Pollution Unseen: How Mercury Permeates the Ocean
By Alexandra Smith
When it comes to marine pollution, the focus tends to be on plastics, which are extremely harmful in their own right, but what about pollutants that are less tangible? Often overlooked, toxins like mercury should be just as alarming as microplastics lining the world’s oceans.
Map of the Western Pacific Ocean with the Mariana Trench. Credit: Amazing Race CC BY
It may seem like the deepest, most inaccessible parts of the ocean would be spared from pollution, but this is far from the truth. A recent study from the University of Michigan found that toxic mercury has made its way to the deepest part of the ocean - the Mariana Trench. How it got there is a point of contention between two groups of researchers. Scientists from the University of Michigan suggest it got there by sinking fish carcasses from near-surface waters, while a Chinese-led group of researchers thinks the mercury hitched a ride on sinking organic matter - microscopic dead plankton and fecal matter.
Before the atmospheric mercury got to the deepest ocean crevice, though, it came from us. Mercury is a naturally occurring heavy liquid metal found in virtually every living thing on Earth. It is released into the atmosphere naturally through volcanic eruptions and the weathering of rocks. But the main cause of release, and what these studies are proposing, is that humans are responsible. Globally, human activities such as gold mining, coal combustion, and cement production emit about 2220 metric tons of mercury per year. As of 2014, there is an estimated 60,000 to 80,000 tons of mercury pollution sitting in the ocean, and mercury pollution in shallow ocean water (300 ft) has tripled since the Industrial Revolution. Prior to this study, it was thought that human-caused mercury only stayed in the upper 1000 meters of the ocean. But due to the intensity and scale of human emissions, that thought is in the past.
Gaseous pollution. Credit Pawel Czerwiński
Practically every bite of food we eat has a bit of mercury in it. As unsettling as this sounds, it is such a small quantity (~0.3 g in one’s lifetime) that it will not cause harm. However, in higher quantities and in the form of methylmercury, it is especially dangerous. Mercury in the atmosphere is transformed by oceanic bacteria into methylmercury, which then can get ingested and cause harm. Through processes called bioaccumulation and biomagnification, methylmercury accumulates and gets amplified as it moves from the bottom of the food chain to the top. It accumulates in biological tissue, harming the organism and the predator that eats it, amplifying in concentration as it travels up the food chain. Biomagnification causes larger predatory fish to have as much as 10 times the mercury concentration than the prey they consume. Consuming significant amounts of fish with high concentrations of mercury, like tuna, is a surefire way of introducing harmful mercury to your body. Many studies have outlined the negative health effects of mercury in the body; links to Alzheimer’s, Parkinson’s, heart attack risk, and decreases in fine motor skills, memory, and attention to name a few.
Biomagnification of Mercury. Credit: U.S. Environmental Protection Agency
The negative effects of mercury on oceanic animals are much less studied than that of humans. Researchers at Florida Atlantic University want to change that. They recently studied 83 different stranded whales and dolphins, and unfortunately found “some of the highest mercury concentrations that have ever been reported in any living thing anywhere, ever”. Two bottlenose dolphins from the coasts of North Carolina and Florida had 1,400 parts per million of mercury in their liver tissue. To put that into perspective, human fetuses suffer neurological damage from just 10 parts per million. These numbers are staggering.
Every animal in the study had considerable physical maladies such as kidney damage and chronic liver disease. These may have been caused by the toxins in their bodies. Unfortunately, it cannot be easily proven that the toxins were the reason for the animals’ deaths, but studies like these are a valuable first step in understanding toxic pollution in offshore, oceanic species.
Representation of beached dolphins. Credit: Simon Varwell/Flickr
Mercury, a mostly invisible pollutant, has potentially harrowing effects on the marine environment. While much is unknown about how marine organisms respond to mercury in their environment, it seems that human studies may be a good indicator. We know that mercury pollution cannot be a good thing in any case. More extensive research into how mercury affects marine animals must be done. Still, for now, hopefully, the troubling effects of mercury on humans will bring some much-needed attention to mercury pollution.
Sources:
Baishaw, S., et al. “Mercury in Seafood: Mechanisms of Accumulation and Consequences for Consumer Health.” De Gruyter, De Gruyter, 1 Apr. 2007, www.degruyter.com/view/journals/reveh/22/2/article-p91.xml.
Brown, Mary. “Should You Avoid Fish Because of Mercury?” Healthline, 14 Sept. 2018, www.healthline.com/nutrition/mercury-content-of-fish#accumulation.
Hansen, Cypress. “Beached Whales, Dolphins on US Coast Had High Levels of Pollutants, Heavy Metals.” The Wire Science, 27 Nov. 2020, science.thewire.in/environment/beached-whales-dolphins-us-coast-high-levels-pollutants-heavy-metals/.
“Mercury - Element Information, Properties and Uses: Periodic Table.” Mercury - Element Information, Properties and Uses | Periodic Table, www.rsc.org/periodic-table/element/80/mercury.
“Mercury Emissions: The Global Context.” EPA, Environmental Protection Agency, 28 Jan. 2020, www.epa.gov/international-cooperation/mercury-emissions-global-context.
“Mercury in the World's Oceans: On the Rise.” NSF, Aug. 2014, www.nsf.gov/news/news_summ.jsp?cntn_id=132171.
University of Michigan. "Fish carcasses deliver toxic mercury pollution to the deepest ocean trenches." ScienceDaily. ScienceDaily, 16 November 2020. www.sciencedaily.com/releases/2020/11/201116161214.htm