My Virtual Reading Room

I think it may have been.

There were a couple of widely-used green dyes which contained arsenic and which were used to colour all kinds of things. Some people reported feeling ill after spending time in rooms that had been hung with paper manufactured with Scheele's Green, only to find the symptoms abated once they changed the decor. There were mass poisonings in some towns because confectioners used the same to colour their sweets (mind you, there it wasn't just arsenic that was a hazard, as lead was used to colour red sweets!). Arsenic was in candles, cloth, medicine, beer... And there was no regulation, as it could easily be bought over the counter.

The book is The Arsenic Century by James C Whorton. It's an interesting read.