeting

Newswise — "Fruity plastic" may seem like a connoisseur's description of the bouquet of a bottle of Chardonnay or Merlot gone bad. However, that was among several uncomplimentary terms that a panel of water "sensory experts" used to describe the odor of drinking water from the plastic piping that is finding its way into an increasing number of homes these days.

The sampling was part of pioneering research on how plumbing materials affect the odor and taste of drinking water, which was reported here today at the 234th national meeting of the American Chemical Society (ACS).

Andrea Dietrich, Ph.D., who reported to the ACS, the world's largest scientific society, pointed out that a rash of costly pinhole leaks in recent years in commonly used copper water pipes has led to renewed interest in lower priced plastic pipes. Dietrich and colleagues at Virginia Tech are among those scientists leading the way in evaluating how plastic might affect water quality and odor.

"Although water is a complex mixture of organic and inorganic chemicals, most people expect their drinking water to have little or no flavor," Dietrich noted. With those expectations, any taste or odor in a glass of water can be "highly noticeable."

Dietrich's team is using two methods to evaluate odors associated with several types of plastic piping. First, sensory panelists smell and describe the odor of the water after it has sat in the pipes for several days. Then, the water undergoes chemical analyses for metals and organics and basic water quality parameters, such as pH.

Using specially prepared, neutral-smelling water as their control, panelists described the test water samples in terms that included "waxy plastic citrus," "fruity plastic" and "burning plastic." Fortunately, the odors are not long lasting, Dietrich said. "We find that after about two months, most of the odors and water quality effects have gone to background." How quickly the odors disappear depends on the amount of water usage, she added. When a household uses more water, the odors fade faster.

Dietrich told the ACS that her group evaluated several types of plastic piping: cPVC (chlorinated polyvinyl chloride), HDPE (high-density polyethylene), and PEX-aA and PEX-b, which are crosslinked polyethylenes. Each is approved and certified for use in drinking water applications by NSF International, an independent certification, standards and testing organization, and ANSI, the American National Standards Institute.

"We found that cPVC has a low odor potential and it doesn't seem to release many organic chemicals," Dietrich said. "HPDE actually had the highest odor production, although it didn't release very many organic materials. The PEX-b pipe had a moderate amount of odors and also a moderate amount of organic chemicals that were released into the air. PEX-a had fewer odors and organics release than the PEX-b pipe."

Asked about her personal preference in plastic piping, Dietrich replied: "I would recommend people talk to their neighbors and find out what type of plumbing materials they have and if they are having problems. We do suspect that certain materials are going to be more compatible in certain areas," due to the differences in water quality from one part of the country to another.

For now, Dietrich's group is focused mainly on the odors imparted by plastic pipes and the analysis of any organic compounds that may leach into the water from the pipes. Asked if there may be any health effects from the leached compounds, Dietrich said that is still under investigation and she doesn't have any answers at this point.

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The paper on this research, POLY 684, will be presented at 2:00 p.m., Thursday, Aug. 23, at Westin Boston Waterfront, Grand Ballroom B, during the symposium, "Polymer Design for Foods and Nutrition: Sensory Issues in Food Packaging."

Andrea M. Dietrich, Ph.D., is a professor of civil and environmental engineering at Virginia Tech in Blacksburg, Va.


The paper on this research, POLY 684, will be presented at 2:00 PM, Thursday, 23 August 2007, during the symposium, "Polymer Design for Foods and Nutrition."

POLY 684
Sensory impacts from polymer pipes interacting with drinking water oxidants

Program Selection: Division of Polymer Chemistry
Topic Selection: Polymer Design for Foods and Nutrition: Sensory Issues in Food Packaging


The odors and chemicals imparted by new commercial polymer pipe materials in contact with drinking water were investigated. Silane-cross-linked polyethylene (PEX-b) leached the greatest amount of organic carbon as well as the greatest number of volatile organic compounds and contributed a weak odor described as "burning-solvent/plastic" . High-density polyethylene (HDPE) leached only minor amounts of organic carbon but many specific organics that imparted a moderate intensity odor described as "waxy/plastic/citrus" . Chlorinate polyvinyl chloride (cPVC) leached the least amount of organic carbon, had the fewest number of compounds identified, and the least impact on water aesthetics. No correlation was found between type of disinfectant (chlorine or monochloramine) present and amount of organic carbon leached or intensity of the odor associated with the polymer. The research indicates that specific polymer-associated organic chemicals determined the odor intensity and descriptor(s). Food processors, water utilities, and consumers and should be aware of these sensory impacts.

Researcher Provided Non-Technical Summary

Briefly explain in lay language what you have done, why it is significant and what are its implications (particularly to the general public)

Our current research is unique in that we comprehensively evaluated and compared the impact of six common new plumbing materials on chemical water quality and odor generation. We filled new pipes with a standard drinking water, allowed the pipe's chemical components to leach/migrate into the drinking water, then performed human sensory assessment and chemical analyses. Some materials were very "smelly" even though they relesed only a small amount of organic carbon to the water; others released more organic carbon but did not smell much. Thus, there is a need for human sensory assessment for evaluating odor impacts of materials; an easy chemical analysis cannot be substituted. In the US, such sensory analysis was discontinued decades ago by the organizations that certify plumbing materials, although sensory assessments are still done in Europe, Australia, and New Zealand.
For the general public, our research elucidates how new materials used by water utilities, the food industry, or homeowners for drinking water convyance can perceivably change, at least in the short term, the water quality at the tap. Armed with this knowledge, consumers and industries can make informed choices about new materials. Polymer pipe manufacturers could also alter their processes to make pipes that minimize chemical and sensory impacts.

How new is this work and how does it differ from that of others who may be doing similar research?

My research group is one of the few worldwide that works at the interdisciplinary interface of human perception, drinking water quality, and materials/chemical constituents. People tend to think that "water is just water" but it is really a complex mix of organic and inorganic chemicals that impart not only hydration, but also minerals and possibly tastes and odors. Because H2O has no flavor and most people expect their drinking water to have little or no "flavor", the release of odorants and tastants from materials to drinking water can be highly noticeable. Odor is one of the least understood senses - the recent 2004 Nobel Prize in Medicine went to Linda Buck and Richard Axel for their discoveries on how the olfaction system actually functions. My applied sensory research is building on fundamental sensory researeh to bring better products ot consumers.
Special Instructions/feedback: I look forward to the ACS meeting and working with the publiity staff.