Bangalore: The Sensex slumped for the fourth straight day shedding 141 points to close at 3-week low of 17,490.81 on selling in metal, auto and oil & gas shares ahead of settlement in this month's derivatives contracts and release of April-June quarter GDP data.

The BSE benchmark index, which had lost 219 points in the last three trading sessions, opened flat today but lost ground as investors turned cautious.

After touching the day's low of 17,471.13, it closed at 17,490.81 -- 140.90 points, or 0.80 per cent, lower than yesterday's close. This is lowest closing value in over three weeks since Sensex ended at 17,412.96 on August 6.

The NSE 50-scrip index Nifty also dipped below the psychological 5,300 level for the first time after August 10 and ended with a loss of 46.80 points at 5,287.80.

Sterlite, which fell 4.69 per cent on reports of a weak metal price outlook, led 21 losers like Bajaj Auto (3.96 pc), Hero MotoCorp (3.3 pc), Bhel (2.89 pc), Hindalco (2.72 pc) in the 30-share Sensex. Traders said index was also pulled down by Infosys, ONGC, RIL and HDFC shares.

"The markets showed signs of weakness ahead of the August series derivatives expiry. While the FIIs trading activity has shown net inflow for entire August, the selling pressure is seen from the Domestic institutions," said Milan Bavishi, Head Research, Inventure Growth & Securities.

Brokers said selling gathered momentum as market players squared positions ahead of the F&O settlement and weak growth in April-June quarter GDP.

Overall, 11 out of 13 sectoral indices closed lower while FMCG and Healthcare indices ended higher.

Concerns on policymakers having limited room to boost the weakening economy amid a 'political stalemate-type situation' in Parliament related to CAG report on coal block allocations also weighed on the market sentiment, they added.

A weak trend in global markets on deepening Eurozone debt crisis and lower earnings by leading companies also soured the mood.