VPE 511: Environment and Environmental Hygiene (2+1)

CHEMICAL AGENTS

Chemical agents may be classified as follows

• Oxidising agents
• Reducing agents
• Acids and alkalis
• Alcohol
• Phenol and cresols
• Dyes
• Detergents and surface active agents
• Miscellaneous organic compounds

Oxidising agents

• Oxidising agents are rapid in action, and can be divided into those which release oxygen oxidation without the release of oxygen the halogens.

Peroxides

• Hydrogen peroxide solution
  • An aqueous solution of hydrogen peroxide is colourless and adourless but has a characteristic taste. Hydrogen peroxide is relatively stable when slightly acidified but decomposes is alkaline media and in contact with organic matter and metals. Hydrogen peroxide is a deodorant by virtue of the strong oxidizing effect of the nascent oxygen produced in contact with organic tissue. The second action is mechanical cleansing action resulting from the rapid release of oxygen

Potassium permanganate

• Consists of dark, adourless, purble crystals with a metabolic luster, which are solubless water giving pink to deep purple solutions depending on concentrations. Solutions of potassium permanganate have strong oxidizing properties without releasing gaseous oxygen.

Halogens

• Sodium Hypochlorite- contains approximately 0.5% W/V of available chlorine.

Reducing agents

• Formaldehyde useful to disinfect straw, clotheing, hay etc a 2% formaldehyde in used as spray.

Sulphur dioxide

• Sulphur dioxide is liberated as a gas when sulphur is ingnited. It is used as fumignant disinfectant for animal houses to destroy bacteria and viruses, parasites and vermin. for every 3m³ of our 0.5 kg of sulphur should be burned. The disadvantage is it attack and corrodes metal, -------- fabries and blackes dyes.

Acids and Alkalis

• The strong mineral acids can be used as disinfectants but their corrosive actions limit their usefulness to disinfection of -------- surfaces.
• Several alkalis are in common use as disinfectant, e.g sodium hydroxide, sodium carbonate and quick lime. Most bacteria are inactivated above pH 9, but a particular property of the alkalis is their antiviral activity. A 4% solution of sodium carbonate (washing soda) is employed in the cleansing and disinfection procedures required after or outbreak of fat and mouth disease.
• Acid alcohol is effective in inactivating bacterial spares.

Phenol and Cresols

• Phenols and cresols and their derivatives such as the various chlorinated cresols and phenyl mercuric compounds are used.
• Phenol is toxic but it is a good disinfectant even at low concentration (0.5%)
• Cresol is straw coloured liquid which darkens with age and exposure, less soluble in water but soluble in organic solvents. Cresol in very effective against acid fast bacteria but less effective against viruses and it has no effect on spores. It act even in the presence of organic matter. Solution of cresol and soap (Lysol) is preferred because of its greater solubility in water. Phenol should not be used in ------ since it ----- mick and mink products. Phenol and cresol are toxic to cats and dogs.
• Cholroxyloenol: Is a white or creamy white crystalline substance with a slight phenolic adour. It is insoluble in water but soluble in organic solvents and soap solutions . It is bactericide mainly against gram positive bacteria.