Top steelmaker ArcelorMittal cut its estimate for global steel demand growth to between 0.5% and 1.5% in 2019 from a previous forecast of 1%-1.5%.
"It's a read-across from the steel side. People are getting a bit nervous about the demand side and seasonally this is also weak period for global industrial demand," said Colin Hamilton, director of commodities research at BMO Capital.
"On the whole, I still have most of these base metals markets in deficit this year, but deficits don't matter without better demand."
Benchmark aluminium on the London Metal Exchange dropped for a third session and slipped 0.9% to $1,784 a tonne in official open-outcry trading, its weakest since July 3.
Three-month LME copper touched its lowest since July 10 at $5,893.50 a tonne before paring losses to $5,905 in official rings, a decline of 0.4%.
* FED: Also weighing on markets were comments by the head of the US central bank that an interest rate cut might not be the start of a lengthy campaign to shore up the economy against risks.
"People are taking it as slightly disappointing because they didn't really signal that they're going to cut again," Hamilton said.
* DOLLAR: The Fed comments helped to propel the dollar index to a 26-month peak, making commodities priced in the US currency more expensive for buyers using other currencies.
* TRADE TALKS: US-Chinese trade talks in Shanghai ended without any meaningful progress, "highlighting the reality that a deal is far from being reached", ANZ said in a note.
* CHINA PMI: Pressure on factories in top metals consumer China eased a little in July thanks to growth-boosting steps from the government, but overall manufacturing activity remained in contraction as the trade war with the United States dented export orders, a private survey showed.
* COPPER TIME SPREADS: The discount of LME cash copper to the three-month contract rose to $24.75 a tonne by Wednesday's close, the deepest discount since June 17, indicating healthy near-term supply. The discount was $6.25 three weeks ago.
* PRICES: LME zinc slid 2% to trade at $2,396 a tonne in official activity after touching $2,386, its lowest since July 12.
Lead shed 1.2% to $1,985 after hitting a two-week low of $1,980 while Nickel, untraded in official rings, was bid down 1.2% to $14,310 and tin was bid down 0.1% to $17,290 after hitting a three-year low of $17,200.