A toxicity test was conducted using the duckweed Lemna in the laboratory using copper sulfate as the

A toxicity test was conducted using the duckweed Lemna in the laboratory using copper sulfate as the reference toxicant to estimate the toxicity of the unknown effluent X.  5 healthy plants of duckweed with 4 fronds each were added to each test beaker. 10 test beakers were used containing either control M-Hoagland’s medium or the listed concentrations of copper sulfate or effluent in the medium. Beakers were covered and placed in a growth cabinet and incubated at 25°C in continuous illumination. After 7 days the number of fronds was counted in each test beaker and the results are listed below.

Conc. of Copper Sulfate (mg/L)   Number of fronds after 7 days
   0 (control)                           50
   0.25                                 43
   0.50                                 38
   1.00                                 33
   1.25                                 31
   2.50                                 26

Conc. of  X (%)         Number of fronds after 7 days
   0 (control)               52
   0.5                     50
   2.0                     48
   5.0                     44
   15                     37
   30                     33

A.  Define what it meant by the IC50  and LOEC of a toxicant?  Using the results and the graph paper provided plot the results and calculate the IC50  and LOEC of copper sulphate and the effluent E for Lemna in the experiment above.
                           
B.   What preliminary conclusion/s can you draw about the toxicity of the effluent E based on the results of this experiment? How would you improve the experimental design?                     

C.    List the advantages and disadvantages of the above toxicity test to evaluate the toxicity of effluent X when compared to the Daphnia acute toxicity test that you conducted in the laboratory.