The articles about Californian water poison are all based on a report released by the Environmental Working Group, which basically just collated EPA and California state water data into one document
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The Environmental Working Group (EWG) is an unapologetically industry-funded organisation that tends to be against industrial chemicals of any kind (for example they are fiercely anti-GMO)pic.twitter.com/0IZKr4OYpJ
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What did the EWG find? Well, they collated a bunch of measurements taken across California over the last 10 years or so, and found amounts of PFAS ranging from 1.1-820.8 parts per trillion
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The reference for PFAS from the EPA, as well as a number of other international agencies, is 70 parts per trillion Immediately, this makes the headline less scarypic.twitter.com/PHSoOWTLUV
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This cutoff of 70 parts per trillion is a very conservative estimate, based on the lowest level that PFAS have ever been demonstrated to cause negative effects in a controlled study, divided by a wide safety margin
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About 2/3 of all of the measurements that the EWG report are below this threshold - in other words, most of California's water is SAFE based on the EWG's publication
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But it's even dicier than that You see, the EWG report the MAXIMUM levels of PFAS found in each of these locationspic.twitter.com/laYShHRqze
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If you have a look at many of these locations, you can see that the average levels are much lower - you can see them here https://sdwis.waterboards.ca.gov/PDWW/index.jsp
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Also, the EWG only reports selected well results, rather than the average of PFAS across each area This may not be representative of the water quality across the regions they picked!
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On top of all of this, there's the fact that we still aren't actually sure that PFAS do cause all of these problems, even at the reference dose (that's why it's not legally enforceable)
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TL:DR - There were some PFAS found in some places in California - Mostly much less than the EPA/CDC reference dose - Dose makes the poison - Your water is probably fine
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Oh also, because it's annoying, PFAS is not one chemical, it's a group of them (the S stands for "substances")
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