State the adverse effects of polyhalogenated compounds. How the adverse effects of chlorofluorocarbons can be prevented ?

Explanation

(i) Methylene dichloride : Exposure to lower levels of methylene chloride in air cause dizziness, nausea, tingling and numbness in the fingers and toes.
In humans, direct skin contact with methylene chloride causes intense burning and mild redness of the skin. Direct contact with the eyes can burn the cornea.
(ii) Trichloromethane (Chloroform) : Inhaling chloroform depresses the central nervous system.
Breathing about 900 parts of chloroform for short time can cause dizziness, fatigue and headache.
Chronic chloroform exposure may cause damage to the liver where chloroform is metabolised to phosgene and to the kidneys, and some people develop sores when the skin is immersed in chloroform.
`2CHCl_(3)+O_(2)overset(" Light ")underset(" Oxidation ")rarr 2COCl_(2)+2HCl`
Chloroform is slowly oxidised by air in the presence an extermely poisonous gas and therefore it is stored in closed dark coloured bottles completely filled so that air is kept out.
(iii) Tetrachloromethane `(C Cl_(4))` : Exposure to carbon tetrachloride causes liver cancer in humans.
The most common effects are dizziness, light headedness, nausea and vomiting, which can cause permanent damage to nerve cells.
In severe cases, the carbon tetrachloride leads rapidly to stupor, coma, unconsciousness or death.
Exposure to `C Cl_(4)` can make the heart beat irregularly or stop. It causes irritation to eyes upon contact.
When `C Cl_(4)` is released into the air, it rises to the atmosphere and depletes the ozone layer.
Depletion is ozone layer is believed to increase human exposure to ultraviolet rays, leading to increased sking cancer, eye diseases anbd disorders, and possible disruption of the immune system.
(iv) Freons : In stratosphere, the freon is able to initiate the radical chain reactions that can upset the natural ozone balance.
Prevention of adverse effects of chlorofluorocarbons (CFCs) : CFCs are highly stable and non - toxic gases. These asre also non - reactive. With the ozone, they initiate the chemical chain reaction and disturbs the natural balance of the ozone layer. If the ozone layer is thinned out, the UV rays reach to the earth which is harmful for flora and fauna. It is recommended that CFCs of refrigerator is replaced by some other compounds.