Wednesday, March 25, 2009

From one of the SAMS Marine Resources students, Jill McColl...

Deep-Sea Disposal of Mine Tailings- Is this the best option?

Tailings are large amounts of crushed rock that is left over after the process of separating the valuable fraction from the worthless fraction during mining. This material contains contaminants including Arsenic and hydrogen sulphide, as well as many radioactive elements. The average mine releases around 100 -150 thousand tonnes per day of tailings over a period of 20 - 40 years, but you can not mine without producing this leftover material, so where should this material go?

Dumping it into a river or into the shallow coastal ocean is an option but it can cause many environmental problems because of the contaminants tailings contain. One of the largest side effects is to the fishing industry because coastal waters are where most of commercial fishing is done and the contaminants will deplete stocks. Another option is to back-fill the mine at the same time as you are mining. This is a great option because the tailings are getting put back where they came from; leading to a minimal environmental impact but this method is very expensive therefore companies are looking for a commercially viable option.

This option could be deep-sea disposal. This is where tailings are pumped through a pipeline into the deep-sea (below 1000m). This has the advantages of only being a small chance of the tailings ever coming in contact with surface waters and the tailings will eventually be subducted into the earths crust at subduction zones. Also the seabed has slightly anoxic conditions and the low temperature can slow down chemical reactions of the tailings with the seabed.

Although there are many advantages, there are also some disadvantages including the smothering effect on the seabed. Another important point is that we have no control over where the tailing end up when they are released and there is a small possibility of the chemicals leeching, which can contaminant the food chain. Is this a chance we wish to take?

In my opinion, deep-sea disposal is the way forward. The advantages of deep-sea mining out weigh the disadvantages, making it the most viable option.


  1. With so little research done, should we go down this road? Or should we wait until further studies have been done to assess the damage?

  2. You mention that this is the way forward and the advantages outweigh the disadvantages, however it is clear thast we need more research on this.

    Does raising the precautionary principle apply in this case? Are there actual or perceived impacts that can have serious or irreversible impacts? If so, what processes are in place to minimise harm?

    The polluter pays is also an interesting point to raise here. The deep sea may be seen as a cheaper and 'out of site out of mind' option (like the atmosphere). However, it is a natural system providing a service (a sink) essentially for free for the mining company. Keeping in mind the lack of science about the impacts, should price be the only determinant as a disposal option?

  3. It does seem to be one of the better options, for human interest at least, and in theory a large amount of the chemicals will be carried away in currents and dispersed far enough that they shouldnt have a major effect. T

    he problem still remains though, that this gets into the food chain and then builds up enough through the trophic layers to have an effect on humans who are then eating the fish.
    This has been seen in the fish around the coast of Japan, who have over the years become toxic due to chemicals released from the huge shipping trade there.

  4. Compared to the other options deep sea disposal is looking like the best one for human interests as Andy has pointed out. This is because the other options either have harmful side effects or are too expensive for it to be viable. Deepsea disposal is a cheap option that many companies will prefer to use. Surely dumping it deep sea is better than in surface waters where it is going to get into the food chain.

    Measures are going to have to be put into place to help prevent contamination with food chain and a better understanding of the science behind deep sea disposal will alo be needed. With all these measures put into place, i believe deep sea disosal is the best option.

    What ever option that is decided to use, there will always be bad aspects of dumping contaminants- whether we dump them on land or in the sea.