See No Evil, Speak No Evil, Synthesise No PFCs


Since the EU banned C-8 PFC compounds back in 2016, the resolution seemed easy: begin using C-6… Now post-Brexit, whispers of C-6 being next grow louder. The scientific community is still reeling at the original loss and continues to scramble to find a suitable alternative. This comes with the context of environmental agency and councils eliminating longer-chain PFCs C10 and C13 back in 2004.

So, what actually are C-8 compounds? What was the cause for the most recent ban? And more importantly, will we ever be able to clean up the mess left behind from the ‘forever chemicals’?

C-6, C-8, C-10 and C-13 are all specific compounds that can be placed under the umbrella term ‘PFCs’ or Perfluorochemicals. Due to their strong intermolecular bonds, they make great coatings for anything that has to repel liquids, moisture, heat or stains—however, these strong bonds also mean that they are hard to break down.

The issue posed was popularised by the 2019 film Dark Waters, retelling only a few anecdotes of Dupont factory workers in West Virginia who sued the big Pharma corp for allowing PFCs to contaminate local water sources and soils knowing they were persistent and dangerous. (They won the suit in 2017).

Let’s break down the causes of why they’re so bad:

Fluorine as an element is extremely electronegative: when bonded, it wants electrons. When bonded to carbon, an electroneutral element (tending to share electrons when bonded), it causes a substantial polarity/dipole moment: the electron density is so intense around the fluorine atom that it leaves the carbon being electron-poor. This creates the ionic charges described in the diagram below.

Diagram of ionic bond between carbon and fluorine
Credit: Benjah-bmm27, Public domain, via Wikimedia Commons

Both are perfect for each other; the carbon is attracted to the negatively charged fluorine, and the fluorine is attracted to the positive carbon. Comparing this to any other carbon-halogen carbon-hydrogen compound, it’s the strongest organic bond for miles.

PFOA (C-8) like the other isotopes have a hydrophilic head and a long, hydrophobic tail of strong carbon-fluorine bonds. This is the reason for PFCs ability to be persistent but water-soluble, simultaneously. Long-chain PFCs (the C-10s, C-14s and over) are known to be even more persistent due to their longer hydrophobic tail and are harder to get rid of, hence their earlier ban than the shorter chains (C-8, C-6) which arguably degrade quicker—if you consider three years of a hazardous chemical persisting in the human body quick.

Historic studies have always shown PFCs can accumulate in mammalian blood proteins, soils and water sources whilst posing a risk of cancer and foetal deficiencies. Specifically in America, where the pharmaceutical and chemical industry is largely privatised, this knowledge hasn’t made much of a change. A recent mass biochemical survey found PFCs were at notable levels in 97% of Americans’ blood.

Whilst banning certain PFCs is good, what do we do with the outstanding waste? There are seemingly two answers: the ol’ tried-and-tested activated carbon and nanofiltration.

  1. Activated carbon provides a large surface area to which hazardous contaminants can adsorb onto. Granular activated carbon (GAC) is made from organic materials with high carbon contents, like wood, lignite, and coal. Through investigation it’s shown to effectively remove PFCs from drinking water when used in a flow-through filter mode, after larger particulates have already been removed. It’s not quite the one-answer resolution we want though, as GAC seemingly has the restriction of not being able to absorb short-chain PFCs.
  2.  Nanofiltration is a proven effective method of treating PFC-contaminated water.  Nanofiltration can remove the PFC particulates whilst keeping the good minerals in tap water. However, this method isn’t very scaleable: each membrane needs to be created for the specific PFC present in the water or soil, and only so much water can be run through the filter each time before it requires maintenance.

An important message to learn from the legacy of PFCs is composites should never be used commercially without a comprehensive understanding of their chemical properties, no matter how tempting. As we stare at the potential ban of yet another repellent without a known alternative, are we predetermined to repeat history? Will we find ourselves using another chemical in haste to meet demand?


2nd year Chemistry student, so I ramble alot.

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