Monday, May 16, 2016

What chemists hear, when physicians talk about chemicals

Also in this week's C&EN, Jessica Morrison looks at PFOA and PFOS in drinking water. Here's a quote from prominent critic of the chemical industry, Dr. Phillippe Grandjean, a physician and adjunct professor of environmental health at the Harvard School of Public Health: 
“People started looking over the last 10 years for adverse effects” from exposure to PFOA and related compounds, says Philippe Grandjean, an environmental health scientist at Harvard T.H. Chan School of Public Health who studied immunotoxicity in children and found a link between exposure to perfluorinated compounds and weakened response to vaccines. “We were thinking in the beginning that a carbon chain wrapped in fluoride ions seems like it won’t do anything. It’s certainly very stable, but the question is, will it interact with biological molecules and cause any adverse effects?”
It's not completely fair to criticize Dr. Grandjean for not quite getting the terminology right for perfluorinated alkyl compounds*, but it sure does grate on my ears.

*"a carbon chain bonded to fluorines" would have been perfectly fine, for example.

10 comments:

  1. Considering Dr. Grandjean is a professor in the School of Public Health, and the public health controversy (real or imagined, I'm not commenting on that) with fluoridated water, this seems like a poor choice of words. I can see the FB posts quoting this physician, as it already has the fluoride, vaccine and exposure buzzwords.

    ReplyDelete
  2. My thought is that it would do whatever an F- anion would do. By a carbon chain wrapped in fluoride ions I assume that you mean a cationic carbon chain with F- as the counterion (i.e. an alkyl chain with NH3+ groups or the like). If you mean a fluorocarbon, then I would suspect that it would have very low biological activity. However, there are multiple enzymatic pathway that could potentially degrade these into toxic downstream products... not being an expert in fluorocarbon metabolism I cannot make an intelligent/(non)snarky comment.

    ReplyDelete
    Replies
    1. Interestingly, I would have agreed about the low bioactivity of perfluoroalkyl compounds, but there seems to be enough indirect evidence that there's something there, there. How much, I dunno.

      Delete
    2. Multiple enzymatic pathway is a possibility! But the presence of fluorine atoms (geminal) pretty much kills the beta oxidation path that is available. And, who knows may be that PFOA and PFOS may be suicide substrate in a manner similar to trifluoroacetic acid!

      Delete
  3. From my dim and distant memories of fluorine chemistry I recall that fluorinated analogues can bugger up enzymes and the like due to fluorine's similar atomic radius to hydrogen but very different chemistry (I'm sure the fluorine chemist who taught me this is now squirming). Certainly possible that fluorinated hydrocarbons could have some activity.

    My view of the description is that it is definitely a faux-pas. Scientists need to use the right terminology when talking about something otherwise it implies they don't understand it properly (as my paragraph above probably demonstrates). The key question in my mind when hearing this is - are these the right people to be doing this research? Are they working with chemists who using fluorine chemistry in making biologically active compounds? I'm now concerned that there methodologies may not be robust and consider all factors.

    ReplyDelete
  4. Perhaps Dr. Grandjean's experience in his Organic Chemistry course was unpleasant and he purposely uses incorrect terminology to irritate his former tormentors. It's like conservative talk show hosts who refer to the Democrat (not Democratic) party.

    ReplyDelete
  5. Kind of unfair to comment on it... except every high schooler who studies chemistry (as is required for medicine) could tell you a fluorocarbon is unlikely to be ionic. Not trying to be too harsh, but...

    ReplyDelete
  6. PFOA is a surfactant, containing a hydrophilic carboxylic acid end and a long hydro- and oleophobic tail. That, by the way, is exactly why it is used in the aqueous emulion poly,erization of TFE to make pTFE. Why would we immediately jump to the conclusion that it would be inert/harmless? Long chain quat surfactants are excellent biocides, for example.

    ReplyDelete
    Replies
    1. Great question, but I did - and it sure appears that I was wrong.

      Delete
  7. PFOA is an endocrine disruptor, that is, it binds to receptors for horomones. like many hormones, it has a rigid lipophilic structure with a polar head. It affects lipid metabolism, and causes peroxyzome proliferation, leading to oxidative stress due to damaging free radicals. Since it is lipophilic and difficult to metabolize, it bioaccumulates over time, yet it has enough water solubility that it can easily get into things that we consume. Longer chains are less soluble and less available in the environment, while shorter chains are more easily excreted, so these are less of a problem even if they have the same toxicity.

    ReplyDelete