Does Samarco's spilled mud impair the growth of native trees of the Atlantic Rainforest?

The failure of the Fundão dam, the largest environmental disaster in the world's mining sector, was responsible for releasing millions of cubic meters of iron ore tailings into the environment. It affected thousands of hectares of the Atlantic Forest domain, one of the biodiversity hotspots for conservation. Considering the urgency to restore the flora of the affected area, we evaluated the effects that iron ore tailings from the Fundão reservoir have on the germination and initial growth of tree species native to the Atlantic Forest in the Rio Doce basin. We demonstrated that the tailings do not affect the seed germination, but do negatively interfere with plant growth. Lower biomass production, height, leaf area, chlorophyll concentration and photosynthesis as well as high concentration of iron was observed in plants grown in the tailings. Thus, we investigated if these deleterious effects were due to the presence of potentially toxic metals or nutritional deficiency imposed by low fertility of the tailings. We concluded that reduced growth was a result of nutritional limitations due to low nutrient availability, low organic matter content and low cation exchange capacity of the tailings. This conclusion was further supported by the application of fertilization, which reversed the deleterious effect of the waste on the growth of plants, assuring physiological levels of iron and nutrients in the shoot. Thus, this strategy should be considered for in situ recovery projects aiming to improve the performance of native plants.