Antimicrobial agents: hypochlorite. Part 2


Hypochlorite is now widely used and is used not only for water purification, but also for some other purposes.

Application of hypochlorite

Dakin’s solution, which is a 0.5% sodium hypochlorite solution, was actively used during the First World War to disinfect wounds and prevent gangrene, and a slightly stronger agent, Milton’s liquid, a 1% hypochlorite solution, became popular as general antiseptic. For many years it has been used to sterilize milk bottles for infants. Washing was carried out according to the technology when, after soaking in Milton’s liquid, the bottle was washed with large volumes of running water. (Thus, only a small amount of hypochlorite entered the child’s digestive tract.)

Solid dichloroisocyanurate (NaDCC) is now preferred over bleaching powder and is also dissolved in water to form a hypochlorite solution. This substance is a derivative of cyanuric acid, the structure of which is a ring formed by carbon and nitrogen atoms, outside the cycle, oxygen is attached to carbon atoms, and hydrogen is attached to nitrogen atoms. Three such hydrogen atoms can be replaced by chlorine, the resulting substance will be called trichloroisocyanuric acid. It is a white crystalline powder used as a disinfectant and as a bleaching agent.

Another option is to replace two hydrogen atoms with chlorine, and neutralize the third hydrogen with alkali, as a result we get NaDCC. This reagent is much more soluble and is sold in the form of tablets for sterilizing drinking water. One of the positive features of such tablets is that they can be stored for up to three years without losing their disinfectant potential, while they are much more resistant to moisture compared to bleaching powder. Unlike chlorine bleach, the solution from these tablets does not damage laundry.

NaDCC is used in swimming pools, hospitals (to collect and disinfect spilled blood and other body fluids), livestock farms, dishwashing, and disinfecting public toilets and mopping floors. It is sold as a remedy for travelers who go to a region where the quality of drinking water is in doubt. And although the taste of water disinfected with NaDCC is not very pleasant, at least it becomes safe to drink. A standard tablet contains 8.5 mg of NaDCC, enough to sterilize one liter of water. When dissolved, the concentration of hypochlorite is two parts per million parts of water, which is sufficient to destroy the bulk of pathogens, but not poison the water.

Hypochlorite keeps swimming pool water and drinking water free from infectious agents, not only fatal ones such as cholera, typhoid fever and meningitis, but also less aggressive ones such as E. coli, which, however, can cause nausea and diarrhea. . Although water chlorination protects us from microbes, this method also has its drawbacks associated with the formation of by-products such as chloramine (NH2Cl) and organochlorins (eg chloromethane). These substances can be found in the water of swimming pools, as well as in the air of indoor swimming pools. Chloramine is formed by the reaction of hypochlorite with ammonia (enters the pool with urine) and evaporates into the air. It is believed that inhalation of chloramine over an extended period of time can lead to asthma symptoms in pool workers.

Organochlorins are formed from tiny amounts of organic substances dissolved in water, so they are present even in tap water. Swimming pools can contain up to twenty times more organochlorins than drinking water, where they are produced by the reaction of human sweat with hypochlorite. And although these data may seem alarming, we should not forget that we are talking about negligible amounts of pollutants that cannot harm even children. Thus, the chlorination of organic substances takes less than one percent of the added hypochlorite.

At a concentration of sodium hypochlorite equal to one part per million parts of water (0.0001%), the log kill is equal to one (90%), and at a concentration of five parts per million parts of water, the log kill reaches two (99%), that is, most microbes are killed in a few minutes. At a concentration of 25 ppm (0.0025%), hypochlorite kills even pathogen spores if they are in prolonged contact with the substance, at a concentration of 500 ppm (0.05%), hypochlorite copes with this task much faster. In most countries, chlorine bleach is sold as a 5% solution, but in some places you can find twice as strong a solution. When one spoonful (10 ml) of a 5% solution is added to ten liters of water, the concentration of the resulting solution will be 50 parts of hypochlorite per million parts of water, this concentration will be enough to kill any microbe. The World Health Organization has recognized hypochlorite as one of the most effective disinfectants for fighting HIV and hepatitis B viruses.

Many modern bleaches have a modified composition; for example, polyacrylates are added to them, thanks to which they adhere more effectively to various surfaces, for example, to the walls of the toilet bowl, and aromatic substances, which mask the smell of hypochlorite. A distinctive feature of these flavors is that they are resistant to the powerful oxidizing action of hypochlorite. Sometimes it seems incredible that a concentrated solution of hypochlorite, which itself suppresses any odor, emits a subtle pleasant aroma.

So where is chlorine bleach used? In the food industry, it is essential for water treatment; in agriculture, it is used to sterilize milk processing equipment; Hypochlorite is the standard disinfectant in food service kitchens, hospitals, and also in our homes — wherever there is a risk of catching an infection.

Hypochlorite Safety

But there are people who are concerned about the safety of the production and use of hypochlorite. They care about three things: how safe is the substance; that it is not natural; and they doubt its use in wastewater treatment, believing that hypochlorite can kill beneficial microorganisms involved in the processing of human waste.

Is hypochlorite safe?

Apparently, yes, if only if you remember the children who drink household bleach, but with timely treatment started, they rarely experience serious health problems. Despite this, occasionally people commit suicide by drinking hypochlorite, although experiments conducted on rats have shown that an adult needs to drink a liter of this substance to be fatal. (There isn’t enough acid in the stomach to neutralize the bleach’s lye and thereby release a gas that is actually deadly.) Hypochlorite is not safe when mixed with strong acids, such as those used to clean toilets. Mixing bleach with acid releases chlorine, which, if inhaled, can lead to serious health problems, so hypochlorite is not used in some places with a susceptible community, such as schools.

Does hypochlorite exist in nature?

The answer to this question is no. In 1996, the Journal of Clinical Research reported that white blood cells produce hypochlorite to fight germs. The enzyme haloperoxidase converts chloride ion into hypochlorite by reacting with hydrogen peroxide, which is present in any living cell. Some cells of the immune system generate hypochlorite using the enzyme myeloperoxidase, which is activated when an infection enters the body. So nature found it expedient to use chlorine bleach before us.

Does hypochlorite kill the bacteria we need to destroy our waste?

And the answer to this question is no. After hypochlorite is added to waste water, it decomposes within a few minutes, this is due to the fact that when it enters an excessive amount of organic reducing agents, its oxidizing ability quickly dries up. In some cases, more than 95% of the hypochlorite is converted to chloride ions during disinfection. Even in countries where hypochlorite is used daily in almost every household and where whole bottles of it are poured into toilets and directly into sewage, there is no evidence of the harmful effects of the substance on putrefactive bacteria.

Chlorination of clothes

Now there are cotton fabrics with an antibacterial insert, the properties of which can be restored by rinsing in a solution of a strong oxidizing agent, such as hypochlorite. The insert is a polymeric material associated with cotton fibers, it contains chlorine atoms attached to nitrogen atoms, this chlorine acts as an oxidizing agent. Clothing made from this material is able to protect against all types of germs, it retains its antiseptic activity as long as reactive chlorine atoms remain on it. However, they can be easily restored by soaking the fabric in a solution of household bleach. These types of materials have proven to be highly effective against microbial protection, including against antibiotic-resistant Staphylococcus aureus (also known as MRSA, short for methicillin-resistant Staphylococcus aureus), as well as against fungi and viruses. The process of making such fabrics was developed by Gang San at the University of California, according to the scientist, the antiseptic properties of the fabric invented by him are preserved after fifty washes.

Source: based on the book by John Emsley «On the benefits and harms of the products we love to buy»

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