EPA has posted a technical advisory on its approved drinking water analytical method (EPA Method 537 Rev. 1.1) for perflourooctanoic acid (PFOA). The advisory clarifies analytical instructions that were being interpreted differently by various laboratories, leading to underreporting of PFOA levels found in some drinking water samples.
At issue is whether labs are quantifying only the linear isomer or both linear and branched-chain isomers during analyses to determine PFOA concentrations. The advisory clarifies that both isomer types should be quantified to prevent underreporting true PFOA concentrations. The advisory also clarifies how available PFOA standards can be used to account for mixed isomers since no certified quantitative mixed standard for PFOA currently exists.
Although there has been underreporting of PFOA concentrations from some labs, EPA’s analysis of the issue shows that the omission of branched isomers from PFOA analyses has a relatively minor effect on reported total concentrations. In particular, EPA has determined that the effect is not significant enough to warrant resampling of PFOA under the Third Unregulated Contaminant Monitoring Rule.