NSF Updates Filter Standard to Include Lead Reduction Requirements
Many Americans are concerned about lead contamination, specifically when it comes to lead paint and lead in older plumbing systems. That being said, manufacturers of residential water treatment products continually strive to meet the needs of consumers who are concerned about lead in their drinking water. These manufacturers often present products that are certified to the NSF/ANSI Standards for drinking water treatment units for lead reduction.
Recent efforts have focused on improving the repeatability of testing for lead reduction of media filters at pH 8.5 under NSF/ANSI 53. In 2004 and 2005, round robin studies, which were led by NSF, identified that various laboratories were obtaining different results when testing filtration systems produced from the same manufacturing lot.
The round robin studies also revealed that the source of differing test results stemmed from the different interpretations on how the lead challenge was prepared in the language of the standard. This minor difference in preparation technique caused a significant difference in the development of particulate lead in the test water. Labs that tested products using nitric acid as a preservative for their concentration lead stock solution would pass the lead pH 8.5 test; however, the same product tested at a laboratory where nitric acid was not used as a preservative, would fail. At the conclusion of the investigation it was revealed that the variation between these tests was the amount of lead particulate produced.
ANSI-Accredited Standards ProcessThe issue was presented to the NSF Joint Committee on Drinking Water Treatment Units and resulted in the formation of the Plumbed-In Lead pH 8.5 Task Group, which investigated the issue. This newly formed task group determined the appropriateness of having particulate lead present in the lead reduction, pH 8.5 tests. A literature search was also performed to determine the presence of particulate lead in those water distribution systems that had issues with lead.
The task group identified and surveyed literature that supported the broad existence of particulate lead in distribution systems. Seven scientific papers found in this search provided field data on the particulate lead levels in distribution systems. The task group concluded that the level and amount of particulate lead varied widely between systems, as well as between samples. This broad variability prevented the establishment of a definite amount of particulate lead that would be representative of the occurrence in real life systems. A statistical analysis of the available data resulted in a particulate 90th percentile level of 68 ppb. However, The Task Group believed that a target level of three times the action level (45 ppb or 30%) was more appropriate due to the limited amount of particulate data available.
New ProtocolOnce an appropriate level of particulate lead was determined, the task group developed a method to produce a challenge solution containing a consistent 30% particulate lead. This was achieved by combining two different concentrated stock solutions –- one creating the particulate lead and one creating the soluble lead for the challenge solution. See chart below for details regarding the final composition of the lead reduction test water.
Validation of the ProtocolIn order to validate the consistency of the results obtained when testing with the new protocol, additional round robin studies were performed. The first of which focused on the ability of the seven participating laboratories to produce the intended challenge water when following the protocol. This round also included a follow-up effort to develop additional information about repeatable preparation of the challenge solution, receiving participation by four of the seven labs.
The second round robin study featured participation by six of the seven laboratories that participated in the first round robin. The focus of this effort was to test carbon block filters prepared from the same lot of carbon block production. The carbon blocks were designed and produced by the manufacturer to marginally fail the test when particulate lead is present. Marginal failures are the situation in which a lack of repeatability of the test is most likely to reveal itself. If the test product is very robust and easily passes the test, possible differences in laboratory results are masked. Similarly, if the product causes an abject test failure, potential differences in laboratory results are difficult to identify.
These round robin studies demonstrated four factors:
1. The test method was complex and required exact adherence to succeed.
2. Areas of the method that were weak were identified and clarified to improve reproducibility.
3. The sensitivity of the method required significant detail and monitoring to ensure each test met the requirements throughout the entire test.
4. The test method could be successfully performed by laboratories and reproducibly evaluate a test system.
The round robin studies resulted in several improvements to the protocol that lead to the reproducibility of the method. These further refinements are included in the figure above.