PFAS in tap water - overview of concentrations
Recent reports of PFAS in tap water are worrying. What levels are really an issue?
I recently wrote a post on PFAS. Though I started off by looking at synthetic and DWR clothing, it ended up being quite a general overview on PFAS.
Ultimately it is at its highest risk if it is in water which is being consumed by humans. Also PTFE coated pans are a concern.
Not surprisingly though reddit is up in arms over the recent reports of PFAS in tap water and even bottled water.
Terminology
PFAS - a family of ~5k molecules, which are made of fluorine and carbon and usually have an extremely long shelf life.
PFOA, PFOS, C8, C8, PFHxS, PFNA - some of the 5k molecules, all under the PFAS family (this one is confusing!)
1 PPM (=mg/L) = 1,000 PPB (=ug/L) = 1,000,000 PPT (=ng/L)
PFAS in drinking water and wells
Here are some extracts:
Sparkling water up to 10 ng/L (=10 PPT): https://www.reddit.com/r/coolguides/comments/13eqpcl/pfas_in_sparkling_water/
PFAS tap water in France up to 140 ng/L (=140 PPT):
https://www.reddit.com/r/PFAS/comments/17ixams/what_i_feared_is_reality_now_pfas_straight_from/
PFAS in the wells around Spokane up to 5200 ng/L (=5.2ug/L=5.2 PPB):
https://www.seattletimes.com/seattle-news/environment/pfas-is-in-the-groundwater-west-of-spokane-whats-known-about-the-contamination-is-only-growing/
Generally high levels around military bases. Article mentions 2.25 million PPT? That would be equal to 2.25 PPM. That’s a lot: https://www.theguardian.com/environment/2023/oct/13/pfas-pollution-us-military-bases-forever-chemicals
Ok, that last number is actually quite insane. I am not super certain on the 2.25 PPM - the article is not very explicit and mentions that number only once as “2.25m”. Is that m really millions?
Looking at numbers, what levels are dangerous?
Going back to the research in the previous post, animal studies indicate:
PFOS, one of the more dangerous compounds shows increased risks from 0.001 mg/kg/day. That’s 1 ug/kg/day which is equal to 1 PPB/kg/day. For a person of 70kg, that’s 70 PPB a day.
The MRL (maximum allowed levels) of PFOS are 0.000002 mg/kg/day. That’s actually 1 PPT/kg/day. For a 70kg person the maximum allowed exposure is 70 PPT / day.
To recap:
Animal studies show damage from 70 PPB of PFAS a day;
Allowed levels, which build in additional safety margin are 70 PPT of PFAS a day.
These levels are for PFOS, which has some of the higher risks of the known PFAS compounds. Not all compounds are fully understood, and there could be more of the ones with bigger risks.
While I am no health expert, the numbers speak for themselves. I probably would not be super worried for myself about a 10 PPT sparkling water. I would really be worried if I was drinking from a 2 PPM well.
The broader environmental impact
One thing I did not get into is the broader environmental impact. In cases where there is no immediate danger to humans, the PFAS tend to still eventually accumulate in the soil, posing a potential risk to the nature and animals. Since these compounds are essentially eternal, we might reach a breaking point through accumulation in the soil at some point.