Mercury Toxicity as a Cause for Stranded Marine Mammals is not a Mystery

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Dr. Bill McGraw, Boquete, Panama

www.newaquatechpanama.com

Approximately 37% of marine mammals are in danger of extinction. The main apparent and reported concern regarding the death of whales and dolphins is the phenomena of animals beaching or “stranding” themselves. Episodic mass stranding events, including the recent reports from California and New Zealand, show up on the radar of the main stream media. Reports regarding the annual numbers of marine mammal stranding by species are scant, however, a reason for this epidemic affecting dolphins and whales is known.

beached pilot whales

I must admit when first searching for total annual numbers on marine mammal strandings, I was a bit perplexed. Although exact global numbers seem hard to come by, I did however unearth a few odd statements. Accordingly, I have listed two quotes from two different popular, yet non-scientific websites, below.

  1. “There are many theories regarding the causes of these strandings throughout the world. Often, the causes of these large events remain a mystery.”
  2. In regards to stranded marine mammals, “Scientists are still searching for the answers that will unlock this mystery.”

A mystery? Seriously? Like Sherlock Holmes or something? Likely there are many different causes related to the stranding of marine mammals but I have no doubt what one of them is for sure, the heavy metal mercury. I found this out by reading over 90 articles, books and abstracts regarding dying marine mammals stranding themselves or depositing their bodies on the shore. About 80 of these sources are listed in the book I have recently published regarding the full story of mercury toxicity. So here I have provided a brief summary regarding the facts as we know them concerning proof that mercury is directly involved in stranding marine mammals.

Information regarding mass mortalities of prehistoric sea creatures provided by fossil records indicates there may have been “mass tidal flat strandings” possibly due to ancient toxic algae blooms but the evidence is not conclusive. Other reports concerning the use of sonar by the US Navy stated that marine mammals can be injured by the use of certain frequencies, in particular in relation to damage of the inner ear. But again, data was not available demonstrating actual injury of stranded marine mammals provided by autopsy, linked to the time period that actual sonar tests were performed.

Although mercury has always been a naturally occurring element, documented research from many sources demonstrates that mercury levels in marine mammals have increased over 10 times compared to the period before the 1800s. More recently, scientific data clearly shows how mercury has increased on a linear basis since the 1970s. This is of course is related to the increase of mercury in the environment due to coal burning, artisanal gold mining and the use of mercury in industries such as the chlor-alkali process and PVC production. This rise in mercury in the environment is strongly correlated with the rise in chronic neurodegenerative disease.

Many research studies have shown that the mercury levels in marine mammals are directly related to the mercury in the prey items they consume, which in turn are high in mercury due to the incredible bioaccumulation properties of the organic form of mercury known as methylmercury. In general, the closer to population centers and the more closed the area of water, the higher the mercury levels in the fish and invertebrates found there. As higher order carnivores such as whales and dolphins consume these mercury rich prey items, they in turn bioaccumulate mercury on a much higher scale.

Graph model of mercury
Graph of the model of total mercury emissions into the atmosphere from 1970 to 2010, data from: Muntean, M., Greet Janssens-Maenhout, Shaojie Song, Noelle E. Selin, Jos G.J. Olivier, Diego Guizzardi, Rob Maas, Frank, Dentener. 2014. Trend analysis from 1970 to 2008 and model evaluation of EDGARv4 global gridded anthropogenic mercury emissions. Science of the Total Environment. Volumes 494-495, 1 October 2014, Pages 337-350

During the 1990s, peer reviewed scientific journals reported some very pertinent information regarding mercury levels in marine mammals. Mercury content in dolphins between areas separated by a distance of as little as 600 miles can be different by a factor of 5 times. So it is obvious and accepted that the area where a marine mammal lives and feeds plays a big part in mercury levels in these animals. Two areas that show high levels of mercury in striped and bottlenose dolphins are the Indian River area of Florida (U.S.) and the Mediterranean Sea.

Mercury in stranded marine mammals has been measured at the highest concentration of any animal ever recorded. Levels of mercury in detoxification organs such as the liver in dolphins found and stranded were between 4,400 and 13,150 ppm (parts per million), which is between 220 and 657 times the level of what would kill a human. For further clarification, information from mortalities resulting from the Minimata disaster would show that a mercury level of 20 ppm in the liver of humans is most certainly life threatening. 

There are studies available that clearly show high levels of mercury in marine mammals killing themselves through stranding. Off the coast of the southern US, mercury levels in the hearts of stranded pygmy whales were 230 times that of healthy animals according to the journal Chemosphere in 2012. In an article from the same journal six years later, false killer whales found stranded off the coast of the tip of South America had mercury levels in liver tissue at 8,000 ppm, which would be 80 times that of healthy resident marine mammals of the area.

dolphins under water

The livers of stranded Indo-Pacific dolphins from brackish waters in China were determined to contain 250 ppm mercury which was determined to be toxic to this marine mammal. These dolphins were stated to be more sensitive to mercury compared to the bottlenose dolphin. Another study reported that 33% of the livers of bottlenose dolphins stranded off the coast of South Carolina and Florida were higher than 100 ppm, a concentration that would be considered toxic. Meanwhile only 15% of live dolphins had as much mercury in their livers.

Selenium has been determined to be the element that provides the protection needed which allows marine mammals to survive the very high levels of mercury in their bodies. Selenium is not only a powerful antioxidant which boosts the immune system which is often depressed due to mercury toxicity, but it also binds (chelates) mercury as mercury selenide (Tiemannite or HgSe). Stranded dolphins always have mercury levels strongly correlated with concentrations of selenium found in the major organs where mercury storage takes place such as liver and kidney tissue. Like humans, marine mammals remove 90% of their mercury burden through the GI (gastrointestinal) tract.

Alzheimer’s Disease, which affects over 45 million people in the US, has been directly linked to neurodegenerative processes caused by mercury toxicity as reported in published medical studies. So it begs the question, can the same be said of stranded marine mammals? As the liver is the main organ of storage and detoxification of mercury, mercury levels in the liver are typically reported in published studies rather than minor mercury storage areas such as the brain. However, I did find one study that documented the mercury concentrations in the brain tissue of stranded whales. Pilot whales beached on the coast of Scotland had mercury concentrations in their brains that were higher than that which would be found in humans with neurodegenerative disorders. For comparison, mercury concentrations of 10-30 ppm in the brains of marine mammals are known to be toxic. Typically between 5-10% of the total amount of mercury ingested by humans ends up being stored in brain tissue with 80% found in the kidneys and about 10% in the liver

Need more proof linking mercury to chronic disease of mammals? Check out the book in digital, and paperback form or borrow it from Amazon’s awesome lending library.

 

Funds Needed for Mercury Toxicity Research

 

Sources for this article not listed in the book Mercury, The Ultimate Truth and Chronic Disease:

  1. https://www.thoughtco.com/why-whales-and-dolphins-beach-themselves-1203590
  2. https://www.ifaw.org/international/our-work/animal-rescue/faqs-about-strandings
  3. https://www.msn.com/en-us/news/us/sick-marine-mammals-turning-up-on-california-beaches-in-droves/ar-BBUxQBF?ocid=spartandhp
  4. https://baleinesendirect.org/en/accumulation-of-heavy-metals-in-a-group-of-stranded-long-finned-pilot-whales-in-scotland/
  5. https://www.nature.com/articles/245385a0
  6. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0110336
  7. https://www.nature.com/news/2011/111011/full/news.2011.586.html
  8. https://gsa.confex.com/gsa/2011AM/finalprogram/abstract_197227.htm