tropical ecologist luis fernandez is the director the carnegie amazon mercury ecosystem project. >> the gold here is not very concentrated. it's only about 2 grams per ton of rock. instead of manually concentrating that tiny amount of gold in a awful lot of rock, you take some of the sediment, some water, and a little bit of mercury, and you mix it up. >> where else does this mercury end up? >> because the mercury is being dumped into the rivers and lakes, it then gets into the food chain, mercury can concentrate in sediments, and be absorbed into the plants, so, in areas that were former mining zones, there is a lot of questions about what's next. >> so this whole area was more recently mined? >> yes, yes. >> it's those questions francisco and his team hope to answer. they showed us how they have begun to test what can grow in degraded land like this. they begin by planting a species known as pioneers. they are fast growing plants natural to the area - that can survive in tough circumstances. >> we are looking at an experiment with fast growing tree species. we have 3 levels of fertili