"On what grounds have you decided a fume event is a "low level" exposure?"
I am not aware of a reported fume event which has resulted in the signs and symptoms of acute or sub-acute organophosphate poisoning.
From Wikipedia: "The effects of organophosphate poisoning on muscarinic receptors are recalled using the mnemonic SLUDGEM (salivation, lacrimation, urination, defecation, gastrointestinal motility, emesis, miosis. An additional mnemonic is MUDDLES: miosis, urination, diarrhea, diaphoresis, lacrimation, excitation, and salivation."
See also:
Organophosphate Toxicity: Background, Pathophysiology, Epidemiology
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493390/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3217786/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4238091/
But I do of course stand to be corrected.
Please note that I am NOT denying that this, or lesser events can occur or may have occurred - it is just that I am not aware of them, nor have I been able to find any verifiable accounts in an aviation context.
I believe that a paper was referenced in a a previous thread where wipe/swab tests were done on cabin surfaces to check for organophosphate residues - the results were negative as far as I recall - I'm sorry that I did not make a note of it so that I could include it in our database.
[BTW, chronic a/o low-grade OP poisoning is more commonly seen in agricultural workers and I specifically teach my students to inquire about such exposure in patients who present with odd symptomatology, since this may mimic a confusing number of disorders]
I believe that it is most important to establish the truth or otherwise of these anecdotal reports (I fly [as SLF] too!).
Finally, a little story about the clinical importance of of observation and asking the patient where they come from and what they do or have been doing. In Casualty I was asked en passant to give an opinion on a woman with moderately severe right arm discomfort of subacute onset. Questioning revealed that she was an American tourist who had arrived the day before, and clinical observation showed a right arm that was slightly more swollen than the left and slightly darker/blueish in colour. My presumptive diagnosis of axillary vein thrombosis was confirmed on duplex ultrasound. She was treated and made a good recovery. She had, of course been carrying heavy luggage with that arm. AVT is uncommon (the last one I saw was 26 years ago), but it illustrates the importance of keeping your clinical wits about you and the essential clinical question unde venis? ["Where do you come from?])
