Question

the depletion of Ozone layer is a cause of concern why

Answer 1

As we know that the ozone layer protect us from harmful ultra violet radiations of sun. Damage to the ozone layer is a cause for concern because the harmful ultraviolet radiation from the sun will reach the earth. This radiation is harmful for all living beings (humans as well as plant).
Harmful effect of ozone on human being:
1) skin cancer
2) Loss of immunity. 
Damage to plant and aquatic life:
1)Lower yields from some plants and cereal crops
2)Negative effects on plant growth
3)Falling plankton populations, which are a primary source of food in marine ecosystems

Steps being taken to limit this damage are: 

• Reduce the use of ozone depleting substances such as chlorofluorocarbons (CFCs). Many countries have already banned the use of CFCs.
• Use ozone friendly sprayers in perfumes, insect-repellants, etc.

Hope this helps you...:)

Answer 2

today there is widespread concern that the also ozone depleted due to release of pollution containing Chemicals like chlorine and bromine. it leads to the entering of UV rays on earth leads to skin cancer ,cataracs etc