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Zinc and Chromium removal mechanisms from industrial wastewater by using water hyacinth, eicchonia crassipes

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par John Gakwavu Rugigana
National University of Rwanda - Master's in WREM (water resources and environmental management) 2007
  

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4.6.3 Discussions on uptake mechanism

The discussion on uptake mechanism for zinc was reported that 56.7% of zinc was
accumulated in petioles, 27.0% in leaves and 16.3% in roots. Table 4.3 indicates that
there is no significant difference (p<=0.05) according to initial concentration and

exposure time (p<=0.05) in uptake mechanisms of zinc, but a high difference (p<=0.05) (significant) was observed in plant parts (p<=0.05) in uptake processes.

Table 4.3: Variability in zinc uptake compared to initial concentration & exposure time.

ANOVA

 
 
 
 
 
 

Source of Variation

SS"

dfc

MSd

Fe

P-valuef

F crit

I.Ca & exposure time Plant plants

Error

Total

0.05
0.22
0.06

0.33

8 2 16

26

0.01
0.11
0.00

1.68

28.75

0.18
0.00

2.59
3.63

a: initial concentration; b: square sums; c: degree of freedom; d: means squared; e: Fischer test; f: probability value.

However, for chromium it was observed that 73.7% was taken up in roots, 14.1% in petioles and 12.2% in leaves. This shows the preference of the plant to store chromium more in roots than in petioles and leaves. Table 4.4 shows that no significant difference (p<=0.05) existed between plant parts (p<=0.05) and also between initial concentrations in uptake processes for chromium (p<=0.05). The inhibition in the uptake was perhaps because of the competition of both the metals for the same site of the plant during metabolism processes of the plants.

Table 4.4: variability in uptake of chromium ANOVA

 
 
 
 
 

Source of Variation

SS"

dfc

MSd

Fe

P-valuef

F crit

plant parts I.Ca.

Error

Total

4.57
2.36
2.14

9.07

2
2
4

8

2.28
1.18
0.53

4.27
2.21

0.10
0.23

6.94
6.94

a: initial concentration; b: square sums; c: degree of freedom; d: means squared; e: Fischer test; f: probability value.

4.7 Translocation Ability (TA)

4.7.1 Variation of translocation ability for zinc

The translocation ability is a parameter, which shows the ability of the aquatic macrophytes to take up the trace elements in the top part of plants (leaves, petioles and flowers). Most times, the translocation ability of roots/leaves seems to be high when compared to roots/petioles, the reason is that more trace elements were accumulated in

petioles. When concentration accumulated in roots compared to one accumulated in leaves is high than roots concentration compared to petioles concentration.

Figure 4.18 shows that the high translocation ability for 1 mg/L was observed for roots/leaves during 1 week, for 3 mg/L for 4 weeks (roots/leaves) and for 6 mg/L was observed for 2 weeks for roots/leaves, this can be explain by a little concentration of metal accumulated in leaves during plants' exposure to zinc.

1.0

0.8

0.6

0.4

values

0.2

0.0

1 week

2 w eeks

4 w eeks

1.2

roots vs

roots vs

roots vs

roots vs

roots vs

roots vs

petioles

leaves

petioles

leaves

petioles

leaves

Time (week) vs TA

1 mg/L 3 mg/L 6 mg/L

Figure 4.18: Translocation ability for Zinc by water hyacinth plants

The Figures 4.19, 4.20 and 4.21 show the correlations between the translocation ability, the metal concentrations and the exposure time of plants to zinc. This behavior indicates positive or negative correlation between the above parameters. It was shown that there is no correlation for 1 week between translocation ability and metal concentrations. For 2 weeks, a negative correlation was found (R square = 0.89) and for 4 weeks, a high positive correlation (R square = 0.97) was observed. This can be explaining by the key role of exposure time versus metal translocation ability by the plants.

1.5

y = -0.7505x + 0.9256
R2 = 0.0133

0.5

0.0

0.0 0.2 0.4 0.6

zinc concentration (mg/L)

roots vs leaves Linear (roots vs leaves)

1.0

TA

Figure 4.19: Translocation ability for 1 week

39

R. J. GAKWAVU (2007) MSc Thesis

TA

y = -10.817x + 5.7303
R2 = 0.8929

1.5

1.0

0.5

0.0

0.42 0.44 0.46 0.48 0.50

Zn conc. (mg/L)

roots vs leaves Linear (roots vs leaves)

Figure 4.20: Translocation ability for 2 weeks

y = 2.0929x - 0.0386
R2 = 0.9752

0.0 0.2 0.4 0.6

Zn conc. (mg/L)

roots vs leaves Linear (roots vs leaves)

1.5

TA

0.5

0.0

1.0

Figure 4.21: Translocation ability for 4 weeks

As shown on the above figures, the positive correlation between translocation ability and zinc concentration increase progressively when the exposure time increases, according to the regression coefficients observed.

4.7.2. Variation of translocation ability for chromium

Figure 4.22 presents the translocation ability of chromium; which is too high when compared to zinc translocation ability. It is explained by the fact more concentration of chromium was in roots, because the translocation ability is to analyze the capacity of plant parts storage.

Translocatioon ability of chromium

1 mg/L 3 mg/L 6 mg/L

Initial concentration

8

6

4

2

0

Translocation
ability

roots/petioles roots/leaves

Figure 4.22: Comparison of roots and shoots in translocation ability

It seems that the translocation ability of chromium is too high as shown in Table 4.5 compared to the zinc's translocation ability. The ability of plants to translocate trace elements of chromium is increased for roots/leaves (5.3 times for 1 mg/L, 6.5 times for 3 mg/L and 6 times for 6 mg/L). The number of times for roots/petioles decreases (4 times for 1 mg/L, 4 times for 3 mg/L and 7 times for 6 mg/L) because the order of storage was leaves<petioles<roots.

Table 4.5: Translocation ability of chromium by the plant

 

I.Ca of chromium (VI)

Roots/shoots

1 mg/L

3 mg/L

6 mg/L

roots/petioles roots/leaves

4.104b
5.288b

3.663b
6.487b

6.831b
5.965b

a: initial concentration; b: times of storage in roots compared to shoots.

The Figure 4.23 reports that the correlation between roots and petioles is high (R square = 0.6) compared to the correlation between roots and leaves (R square = 0.3), this is because less quantity of Cr (VI) was translocated in leaves.

correlation between roots and shoots

8 y = 1.3635x + 2.139

R2 = 0.6314

6

4

y = 0.3385x + 5.2363
R2 = 0.317

0

0 1 2 3 4

conc. (mg/L)

roots/petioles roots/leaves

Linear (roots/petioles) Linear (roots/leaves)

x times roots/shoots

2

Figure 4.23: Correlation of roots vs. shoots

4.7.3 Discussions on translocation ability

Table 4.6 indicates the ANOVA 2 which shows the variability in translocation ability for zinc. It can be seen that the difference is not significant (p<=0.05) between metal concentration (p<=0.05) and no significant difference (p<=0.05) between roots and shoots translocation.

Table 4.6: variations in translocation ability of zinc ANOVA

 
 
 
 

Source of Variation

SS

df

MS

F

P-value

F crit

metal concentration roots/shoots

Error

Total

0,42 0,13 1,01 1,56

5 2 1 0 17

0 , 08
0,07
0,10

0,84
0,65

0,55
0,54

3,33
4,10

Stratford et al. (1984) found that the metals accumulations in water hyacinth increased linearly with the solution concentration in the order of leaves<petioles<roots in water hyacinth. For this research, the situation is different because the following order was observed: leaves<roots<petioles. When the concentration is high, the water hyacinth plant can accumulate little concentration in plant cells. The high translocation ability was observed for roots/leaves (1.114) for 1 week and the low translocation ability was observed for roots/petioles (0.109) for 4 weeks. Most of times, the translocation ability of roots/leaves seems to be high when compared to roots/petioles. The reason is that more trace elements were accumulated in petioles. When concentration accumulated in roots compared to one accumulated in leaves is high than roots concentration compared to petioles concentration.

Stratford et al. (1984) found that the metals accumulations in water hyacinth increased linearly with the solution concentration in the order of leaves<petioles<roots in water hyacinth. This agrees with the results of this study in the case of chromium concentration accumulation in water hyacinth plants, where the high concentration was accumulated in roots followed by petioles and then leaves.

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