Mercury pollution occurs when factories burn coal or mining operations release run-off into lakes and rivers, where microorganisms convert it to methylmercury that is taken up by plants and small fish; as these fish become consumed by larger ones, more methylmercury accumulates throughout their food chains and becomes concentrated further up.
Learn about how mercury accumulates in fish that people eat, and why pregnant women, breastfeeding mothers, and young children should avoid eating fish as often.
Human Consumption
Most mercury found in fish comes from both natural and industrial sources. It enters the ocean through burnt coal or fossil fuel burning, mining run-off, or industrial activities such as waste processing plants; then microscopic marine algae known as phytoplankton absorb the mercury before being eaten up by zooplankton, tiny marine animals that form part of food chains in ocean environments. Larger fish then consume these organisms, passing along any remaining mercury to their bodies which then passes to those higher up the food chain – this process is known as bioaccumulation; as higher up in food chains a fish is, more mercury it contains.
Due to how slowly mercury leaves our bodies, its build-up over time. A person who consumes fish with 100 micrograms of mercury typically will accumulate 50 micrograms after 50 days; 25 micrograms after 250 days; and 13 micrograms within a year if eating fish frequently – hence why pregnant women and those eating lots of seafood are advised to limit their intake.
Mercury consumption at high enough levels may pass through the placenta into the baby’s system and contribute to impaired development, leading to mental retardation or learning disabilities later in life. Children who regularly consume large quantities of fish could also be vulnerable.
The best way to reduce mercury releases into the environment is through eliminating fossil fuel use like coal for electricity generation, but due to recent moves by Trump administration to rollback Obama-era plans reducing coal emissions this is no longer an effective approach. This presents an immense threat.
Mercury contamination poses another significant challenge; it cannot simply be flushed away down the drain. Mercury attaches itself to proteins in fish muscles, rendering it immune from removal through cleaning or cooking methods. While eating low mercury fish such as tuna is important, ultimately we need to shift away from fossil fuels towards renewable energies as a safeguard.
Natural Sources
Mercury can be found naturally in rocks, soil and water throughout the environment; however, human activities have also contributed to its release into the air, land and water by burning fossil fuels (like coal, oil and natural gas); incinerating medical waste or garbage; mining for gold or copper and so forth. Mercury released into the air travels via wind and rain to local water bodies where it settles into sediments at lakes, rivers and oceans. There it can then be transformed by microorganisms into methylmercury which travels up the food chain as part of food chains. Methylmercury builds up in predator fish such as bass and tuna that consume smaller ones like sardines and anchovies, like bass or tuna. Over their long lives, these larger fish may accumulate higher concentrations of mercury – known as biomagnification – with each step further up their food chains.
Mercury is highly soluble and difficult to flush out of the body, making it highly absorbable by living organisms that ingest it. Most organic mercury is taken up by phytoplankton – single-celled algae found at the base of most aquatic food chains – with small fish eating them then taking in its methylated form as food, which builds up over time; highest amounts are seen in long-lived predator fish such as tuna, shark, swordfish and king mackerel species.
Anchovies, herring, mackerel and salmon tend to contain lower concentrations of mercury than smaller fish that feed off them – such as anchovies, herring, mackerel and salmon – but even these low-contaminant varieties still contain some mercury in their flesh, meaning even when eating the recommended two servings per week of low-contaminant species may still contain too much. One effective strategy to limit mercury consumption is choosing low-contaminant options like clams shrimp oysters scallops as they contain less mercury while providing important nutritional benefits like omega-3 fatty acids.
Industrial Sources
Mercury can be found naturally throughout nature; however, human activities increase its airborne presence through coal-fired electricity generation, metal smelting, mining and other industrial activities that produce human-made emissions of mercury that flow into the atmosphere and eventually down into our water bodies.
Once in the water, bacteria convert elemental mercury to toxic methylmercury which is readily absorbed by small aquatic organisms and then passed on down food chains to larger animals like fish with long lifespans accumulating higher concentrations of mercury in their bodies over time.
As methylmercury has the unique property of bonding to protein molecules found in fish and animal meats, people consuming those fish absorb mercury through the meat itself and increase their level of mercury exposure as more larger fish they eat are consumed. The more mercury a person ingests through diet alone, the higher will be their overall exposure level.
Mercury accumulates in fish bodies because it’s difficult to expel through natural bodily processes alone, combining with other chemicals in their system such as fatty acids to disrupt proper functioning and lead to numerous health issues.
Human industry produced most of the mercury found today in ocean waters during the Industrial Revolution that began around 1800 and ended around 1900. Most of it entered lakes, rivers and the sea through pollution from burning fossil fuels, soil erosion and mining; rain/snow runoff; wastewater discharges from waste treatment facilities or other sources also contributed.
Mercury in the ocean can take many forms, from pure elemental mercury to sulfides, heavy metals and organic compounds. Sulfides and heavy metals can be difficult to eliminate while organic compounds interact with enzymes necessary for fish protein function – creating an immense risk to all life forms in its path – with higher upstream food chains being particularly at risk from mercury pollution.
Bioaccumulation
Mercury is highly toxic and accumulates rapidly in animals that ingest it, with sharks, swordfish and tuna having particularly high concentrations due to two of mercury’s properties: binding easily with tissue and bioaccumulating or building up over time in organisms as it travels up the food chain.
Methylmercury begins its journey when microscopic marine algae known as phytoplankton absorb mercury from the water and transfer it to their cells, before being eaten by tiny marine organisms known as zooplankton, which in turn are consumed by small fish, followed by larger ones who take in more mercury through eating these smaller fish, then passing it along further via biomagnification processes involving larger animals eating these smaller ones – often at concentrations ten times or more higher than that found in those organisms eaten, thus creating even higher concentrations than was originally present before in these larger organisms! This process is known as biomagnification.
Therefore, both EPA and FDA advisories advise pregnant women, infants, and young children limit their consumption of certain types of fish during gestation and breastfeeding. Omega-3 rich species like anchovy, catfish, lake whitefish salmon and trout should also be encouraged as food sources.
Mercury levels increase as one moves higher up the food chain, so scientists advise pregnant and breastfeeding women to limit their consumption of certain large predatory fish like tuna, sardines, sharks and swordfish as well as canned tuna. There are other species which contain less mercury (but still high omega-3 fatty acid levels), including herring, anchovy cod smelt lake whitefish black cod shrimps etc.
Fish and shellfish remain an integral component of a healthy diet despite any associated risks, providing both omega-3 fatty acids as well as protein and other essential nutrients.