# Forever chemicals and blood donation

I saw a headline saying that donating blood lowers the level of forever chemicals in your body. This post will give a back-of-the-envelope calculation to show that this idea is plausible.

Suppose there are chemicals in your bloodstream that do not break down and that your body will not filter out. Suppose you have about 5 liters of blood and you donate 500ml of blood at a time, 10% of your total blood volume.

Presumably the blood you donate has the same proportion of forever chemicals as the blood you keep, so you lose 10% of your forever chemicals in a blood donation.

Assume you don’t absorb more forever chemicals after you start donating blood, and your body replaces the donated blood with new blood free of forever chemicals.

The quantity of forever chemicals in your blood after n donations is 0.9n times the original amount. How many donations would it take to reduce your level of forever chemicals by half?

We need to solve

0.9n = 0.5.

Taking logs we find

n = log(0.5)/log(0.9) = 6.58.

So after 7 donations, you should have reduced the level of forever chemicals in your blood by about a half. Assuming you donate every 8 weeks, this would take a little over a year.

This is just a simplistic calculation. The result could be inaccurate or even entirely incorrect for any number of reasons. But it does show that the idea that blood donation lowers forever chemical levels is plausible.

## 4 thoughts on “Forever chemicals and blood donation”

1. DV Henkel-Wallace

Uh oh, I donate my plasma regularly. They take the blood. Spin out the plasma and platelets, and put the rest back in my body.

2. I donate RBC regularly.

This is heartening, news, but one potential bit of shade: somethings do not remain in circulation, they may instead remain lodged in organ tissue.

I guess the good news is if I donate one of my kidneys, I’ve also cut my risk there in half.

3. Yeah, there’s both levels in the blood and levels in the organs. And there are other hormones and whatnot that control the relative levels.

I donate blood regularly to reduce iron buildup for similar reasons.

4. On the more plausible assumption that the forever chemicals are roughly homogeneously spread through the body (rather than in the blood only), then 500 ml of blood (about 500 g) represents only 1% or less (assuming average body mass of 50 – 70 kg). This means that 70 or so donations would be required to get to half…

But none of this matters anyway:the assumption that you can do this without concurrent intake is false. Forever chemicals are now Everywhere.

In 2022, it was found that levels of at least four perfluoroalkyl acids (PFAAs) in rainwater worldwide ubiquitously and often greatly exceeded the EPA’s lifetime drinking water health advisories as well as comparable Danish, Dutch, and European Union safety standards, leading to the conclusion that “the global spread of these four PFAAs in the atmosphere has led to the planetary boundary for chemical pollution being exceeded.

https://en.wikipedia.org/wiki/Per-_and_polyfluoroalkyl_substances