I just found this post by Phil P. from 2002.  He seems to indicate that
it's not that dangerous:

http://groups.google.com/group/rec.pets.cats.health+behav/msg/5be3c4a554c
20acc?hl=en&

<sam...@aol.com> wrote in message
news:adff1j$niq$1@slb3.atl.mindspring.net...

A pet food can contain an antioxidant (or any ingredient) without it
being
listed on the label.

The FDA requires pet food manufacturers to list all the ingredients and
sub-ingredients on the labels.  However, the Code of  Federal Regulations
allows exceptions to this rule.  Sub-ingredients could be an antioxidant
added by a supplier and not the manufacturer.  IOW, the manufacturer
could
have bought the fat compontent from a supplier already preserved with a
chemical antioxidant.  However, in many cases, the decision to include or
exclude a sub-ingredient from the label depends of the amount of that
ingredient in the final product - which is allowed by the Code of  
Federal
Regulations.

No. Ethoxyquin has been studied for more than three-quarters of a
century.
The safety range of ethoxyquin is *very* wide and the amount used in pet
foods is not remotely close to dangerous. The amount allowed as a
preservative is 0.015%, which is an extremely low concentration. Any
ingredient can be toxic if cat receives too much.

Chemical preservatives are much more effective and actually safer than
so-called "natural preservatives".  Retarding oxidation *consumes*
naturally
occurring antioxidants and results in vitamin deficiency.  Chemical
preservatives spare other antioxidants and minimizes vitamin deficiency.

Most people are under the erroneous impression  that "Preserved with
Mixed
Tocopherols a Source of Vitamin E" means the cat is getting more vitamin
E.
This is not true.  The type of vitamin E used as preservatives are *not*
bioavailable to the cat.  The bioavailable form of vitamin E is very
unstable and the amount needed to retard rancidity would be *toxic*.

If you look hard enough you'll find "adverse effects" for almost anything
if
its taken in large enough quantities.  It all depends on the agenda of
whose
writing the article...  However, there is not a single documented case of
disease or death associated with ethoxyquin, BHT, or BHA in the
Veterinary
Medical Database at Purdue.  So all the so-called "reports" and
"studies" of
the perils of chemical antioxidants should be taken with a grain of salt.

Canned foods don't require *any* preservatives.

Phil.