Exchange-traded funds tracking the real estate and housing sector were among the worst performers Monday, after a Federal Reserve official offered a bearish outlook for the sector. San Francisco Fed President Janet Yellen told the National Association for Business Economics that the recent financial market turmoil will prolong the housing sector adjustment. Vornado Realty Trust ( VNO) and ProLogis ( PLD) were both lower by more than 1%. The Ultra Real Estate ProShares ( URE) was falling 72 cents, or 1.7%, to $41.52. The First Trust S&P REIT ( FRI) ETF was down 69 cents, or 3.9%, to $17.11. The SPDR Dow Jones Wilshire International Real Estate ( RWX) was off by $1.32, or 2.2%, to $58.63. Homebuilders and construction were also under pressure. D.R. Horton ( DHI), Lennar ( LEN), Hovnanian ( HOV), Toll Brothers ( TOL) and Beazer Homes ( BZH) all slid by 2.4% or more. The PowerShares Dynamic Building & Construction ( PKB) lost 48 cents, or 2.5%, to $1.71. The SPDR S&P Homebuilders ( XHB) was down 33 cents, or 1.4%, to $22.91. The iShares Dow Jones U.S. Home Construction ( ITB) shed 24 cents, or 1.1%, to $21.75. Basic materials-related ETFs were also lower. Among individual stocks, Alcoa ( AA), Nucor ( NUE) and Freeport-McMoRan ( FCX) were losing 1% or more. The Ultra Basic Materials ProShares ( UYM) eased $2.37, or 2.9%, to $79.36. The iShares Dow Jones U.S. Basic Materials ( IYM) was off 76 cents, or 1.1%, to $67.15. The Vanguard Materials ( VAW) was down 98 cents, or 1.2%, to $80.07. There were few winners during Monday's losing session. The United States Natural Gas ( UNG) ETF was rising 3.6% as natural gas tacked on 18 cents to $5.68 per million British thermal units. The ETF was up $1.23 to $35.57.