Testing POU RO Systems for Reduction of PFOA and PFOS
By Rick Andrew
Last month’s Water Matters column covered testing of POU activated carbon systems for reduction of PFOA and PFOS. In addition to updating NSF/ANSI 53, the NSF Joint Committee on Drinking Water Treatment Units has also recently updated NSF/ANSI 58 for POU RO systems to include these requirements for claims.
In their May 2018 meeting, the committee unanimously voted to establish requirements in the NSF/ANSI DWTU Standards for reduction by activated carbon, by anion exchange resin and by POU RO. The result is that now the requirements (including test protocols) for evaluation of activated carbon systems have been added to NSF/ANSI 53 and NSF/ANSI 58. Work continues to develop a test protocol for treatment by anion exchange resin, which will be added to NSF/ANSI 53. The contaminant reduction test protocols for activated carbon and POU RO were based very closely on the protocols previously developed by NSF for NSF P473 Drinking Water Treatment Units–PFOA & PFOS, which addressed both active media systems and POU RO systems.
Testing POU RO systems
NSF/ANSI 58 now specifies test methods and reduction criteria for establishing claims of reduction for POU RO systems. The basic test methodology reduction is the same as other chemical reduction tests under NSF/ANSI 58. The protocol is a one-week test, which includes multiple samples of the contaminant challenge water and the treated water taken throughout the week-long test protocol. These samples are collected under a variety of operating conditions designed to simulate different modes of real-world operation, resulting in a robust evaluation of the ability of the system to consistently provide effective treatment.
Challenge water characteristics
Like many other contaminant reduction tests in NSF/ANSI 58, the test water used is the TDS reduction test water. Preparation of this water starts with chlorine-free deionized water, with turbidity ≤ 1 NTU; pH 7.5 ± 0.5; temperature 25 ± 1°C and conductivity 1 μS/cm. Sodium chloride is added to this water to achieve a concentration of 750 ± 40 mg/L TDS. Once this water is prepared, the PFOA and PFOS are added to achieve the target concentrations.
PFOA and PFOS concentrations
The concentration of PFOA and PFOS in the challenge water is specified, as well as the level of treatment that is required. Because the US EPA health advisory addresses the total concentration of both PFOS and PFOA, NSF/ANSI 58 specified one test that includes a mixture of both as the contaminant challenge. This is consistent with the approach under NSF/ANSI 53, as discussed last month. Again similar to NSF/ANSI 53, the challenge water concentration for PFOS set in NSF/ANSI 58 is based on a review of US EPA occurrence-data generated under US EPA’s UCMR3 monitoring samples from 2013 to 2015. The level is set at the expected value at which 99 percent of the population will be exposed to waters of lower concentration, which is 1.0 µg/L (or 1.0 part per billion) PFOS.
For PFOA, the challenge water concentration is also consistent with NSF/ANSI 53 and was developed from private well and public water supply sampling in Hoosick Falls, NY, one of the sites where contamination by PFAS has been investigated. The level was set at the expected value at which 90 percent of that population will be exposed to waters of lower concentration. The result of this approach based on using Hoosick Falls monitoring sample results was that the challenge concentration is higher than the maximum concentration detected under US EPA’s UCMR3 occurrence data from 2013 to 2015. This influent challenge value is 0.5 µg/L (or 0.5 parts per billion) PFOA. Combining these levels of 1.0 µg/L PFOS and 0.5 µg/L leads to a total challenge of 1.5 µg/L PFOS and PFOA. This is the same challenge level as under NSF/ANSI 53.
NSF/ANSI 58 also specifies levels of treatment for PFOS and PFOA reduction. Once again consistent with NSF/ANSI 53, NSF/ANSI 58 requires a total combined maximum effluent concentration of 0.07 µg/L, which is 0.07 parts per billion, equivalent to 70 parts per trillion. This level is based on the previously mentioned US EPA health advisory, which was issued in 2016.1 To develop this level, US EPA considered a number of toxicological studies and risk assessments. They also incorporated a margin of protection for sensitive populations. See Figure 1 for the reduction requirements, according to NSF/ANSI 58.
The levels being tested under NSF/ANSI 58 are very, very low; the analytical method is a special one that is detailed in Annex F of the standard. In this method, water samples are directly injected and then analyzed by liquid chromatography triple-quadrupole mass spectroscopy (LC/MS/MS) in electrospray negative mode, with method sensitivity of 10 ng/L. This is the same analytical method that is specified in NSF/ANSI 53.
NSF/ANSI 58 already contains significant, detailed requirements for user instructions. The addition of the reduction claim means that there are additional requirements added to the performance data sheet. Figure 2 indicates how the claim is described in the performance data sheet for those treatment systems conforming to NSF/ANSI 58 that meet the requirements.
Continuing to advance the standards
The NSF Joint Committee on Drinking Water Treatment Units is very active, continuously monitoring the latest scientific publications and studies and working to update the standards to meet the current needs of stakeholders. PFAS contamination of water has become a major issue over the last several years and the joint committee has responded by adding requirements into NSF/ANSI 58 and NSF/ANSI 53. The expansion of these standards help manufacturers provide proven equipment to end users that can be relied upon with confidence to provide robust solutions to contamination problems as we develop a full understanding of the scope of these problems, as well as the solutions.
- US EPA. FACT SHEET: PFOA & PFOS Drinking Water Health Advisories. https://www.epa.gov/sites/production/files/2016-06/documents/drinkingwaterhealthadvisories_pfoa_pfos_updated_5.31.16.pdf
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: Andrew@nsf.org