We determined the toxic effects of seven metals, copper(Cu), manganese (Mn),zinc(Zn),cobalt(Co), molybdate(Mo),lead(Pb),andcadmium(Cd) on the microalgae Tetraselmis chuii (Butcher,1959). We exposed 50 mL of cultivated microalgae(f/2 Guil-lard) in the exponential growth phase, with three rep-licates, to concentrations of0(control),0.1,1.0,5.0, 10,25,and 50ugL-1ofeach metal for 72 hours. The cellular count was recorded daily to evaluate any po-tential lethal effects. An increase in cellular density was seen in the control treatment. All treatments ex-posed to metals showed a logarithmic increase in cell density within 48 hours, with a cellular decrease that became evident later on. This study result with an in-significant decrease at low concentrations of Cd, Pb, and Cu at 24 hour was probably attributed to their use as micronutrients at these low concentrations. The most lethal effect was observed with Cd treat-ment, which killed 50 of the microalgae population at a concentration of 0.62 μg L-1In this study， this concentration was three times lower than that oflead and mercury, while being ten times lower than that of cobalt and molybdate. To elucidate the adverse ef-fects on seawater environments, the microalgae Tetraselmis chui is recommended as amodel species.
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