Dear Editor,

I note in the Jamaica Observer article ‘Fish fuss’ published on Saturday, July 1 that UC Rusal has begun “restocking the Rio Cobre” with tilapia fish.

The photo in the article shows the red variety of tilapia. This variety is sold as fingerlings to fish farmers and as such they are sorted to be males which grow to a larger size. The restocking is apparently more of a sop to the Rio Cobre fishers than a true restocking, which would be the replenishment of the native — and some non-native — fish, shrimp, eels, and other animals which made up the ecosystem prior to UC Rusal’s decimation of the Rio Cobre’s animal and plant life by the release of caustic and flocculant into the river.

A population of mostly male fish is a monocultural dead end. The affected area extends not only from the release point downwards, but also extends into the sea where it exits the river, as I have been advised that the fishing is no longer as good as before the releases.

One does not know what the effect of the flocculant is on the aquatic life, but it should be noted that the use of a flocculant is to cause suspended material in the caustic liquor (the caustic treated bauxite in which the aluminum oxide is dissolved) to clump together and settle out. Does anyone know what flocculant UC Rusal uses and its level of toxicity? The National Environment and Planning Agency should know, but I have never heard it mentioned. It would bind to the suspended material in the Rio Cobre as well, settling to the river bed and the sea floor at its outflow, releasing and degrading gradually over time into the river flow and sea.

The caustic, being soluble, will disperse relatively quickly, affecting river and sea life far downstream, but I would like to know about the effects of the flocculant, short and long term. Information, such as the the lethal dose that will kill 50 per cent of the exposed population (LD50) of the material, would be instructive as to the containment requirements for the red mud.

Years ago, I knew of a situation in which water supply for the north coast, not far from Dunn’s River, was being developed and various sources were being looked at. One was found to be contaminated by caustic seeping from a red mud lake into the aquifer and could not be used.

So the effects of bauxite mining and processing have not yet been fully made known to the general public.

Howard Chin

Member Jamaica Institution of Engineers

hmc14@cwjamaica.com