3.1 Concentration characteristics of TEs in park dust
Concentration characteristics of 9 TEs in park dust were exhibited in Table 1. The average concentrations of Cu, Zn, Cd, Sb and Pb were higher than their corresponding background values of Hubei Province (CNEMC, 1990), with 1.54, 2.20, 2.24, 1.07 and 1.71 times of background values, respectively. The concentrations of Cr, Mn, Ni and As were lower than their background values of Hubei Province. These demonstrated that Cu, Zn, Cd, Sb and Pb had accumulated to different degrees. Furthermore, the coefficient of variation values of 9 TEs were between 0.38–1.28, among which Cd (1.11) and Cu (1.28) showed a high artificial influence. Compared with the risk screening values of level II criterion of the Chinese Environmental Quality Standard for Soils (CEPA, 1995), the mean concentration of dust Cd was 0.38 mg·kg− 1, which was higher than the risk screening value, and the others were all lower than their risk screening values. Compared with the Soil Environmental Quality Risk Control Standard for Soil Contamination of Development Land (MEE, 2018), the average concentrations of all TEs were lower than their risk control values.
Table 1
Statistical characteristic of TEs in urban park dust
Element | Cr | Mn | Ni | Cu | Zn | As | Cd | Sb | Pb |
Minimum (mg·kg− 1) | 1.63 | 21.68 | 0.75 | 1.01 | 4.07 | 0.76 | 0.10 | 0.04 | 0.87 |
Mean (mg·kg− 1) | 72.01 | 682.12 | 28.18 | 47.37 | 184.20 | 10.26 | 0.38 | 1.77 | 45.78 |
Maximum (mg·kg− 1) | 173.71 | 1930.94 | 127.85 | 386.82 | 695.75 | 23.00 | 1.72 | 4.22 | 127.09 |
Standard deviation (mg·kg− 1) | 33.92 | 308.52 | 18.57 | 60.74 | 124.23 | 3.89 | 0.42 | 0.84 | 28.02 |
Coefficient of Variation | 0.47 | 0.45 | 0.66 | 1.28 | 0.67 | 0.38 | 1.11 | 0.47 | 0.61 |
Background value a (mg·kg− 1) | 86 | 712 | 37.3 | 30.7 | 83.6 | 12.3 | 0.17 | 1.65 | 26.7 |
Risk screening value b (mg·kg− 1) | - | - | 150 | 2000 | - | 20 | 20 | - | 400 |
Grade II c (mg·kg− 1) | 150 | - | 40 | 50 | 200 | 40 | 0.30 | - | 250 |
a CNEMC (China National Environmental Monitoring Centre), 1990. Soil Elements Background Values in China. China Environmental Science Press (in Chinese). |
b Soil environmental quality standard, Ministry of Ecology and Environment of the People’s Republic of China (MEE), 2018. Soil environmental quality Risk control standard for soil contamination of development land (GB36600-2018) [R]. MEE, Beijing (in Chinese). |
c Chinese Environmental Protection Administration (CEPA), 1995. Environmental Quality Standard for Soils (GB15618-1995) (in Chinese). |
3.2 Contamination assessment of TEs
EF, CF and PLI were calculated in this research to ulteriorly evaluate contamination status of TEs in park dust, the results were revealed in Fig. 2. The mean EF values of TEs were in the order of Zn (2.23) > Cd (2.10) > Pb (1.83) > Cu (1.47) > Sb (1.14) > As (0.95) > Ni (0.79) > Cr (0.21). Zn and Cd were moderate enrichment, Pb, Cu and Sb were slight enrichment, and As, Ni and Cr had no obvious enrichment. From the perspective of the proportion of different enrichment levels (Table S4), the EF values of the sampling points of Ni (7.5%), Cu (70%), Zn (95%), As (35%), Cd (65%), Sb (62.5%) and Pb (90%) were greater than 1, expressing that these TEs were more or less interfered by human factors. Particularly, 2.5% of Cu samples, 7.5% of Cd samples and 2.5% of Pb samples were significant enrichment, and the significant enrichment areas were mainly concentrated in the central and northeastern parts of the study area, indicating that Cu, Cd and Pb from the park dust in these areas conspicuously affected by anthropogenic activities.
As manifested in Fig. 2b, the mean CF values of Cu, Zn, Cd, Sb and Pb were 1.54, 2.20, 2.32, 1.07 and 1.71, respectively. The samples with CF values of Cu, Zn, Cd, Sb and Pb exceeding 1 showed higher percentages, which were 47.5%, 90.0%, 57.5%, 47.5% and 77.5%, respectively (Table S4). These pointed that Cu, Zn, Cd, Sb and Pb were catholically contaminated in the study field, especially Cd pollution was the most serious. On account of the CF, the PLI were computed to synthetically appraise the contamination conditions of park dust TEs in research area. The range PLI was 0.05–3.36, and the mean was 1.18 (Fig. 2b), indicating that the research region was moderately contaminated. The ratio of non-pollution, moderate pollution and severe pollution in the study area were 50.0%, 35.0% and 15.0%, respectively, and there was no heavy pollution spot. Consequently, the study area was mainly exposed to moderate contamination, and Cd contamination was the worst.
3.3 Effect of dust particle size on TE consistence
Particle size distribution is an important factor affecting the TE concentration of dust. Table 2 exhibited the effect of dust particle size on TEs concentrations. The concentrations of Cr, Cu, Zn and Pb increased with the decreased of dust particle size, which was concordant with the conclusion that the smaller the dust particle size, the stronger the adsorption capacity, and the higher the TE concentration (Bian and Zhu, 2009; Acosta et al., 2011). Nevertheless, in different particle sizes, the average contents of Mn, Ni and Sb were shown as 150µm > 75µm > 250µm. And the mean content of Cd was 150µm > 250µm > 75µm. The content of As was greatest in dust of 250µm, followed by 150µm and then 75µm. Perhaps this related to diverse elements such as the accumulation of fine-grained substances by iron-containing oxides and TEs emitted by mortal activities. Previous studies can also sustain this result, there was no distinct discrimination of Sb content in different particle sizes (Wang et al., 2006) and Cd had the highest content in coarse particle size dust (Acosta et al., 2011).
Table 2
Statistical description of TEs contents of dust with different particle sizes in the study area (mg·kg− 1)
Element | Cr | Mn | Ni | Cu | Zn | As | Cd | Sb | Pb |
75µm |
Minimum | 1.63 | 21.68 | 0.75 | 1.01 | 4.07 | 0.76 | 0.03 | 0.04 | 0.87 |
Mean | 72.01 | 682.12 | 28.18 | 47.37 | 184.20 | 10.26 | 0.40 | 1.77 | 45.78 |
Maximum | 173.71 | 1930.94 | 127.85 | 386.82 | 695.75 | 23.00 | 1.72 | 4.22 | 127.09 |
Standard deviation | 33.49 | 304.52 | 18.33 | 59.97 | 122.66 | 3.85 | 0.40 | 0.83 | 27.67 |
Coefficient of Variation | 0.47 | 0.45 | 0.65 | 1.27 | 0.67 | 0.37 | 1.02 | 0.47 | 0.60 |
150µm |
Minimum | 36.41 | 347.40 | 14.31 | 14.73 | 71.47 | 3.57 | 0.02 | 0.79 | 21.65 |
Mean | 69.65 | 713.30 | 28.61 | 39.94 | 167.69 | 10.38 | 0.51 | 1.88 | 44.35 |
Maximum | 145.87 | 1273.81 | 74.48 | 177.52 | 359.46 | 20.69 | 5.47 | 6.04 | 104.74 |
Standard deviation | 21.68 | 200.20 | 10.29 | 27.11 | 79.48 | 4.18 | 0.86 | 1.07 | 21.27 |
Coefficient of Variation | 0.31 | 0.28 | 0.36 | 0.68 | 0.47 | 0.40 | 1.69 | 0.57 | 0.48 |
250µm |
Minimum | 32.19 | 289.78 | 14.02 | 13.19 | 56.62 | 5.08 | 0.02 | 0.53 | 13.97 |
Mean | 61.45 | 639.22 | 27.95 | 32.82 | 151.53 | 11.28 | 0.43 | 1.66 | 39.03 |
Maximum | 108.57 | 986.37 | 51.32 | 70.74 | 398.83 | 18.70 | 3.52 | 3.95 | 79.54 |
Standard deviation | 15.61 | 146.40 | 8.78 | 12.60 | 73.88 | 4.18 | 0.65 | 0.79 | 14.66 |
Coefficient of Variation | 0.25 | 0.23 | 0.31 | 0.38 | 0.49 | 0.37 | 1.52 | 0.47 | 0.38 |
3.4 Chemical speciation and bioactivity of TE
The chemical speciation of TE in dust determines the discrepancy in environmental geochemical activities of TE, and also affects the grade of bio-utilization of TE. In this research, the chemical speciations and migration conversions of Cr, Mn, Ni, Cu, Zn, Cd and Pb were investigated, and the chemical speciation comprised acid-soluble (F1), reducible (F2), oxidizable (F3) and residual (F4). The statistical results were revealed in Table S5. The average contents of Cr, Mn, Ni, Cu, Zn, Cd and Pb were ranked among the 4 chemical speciations, Cr: F4 > F3 > F1 > F2; Mn: F1 > F4 > F2 > F3; Ni: F4 > F3 > F1 > F2; Cu: F4 > F1 > F3 > F2; Zn: F1 > F4 > F3 > F2; Cd: F4 > F1 > F3 > F2 and Pb: F4 > F2 > F1 > F3. Combined with Fig. S1, it could be concluded that except Mn and Zn, the concentrations of Cr, Ni, Cu, Cd and Pb were most prominent in the residual state, accounting for 82.75%, 43.90%, 39.64%, 54.23% and 43.19%, respectively. The residue content of Cr accounted for the highest proportion, which might due to the fact that Cr is a lithophile element and is easy to form stable oxyacid anions, usually combined with silicon dioxide, iron oxide and magnesium oxide.
It is generally believed that the acid-soluble state of TEs is directly available to organisms, while the reducible and oxidizable states are potentially available to organisms. The higher the ratio of the three chemical speciations, the greater the bioavailability. The bioavailabilities of Cr, Mn, Ni, Cu, Zn, Cd and Pb were Zn (78.97%) > Mn (66.40%) > Cu (60.37%) > Pb (56.81%) > Ni (56.10%) > Cd (45.77%) > Cr (17.25%) in the study (Fig. S1).
3.5 Pearson correlation analysis
This research conducted correlation analysis of Cr, Mn, Ni, Cu, Zn, As, Cd, Sb and Pb to provide a scientific basis for TE source identification (Wang et al., 2019). All TEs data conformed to normal or approximately normal distribution, and Pearson correlation coefficient matrix of 9 TEs was manifested in Table S6. From Table S6, the correlation coefficients of Mn-Cr (r = 0.695), Ni-Cr (r = 0.669), As-Cu (r = 0.737), Zn-Pb (r = 0.675), Sb-Cu (r = 0.721), Sb-Cd (r = 0.793) and Cd-Cu (r = 0.686) were greater than 0.65, certifying that Mn, Cr and Ni; As and Cu; Zn and Pb; and Sb, Cu and Cd had a stronger correlation, and their sources were probably more similar. Previous researches have shown that Mn, Cr and Sb were generally derived from the parent material (Wen et al., 2020). As and Cu were mainly related to agricultural activities (Baltas et al., 2020; Wang et al., 2020). Traffic exhaust emissions and vehicle wears were deemed to be the main sources of Pb and Zn (Adimalla et al., 2020). And other studies which indicated that industrial activities would release a large amount of Sb, Cu and Cd (Soltani et al., 2015; Liang et al., 2017).
3.6 Source parsing of dust TEs
The PMF model was utilized to qualitatively identify the source of TE and quantify its contribution to the content of TE in park dust. The model was run 13 times, and the number of factors was determined according to the stable Q value produced during the running process, combined with the characteristics of TEs contents in dust, pollution evaluation and related analysis results, 3 factors were finally determined in this study (Fig. 3). the signal-to-noise ratios (S/N) of every TE was higher than 2, and the fitting coefficients (R2) were all greater than 0.75, which ensured the rationality of the model and the excellent fitting effect. The first factor was delimited by Cd (93.4%), Pb (59.5%), Zn (61.4%), Cu (54.6%) and Sb (41.8%), explicating 46.62% of three sources (Fig. 3a). The average EF values of Cd, Pb, Zn, Cu and Sb in park dust were > 1, indicating enrichment. In addition, in order to intuitively reveal the spatial distribution of TEs empoison from the park dust in the study area, Kriging interpolation was performed. Fig. S2 exhibited the consequence of kriging interpolation. The high values district of Cd, Pb, Zn, Cu and Sb were situated in the east of the research region, thus they may have the similar enrichment methods. The industrial distribution in the eastern part of the study area is relatively dense, with steel, metallurgy, petrochemical and other factories. Studies have donated that industrial activities would release TE particles such as Cd, Pb, Zn, Cu and Sb into the surrounding environment (Xiao et al., 2014; Sabouhi et al., 2016; Cui et al., 2020; Yang et al., 2020; Jiang et al., 2021; Wang et al., 2021). Cd is deemed to be a symbolic element of industrial activities. Substantial Cd was liberated into the surrounding environment in the form of the three wastes via electroplating, alloy processing, pigments, machinery manufacturing and other industrial machinery activities, ultimately polluted the surrounding environment (Guan et al., 2019). Sb is widely utilized in sundry industries, comprising colored glass processing, hardener in alloy production and flame retardant in textile and plastic production, etc (Vleeschouwer et al., 2014; Huang et al., 2021). Machinery manufacturing and ore smelting discharged Cu-containing pollutants into the environment (Cai et al., 2015). Moreover, the hot spots of Pb and Zn were concentrated along the periphery of traffic routes and densely traffic areas (Fig. S2). Zn is regularly applied as reinforcing agent and activator in the tire manufacturing industry, and corrosion and wear of automobile galvanized parts were also momentous sources of Zn (Cai et al., 2019a; Mohsen et al., 2021). As an identification element of transportation, Pb chiefly came from the emission of automobile exhaust. Besides, the wear of vehicle engines and brakes, and the use of lead-acid batteries were also the main reasons for the enrichment of Pb in the environment. In summary, factor 1 can be considered as mixed sources of industrial activities and transportation activities.
Factor 2 accounted for 25.56% of three sources, with Cr (45.7%), Mn (44.9%) and Ni (43.1%) as the main contributing elements (Fig. 3b). The concentrations of Cr, Mn and Ni were lower than their background values. Besides, the EF analysis results displayed that the average EF values of Cr and Ni were both < 1, indicating no enrichment. All of the above revealed that Cr, Mn and Ni were restricted by low human interference, and depend more on natural factors, such as soil parent materials, rock weathering and other factors. Scholars have analyzed the sources of these TEs and discovered that the sources of these TEs were mainly classified as natural sources. The study of Micó et al. (2006) showed that the concentrations of Cr, Mn and Ni were principally related to the parent rock factor, and corresponding the diagenetic components in the principal component analysis. Amaya et al. (2009) perceived that soil-forming factors were the main controlling factors for the concentration of Cr, Mn and Ni in NW Spain. The study of Xiao et al. (2014) on TEs in Guangzhou urban forest park showed that the Mn element in dust was mainly related to natural factor. Guo et al. (2020) analyzed the source of heavy metals in the park dust. And the results exhibited that Ni was related to the soil-forming parent material, and the P value of correlation analysis between Ni and Cr was < 0.01, which was related, thus both Cr and Ni were derived from natural source. In addition, Fig. S2 showed that the concentrations of Cr, Mn and Ni have high-value areas in the middle of the study area. The survey found that there are several aluminum manufacturing factories and metal processing factories near the parks in the high value area. The Cr, Mn and Ni released by the processing and manufacturing industries may enter the environment, resulting in a small-scale high-value area. Consequently, natural source was the major source of factor 2.
The factor 3, which accounted for 27.82% of three sources, exhibited great loading of As (71.7%) and Cu (39.86%) (Fig. 3c). EF results revealed that 35% of As samples and 70% of Cu samples were enriched in different degrees, which implied that dust As and Cu interfered by human activities. Meanwhile, the high-value areas of As and Cu were located around several large parks (Fig. S2), thus their sources possibly interrelated to certain activities in the park. Studies have shown that some chemicals containing As and Cu were often applied as raw materials in fungicides, pesticides and herbicides. Calcium arsenate and sodium arsenate were widely utilized as herbicides (Chen et al., 2005). Copper sulfate-ammonia complex and copper sulfate were often used in pesticides and fungicides (Cai et al., 2015). Simultaneously, the use of chemical fertilizers (phosphate fertilizers, etc) with high As concentration were also the reason for the high content of dust TEs in the research district (Cai et al., 2019b). In addition, these parks in this study have been established for a long time, some facilities have been aging, the corrosion of some alloy objects in the park and the peeling of wall coatings would release As and Cu into the environment. In conclusion, factor 3 was deemed to be a mixed source of agricultural activities and the aging of park infrastructures.
3.7 Potential ecological risk assessment of TE in park dust
Box plot and spatial distribution map of PER in park dust TEs were manifested in Fig. 4. The \({E}_{r}^{i}\) of TEs were Cd > > Pb > As > Cu > Sb > Ni > Zn > Cr > Mn. Among 9 TEs, the mean \({E}_{r}^{i}\)of Cd was the largest (73.9), reaching a relatively high ecological risk level. And the average \({E}_{r}^{i}\)of the others were all less than 30, which were only at a slight ecological risk (Table S7). Perhaps it was likely due to that the toxicity coefficient of Cd was greater than that of other TEs. The mean PER value of TEs in park dust was 114, according to the risk level, the entire research area belonged to the higher risk level. The contributions of the three sources of TEs to PER were factor 1 (75.75%) > factor 3 (16.79%) > factor 2 (7.46%). Notably, the PER value of factor 1 (mixed sources of industrial activities and transportation activities) was 86.6, which achieved higher ecological risk and was the largest contributor to the PER in the study area. From Fig. 4, it also revealed that the hot spots of PER in the research domain were mainly concentrated in developed industrial areas in the east of research region and traffic-intensive areas. In short, industrial and transportation activities were the priority sources of dust TEs in the parks of the research domain. Therefore, priority should be given to monitoring and management of intensive transportation activities and industrial activities such as steel processings, metallurgical industries and petrochemical industries and so on.
3.8 Quantify human health risks from different sources
In this study, the HHR model provided by the US EPA combined with the PMF model was applied to evaluate the health risks of 8 TEs (Cr, Mn, Cu, Zn, As, Cd, Pb and Ni) in park dust. The evaluation results were paraded in Table 3. As revealed in Table 3, the non-carcinogenic risk values of adults and children were 3.55E-01 and 5.65E-02, respectively. The non-carcinogenic risk values of adults and children were less than 1, indicating that TEs in park dust would not cause obvious non-carcinogenic risks to adults and children. Moreover, whether for adults or children, Cr was the biggest contributor to non-carcinogenic risk, followed by As > Pb > Mn > Ni > Cu > Cd > Zn. Fig. S3 showed that the high-value areas of non-carcinogenic risks for children and adults were mainly concentrated around several large parks in the study area. And the non-carcinogenic risks created by various sources were Factor 3 > Factor 1 > Factor 2. Source 3 accounts for 43.14% of the three sources and was the master source of TEs. Therefore, the daily management activities of the park (such as the use of fertilization, weeding and disinfection, etc.) require reasonable control. And as the main contributors to the non-carcinogenic risk of adults and children, As, Cr and Pb also need to attract attention.
Table 3
Non-cancer (total hazard index) and cancer risk (total cancer risk index) of TEs from three different sources
| Child | | | | Adult | | |
Factor 1 | Factor 2 | Factor 3 | Total | Factor 1 | Factor 2 | Factor 3 | Total |
| Hazard index of each TE and total hazard index |
Cr | 3.93E-02 | 5.86E-02 | 3.03E-02 | 1.28E-01 | 6.40E-03 | 9.54E-03 | 4.92E-03 | 2.09E-02 |
Mn | 9.08E-03 | 1.56E-02 | 1.01E-02 | 3.47E-02 | 2.18E-03 | 3.75E-03 | 2.42E-03 | 8.35E-03 |
Cu | 2.41E-03 | 1.03E-03 | 9.72E-04 | 4.42E-03 | 3.42E-04 | 1.47E-04 | 1.38E-04 | 6.27E-04 |
Zn | 1.43E-03 | 7.62E-04 | 1.35E-04 | 2.33E-03 | 2.04E-04 | 1.09E-04 | 1.93E-05 | 3.32E-04 |
As | 3.27E-02 | 3.16E-03 | 9.08E-02 | 1.27E-01 | 4.62E-03 | 4.46E-04 | 1.28E-02 | 1.79E-02 |
Cd | 2.49E-03 | 8.06E-07 | 1.77E-04 | 2.67E-03 | 4.27E-04 | 1.38E-07 | 3.03E-05 | 4.58E-04 |
Pb | 2.99E-02 | 8.50E-03 | 1.18E-02 | 5.03E-02 | 4.29E-03 | 1.22E-03 | 1.70E-03 | 7.21E-03 |
Ni | 1.39E-03 | 2.27E-03 | 1.61E-03 | 5.28E-03 | 1.97E-04 | 3.23E-04 | 2.29E-04 | 7.49E-04 |
total hazard index | 1.19E-01 | 9.00E-02 | 1.46E-01 | 3.55E-01 | 1.87E-02 | 1.55E-02 | 2.23E-02 | 5.65E-02 |
| Cancer risk of each TE and total cancer risk Index |
Cr | 4.73E-06 | 7.05E-06 | 3.64E-06 | 1.54E-05 | 3.27E-06 | 4.87E-06 | 2.51E-06 | 1.07E-05 |
As | 1.26E-06 | 1.21E-07 | 3.49E-06 | 4.87E-06 | 7.75E-07 | 7.49E-08 | 2.15E-06 | 3.00E-06 |
Cd | 7.36E-08 | 2.38E-11 | 5.21E-09 | 7.88E-08 | 5.20E-08 | 1.68E-11 | 3.68E-09 | 5.57E-08 |
Pb | 7.18E-08 | 2.04E-08 | 2.84E-08 | 1.21E-07 | 4.36E-08 | 1.24E-08 | 1.72E-08 | 7.32E-08 |
Ni | 1.93E-06 | 3.16E-06 | 2.25E-06 | 7.34E-06 | 1.17E-06 | 1.92E-06 | 1.36E-06 | 4.45E-06 |
total cancer risk index | 8.07E-06 | 1.04E-05 | 9.41E-06 | 2.78E-05 | 5.31E-06 | 6.88E-06 | 6.05E-06 | 1.82E-05 |
Regarding cancer risk, the values for adults (1.82×10− 5) and children (2.78×10− 5) were both between 10− 6 − 10− 4, which were within the carcinogenic risk range for the humanity, explaining that the carcinogenic risks of TEs from park dust in study area to adults and children were both within an acceptable range. The devotions of different TEs to carcinogenic risk from high to low were Cr > Ni > As > Pb > Cd, indicating that Cr were the cardinal cancer risk element. This is consistent with the results of the carcinogenic risk assessment of heavy metals in dust from Jiaozuo Park by Han et al. (2020). In addition, the devotion of different sources in carcinogenic risk were Factor 2 > Factor 3 > Factor 1. Factor 2 was the biggest contributor to carcinogenic risk. From Fig. S3, the carcinogenic risk had a small range of high-value areas in the dense distribution area of large parks, indicating that the daily activities of insecticide and pesticide spraying in the park were also important factors leading to carcinogenic risk. Exposed to the same environment, children were more sensitive to dust TEs than adults, and certain particular behaviors of children (for instance, hand-to-mouth and object-to-mouth) lead to a much higher risk of children being exposed to TE than adults.
The health risks of adults and children under different exposure routes were calculated, and the results were exhibited in Table S8. Contrasting the three exposure routes, it could be found that both the non-carcinogenic risk entropys and carcinogenic risk indexs of children and adults were all expressed as oral ingestion > dermal contact > respiratory inhalation. It authenticated that oral ingestion was the chief exposure pathway for non-carcinogenic and carcinogenic health risks. Previous studies have also reached the same conclusion that oral ingestion was the master pattern of human exposure to dust TE ( Shahab et al., 2018; Adewumi and Laniyan, 2020; Shah et al., 2020; Behnam et al., 2020).