Bleach as a Steriliser

Hi @longinthetooth,
Thanks for starting this interesting topic and to everyone who has left a reply. You might find @JemmaCastle’s story on chemicals in cleaners of interest. We also review a variety of different cleaning products (about a third of which contain bleach).

When used correctly, household bleach is safe and breaks down quickly keeping the environment safe. However, make a mistake and it can be dangerous. Personally, when it comes to sterilisation, I opt for boiling water or steam cleaning equipment as it’s easier and a bit more pleasant on the nose.

2 Likes

@phb @trevor3
Trevor is technically correct. Bleach is not considered as being able to sterilise a product, it is only a disinfectant. There is a subtle difference here but it is important. To sterilise something you need to kill all organisms present (this includes viruses, bacteria, bacterial spores and fungi) but to disinfect you only have to remove most harmful organisms. (See table at http://www.diffen.com/difference/Disinfect_vs_Sterilize).Bleach (and the majority of chemicals) are only disinfectants as they are unable to kill all types of organism effectively. For example bacterial spores are often not killed by chemicals except at extreme concentrations. Most people use the terms sterilise and disinfect interchangeably but they do mean different things.
While bleach is effective, the overall effectiveness is affected by a number of factors including;

  • Acidity of the solution (not generally a consideration in household use)
  • The amount of organic material present (particularly proteins like blood) as bleach reacts with this material in doing its job and is quickly consumed from the cleaning solution and thus the solution loses effectiveness.
  • It evaporates from the solution and therefore needs to be replaced daily.
    A good discussion of this is available at http://oregonstate.edu/dept/larc/sites/default/files/pdf/chlorine-fact-sheet.pdf

Based on the information in the Oregon University fact sheet you would need about 100ml bleach in 1 litre to create a generally effective disinfecting solution for surface disinfection use. This is based on buying a 5% solution of bleach. It is important to be aware that the % bleach in a bottle you purchase is probably greater than the stated % when you buy it in the sealed bottle but the % will drop over time while stored in your cupboard. This is generally why bleach has a ‘use by’ date on it. The manufacturer has calculated that the % bleach will be at least the stated level up until this date.

2 Likes

The other major factor that affects the potency of bleach as a disinfectant, mould remover, etc., is that in most commercial bleach solutions they contain a surface active agent (watch them froth when agitated in water) that helps penetrate the bacterial or fungal cell wall, where a plain solution of Sodium Hypochlorite (bleach) [Milton has no surface active agent], might be ineffective. The surface active agent is usually what is called a non-ionic surface active agent that does not inhibit the actions of the main ingredient Sodium hypochlorite. Commercial bleaches may also contain stabiliser agents to prevent excessive loss of potency during storage. Not all bleaches are created equally.

1 Like

This highly technical blurb about Sterilisation vs disinfectant isn’t really the topic I raised.
In layman’s terms I have referred to the type of applications, eg, making swimming gear, toilets and baby bottles safer to use.
That although many products give the allusion that they are something special, in fact most are merely bleach!
Additionally we are told to avoid bleach for such purposes as it is harmful to the environment.
Further that that there is virtually no way a layman would know they are probably using a lot more than needed to do the job, and in doing so are inadvertently harming our sewers and hence environment.
That probably it would be better to merely use cheap bleach in the appropriate dilution, if only Choice would help or guide us us with some science based info!

@longinthetooth
As I said in my original post an effective surface disinfection solution is about 100ml in 1 litre. The 1/4 to 1/2 teaspoon in 1 litre you outline would be of next to no effect. There is just not enough hypochlorite (active ingredient of bleach) to have any meaningful level of interaction with potentially harmful organisms.
But I do agree with you that there is absolutely no need to pick a brand name bleach to achieve a good outcome. @tmar5954 is right though that some products do contain extra additives (e.g detergents) that improve the effectiveness of the product under specific circumstances. But as far as ‘killing’ power goes the only consideration is the concentration of bleach in the product. Same concentration = same effectiveness.

From what the cleaner at the office tells me is that the only difference between brands of chlorine is the smell.
The cheap brands are unpleasant to work with because of this. Other than that bleach is bleach.

However you just need to be aware that bleach removes the colour of mould, so the black is gone and you get a warm fuzzy feeling that you have done a good job. but the mould is still there, you just cannot see it.

If you want to do a good job use your grandma’s old pressure cooker and boil what ever you want cleaned. No need to place the weight valve in place, just boil hard. (The higher the pressure in a vessel the higher the temperature of the boiling water) No nasty chemicals.

Hi @jyrn.

Sorry to be picky, but bleach is a sterilising agent. Even the links that you have provided indicate and report such, namely…

'Chemical sterilization – Chemicals like Ethylene oxide, Ozone, Bleach, Glutaraldehyde and Formaldehyde, Phthalaldehyde, Hydrogen Peroxide, Dry…"

Sodium hypochlorites (the active ingredient of bleach) is also an approved for the food industry to sterilise high risk foods such as fresh salad greens. Such high risk foods have potential to contain pathogens or their propagules which may impact on human health…these include bugs which cause gastro type infections/disease.

I find this topic interesting in that 40 or more years ago, every housewife would have known the answer to the original question. So much that was once common knowledge has been lost. People throw out milk and other food as soon as the Used By Date arrives, in the belief that it will be bad for you, regardless of its condition. TV ads encourage us to buy products that kill “99.9% of germs”, and spray half the house with them in case the baby gets a germ while sitting on the floor.
A few years ago the Austin Hospital in Melbourne found that bugs were becoming resistant to the special cleaning products that they used throughout the buildings. So they conducted a trial using the old method of bleach and water, and it worked well - and was much cheaper. Surprise, surprise.

1 Like

Lots of good, accurate info here. The only thing not mentioned was when I looked at my liquid bleaches the other active ingredient was sodium hydroxide a.k.a. Caustic soda. So be wary about how you use it. Sodium hydroxide, apart from being very corrosive to skin and other tissue, can react quite violently with acids. I use bleach for cleaning the shower base & toilet ect. But would never consider it for anything I might come into contact with my body. Cheers.

Even if you use a bleach product with no sodium hydroxide (it’s there to aid cleaning action) you must never mix it with an acid. It will release chlorine gas. You don’t mix chemicals unless you know what you’re doing. The MSDS provides this sort of information.

There is no problem with using bleach solutions on things that will come into contact with your body. You rinse off the bleach after it has done its job. It leaves no residue.

@Albie, the sodium hydroxide is added to slow the decomposition of sodium hypochlorite into sodium chloride and sodium chlorate…namely to prolong the storage life of the product. It is usually added at very low concentrations .

Power force alpine thick bleach NaOH = 13 g/l; Power force liquid bleach 9g/l. I don’t regard that as insignificant.

@trevor3 I think you might be thinking of mould and mildew - terrible problems that we keep trying to fight with bleach. They’re a different kind of yuck.

Hey! I see that Choice has a new article about it. Great minds. :wink:
https://www.choice.com.au/home-and-living/laundry-and-cleaning/surface-cleaners/articles/getting-rid-of-mould

1 Like

There is more than one chemical marketed as bleach.

Traditionally, “bleach” usually meant a weak solution of sodium hypochlorite or a related chemical. In water, hypochlorite partially forms hypochlorous acid, which is a powerful oxidizing agent, and does the disinfection.

These days, although sodium hypochlorite is still available, many bleaches use a weak hydrogen peroxide solution as the active ingredient, marketing it as oxygen bleach (instead of chlorine bleach), environmentally friendly bleach, or colour fast/fabric safe bleach.

There are others, but these are the most common ones. There are a couple of reasons that usage instructions may be a bit vague. These chemicals work because they are highly reactive, which and they are rapidly consumed in the process. The amount of disinfectant required depends on how much there is for it to react with, so it’s always best to remove as many contaminants by rinsing, for example, before disinfection. Also, disinfection byproducts can be unpleasant. Foer example, the “chlorine” smell that people associate with indoor swimming pools is actually chloramine, formed by oxidation of ammonia by hypochlorous acid, and there is a lot of effort put into preventing organic matter getting into municipal water tanks not just because of the added cost of the extra disinfectant, but because carcinogenic trihalomethanes can be formed as a result of the disinfection process.

The other reason that usage instructions are a bit vague is that both sodium hypochlorite and hydrogen peroxide are unstable, meaning that they degrade over time. The rate of degradation varies with storage conditions such as temperature. The manufacturer doesn’t know how long you’ve had your bottle of bleach, or how you’ve stored it, so they don’t really know either the strength of the solution in your bottle or the level of reactive contaminants on the item you want to sterilize, making it a difficult job to provide one size fits all general guidance. Most of the liquid is just water, so when you use it, you can’t really tell if there is surplus active agent, or if it’s been completely depleted.

I would use a hydrogen peroxide based bleach rather than a hypochlorite based one for articles that people touch, because hydrogen peroxide breaks down into water and oxygen.

I don’t know exactly what you are sterilizing, but perhaps the manufacturer can provide some advice. Heat and UV radiation can also be effective in the right application, so it may be that boiling water or drying in the sun is a viable alternative. There may not even be any need for supplementary sterilisation beyond drying if the equipment is only used in chlorinated water.

1 Like

I’ve been using bleach as a means to sterilise drinking water when out. Chlorine liquid bleach is a good way to do this, a few drops per litre and some standing time are all that’s needed, bacteria are killed and the bleach evaporates out of the water.

The recommended dose is just two to four drops per litre, so bleach is definitely a potent antibacterial.

Thanks teddlesruss. You maybe the first to cotton on to my reason for posting this :slight_smile: Essentially if we are to use bleach, then lets use it properly, sensibly, and that is where Choice’s experts and scientist can educate us all. Propitiatory products contain bleach, with little guidance to its use, implying the more the merrier. So as you tell us just a few drops can help with drinking water, and my reckoning is maybe as little as half a teaspoon in a half litre of water seems to be sufficient for toilet cleaning.
However, media messages imply it isn’t a good thing to use at all. I’m keen on doing anything better to improve the environment, and Bleach may damage the underlying water system. Maybe there are better alternatives, if so, but then they need to be compared with the smartest dilution of bleach, ie, fit for purpose.
So still waiting for the Choice experts input!

One of the biggest problems with chlorine bleach is that it denatures and decomposes quite readily in normal exposure to air and sunlight. So when used in proper quantities rather than slathered onto anything, it’s quite environment friendly. As I said, you can make a litre of water bacteria free with only four drops of chlorine bleach, and it’s safe to drink after a few hours exposure to air and sunlight. So using a proper dilution is probably not going to do much harm.

But you’re right, it’s used in a lot of cleaning products and generally the manufacturers err on the generous side just to be sure their product will perform well, and so it needs us consumers to keep an eye an what we use and how we use it.

Unless you keep liquid bleach containing products in a temperature stable environment away from light, the bleach decomposes quite rapidly, and even under average cleaning cupboard conditions a bottle of liquid bleach is pretty weak after a year and probably beyond use after two.

I’ve also found that calcium hypochlorite powder is much more shelf stable and longer lasting in dry form than liquid chlorine bleaches, gives the same results, and also decomposes just as readily once made up into a solution. A little powder bleach can be made up pretty much as needed (and only as much as needed,) so you don’t end up throwing out as much decomposed bleach (and the attendant plastic jug it comes in) and therefore less pollution gets into the environment.

Agree @teddlesruss

Sodium hypochlorite is NaOCl. Since table salt is NaCl, bleach is very similar to table salt and reverts to table salt if left out. For example, the bleach in tap water will be gone if you let an open container of water stand for 24 hours. This is especially important if you have fish in an aquarium. Fresh tap water will kill fish because of the chlorine. But if you let the water stand for 24 hours, it is fine for fish.

It is unlikely to have any long term impacts on groundwater, unless it is pumped in very large volumes (which would be a criminal/environmental damage under state legislation). Even in this case, the groundwater will go saltier and may have a chlorine smell for a short period until the chlorine reacts with other ions in the groundwater and neutralised.

And it is pretty safe, so safe that people drink it every day in their tap water and swim in it in swimming pools.

1 Like

A post was split to a new topic: Do you think eucalyptus oil can be considered disinfectant?

Not so good for swimming pools though…