· 4 min read
The study “Crosslinked polyethylene (PEX) drinking water pipe: Carbon leaching, impacts on microbial growth, and developmental toxicity to zebrafish” by Christian Ley Mathews, Ola Wasel, Kristofer P. Isaacson, Caitlin R. Proctor, Miriam Tariq, Amisha D. Shah, Jennifer L. Freeman and Andrew J. Whelton contains several key pieces of misinformation regarding PEX and NSF/ANSI/CAN 61: Drinking Water System Components-Health Effects. The study does a disservice to the plumbing industry by diverting attention away from respected, well-established testing and health standards. It is important that consumers understand the science involved in testing PEX products to NSF/ANSI/CAN 61 to evaluate their suitability for use in drinking water systems that we all use daily.
According to the authors, the scope of this study was to:
NSF/ANSI/CAN 61 is the US and Canadian national standard for evaluating health effects of all drinking water components. It is also required in many other countries in South America, the Middle East and Asia.
The testing methods in NSF/ANSI/CAN 61 are representative of daily use so that exposure levels can be realistically assessed. To receive standard certification, any contaminants that migrate from the product must meet toxicology safety thresholds. The standard requirements are rigorous and based on scientific methods to ensure the highest level of public health protection. Additionally, the standard is consistently reevaluated to ensure it meets the latest science and technology available.
The testing of TOC migration concentrations in this study involved exposing pipe to high concentrations of chlorine (200mg/L) for three hours followed by leaching studies with chlorine between 0 and 3.5 mg/L for up to 120 hours. These levels of chlorine are well beyond what would be found in a typical plumbing system. While water may occasionally sit stagnant for several days, it would not be a normal daily occurrence to drink water that has been stagnant for 120 hours. Additionally, the value of TOC testing is low because results cannot be associated with health-based acceptance criteria. Testing to NSF/ANSI/CAN 61 quantifies each individual contaminant and evaluates the toxicology of those contaminants.
The study did not provide the concentration of the contaminants, which are needed to evaluate the data for health concerns; therefore, no statement on the toxicological impact of the extractables is possible. The daily dose of contaminants that an individual would receive is important as the purpose of NSF/ANSI/CAN 61 is to measure and evaluate the potential health effects of the contaminants consumed on a daily basis over the lifetime of a person. Additionally, the extraction protocols used in the study to identify contaminants that may migrate from PEX were not representative of normal use.
Most of the contaminants that were observed were extracted using n-hexane. N-hexane is an organic solvent, similar to gasoline, that is not representative of drinking water. This testing environment is not representative of normal use scenarios considering contaminants that are not soluble in water, and thus would not extract, may be soluble in n-hexane. For this reason, it is not surprising that contaminants were detected using the solvent. In order to draw an accurate test result for end-use application, real world scenarios must be used. In this case, they were not.
Additionally, most of the contaminants reported in the study are not commonly detected in standardized testing using drinking water for extraction. Most importantly, all identified contaminants in the study are currently included in the NSF/ANSI/CAN 61 test procedures and therefore, if identified, would need to be present at the pre-established safe levels of exposure for the product to be certified (see NSF/ANSI/CAN 600 for current drinking water criteria).
Zebrafish were used to test for potential toxicity resulting from long term exposure of water in PEX tubing for 60 days. The data showed that no alterations in hatching rates, survival rates or behavior occurred in the zebrafish population under any condition. Significant changes were detected in total body length and brain length for PEX-b and PEX-c at 23°C, which the researchers claim indicates abnormal development. However, the standard deviation of these measurements was greater than the difference between treated and control means, and interestingly, no significant changes occurred for any PEX at 55°C, where increased temperature would be expected to increase leachates. Furthermore, drinking water that has been stagnant for 60 days is not a normal everyday occurrence and is not representative of the normal environment of zebrafish or water consumed by humans.
In summary, the study used unrealistic end-use scenarios and extraction methods, developed data that was often not duplicated in standardized testing, and reported results that could not be accurately evaluated for health effects. NSF is committed to protecting public and planet health and is confident in the requirements set in the standard. Separate from its testing services, NSF encourages interested parties to participate in the well-established, scientifically-supported standards development process to help support public health protection.