Bleach

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To bleach something, is to remove or lighten its color, sometimes as a preliminary step in the process of dyeing; a bleach is a chemical that produces these effects, often via oxidation. Common chemical bleaches include "chlorine bleach", a solution of sodium hypochlorite (NaClO), and "oxygen bleach", which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate or sodium percarbonate. Bleaching powder is calcium hypochlorite.

Other bleaches

Chlorine dioxide is used for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, and in a number of other industries. This can result in formation of dioxins, and the paper industry has begun to use peroxides instead.

In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g. bromates) are used as flour bleaching and maturing agents.

Not all bleaches have to be of an oxidizing nature. Sodium dithionite is used as a powerful reducing agent in some bleaching formulas.

Hazards

A problem with chlorine is that it reacts with organic material to form trihalomethanes like chloroform, which is a well known carcinogen. There is debate over whether any risk from the chloroform in treated drinking water is worth the benefits. However, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organochlorine-persistent organic pollutants (including dioxins), does not have any benefits. As a consequence over 80 % of the woodpulp is nowadays bleached with chlorine dioxide, reducing the dioxin generation under detectable levels.

Chlorine is a respiratory irritant. It also attacks mucous membranes and burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine should not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week).

Another hazard is the formation of acrid chloramine fumes when hypochlorite bleach comes into contact with ammonia or urine, which, though not nearly as dangerous as chlorine, can cause severe respiratory distress.

For these reasons, some consumers prefer the use of natural cleaning products as an alternative to bleach.

History

Chlorine was first characterized by the Swedish chemist Carl Wilhelm Scheele in 1774. (As an adherent of the Phlogiston theory, he called it "dephlogisticated marine acid".) French chemist Claude Louis Berthollet, noting the bleaching properties of chlorine, invented hypochlorite bleach in 1789. In French, bleach is known as Eau de Javel, after the village where it was manufactured.

Several alternatives to bleach have recently appeared in industrialized countries. These substances are touted as being less toxic, and the use of bleach as a stain remover has become less popular in the United States. However, due to the recent upsurge of illness due to methicillin-resistant Staphylococcus aureus (known as MRSA) and other bacterial pathogens susceptible to bleach, the bleach industry has recovered somewhat, and the use of bleach as a disinfectant is increasing in a variety of industrial and commercial, as well as household settings.