I'm not an expert, but oil wreaks havoc to nature and life, if it spills. So there is problem nr 1. I don't know how much time nature needs to rebound from such

I'm not an expert, but oil wreaks havoc to nature and life, if it spills. So there is problem nr 1. I don't know how much time nature needs to rebound from such spills, but I know, that (crude) oil on beaches makes them unhabitable for years. Problem Nr. 2: plastics made from oil are different from, well oil. They're a product, that doesn't occur in nature, as far as I know. Plastics are hormonally active in the body. There might be thousands of different plastics and nobody really knows how they're reacting with animals, nature and so on. But the short answer is: petroleum kills, that stuff is dangerous as hell.