Bioaccumulation: A Growing Threat

by Alice C.

Most people know that tuna has high concentrations of mercury, yet they do not know why. The reason that tuna contains mercury is bioaccumulation – a phenomenon with which many people are unfamiliar, and yet stands as one of the greatest threats facing the health of the Puget Sound and ocean as a whole.

Defined by the Environmental Protection Agency as “the accumulation of chemicals in the tissue of organisms through any route, including respiration, ingestion, or direct contact with contaminated water, sediment, and pore water in the sediment,” bioaccumulation touches every part of the ecosystem and disproportionally affects those organisms at the top of the food web. Because tuna are the apex predators of their open ocean ecosystem, mercury accumulates in the fatty tissues of their bodies. Mercury and other heavy metals fall under the category of PBTs, or persistent, bioaccumulative, and toxic pollutants, which pose a threat to human and environmental health. PBTs are typically fat-soluble and remain in the body for a long period of time, eventually causing physiological problems above certain concentrations.

Bioaccumulation can come from any number of sources, including oil and grease, chlorinated pesticides, heavy metals, and synthetic industrial compounds. Carried by runoff from urban areas and roadways, oil and grease can have severe effects on marine ecosystems. Additionally, chlorinated pesticides like DDT, well-known for its harmful effects on the eggshells of birds of prey, can find its way to the ocean in runoff from farms in countries where it is still in use. Heavy metals, such as mercury, copper, lead, and zinc, accumulate in the fatty tissue of large fish and marine mammals, and at high enough concentrations can cause neurological damage and death. Phthalates, polychlorinated biphenyls (PCBs), and dioxins are all synthetic toxic chemicals that persist in the environment and tend to cause severe damage to animal and human health. Studies have shown a correlation between PCBs and cancer, and both PCBs and dioxins are known to wreak havoc on the immune, endocrine, reproductive, and nervous systems.

Here in the Puget Sound, bioaccumulation poses a growing threat to our marine environment, especially to local salmon populations, resident and transient orca whales, and other marine mammals. Orcas in the south Puget Sound are some of the most PCB-polluted mammals in the world, and local harbor seals are seven times more contaminated with PBTs than harbor seals in the neighboring Strait of Georgia. The Puget Sound region is home to more than 4.5 million people, all living and working around the second largest marine estuary in the country. Our actions affect the health of the Puget Sound – every year, millions of pounds of toxic chemicals flow into the Sound from surface runoff, wastewater pipes, and groundwater discharges.

As the Puget Sound region becomes more populated and urbanized, we must be cognizant of the effects we have on the local marine ecosystem. To reduce the impact of bioaccumulation, we can use less plastic, as many synthetic PBTs come from plastics, we can filter our stormwater runoff, and we can research methods of removing PBTs from the marine environment. In terrestrial ecosystems, studies have shown that phytoremediation (using plants to filter soil) and mycoremediation (using fungi to filter soil) have effectively removed and broken down PBTs. Perhaps a similar solution can be found for marine bioaccumulation.


“Bioaccumulation.” USGS – U.S. Geological Survey. U.S. Department of the Interior, 4 Aug. 2015. Web. 12 Oct. 2015. <>.

DiFranco, Daniel, and Pamela Johnston. “Bioaccumulation.” The Encyclopedia of Earth. Ed. Sidney Draggan. National Council for Science and the Environment, 10 June 2010. Web. 12 Oct. 2015. <>.

“Threats to Puget Sound.” Washington State Department of Ecology. N.p., n.d. Web. 12 Oct. 2015. <

Categories Science

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