Food Safety 343tion over a day. This is the maximum intake level,
which is judged to result in no adverse toxicological
effect following such exposure. The ARfD value
includes a safety factor to ensure that older people,
infants and children, and those under stress due to
illness are protected.
Veterinary drug residues
Veterinary drugs include antibacterial compounds,
hormones, and nonsteroidal anti-infl ammatory prep-
arations. As animal husbandry practices have intensi-
fi ed over the past few decades, antibacterial substances
have been increasingly used as growth promoters
to increase feed conversion effi ciency, and for pro-
phylaxis and therapy to prevent outbreaks and treat
disease. Similarly, hormones are administered to
increase growth rate and meat yield. Table 14.6 shows
the main types of antibacterial and hormonal
compounds.
Veterinary drugs are metabolized in the animal
and are excreted in the urine and feces over time as
the detoxifi cation process continues. Hence, residue
traces of drugs or their metabolites can be found
in major organs, muscles, and body fl uids. In
general, antibacterial drugs are found in greatest
concentration in the kidney, lesser concentrations in
the liver and lowest concentrations in the muscle
tissue, whereas hormones tend to concentrate in the
liver.
The excessive use of antibacterial compounds in
animal husbandry has raised concerns about the
development of resistant bacteria and the effect that
this may have on the usefulness of antibiotics in
human medicine. There have also been concerns
about the risk of allergic reactions in humans to anti-
bacterial residues in food of animal origin. The use of
hormones has raised issues surrounding the effects of
hormone residues in foods of animal origin on human
metabolism.Environmental and industrial contaminants
These contaminants are of environmental origin or
are by-products of industrial processes.
Polyhalogenated hydrocarbons (PHHs) are a cate-
gory of environmental contaminants that includes
toxaphene, dioxins, and polychlorinated biphenyls
(PCBs). Certain polyhalogenated hydrocarbons are
manufactured for use in plastics, paints, transformers,
and herbicides; although their use is now either
banned or severely restricted. In most industrialized
nations the compounds have become ubiquitous in
the environment. Hence, contamination of the food
chain is inevitable and it has been estimated that in
Western industrialized countries 90% of human
exposure is through ingestion of contaminated foods
such as fi sh and milk.
Foods that are rich sources of fats and oils tend to
accumulate PHHs because the compounds are lipo-
philic and bioaccumulate in lipid-rich tissues and
fl uids. Oily fi sh from areas such as the Baltic Sea,
where levels of PHHs in the water are high, may
contain elevated levels of these contaminants. Simi-
larly, cows that graze on polluted pasture can accu-
mulate unacceptable concentrations of PHHs in their
milk. A recent incident in Belgium introduced PCBs
and dioxins into the food chain via contaminated
animal feed resulting from the accidental incorpora-
tion of industrial oil into the feed ration. The biologi-
cal half-life of PHHs can range from a matter of
months to 20 years in human adipose tissue. Hence,
they are persistent and accumulate in the body. Expo-
sure to PHHs can result in a variety of toxic effects
that can be carcinogenic, including dermal toxicity,
immunotoxicity, reproductive effects, and endocrine
disruption.
Metals, metalloids, and their compounds have long
been associated with food poisoning, with lead and
mercury probably the best documented hazards.
Metals are released into the environment as a result
of natural geological action and also as a result of
man-made pollution from industrial processes.
Metals have an affi nity for biological tissue and
organic compounds, and hence they are often easily
absorbed into the body and can often accumulate in
organs and fat deposits. Table 14.7 shows some of the
main metals linked with food-borne toxicity.Table 14.6 Main types of veterinary drugs
Antibacterial compounds Hormones
Aminoglycosides β-Agonists
β-Lactams Resorcylic lactones
Fluoroquinolones Steroids
Macrolides Stilbenes
Sulfonamides Thyrostat
Tetracyclines
Quinolones