Mercury in Fish
What is Mercury?
Mercury (Hg), a toxic element, is a famous heavy metal found in the earth’s crust. It
enters our environment through:
Natural Sources - weathering of rocks, volcanic eruptions and deep-sea vents.
Man-made Sources - combustion of fossil fuels (like oil and coal), incineration of
mercury-containing products (such as batteries and fluorescent light bulbs), and
manufacturing processes.
Existing Reservoirs - man-made and natural sources of mercury already deposited into
the environment are re-released and evaporate into the atmosphere.
What are the Different Forms of Mercury?
Mercury pollution is both a local, regional and global problem. Wind can carry
airborne mercury great distances before it is deposited on land and water, primarily by
rain and other types of precipitation. In addition, mercury exists in three forms in the
environment:
Elemental Mercury – is the most volatile and dominant form of mercury in the
atmosphere; released by combustion sources, like coal-fired power plants and
incinerators burning mercury-containing products; some elemental mercury adheres to
dust and ash particles and deposits onto the earth without traveling great distances; most
elemental mercury is released as a vapor and remains in the atmosphere, sometimes for
up to a year, until it reacts with ozone, or other oxidants, to form ionic mercury
Ionic Mercury - formed in the atmosphere from elemental mercury vapor; also
directly emitted through combustion of coal and mercury-bearing waste; highly soluble
form; returns to earth’s surface with rain and snow; converted by bacteria to organic
mercury. In the hydrosphere and associated sediments it can exist as 0, +1,+2 species
depending on redox potentials, the pH, the strength of the ligands present, and other
environmental conditions.
Organic Mercury (methylmercury and dimethylmercury) – the most toxic form
humans are usually exposed to. It is built up and bioaccumulated under suitable
conditions by bacteria.
Why is Mercury Important to US?
Because airborne mercury can be carried by wind for great distances, mercury is an
extremely widespread pollutant, contaminating remote lakes once thought to be pristine
hundreds of miles from the nearest mercury source.
Through deposition, airborne mercury in the air can fall on the ground or enter
aquatic environment. Then bacteria convert mercury to methylmercury derivatives. Then
they can be taken up into the food chain and ultimately the fish and seafood we eat.
Bioaccumulation of mercury is extremely efficient in the aquatic food chain. It is
discovered that fish at the highest trophic level has highest amount of mercury in its body
tissues about one million times higher than the mercury concentration in the water.
Levels of mercury in rainwater are in the range 5–100 ng/L. Naturally occurring
levels of mercury in groundwater and surface water are less than 0.5 μg/L, although local
mineral deposits may produce higher levels in groundwater. An increase in the mercury
concentration up to 5.5 μg/L was reported for wells in Izu Oshima Island (Japan), where
volcanic activity is frequent. The concentration range for mercury in drinking-water is the
same as in rain, with an average of about 25 ng/L. There have been no reports of
methylmercury being found in drinking-water.
Who is at Risk from Mercury Exposure?
Eating contaminated fish is the major source of human exposure to methylmercury.
The population most at risk is fetuses, infants, and young children. Consequently, fish
consumption by pregnant women, young children, and women of childbearing age (ages
15-44) is cause for concern because of the likelihood of mercury exposure. In addition,
people who eat a lot of commercial fish or seafood, and people who rely on self-caught
fish such as Native Americans and other subsistence fishers can also be highly exposed.
Methylmercury can threat to ecosystems as well. It was found alarmingly high levels
of mercury in some endangered fish-eating birds and mammals such like bald eagle,
dolphins, and killer whales. Mercury poisoning has also contributed to the death of
terrestrial mammals such as polar bear which mainly prey on seals.
Health Effects from Eating Mercury Contaminated Fish
Mercury is a potent neurotoxin. Because of the properties of high lipophiic and
bioconcentratable, methyl mercury derivatives have greater toxicity than other forms.
Consumption of contaminated fish is the major route of human exposure to
methylmercury. Accumulated mercury is unevenly distributed in various organs in the
body. It is mercury in the brain that leads to the neurological dysfunctions.
Methylmercury is also a developmental neurotoxicant. It is particularly hazardous to
developing fetuses, infants and young children, with resulting effects including delays in
learning motor functions (walking, talking and speaking). Methylmercury transfers from
women to fetuses across the placenta and to infants through breastfeeding. It will cause
serious problem on brain development.
Any Solutions of this Problem?
-Please think about any possible solution for our mercury food contamination.