TORONTO (Reuters) - The Toronto Stock Exchange's main index plunged more than 3 percent yesterday, weighed down by falling commodity prices and closing in on January's 2008 low.

The heavyweight materials and energy sectors led the way down. Oil prices tumbled on expectations OPEC would leave targets unchanged and as the hurricane threat to US oil operations in the Gulf of Mexico eased.

In the oil patch, Canadian Natural Resources fell 6.9 percent to C$74.50.

A drop in metals prices hurt the materials sector, where fertilizer producer Potash Corp of Saskatchewan, one of the biggest losers, was down 7.5 percent to C$150.27.

The large financial sector held up better than the resource groups, but still fell 1.2 percent as worries about the ability of US investment bank Lehman Brothers to raise capital fuelled concern about the broader banking sector.

"I think with the global slowdown that we have, it's not surprise that the commodities have been reduced in prices to where they right are now," said Adrian Mastracci, portfolio manager and president at KCM Wealth Management Inc.

"I do think in the long term the demand for commodities will pick up again. It just doesn't look as if it will happen in the very near future, right now it looks gloomy," he said.

The S&P/TSX composite index closed down 487.88 points, or 3.86 percent, at 12,146.76 with eight out of 10 sectors down.

After posting triple-digit losses in five out of six sessions, the index came closer to the 2008 lows it hit in January. Since last Tuesday, the index has dived more than 11 percent.

The energy sector was down 6.5 percent and the materials sector was down 8.2 percent. Canadian Oil Sands Trust fell 10.6 percent to C$40.00, and Inmet Mining slid 9.7 percent to C$49.80.

In the banking group, Bank of Montreal fell 1.4 percent to C$47.82, while Canadian Imperial Bank of Commerce was down 1.4 percent at C$63.50.