WRAY4PAY

Over fifty years of data show a peak in PFAS (also known as "forever chemicals") content in seabird eggs in the 90s, followed by a decrease as regulations went into effect. The most recent findings show a 70% decrease of most common PFAS.

We are making genuine progress! Producers are dramatically altering how much they use PFAS and how much gets released in effluent, but also there's a lot better understanding of how to remove PFAS from the environment!

you can think of this sort of like how water wicks into a paper towel. the water gets stuck to the paper because it's attracted to it via capillary forces, even though there's no chemical reaction going on.

the two main methods used are granular activated carbon (GAC) adsorption and ion exchange (IX).

activated carbon is already pretty familiar to a lot of us; it's the stuff in a lot of replaceable water filters. the activated carbon has a huge internal surface area, and that allows for the fairly weak intermolecular forces to add up and allow contaminants to get "stuck" onto the surface of the activated carbon. over time, the activated carbon gets filled with junk, and you have to replace it.

GAC is essentially this, except that the activated carbon is granularized and produced in specific ways to maximize how much it attracts certain chemicals. this can be tuned because activated carbon gets its massive surface area from internal "pores", and various processes will change how large and frequent those pores are.

It's essentially a Russian nesting doll of pores, and controlling the size of the larger pores influences the permeability of the activated carbon and controlling the size of the smaller pores (micropores) influences what exactly is most attracted to the activated carbon.

However, GAC has a few major downsides:

It is not specific to PFAS. This is more of a mixed blessing because it was already frequently used and well understood, and the infrastructure for producing and distributing it already existed. However,

It loses effectiveness over time and must be replaced. This is a continued cost, albeit a low one, but this has one final major issue

As time goes on, the PFAS previously adsorbed to the activated carbon is desorbed and replaced by other things that have a higher affinity for the activated carbon.

As such, ion exchange (IX) was always very compelling. The whole point of it relies on the fact that PFAS molecules are predominantly made of two parts: An acid head group (either a carboxylic or sulfonic acid group) and a perfluorinated tail.

The head groups on the right are what become ionized—or specifically, deprotonated. A hydrogen leaves and is replaced with a metal cation (usually sodium), forming a PFAS salt (chemical meaning of salt!). These are much more soluble in water because of polarity reasons, and so the mobile PFAS molecules are almost always in that salt form.

By passing through these PFAS salts through a permeable polymer matrix that has (1) numerous positively charged groups like quaternary amines and (2) highly mobile negative ions loosely attached to those stationary positive groups (most often chlorides), you can actually get the PFAS to be "stuck" inside the polymer matrix and what comes out is just good ol' sodium chloride, or salt (culinary meaning of salt!).

This shows a version with hydroxide (OH-) ions as the mobile anion, but it's the same idea. The +NR3 in yellow are stuck to the polymer matrix, but the OH- can freely move around. However, without another anion to replace the OH-, the ionic attraction prevents the hydroxides from leaving.

In comes the PFAS. Despite being slightly soluble in water, the anionic PFAS aren't really that mobile, and when they pass through, it's much easier for the hydroxide ions to leave. Another very important effect is that the long perfluorinated tail of the PFAS is attracted to the polymer matrix, whilst the counterions are ONLY attracted via the ionic force. Thus, PFAS would much rather hang out in the polymer matrix.

Of course, IX has its own downsides

These resins are much more expensive, both to manufacture and to transport.

While they can be "regenerated", it's a tricky process that currently requires the use of nearly anhydrous methanol, which is both poisonous and extremely flammable, increasing the operating costs.

As the hydrophobic tail is a key part of allowing the PFAS to stick to the matrix, short-chain PFAS are very poorly dealt with by this system. This is exacerbated by competition between different PFAS molecules, as long-chain ones will cause short-chain ones to desorb.

Overall, the best method appears to be using a series of ion exchange resins followed by an activated carbon filter. The ion exchange will capture the bulk of the PFAS molecules, and the activated carbon will grab any stragglers. Effective filtering of other contaminants prior to the PFAS removal system will also ensure minimal competition in the activated carbon.

Quiet Air

Digital watercolor speedpaint. I don't usually use watercolor brushes so was just messing around with it.

She got the idea for the study while walking with her advisor at Stanford to discuss her thesis topic, and the paper she eventually published in the Journal of Experimental Psychology in 2014 is sharp enough that it should have ended the seated meeting on the day it came out.

She ran 4 experiments on 176 people. Same person tested twice. Once sitting, once walking. The creativity tasks were the standard ones psychologists have used for decades to measure how good a brain is at generating novel useful ideas.

81% of participants in the first experiment produced more creative ideas while walking than while sitting. In the second experiment, 88%. In the third, 100%. Every single person walked into a more creative version of themselves. On average, people generated 60% more novel useful ideas the moment their legs started moving.

The skeptical question is the obvious one. Maybe it was the fresh air. Maybe it was the scenery passing by. Maybe it was the change of environment doing the work, not the walking itself.

Oppezzo killed every one of those explanations with one experimental decision. She put people on a treadmill facing a blank wall. No scenery. No fresh air. No environmental change. Just legs moving in place while staring at white drywall. The 60% boost held.

Then she ran the experiment that closed the case completely. She took participants outside in two conditions. Half of them walked through a Stanford courtyard. The other half were pushed through the exact same courtyard in a wheelchair. Same outdoor stimulation. Same scenery passing at the same speed. The only difference was whether the legs were moving.

The walkers produced dramatically more novel high-quality ideas than the wheelchair group. The outdoors did almost nothing on its own. The walking did everything.

She also tested the opposite kind of thinking. Convergent thinking. The kind where there is one right answer and you have to narrow down to it. Word puzzles where 3 words share a hidden fourth word that connects them. The seated participants did slightly better on these. Walkers got slightly worse.

Walking is not a general intelligence enhancer. It does one specific thing. It opens up the divergent search inside your brain. The part that generates options. The part that produces unexpected connections. The part that takes a problem and finds five ways into it instead of one.

When you need to converge on the single right answer, sit down. When you need to find the answer in the first place, get up.

The mechanism is now well understood. Walking selectively activates what neuroscientists call the default mode network, the system inside your brain that runs when you are not consciously focused on anything. The DMN is where mind-wandering happens. Where memories cross-reference each other. Where ideas that have been sitting in separate folders inside your head finally bump into each other.

When you sit at a desk and force yourself to concentrate, you suppress the DMN. When you walk at a natural pace, the executive part of your brain gets just busy enough handling the walking that the DMN comes online and starts doing the work that focus was blocking.

The most useful finding in the entire paper is the one almost nobody quotes. The boost did not turn off the moment people stopped walking. Participants who walked first and then sat back down stayed elevated. Their next round of seated creativity work was still significantly better than people who had been sitting the whole time. The rest lingered for at least several minutes after the legs stopped moving.

You do not need to do creative work while walking. You need to walk before the creative work. The brain holds the state.