Hello, as it too late fo apply for funding to any research council or institution I realized I have to search for a sponsor in the private sector and industry. However get in contact with private companies is not easy, can you please advice me on the correct approach?My research is based on marine pollution anf effects therefore I ve started to search for companies involved in the sector.

Your first priority should be to find an academic who works on the topic you are interested in. You will not be able to find an industrial sponsor for your project without academic help. Even then, unless your research proposal has a direct commercial relevance to them they are unlikely to back it. If you cannot fund yourself, then you may be better delaying the start of your PhD until the next academic year. In the mean time try to get some relevant work experience.