From the June 3, 1885 New York Times:

“The Health Commissioner of Brooklyn held a conference on Friday last with the men who are engaged in pickling cucumbers in that city. He discovered, it is said, that nearly all of them colored their pickles with a solution of copper. He gave them a warning, and then issued an order forbidding the sale in Brooklyn of pickles colored this way.

On the following Saturday evening little Mary Martin, 8 years old, who lived in Adelphi-street, Brooklyn, was fatally poisoned by a pickle that had been colored with sulphate of copper. The pickle had been bought at a grocery store near her home. She died Monday night, and an autopsy established the cause of death beyond a doubt. Moreover, analysis proved that a part of the pickle which the child had not eaten contained enough poison to kill a man.”