3.1 Potentially Toxic Element concentrations in stagnant stormwater and the risk of adverse effects
Table 1 shows the statistics summary of the total PTEs, where Al, Fe, and Zn showed the highest maximum concentrations (52.4, 50 and 23.1 mg L− 1 respectively). The PTE determined concentrations by sampling point are in SI 2; Zinc in storm water can relate to sources as tire dust, motor oil, corrosion of roof, brake, facades and galvanized surfaces (Brown and Peake, 2006; McKenzie et al., 2009). Other authors have observed the correlation between Zn concentrations in urban runoff sediments from various cities around the world and the amount of fuels sold in those cities (Milik and Pasela, 2018); Al urban sources relate to corrosion of building materials, such as galvanized metal roofing and gutters (Ogburn et al., 2012); Cu, Pb, Mn, Cr and Ti showed the maximum concentrations from 1 to 4 mg L− 1 (1.1, 3.52, 1.37, 2.88 and 2.28 mg L− 1, respectively). Other PTEs showed maximum concentrations < 1 mg L− 1. The primary sources of Cu are vehicle brake wear, roofing materials, parking lots, treated lumber, building siding, and vehicle exhaust (WSDOE, 2017). Fuels and products of surface and rubbing type are often the source of Pb, which is associated with road traffic and its intensity (Milik and Pasela, 2018). The presence of manganese (Mn) could be related to the use of the methylcyclopentadienyl manganese tricarbonyl (MMT) gasoline additive, moving engine parts, as well as, brake and tire wear (Huber et al., 2016; Müller et al., 2020). Concrete pavement materials and synthetic play surfaces were reported to leach Cr, also vehicle wear contributes to Cr pollution (Müller et al., 2020). Titanium (Ti) main source in runoff is the wear of white road marking paint containing titanium dioxide as pigment (Huber et al., 2016)
The highest coefficient of variation (CV) were observed for Ni and Zn (CV > 1). Cd, Sb, Pb, Mn, Cr, Al and Tl showed a CV from 0.7 to 0.9, which shows the great variation of observed concentrations for these metals at different sampling points.
The PTE concentrations observed in runoff in other parts of the world by other authors is found in Table 1. The observed PTE mean concentrations of Zn, Cu, Pb, Cd and Ni were higher than the mean PTE concentrations observed by Nabizadeh et al.. (2005) in the city of Tehran, Iran. Zn concentrations were 11.9 times higher; Pb and Cu concentrations were 14 times higher than those observed in the present study. Similarly, the observed mean concentrations in Al, Fe, Zn, Cu, Pb, Mn and Cr were higher than those observed by Taka et al., (2022) in runoff from three locations in the city of Helsinki (Southern Finland) with different urban intensity (Table 1). When more urbanized (66%) Helsinki locations were compared, Al, Fe, Zn, Cu, Pb, Mn and Cr were 21, 14, 130, 10, 900, 24 and 200 times higher (respectively) than mean concentrations observed in the present study. Likewise, the observed mean concentrations in this study for Al, Fe, Zn, Cu, Pb, Mn, Cr, Ti, Cd, As, V, Ni and Co were 36, 21, 17, 10, 19, 34, 3.5, 3, 160, 96, 12.5, 5 and 25 times higher than those observed in Singapore urban runoff (Joshi and Balasubramanian, 2010). These results may be due to a concentration effect in stagnant water. Similarly, Tokatlı and Varol (2021) investigations revealed that studied ponds (in an agricultural region of Turkey) had higher total mean PTE concentration likely due to their low water volume.
The risk of adverse effects to aquatic life was assessed by comparing determined PTE concentrations with Mexican. Australian and US guidelines.
The concentrations observed in Al, Fe, Cu, Cr and As exceeded the Mexican Criteria for protection of aquatic life (CE-CCA-001/89); Al, Zn, Cu, Pb, Cd, Ag, As, Sb, V, Ni, Co, Tl and concentrations exceeded the Australian Guidelines for Fresh and Marine Water Quality (Australian Government, 2018). Likewise, Zn, Pb, Cd, and As concentrations surpassed the US National Recommended Water Quality Criteria - Aquatic Life Criteria (US-EPA, 2019).
Table 1
Summary statistics of the total potentially toxic elements (PTEs) (mg L-1) in stagnant stormwater from Hermosillo, Sonora, México and in runoff of other parts of the world, compared with guidelines values.
| This study | Tehran city1 | Helsinki (*36%)2 | Helsinki (*52%)2 | Helsinki (*66%)2 | Singapore3 | Mexican criteria4 | Australian guidelines5 | US-EPA6 |
| Stagnant rainwater | Runoff | Runoff | Runoff | Runoff | Runoff | Freshwater | Freshwater | Freshwater |
| Mean | Min | Max | SD | CV | Mean | Mean | Mean | Mean | Mean | Min | Max | | | |
Al | 17.67 | 4.21 | 52.49 | 13.2 | 0.7 | - | 0.542 | 1.128 | 0.814 | 0.49 | 0.14 | 0.79 | 0.05 | 0.055 | - |
Fe | 18.44 | 3.21 | 50.01 | 12.5 | 0.6 | - | 0.583 | 1.39 | 1.29 | 0.848 | 0.189 | 3.03 | 1 | - | - |
Zn | 7.54 | 0.24 | 23.18 | 7.7 | 1.02 | 0.63 | 0.018 | 0.047 | 0.058 | 0.43 | 0.08 | 0.96 | - | 0.008 | 0.12 |
Cu | 0.42 | 0.1 | 1.12 | 0.2 | 0.7 | 0.03 | 0.007 | 0.022 | 0.039 | 0.04 | 0.01 | 0.08 | 0.003 | 0.001 | - |
Pb | 0.96 | 0.04 | 3.52 | 0.8 | 0.9 | 0.07 | 0.004 | 0.004 | 0.001 | 0.05 | 0.005 | 0.205 | - | 0.0034 | 0.0025 |
Mn | 0.48 | 0.12 | 1.37 | 0.3 | 0.7 | - | 0.0123 | 0.0191 | 0.0205 | 0.014 | 0.004 | 0.041 | - | 1 | - |
Cr | 0.66 | 0.1 | 2.88 | 0.6 | 0.9 | - | 0.0014 | 0.0031 | 0.0033 | 0.185 | 0.042 | 0.269 | 0.01 | 1.9 | - |
Ti | 0.96 | 0.37 | 2.28 | 0.6 | 0.5 | - | - | - | - | 0.283 | 0.054 | 1.914 | - | - | - |
Cd | 0.16 | 0.01 | 0.47 | 0.12 | 0.7 | 0.04 | - | - | - | 0.001 | 0.0009 | 0.004 | - | 0.0002 | 0.00072 |
Ag | 0.05 | 0.01 | 0.15 | 0.03 | 0.6 | - | - | - | - | - | - | - | - | 0.00005 | - |
As | 0.58 | 0.06 | 0.97 | 0.2 | 0.4 | - | - | - | - | 0.006 | 0.00075 | 0.013 | 0.2 (As 3+) | 0.024 | 0.15 |
Sb | 0.1 | 0.01 | 0.3 | 0.07 | 0.7 | - | - | - | - | - | - | - | - | 0.009 | - |
V | 0.05 | 0.01 | 0.14 | 0.03 | 0.6 | - | - | - | - | 0.004 | 0.0005 | 0.019 | - | 0.006 | - |
Ba | 0.31 | 0.05 | 0.88 | 0.2 | 0.6 | - | - | - | - | - | - | - | - | - | - |
Ni | 0.04 | 0.01 | 0.29 | 0.05 | 1.17 | 0.03 | - | - | - | 0.008 | 0.003 | 0.013 | - | 0.011 | 0.052 |
Be | 0.01 | 0.01 | 0.02 | 0.004 | 0.3 | - | - | - | - | - | - | - | - | - | - |
Co | 0.01 | 0.01 | 0.03 | 0.007 | 0.4 | - | - | - | - | 0.0004 | 0.0002 | 0.002 | - | 0.001 | - |
Tl | 0.13 | 0.01 | 0.25 | 0.1 | 0.7 | - | - | - | - | - | - | - | - | 0.000003 | - |
Sn | 0.14 | 0.07 | 0.3 | 0.06 | 0.4 | - | - | - | - | - | - | - | - | - | - |
Se | 0.34 | 0.11 | 0.65 | 0.1 | 0.4 | - | - | - | - | - | - | - | - | 0.011 | - |
1 (Nabizadeh et al., 2005). 2 (Taka et al., 2022). 3 (Joshi and Balasubramanian, 2010). 4 Criteria for protection of aquatic life (CE-CCA-001/89). 5 95% species protection level (Australian Government, 2018). 6 Chronic exposure values (US-EPA, 2019). *percentage of the studied catchment imperviousness.
3.2 Associations among potentially toxic elements and sources
Spearman’s correlation coefficients of PTEs are in Fig. 2. The results showed that significant (p value < 0.01) very strong positive correlations (> 80) existed between Ag and Cu, Cr, Al; As and Cr; Mn and Al, V, Ti, Fe, Ba; Al and V, Ti, Fe, Ba; V and Ti, Fe, Ba; Ti and Fe, Ba; Fe and Ba showing that these PTEs possibly have similar origins.
Significantly (p value < 0.01) strong positive correlations (between 60 and 79) were obtained between Se and Sb, Co; Cd and Ag, Cu; Ag and As, Mn, Ti, Fe, V, Ba; Cu and Cr, Al, Mn, Ti, Fe; Sb and Pb; As and Ag indicating that these elements have similar environmental behaviors or sources.
On the other hand, Sn exhibited moderate positive significant correlation with Cu (54. p value < 0.01). As (53, p value < 0.01) and Cr (46, p value < 0.05). Zn showed moderate positive significant correlation with Pb (48, p value < 0.01) and Se (41, p value < 0.05). Ni presented a positive significant (p value < 0.01) and moderated correlation with Sb (59).
Tl presented a weak positive significant (p value < 0.05) correlation with Zn (37) and Pb (39). Finally, Be was significantly, positively and weakly correlated with Sb (46); Co displayed a significant (p value < 0.05) positive and weak correlation with Zn (38) and Pb (41).
Thus, in agreement with the HA cluster (Fig. 2), five groups of PTEs were identified possibly relating their sources and origin: (1) Ti, Al, Mn, Fe, V and Ba, 2) Cr, Sn and Sn, 3) Cu, Ag and Cd, 4) Pb, Zn, Tl, Ni, 5) Co, Se, Sb, Be. The PTEs integrating group 1 showed the highest correlation coefficients (> 90).
Correlation and the hazard quotient (HA) analysis observations were confirmed by the PCA results. Figure 3 shows the performed PCA; 63.35% of the total variability was explained by the two principal components, the majority by PC1 (45.7%). According to the observed positive correlations, four groups of PTEs were identified. The first formed by Mn, Al, V, Ti, Fe and Ba; the second by Cu, Ag and Cd; the third by Cr, As and Sn; the fourth formed by the two subgroups: (a) Pb, Zn, Tl, Ni and (b) Co, Se, Sb, Be. Group 2 has some correlation with group 1 and 3. This group conformation could be related to its origin.
The PCA conducted also allowed identifying 4 groups of samples (Fig. 3) sharing similar PTE concentrations. The first one was composed by samples 21, 22, 23, 24, 27; the second one by samples 16, 17, 18, 19, 20, 25, 26, 28, 29, 30; the third one by samples 5 to 7, and the fourth one by samples 1, 2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 15, suggesting different PTE sources. Groups 1 and 2 appears to be more related, as well as, groups 3 and 4. Groups 1 and 2 were correlated to Sn, As, Cr, Ag, Cr and Cd. While groups 3 and 4 were more correlated to Co, Sb, Se, Be, Ni, Zn, Pb and Tl. Based on the sample location, these observations probably indicate that the main sources of Sn, As, Cr, Ag, Cr and Cd are located from the center to the northwest, whereas the main sources of Co, Sb, Se, Be, Ni, Zn, Pb and Tl are located from the center to the southeast of the sampling site (see Figs. 1 and 2).
Selenium is mainly present in samples from group 1 (except for 5, 6, 7, and 15); Co is present in most of the samples from group 1 (except for 5, 7, and 14) while it is only present in three samples from group 2. This group showed the highest concentrations of Pb (> 1 mg L− 1) except for sample point 16 (0.4 mg L− 1). Similarly, Sb globally showed the highest concentrations in group 1 (from 0.06 to 0.19 mg L− 1) except for sampling points 7 and 16. Tl is only present in four samples from group 1; Cr is present in higher concentrations in group 2 (> 0.89 mg L− 1) except for sample 16 from group 1 (1 mg L− 1); As is present in all the samples from group 2. Be and Ni concentrations do not show a wide variation among all the samples. Likewise. Zn is present in all the samples at similar concentrations, nevertheless those with higher concentrations belong to group 1 (samples 7 to 11; 12.6 to 23 mg L− 1). Ag, Cu, Al, Mn and V also show similar concentrations among both groups but samples with higher concentrations belong to group 2 (For Ag: samples 21 to 24 at concentrations from 0.11 to 0.15 mg L− 1. For Cu: samples 20 and 21 at 1.1 mg L− 1. For Al: samples 21 to 24 and 27 at 31 to 52 mg L− 1. For Mn: samples 22 to 24 and 27 at > 1 mg L− 1. For V: samples 22 to 24 and 27 at 0.1–1.14 mg L− 1). Finally, Cd, Ba, Fe, Ti and Sn do not show a clear pattern between these groups of samples.
3.3 Health risk assessment
The health risk assessment was performed supposing dermal contact with stagnant stormwater based on measured total PTE concentrations. Non-carcinogenic health risk for Sn was not evaluated because a RfDdermal value for that element was not available. Calculated dermal absorbed doses for adults and children are in SI 5 and 6, respectively.
For adults the HQ remained < 1 for inspected PTEs, except for Cd and Sb (see SI 7). Cd HQs > 1 varied from 1.8 to 7.7. Sb HQ > 1 were between 1 and 2. For children Se, Cd, As, Sb, and Tl showed HQ > 1 (see SI 8). Se HQs > 1 varied between 1.2 and 2.2. Cd HQs > 1 were from 1.6 to 19. As HQ > 1 ranged from 1 to 1.6. Sb HQs > 1 go from 1 to 7.9. Tl showed HQs > 1 only at two sampling points.
The hazard index (HI) allowed us to understand the health risk from chemical mixtures. Table 3 shows the calculated HI for adults and children. Table 2 shows that calculated HI for adults are > 1 for 90% of the samples and 100% for children, which indicates that if adults or children enter in contact with stagnant stormwater in Hermosillo adverse non-carcinogenic health effects can potentially occur.
Table 3
Hazard Index (HI) for adults and children by sampling point.
Sampling point | HI | HI |
Adults | children |
1 | 1.89 | 4.84 |
2 | 8.28 | 21.26 |
3 | 6.77 | 17.39 |
4 | 2.38 | 6.12 |
5 | 0.98 | 2.52 |
6 | 3.18 | 8.17 |
7 | 5.79 | 14.86 |
8 | 4.72 | 12.10 |
9 | 5.06 | 12.98 |
10 | 3.99 | 10.25 |
11 | 3.45 | 8.87 |
12 | 3.41 | 8.75 |
13 | 2.94 | 7.53 |
14 | 2.91 | 7.47 |
15 | 3.02 | 7.74 |
16 | 1.09 | 2.79 |
17 | 6.08 | 15.60 |
18 | 1.61 | 4.13 |
19 | 0.63 | 1.61 |
20 | 0.56 | 1.45 |
21 | 7.22 | 18.52 |
22 | 8.54 | 21.91 |
23 | 4.48 | 11.50 |
24 | 3.68 | 9.45 |
25 | 3.03 | 7.78 |
26 | 3.44 | 8.83 |
27 | 2.43 | 6.24 |
28 | 2.72 | 6.99 |
29 | 3.53 | 9.07 |
30 | 3.89 | 9.97 |
The dermal carcinogenic risks were determined for Pb, Cr, Cd, As, Ni, and Be due to the availability of a SFo. The calculation of incremental lifetime cancer risks (ILCRs) indicates a potential cancer risk from lifetime exposure to Cr, Cd, As, Ni, and Be (Table 4) by dermal contact with stagnant stormwater in Hermosillo; Cd showed higher HQ, HI, and ILCR. The epidemiological data suggest that Cd exposure may be related to various types of cancer (breast, lung, prostate, nasopharynx, pancreas, and kidney), as well as environmental Cd, which is a risk factor for osteoporosis (Genchi et al., 2020); Sb also showed HQ > 1 for children and adults; antimony can cause adverse effects on human health. with particular impacts on skin, eyes, gastrointestinal tract, and respiratory system (Jiang et al., 2021). Se and As also threaten children’s health (HQ > 1). High contents of Se can result in disorders, such as, nail brittleness, hair loss, gastrointestinal dysfunctions, skin rash, “garlic-breath” smell and neurological disorder (Ullah et al., 2018); As has been associated with gastroenteritis, neurological manifestations, vascular changes, diabetes, and cancers (bladder, lung, liver, kidney, and prostate) (Abernathy et al., 2003). The results in the present study indicate that risk management measures should be taken.
Table 4
Incremental Lifetime Cancer Risk (ILCR) by sampling point.
Sampling | Pb | Cr | Cd | As | Ni | Be |
point |
1 | 4.30E-07 | 1.65E-04 | * | * | 2.41E-05 | 2.03E-04 |
2 | 1.31E-06 | 2.60E-04 | 1.12E-02 | * | 2.81E-05 | 2.03E-04 |
3 | 7.94E-07 | 4.14E-04 | 5.77E-03 | 2.07E-05 | 1.17E-04 | 2.03E-04 |
4 | 4.04E-07 | 2.95E-04 | 5.77E-04 | * | 4.82E-05 | 2.03E-04 |
5 | 4.45E-07 | 1.42E-04 | * | 3.63E-05 | 4.02E-06 | 2.03E-04 |
6 | 6.86E-07 | 1.77E-04 | 3.17E-03 | 1.04E-05 | 4.02E-06 | 2.03E-04 |
7 | 8.27E-07 | 2.01E-04 | 7.78E-03 | 5.36E-05 | 8.03E-06 | 2.03E-04 |
8 | 6.49E-07 | 1.42E-04 | 4.90E-03 | 1.38E-05 | 1.21E-05 | 4.06E-04 |
9 | 6.08E-07 | 1.30E-04 | 5.77E-03 | * | 1.61E-05 | 4.06E-04 |
10 | 5.97E-07 | 1.65E-04 | 3.75E-03 | * | 1.21E-05 | 2.03E-04 |
11 | 5.94E-07 | 1.30E-04 | 1.73E-03 | * | 1.61E-05 | 4.06E-04 |
12 | 5.16E-07 | 1.42E-04 | 1.15E-03 | * | 1.61E-05 | 4.06E-04 |
13 | 4.67E-07 | 1.18E-04 | * | * | 1.61E-05 | 4.06E-04 |
14 | 4.12E-07 | 1.42E-04 | 2.88E-04 | * | 8.03E-06 | 4.06E-04 |
15 | 4.45E-07 | 1.18E-04 | 1.44E-03 | * | 1.21E-05 | 4.06E-04 |
16 | 1.63E-07 | 1.23E-03 | * | 1.35E-04 | 1.61E-05 | 4.06E-04 |
17 | 3.71E-08 | 1.08E-03 | 8.65E-03 | 1.02E-04 | 2.81E-05 | 2.03E-04 |
18 | 5.57E-08 | 1.05E-03 | 1.15E-03 | 1.16E-04 | 2.01E-05 | 2.03E-04 |
19 | 1.48E-08 | 1.05E-03 | * | 1.09E-04 | 1.21E-05 | 2.03E-04 |
20 | 2.60E-08 | 1.05E-03 | * | 1.11E-04 | 8.03E-06 | 4.06E-04 |
21 | 2.04E-07 | 3.40E-03 | 1.12E-02 | 1.49E-04 | 1.21E-05 | 2.03E-04 |
22 | 1.45E-07 | 2.10E-03 | 1.36E-02 | 1.44E-04 | 1.21E-05 | 2.03E-04 |
23 | 8.16E-08 | 1.48E-03 | 6.34E-03 | 1.61E-04 | 4.02E-06 | 2.03E-04 |
24 | 9.28E-08 | 1.48E-03 | 4.90E-03 | 1.68E-04 | 4.02E-06 | 2.03E-04 |
25 | * | 1.05E-03 | 4.32E-03 | 1.16E-04 | 8.03E-06 | 2.03E-04 |
26 | 6.68E-08 | 1.23E-03 | 4.61E-03 | 1.19E-04 | 1.21E-05 | 2.03E-04 |
27 | 9.28E-08 | 1.21E-03 | 3.17E-03 | 1.21E-04 | 1.61E-05 | * |
28 | 6.68E-08 | 1.13E-03 | 3.17E-03 | 1.16E-04 | 1.61E-05 | * |
29 | 6.68E-08 | 1.09E-03 | 4.90E-03 | 9.51E-05 | 1.21E-05 | * |
30 | 4.45E-08 | 1.09E-03 | 5.77E-03 | 1.31E-04 | 8.03E-06 | * |
* determined concentrations in water were under detection limits