Sodium hypochlorite as a disinfectant

Disinfectants Sodium hypochlorite

Sodium hypochlorite

Sodium hypochlorite (NaOCl) is a compound that can be effectively used for water purification. It is used on a large scale for surface purification, bleaching, odor removal and water disinfection.

Sodium hypochlorite has a long history. Around 1785 the Frenchman Berthollet developed liquid bleaching agents based on sodium hypochlorite. The Javel company introduced this product and called it ‘liqueur de Javel’. At first, it was used to bleach cotton. Because of its specific characteristics it soon became a popular compound. Hypochlorite can remove stains from clothes at room temperature. In France, sodium hypochlorite is still known as ‘eau de Javel’.

Sodium hypochlorite is a clear, slightly yellowish solution with a characteristic odor.
Sodium hypochlorite has a relative density of is 1,1 (5,5% watery solution).
As a bleaching agent for domestic use it usually contains 5% sodium hypochlorite (with a pH of around 11, it is irritating). If it is more concentrated, it contains a concentration 10-15% sodium hypochlorite (with a pH of around 13, it burns and is corrosive).
Sodium hypochlorite is unstable. Chlorine evaporates at a rate of 0,75 gram active chlorine per day from the solution. Then heated sodium hypochlorite disintegrates. This also happens when sodium hypochlorite comes in contact with acids, sunlight, certain metals and poisonous and corrosive gasses, including chlorine gas. Sodium hypochlorite is a strong oxidator and reacts with flammable compounds and reductors. Sodium hypochlorite solution is a weak base that is inflammable.
These characteristics must be kept in mind during transport, storage and use of sodium hypochlorite.

Due to the presence of caustic soda in sodium hypo chlorite, the pH of the water is increased. When sodium hypo chlorite dissolves in water, two substances form, which play a role in for oxidation and disinfection. These are hypochlorous acid (HOCl) and the less active hypochlorite ion (OCl — ). The pH of the water determines how much hypochlorous acid is formed. While sodium hypochlorite is used, hydrochloric acid (HCl) is used to lower the pH. Sulfuric acid (H2SO4) can be used as an alternative for acetic acid. Less harmful gasses are produced when sulfuric acid is used. Sulfuric acid is a strong acid that strongly reacts with bases and that is very corrosive.

Sodium hypochlorite can be produced in two ways:
— By dissolving salt in softened water, which results in a concentrated brine solution. The solution is electrolyzed and forms a sodium hypochlorite solution in water. This solution contains 150 g active chlorine (Cl2) per liter. During this reaction the explosive hydrogen gas is also formed.
— By adding chlorine gas (Cl2) to caustic soda (NaOH). When this is done, sodium hypochlorite, water (H2O) and salt (NaCl) are produced according to the following reaction:
Cl2 + 2NaOH + → NaOCl + NaCl + H2O

Sodium hypochlorite is used on a large scale. For example in agriculture, chemical industries, paint- and lime industries, food industries, glass industries, paper industries, pharmaceutical industries, synthetics industries and waste disposal industries. In the textile industry sodium hypochlorite is used to bleach textile. It is sometimes added to industrial waste water. This is done to reduce odors. Hypochlorite neutralizes sulphur hydrogen gas (SH) and ammonia (NH3). It is also used to detoxify cyanide baths in metal industries. Hypochlorite can be used to prevent algae and shellfish growth in cooling towers. In water treatment, hypochlorite is used to disinfect water. In households, hypochlorite is used frequently for the purification and disinfection of the house.

By adding hypochlorite to water, hypochlorous acid (HOCl) is formed:
NaOCl + H2O → HOCl + NaOH —

Hypochlorous acid is divided into hydrochloric acid (HCl) and oxygen (O). The oxygen atom is a very strong oxidator.
Sodium hypochlorite is effective against bacteria, viruses and fungi. Sodium hypochlorite disinfects the same way as chlorine does.

Sodium hypochlorite is applied in swimming pools for water disinfection and oxidation. It has the advantage that microorganisms cannot build up any resistance to it. Sodium hypochlorite is effective against Legionella bacteria and bio film, in which Legionella bacteria can multiply.
Hypochlorous acid is produced by the reaction of sodium hydroxide with chlorine gas. In water, the so-called ‘active chlorine’ is formed.
There are various ways to use sodium hypochlorite. For on-site salt electrolysis, a solution of salt (NaCl) in water is applied. Sodium (Na + ) and chloride (Cl — ) ions are produced.
4NaCl — → 4Na + + 4Cl —

By leading the salty solution over an electrolysis cell, the following reactions take place at the electrodes:
2Cl- → Cl2 + 2e- 2H2O + 2e- → H2 + 20H —
2H20 → O2 + 4H + + 4e-

Subsequently, chlorine and hydroxide react to form hypochlorite:
OH — + Cl2 → HOCl + Cl —

The advantage of the salt electrolysis system is that no transport or storage of sodium hypochlorite is required. When sodium hypochlorite is stored for a long time, it becomes inactive. Another advantage of the on site process is that chlorine lowers the pH and no other acid is required to lower pH. The hydrogen gas that is produced is explosive and as a result ventilation is required for expolsion prevention. This system is slow and a buffer of extra hypochlorous acid needs to be used. The maintenance and purchase of the electrolysis system is much more expensive than sodium hypochlorite.
When sodium hypochlorite is used, acetic or sulphuric acid are added to the water. An overdose can produce poisonous gasses. If the dosage is too low, the pH becomes to high and can irritate the eyes.
Because sodium hypochlorite is used both to oxidize pollutions (urine, sweat, cosmetics) and to remove pathogenic microorganisms, the required concentration of sodium hypochlorite depends on the concentrations of these pollutions. Especially the amount of organic pollution determines the required concentration. If the water is filtered before sodium hypochlorite is applied, less sodium hypochlorite is needed.

There is no threshold value for to sodium hypochlorite exposure. Various health effects occur after exposure to sodium hypochlorite. People are exposed to sodium hypochlorite by inhalation of aerosols. This causes coughing and a sore throat. After swallowing sodium hypochlorite the effects are stomach ache, a burning sensation, coughing, diarrhea, a sore throat and vomiting. Sodium hypochlorite on skin or eyes causes redness and pain. After prolonged exposure, the skin can become sensitive. Sodium hypochlorite is poisonous for water organisms. It is mutagenic and very toxic when it comes in contact with ammonium salts.

Sodium hypochlorite in swimming pools

The concentration of sodium hypochlorite that is found in swimming pools is generally not harmful to people. When there is too much chlorine in the water, this burns the body tissues, which causes damage to air tracts, the stomach and the intestines, the eyes and the skin. When sodium hypochlorite is used in swimming pools, it sometimes causes red eyes and it gives off a typical chlorine odor. When there is a lot of ureum (a mixture of urine and sweat) present, hypochlorous acid and ureum react to form chloramines. These chloramines irritate mucous membranes and cause the so-called ‘ chlorine smell’. In most swimming pools, these problems are prevented by water purification and ventilation. Eyes irritation disappears after a while.

Sodium hypochlorite as a disinfectant has the following advantages:
It can easily and be stored and transported when it is produced on-site. Dosage is simple. Transport and storage of sodium hypochlorite are safe. Sodium hypochlorite is as effective as chlorine gas for disinfection. Sodium hypochlorite produces residual disinfectant.

Sodium hypochlorite is a dangerous and corrosive substance. While working with sodium hypochlorite, safety measures have to be taken to protect workers and the environment. Sodium hypochlorite should not come in contact with air, because that will cause it to disintegrate. Both sodium hypochlorite and chlorine do not deactivate Giardia Lambia and Cryptosporidium.

What is the legislation for sodium hypochlorite?
The regulation for sodium hypochlorite is the same as the regulation considering chlorine.

Discharge demands

When cooling tower water is tapped from a river or lake, and must be discharged into the same water body after it has been used, it must meet certain discharge demands. Additionally, the water temperature may not be too high, because warm water has a low oxygen content, which promotes algal growth. This can cause fish mortality and a decrease in water biodiversity.

United States

Discharge demands for cooling tower water in the USA are mentioned in the Clean Water Act (CWA) and are established by the Environmental Protection Agency (EPA).

More information on water disinfection?:


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The Trouble With Ingredients in Sunscreens

Sunscreen is a body care product that consumers are directed to apply a thick coat over large areas of the body and reapply frequently. Thus, ingredients in sunscreen should not be irritating or cause skin allergies, and should be able to withstand powerful UV radiation without losing their effectiveness or forming possibly harmful breakdown products. People might inhale ingredients in sunscreen sprays and ingest some of the ingredients they apply to their lips, so ingredients must not be harmful to lungs or internal organs. Furthermore, sunscreens commonly include ingredients that act as “penetration enhancers” to help the product adhere to skin. As a result, many sunscreen chemicals are absorbed into the body and can be measured in blood, breast milk and urine samples.

For these reasons, the Food and Drug Administration is now proposing significant changes in how sunscreen ingredients are evaluated for safety. FDA is proposing that all current and potential new ingredients be adequately tested for safety, including with studies to determine whether the ingredients penetrate the skin and can cause endocrine disruption, cancer or other health harms.

FDA has put the entire sunscreen industry on alert by proposing that in just two instances do we have enough safety information about ingredients to determine whether they’re safe and effective: zinc oxide and titanium dioxide. For 12 other ingredients, the FDA has said there isn’t enough data to determine whether they’re safe. In particular, FDA raised concerns about the substantial skin absorption of oxybenzone, its potential to affect hormone levels and the increased absorption susceptibility of children (FDA 2019). Lab studies shows that some chemical UV filters may mimic hormones, and physicians have reported sunscreen-related skin allergies, which raises important questions about unintended human health consequences from frequent sunscreen application.

Active ingredients in sunscreens function as either mineral or chemical UV filters that keep harmful rays from the skin. Each uses a different mechanism for protecting skin and maintaining stability in sunlight. The most common sunscreens contain chemical filters. These products typically include a combination of two to six of the following active ingredients: oxybenzone, avobenzone, octisalate, octocrylene, homosalate and octinoxate. Mineral sunscreens use zinc oxide and/or titanium dioxide. A handful of products combine zinc oxide with chemical filters.

When the FDA began to consider sunscreen safety, it grandfathered in active ingredients from the late 1970s without reviewing the evidence of their potential hazards. In February 2019, the agency released its final draft sunscreens monograph, which contains insufficient health and safety data to designate 12 of the 16 sunscreen filters allowed for use in the U.S. as generally recognized as safe and effective, or GRASE. These 12 ingredients include some of the most commonly used UV filters, including oxybenzone, octinoxate, octisalate, octocrylene, homosalate and avobenzone. According to the agency, “nearly all of these sunscreen active ingredients … have limited or no data characterizing their absorption.”

Drawing on the available literature, the agency concluded that the risks of using aminobenzoic acid (PABA) and trolamine salicylate outweigh their benefits, and it proposed classifying them as unsafe. The FDA monograph giving the GRASE designation to just two active sunscreen ingredients: zinc oxide and titanium dioxide.

The Danish EPA reviewed the safety of active ingredients in sunscreen and concluded that most lacked enough information to establish their safety (Danish EPA 2015). In the case of 16 of the 19 ingredients studied, there was no information about their potential to cause cancer. And though the published studies suggest that several chemical filters interact with human sex or thyroid hormones, there was not enough information about any of them to determine the potential risks to humans from hormone disruption.

EWG has reviewed the existing data about human exposure and toxicity for the nine most commonly used sunscreen chemicals. The most worrisome is oxybenzone, which can cause allergic skin reactions (Rodriguez 2006). In lab studies, it is a weak estrogen and has potent anti-androgenic effects (Krause 2012, Ghazipura 2017).

The Centers for Disease Control and Prevention routinely detect oxybenzone in more than 96 percent of Americans. Study participants who reported using sunscreen have higher oxybenzone exposures (Zamoiski 2015). Investigators at University of California, Berkeley, reported a dramatic drop in teen girls’ exposure to oxybenzone in cosmetics when they switched from their usual products to replacements that did not contain this chemical (Harley 2016).

In an evaluation of CDC-collected exposure data for American children, researchers found that adolescent boys with higher oxybenzone measurements had significantly lower total testosterone levels (Scinicariello 2016). The researchers cautioned that their results offer a single-day snapshot; they are not a controlled study of the effect of multiday exposures. The study did not find a similar hormone effect in younger boys or females.

Three other studies reported statistically significant associations between oxybenzone exposure during pregnancy and birth outcomes. One reported shorter pregnancies in women carrying male fetuses; two reported higher birth weights in baby boys; and one found lower birth weights in baby girls (Ghazipura 2017).

Intentional dosing studies of people are rare. In one, volunteers applied a lotion containing oxybenzone and two other sunscreen ingredients. Researchers reported a minor but statistically significant decrease in testosterone in men, accompanied by a minor increase in inhibin B, another male sex hormone (Janjua 2004). The researchers concluded these differences were normal variations and not attributable to sunscreen exposure. In any event, critics argue the exposures were too short to be conclusive (Krause 2012).

According to the latest FDA sunscreens monograph, the agency needs further data to determine the GRASE status of oxybenzone, given that the “available literature … indicat[es] that oxybenzone is absorbed through the skin to a greater extent than previously understood and can lead to significant systemic exposure.… The significant systemic availability of oxybenzone … is a concern, among other reasons, because of questions raised in the published literature regarding the potential for endocrine activity.” Given the pervasiveness of oxybenzone exposures, we need further study to clarify its association with hormone disruption in children and adults.

EWG recommends consumers avoid sunscreens with oxybenzone. But sunscreen users are exposed to other active ingredients too. Margaret Schlumpf of the University of Zurich detected four other sunscreen filters along with oxybenzone in Swiss women’s breast milk, which suggests that the developing fetus and newborns may be exposed to these substances (Schlumpf 2008, Schlumpf 2010). She detected at least one sunscreen chemical in 85 percent of milk samples.

Some experts caution that the unintentional exposure to toxic active ingredients erodes sunscreens’ benefits (Krause 2012, Schlumpf 2010). But most experts conclude that more sensitive tests are needed to determine whether sunscreen chemical ingredients pose risks to frequent users (Draelos 2010, Gilbert 2013).

Active ingredient toxicity

This table outlines human exposure and hazard information for nine FDA-approved sunscreen chemicals. With each sunscreen, we asked these questions:

  • Will the chemical penetrate skin and reach living tissues?
  • Will it disrupt the hormone system?
  • Can it affect the reproductive and thyroid systems and, in the case of fetal or childhood exposure, permanently alter reproductive development or behavior?
  • Can it cause a skin allergy?
  • What if it is inhaled?
  • Are there other toxicity concerns?

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