A food contaminant, based on dictionary definitions, may be
described as a substance that makes a food impure. Foods are
complex mixtures, of course, so it may be more useful to define a
contaminant as something that would not normally be present in
the food, has been introduced inadvertently from an external
source or as a result of microbial, fungal or animal activity, or even
just as something undesirable. Mycotoxins produced by fungal
activity are an obvious example and are dealt with in another
article in this volume. The issue becomes more complicated when
food processing and cooking are involved, as these may bring about
substantial changes in composition, including the production of
substances that are not present in the raw food