From the potassium permanganate msds:
Just don't eat more than 9 grams, and also your wife can go off the pill...The estimated lethal human dose by ingestion is 10 grams, with death being delayed by up to one month: Oral, rat: LD50 = 1090 mg/kg. Oral, human: LDLo = 143 mg/kg.
Epidemiology: The U.S. EPA stated that epidemiological studies of inorganic manganese compounds in humans indicate effects on the respiratory system at levels below 1 mg/m3.
Reproductive Effects: Men exposed to manganese dusts showed a decrease in fertility.
Neurotoxicity: Manganese is neurotoxic.
Potassium alum -- used in pickleing/canning foods, in deorderants -- but this is not to say that all the chemicals we put in our foods or under our arms are actually safe.
The latter.To be clear, do you mean more toxic than dichromates or more toxic than dichromate clearing baths?
Mark -- Most carbon printers of old used the double transfer method -- to get the image back to its original orientation (and hide any relief). Since in double transfer exposes both sides of the tissue to water, just about all the dichromate is washed off...thus you may not read much about clearing needs in the older literature.
Another way to clear single transfer is using sodium or potassium metabisulfite. But because this greatly softens the gelatin, it can cause frilling and bubbling of the image. It is recommended that one allows the print to dry for a day or two, which hardens the gelatin -- then clear it in the metabisulfite. I use the Potassium alum right after the cooling bath, followed by the wash. Fits better into my work-flow.