5 ms·
This is an exaggeration, of course. The EPA guideline of 70 ppt for PFAS is probably just too low compared to other standards. For example, a Canadian guideline
by cato_the_elder 4y ago
This is an exaggeration, of course. The EPA guideline of 70 ppt for PFAS is probably just too low compared to other standards. For example, a Canadian guideline suggests an MAC of 200 ppt for PFOA, and 600 ppt for PFOS. These are the most common PFAS. Also, these are based on a lifetime exposure, and short term exposure to these amounts is probably not particularly harmful.
Additionally, even in the US, the guidelines by the individual states vary between 13 to 1000 ppt. [2]
[1]: https://www.canada.ca/en/services/health/publications/healthy-living/water-talk-drinking-water-screening-values-perfluoroalkylated-substances.html https://www.canada.ca/en/services/health/publications/health...
[2]: https://www.nature.com/articles/s41370-018-0099-9 https://www.nature.com/articles/s41370-018-0099-9
- koheripbal 4y agoHow can we have a guideline for ALL PFAS? They are all completely different molecules with different Hazzard levels - likely many safe. These generalizations make conversations about them useless.
- superchroma 4y agoThere is insufficient evidence for "likely many safe". You can't just start throwing that around.
- koheripbal 4y agoThe burden of evidence is demonstrating that they are each unsafe. Lumping a hundred chemicals under a label and then claiming that any time ANY of them are found that they are harmful, is dishonest.
- djbusby 4y agoWhich generalization should we change ? The "they aren't safe" or the "likely many safe" one?
- eurasiantiger 4y agoThe guideline is 0.02 ppt for PFOS and 0.004 ppt for PFOA.
- cato_the_elder 4y agoI think you have the units, the number of the zeroes, and and the actual figures wrong. Each µg/L is 1,000 ppt (part per trillion, i.e. ng/L).
- eurasiantiger 4y agoNo. 1 µg/L = 1,000,000 ppt 1 ng/L = 1,000 ppt You can find the figures here: https://www.epa.gov/sdwa/questions-and-answers-drinking-water-health-advisories-pfoa-pfos-genx-chemicals-and-pfbs#q5 https://www.epa.gov/sdwa/questions-and-answers-drinking-wate... Rain water and ocean spray already exceed these limits by hundreds of thousands to several million times.
- cato_the_elder 4y ago> 1 ng/L = 1,000 ppt I don't think so. See here (the green box in the upper right corner of page 2): https://www.epa.gov/sites/default/files/2015-09/documents/epa816f15001.pdf https://www.epa.gov/sites/default/files/2015-09/documents/ep... > nanograms per liter (ng/L) = parts per trillion (ppt) Or alternatively: https://pubs.usgs.gov/circ/circ1133/conversion-factors.html https://pubs.usgs.gov/circ/circ1133/conversion-factors.html
- eurasiantiger 4y agoI don’t know what to tell you. Is this one of those billion/trillion differences again? In that case the EPA values are definitely off by a factor of 1000 when compared to SI units, so maybe rainwater is then only some hundreds to some thousands of times over the limit. https://www.google.com/search?q=1+ng%2FL+in+parts+per+trillion https://www.google.com/search?q=1+ng%2FL+in+parts+per+trilli...
- justbored123 4y ago
- jcrben 4y agoSince PFAS never really breaks down and we're still creating it, is a 200 ppt inevitable at some point?
- superchroma 4y agoThe scary thing for me is that it's in the rain, so it'll be in crops, water reservoirs, trickling into the water table and into drinking supply. We have to stop this right now.
- bob1029 4y ago> You can't use techniques like distillation to remove PFAS Can we get a citation on this? I’m not a chemical engineer, but distillation seems like a pretty good way to get rid of virtually everything.
- superchroma 4y agoI'm sorry, I had it wrong. I've checked my facts. It works. This is actually a relief for me.
- loosescrews 4y agoRain is a form of distillation.
- superchroma 4y agoThis is a good point. I don't know what to think now. I presume 3M isn't spraying this stuff into the air as an aerosol.
- tadfisher 4y agoPFAS components do end up in the atmosphere from the manufacturing process, which is how it precipitates (droplets nucleate around the airborne particles). Same story with any particulate emissions, like soot, dust, tires, etc.
- specialist 4y agoI'd settle for 0 ppt.
- southerntofu 4y agoI'd settle for what's already here and it's too late, but stop this industrial madness right now without further delay.
- bergenty 4y agoResearch suggests even the EPA recommendation is too high.
- Panoramix 4y agoWhat short term exposure? if it's in the rain in Antarctica then you can bet it's in your water, vegetables: it's likely a lifelong exposure.
- spywaregorilla 4y agoGuidelines for all of these things individually seem to ignore the likely unstudied possibility that they have synergistic effects. Or even just additive effects because many of them are so similar to each other.