Total phenolic and tannin contents in macrophyte extracts are shown in Table 1. S. auriculata and P. parviflora leaves contained the highest phenol and tannin levels, with no statistical difference (p < 0.05).
Table 1
Total phenolic and total tannin content in extracts of macrophytes samples.
Sample
|
Phenol content
(mg GAE g− 1)
|
Tannin content
(mg GAE g− 1)
|
P. parviflora leaves
|
61.12c (1.26)
|
5.32b,c (1.29)
|
P. parviflora petiole/stem
|
16.36a (0.35)
|
0.56a (0.13)
|
P. parviflora roots
|
29.23b (1.24)
|
4.24b (0.12)
|
S. auriculata
|
62.56c (1.24)
|
6.21c (0.46)
|
The results are expressed in mg GAE (gallic acid equivalent) per g of extract. |
Different letters represent significantly different means (p < 0.05). |
The variation among P. parviflora samples could be linked to the roles of analyzed structures. Leaves, which are photosynthetic, displayed the highest phenol content. Phenolic compounds, linked to UV absorption, might be more abundant in leaves due to their photoprotective effect.
The primary compounds in macrophyte samples were identified using UV, MS, and MS/MS data, compared with published information (Table 2–5). Predominantly, they comprised flavonoids and phenylpropanoids.
Table 2
Identification of the constituents from hydroethanolic extract of Salvinia auriculata by LC-DAD-MS/MS.
Peak
|
RT
(min)
|
Compound
|
Molecular
Formula
|
Error
Ppm
|
UV
(nm)
|
Negative mode (m/z)
|
Positive mode (m/z)
|
MS
|
MS/MS
|
MS
|
MS/MS
|
1
|
5.3
|
Unknown
|
C14H16O9
|
-2,4
|
260–297
|
327.0729
|
191.0635;173.0485
|
329.0874
|
-
|
2
|
6.4
|
4-O-E-caffeoylquinic
|
C16H18O9
|
-2,8
|
297–325
|
353.0888
|
191.0548;179.0277
173.0345; 161.0196
|
163.0386
|
-
|
3
|
10.7
|
4-O-E-caffeoylquinic
|
C16H18O9
|
-2,1
|
300–325
|
353.0885
|
191.0571; 179.0375; 173.0456; 161.0161
|
355.1037
|
163.0390; 145.0279
|
4
|
14.8
|
Unknown
|
C10H10O3
|
2,8
|
304–334
|
177.0548
|
161.0244
|
-
|
-
|
5
|
16.6
|
Unknown
|
C18H24O10
|
3,3
|
285
|
399.1284
|
153.0273
|
-
|
-
|
6
|
18.0
|
Unknown
|
C31H30O15
|
-0,7
|
283–329
|
641.1516
|
449.1000; 405.0954; 327.0566; 297.0419; 271.0588; 191.0570; 173.0441; 161.0223
|
643.1681
|
311.0581; 299.0575; 271.0578; 231.0693; 191.0350; 163.0403
|
7
|
19.0
|
Kaempferol-O-hexoside
|
C21H18O12
|
-1,2
|
266–346
|
461.0731
|
285.0388
|
463.0880
|
287.0569
|
8
|
20.0
|
3,4-dicafeoylquinic acid
|
C25H24O12
|
-2,1
|
297–325
|
515.1206
|
335.0795; 191.0562; 179.0344; 173.0477; 161.0250; 155.0380
|
517.1361
|
163.0399
|
9
|
20.2
|
Unknown
|
C31H30O14
|
-0,1
|
283–329
|
625.1564
|
433.0786; 281.0457; 191.0571; 161.0251
|
627.1737
|
283.0591; 163.0395
|
10
|
20.6
|
3,5-dicafeoylquinic acid
|
C25H24O12
|
-1,4
|
298–329
|
515.1202
|
191.0570; 179.0340; 161.0270
|
-
|
-
|
11
|
21.9
|
Salviniside II derivative
|
C22H18O12
|
-1,3
|
330
|
473.0732
|
413.0480; 285.0481; 241.0490
|
475.0890
|
313.0342; 295.0262; 267,0279
|
12
|
22.1
|
4,5-dicafeoylquinic acid
|
C25H24O12
|
-0,3
|
298–329
|
515.1197
|
325.0149; 191.0596; 179.0330; 173.0470; 161.0213
|
499.1243
|
-
|
13
|
23.1
|
Salviniside II derivative
|
C22H18O12
|
-1,0
|
330
|
473.0730
|
413.0548; 327.0514; 267.0216; 241.0516
|
475.0894
|
313.0362; 267.0297; 239.0362
|
14
|
25.3
|
Unknown
|
C27H23NO13
|
-1,9
|
284–329
|
568.1108
|
413.0473; 241.0603
|
570.1233
|
313.0331; 295.0226
|
“Unknown” are the non identified compounds. |
In the S. auriculata extract, we observed 14 peaks (Table 2). Among these, peaks 2 and 3 had the ion at m/z 353 as the base peak in the negative ionization spectrum, along with two bands near 299 and 325 nm in the UV spectrum, characteristic of caffeoylquinic acids. Peaks 2 and 3 exhibited product ions at m/z 191 due to the loss of the caffeoyl unit, m/z 179 related to the quinic unit's loss, and m/z 173 for the dehydrated quinic acid unit. As only the caffeoylquinic acid esterified at position 4 produces the product ion at m/z 173, these peaks were identified as 4-O-E-caffeoylquinic acid (GOBBO-NETO, 2007).
Compounds 11 and 13 displayed intense ions at m/z 473.0732 and 473.0730, respectively, in alignment with the molecular formula C22H18O12. These peaks were recognized as derivatives of salviniside II (Li et al., 2013). Peak 7 exhibited bands at 265 and 345 nm in the UV spectrum, characteristic of flavonol structures. This compound bore the molecular formula C21H18O12, with ions m/z 461.0731 [M-H]- and 463.0880 [M + H]-, and a key fragment at m/z 285, harmonizing with flavonoid aglycone kaempferol. Hence, this compound was identified as kaempferol-O-hexoside (SADEER et al., 2019).
Peaks 8, 10, and 12, with retention times of 20.0, 20.6, and 22.1 min, displayed bands at 285 and 314 nm in the UV spectrum, along with m/z 515 [M + H] + and 513 [M-H]-, encompassing molecular formula C25H24O12, compatible with dicaffeoylquinic acids (CLIFFORD et al., 2003, 2005). Peaks 10 and 12 were validated as 3,5 and 4,5-dicaffeoylquinic acids, respectively, using genuine standard injection. The fragment ions of peak 8 were juxtaposed with identification cues suggested by Clifford et al. (2003, 2005) for dicaffeoylquinic acids. In these guidelines, the fragment ion at m/z 173 functions as a diagnostic indicator of a caffeic unit esterified at the fourth position of quinic acid. This data, coupled with the absence of characteristic ions of 1,4-dicaffeoylquinic acid (m/z 299 and m/z 203), substantiated the identification of this compound as 3,4-dicaffeoylquinic acid (GOBBO-NETO 2007).
In the extract of P. parviflora leaves (Table 3), 19 peaks were detected. Peaks 1, 2, 4, and 7, displaying the base ion at m/z 209, were suggested based on their molecular formulas and UV spectra as derivatives of caffeoyl glucarate. Peaks 3 and 6, exhibiting two bands in the UV spectra within the range of 300 to 324 nm and 299 to 325 nm, respectively, displayed the base ion at m/z 371. Both peaks 3 and 6 also showed product ions at m/z 191, with peak 6 additionally featuring an ion at m/z 209, characterizing them as isomers of caffeoyl glucarates (LORENZ et al. 2014).
Table 3
Identification of the constituents from hydroethanolic extract of Pontederia parviflora (leaves) by LC-DAD-MS/MS.
Peak
|
RT
(min)
|
Compound
|
Molecular
Formula
|
Error
Ppm
|
UV
(nm)
|
Negative mode (m/z)
|
Positive mode (m/z)
|
MS
|
MS/MS
|
MS
|
MS/MS
|
1
|
3.2
|
Caffeoyl glucarate derivatives
|
C6H10O8
|
-3.9
|
300–324
|
209.0311
|
-
|
-
|
-
|
2
|
4.2
|
Caffeoyl glucarate derivatives
|
C6H10O8
|
0.1
|
300–324
|
209.0303
|
-
|
-
|
-
|
3
|
4.5
|
Isomers of caffeoyl glucarates
|
C15H16O11
|
-1.1
|
300–326
|
371.0624
|
191.0234
|
-
|
-
|
4
|
4.8
|
Caffeoyl glucarate derivatives
|
C6H10O8
|
-0.5
|
300–324
|
209.0304
|
-
|
-
|
-
|
5
|
5.7
|
Tryptophan derivative
|
C11H11N2O2
|
1.2
|
280
|
203.0824
|
-
|
-
|
-
|
6
|
6.2
|
Isomers of caffeoyl glucarates
|
C15H16O11
|
-2.2
|
299–325
|
371.0628
|
209.0254; 191.0182
|
-
|
-
|
7
|
6.5
|
Caffeoyl glucarate derivative
|
C6H10O8
|
-0.9
|
300–324
|
209.0303
|
-
|
-
|
-
|
8
|
9.9
|
Unit of caffeic acid
|
C9H8O4
|
0.6
|
299–320
|
179.0349
|
-
|
163.0371
|
-
|
9
|
10.6
|
Isomer of caffeoylquinic acid
|
C16H18O9
|
1.9
|
285–325
|
353.0871
|
191.0572; 161.0197
|
163.0375
|
-
|
10
|
12.1
|
Caffeic acid derivatives
|
C14H15O8
|
3.6
|
299–324
|
311.0786
|
271.0942; 255.0767; 179.0354; 161.0316; 149.0488
|
625.1748
|
163.0377
|
11
|
12.9
|
Unknown
|
C13H12O8
|
-4.1
|
300–325
|
295.0471
|
179.0384
|
-
|
-
|
12
|
13.3
|
Caffeic acid derivatives
|
C14H15O8
|
1.0
|
300–324
|
311.0787
|
311.0823; 271.0922; 243.0617; 179.0356; 161.0252; 149.0456
|
313.0898
|
163.0379
|
13
|
14.1
|
Unknown
|
C16H16O8
|
-4.8
|
285–320
|
335.0789
|
179.0434; 161.0292
|
-
|
-
|
14
|
16.8
|
Unknown
|
C14H14O7
|
-3.0
|
298–324
|
293.0676
|
179.0378; 161.0228
|
-
|
-
|
15
|
20.0
|
Kaempferol-O-rutinoside
|
C27H30O15
|
-2.2
|
269–346
|
593.1525
|
477.0882; 285.0415
|
595.1640
|
2870549
|
16
|
20.0
|
3,4 dicafeoylquinic acid
|
C25H24O12
|
-0.9
|
269–346
|
515.1200
|
191.0603; 179.0335; 173.0407; 161.0183
|
-
|
-
|
17
|
20.6
|
3,5 dicafeoylquinic acid
|
C25H24O12
|
-1.5
|
280–320
|
515.1162
|
-
|
-
|
-
|
18
|
22.2
|
4,5 dicafeoylquinic acid
|
C25H24O12
|
-1.5
|
280–320
|
515.1202
|
-
|
-
|
-
|
19
|
23.1
|
Kaempferol-O-ramnoside-O-malonil-O-hexoside
|
C30H32O18
|
0.2
|
267–347
|
679.1515
|
635.1623; 489.1055; 285.0380
|
681.1630
|
287.0554
|
20
|
26.4
|
Kaempferol derivative
|
C29H32O16
|
-0.6
|
273–335
|
635.1622
|
-
|
-
|
-
|
21
|
30.4
|
Unknown
|
C18H32O5
|
-3.4
|
276–311
|
327.2188
|
171.1031
|
-
|
-
|
22
|
31.4
|
Unknown
|
C18H34O5
|
-3.5
|
276–311
|
329.2345
|
229.1431; 211.1313; 171.0995
|
-
|
-
|
23
|
31.6
|
Unknown
|
C19H12O4
|
2.9
|
276–308
|
303.0654
|
274.0646
|
305.0817
|
277.0761; 259.0711; 249.0938; 231.0808; 213.0638; 203.0872
|
24
|
33.3
|
Unknown
|
C19H12O3
|
-4.3
|
276
|
287.0726
|
287.0773
|
289.0848
|
271.0725; 261.0924; 243.0786; 233.0945; 215.0837
|
25
|
35.0
|
Unknown
|
C18H30O4
|
-1.0
|
273–311
|
309.2075
|
183.0064
|
-
|
-
|
“Unknown” are the non identified compounds. |
Peak 5 demonstrated a base ion at m/z 203 in negative ionization mode, along with two ions at m/z 188 and m/z 205 in positive ionization mode. Furthermore, a product ion at m/z 170 was observed. This compound was identified as a derivative of tryptophan (LIU et al. 2015).
Peak 8 displayed an ion at m/z 179 and lacked product ions in the fragmentation spectrum. However, relying on its UV spectrum and the molecular formula obtained from the software, this peak was suggested to represent a unit of caffeic acid, a product ion resulting from the fragmentation of caffeoylquinic acid (GOBBO-NETO, 2007). Peak 9, akin to peaks 2 and 3 of S. auriculata, exhibited the base ion at m/z 353 and two bands in the UV spectrum ranging from 285 to 325 nm, along with product ions at m/z 191 and m/z 161. This peak was identified as an isomer of caffeoylquinic acid (GOBBO-NETO, 2007).
Peaks 10 and 12 displayed ions at m/z 311 [M-H]-, consistent with the molecular formula C14H15O8. However, peak 10 featured a main ion at m/z 625 [M + H]+, potentially indicating a dimer, while peak 12 exhibited m/z 313 [M + H]+. These compounds were recognized as derivatives of caffeic acid connected to a unit of D-erythrono-1,4-lactone or D-threono-1,4-lactone (CCANA-CCAPATINA et al., 2017).
Peaks 15 and 19 exhibited two bands in the UV spectrum near wavelengths of 265 and 345 nm (typical of flavonols), along with ions at m/z 593.1525 [M-H]- and 679.1515 [M-H]-, respectively. The compounds possessed the molecular formulas C27H29O15 and C30H31O18, sharing the main fragment at m/z 285, akin to compound 7 of S. auriculata. Compound 15 was identified as Kaempferol-O-rutinoside (HERRANZ-LÓPEZ et al., 2012), and compound 19 as Kaempferol-3-O-rutinoside-7-O-rhamnoside (JU et al., 2018).
Peak 20 featured a base ion at m/z 635, with the identical molecular formula as peak 19, albeit without any fragmentation. Hence, this peak was identified as a derivative of kaempferol (SADEER et al., 2019). Compounds 16, 17, and 18 were designated as 3,4, 3,5, and 4,5-dicaffeoylquinic acids, congruent with their presence in S. auriculata peaks 8, 10, and 12 (CCANA-CCAPATINA et al., 2017).
In P. parviflora petiole/stem (Table 4), 7 peaks were detected. Peaks 2 and 3 exhibited the base ion at m/z 311 [M-H]-, with two bands in the wavelength range of 294 to 329 nm and 300 to 322 nm in the UV spectra, respectively, along with the molecular formula C14H15O8. Although peak 2 lacked fragmentation in the MS/MS spectrum, based on UV data and the molecular formula, this compound was tentatively identified as a derivative of chlorogenic acid. Peak 3 displayed a product ion at m/z 179 [M-H]-, linked to the caffeoyl unit. Furthermore, it demonstrated the ion at m/z 313 [M + H] + with a product ion at m/z 163 [M + H]+. Considering the calculated molecular formulae, these resemblances were noted with peaks 10 and 12 of P. parviflora leaves. Consequently, this compound was identified as a caffeic acid derivative connected to a unit of D-erythrono-1,4-lactone or D-threono-1,4-lactone (CCANA-CCAPATINA et al., 2017).
Table 4
Identification of the constituents from hydroethanolic extract of Pontederia parviflora (petiole/stem) by LC-DAD-MS/MS.
Peak
|
RT
(min)
|
Compound
|
Molecular
Formula
|
Error
Ppm
|
UV
(nm)
|
Negative mode (m/z)
|
Positive mode (m/z)
|
MS
|
MS/MS
|
MS
|
MS/MS
|
01
|
5.7
|
Unknown
|
C11H12N2O2
|
0.0
|
283
|
203.0826
|
-
|
-
|
-
|
02
|
12.1
|
Chlorogenic acid derivative
|
C14H16O8
|
-5.0
|
294–329
|
311.0788
|
-
|
-
|
-
|
03
|
13.4
|
Caffeic acid derivative
|
C14H16O8
|
-1.0
|
300–322
|
311.0775
|
179.0401
|
313.0921
|
163.0386
|
04
|
20.0
|
Unknown
|
C27H30O15
|
0.2
|
285–330
|
593.1511
|
-
|
595.1664
|
287.0555
|
05
|
23.3
|
Unknown
|
C30H32O18
|
1.2
|
290–345
|
-
|
-
|
681.1653
|
287.0550
|
06
|
30.5
|
Unknown
|
C18H31O5
|
-1.8
|
285
|
327.2197
|
211.1362
|
-
|
-
|
07
|
32.5
|
Unknown
|
C14H17O4
|
1.8
|
283
|
249.1128
|
-
|
-
|
-
|
“Unknown” are the non identified compounds. |
For P. parviflora roots (Table 5), 9 peaks were discerned. Peak 3 exhibited two bands within the wavelengths of 280 to 310 nm in the UV spectra and the ion at m/z 163 [M-H]-, consistent with the molecular formula C9H7O3, implying a coumaric acid molecule (DUGO et al., 2008).
Table 5
Identification of the constituents from hydroethanolic extract of Pontederia parviflora (roots) by LC-DAD-MS/MS.
Peak
|
RT
(min)
|
Compound
|
Molecular
Formula
|
Error
Ppm
|
UV
(nm)
|
Negative mode (m/z)
|
Positive mode (m/z)
|
MS
|
MS/MS
|
MS
|
MS/MS
|
01
|
1.2
|
Unknown
|
C12H22O11
|
-7.7
|
269
|
341.1116
|
191.0588
|
365.1092
|
203.0522
|
02
|
1.2
|
Unknown
|
C18H17O9
|
-4.1
|
269
|
377.0893
|
-
|
|
|
03
|
13.3
|
Coumaric acid
|
C9H9O3
|
-0.1
|
280–310
|
163.0401
|
-
|
-
|
-
|
04
|
19.1
|
Unknown
|
C9H10O4
|
-1.5
|
275–308
|
181.0509
|
-
|
-
|
-
|
05
|
19.9
|
Unknown
|
C9H16O4
|
-12.7
|
276–310
|
187.1000
|
-
|
-
|
-
|
06
|
30.1
|
Unknown
|
C17H14O7
|
-4.3
|
276–311
|
329.0681
|
299.0270; 271.0236; 227.0467; 199.0431; 161.0193
|
331.0822
|
315.0521; 302.0464; 287.0549; 270.0489; 258.0514; 242.0549
|
07
|
31.5
|
Unknown
|
C18H34O5
|
-2.1
|
276–312
|
329.2340
|
211.1341; 171.1042
|
667.3233
|
433.2096; 389.1835; 261.1318; 217.1060; 173.0796; 155.0716
|
08
|
31.7
|
Unknown
|
C13H18O3
|
-3.1
|
276–310
|
221.0663
|
-
|
-
|
-
|
09
|
33.1
|
Unknown
|
C18H10O3
|
-1.7
|
276–312
|
273.0562
|
245.0636
|
-
|
-
|
“Unknown” are the non identified compounds. |
The results obtained from the heavy metal quantification tests in the biomass of the studied macrophytes (Table 6) demonstrated that, barring Ni and Mo in P. parviflora, the metal concentration escalated after the extraction of secondary metabolites. Employing ICP-OES, it was apparent that the heavy metals existing in the macrophytes' biomass were not predominantly complexed with the plants' metabolites, or at least, a majority of these metals were not. This is inferred from the elevation of metal levels in samples where metabolites were removed. Although secondary metabolites encompass clusters such as –OH- and –COO-, known to form bonds with metals (SARASWAT and RAI, 2010; ALI et al., 2013), our results imply that metals are chiefly associated with plant structures that persist throughout the process of secondary metabolite extraction, such as cell walls and vacuoles. Additionally, no correlation was established between the content of total phenols and tannins in the samples and the metal accumulation capacity, further affirming that the secondary metabolites in these plants are not primarily responsible for phytoremediation. The calibration parameters acquired for the ICP-OES are accessible in the Supplementary Material (Table S1).
Table 6
Concentration (mean ± deviation, n = 3) in µg g− 1 of As, Cd, Cr, Mg, Mn, Mo, Ni and Pb found in P. parviflora-leaf (PPA-F), P. parviflora - petioles/stems (PPA-C), P. parviflora-roots (PPA-R) and S. auriculata.
Sample
|
Means (standard deviation)
|
As
|
Cd
|
Cr
|
Mg
|
Mn
|
Mo
|
Ni
|
Pb
|
PPA-F – I
|
0.331a
(0.013)
|
<DL
|
0.179a
(0.001)
|
>LPC
|
>LPC
|
0.419c
(0.001)
|
0.1254a
(0.0003)
|
0.256a
(0.010)
|
PPA-F – II
|
0.371b
(0.016)
|
<DL
|
0.499c
(0.002)
|
>LPC
|
>LPC
|
0.464d
(0.003)
|
0.2108c
(0.0003)
|
0.318c
(0.005)
|
PPA-C – I
|
0.361ab
(0.006)
|
<DL
|
0.434b
(0.008)
|
>LPC
|
>LPC
|
0.267b
(0.004)
|
0.2142c
(0.001)
|
0.287b
(0.003)
|
PPA-C – II
|
0.425c
(0.013)
|
<DL
|
0.519c
(0.012)
|
>LPC
|
>LPC
|
0.192a
(0.001)
|
0.1805b
(0.0008)
|
0.385d
(0.006)
|
PPA-R – I
|
0.835d
(0.005)
|
0.0232 a
(0.0002)
|
1.026d
(0.004)
|
>LPC
|
>LPC
|
0.186a
(0.001)
|
0.2497d
(0.001)
|
0.924e
(0.0005)
|
PPA-R – II
|
1.134f
(0.015)
|
0.0318 b
(0.0004)
|
1.264e
(0.007)
|
>LPC
|
>LPC
|
0.266b
(0.005)
|
0.3034e
(0.0007)
|
1.077g
(0.006)
|
SAL – I
|
1.081e
(0.012)
|
0.0402 c
(0.0004)
|
1.254e
(0.006)
|
>LPC
|
>LPC
|
0.541e
(0.003)
|
0.3660f
(0.002)
|
1.054f
(0.008)
|
SAL – II
|
1.471g
(0.016)
|
0.0459 d
(0.0002)
|
1.516f
(0.009)
|
>LPC
|
>LPC
|
0.623f
(0.004)
|
0.4506g
(0.0005)
|
1.235h
(0.007)
|
<DL: samples with concentrations below the detection limit of the equipment. Means followed by the same letter in the column do not differ from each other by the Tukey test, considering the nominal value of 5% of significance. > UPC: sample with concentration above the highest concentration point of the calibration curve (2µg g− 1). |
Samples with “I” are samples of dried plant material that have not gone through the extraction process and “II” samples are samples that have had their secondary metabolites removed in the extraction process. |
We also observed that the roots of P. parviflora exhibit higher metal accumulation compared to the petiole/stem and leaves. This disparity could be attributed to the roots' closer interaction with the contaminated environment. P. parviflora, as an emerging macrophyte, has its roots firmly affixed to the substrate, while the leaves and a section of the petiole/stem remain above the water surface.
To assess the plant biomass's capacity (pre- and post-extraction procedure), Cadmium Removal trials were conducted using three different Cd solution concentrations (0.2 and 3.5 µg/mL of Cd in acidic water). The outcomes (Table 7) revealed that at the 0.2 µg/mL solution, all samples demonstrated a decrease in Cd concentration, signifying the macrophytes' ability to capture this metal. However, in the 3.5 µg/mL solutions, the samples exhibited minimal reduction in Cd content. Notably, when in contact with sample P. parviflora - roots I, there was an elevation in Cd concentration. These findings imply a saturation of the trapping system in the plant material and suggest that the presence of metabolites in the biomass (samples before the extraction process) does not influence the metal trapping system. This conclusion is drawn from the lack of correlation between the presence of these metabolites and the enhanced removal of metals.
Table 7
Mean values (± standard deviation, n = 3) of the residual concentration evaluated after the removal tests, the values presented are the residual cadmium concentration after the contact time of the control solution with the biomass.
Sample
|
Assay 0.2 µg mL-1
|
Assay 3.5 µg mL-1
|
Control
|
0.200 (± 0.00010)
|
3.350 (± 0.0024)
|
PPA-F – I
|
0.026 (± 0.00008)e
|
2.940 (± 0.0110)b
|
PPA-F – II
|
0.058 (± 0.00007)c
|
3.260 (± 0.0020)c
|
PPA-C – I
|
0.019 (± 0.00008)g
|
3.260 (± 0.0020)c
|
PPA-C – II
|
0.012 (± 0.00014)a
|
3.200 (± 0.0010)c
|
PPA-R – I
|
0.014 (± 0.00017)d
|
3.430 (± 0.0010)cd
|
PPA-R – II
|
0.008 (± 0.00006)f
|
3.300 (± 0.0010)e
|
SAL – I
|
0.030 (± 0.00001)bc
|
3.380 (± 0.0020)e
|
SAL – II
|
0.011 (± 0.000005)a
|
2.530 (± 0.0008)a
|
Means followed by the same letter in the column do not differ from each other by the Tukey test, considering the nominal value of 5% of significance. |
The concentration of Cd in (µg mL− 1). Samples with “I” are samples of dried plant material that have not gone through the extraction process and “II” samples are samples that have had their secondary metabolites removed in the extraction process. |
Despite the absence of extraction enhancement, the attained results regarding extract yield and the percentage of phenolic compounds present promising potential. Tannins and phenolic compounds commonly possess well-recognized antioxidant and antiradical properties, constituting the primary biological activities linked to phytoremediation processes, involving metal sequestration and chelation (ZHENG and WANG, 2001; DAI and MUMPER, 2010).
Regarding the disparity in metal content between biomass samples with and without secondary metabolites, it's noteworthy that the removal of metabolites led to elevated metal levels within the structures of the samples. Although existing literature links metal complexation with secondary metabolites, it's important to consider that plant tissues contain catechol subunits within lignins and lignans, which provide potential binding sites for metal atoms within the plant structure (SARASWAT and RAI, 2010; ALI et al., 2013).
As demonstrated in Table 6, the metal content escalates upon the removal of plant biomass metabolites. Samples with removed metabolites comprise a higher proportion of structures that contribute to plant tissue formation, such as lignins, which remain intact during the extraction process. Consequently, we hypothesize that the metals detected in these samples could be complexed within these structures. The exception to this trend is observed in the case of Mo and Ni in PPA-C, where this logic is reversed.
Among the assessed metals, certain ones are integral to plant metabolism, constituting essential micronutrients. However, in most instances, these metals are present at levels designating them as contaminants within the collection areas of these plants. Generally, they possess high toxic potential. Furthermore, their presence in aquatic ecosystems fuels extensive debate, interest, and concern. This is particularly significant since their concentrations in natural waters are also subject to stringent limitations.
The results presented for Cd removal assays in a contaminated aqueous medium (Fig. 1, Table 7) indicate a low saturation point for the phytoremediation system in relation to this metal. At Cd concentrations of 0.2 µg mL-1, there was a reduction in all residual aqueous samples, ranging from 71% (PPA-F II) to 96% (PPA-R II). At concentrations of 3.5 µg mL-1 Cd, certain samples exhibited an increase in residual aqueous concentrations, with higher Cd contents than the control (PPA-R I and SAL I, both containing metabolites). In assays with a concentration of 3.5 µg mL-1, the most favorable removal result was achieved in SAL II, with a 24.5% reduction.
The presence of other ions can impact the potential for metal removal due to competition for binding sites. It is essential to observe the ionic balance in control solutions and the dried biomass to enhance contaminant removal potential (Saraswat and RAI 2010).
The elevated Cd contents observed after biomass intervention (cadmium removal assay) at higher metal concentrations can be explained by the scheme depicted in Fig. 2. This scheme illustrates situations where biomass binding sites become saturated and complexed with other ions from the environment. This fact potentially compromises the ability of these vegetables to remove ions. Nevertheless, as the dry biomass persists, water absorption continues, resulting in the residual (aqueous) solution retaining Cd mass in the reduced volume of the medium (water), consequently elevating the Cd concentration in this residual solution.