The S&P 500 gained about 6% in the third quarter although equity ETFs ended the three-month period with a down week as some of the shine came off the Federal Reserve’s QE3 program.

The U.S. blue-chip index was poised for a 1.6% decline this week in midday trading Friday, while the Dow slid 1.4% and the Nasdaq Composite shed 2.2%.

On Friday, investors were disappointed by weak manufacturing data in the Chicago area while fresh concerns emerged over the health of Spain’s banking system. The iShares MSCI Spain (NYSEArca: EWP) and iShares MSCI Italy (NYSEArca: EWI) were both down more than 3%. [Spain, Greece ETFs Backpedal on Protests]

“We had been seeing good data recently, but now we seem to be following the slowdown in China and Europe and we’re seeing weakness,” said Paul Nolte, managing director at Dearborn Partners, in a Reuters report.

The Spain ETF was this week’s steepest decliner with a loss of 6% in afternoon dealings Friday.

In U.S. stocks, homebuilder ETFs also pulled back sharply on sluggish home-sales data following their big third-quarter rally.

Conversely, this week’s top gainers were Treasury funds and volatility-linked ETFs on the safety trade. In commodities, natural gas was the leader.

The top three unleveraged ETFs this week were U.S. Natural Gas Fund (NYSEArca: UNG), Vanguard Extended Duration Treasury (NYSEArca: EDV) and PIMCO 25+ Year Zero Coupon U.S. Treasury Index (NYSEArca: ZROZ) with gains of at least 3%.

The bottom three unleveraged ETFs this week were iShares MSCI Spain, Global X Uranium (NYSEArca: URA) and iShares MSCI Italy with losses of 5% or more.

In next week’s economic data, look for reports on ISM manufacturing, construction spending, motor vehicle sales, ISM non-manufacturing, factory orders and the ADP employment report. However, the main event will be Friday’s nonfarm payrolls report for September.