Testing for PFAS in Drinking Water: EPA Method 533

The level of Per- and Polyfluoroalkyl Substances (PFAS) in drinking water in the US seems to be higher than what is acceptable as safe, hence the need for strict testing and monitoring of drinking water. A recent GAO report covering 6 states showed that 18% of water systems (978 out of 5,300) have at least two PFAS above the Environmental Protection Agency’s (EPA) revised health advisory levels (interim 2022). This means that 9.5 million people are exposed to adverse health outcomes. EPA has created a roadmap with the aim of researching, restricting, and remediating PFAS.

What Are PFAS?

PFAS, the abbreviation of Perfluoroalkyl and Polyfluoroalkyl Substances, refers to a wide group of  manmade chemical compounds that have been used in the manufacture of consumer products since the 1940s. They include cleaning products, non-stick cookware, water resistant fabrics, personal care products, and carpets among others. Due to their resistant properties, PFAS are able to persist in the environment for a long time and easily find their way to drinking water sources. As per the EPA guidelines, PFAS in drinking water should not exceed 2-3 ng/l (nanogram per liter).

Do PFAS Cause Cancer?

PFAS are believed to have carcinogenic properties. The International Agency for Research on Cancer (IARC) classifies Perfluorooctanoic Acid (PFOA) which is a type of PFA, as a human carcinogen. PFA exposure has been linked to cancers that affect the kidneys and testis. 

Method 533 – A Validated Method For PFAS Testing 

In December 2019, EPA announced a new and validated method for testing PFAS in drinking water. This new method will help both the government as well as private laboratories to accurately measure PFAS in drinking water. Method 533 measures up to 25 PFAS while the previous test, Method 537, could only measure 14 PFAS. As per the revised unregulated contaminant Monitoring Rule #5 effective from next year, drinking water samples will need to be tested for 29 PFAS. 

Method 533 incorporates isotope dilution which is an analytical technique that minimizes sample matrix interference, hence improving data quality. It was released in December 2019 as an improvement of method 537. 

Which Analytes Can be Tested by Method 533?

1. 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid
2. 9-Chlorohexadecafluoro-3-oxanonane-1-sulfonic acd 
3. 4,8-Dioxa-3H-perfluorononanoic acid
4. Hexafluoropropylene oxide dimer acid  
5. Nonafluoro-3,6-dioxaheptanoic acid 
6. Perfluorobutanoic acid  
7. Perfluorobutanesulfonic acid 
8. 1H,1H, 2H, 2H-Perfluorodecane sulfonic acid 
9. Perfluorodecanoic acid 
10. Perfluorododecanoic acid 
11. Perfluoro(2-ethoxyethane)sulfonic acid 
12. Perfluoroheptanesulfonic acid 
13. Perfluoroheptanoic acid  
14. 1H,1H, 2H, 2H-Perfluorohexane sulfonic acid 
15. Perfluorohexanesulfonic acid 
16. Perfluorohexanoic acid 
17. Perfluoro-3-methoxypropanoic acid 
18. Perfluoro-4-methoxybutanoic acid 
19. Perfluorononanoic acid 
20. 1H,1H, 2H, 2H-Perfluorooctane sulfonic acid  
21. Perfluorooctanesulfonic acid  
22. Perfluorooctanoic acid  
23. Perfluoropentanoic acid 
24. Perfluoropentanesulfonic acid 
25. Perfluoroundecanoic acid 

Method 533: Sample Collection and Preparation

The drinking water samples should be collected in single use plastic water bottles which can either be made of polypropylene or polyethylene. The size of the bottle should be equal to the size of the sample required since subsampling from the same bottle is not permitted. Lab staff must wash their hands thoroughly before handling the samples. They must also don nitrile gloves. The sample is collected by running the tap and allowing it to flush until a stable temperature has been achieved. Proceed to cap the sample bottle and add the preservative, ammonium acetate in this case, at a concentration of 1g/L. Now agitate the bottle to dissolve the preservative and store it sealed until the time for extraction, which should not exceed 28 days.

Method 533: Testing Method

The testing begins with fortifying the sample isotope analogues of the method 533 analytes. The isotope diluted sample is then passed through a positively charged polystyrene divinylbenzene SPE cartridge to extract the method 533 analytes. The cartridge is then rinsed with ammonium acetate and then eluted from the solid phase  using a mixture of methanol and ammonium hydroxide. The extract is dried in a heated water bath with nitrogen and analyzed using LC-MS/MS technique. The isotope dilution technique is used to calculate the concentration of each analyte. 

Method 533: Data Analysis and Calculations 

Data analysis and calculations for method 533 depend on the different types of standards that are usede. This is because the samples can contain both branched and linear isomers of the analytes but quantitative standards for branched isomers to match all the method analytes do not exist. 

PFAS are common contaminants in drinking water that can jeopardize public health and cause some types of cancers. Therefore, EPA prioritizes water testing to safeguard public health and well-being. A LIMS for drinking water labs helps keep track of all samples throughout their entire life cycle, manage tests and test results, generate custom certificates of analysis (CoAs), and report results to customers and regulatory agencies. Furthermore, a LIMS supports drinking water testing labs in meeting quality control requirements and compliance goals while reducing the turnaround time.

Method 533 -An Improvement over Method 537

While methods 537 & 533 have many similarities, EPA has made significant improvements to the latter to improve the accuracy and effectiveness of lab methods in testing for PFAS in drinking water. For starters, method 533 is able to test for 11 additional PFAS over its predecessor. However, it is important to note that a few PFAS that are tested under method 537 are excluded in method 533. Together, methods 537 & 533 can measure a total of 29 PFAS in drinking water.

Another key difference between the two methods is the holding time for each. While method 537 allows 14 days for extraction and analysis, method 533 allows up to 28 days for the same. Lastly, method 537 uses Trisma as a preservative while method 533 uses ammonium acetate. Hopefully, the improvements made upon method 533 will lead to better detection of PFAS with the overall aim of improving the safety of drinking water for humans from all walks of life.