The CFIA regularly tests domestic and imported commercial fish and shellfish, both freshwater and
marine, in order to enforce the mercury guideline of 0.5-1.0 parts per million (ppm) for total
mercury in domestically produced and imported fish.
The recommendation is to consume a variety of fish, as this minimizes your exposure to any
particular toxin that may accumulate in a particular fish species.
Health Canada recommends consumers limit their consumption of shark, swordfish, fresh or
frozen tuna, orange roughy, escolar and marlin to a maximum of no more than 150g per
week (excluding canned light tuna). For children, pregnant women and women of
childbearing age, consumption of these fish is more restricted.
The reason these fish are limited for children, is that children are at a stage of rapid development
with metabolic rates higher than that of an adult, resulting in a greater ability to absorb
substances (e.g., their level of gastro-intestinal absorption and retention is greater). In addition,
the immature or developing organs and systems of children are less able to get rid of mercury.
There is also less ability to repair the damage caused by mercury due to their cellular repair
mechanisms not being fully developed.
Methyl mercury ingested by a pregnant woman can be passed from the maternal blood to the
developing fetus by crossing the placental barrier. It can accumulate in the unborn baby's blood
at concentrations higher than the concentration in the mother. Mercury can also be transferred
through breast milk to a nursing infant.
With chronic maternal fish consumption, infants may appear normal during the first few months of
life but later display IQ deficits, abnormal muscle tone, reduced motor function, and lower
attention and visuospatial performance. In recent human studies, neuropsychological deficits are
detected in children aged seven years following prenatal exposure to methyl mercury. Increased
blood pressure in children exposed prenatally to methyl mercury has also been reported.
Halogens and Organic Halogens
• Chlorine o|82
Polybrominated biphenyl (PBB)
Polychlorinated biphenyls (PCB's)
PCB's refer to a group of at least 50 widely used compounds containing chlorine that can
accumulate in the food chain and cause a variety of harmful effects (fatigue, eye irritation, growth
retardation in children when exposed prenatally). They are man-made and were banned in North
American in 1977. They can still be found remaining in the environment, because they do not
break down and are difficult to destroy. So we are still exposed to small amounts of PCB's,
typically through food consumption. The levels we are exposed to however are well below what
Health Canada determines could cause adverse health effects.
See page 25 (527) of your textbook for suggestions on how to minimize your risk of PCBs
• Define toxin and discuss examples of natural toxins;
Food Additives: substances added to food either intentionally or by accident that become part of
the food and affect its characteristics (like colour or flavour).
Most food additives are done purposely (intentional additives), including sugar, colourings, salt, baking
soda, etc. Some additives however are contaminants that are accidently introduced
(indirect / incidental additives). These substances can be accidently introduced to the food during
the production, processing or packaging process. Food additives have been used for OS82
thousands of y