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Beached whale in the Firth of Forth, Scotland, being removed using earth-moving equipment, September 2013. Photo: Patrick Down via Flickr (CC BY-NC).
Beached whale in the Firth of Forth, Scotland, being removed using earth-moving equipment, September 2013. Photo: Patrick Down via Flickr (CC BY-NC).
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Heavy metal poisoning in Scotland's beached whales

The Ecologist

15th February 2016

High levels of toxins mercury and cadmium have been found in all organs of the whales recently beached on Scotland's North Sea coast, including the brain. The research shows that rising mercury levels in the oceans leads to toxic stress in the long-lived marine mammals.

They found very high concentrations of mercury in the brain of all the whales older than nine years and in three the concentration was higher than levels at which severe neurological damage would occur in humans.

A pod of whales stranded in Fife in 2012 had high concentrations of toxic chemicals, some of which had reached the mammals' brains, scientists have discovered.

The pod of long-finned pilot whales were stranded on a beach between Anstruther and Pittenweem in Scotland, on 12th September 2012.

Out of the 31 mammals which beached only 10 could be refloated and 21 - 16 females and five males - died.

Scientists from the University of Aberdeen, in collaboration with the Scottish Marine Animal Stranding Scheme, found mercury at levels high enough to cause severe neurological damage in humans. They also demonstrated for the first time that the toxic element cadmium can cross the blood-brain barrier.

"This pod of whales provides unique new insights because we were able to look at the effects on a large number of whales from the same pod and how this varied according to age", said author Dr Eva Krupp, an environmental analytical chemist from the University of Aberdeen.

"We were able to gather an unprecedented number of tissue samples from all the major organs including the brain and as a result we can see for the first time the long term effects of mammalian exposure to the environmental pollutants.

Unique insights into mammalian response to environmental pollutants

Their report, published in the journal Science of the Total Environment, shows a clear correlation between the increased levels and the age of the mammals, suggesting toxic stress increases the longer the mammals live.

This could demonstrate that this species of marine mammal are less susceptible to mercury poisoning than humans, but that they cannot entirely discount the possibility that it is a factor leading to whales navigating off course.

"We can see clear evidence that mercury is being transported through the blood stream to all organs where it accumulates over the lifespan", explained Dr Krupp.  "As well as an increased concentration of mercury in the brain as the whales become older, we see a similar effect with cadmium, which has not been previously reported.

"It is known that cadmium can penetrate the blood brain barrier in the new-born or developmental stages but it was not thought to do so in adults. Our findings are significant because we can demonstrate for the first time that cadmium is in the brain tissue and that its levels increase with age.

"Although the body has a natural defence mechanism in the form of the element selenium, which detoxifies these harmful chemicals, we found that the majority of selenium is not available for the synthesis of essential proteins in older animals. This indicates that the longer mammals live, the less able they may be to cope with the toxic effects."

Pollution may be respoinsible for whale strandings

Dr Krupp collected and analysed samples from the whales together with PhD students Cornelius Brombach and Zuzana Gajdosechova. Analysis of samples revealed that the level of mercury in the whales increased in correlation to the age of the mammals, which ranged from under a year to 36 years.

They found very high concentrations of mercury in the brain of all the whales older than nine years and in three the concentration was higher than levels at which severe neurological damage would occur in humans.

Previous scientific studies have shown that mercury concentrations in the oceans have notably risen since the industrial revolution and through goldmining activities, which may in turn lead to an increase of mercury levels in marine mammals.

"So far, we have no indication that the mercury and cadmium levels in the brain cause disorientation, which in some cases can lead to strandings, but there is a potential for higher stress in these iconic animals due to rising toxic metal concentration in the oceans", Dr Krupp added.

"More research is needed to investigate whether this is a factor in strandings, particularly where other explanations such as illness or weather events cannot be found."

The stranding of five sperm whales along England's east coast during January this year may give them just the chance they need to explore this crucial question.

 


 

The paper: 'Possible link between Hg and Cd accumulation in the brain of long-finned pilot whales (Globicephala melas)' is by Zuzana Gajdosechova et al and published in Science of the Total Environment.

 

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