A toxicity test was conducted using the duckweed Lemna in the laboratory using c
ID: 61439 • Letter: A
Question
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
Define what it meant by the IC50 and LOEC of a toxicant? Using the results plot the results and calculate the IC50 and LOEC of copper sulphate and the effluent X for Lemna in the experiment above.
What preliminary conclusion/s can you draw about the toxicity of the effluent X based on the results of this experiment? How would you improve the experimental design?
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
Explanation / Answer
Well, LOEC (Lowest Observed Effect Concentration) is the lowest concentration of an effluent or a toxicant in a chronic bioassay that caused an adverse effect statistically different from the control.It is also referred to as the Lowest Observed Effect Level (LOEL).
On the other hand, IC50half maximal inhibitory concentration (IC50) is a measure of the effectiveness of a substance in inhibiting a specific biochemical function. IC50 would be the estimated concentration of toxicant that would cause a 50% reduction in mean number of fronds produced in this case.
Since I am unable to load the graph, the values derived for IC50 for copper sulphate is approximately 2.6mg/L. While the smae for effluent X is approximately 60 mg/L.
This data allows us to draw a preliminary conclusion that Copper sulphate is a better toxicant (more toxic) than the unkown effluent X.
.
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