RCMP Superintendent Ron Allen told a Toronto-area news conference the 75 percent pure powder was first detected in a maritime shipping container in Halifax, Nova Scotia, by X-rays last month.
Allen said the street value was hard to assess because of the purity, but estimated it was worth more than $8 million. The 81 slim boxes of heroin was concealed among 430 cartons of towels, the Toronto Star said.
Allen said the powder was replaced with look-alike material and allowed to continue its trek to Toronto by rail.
Four men ranging in age from 39 to 82 who tried to claim the boxes were arrested, and a subsequent raid on a house east of Toronto netted a hand grenade and ammunition, the Toronto Sun said.