A fishy story about mercury

I asked my friend if he heard about the Japanese man who had eaten sushi twice a day for two decades before dying of mercury poisoning. His priceless response: "At least he got to enjoy sushi twice a day for two decades." This short exchange illustrates very well the trade-offs we face every day as we aspire to preserve our good health.
Joking aside, should we be concerned with mercury and its baneful effect on our health? What is mercury anyway?

There are three chemical forms of mercury: elemental, inorganic, and organic, notably, methyl mercury. Exposure of the general population is primarily to methyl mercury and occurs through the consumption of fish and seafood. To a much lesser extent, the general population is exposed to inorganic mercury through dental amalgams.
Studies have shown that inorganic mercury comprises less than a quarter of total blood mercury. Thus, a measurement of total blood mercury consists primarily of methyl mercury.

Chronic exposure to methyl mercury may cause numbness and tingling in the extremities, blurred vision, deafness, lack of muscle coordination and intellectual impairment, as well as adverse effects on the cardiovascular, gastrointestinal and reproductive systems. Prenatal exposure may interfere with fetal development of the central nervous system and cause neurological and developmental delays. Women who are exposed to methyl mercury and breastfeed may also expose the child through the milk.

Preliminary results from the Canadian Health Measures Survey taken in 2008/09 show that the geometric mean blood mercury level of Canadians aged 20 to 79 is 0.91μg/L. Fewer than 1% of Canadians have total mercury concentrations above the current Health Canada blood guidance value of 20 μg/L established for the general adult population.However, there is some controversy at how these maximum tolerable levels are established. Because mercury can be toxic at any concentration, some experts maintain that the blood guidance value should be ten times lower, or 2μg/L. If this were the case, more than 10% of Canadians suffer today from potentially toxic levels of mercury. How do mercury releases end up in our bodies and what can we do to avoid it?

Mercury that is released into the environment may be deposited into water where microorganisms can convert it to methyl mercury, a highly toxic form of mercury that can build up, or bioaccumulate, in living tissue. Small organisms and plants take up mercury as they feed and this mercury tends to accumulate in their tissues. As larger animals, higher up the food chain, consume these plants and organisms, methyl mercury is bioaccumulated at a more concentrated level. The process continues as you move up the food chain, with levels of mercury increasing in larger, predatory species. This process is known as biomagnification.

It's not all bad news, however. The liver can and does detoxify our system from this and other metals, so long as we do not load our bodies with too much mercury. Many studies have been made measuring the amount of mercury found in different species of fish. There are many kinds of fish that are very low in this harmful metal and can be eaten and enjoyed several times a week without risk of bioaccumulation, namely, flounder, haddock, ocean perch, salmon, sardine, scallop, shrimp, sole and tilapia. This list is not exhaustive. If you don't see your favourite I recommend that you look it up and confirm how often you can safely eat it. In this way, you can be sure that your natural detoxification system is eliminating this toxic metal faster than you may be ingesting it.

Finally, one last comment which could indeed save your life: Mercury vapours are extremely toxic. If you accidentally break a fluorescent light (or a CFL), you must leave the area immediately and ventilate the room for about 15 minutes. Only then will it be safe to return to clean up the mess. Do not touch the broken pieces, simply sweep everything into a thick garbage bag and dispose at a hazardous waste centre.