The S&P/TSX composite index closed down 217.29 points to 14,425.55.
The Toronto market's move mirrored a slide in the prices for both oil and gold.
Kevin Headland, director of capital markets and strategy at Manulife Asset Management, said the market was still experiencing a "hangover" from last week, when the Bank of Canada cut its benchmark interest rate by a quarter of a percentage point.
He said markets have been hurt by recent news that Canada may be in a technical recession, defined as two consecutive quarters without economic growth, and that the country's exports have been outpaced by imports recently despite a falling Canadian dollar.
"We're in a net trade deficit and we're a trade surplus country," he said. "We rely on a trade surplus for our economic growth."
The August contract for gold ended the day down $25.10 to US$1,106.50, while the September contract for crude oil closed down 77 cents to US$50.44.
"It's still a commodities-based index," Headland said. "You're not seeing any reason to move higher and you're just getting pushed back by oil prices."
Headland said that indicators show the worldwide supply of oil is at its highest point in a decade, even before factoring in the impact of the recent nuclear deal with Iran that includes returning some of that country's oil supplies to the global market.
"The expectation is that oil could go even weaker from here," he said. "Companies have kept up production. I won't say the world is awash with oil but there's enough supply, enough inventory to go around."
In Halifax, Natural Resources Minister Greg Rickford said on Monday that Canada needs to find new buyers and new markets for its oil.
The August crude contract, which expired at the end of Monday's session, settled at US$50.15.
The slide in gold reflects the commodity's decreasing value as a safe haven for investors, Headland said.
Headland added that despite recent events in Greece and China — the latter a country where a stock-market free-fall was only halted by government intervention — the world's economy has less uncertainty.
And with stock markets recovering in the United States, Headland said, gold loses its lustre as a place to park your money.
"I wouldn't be surprised to see it bounce back off this low, but I think we're going to see lower gold in this range for quite some time," he said.
The August contract for natural gas closed down 4.7 cents to US$2.82.
In the U.S., the Dow Jones industrial average climbed 13.96 points to end the day at 18,100.41, while the Nasdaq gained 8.72 points to a record 5,218.86. The S&P 500 added 1.64 points to total 2,128.28.
The Canadian dollar closed down 0.06 of a cent to 76.94 cents US.