Hi:

Wax is a liphophilic sink, binding lots of different chemicals.  Years ago,
I killed two colonies placed on comb that had been stored in a closet with
an old Vapona pest strip.

We can find metals, organics, and lots of other things in wax. If one finds
chemicals in wax, you often have no idea of where or when the chemical got
into the wax - especially since beekeepers often keep combs for years.

However, old comb is not necessarily worse than new comb in terms of
contaminant levels.  Bees rebuild comb and in doing so may "dilute" out
some of the contaminants captured in the old comb.  Volatile organic
chemicals (solvents, some of the by-products of burning gasoline and
diesel, etc.) seem to be in a constant state of flux with the wax, both
being taken up and released, depending on temperature, humidity, etc.  Lots
of complex surface chemistry is going on.

Cheers

Jerry
Jerry J. Bromenshenk
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http://www.umt.edu/biology/bees