I’m currently writing the page and accompanying questions for Topic A.10 Environmental impact – heavy metals, which is the last part of Option A.

Earlier this month, on 5 November 2015, two dams at the Samarco mine in the south-eastern state of Minas Gerais in Brazil burst.

Horses struggling in the mud in Bento Rodrigues the day after the dam burst.

The red mud effluent, containing toxic iron waste from the mining operations, destroyed the town of Bento Rodrigues causing at least nine deaths with nineteen people still missing. The water is now making its way downriver to the Atlantic Ocean polluting the water supplies of hundreds of thousands of people. It is reported that the polluted water (and the ground it has flooded) contains arsenic and the heavy metals zinc, copper and mercury and is killing virtually all of the aquatic life along a 300 mile stretch. It is likely to do further severe damage to marine ecosystems when it enters the ocean. The Brazilian president, Dilma Rousseff, has called it the biggest environmental disaster to ever hit Brazil.

Topic A.10 considers how the presence of heavy metals in polluted water can be removed by precipitation, adsorption or chelation. These techniques work for the relatively small-scale operations in water treatment plants etc. but how relevant are they to disasters on this scale? The challenges facing the Brazilian Government and the joint owners of the mine, the Anglo-Australian company BHP Billiton and the Brazilian iron ore company Vale, are huge. In fact, it is difficult to see how they can ever completely remove the heavy metals from the polluted area. All they can really hope is they are eventually diluted to innocuous levels. Some initial estimates say that this may take up to 100 years. Clearly more thought must be given to preventing disasters such as this happening in the first place.