Mercury, the smallest planet, closest to the sun and also an incredibly dangerous neurotoxin you’ve likely consumed without realizing it. We’ve already talked about Lead poisoning but that isn’t the only heavy metal we should be on guard for. Mercury is dangerous in every form but most commonly we will encounter it either as methylmercury or elemental( metallic) mercury. Methylmercury is the form of mercury that you may have heard exists in certain fish and seafoods. It is terribly toxic to mammals and builds up in aquatic animals through mechanisms such as bioaccumulation and biomagnification.

Bioaccumulation is where a chemical in the environment builds up in an organism over time usually through direct exposure or a contaminated food source. An example of this would be salmon swimming in a contaminated river or stream. The chemical contamination is slowly building up in the salmon due to the contamination of their environment. A heavy chemical like mercury is hard to expel once absorbed so even through small increments, the slow accumulation of the chemical is measurable and significant. Biomagnification conversely is when the concentration of a chemical contaminate in one organism is passed on to another organism where it builds up due to the second organism being higher in the food chain and eating a significant amount of the first organism (See Fig. 1.1). This would happen if say, a bear, were to eat the contaminated salmon from our earlier example. Similarly, humans, as an apex predator, tend to consume organisms all along this type of food chain including those at the top of their own chain, thus consuming organisms who have the highest concentration of chemical contaminants. While this consumption of mercury may not cause you to immediately show symptoms of poisoning, it will build up in the body over time and problems can develop once a certain threshold is reached.

Fig. 1.1 National Geographic image detailing Biomagnification and Bioaccumulation

Metallic mercury is the other form we are commonly exposed to. This is the form that can be found in thermometers, some light bulbs and old dental fillings and enters the body as a metallic vapor as it is outgassed from the amalgams(mercury compound or mixtures) and inhaled. This metallic mercury passes easily through the blood brain barrier and into the brain. Though some of this chemical will be broken down into mercuric mercury and excreted, some will adhere to the red blood cells and build up in the brain and nervous system.

While anyone would be negatively impacted by the build up of mercury in either form, it can be incredibly detrimental for developing infants. Whether they are exposed through the mother’s exposure in utero or through the mother’s breast milk, this exposure can impact a developing child’s IQ and cause neurocognitive deficits as well as impacting motor skills and spatial awareness. This is one reason a doctor may recommend that a pregnant mother suspend the consumption of fish throughout the pregnancy and even through the breast feeding stage. Limiting the build up of mercury in a developing child is paramount when one considers the long-term effects mercury can have.

In adults, the impact of mercury can include a wide range of symptoms. Notably immune dysfunction, reduced color vision and changes in coordination, mental concentration and short term memory have all been linked to mercury exposure. The vapor can cause pneumonitis, or a typically noninfectious form of lung inflammation, as well as more general symptoms such as fatigue, weight loss and gastrointestinal issues. A correlation between mercury exposure and heart disease, hypertension and stroke has also been noted.

So, now that we’ve firmly established the issue with mercury exposure, what do we do when mercury is within our environment and we are likely being exposed to it in some form everyday? First, educating oneself on the correct way to dispose of household sources of mercury, such as broken light bulbs or thermometers allows one to limit acute mercury exposure for oneself and anyone else in your household. Second, limiting the use of mercury containing items in general will go a long way to preventing unnecessary exposure. Third, supporting the general adoption of mercury alternatives either on a global, national or local level will help push us collectively in a direction that will be safer for generations to come. Last, but possibly the most important step is continuing to educate yourself on the impacts of mercury and educating those around you so that others can take similar precautions and join you in monitoring this global issue.

Sources and Further Reading:

EPA guideline for Mercury: https://www.epa.gov/mercury/health-effects-exposures-mercury