So, what on earth IS happening to phosphine fumigation PART 2

In the last part of this series I went through the fundamental change to phosphine registration- one treatment "per batch."

This was due to concerns of pesticide residue in food which is a fair shout. The manufacturers of metal phosphides have had some independent testing done and the results are currently being ratified by BAuA in Germany. We await their conclusions with baited breath!

So, what about the other changes?

2. The Workplace Exposure Limit for phosphine gas has been reduced to 0.01ppm. That means that any level above 0.01 parts of phosphine in one million parts of air is now considered toxic.

This is basically as close to zero as we can get. It used to be 0.1ppm, what has changed? Why has this gone down by a factor of ten?

The funny thing is, when it first came out, we all just thought this was a typo! Sadly, it turns out we were wrong. It's all to do with the latest Biocidal Product Assessment for Phosphine (PT18) Link below:

http://dissemination.echa.europa.eu/Biocides/ActiveSubstances/0004-18/0004-18_Assessment_Report.pdf


What happens during these Biocidal Product assessments under Directive 98/8/EC? Good question! I'm sure you ask that question most days...

Every biocidal product has to be assessed for toxicity, obviously. The boffins have to work out that the biocide will do its job effectively. Well, it turns out that it would be expensive (and presumably massively unethical) to re-do a lot of toxicity tests every time a toxic product gets re-registered.

Some oddball, back in the 1998, did the nasty work for us and subjected captive rats to levels of phosphine over 90 days in one test and 1 year in another(!) to assess its toxicity. Wow, 90 days is a long time but I suppose science is science and who am I to question their methods?

So, during a Product Assessment under Directive 98/8/EC the modern (office based) regulatory professional leaves the science in the labs and just adjusts the old toxic levels using an adjustment factor (for some reason they picked x100) to be more in line with modern standards. If they are working from historical animal studies, they use a factor of 100. If they are working from historical human studies, they use a factor of 10. If this all appears to be picked out of thin air that's because.... (insert conclusion here).
The end result of this is that phosphine now has a WEL of 0.01ppm
There are three areas where this change might become significant

1. Receiving shipping containers from abroad that have been fumigated
2. Receiving ships from abroad that have been fumigated
3. Picking the correct RPE to keep operators safe- is it possible?
4. Detecting phosphine down to 0.01ppm- is it even possible?

Cargo in Containers
No issue here.... except.... as I've mentioned in previous articles, phosphine is a slightly sticky beast. It has a free electron pair and some un-charged covalent bonds,

If you have received fumigated cargo that has any carbon chains in it (here we are thinking any natural substance) there will be some phosphine sticking to it with weak hydrogen bonds. So, rice, fruit, beans, peas, cereals, feed, wood, seeds, oil will all have a sticky layer of phosphine on it.

This is not a problem because fumigators will clear containers until they are free of phosphine gas. The problem comes when they seal the containers back up to deliver them to customers and all of a sudden the desorbtion of phosphine from the cargo creates a toxic atmosphere inside the container again, just ready for a forklift truck driver to rumble in...

This means that a secondary checks should be made before and during unloading. Otherwise who is to tell that warehouse workers aren't being subjected to chronic fumigant exposure at levels that are now deemed illegally high.

Bulk Cargo in Ships 

This tends to be where the most phosphine accidents happen. There appears to be an accident about once a year with cargoes setting on fire, dock workers being exposed to toxic gas and even seamen and superintendents being killed. So we have to be very careful around bulk fumigations on ships.
The workplace exposure limit is now 0.01ppm. Can a fumigator really claim to have reduced the gas levels throughout a bulk cargo to those levels?

At Dealey we screw in spearators to lower the levels quicker but, to my knowledge, we are the only guys in England doing this. With gas distributed ten metres down into grain at levels of 200ppm, how is it possible to clear a bulk ship without being present for the duration of the unloading process or by doing some serious probing?

With the best will in the world, we can probe to about 4 metres, beyond that, it's a struggle. Really, the only way to clear a cargo down to the safe levels required is now a stop-start unloading operation and the presence of a trained fumigator throughout. Anything else and the stevedores and seamen will be exposed to phosphine at >0.01ppm.

Picking RPE for 0.01ppm

As if all the above wasn't arbitrary enough, there is more to consider with the RPE (respiratory protection equipment) protection factors used across the EU. If you thought these were standardised and everyone had the same rules, you would be wrong.

The standard B2P3 mask we use in the UK has a protection factor of 20x. That means that if the WEL is now 0.01ppm, an operator will only be protected to 0.2ppm. This is well below the levels that fumigator may encounter. So what were they thinking at BaUA when they made this change, surely it can't be practically implemented...?

Well, it transpires that the protection factor of exactly the same filter mask in Germany is...400x !!!!
So our German colleagues are protected to 4ppm. Using the same equipment. Entschuldigung, that is weird.

We have been asking for clarification on this point and have been given an array of purely arbitrary answers which I won't go into here. The conclusion always remains the same- if you are operating in the UK, just use SCBA. The fact that SCBA used in grain sinks a technician up to his waist, increasing the likelihood of overheating, subsidence, engulfment and suffocation is apparently not an issue.

We have politely declined to adopt this advice and we are currently refining our methods for engineering controls instead.

Detecting phosphine to 0.01ppm 

If you have got this far, I salute you. I've had to write this piece in several sittings just to avoid getting too depressed.

Detecting to 0.01 ppm of phosphine is possible, even easy, in a lab. Try it in the field though, there's way too much swirling wind and mild fluctuations to get reliable results. The only apparatus on the market that can claim to take field measurements down to 0.01ppm is the German manufactured Drager PAC7000.

The only problem with this piece of kit is- it has a margin of error of ± 0.02 ppm. I don't think I need to elaborate on this point any further. "You do the math," or as we say in Suffolk "do you the maths."

In Conclusion

There are always changes made to regulatory approvals which will have an effect on the practicalities of the application of any biocidal substance. The regulators will make the change then wait for the push-back. If the push-back is non-existent or small enough to suggest small changes, they have done their job well.

Ergo, it is up to us as an industry to make as much noise as we can to show just how impractical these changes are. Feel free to take this article and any others I write and nail them to the doors of churches, I'm sure all sorts of counter-arguments and difficult questions will emerge, but at least we are pushing and, hopefully, the (normally so diligent) regulators will see that this time they have fallen well short of the mark.

Thanks for reading.