4.2. Toxicity of the Leachate to Root Growth in A. cepa
The degree of toxicity of the tested samples to A. cepa root was assessed by means of root length
values measured 72 h after exposure to the test medium. Root growth was assumed to be maximum
(100%) in controls. Table 2 shows the effect of e-waste simulated leachate sample on the root growth of
A. cepa. Root growth in percentage of control decrease with increased concentration of samples. The
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highest percentage root growth of 77.1% was recorded for 5% concentration corresponding to 22.9%
root growth inhibition. While the least percentage root growth of 19.7% corresponding to root growth
inhibition of 80.3% was obtained at 100%, which was the highest concentration tested in Table 2 and
Figure 3. Inhibition of root growth by e-waste leachate was strictly concentration-dependent as
illustrated in Figure 3. The curve shows a linear relationship of consistent decrease in % root growth
with increase concentration, and the root growth inhibition varied statistically at P < 0.05 probability
level increasing in statistical significance with increase concentration Table 2. From the graph, 50%
effective concentration (EC50) was deduced to be 37.5%. This corresponds to the concentration of
e-waste leachate at which root growth inhibition amounts to 50% of the control.
Exposure of Allium cepa roots to the leachate at 0, 5, and 10% did not cause any change in colour of
roots; however, at higher concentrations of 25 and 50%, roots were pale and at 100%, the roots were
dark brown/black in colour. The root malformations observed at these leachate concentrations were
twists, ‘crotchet hooks’ (root tips bent upwards resembling hooks) and c-tumor (abnormalities appearing
as swellings of the root tips) (Figure 2).