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

(Beth Clifton collage)

by Bill McGraw

(Ph.D. in aquaculture, Boquete, Panama; www.newaquatechpanama.com)

Approximately 37% of marine mammal species are in danger of extinction, according to the International Union for the Conservation of Nature. Among the most often reported concerns regarding deaths of whales and dolphins are the phenomena of these animals beaching or “stranding” themselves en masse.

Episodic mass stranding events, including recent reports from California, Ireland, and New Zealand, show up on the radar of the mainstream media. Reports regarding the annual numbers of marine mammal strandings by species are scant, however, as many strandings occur in remote areas, and are lightly documented, if at all.

(Beth Clifton collage, based on 1577 etching)

Mass strandings: not new, but more frequent

Fossil evidence indicates that mass strandings of whales and dolphins have occurred from time to time for millions of years. Historical records show that exploiting mass strandings was part of the way of life of many coastal cultures around the world, beginning long before the advent of commercial whaling.

Data from recent decades, though, suggests that mass strandings are now much more frequent than in times when whales and dolphins were much more abundant.

Several reasons for this epidemic affecting dolphins and whales are known. The shock waves generated by underwater explosions and volcanic eruptions are one explanation for mass strandings. Infections and exposure to neurotoxins associated with algal blooms are another. Sonar used at frequencies that damage the inner ears are yet another.

(See War of the Whales and U.S. Navy agrees to blow up & deafen fewer whales.)

(Beth Clifton collage)

Doesn’t take Sherlock Holmes to identify mercury

But there is another relatively seldom mentioned causal factor which, when present, can make whales and dolphins more susceptible to all of the above, and appears likely to lead to mass strandings even if none of the other known causal factors are present.

Popular, yet non-scientific web sites amplify statements such as these:

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? As in The Adventures of Sherlock Holmes?

(Beth Clifton collage)

Mercury in marine mammals is up tenfold

As mentioned, there are many different causes related to the stranding of marine mammals, but one of them is, for sure, increasing exposure to 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, Mercury: The Ultimate Truth and Chronic Disease.

While the book goes into depth and detail, here is a brief summary regarding the facts as we know them concerning proof that mercury is directly involved in stranding marine mammals.

Documented research from many sources demonstrates that mercury levels in marine mammals have increased over 10 times compared to the period before the 19th century, when commercial whaling had not yet begun to visibly deplete whale populations, but mass strandings, though not unknown, remained rare events.

(Beth Clifton collage)

Increasing industrial use of mercury

More recently, scientific data clearly shows how mercury exposure 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, the use of mercury in PVC plastic production, and the use of mercury in chlor-alkali process of making the commonly used industrial chemicals chlorine, hydrogen, and sodium hydroxide.

This rise in mercury is strongly correlated with rising incidence of chronic neurodegenerative diseases in humans––and, though less documented and publicized, in other animals.

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 methyl mercury.

(Beth Clifton collage)

Food chain accumulation

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. The higher mercury levels in the sea life in an area in turn create higher levels of mercury in dolphins and whales who feed in the same area.

Dolphins and toothed whales, the species most vulnerable to stranding, tend to bio-accumulate mercury from the fish they eat; grey whales from the bottom-feeding shrimp and shellfish that form most of their diet.

Note that filter-feeding baleen whales, who eat mainly krill and plankton far offshore, rarely become stranded, and––though they often live in large family groups––almost never strand en masse.

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

(Beth Clifton collage)

Marine mammals show highest mercury levels on record

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 five times. So it is obvious and accepted that the area where a marine mammal lives and feeds plays a big part in determining the mercury levels they absorb.

Two areas that show high levels of mercury in striped and bottlenose dolphins are the Indian River area of Florida and the Mediterranean Sea.

Mercury in stranded marine mammals has been measured at the highest concentrations ever found in any animal.

Levels of mercury in mercury-detoxification organs, such as the livers of dolphins found dead from stranding, were between 4,400 and 13,150 parts per million, which is between 220 and 657 times the level of what would kill a human.

(Beth Clifton collage, based on aerial view of Minamata Bay)

Minamata Bay

The historical benchmark for the harm that mercury can do to humans is remembered as the Minamata Bay disaster, named after a location in coastal Japan.

For decades, 1932-1968, politicians looked away as fishers marketed catches collected from Minamata Bay, contaminated by mercury and other toxins discharged for decades from a nearby chemical processing plant.

More than 3,000 people (and thousands of cats, both pets and waterfront scavengers, who exhibited symptoms first) eventually suffered from effects of mercury poisoning that came to be known as “Minamata Syndrome.” Forty years of lawsuits followed the eventual identification of the cause, as the survivors sought compensation.

Information from mortalities from the Minamata disaster shows that a mercury level of 20 parts per million in the liver of humans is life-threatening.

False killer whales. (Beth Clifton collage)

Mercury in stranding cases

There are studies available that clearly show high levels of mercury in marine mammals killing themselves through stranding. Off the coast of the southern U.S., 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 parts per million, which would be 80 times that of healthy resident marine mammals of the area.

In other studies, stranded whales and dolphins show high levels of parasites and viruses resulting from depressed immune systems. One of the biggest effects of mercury toxicity is the depression of the immune system.

(Beth Clifton collage)

Mercury & selenium

Another study reported that 33% of the livers of bottlenose dolphins stranded off the coast of South Carolina and Florida were higher than 100 parts per million, a concentration that would be considered toxic. Meanwhile only 15% of live dolphins had as much mercury in their livers.

The livers of stranded Indo-Pacific dolphins from brackish waters in China were determined to contain 250 parts per million of mercury, which was determined to be toxic to this marine mammal. These dolphins were stated to be more sensitive to mercury than the bottlenose dolphins.

Moreover, as selenium has been determined to be the element that binds mercury as mercury selenide (Tiemannite or HgSe), stranded dolphins typically have mercury levels strongly correlated with concentrations of selenium, a formerly little-used metal that over the past half century has come into common use in making printers, photocopiers, and photovoltaic cells. Like humans, marine mammals remove 90% of their mercury burden through the gastrointestinal tract.

Beached pilot whales. (Carroll Cox photo)

Alzheimer’s Disease

Alzheimer’s Disease, which affects nearly 30 million people worldwide, has been directly linked to neurodegenerative processes caused by mercury toxicity as reported in published medical studies. This begs the question, can the same be said of stranded marine mammals?

As the liver is the main organ involved in storage and detoxification of mercury, mercury levels in the liver are typically reported in published studies, rather than the mercury concentrations in minor storage areas such as the brain.

However, I did find one study listing 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.

Bill McGraw, Ph.D.

For comparison, mercury concentrations of 10-30 parts per million in the brains of marine mammals are known to be toxic. Typically between five and ten percent 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.

Mercury, The Ultimate Truth and Chronic Disease is available c/o https://www.amazon.com/gp/product/B07Q52QG2J/ref=dbs_a_def_rwt_bibl_vppi_i0

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

https://www.thoughtco.com/why-whales-and-dolphins-beach-themselves-1203590

https://www.ifaw.org/international/our-work/animal-rescue/faqs-about-strandings

https://www.msn.com/en-us/news/us/sick-marine-mammals-turning-up-on-california-beaches-in-droves/ar-BBUxQBF?ocid=spartandhp

https://baleinesendirect.org/en/accumulation-of-heavy-metals-in-a-group-of-stranded-long-finned-pilot-whales-in-scotland/

https://www.nature.com/articles/245385a0

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0110336