Podcast: The effects of metal pollution on fish

Bike in river

11 November 2014 by Richard Hollingham

This week in the Planet Earth podcast, Jamie Stevens and Josie Paris of the University of Exeter explain how some fish have adapted to heavily polluted rivers in southwest England.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Richard Hollingham: This time in the Planet Earth podcast - fish that have adapted to heavily polluted rivers. I'm Richard Hollingham and I have come to Dartmoor, and really this is the perfect English country scene. There's a blue sky, a gentle breeze and I'm standing next to a gently rippling clear stream overhung by oak trees, and you wouldn't expect to find pollution in areas like this. But with its long history of tin and copper mining many of the streams and rivers, particularly in West Cornwall are heavily contaminated with metals. I'm with Jamie Stevens and Josie Paris from the University of Exeter who have been studying salmon and trout in the waterways of Devon and Cornwall.

Now, Jamie, some of the rivers in this area are polluted with metal contamination from, well, not even decades, not even centuries but thousands of years of tin and copper mining.

Jamie Stevens: This is one of the things that first drew people to this area. Metals that were produced were one of the big attractions, for instance, to the Romans, and of course once you start digging into soil and once you start digging into rocks, that natural process by which waterways and rain erode rocks and dilute metals out that speeds up quite rapidly. What we know from our archaeological records is that at certain times there have been massive amounts of metals and other pollutants entering the streams and waterways, particularly in West Devon and across Cornwall and this, obviously, has had an impact on the life within the rivers and streams of this region and that's sometime that my group has been studying now for the past 15 years.

Richard Hollingham: Josie, what do these rivers actually look like, I mean compared to the beautifully clear river that is running past us here?

Josie Paris: Some of the rivers in Cornwall actually run red with the iron that is flowing through the river and you can still see that today.

Richard Hollingham: You've got these rivers that run red - were you even expecting to find fish there?

Josie Paris: We were quite surprised when we sampled the rivers to see the quantities of fish that we were finding. They all seemed to be quite big and healthy and support large numbers of trout populations. When we look at these fish genetically they seem to be quite genetically distinct from one another which is the signature of adaption to these metals. And what we also find experimentally, if you look at these fish in the lab, is that if you put a metal naïve fish or a fish from a clean river into river water that mimics the metals in these rivers, they don't tend to fare very well.

Richard Hollingham: Jamie, what's going on then? These fish are managing to adapt to these rivers and over what sort of time scale?

Jamie Stevens: If you have the genes to allow you to live within those rivers, there is no reason why you can't do very well and that's why I think we're seeing quite healthy numerical populations of fish. We are also seeing the first signs that these fish... they are not just coping with the metals within the river but they are actually adapting to metals within the river, so we're seeing the first signs of a change in the genetics of the fish to allow them to live in these environments. For us as biologists and geneticists that's really very interesting. To see something so pronounced on a very local scale within our own small area of England.

Richard Hollingham: And, Josie, what sort of time scale is this process happening over? I mean are we talking hundreds of years or longer?

Josie Paris: We've used some statistical simulations to model when these genes are likely to have arrived in these populations and what we have found is that many of these populations, their gene variance, seem to have arisen during the Middle Ages where there was a lot of mining activity in the region. There is a particular river, the river Hayle in Cornwall within which we see a big split between populations upstream and downstream of a very heavy metal contaminated site. And what we see here is this split has been timed to the eighteen hundreds where we know that the mines around this area were being actively exploited for metals.

Richard Hollingham: So actually that's only, what, a couple of hundred of years that this change has taken place?

Josie Paris: Yeah, absolutely. It is a very fast adaption but you would expect that with something at such a high selective pressure is going to affect the genetics of fish quite quickly.

Richard Hollingham: Now, Jamie, you touched on some of the underlying biology here and obviously that is interesting and what's going on is interesting but does this have wider implications than just for Devon and Cornwall?

Jamie Stevens: Yes, it does. As we see rivers come under increasing pressures from anthropogenic activity, we are likely to see more and more instances where fish populations suffer. There's a great debate in the salmonid biology community about the pros and cons of the activity of stocking, but there are instances where it may be appropriate to take fish from a river which has similar characteristics to a river that has just lost its fish to be able to re-establish a population, and if we can know something about the genetic profiles of fish within some of these heavily metal impacted rivers they give us a reservoir, as it were, which we might be able to usefully re-seed rivers that have been more recently impacted by detrimental human activity.

Richard Hollingham: What about the underlying biology here. This has given you a cold insight into how quickly a species can adapt to a changing environment.

Jamie Stevens: Yeah, I mean for us it is fascinating and one of the things that we are also becoming conscious of is we bandy the term 'metals' around, but actually I'm on a steep learning curve here but there are a lot of metals out there and some work by colleagues in the department in Exeter has shown that actually responses to metals in the lab, fish adapt differently to different metals, so I think we have to be quite careful and go in with our eyes open when we talk about metal tolerance. Fish that respond to, for instance, heavy doses of arsenic maybe up regulating genes or taking on different variant profiles that will be very different and may not confer, for instance, tolerance to iron or something like that, so we're really starting to dig into that fine level of variation, a fine level of tolerance and at the same time we're working with colleagues at the Camborne School of Mines to understand the range of different metals that have gone into the rivers and streams of West Devon and Cornwall over the millennia.

Richard Hollingham: Jamie Stevens and Josie Paris from the University of Exeter, thank you. You can find pictures of us here on the Planet Earth online Facebook and Twitter feeds and that's the Planet Earth podcast from the Natural Environment Research Council, from beautiful sunny Devon. I'm Richard Hollingham and thanks for listening.