How Oysters May Help Reduce Nitrogen Pollution

oyster farm

Story at-a-glance -

  • Oysters have a unique microbiome growing on their shells and in the sediment around them that have the capacity to process nitrogen compounds into harmless nitrogen gas
  • Nutrient pollution from excess nitrogen and phosphorus reaches waterways through ground water runoff, industrial wastewater treatment plants and septic tanks, and has become one of the costlier environmental problems
  • Excess nitrogen is responsible for a growing number of toxic algae blooms, some of which are so large they are visible from space
  • Algae blooms severely reduce the amount of oxygen in the water, destroying the local ecosystem and producing toxins that are dangerous to fish and humans

By Dr. Mercola

A raw oyster has an unpalatable appearance and generally a high, visual "ick" factor. However, before humans began destroying the oyster's natural habitat, this little saltwater, bivalve mollusk provided a nutrient-rich source of calcium, iron, protein and zinc.1 Oysters have also been prized for their aphrodisiac qualities, as they increase sperm and testosterone production and play a role in the libido of both genders.

High levels of zinc in the oyster are likely responsible for the aphrodisiac quality and for supporting your immune system.2 This dietary mineral is used as a cofactor in a number of critical enzymes. Organic, raw sesame seeds, pumpkin seeds and cashews are also rich in zinc and likely a far healthier option.

Oysters filter algae and other food particles from water as it constantly is drawn over their gills. This means that most small particles are drawn into the oyster and their digestive tract. Several recent studies have analyzed how environmental pollution affects the life cycle of the oyster. When carbon dioxide enters water, it lowers the pH and effectively kills oysters.3

Another study found when oysters ingest microbeads of plastic in the ocean, it affects the animal's ability to reproduce and grow, resulting in 40 percent less offspring and 20 percent smaller animals.4 Between 5.3 million and nearly 14 million U.S. tons of plastic enters the ocean every year.5 Scientists who measured how much plastic enters the ocean yearly expect that if disposal methods do not change, the cumulative impact to the ocean will reach 170.8 million tons by 2025.6

According to a report by the British Department for Environment Food and Rural Affairs, eating six oysters could introduce approximately 50 microbeads of plastic into your body.7 On the upside, a recent research study now suggests that science could take advantage of the oyster's filtering system and unique microbiome to help repair the ocean environment.

Nutrient Pollution Leads to Algae Blooms and Dead Water

According to the U.S. Environmental Protection Agency (EPA), nutrient pollution from excess nitrogen and phosphorus in the environment is one of the most widespread, costly and challenging problems.8 Nitrogen is one of the most abundant elements in the air, and naturally found in gas form. It is a critical component in the production of proteins in living organisms. Bound in gas form, nitrogen is useless to most organisms.9

Nitrogen availability in nature is controlled by bacteria that convert nitrogen gas to a form that is more bioavailable to plants and animals. This naturally controlled cycle has been severely impacted by human waste and the injection of nitrogen-based fertilizers into the environment. Called nutrient pollution, it has impacted much of the waterways around the world for decades, creating environmental and financial problems.10

Excess nitrogen and phosphorus in the water causes algae to grow faster than the local ecosystem can handle, resulting in large algae blooms like the one reported at Lake Okeechobee, Florida, that was so large it could be seen from space.11 Miles of southern Florida coastline and waterways were affected and could be traced to the nation's second largest freshwater lake, Lake Okeechobee.12

John Campbell, spokesman for the U.S. Army Corp of Engineers Jacksonville District, reported decades of fertilization runoff from farms, combined with warmer temperatures, promoted the growth of the blue-green algae.13 Nitrogen may also enter the waterways from industrial wastewater treatment plants and from septic tanks or stormwater runoff in urban areas and farms.14

Water from the lake was routinely discharged into local canals to prevent flooding and substantially contributed to the putrid blooms that proliferated through the canals, estuaries and along the coastline. These large growths of algae reduce or eliminate oxygen in the water that fish and other aquatic life need to survive. During an algae bloom, large numbers of fish may get sick and die, and elevated toxins and bacterial growth may harm humans if they come into contact with contaminated fish or shellfish, or drink the water. 15

This results in dead zones in the water16 where life cannot be found, and a loss of sea grass necessary for the survival of some marine life.17 Nutrient pollution also reaches the ground water, affecting the source of drinking water for millions in the U.S. Even at low levels, the added nitrogen-based compounds can be harmful.

Oyster Microbiome May Enhance Denitrification

Researchers from the Virginia Institute of Marine Science set out to determine how much of an impact the oyster may have in reducing excess nutrients from water.18 The research stemmed from the knowledge oysters impact nitrogen in the environment in two different ways:

  • The oysters sequester nitrogen in the environment in their tissue and cells where it remains until the oyster dies. Nitrogen could be completely removed if the dead oysters were harvested and the shells were not returned to the water.
  • Oysters create a specific microbiome of bacteria living along the oyster reefs, in low light with a steady supply of fresh oxygen. These bacteria perform a process called denitrification, during which nitrogen compounds are turned back into nitrogen gas.

In the first study, the oysters appeared to reduce other pollutants from their immediate environment, but at a lower rate than nitrogen. Building on their initial research, a team from the same university attempted to identify and quantify the bacteria in the oyster's gut and shell responsible for the denitrification process.19 The researchers used a computer program to infer bacterial activity based on the sequence of RNA genes.20 According to one of the researchers:21

“We found that oyster shells contain unique microbial communities with higher denitrification activities than sediments. It’s thus possible to reduce nutrients at the beginning of an oyster restoration project as shell microbiomes are actively removing fixed nitrogen.”

In this initial study to identify the specific bacteria carrying genes associated with oyster guts, shells and reef sediment, the scientists combined a genomic database with a program they devised. They then measured the rate of denitrification in laboratory chambers and discovered a much higher rate in the chambers with live oysters and shells. When they compared these results with the genes in three microbiomes they found a high correlation between rates of denitrification and a gene sequence call nosZI.22

The researchers caution that while the results are encouraging, more study is needed as the processes are complex and require the coordinated expression of several genes. They pointed out that while an organism may carry the gene, it may not be expressed. They remain cautiously optimistic about future studies and the potential for oyster beds to help reduce nutrient pollution in saltwater waterways.

Oyster Reefs Protect the Land and Marine Life

Oysters also provide a mechanical benefit. As they multiply, the mollusks create oyster reefs. These areas function much like coral reefs, giving other plants and animals structures in which to live.23 In this video from Nature Conservancy, you'll discover how these reefs are being rebuilt and the benefits to the environment.

Large aggregations of oysters are also called oyster bars, oyster banks, oyster bottoms and oyster beds.24 These terms are often used interchangeably and are not well defined. As they reproduce and settle on the shells of other oysters, they create massive physical structures. These reefs have been negatively affected in a number of ways by human interaction.

Boat wakes slowly erode the reef, pollution poisons the oysters and inhibits reproduction and growth, and intense harvesting have all contributed to the 85 percent reduction in oyster reefs around the world.25 Oyster reefs are sometimes called living shorelines,26 as they often develop in estuary waters near the mouths of rivers. Oyster reefs act as a living breakwater that mitigates coastal erosion and facilitates wildlife growth in the area.27

These shorelines where fresh water and saltwater meet are often the most degraded and at-risk areas as they are sensitive to changes in sea level, storm damage and human utilization. Large, healthy oyster reefs help protect the marshlands and coastline from damage.28

Coastal marshlands provide essential habitat for birds, fish and marine life. Approximately 75 percent of commercial fish and shellfish and nearly 90 percent of fish caught for recreation depend on these estuaries.29 Without the development and growth of oyster reefs these areas are in greater danger of damage.

Oysters Filter More Than Plastic and Nitrogen

Scientists may be able to harness the power of the oyster to filter excess nitrogen from the oceans, but these little marine animals don't stop with nitrogen. One study by the University of North Carolina Wilmington (UNCW) found oysters harvested from Brunswick and New Hanover counties had some of the highest levels of arsenic in the U.S.30 Ten heavy metals were found in the sediment and oyster tissue.

The researchers were surprised to also find triclosan at each of the sites tested while testing for polycyclic aromatic hydrocarbons (PAH). Hot spot locations were noted to have levels of PAH in the oyster bodies and surrounding sediment between two and 24 times greater than EPA levels. Steven Skrabal, Ph.D., professor for Marine Science at UNCW, commented on the discoveries saying,31 "From a human health standpoint, some of them are carcinogenic, so it's kind of good to know what levels are in the oysters."

In Portland, Oregon, scientists found native Olympia oysters from Coos and Natarts bays contained a dangerous cocktail of pharmaceuticals and chemicals in their flesh,32 including pain relievers, antibiotics, PCBs, pesticides and mercury that had likely entered the bay from groundwater runoff and wastewater discharge. Elise Granek, Ph.D., associate professor of Environmental Science and Management, succinctly points out the danger of eating marine animals living in oceans polluted by chemicals:33

"There are no federal or state guidelines for screening consumption of multiple contaminant types. We’ve found oysters that contain pharmaceuticals, carcinogenic compounds and mercury, and we don’t know the effects or synergies of taking this combination of drugs and chemicals together. Commercial and native oysters may contain similar contaminants because the two species both filter their food out of the surrounding water.”

Federally Acceptable Levels Not Enough to Protect Your Health

Following the Deepwater Horizon oil spill in the Gulf of Mexico, oysters tested positive for toxic heavy metals at levels greater than considered safe for human consumption.34 Two years after the spill a team of scientists from the California Academy of Sciences detected evidence that heavy metals and other contaminants from the spill had been incorporated into the shells and tissue of the oysters,35 potentially leading to bioaccumulation in predatory animals further up the food chain.

Independent testing of seafood increased after the oil spill in the Gulf of Mexico as government agencies insisted within months that the seafood was safe to eat. Government inspectors were using a smell test to tell if the fish were safe.36 Gulf fisherman were not satisfied and questioned whether the fish was safe to feed their families. They demanded more thorough testing to measure the effects of the oil and the dispersants to fight the slick. Rusty Graybill, a fisherman from Louisiana, commented to an NBC journalist:37

"If I put fish in a barrel of water and poured oil and Dove detergent over that, and mixed it up, would you eat that fish? I wouldn't feed it to you or my family. I'm afraid someone's going to get sick."

A year later the FDA continued to insist the fish were safe to eat, although a study by the National Resources Defense Council cast serious doubt on that claim.38 By 2015, the crabs and oysters tested with lower levels of contaminants, but the population of mollusks and shrimp have drastically declined.39 Al Sunseri owns 135-year-old P&J Oyster Co., a harvester and distributor in New Orleans. He spoke to a journalist from The Salt, saying:40

"They're saying that the oyster landings are the same as what they were pre-oil spill, and there's no way. If it was, we would not have a 300 percent increase on the dock for the price of oysters. I attribute it all to the Deepwater Horizon oil disaster, and I'll never say it's anything but a disaster. It's not a spill, because spills are easily cleaned up, and this is the gift that keeps on giving."

Your Best Seafood Options

Eating seafood from contaminated waters increases your risk of polluting your own body with chemicals and pharmaceuticals that damage your health. Unfortunately, the large majority of wild-caught fish are too contaminated to eat as most waterways are contaminated with mercury, heavy metal and chemicals. But eating farmed fish is not the answer either, as many farmed fish are heavily contaminated as well. Farmed salmon has been declared one of the most toxic foods of all.

As a general rule I recommend eating only authentic wild-caught Alaskan sockeye salmon or smaller fish with short life cycles, such as sardines, anchovies, mackerel or herring. These fish are good choices to get omega-3 fats in your diet while minimizing your exposure to toxins. To encourage you to try these fish, I recommend you experiment by adding anchovies or sardines to your next salad. You may also want to check out my personal lunch recipe and healthy baked salmon recipe.

Post your comment