Last updated: 12 November 2016: section on lead added

Mercury in the Can of Tuna

Many grocery stores now warn that it is not advisable for pregnant women to eat too many cans of tuna. The reason is because these cans increasingly contain significant amounts of mercury.
The mercury in these cans has nothing to do with the cans themselves but with the tuna. Mercury is a problem in fish in general, not just tuna.
So how does the mercury get into the fish, and ultimately into the food chain? This page summarizes some of the facts about mercury.
• What is Mercury (Hg) and what are its properties?
• one of the heavy metals (others include lead (Pb) and Cadmium (Cd))
• high density/specific gravity
• liquid at room temperature
• vapor highly toxic
• inhaling Hg vapor can lead to damage of the brain and nervous system; also weakens immune system
• What is Mercury used for?
• electrical switches
• amalgam in dental fillings (silver amalgam)
• to extract gold and silver from dirt
• Where does the Mercury in the Cans of Tuna come from?
• in the U.S.: above all, unregulated burning of mainly coal (but also oil)
  (this now exceeds the amounts that come from volcanic eruptions)
• also from incineration of waste (e.g. Hg in batteries!)
• from gold mining runoffs (silver now less relevant), especially in the Amazon area
Mercury can travel long distances when airborne; e.g. power plants in the eastern and central U.S. pollute lakes in Nova Scotia, Canada. In animals (and humans), Mercury is not reduced during metabolism. In fact, it is accumulated and often stored in the bones instead of Calcium. In older humans, the Calcium gets released back into the body when it needs it, and so also Mercury goes back into the blood stream.
When mercury gets into the food chain the it is also accumulated from one prey animal to the next, with humans being the last link in the food chain and so receiving the most amount of Hg.

DID YOU KNOW? The mad hatter in Lewis Carroll's "Alice's Adventures in Wonderland" may have been "mad" because of exposure to mercury. Mercury was used in the process of curing felt used in some hats. Early symptoms for the neurological damage from inhaling mercury included confused speech and distorted vision. More serious poisoning led to psychotic symptoms, such as hallucinations. Since the consequences of mercury poisoning were unknown back then, people appeared to have gone mad for no reason.

Lead in the House

• What is Lead (Pb) and what are its properties?
• one of the heavy metals (others include mercury (Hg) and Cadmium (Cd))
• high density/specific gravity; denser than most common materials
• soft and malleable at room temperature
• was known to prehistoric people
• established as poisonous as late as late nineteenth century
• Some properties why Lead (Pb) is used
• low melting temperature
• ductility
• relative inertness against oxygen attack
• easier to mine than many other metals
• relatively inexpensive
• Some things Lead (Pb) is used for
• lead-acid batteries
• bullets
• weights
• part of solder
• pewters
• fusible alloys
• radiation shield
• Health risks of Lead (Pb)
• ingestion of lead-based paint is the major source of lead exposure for children
• lead poisoning can cause physical, behavioral and intellectual problems in children
• health effects of lead exposure cannot be corrected
• lead is a neurotoxin that accumulates in soft tissue and bones
• poisonous whether inhaled or swallowed
• damages nervous system and causes brain disorders
• crosses blood-brain barrier by mimicking calcium
• excessive lead causes blood disorders in mammals

In the U.S., the primary source of lead poisoning is inhaling or ingesting of dust or soil that has been contaminated by lead-based paint found in homes constructed before 1978. Dust and soil contamination is caused by
• deteriorated lead-based paint
• lead-based paint that is disturbed during renovations, routine maintenance or painting
• friction and impact surfaces of doors, cabinets, windows and floors that rub painted surfaces
• old plumbing

DID YOU KNOW? corrosive drinking water can leach lead out of old plumbing and contaminate the drinking water. This happened in 2015 after the city of Flint, MI disconnected itself from the Detroit Water Department and get water from the Flint River instead. Between 6,000 and 12,000 children were exposed to lead. Check out entry at wikipedia.