The Age of Diminishing Returns

But there will be plenty more toxic materials, in particular heavy metals such as mercury, which will remain dispersed in the ecosystem for hundreds of thousands or even millions of years. For instance, we don't really know what the human-health consequences will result from having dispersed large amounts of heavy metals like mercury, cadmium, chromium, and so on, in the ecosystem. The ecosystem can surely adapt to these substances, in the long run, but it will not be without pain and our near future descendants will be the ones suffering most for the adaptation.  
http://www.resilience.org/stories/2014-04-18/the-age-of-diminishing-returns