3 ms·

I wonder if this has to do with limits being set below the detection limit of existing technology.

alan-hn 2y ago
Why do you think they would set limits below the LOD for existing techniques? I assume the EPA of all organizations understands current chemical analysis technology
amarant 2y ago
More likely it's companies selling drinking water who don't want to spend money on quality..
hanniabu 2y ago
Even if that was the case, that would just mean anything detectable is over the limit. Pretty simple.
- emestifs 2y ago
  3.6 ppb, not great not terrible[1] [1]: https://www.youtube.com/watch?v=w-YDV6vC2qo https://www.youtube.com/watch?v=w-YDV6vC2qo
hwillis 2y ago
Wrong. The EPA limit is 4 ng/L for PFOA and PFOS: https://www.epa.gov/system/files/documents/2024-04/drinking-water-utilities-and-professionals-technical-overview-of-pfas-npdwr.pdf https://www.epa.gov/system/files/documents/2024-04/drinking-... An off the shelf Agilent spectrometer with EPA approved methods can detect PFOA at .28 ng/L and PFOS at .78 ng/L: https://www.agilent.com/cs/library/applications/application-analysis-legacy-and-emerging-pfas-water-1290infinity-6495btriplequad-5994-0919en-agilent.pdf https://www.agilent.com/cs/library/applications/application-... This limit is not even the lowest EPA limit in drinking water. Radium is limited to ~5 picograms per liter, 1000x lower that the PFOA/PFOS limit. Dioxin is 0.03 ng/L. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations https://www.epa.gov/ground-water-and-drinking-water/national...
- mensetmanusman 2y ago
  I see, their prior recommendation in 2022 was 0.004 ppt or ng/L, so they backed away from being an order of magnitude below the detection limit. Thanks for the update!
  - hwillis 2y ago
    It was a health advisory in 2022, and it was revised from .004 ppt (note that you are off by an order of magnitude) to zero. Per the EPA: > Drinking water health advisories (HAs) provide information on contaminants that can cause human health effects and are known or anticipated to occur in drinking water. *EPA's HAs are non-enforceable and nonregulatory* and provide technical information to drinking water system operators The update was because of additional evidence of cancers. The EPA always acknowledged that .004 ppt is not reasonably detectable, but the point of an advisory is to note the level that is evidenced to be dangerous. Its a goal, and the new goal is "as good as possible". It should be obvious why the EPA should set requirements to reduce toxins while also noting what is a safe level. https://www.epa.gov/system/files/documents/2022-06/technical-factsheet-four-PFAS.pdf https://www.epa.gov/system/files/documents/2022-06/technical...

Why do you think they would set limits below the LOD for existing techniques? I assume the EPA of all organizations understands current chemical analysis technology

amarant 2y ago

More likely it's companies selling drinking water who don't want to spend money on quality..

hanniabu 2y ago

Even if that was the case, that would just mean anything detectable is over the limit. Pretty simple.

emestifs 2y ago
3.6 ppb, not great not terrible[1] [1]: https://www.youtube.com/watch?v=w-YDV6vC2qo https://www.youtube.com/watch?v=w-YDV6vC2qo

hwillis 2y ago

Wrong. The EPA limit is 4 ng/L for PFOA and PFOS: https://www.epa.gov/system/files/documents/2024-04/drinking-water-utilities-and-professionals-technical-overview-of-pfas-npdwr.pdf https://www.epa.gov/system/files/documents/2024-04/drinking-... An off the shelf Agilent spectrometer with EPA approved methods can detect PFOA at .28 ng/L and PFOS at .78 ng/L: https://www.agilent.com/cs/library/applications/application-analysis-legacy-and-emerging-pfas-water-1290infinity-6495btriplequad-5994-0919en-agilent.pdf https://www.agilent.com/cs/library/applications/application-... This limit is not even the lowest EPA limit in drinking water. Radium is limited to ~5 picograms per liter, 1000x lower that the PFOA/PFOS limit. Dioxin is 0.03 ng/L. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations https://www.epa.gov/ground-water-and-drinking-water/national...

mensetmanusman 2y ago
I see, their prior recommendation in 2022 was 0.004 ppt or ng/L, so they backed away from being an order of magnitude below the detection limit. Thanks for the update!
- hwillis 2y ago
  It was a health advisory in 2022, and it was revised from .004 ppt (note that you are off by an order of magnitude) to zero. Per the EPA: > Drinking water health advisories (HAs) provide information on contaminants that can cause human health effects and are known or anticipated to occur in drinking water. *EPA's HAs are non-enforceable and nonregulatory* and provide technical information to drinking water system operators The update was because of additional evidence of cancers. The EPA always acknowledged that .004 ppt is not reasonably detectable, but the point of an advisory is to note the level that is evidenced to be dangerous. Its a goal, and the new goal is "as good as possible". It should be obvious why the EPA should set requirements to reduce toxins while also noting what is a safe level. https://www.epa.gov/system/files/documents/2022-06/technical-factsheet-four-PFAS.pdf https://www.epa.gov/system/files/documents/2022-06/technical...