344 Introduction to Human Nutrition
Lead toxicity has many symptoms, but the main
issue relates to its effects on the nervous system of
children. Here, lead interferes with the transmission
of nervous signals around the body. This can manifest
itself in a reduced intelligence quotient (IQ) and
coordination problems. In adults, exposure to lead
can result in hypertension and other blood effects
such as anemia. Cadmium is most often accumulated
from occupational exposure or smoking and is known
to affect the respiratory system. However, food expo-
sure tends to be at a low level over longer periods. In
this regard, cadmium bioaccumulates in the kidney
and can cause renal damage. Mercury and its com-
pounds also bioaccumulate in the body, where they
are most frequently associated with neural effects and
renal damage. In particular, methylmercury is highly
toxic particularly to the nervous system, and the
developing brain is thought to be the most sensitive
target organ for methylmercury toxicity.
Arsenic is most often an occupational hazard, but
it can also be ingested with food and is responsible
for acute and chronic poisoning. The toxicity of
arsenic depends on its oxidation state and the type of
complex that it forms with organic molecules in the
body. Chronic effects include gastroenteritis, nephri-
tis, and liver damage. Arsenic is also considered to be
a carcinogen. Other metals are also known contami-
nants and their toxic effects are diverse. Although this
is not an exhaustive list, these metals include alumi-
num, copper, tin, zinc, and chromium.
Process contaminants
These types of contaminant occur during the process-
ing and production of foods, and include acrylamide,
PAHs, chloropropanols, and nitrosamines.
Acrylamide is a reactive unsaturated amide that has
found several industrial uses. In 2002, it was discov-
ered to occur in a variety of fried and baked foods,
in particular carbohydrate-rich foods that had been
subjected to high-temperature cooking/processing.
Acrylamide has been shown to be neurotoxic in
humans. It has been shown to induce tumors in labo-
ratory rats and has been classifi ed as a probable
human carcinogen, and as such several international
bodies have concluded that dietary exposure should
be as low as reasonably achievable. The most signifi -
cant pathway of formation of acrylamide in foods has
been shown to arise from the reaction of reducing
sugars with asparagines via the Maillard reaction at
temperatures above c. 120°C. Acrylamide has been
found in a wide range of heat-treated foods; it is
found in both foods processed by manufacturers and
foods that are cooked in the home. Acrylamide has
been found to be most prevalent in fried potato prod-
ucts (such as French fries and potato chips), cereals,
bakery wares, and coffee.
PAHs are a group of over 100 different chemicals
that are formed during certain technological pro-
cesses and are common environmental contaminants.
They are formed during incomplete combustion of
coal and oil. They are also formed during barbecuing
or grilling meat. Human exposure usually results
from air pollution and from cigarette smoke. Foods
most likely to be contaminated by PAHs are grilled or
charred meats. PAHs are toxins that have been docu-
mented by the WHO as genotoxic, immunotoxic, and
carcinogenic. Long-term exposure to foods contain-
ing PAHs can lead to serious health risks. In a recent
Europe-wide incident, PAHs were found in pomace
olive oil, which resulted in a major product recall.
3-Monochloro-propane-1,2-diol (3-MCPD) is a
member of a group of contaminants known as
chloropropanols, which includes known genotoxic
animal carcinogens such as 1,3-dichloropropan-2-ol.
3-MCPD is a by-product in soy sauce and in hydro-
lyzed vegetable protein produced through acid hydro-
lysis. It can also be present as a contaminant in some
food additives, and in epichlorhydrin/amine copoly-
mers, used as fl occulants or coagulant aids in water
treatment, and may be present in drinking water
(opinion of the European Scientifi c Committee on
Food, adopted on 30 May 2001).Microbial toxins
Food poisoning can occur as a result of the ingestion
of food containing preformed toxins that originate
from bacterial growth, fungal growth, or algal growth.
In the case of bacteria the toxin is absorbed into the
bloodstream via the intestine and therefore illnessTable 14.7 Metals in the food chain
Metal Main food sources
Lead Shellfi sh, fi nfi sh, kidney, liver
Cadmium Shellfi sh, kidney, cereals, vegetables
Mercury Finfi sh
Arsenic Meat, vegetables, seafood