Halogens:

Halogens exist as diatomic molecules in the free state and form salt like compounds with sodium and most other metals. Iodine and chlorine are the most important antimicrobial agents. Iodine is used as a skin antiseptic and kills by oxidizing cell constituents and iodinating cell proteins. Spores can be destroyed at higher concentrations. Iodine is often applied as tincture of iodine, 2% or more iodine in a water-ethanol solution of potassium iodide. Skin scars result and sometimes iodine allergies can result. In today's date, brands like Wescodyne for skin and laboratory disinfection and Betadine for wounds is being used as iodine is complexed with an organic carrier to form iodophor; and these are mostly used in hospitals for preoperative skin degerming and in hospitals and laboratories for disinfection.

Chlorine is mostly used as a disinfectant for municipal water supplies and swimming pools and also employed in dairy and food industry. It may be applied as chlorine gas, sodium hypochloride or calcium hypochloride, all of which yield hypochlorous acid (HClO) and then atomic oxygen. The result is oxidation of cellular materials and destruction of vegetative bacteria and fungi, although not spores. One potential problem is that chlorine reacts with organic compounds to form carcinogenic trihalomethanes, which must be monitored in drinking water. Ozone sometimes has been used successfully as an alternative to chlorination in Europe and Canada. Small amounts of drinking water can be disinfected with halazone tablets. It slowly releases chloride when added to water and disinfects it in about half an hour.

Heavy metals:

Heavy metals such as mercury, silver, arsenic, zinc and copper were used as germicides and these have been most recently superseded by other less toxic and more effective germicides. A 1% solution of silver nitrate is often added to the eyes of infants to prevent ophthalmic gonorrhea but now erythromycin is used instead of silver nitrate because it is effective against Chlamydia as well as Neisseria . Silver sulfadiazine is used on burns. Copper sulphate is an effective algicide in lakes and swimming pools. The action of these heavy metals is mostly on the proteins, and they combine often with their sulfhydryl groups, and inactivate them. They may also precipitate cell proteins.