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Only the dose makes the poison

I have been writing these columns for a number of years and generally they are about politics. However, occasionally science enters into the political realm. As a chemist with a Ph.D.

I have been writing these columns for a number of years and generally they are about politics. However, occasionally science enters into the political realm. As a chemist with a Ph.D. my view of these issues is informed by my understanding of science.

Sometimes the science actually drives the political agenda. Take climate change as an example. The climatologists, meteorologists, physicists and chemists working on understanding climate change could have kept the whole thing quiet.

They could have simply done the research and published in learned journals. They could have spent the last two decades not saying anything to the general public. But if they had done that, all of the strange weather and increases in temperature would have remained unexplained to the general public.

So scientists chose to speak out and publicly present their data. The consequence has been a raging "controversy" in the media when no controversy really exists. But the science should have driven the political agenda.

Other times it is the political or societal agenda that drives the science. This is much more common and can often lead to hyperbolic fear.

All of this is to preface a few comments on the Mount Polley mining disaster. Yes, it is a catastrophe. Yes, it shouldn't have happened. Yes, cleaning it up will be a major undertaking.

But, no, it is not a "natural disaster" as I heard one reporter describe it. Nor it is going to contaminate all of B.C. or make the Fraser River toxic.

It is certainly not comparable to the tailing ponds spills in the tar sands. And its long term impacts are not likely to be the death of Quesnel Lake and all of the adjacent waterways.

It is hard to find a starting point for discussing the incident in all of the rhetoric, but maybe the concept of toxicity would be good place. What do we mean when we say that something is toxic?

You would think that would be an easy question to answer: "A toxic substance is one that kills things."

Unfortunately, it is not that simple. If it was human beings and all of the other animals on the planet would never have evolved in the first place. After all, by this definition, both oxygen and water are toxic under the right circumstances.

In the case of the Mount Polley breach, many people have expressed concerns about toxic substances such as arsenic, lead and mercury being in the tailing pond. Fair enough.

However, all three of those elements are found in the ground around us. Dig up dirt anywhere in northern B.C. and you are likely to find at least one of those elements present.

Why? Because they are elements. Arsenic, for example, is not something that is made by mining. It is an element that is extracted during the process of mining. It is already in the ground along with a myriad of other elements - such as silicon, aluminum, iron, copper, oxygen, sulphur, mercury and lead - all of which get extracted by mining.

But everyone knows that arsenic is a poison, isn't it? It depends.

To quote Paracelsus: "Only the dose makes the poison."

Arsenic is only poisonous at high concentrations.

Quesnel Lake is 266 square kilometres in size with an average depth of 159 metres and holds 43.3 billion cubic metres of water. While the 10 million cubic metres of water released from the tailing pond sounds like a lot, it is dwarfed by the amount of water in the lake in the first place. The tailing pond water was diluted by a factor of 4,330 when mixed into the lake.

If all of the arsenic at Mount Polley - some 406 tonnes - was dissolved into the tailing pond water, it would have only resulted in a concentration of 40.6 parts per million. And with a dilution factor of 4,330 upon hitting the Quesnel Lake, that number drops 10 parts per billion.

That is consistent with Health Canada's drinking water guidelines.

However, arsenic is not particularly soluble. Most of the 406 tonnes in the tailing pond is in the sediment. The amount in the tailing pond water was likely consistent with drinking water standards. Hence, the notion that the spill produced toxic levels of arsenic in the lake, as a whole, is likely to be unfounded.

The water from the tailing pond isn't really the issue. The issue is the sediment and how bio-available the elements in the sediment are. Again, the total volume of sediment is not large compared to the lake as a whole. There is some risk, but certainly not at the hyperbolic level that has played out in the media.

The best thing that can happen at this point is to let the scientists sort out the details and let the results determine the consequences. Letting the politics drive the show just causes a lot of unnecessary fear.