Finding a Fumigant

Looking back at my time as a laboratory-based microbiologist, I spent most of my career using formaldehyde to fumigate microbiological safety cabinets, high containment level areas and cleanrooms. I performed my first fumigation of a microbiological safety cabinet in 1999 and even then there was talk of formaldehyde being banned for use as a fumigant. It has been suspected for many years that formaldehyde is carcinogenic, so why it has taken so long to be classified as such is a mystery. It is only now, thanks to a combination of REACH regulations and the Biocidal Products Regulation, that its days of use in the EU as a fumigant in “public areas” are numbered. That decision is due imminently and may already have been announced when this article is published...

Many companies have long since moved away from formaldehyde, but others have stuck with it for a number of reasons – cost, of course, is one of these, but so too is the time and resources required to research, trial and validate a new system. Time is money and revalidating a whole site or facility means a lot of down-time. Had I stayed in my previous post, attempting to arrange the time to revalidate those labs with the area managers would have been a total nightmare – and the inconvenience of a lengthy shutdown for them would have been close to intolerable. Two of the alternative chemicals, peracetic acid and chlorine dioxide, both produce highly toxic and possibly corrosive chemicals when they react with formaldehyde. Formaldehyde can linger in HEPA filters for many months post fumigation, so they need to be replaced even before a trial, let alone a validation, which increases the expense significantly.

The reason to move away from formaldehyde is ultimately a health and safety one, so what should companies still using formaldehyde turn to now? Larry Joslyn describes the ideal fumigant as one that should leave no residues, or that can be rapidly removed to safe levels following fumigation (1). There are plenty of systems available that claim ‘no residue’ and ‘rapid removal’ post fumigation. Each manufacturer or distributor provides – as part of the product literature – papers written in conjunction with customers claiming to prove the effectiveness of their system. As a customer, I would be a little skeptical; few (if any) manufacturers will publish data that suggest their system is not effective. For me, there are too few independent comparison studies of fumigation systems. So many ‘studies’ seem to come from a distinct angle: extolling the virtues of a favored system. Which one are you going to believe? That was always my conundrum when seeking systems to replace formaldehyde.

The choice of chemical was of greatest importance. It has to show the desired efficacy against the microorganisms handled in those laboratories. In a facility handling pathogens, the chemical chosen has to be effective against the most resilient pathogen the facility handles in the event of a spillage of a high-titer culture. Regarding the efficacy of these fumigation systems in that scenario, there are few papers available that use simulated spills – and most studies take place in pristine cleanrooms where there are few variables to affect the results. Using a substitute organism to replicate a spill puts the operator and the room it is being performed in at risk, so those studies are few and far between.

I would say that choosing a fumigation system in a facility that doesn’t handle pathogens is considerably easier than one that does, based on the requirement of efficacy against particular pathogens. However, here is another factor that may muddy the water: I’ve heard some say that the existing standard of achieving a 10,000,000 kill of spores is too harsh, partly because cleanrooms don’t have that spore level. In addition, there is a danger of false positives because of the way biological indicators are made. Personally, I can’t see the regulators changing those regulations, as the worst-case scenario must always be considered.

If I had to choose a new fumigation system, my feeling is that there is a lack of independent data out there giving a more transparent comparison of fumigation methods. Whatever system you choose I hope that it is appropriate for your needs and ultimately works to your specifications.