values were calcu-
lated for 4, 7, 10 and 14 d intervals. The toxicity of
each metal increased with exposure time; thus the 4 d
LCso values of 10.20, 6.33 and 1.03 mg 1-1 were
considerably higher than the 14 d LCso values of 1.15,
0.49 and 0.19 mg 1-1 f3r zinc, cadmium and copper
respectively