It’s no secret that our oceans have suffered greatly at the hand of mankind, but extinction of wildlife isn’t the singular issue anymore. Ironically, survival has become increasingly more dangerous for marine species as polluted seawater turns toxic — and now, humans are getting a dose of their own poison as well.
Pollution via Runoff
According to the NOAA (National Oceanic and Atmospheric Administration), “80% of pollution to the marine environment comes from the land”. Industrial runoff, oil and lethal fluids from all vehicle types, fecal matter from septic tanks, pesticides and agricultural herbicides, and silt from coastal construction sites are all prime examples of the unwelcome debris that flushes into the ocean after heavy rainfall.
This indirect pollution, referred to as non-point source pollution, is not exclusively reserved for those who live on the shoreline; for instance, gallons of fertilizer used by in-land farmers has a high potential of getting swept into runoff leading to local streams and groundwater, “eventually being deposited into estuaries, bays, and deltas” as explained by National Geographic. Many fertilizers contain nitrogen-rich formulas that, if allowed to overwhelm a gulf, depletes the water of oxygen, destroys the marine habitat, and reduces what was a flourishing ecosystem to nothing but algae and decay.
Referred to by the NOAA as a hypoxic environment, it is commonly called a “dead zone” or biological desert, and no ocean on earth is immune.
Solid Waste Pollution
The most recognizable form of ocean pollution is the dumping of solid waste into open water. The Great Pacific Garbage Patch serves as the disturbing poster child of this irresponsible and improper method of waste disposal, wherein humans- be them individuals or businesses -remove non-biodegradable and non-compostable waste materials and displace them into the sea. National Geographic explains:
“About 80% of the debris in the Great Pacific Garbage Patch comes from land-based activities in North America and Asia…The remaining 20% of debris in the Great Pacific Garbage Patch comes from boaters, offshore oil rigs, and large cargo ships that dump or lose debris directly into the water. The majority of this debris—about 705,000 tons—is fishing nets.”
From computer monitors to toys to household appliances, plastic is the primary ingredient in our oceanic trash stew. Virtually indestructible, plastic does not biodegrade under the sun’s rays, instead merely splintering into smaller and smaller pieces (called microplastic) that are most commonly redistributed into marine habitats through animal ingestion, with marine birds and deep sea fish alike mistaking microplastic for food and larger mammals getting tangled up in netting. This unfortunate series of events has resulted in an up-tick of marine animal death.
Mercury Toxicity in Seafood
Tasteless, odorless, and invisible to the naked eye, mercury is a highly toxic chemical that regularly circulates throughout our oceans and contaminating several species of seafood. There are 3 origins of mercury emission in the world:
- 30% Anthropogenic: coal burning, oil refining, iron and cement production, etc
- 60% Re-Emission: mercury is reintroduced into the atmosphere through naturally occurring cycles like floods and fires
- 10% natural sources: volcanoes and geothermal vents emit traces of mercury
Be it coal-mining emissions in the U.S., gold mining emissions in Ghana, or mercury-laden fish food in Chinese aquaculture, the toxin manages to hitch a ride into ocean water and accumulate into marine ecosystems from bottom to top.
Algae are the first species to ingest these concentrations of mercury, which is then absorbed as methyl mercury, and thus the natural food chain becomes incrementally more poisoned as it cycles. This steady increase in mercury toxicity via the ingestion-based exposure is called biomagnification.
Humans are no less immune to methyl mercury biomagnification than any shark or halibut, therefore serious precautions must be taken before consuming seafood.
What Seafood Is Safest?
Considering the fact that marine species measuring on the larger end of the scale are more contaminated with mercury- and have most likely consumed smaller fish that have ingested microplastic -the consensus is the larger the fish, the more toxic it is. Based in NRDC’s mercury guide:
Least safe: King mackerel, marlin, orange roughy, shark, swordfish, tilefish, ahi tuna, and bigeye tuna. Tuna is the most common source of mercury exposure in the U.S.
Safe: Fish and shellfish like eel, salmon, crab, and clam are lower in mercury.
Safest: Anchovies, sardines, and scallops and lowest in mercury.
While you’ll have to carefully consider your next plate of sushi, understanding the pollution swirling within our seawater and the true levels of toxicity in our marine life is worth the small sacrifice.