Researchers at the University of Michigan and the University of Hawaii say they've solved the mystery of how mercury gets into the fish, and they say levels of the toxin in Pacific fish will rise in the coming decades.
They say mercury contamination in fish is a global problem and the only way to solve it is to reduce global emissions of mercury.
University of Michigan Professor Joel Blum advises people to try to limit their consumption of swordfish, tuna, shark and tile-fish which have been found to have the highest levels of mercury.
Presenter: Geraldine Coutts
Speaker: Professor Joel Blum, Earth & Environmental Sciences, University of Michigan
BLUM: We've known for many years that mercury is emitted to the atmosphere from coal-fired power plants and is deposited onto the ocean in rain. But there are several different forms of mercury, and the mercury must be transformed into a form that is bioaccumulative in fish and what we didn't know was how that process took place in the ocean or where it took place in the ocean and we've solved that mystery.
COUTTS: Well, how extensive is the problem? So the mercury gets into the fish and then the fish emit it into the ocean and people swimming in it, the eco-systems. I mean how far afield does this contaminate?
BLUM: Well, the only health concern is through eating fish and it's only fish that eat other fish, that are predatory and that live at great depths in the ocean that have the high levels of mercury. So people can limit their exposure to mercury by limiting their consumption of just a certain number of types of fish, such as swordfish, tuna, shark and tile-fish which are the ones that have the highest levels of mercury.
COUTTS: Well hmm, that would send nervousness right across the Pacific region hearing that, especially tuna, because it's a growth industry and provides a lot of the economies much funding into their economies. So what message should they be hearing?
BLUM: Well, the message should not be that people should stop eating fish. Fish is very, very health, it provides a lot of very essential nutrients. The key is that when you're eating those fish that have the higher levels of mercury, that one should just be careful not to eat more than one or two servings per week in order to limit their exposure. And this is particularly important for young women, of childbearing age because of the effect that mercury can have a developing foetus.
COUTTS: But, just the mention of tuna alone and mercury could have ramifications for the tuna industry of the Pacific?
BLUM: Well, it's been known. This is not a new finding. We've known that there are significant levels of mercury in tuna and, in fact, there's a global treaty that was recently passed by the UN, where countries have agreed to start working towards limiting the emissions of mercury with the goal of bringing the concentrations of mercury in fish down. So what's new from our work is we understand the process much better and we've filled in some of the missing pieces of the puzzle of how the mercury finds its way into fish, but the fact that mercury is in fish is something that's been known for a very long time.
COUTTS: India and China, are they they only two, because we know and in Australia, we've heard stories of mercury in fish off Tasmania for decades, so is that also an issue of coal-fired power stations?
BLUM: Well, so mercury once it gets into the atmosphere, can stay in the atmosphere up to a year and so it can circulate, so mercury that's emitted from one continent can find its way around the globe. So mercury is truly a global problem. It is true that down wind of areas where there's large emissions of mercury from coal combustion can sometimes have higher levels, but in general, you can't escape the fact that there's some mercury in the atmosphere everywhere. So the amount of mercury that's emitted is largely dictated by the amount of coal that's being combusted in a particular region and also on top of that, how common the emissions control devices are that are put onto power plants.
And it just so happens that China and India have rapidly increased their use of coal and they're share of the global mercury emissions has gone up relative to other countries where other continents that used to be the most important sources, such as North America and Europe, which have actually reduced mercury emissions.
COUTTS: Ah, mercury poisoning. How is that identified?
BLUM: Hmm, the main problem from mercury is impaired neurological development, especially in young children and in developing foetuses and it's basically produces damage to the central nervous system. If one suspects there's a problem, there's some simple tests that can be done of the mercury concentration of people's hair, in particular, and there are other tests as well that can be used to figure out if they've been exposed to too much mercury.
COUTTS; So, I'm guessing the problem isn't going to go away anytime soon if the emissions from India and China are actually on the rise. The solution to this would be to go the other way?
BLUM: That's true, things are not going to change quickly, but there is an increasing use of emissions-control devices on power plants which reduce considerably the amount of emissions and also there is now, just very recently, this UN treaty, where countries have agreed to at least begin the process of finding ways to limit the emissions of mercury.
One of the things that our study showed though, is that mercury enters the food web of the fish deep in the ocean and so it's not just the amount of mercury that's deposited to the surface of the ocean that matters, but there's a delay where that mercury has to work its way down deeper into the ocean where it gets transferred into the more toxic form of organic mercury. So for that reason, we can only hope that the global treaty will eventually result in limited emissions and then once that mercury works its way out of the system, eventually we should have lower levels, but it's not going to happen anytime soon. You're correct about that.