Modern food processing came about as a way to preserve food to feed military troops. Before the industrial revolution, this need was met by salt preservation. Early canned foods were even less appealing than modern ones, because they used lead in cans.
That reminds me, the hazardous substances that people used to use for various things is pretty interesting. Of course everyone knows about lead paint and asbestos tiles. Lead was used in ancient Rome to sweeten wine, which was why the emperors tended to go nuts. It was also used in make-up by the ancient Egyptians.
We all know about how mercury has been used in vaccines, but it is also used in mascara. Maybe this is Jenny McCarthy's problem.

Cinnabar, which is a common ore of mercury, was used for decorative purposes by the Olmec as well as in Chinese lacquerware and medicine. (I believe it's still used in Chinese medicine.) It's also been refined to a powder (vermilion) and used as a food coloring.
Women also used to use belladonna, even though it was known to be poisonous, because it made their cheeks red.
reminds me of the phrase 'mad as a hatter', which some believe derives from Mercury poisoning suffered by hatters in the 18th century and 19th century, when mercury was used in the manufacture of felt. Absorption of mercury through the skin can cause Korsakoff's syndrome.
& also, from QI "The Emperor Charlemagne's party trick was to throw a tablecloth made out of asbestos onto a fire."