4.1. Grain size
According to the grain size analysis results of surface sediments in the study area, sand is the dominant grain size overall. At most sites, the sand content exceeds 80%, the contents of gravel and fine particles (clay and silt) were very small (avg. 6.25 and 2.38%, respectively). Grain size is significantly influenced by the flow rate and flow velocity of the surface water; the textural parameters derived from the grain size analysis reflect the energy conditions in the sedimentation environment. In a low-energy environment, the sediments are fine, although in a high-energy environment, the sediments are coarse (Kim et al. 2017). In this study, the grain size distribution explains the high-energy environment in the stream producing by the dominance of sand size particles, in which the water flux is high and the slope is steep thereby preventing the sedimentation of fine-grained particles. The sedimentation process occurs on the banks of rivers and in backwaters.
4.2. Sediment Mineralographic composition
XRD studies revealed the presence of different minerals as: Quartz, Calcite, Sanidine, Albite, Biotite, Wickenburgite, Lipsconmbite, Phengite, Gypsum and Muscovite. In all the samples a predominance of Quartz crystals (36 to 51%) and Calcite (6 to 18%) were shown by XRD; Albite was present in four samples (11.5 to 19.2%), sanidine was present in three samples (11. 8 to 13.9%).
The minerals founded in the sediment samples, the presence of aluminosilicate minerals that are minerals composed of aluminum oxide and silicon dioxide such as Albite, Sanidine, Biotite, Muscovite, Wickenburgite stood out. This is related to the aluminosilicate minerals of igneous and metamorphic rocks are generally unstable in earth-surface weathering conditions, these elements transformed to stable end-products (crystalline clay minerals, oxides and hydroxides) that largely conserve aluminum and iron (Farmer, 1986).
4.3. Metals concentrations in sediments
Compared with Canadian Sediment Quality Guidelines (CCME, 1999) for aquatic life protection, metal contents were above the probable effect level (PEL) in 87.5 % of samples for As,75% for Zn, 62.5 % Pb, 50% for Cd and Cu and 25% for Ni (Table 1). The concentrations of heavy metals of sediment samples were contrasted with the TEC, PEC and PEL values, the results are summarized in Table 1 (MacDonald et al., 2000). The concentrations of Ni were below the TEC values for 50% of the samples, indicating that there are no adverse effects in these samples (M1, M2, M3, M7 and M8 samples). The results showed that more than 50% of the samples were found between the TEC and PEC values for As, Cd, Cu and Zn, indicating that concentrations of these metals occasionally could exhibit adverse effects on the ecosystem. All sites exceeded the TEC levels for As, Cd, Cu, Pb, Zn demonstrating high level of pollution only M1 is below of TEC value for Pb; in case of Ni two sites exceeded the TEC values (M4 and M6).
Table 1
Metal concentrations of surface sediments in the study area, background values, Canadian Sediment Quality Guideline values (SQGs), PEL, TEC and PEC used in this study (mg/kg).
Sites/SQGs
|
Al
|
As
|
B
|
Ba
|
Cd
|
Co
|
Cr
|
Cu
|
Fe
|
Mn
|
Ni
|
Pb
|
Zn
|
mg kg− 1
|
PEL
|
|
17
|
|
|
3.53
|
|
90
|
196.6
|
|
|
75
|
91.3
|
314.8
|
TEC
|
|
9.79
|
|
|
0.99
|
|
43.4
|
31.6
|
|
|
22.7
|
35.8
|
121
|
PEC
|
|
33
|
|
|
4.98
|
|
111
|
149
|
|
|
48.6
|
128
|
459
|
M1- San Martín
|
16771
|
<l.c.
|
15.8
|
154
|
2.10
|
5.20
|
5.00
|
209.0
|
18637.0
|
231.0
|
18.70
|
35.60
|
351
|
M2-R. San Juan
|
16610.00
|
39.30
|
16.80
|
151.00
|
1.80
|
6.10
|
2.50
|
68.30
|
20009.0
|
362.0
|
16.60
|
94.20
|
144
|
M3-R.Cacalotenango
|
18313.00
|
48.80
|
12.80
|
173.0
|
16.20
|
7.20
|
<l.c.
|
78.40
|
20526.0
|
795.0
|
15.70
|
265.0
|
2008
|
M4-R. Pte Tecalpulco
|
20303.00
|
25.50
|
31.20
|
278.0
|
50.40
|
7.80
|
5.50
|
393.0
|
20614.0
|
2710.0
|
111.0
|
244.0
|
4509
|
M5-R. Taxco Acolco
|
19032.00
|
24.70
|
15.90
|
104.0
|
5.50
|
7.20
|
<l.c.
|
41.80
|
23223.0
|
334.00
|
18.6
|
160.0
|
967
|
M6-El Milagro
|
22982.00
|
<l.c.
|
19.90
|
143.0
|
2.00
|
9.00
|
9.40
|
117.0
|
20930.0
|
105.00
|
24.2
|
13.90
|
142
|
M7-R. Campuzano
|
12086.00
|
21.30
|
13.80
|
88.0
|
9.40
|
6.30
|
<l.c.
|
55.90
|
22301.0
|
660.00
|
20.00
|
189.0
|
1763
|
M8-R. San Juan Metlapa
|
22849.00
|
17.10
|
21.60
|
227.0
|
2.20
|
5.20
|
17.10
|
502.0
|
15366.0
|
298.00
|
15.40
|
32.60
|
811
|
Mean
|
18618.25
|
29.45
|
18.48
|
164.7
|
11.20
|
6.75
|
7.90
|
183.1
|
20200.7
|
686.88
|
30.03
|
129.2
|
1336.9
|
Max
|
22982.0
|
48.8
|
31.2
|
278.0
|
50.4
|
9.0
|
17.1
|
502.0
|
23223.0
|
2710.0
|
111.0
|
265.0
|
4509
|
Min
|
12086.0
|
17.1
|
12.8
|
88.0
|
1.8
|
5.2
|
2.5
|
41.8
|
15366.0
|
105.0
|
15.4
|
13.9
|
142
|
Background values (Rudnick and Gao 2014)
|
81500
|
4.8
|
17
|
628
|
0.09
|
17.3
|
92
|
28
|
50400
|
774
|
47
|
17
|
67
|
SQGs-PEL-Probable Effect Level Threshold |
TEC-Threshold Effect Concentration and PEC-Probable Effect Concentration (MacDonald et al., 2000). |
The results also showed values higher than PEC, for Pb, Zn and As in 50%, 37.5%, 25% of the samples respectively indicating that adverse biological effects often can be occur. From all selected sites, sample M6 was below PEC and PEL for all metals. For all other sites, As, Zn and Pb found to be the metals of the highest importance due the PEC and PEL values are exceeded for As and Zn in 6 samples (M2, M3, M4, M5, M7 and M8) and Pb in 5 samples (M2, M3, M4, M5 and M7)
4.4. Degree of metal enrichment and ecological risk assessment
The Index of geoaccumulation (Igeo) values are presented in Table 2. The Igeo values of Al, B, Ba, Co, Cr and Fe at all sampled sites were less than zero, suggesting that these sites were not polluted. The values of Igeo for As were greater than 1 but less than 2 in the sediments of M4, M5, M7, and M8, which were classified as moderately contaminated while the samples M2 and M3 were considered as moderately to heavily contaminated. Cadmium was the metal that presented the highest contamination in all the sampled sites, the sediment samples were grouped in heavily contaminated for M1, M2 and M6, heavily to very contaminated for M8 and extremely contaminated for M3, M4, M5 and M7. Zinc, lead and copper are the three metals that have the greatest influence the contamination of river sediments, since they present the highest contamination values of the accumulation index; In the case of zinc, these Igeo values were classified as uncontaminated to moderately contaminated (M2 and M6), moderately contaminated (M1), moderately to heavily contaminated (M5 and M8), heavily to very contaminated (M3 and M7) and extremely contaminated (M4).
Table 2
The values of Geoaccumulation indices (Igeo) of heavy metals for sediments in San Juan-Taxco River basin.
Sites
|
Geoaccumulation indices (Igeo)
|
Al
|
As
|
B
|
Ba
|
Cd
|
Co
|
Cr
|
Cu
|
Fe
|
Mn
|
Ni
|
Pb
|
Zn
|
M1-R. San Martín
|
-2.87
|
-
|
-0.69
|
-2.61
|
3.96
|
-2.32
|
-4.79
|
2.32
|
-2.02
|
-2.33
|
-1.91
|
0.48
|
1.80
|
M2-R. San Juan
|
-2.88
|
2.45
|
-0.60
|
-2.64
|
3.74
|
-2.09
|
-5.79
|
0.70
|
-1.92
|
-1.68
|
-2.09
|
1.89
|
0.52
|
M3-R. Cacalotenango
|
-2.74
|
2.76
|
-0.99
|
-2.44
|
6.91
|
-1.85
|
-
|
0.90
|
-1.88
|
-0.55
|
-2.17
|
3.38
|
4.32
|
M4-R. Pte Tecalpulco
|
-2.59
|
1.82
|
0.29
|
-1.76
|
8.54
|
-1.73
|
-4.65
|
3.23
|
-1.87
|
1.22
|
0.65
|
3.26
|
5.49
|
M5-R. Taxco Acolco
|
-2.68
|
1.78
|
-0.68
|
-3.18
|
5.35
|
-1.85
|
-
|
-0.01
|
-1.70
|
-1.80
|
-1.92
|
2.65
|
3.27
|
M6-El Milagro
|
-2.41
|
-
|
-0.36
|
-2.72
|
3.89
|
-1.53
|
-3.88
|
1.48
|
-1.85
|
-3.47
|
-1.54
|
-0.88
|
0.50
|
M7-R. Campuzano
|
-3.34
|
1.56
|
-0.89
|
-3.42
|
6.12
|
-2.04
|
-
|
0.41
|
-1.76
|
-0.81
|
-1.82
|
2.89
|
4.13
|
M8-R. San Juan Metlapa
|
-2.42
|
1.25
|
-0.24
|
-2.05
|
4.03
|
-2.32
|
-3.01
|
3.58
|
-2.30
|
-1.96
|
-2.19
|
0.35
|
3.01
|
Mean
|
-2.74
|
1.94
|
-0.52
|
-2.60
|
5.32
|
-1.97
|
-4.42
|
1.58
|
-1.91
|
-1.42
|
-1.62
|
1.75
|
2.88
|
Max
|
-2.41
|
2.76
|
0.29
|
-1.76
|
8.54
|
-1.53
|
-3.01
|
3.58
|
-1.70
|
1.22
|
0.65
|
3.38
|
5.49
|
Min
|
-3.34
|
1.25
|
-0.99
|
-3.42
|
3.74
|
-2.32
|
-5.79
|
-0.01
|
-2.30
|
-3.47
|
-2.19
|
-0.88
|
0.50
|
Igeo for lead element were categorized as uncontaminated in sample M6, uncontaminated to moderately contaminated in samples M1 and M8, moderately contaminated for sample M2, moderately to heavily contaminated in samplesM5 and M7 and heavily to very contaminated for M3 and M4. For copper Igeo values were classified as uncontaminated in sample M5, uncontaminated to moderately contaminated in samples M3, M4 and M7, moderately contaminated for sample M6, moderately to heavily contaminated in samplesM8 and M4. According to the calculation of each sampling point, the order of the metals according to the Igeo evaluated is as follows: Cd > Zn > Pb > Cu > As > Mn > Ni > B > Fe > Co > Ba > Al > Cr. The critical points associated with the geoaccumulation of metals were M3, M4 and M8; the first with four metals in the range of heavily to very heavily contaminated and the rest with three.
The results from this study show that the Cd enrichment factor, EF (Cd), ranges from 78.81 to 2247.94, EF (Zn) from 7.52 to 270.15, EF (Pb) from 2.9 to 74.97, EF (As) from 12.71 to 45.25, EF (Cu) from 6.39 to 63.95, EF (Mn) from 0.48 to 14.05, EF (Ni) from 1.17 to 9.48, EF (Fe) from 1.09 to 2.98, EF (Ba) from 0.71 to 1.78, EF (Co) from 1.07 to 2.46 and EF (Cr) from 0.13 to 0.66 (Table 3). The average enrichment factors of Ba (1.14), Co (1.75) and Fe (1.84) are found to be less than 3 (EF < 3) (Table 3), indicating minor enrichment.
Table 3
The values of enrichment factor (EF) of studied heavy metals for sediments of all sites studied in San Juan-Taxco River Basin
Sites
|
Enrichment factor (EF)
|
Al
|
As
|
B
|
Ba
|
Cd
|
Co
|
Cr
|
Cu
|
Fe
|
Mn
|
Ni
|
Pb
|
Zn
|
M1-R. San Martín
|
1
|
-
|
4.52
|
1.19
|
113.39
|
1.46
|
0.26
|
36.27
|
1.80
|
1.45
|
1.93
|
10.18
|
25.46
|
M2-R. San Juan
|
1
|
40.17
|
4.85
|
1.18
|
98.13
|
1.73
|
0.13
|
11.97
|
1.95
|
2.29
|
1.73
|
27.19
|
10.55
|
M3-R. Cacalotenango
|
1
|
45.25
|
3.35
|
1.23
|
801.07
|
1.85
|
-
|
12.46
|
1.81
|
4.57
|
1.49
|
69.40
|
133.38
|
M4-R. Pte Tecalpulco
|
1
|
21.33
|
7.37
|
1.78
|
2247.94
|
1.81
|
0.24
|
56.34
|
1.64
|
14.05
|
9.48
|
57.62
|
270.15
|
M5-R. Taxco Acolco
|
1
|
22.04
|
4.01
|
0.71
|
261.69
|
1.78
|
-
|
6.39
|
1.97
|
1.85
|
1.69
|
40.30
|
61.81
|
M6-El Milagro
|
1
|
-
|
4.15
|
0.81
|
78.81
|
1.84
|
0.36
|
14.82
|
1.47
|
0.48
|
1.83
|
2.90
|
7.52
|
M7-R. Campuzano
|
1
|
29.92
|
5.47
|
0.94
|
704.30
|
2.46
|
-
|
13.46
|
2.98
|
5.75
|
2.87
|
74.97
|
177.44
|
M8-R. San Juan Metlapa
|
1
|
12.71
|
4.53
|
1.29
|
87.19
|
1.07
|
0.66
|
63.95
|
1.09
|
1.37
|
1.17
|
6.84
|
43.18
|
Mean
|
1
|
28.57
|
4.78
|
1.14
|
549.07
|
1.75
|
0.33
|
26.96
|
1.84
|
3.98
|
2.77
|
36.17
|
91.18
|
Max
|
1
|
45.25
|
7.37
|
1.78
|
2247.94
|
2.46
|
0.66
|
63.95
|
2.98
|
14.05
|
9.48
|
74.97
|
270.15
|
Min
|
1
|
12.71
|
3.35
|
0.71
|
78.81
|
1.07
|
0.13
|
6.39
|
1.09
|
0.48
|
1.17
|
2.90
|
7.52
|
Although the average enrichment factors of B (4.78) and Mn (3.98) are found between 3 and 5 (EF = 3 a 5; Table 3), suggesting that these metal contaminations are currently not a major concern although moderate enrichment; Copper, lead and zinc presented very severe enrichment (25 < EF < 50) and extremely severe enrichment (EF > 50), the average enrichment factors for these heavy metals were 26.96, 36.17, and ranged from 6.39 to 639, 2.90 to 74.97 and 7.52 to 270.15 respectively. Arsenic in almost all samples sites presented very severe enrichment except for M8 (San Juan Metlapa), with a minimum 12.71 and a maximum 45.25.
The Cd presents extremely high enrichment in all the points evaluated. The points of attention correspond to the M21, M7, M9, M10 and M17, the first with very severe enrichment with four of the twelve metals and the rest with three of the twelve metals.
The results of contamination factors (CFs) and individual and global pollution load index (PLI) for the sediment from samples sites in the San Juan, Cacalotenango and Taxco Rivers are summarized in Table 4. The CF values for Cd were > 6 in all the studied sediments, indicating “very high contamination” by Cadmium. The CF values for Zn, Pb, Cu and As present “very high contamination” and “considerable contamination”. The CF values for Al, Ba, Co, Cr and Fe in all the samples denotes “low contamination” for all the sediments. The critical sites correspond to M3, M4, M5, M7 and M8; the first with four extremely enriched CF values and the rest with three. The level of CF values for each heavy metal in the sediment was in the order: Cd > Zn > Pb > Cu > As > Mn > Ni > Fe > Co > Ba > Cr. These results indicated that the contamination is relatively high; there are serious impacts of pollution related heavy metals in the nearby areas to abandoned mining tailings and where heavy metals processing (jewelry) is done and untreated sewage. Among all metals, contamination by Cd is the highest in all the sediment samples in a range of CF values of 20 to 560.
Table 4
Metal contamination factors (CFs) and Pollution load indices (PLIs) for sediments of all sites studied in San Juan-Taxco River basin.
Sites
|
Contamination factors (CFs)
|
Al
|
As
|
B
|
Ba
|
Cd
|
Co
|
Cr
|
Cu
|
Fe
|
Mn
|
Ni
|
Pb
|
Zn
|
PLI
|
M1-R. San Martín
|
0.21
|
-
|
0.93
|
0.25
|
23.33
|
0.30
|
0.05
|
7.46
|
0.37
|
0.30
|
0.40
|
2.09
|
5.24
|
0.796
|
M2-R. San Juan
|
0.20
|
8.19
|
0.99
|
0.24
|
20.00
|
0.35
|
0.03
|
2.44
|
0.40
|
0.47
|
0.35
|
5.54
|
2.15
|
0.862
|
M3-R. Cacalotenango
|
0.22
|
10.17
|
0.75
|
0.28
|
180.00
|
0.42
|
-
|
2.80
|
0.41
|
1.03
|
0.33
|
15.59
|
29.97
|
2.078
|
M4-R. Pte Tecalpulco
|
0.25
|
5.31
|
1.84
|
0.44
|
560.00
|
0.45
|
0.06
|
14.04
|
0.41
|
3.50
|
2.36
|
14.35
|
67.30
|
2.829
|
M5-R. Taxco Acolco
|
0.23
|
5.15
|
0.94
|
0.17
|
61.11
|
0.42
|
-
|
1.49
|
0.46
|
0.43
|
0.40
|
9.41
|
14.43
|
1.434
|
M6-El Milagro
|
0.28
|
-
|
1.17
|
0.23
|
22.22
|
0.52
|
0.10
|
4.18
|
0.42
|
0.14
|
0.51
|
0.82
|
2.12
|
0.718
|
M7-R. Campuzano
|
0.15
|
4.44
|
0.81
|
0.14
|
104.44
|
0.36
|
-
|
2.00
|
0.44
|
0.85
|
0.43
|
11.12
|
26.31
|
1.593
|
M8-R. San Juan Metlapa
|
0.28
|
3.56
|
1.27
|
0.36
|
24.44
|
0.30
|
0.19
|
17.93
|
0.30
|
0.39
|
0.33
|
1.92
|
12.10
|
1.194
|
Mean
|
0.23
|
6.14
|
1.09
|
0.26
|
124.44
|
0.39
|
0.09
|
6.54
|
0.40
|
0.89
|
0.64
|
7.61
|
19.95
|
1.44
|
Max
|
0.28
|
10.17
|
1.84
|
0.44
|
560.00
|
0.52
|
0.19
|
17.93
|
0.46
|
3.50
|
2.36
|
15.59
|
67.30
|
2.83
|
Min
|
0.15
|
3.56
|
0.75
|
0.14
|
20.00
|
0.30
|
0.03
|
1.49
|
0.30
|
0.14
|
0.33
|
0.82
|
2.12
|
0.72
|
The PLI values estimated by sampling points ranged from 0.72 to 2.83 (Table 4); These indicate that samples M1, M2 and M6, where PLI was below 1 were classified as unpolluted, the samples M5, M6 and M8 were considered as Moderately polluted but samples M3 and M4 were reported as heavy polluted. For the estimation of global value it were considering all the samples and making correction for points M1, M3, M5, M6 and M7, which are the points in which they do not have concentrations of As and Cr, therefore n = 12, the global value of PLI for the entire study area was 1.29 which makes it a moderately contaminated area (Fig. 2). This indicates that the San Juan, Taxco and Cacalotenango rivers are in a state of contamination due to the influence of the 13 metals evaluated, being Cd, Zn, Pb and Cu the most influential.
The ecological risk of metals in fluvial sediments of San Juan-Taxco river system were assessed through potential ecological risk indices (\({E}_{r}^{i}\) and RI) and summarized in Table 5. \({E}_{r}^{i}\) values for cadmium in all cases indicated low risk, while for As the values were between 35.6 and 101.1 indicating low ecological risk for M8, moderate for M4, M5 and M7 and appreciable for M2 and M3. The \({E}_{r}^{i}\) values for lead showed low ecological risk in samples M1, M2, M6 and M8, and moderate in samples M3, M4, M5 and M7. In the case of Cu, the values in almost all the samples showed a low ecological risk, but in the M4 a moderate and M8 appreciable ecological risk. In addition, the values of RI at all sites were > 600, which indicated very high ecological risk for the studied area.
Table 5
Potential ecological risk indices Er i and RI for studied metals in the San Juan-Taxco River basin
Sites
|
Er i
|
RI
|
Risk grade
|
As
|
Cd
|
Cr
|
Cu
|
Pb
|
M1-R. San Martín
|
|
700.0
|
0.109
|
37.32
|
10.47
|
747.90
|
very high
|
M2-R. San Juan
|
81.88
|
600.0
|
0.054
|
12.20
|
27.71
|
721.83
|
very high
|
M3-R. Cacalotenango
|
101.67
|
5400.0
|
|
14.00
|
77.94
|
5593.61
|
very high
|
M4-R. Pte Tecalpulco
|
53.13
|
16800.0
|
0.120
|
70.18
|
71.76
|
16995.19
|
very high
|
M5-R. Taxco Acolco
|
51.46
|
1833.3
|
|
7.46
|
47.06
|
1939.31
|
very high
|
M6-El Milagro
|
|
666.7
|
0.204
|
20.89
|
4.09
|
691.85
|
very high
|
M7-R. Campuzano
|
44.38
|
3133.3
|
|
9.98
|
55.59
|
3243.28
|
very high
|
M8-R. San Juan Metlapa
|
35.63
|
733.3
|
0.372
|
89.64
|
9.59
|
868.56
|
very high
|
Mean
|
61.35
|
3733.33
|
0.17
|
32.71
|
38.03
|
3850.19
|
|
Max
|
101.67
|
16800.00
|
0.37
|
89.64
|
77.94
|
16995.19
|
|
Min
|
35.63
|
600.00
|
0.05
|
7.46
|
4.09
|
691.85
|
|
In summary, the \({E}_{r}^{i}\)and RI indices for the studied elements in the surface sediment at all sites showed that San Juan, Cacalotenango and Taxco river pose any potential ecological risk with major contribution of As and Cd (Table 5 and Fig. 3). The results of heavy metal pollution in surface sediments of San Juan – Taxco river system indicated that the contamination is relatively high. There are serious impacts of heavy metal pollution, related to mining tailings, these have been washed down by the rain towards the rivers bed in the areas near these deposits, non-point source release that carries toxic elements (with heavy metals content as phosphate fertilizers, insecticides and fungicides, etc.), municipal wastewater and discharge with wastes from workshops of metal processing for handicraft and jewelry. The major steps in the manufacturing process of handicrafts and handmade jewelry include refining and alloying with other metals, smelting process and framing the metals, soldering, palatinate, polished, or etched of the piece. Each task is generally accomplished by the use of some substances and actives of heavy metals as Cd, Zn, Ni. For example, Cadmium (Cd) traditionally has been used in jewelry solders or galvanized with zinc is used too (Clausell, 2010). Among all metals, contamination by Cd is the highest followed in order of importance by Zn, Pb, Cu and As.
4.5. Worldwide comparison of heavy metal concentration
The concentrations of heavy metals of San Juan-Taxco river system were compared with other major polluted rivers in Mexico and worldwide and summarized in the Table 6. The comparison of the heavy metals concentrations with other Mexican rivers showed that, this system presents higher concentrations of As, Cd, Ni, Fe, Cu and Zn than those reported in the Atoyac river; Cd, Cu, and Zn higher than those reported in the Panuco River and exceeds the concentrations of As, Fe, cu, Ni, Zn measured in the Coatzacoalcos River.
A worldwide comparison of metal concentrations in fluvial sediments of San Juan-Taxco River system with those from other river environments showed higher concentrations, the comparison with Zarrin-Gol River in Iran in As, Ni, Zn and Fe, the sediment concentrations of Cd, Cu, Ni, Pb and Zn in the present study exceed those reported in the Yantze, Yellow, Ganga and Euphrates rivers.
Table 6
Comparison of metal concentrations with other riverine environments worldwide
|
As
|
Cd
|
Cr
|
Cu
|
Ni
|
Pb
|
Zn
|
Fe
|
|
Metal concentrations (mg kg− 1)
|
Present study
|
17.1–48.8
|
1.8–50.4
|
2.5–17.1
|
4.3–502
|
15.4–111
|
2.5–13.9
|
45.09–142
|
15,366 − 23,223
|
Studies in Mexico
|
|
|
|
|
|
|
|
|
Atoyac River (Morales et al., 2017)
|
0.16
|
2.58
|
24.5
|
10.2
|
14.4
|
27.1
|
31.5
|
19,180
|
Panúco River (Jonathan, et al., 2013)
|
-
|
1.79–1.89
|
17.03–21.69
|
22.58–34.13
|
-
|
39.01–51.35
|
74.78-122.45
|
11,331 − 14,575
|
Coatzacoalcos River (Ruiz-Fernández et al., 2012)
|
5–10
|
-
|
29–92
|
15–30
|
18–35
|
11–30
|
64–109
|
-
|
World wide studies
|
|
|
|
|
|
|
|
|
Yangtze River (Wang, 2015)
|
9.1
|
0.19
|
79.1
|
24.7
|
31.9
|
23.8
|
82.9
|
-
|
Yellow River (Ma et al,.2015)
|
-
|
0.1–0.3
|
61.3-139.5
|
14.1–30.3
|
19.3–34.6
|
15.5–24.6
|
39.9–74.6
|
-
|
Tinto River (García et al., 2012)
|
1130
|
2.75
|
56
|
805
|
17
|
2230
|
901
|
11,500
|
Tigris River (Varol and Sen, 2012)
|
|
7.9
|
-
|
2860
|
|
66
|
1061
|
-
|
Ganga River (Pandey and Singh, 2017)
|
-
|
1.7
|
69.9
|
29.8
|
372
|
26.7
|
67.8
|
31,988.6
|
Euphrates River (Salah et al. 2012)
|
-
|
1.9
|
58.9
|
18.9
|
67.1
|
22.6
|
48
|
2,249.5
|
Zarrin-Gol River (Mavandi et al., 2017)
|
21.91
|
-
|
37.67
|
-
|
12.39
|
-
|
32.68
|
13,751
|
Concentration of Fe were found higher than the values in Tinto River and Euphrates Rivers (Table 6). The Fe abundance in these sediments has been attributed: weathering, erosion and other natural sources, large-scale human activities (mining release, municipal solid waste and agricultural activities). Cadmium values are considerably high, compared to the other rivers of Mexico and the world as presented in Table 6; the results shown concentrations in all study sites above of the background values and these vales is associated with wastes from: mining and handicrafts and jewelry industry, urban and agricultural runoff. Concentration of Pb in this study was found lower than the reported in Atoyac, Panuco, Coatzacalcos, Yangtze, Yellow, Tinto, Ganga and Euphrates Rivers. This metal is mainly associated with Fe oxide fraction and shows high retention in sediments. Pb and Zn concentrations is attributed that tailings are being washed down by the action of rain towards the riverbed. Zn is one of the most abundant elements in the sediment of San Juan-Taxco system (Table 6). Those values are higer than the values reported in Atoyac, Panuco, Coatzacalcos,Yangtze, Yellow, Ganga, Euphrates and Zarrin Rivers (Wang et al. 2015; Ma et al., 2015; Pandey and Singh, 2017; Salah et al., 2012).
The rivers in the mining region of Taxco constantly receive trace amount of heavy metals from terrigenous sources weathering of rocks. Continuous or intermittent but relatively higher input of heavy metals to rivers and streams is linked to anthropogenic sources (Armieta et al., 2004; Dotor et al., 2017). The comparison study reveals that globally the average metal concentrations in San Juan-Taxco River system are similar compared to other polluted riverine environments as summarizes in Table 6.
4.6. Cluster analysis
The cluster analysis was performed to identify the relationship between the heavy metals in sediment samples (Fig. 4). The first of the cluster group includes Al and Fe (cluster 1), As, B, Cd, Co, Ni, Ba, Pb, Cu, Mn and Zn take part of cluster 2. The dendrogram indicates that the first group originates from the minerals present in the study area and group 2 is mainly associated with anthropogenic activities.