question: How do brass doorknobs disinfect themselves?
comment: Brass is a copper alloy. Copper is electro conductive. As electrons move around, they interfere with microbes functioning. Copper IUDs work similarly, "zapping" sperm. Edit: a quick Google search says sweat from hands can corrode the surface metal in as little as an hour, rendering the antibacterial effect null. You still gotta clean them.
passages: Of concern is the fact that door handles are instrumental in the spread of many infections. However, some materials, e.g. brass, copper and silver, are slowly poisonous to many germs. The exact mechanism is not known, but is commonly thought to be via the oligodynamic effect, perhaps by some other electrostatic effect. Brass and copper, for example, disinfect themselves of many door handle bacteria within eight hours. Other materials such as glass, porcelain, stainless steel and aluminium do not have this effect. Self-disinfecting door handles are particularly important in hospitals, but useful in any building.
  
  Section::::External links.
   Many factors determine the suitability and population of bacteria. The material of the handle itself contributes to the growth of bacteria, with most door handles being constructed with stainless steel these are more than suitable homes for bacteria. The material affects the time bacteria can survive on door handles, but more so the temperature and humidity of the surrounding air, depending on this bacteria can thrive anywhere from a few hours to a few weeks.
   Health concerns surrounding brass stem from lead contamination. Lead is sometimes added to enhance the machinability of brass. It is often present in concentrations around 2%. Thirteen key manufacturers were sued by the California state attorney general on October 1999. Lab tests revealed the average brass key contained more than the acceptable limit of lead. They were required to reduce the lead content to 1.5% after April 2001. By January 1, 2010, the California law states that brass containing less than 0.25% lead must be used for each component that comes into contact with the wetted surface of pipes, plumbing fittings and fixtures. On the other hand, the copper in brass does create a natural germicidal or oligodynamic effect. Brass doorknobs will virtually disinfect themselves within eight hours.
   Section::::Regulations of PBDEs.
   Some of the locations where these opportunistic pathogens can grow include faucets, shower heads, water heaters and along pipe walls. Reasons that favor their growth are "high surface-to-volume ratio, intermittent stagnation, low disinfectant residual, and warming cycles". A high surface-to-volume ratio, i.e. a relatively large surface area allows the bacteria to form a biofilm, which protects them from disinfection.
  
  Section::::Regulation.
   The bactericidal properties of brass have been observed for centuries, particularly in marine environments where it prevents biofouling. Depending upon the type and concentration of pathogens and the medium they are in, brass kills these microorganisms within a few minutes to hours of contact.
  
  A large number of independent studies confirm this antimicrobial effect, even against antibiotic-resistant bacteria such as MRSA and VRSA. The mechanisms of antimicrobial action by copper and its alloys, including brass, are a subject of intense and ongoing investigation.
  
  Section::::Season cracking.
   Residual chlorine and other disinfectants may also react further within the distribution network — both by further reactions with dissolved natural organic matter and with biofilms present in the pipes. In addition to being highly influenced by the types of organic and inorganic matter in the source water, the different species and concentrations of DBPs vary according to the type of disinfectant used, the dose of disinfectant, the concentration of natural organic matter and bromide/iodide, the time since dosing (i.e. water age), temperature, and pH of the water.
   Section::::Pollution due to PCBs.:Italy.
  
  The Italian company Caffaro, located in Brescia, specialized in producing PCBs from 1938 to 1984, following the acquisition of the exclusive rights to use the patent in Italy from Monsanto. The pollution resulting from this factory and the case of Anniston, in the US, are the largest known cases in the world of PCB contamination in water and soil, in terms of the amount of toxic substance dispersed, size of the area contaminated, number of people involved and duration of production.
   The number of viable "Staphylococcus spp". organisms on surfaces containing copper and its alloy were reduced by half to one-thirtieth of that on control surfaces, depending upon surface humidity and the frequency of contact. Similar definitive findings were also obtained for "Pseudomonas aeruginosa".
   Physical removal is typically done as a first step. Small diameter pipes are sometimes cleaned with a wire brush, while larger lines can be scrubbed and flushed clean with a sewer jetter. The pumping equipment in the well must also be removed and cleaned. 
   Since bacteria likes wet and humid surroundings, the type of the handle – whether it is a lever or a knob – makes a difference. Depending on the size and material, the life conditions for bacteria differ. While door handles are usually made of metal, doorknobs tend to be wooden, meaning they can absorb and retain dampness for a longer time making the perfect conditions for germs and bacteria to thrive. Although the commonly shaped metal handles can be more easily cleaned as they have a more wipeable surface, round knobs have a smaller size which mean a smaller area for the bacteria to live on.
   Myxospores are extremely tough: "it was shown that "Myxobolus cerebralis" spores can tolerate freezing at −20°C for at least 3 months, aging in mud at 13°C for at least 5 months, and passage through the guts of northern pike "Esox lucius" or mallards "Anas platyrhynchos" without loss of infectivity" to worms. Triactinomyxons are much shorter-lived, surviving 34 days or less, depending on temperature.
  
  Section::::Pathology.
   As with the Shrewsbury factory, a new design and management team was created with a group of around twenty management & technical staff moving from Glasgow to Worcester to expand production, further develop mechanical values and service this new market. In addition the factory created employment for between 300 and 500 local Worcester people.
  
  Section::::History.:Civic clean water and sewage systems.
   These bacteria can infect many different types of organs, but are most notable for the infections of the testes and ovaries of their hosts. "Wolbachia" species are ubiquitous in mature eggs, but not mature sperm. Only infected females, therefore, pass the infection on to their offspring. "Wolbachia" bacteria maximize their spread by significantly altering the reproductive capabilities of their hosts, with four different phenotypes:
  
  BULLET::::- Male killing occurs when infected males die during larval development, which increases the rate of born, infected, females.
   Several powerful oxidizing agents are used in disinfecting and treating drinking water, and many of these also cause the formation of DBPs. Ozone, for example, produces ketones, carboxylic acids, and aldehydes, including formaldehyde. Bromide in source waters can be converted by ozone into bromate, a potent carcinogen that is regulated in the United States, as well as other brominated DBPs. 
  
  As regulations are tightened on established DBPs such as THMs and HAAs, drinking water treatment plants may switch to alternative disinfection methods. This change will alter the distribution of classes of DBP's.
  
  Section::::Occurrence.
   Zinc pest
  
  Zinc pest (from German "Zinkpest"), also known as zinc rot and mazak rot, is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities. While impurities of the alloy are the primary cause of the problem, environmental conditions such as high humidity (greater than 65%) may accelerate the process.
   Just like all the factors above, the actual place where the door handles are located is crucial when it comes to the life expectancy of bacteria. As we know, all handles in public places, e.g. bathrooms, toilets and front doors, are the most dangerous ones because these places come in contact with people’s hands most frequently transferring a wide variety of germs onto them. On the other hand, there are places like ordination rooms and laboratories where bacteria is unlikely to survive, however despite being kept clean and sanitised, there is still a possibility of infective organisms.
   Door handle bacteria
  
  Everyday door handles are often hotspots for bacteria, public handles especially. Because of the frequent and inevitable use of most door handles, it can often be expected that bacteria are present.
   Section::::Toxicodynamics and reactivity.
  
  Section::::Toxicodynamics and reactivity.:Reactions and mechanism of action.
   Section::::Biological synthesis in micro-organisms.
   Section::::Classes of PBDEs.
   Section::::Types.:Inorganic compounds.
  
  Section::::Types.:Inorganic compounds.:Chlorine.
  
  This group comprises aqueous solution of chlorine, hypochlorite, or hypochlorous acid. Occasionally, chlorine-releasing compounds and their salts are included in this group. Frequently, a concentration of  1 ppm of available chlorine is sufficient to kill bacteria and viruses, spores and mycobacteria requiring higher concentrations.
  
  BULLET::::- Sodium hypochlorite
  
  BULLET::::- Calcium hypochlorite
  
  BULLET::::- Chloramine
  
  BULLET::::- Chloramine-T
  
  BULLET::::- Trichloroisocyanuric acid
  
  BULLET::::- Chlorine dioxide
  
  Section::::Types.:Inorganic compounds.:Iodine.
  
  BULLET::::- Iodine
  
  BULLET::::- Iodophors
  
  Section::::Types.:Inorganic compounds.:Acids and bases.
  
  BULLET::::- Sodium hydroxide
  
  BULLET::::- Potassium hydroxide
  
  BULLET::::- Calcium hydroxide
  
  BULLET::::- Magnesium hydroxide
  
  BULLET::::- Sulfurous acid
  
  BULLET::::- Sulfur dioxide
  
  Section::::Types.:Terpenes.
  
  BULLET::::- Thymol
  
  BULLET::::- Pine oil
  
  Section::::Types.:Other.
   "Paenibacillus larvae" is a rod-shaped bacterium, which is visible only under a high power microscope. Larvae up to 3 days old become infected by ingesting spores that are present in their food. Young larvae less than 24 hours old are most susceptible to infection. Spores germinate in the gut of the larva and the vegetative form of the bacteria begins to grow, taking its nourishment from the larva. Spores will not germinate in larvae over 3 days old. Infected larvae normally die after their cell is sealed. The vegetative form of the bacterium will die but not before it produces many millions of spores. Each dead larva may contain as many as 100 million spores. This disease only affects the bee larvae but is highly infectious and deadly to bee brood. Infected larvae darken and die.
   Swine flu is one of many diseases that are contracted by person to person contact. In April 2009 the virus was discovered in the USA, 2 months later in June the CDC (center for disease control) announced the disease as a pandemic. It is believed that door handles provide a suitable environment for the disease to spread on, as the virus can survive on these metallic surfaces from 2 up to 8 hours. Door handles provide a popular medium for the disease to spread as every person uses the handle, they can extend the duration that the microorganisms survive.
   BULLET::::- In the early 2000s, residents of the city of New Plymouth, New Zealand, reported many illnesses of people living around and working at the Dow Chemical plant. This plant ceased production of 2,4,5-T in 1987.
  