Key Asian markets slumped, today, as shares in commodity trading firms took another tumble. China's Shanghai Composite index slipped 2 percent, led lower by commodity and energy shares. Japan's Nikkei 225 index plummeted 4.1 percent; and Hong Kong's Heng Seng plunged 3 percent.In the European markets, the UK's FTSE-100 had dropped 0.5 percent, but France's CAC-40 had climbed 0.2 percent, and Germany's DAX had gained 0.3 percent in intra-day trade.Commodities struggled after fears of weaker demand pushed them to multi-year lows overnight. Giant mining and trading firm, Glencore's Hong Kong-listed shares fell about 28 percent. Commodity-linked currencies were hit hard, with the Australian dollar trading near 6 1/2-year lows before recovering.