A biocide is a chemical substance capable of killing living organisms, usually in a selective way. Biocides are commonly used in medicine, agriculture, forestry, and in industry where they prevent the fouling of water and oil pipelines. Some substances used as biocides are also employed as anti-fouling agents or disinfectants under other circumstances: chlorine, for example, is used as a short-life biocide in industrial water treatment but as a disinfectant in swimming pools. Many biocides are synthetic, but a class of natural biocides, derived from e.g. bacteria and plants, includes brassica oleracea, brassica oleracea gemmifera, and clostridium botulinum bacteria.
A biocide can be:
* A pesticide: this includes fungicides, herbicides, insecticides, algicides, molluscicides, miticides and rodenticides.
* An antimicrobial: this includes germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoals and antiparasites. See also spermicide.
Biocides can be added to other materials (typically liquids) to protect them against biological infestation and growth. For example, certain types of quaternary ammonium compounds (quats) are added to pool water or industrial water systems to act as an algicide, protecting the water from infestation and growth of algae. Chlorine is also added during wastewater treatment to kill micro-organisms, algae, and so on. It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl) which acts as a general biocide killing germs, micro-organisms, algae, and so on. Halogenated hydantoin compounds are also used as biocides.
Hazards and environmental risks
Because biocides are intended to kill living organisms, many biocidal products pose significant risk to human health and welfare. Great care is required when handling biocides and appropriate protective clothing and equipment should be used. The use of biocides can also have significant adverse effects on the natural environment. Anti-fouling paints, especially those utilising organic tin compounds such as TBT, have been shown to have severe and long-lasting impacts on marine eco-systems and such materials are now banned in many countries for commercial and recreational vessels (though sometimes still used for naval vessels).
Disposal of used or unwanted biocides must be undertaken carefully to avoid serious and potentially long-lasting damage to the environment.
European Community Classification
The Biocidal Products Directive 98/8/EC (BPD), the classification of biocides, is broken down into 23 product types (i.e. application categories), with several comprising multiple subgroups:
MAIN GROUP 1: Disinfectants and general biocidal products
* Product-type 1: Human hygiene biocidal products
* Product-type 2: Private area and public health area disinfectants and other biocidal products
* Product-type 3: Veterinary hygiene biocidal products
* Product-type 4: Food and feed area disinfectants
* Product-type 5: Drinking water disinfectants
MAIN GROUP 2: Preservatives
* Product-type 6: In-can preservatives
* Product-type 7: Film preservatives
* Product-type 8: Wood preservatives
* Product-type 9: Fibre, leather, rubber and polymerised materials preservatives
* Product-type 10: Masonry preservatives
* Product-type 11: Preservatives for liquid-cooling and processing systems
* Product-type 12: Slimicides
* Product-type 13: Metalworking-fluid preservatives
MAIN GROUP 3: Pest control
* Product-type 14: Rodenticides
* Product-type 15: Avicides
* Product-type 16: Molluscicides
* Product-type 17: Piscicides
* Product-type 18: Insecticides, acaricides and products to control other arthropods
* Product-type 19: Repellents and attractants
MAIN GROUP 4: Other biocidal products
* Product-type 20: Preservatives for food or feedstocks
* Product-type 21: Antifouling products
* Product-type 22: Embalming and taxidermist fluids
* Product-type 23: Control of other vertebrates