Hello Amira!

Intro

Your intro starts off very well (the first sentence is excellent), but by the end of the first paragraph readers are a little puzzled.

What do you mean by ‘it suits them’?  This needs to be clearer. In the final sentence, we are wondering if you are going to change all our ideas about the relationship between health and office work. Let’s see…it could be interesting

Usage

• Sedimentary →sedentary. It means sitting. So does sedimentary, but that’s for rocks and sand and geology.
• Nowadays, the image of office work as a safe and healthy occupation is destroyed. → has been damaged.
• Many people have mentioned that office jobs and sedimentary-related diseases are inextricably linked together.
• it’s methods → its methods (possessive -  no apostrophe)
• environmental pollutions →  environmental pollution
• the best way of standing on chairs → how to sit properly
• It would result in or has a high likelihood to result in back pain and more pressure on heart. → (This is unclear. Let’s get rid of the pronoun ‘it’).

Poor posture at work can result in back pain and circulation problems

Let's shorten!

Another important factor which has many knock on effects on employers is the sort of pollution existing in work place atmosphere. (21 words)

(No knock-on effects, please. Are there any other kind? Great for speaking, but don’t use this phrase in writing. If it means anything, it’s the effect of an effect). Let’s shorten and see what we get:

Atmospheric pollution or air quality in offices is another issue. (11 words)
OR
Air quality in offices is another issue. (7 words) 

 Figures - NO!!!

Statistics show that more than sixty one percents of employers in offices

No, don’t go there. Don’t use figures. This isn’t a research paper -  there’s no need for statistics. They are tested in Task 1. Just write ‘many’ or ‘a large number’ or ‘a majority’ and don’t use the word statistics.

Many employees don't know how to sit properly when working...

Quotes

As many researchers assert, teaching many scientific proofs about physical situations would be able to prevent many office related diseases.

I’m sure you know my opinions about quotes. Here we have ‘many researchers.’ Does it make the sentence stronger?

As many researchers assert, teaching many scientific proofs about physical situations would be able to prevent many office related diseases. (20 words)

 Simple exercises and basic health awareness would prevent many office diseases. (11 words).  

Examples: Be Careful. Don't Invent. Use YOUR experience.

Amira, be careful with your examples and with using external sources to try to back up your arguments.

You mention Berlin in paragraph three.

Offices in big cities often located in noisy and polluted part of town, so that workers are working in a very dense and dirty area. As a result, in Berlin, planners had decided to decline the density of offices in certain are during ten years and had distributed them uniformly in the country. This plan not only yields to a better traffic situation in Berlin, but it also come to more healthy working environments.

A quick search for offices and air quality in Berlin revealed – Nothing. Well, I did find this article 

But there’s nothing out there about moving offices out of Berlin  (decentralizing) or why if it had poor quality air in the first place.  There’s this also, which looked at ways of getting people to reducing car use and having lower emissions,   and this which is very similar.

It’s better not to be too specific with examples.  Don’t make them up, and don’t use them unless the examiner is likely to know them.  It’s a short opinion essay, not a research paper.

One point which you have overlooked is the office air quality itself -  air-conditioning, fumes from carpets, computers, photocopies, inadequate ventilation, etc.

Conclusion

Finally, now we can go back to the intro and see that it needs some rewriting:

While I accept that it may suit them, I believe that such illnesses are deeply rooted in poor general knowledge about health and it’s methods and also environmental pollutions in working places. (32 words -  much too long)

The easiest thing is to delete.

I believe that most office-related illnesses are due to poor health knowledge and poor air quality. (16 words)