Bioaccumulation and
biomagnification
Marine organisms absorb toxins and heavy
metals that enter the oceans from natural sources, such as volcanoes
and the erosion of soils; more worryingly though, many of these toxins
today originate from manmade sources, such as the burning of fossil
fuels. These toxins accumulate through the food chain as one
animal eats another, a process known as bioaccumulation.
Bioaccumulation occurs when an organism absorbs a
toxic substance at a rate greater than it can be removed. These
toxins generally accumulate in the greatest quantities in large
predatory animals, such as sharks, resulting in an amplification of
their toxicity, known as biomagnification.
The effects of these toxins
on predatory species, such as sharks, remains unclear, but what we
do know is that they do not want them and will even resort to
offloading toxins to their offspring in a desperate attempt to
remove them. As many sharks are positioned at the top of the food
chain, they are the final stop for many poisons in our oceans.
Additionally, as some shark species live
for more than 50 years, the levels of toxins built up in their bodies
are often much greater than in any other marine organism.
When we eat sharks, we also consume and
accumulate their toxins and, for humans, the effects can be
fatal.
Methylmercury: a hidden
danger
Methylmercury is an organic form of mercury,
which is a
neurotoxin. Organisations throughout the world (including the
United States Environmental Protection Agency (USEPA), the World
Health Organization (WHO) and the Food and Agriculture Organization
of the United Nations (FAO)) recognise mercury to be a dangerous
neurotoxin and warn against eating sharks, especially for
pregnant women, women who plan to become pregnant, and children. Methylmercury exposure can also cause
serious neurological disorders,
heart problems, and has been linked to
infertility. In addition, a
2012 study found that 79% of shark fins tested contained
high levels of BMAA, a dangerous neurotoxin linked to increased risk
of Alzheimer’s and other degenerative brain diseases.
Fish with the highest levels of methylmercury include shark, swordfish and tilefish. Be aware that shark is sold under various other names, such as Flake, Rock Salmon, Rock Cod, Dogfish, Dried Cod/Stockfish, Pearl Fillets, Lemonfish, Verdesca (Blue Shark), Smeriglio (Porbeagle Shark), Palombo (Smoothound), Spinarolo (Spiny Dogfish), and many more imaginative names.
Do I really need to be concerned about methylmercury?
Consumption of sharks poses a real threat to human health; even small quantities of shark meat can contain large amounts of poisonous methylmercury. The human body assimilates >95% of ingested methylmercury. It passes the blood-brain barrier easily and reaches the brain at full, undiluted strength, something other toxic substances cannot do. In a pregnant woman, for example, the mechanism that separates her bloodstream from that of the embryo (diaplacentary barrier) is also bypassed without any problem. Subsequently, the accumulation of methylmercury in the developing brain and other vital organs of the foetus cannot be prevented. Massive developmental disorders of the brain and the peripheral nervous system, severe damage to kidneys and mutations can result. The fact that high doses of methylmercury over a short time period can cause more severe, and sometimes irreversible, damage than lower doses over a long period of time makes this problem even more serious.
Join our campaign to Go Mercury Free by saying no to consuming sharks and other large predatory fish.