Hypochlorites (HClO) do in fact generate chlorine gas when mixed with dilute acids.

This is the basis of your decontamination process, the bacteria get killed by it. This happens in your swimming pool, in your toilet bowl and in your bacterial cultures and when you bleach your clothes (if you choose to use any hypochlorites). If you open a bottle of bleach and have a sensitive nose, you can smell chlorine.

BTW, your white blood cells use the same chemistry to defend yourself against bacteria.

While chlorine gas is toxic, remember that the dose is what makes a poison. With high enough doses you can kill someone with plain water. The hypochlorite solutions that are commercially available will not reach chlorine concentration where you would need to fear for your safety - if this is the underlying concern.

Thanks, Sonja. I guess I always thought it was reactive Cl-, not chlorine gas Cl2, that was responsible for destroying cells. I spend about two hours a week in a well-ventilated bacteria hood decontaminating liquid cultures grown in TSB. I am very sensitive to many chemicals, but every time I do this process I get light-headed, nauseous, my nose and throat and eyes burn and it aggravates my asthma and gives me a bad headache for the remainder of the day. When I get home on the day I do this process, my family says I reek like a swimming pool and I have to shower immediately to get rid of the smell, and the burning in my eyes and nose. I was explaining to a colleague about how sensitive I am to chemicals and used this as an example when they informed me that mixing many types of liquid broth and bleach will form noxious gases. They were concerned for my health... which in turn made me concerned. I don't know what else to do, as these cultures are highly infectious and must be bleached, and I'm already using a hood, but I thought I would look into the matter a little more. Thanks for you input.

Hi Cassandra,

First, if Cl- were active, you could use NaCl instead. If something smells it cannot be an ion, it must be a gas.

Second, when it comes to hoods, there are two different principles, chemical fume hoods and laminar air flow hoods and I have experienced that many people do not know the difference.

When using the first one, which is the right one when dealing with chemicals, you should not smell a thing, because all the air is sucked out of the hood and adjacent room into the vent above the hood, unless the hood is malfunctioning.

Laminar air flow hoods work differently. They filter the lab air through a HEPA filter in the hood and blow it at you. You should not be surprised to smell like a swimming pool when using this type of hood.

Such a laminar air flow hood would be appropriate to handle cultures in aseptic technique, but not for a chemical reaction that you are ultimately doing when bleaching your cultures.

Third, if you are concerned with your health, you should talk to your supervisor and the safety people in your work environment. They need to know to address it.

Thanks Sonja. I suppose you're right about the Cl-, I was apparently confused. We are using biosafety cabinets which incorporate BOTH laminar flow and a fume hood, which protects the samples and the technician. I work in all 3 types of hoods and know their flows very well. I guess I'm just really sensitive to the smell, but I'll make sure the BSC have been inspected this year. Thanks again for your input.

Dear Cassandra

I think that liberation of chlorine can happend if the pH of the culture media is acidic, as Sonja comented. Specially in media with high glucose, pH can decrease drastically due the cellular metabolism of sugars, they can produce high amounts of citric acid (levels should change depending of the microorganism). In my experience I never had problems with this matter, and I am not sure if the amount released can be toxic. I usually autoclave the culture media to sterilize. If you read something else, let me know

Hi Cassandra,

   I just finished mixing bleach with minimal media after growing E. Coli and it definitely stinks to high heaven.  I was looking for the reason when I found this thread. Bleaching LB and TB cultures doesn't seem to have nearly the same quantity of noxious fumes released, but minimal media cultures are a different story (ingredients: glycerol, glucose, phosphates, ammonia, amino acids). Maybe it's the bleach + ammonia combo?

-Jonathan W

Because of fumes, we use Lysol to disinfect the culture flasks after growing the plasmid prep. Make sure contact time is longer