3.1 Geological factors linked to health
The result of the measurement shows that the radiation dose rate of the whole area is <0.20 mSV/a, thus the radioactivity index is Grade 1. The landform of the study area is terraced (Jiang et al., 2002). The study area is generally 800-1500 m above sea level, with higher and lower terrain in the south and north, respectively, and mountains, hills, and plains accounted for 11.5, 63.1 and 25.4% of the country's total area, respectively (Nie et al., 2021). Finally, the three secondary indicators of geological landforms were calculated according to the weights based on the spatial overlay of ArcGIS, and the results are shown in Fig. 2. Notably, in the geological and geomorphological evaluation results of the study area, the first-grade range is mainly distributed in the central and northern parts, the second-grade accounts for the most part, and the third-grade accounts for only a tiny fraction of the southern part because the terrain exceeds 1000 m.
3.2 Water resources and climate factors linked to health
According to the population survey and the literature, the comfort level of climatic conditions in the study area is in the secondary range (Ren et al., 2022), and the number of days with an air quality index >100 is 111 days (Li et al., 2017), which is also in the secondary range. This secondary indicator considers the average value across the region. Therefore, the climatic condition score of the primary indicator in the study area is calculated as: 90(0.6*90+0.4*90).
The study area, Anji, is in the Taihu Lake plain (Chen et al., 2020), where water resources are more abundantly distributed. According to the zoning results presented in Table S1, the study area belongs to Zone 5, but the total amount of water resources is abundant and the per capita possession is minor in China. Therefore, in addition to evaluating the per capita water resources, the per capita water resources in the study area were evaluated to be 1000-3000 m3 (Zhou et al., 2018).
The surface water was sampled and analyzed in the area, and the evaluation standard adopted the national standard (Chinese EPA, 2002). Statistics show that (Table 2、Table 3): Cd, Hg, Cu, Se, Zn, and fluoride meet the national “Nature Reserve and Source Water Standards” (Class I). Cr, Pb, ammonia nitrogen, and phosphate in some areas reached the “centralized living drinking water surface water source level 1 standard” (Class II). The surface water quality in the region is excellent; water belonging to classes Ⅰ and Ⅱ can be used as a direct source of drinking water and industrial and agricultural production. The shallow groundwater environment in the area was sampled and analyzed, and the national groundwater quality standards (Chinese AQSIQ, 2017) were used for evaluation. Therefore, comprehensive analysis indicated that the secondary index water quality score is 100. The content of water quality indicators is complex; combined with the remaining secondary indicators, the comprehensive evaluation indicated that the score of the entire region of primary water resource indicators was 99(0.1*100+0.1*90+0.8*100).
Table 2 Surface water quality assessment
Surface
water
|
Sampling sites
|
pH
|
Phosphate
(mg/L)
|
Ammonia
Nitrogen
(mg/L)
|
Fluoride
(mg/L)
|
Zn
(mg/L)
|
Cu
(mg/L)
|
Cd
(mg/L)
|
Pb
(mg/L)
|
Hg
(mg/L)
|
Se
(mg/L)
|
Cr6+
(mg/L)
|
1
|
7.9
|
0.16
|
<0.03
|
0.15
|
<0.01
|
<0.005
|
<0.001
|
<0.001
|
<0.0001
|
<0.004
|
<0.01
|
2
|
7.4
|
<0.10
|
0.19
|
0.14
|
0.02
|
<0.005
|
<0.001
|
0.001
|
<0.0001
|
<0.004
|
<0.01
|
3
|
8
|
<0.10
|
0.05
|
0.06
|
<0.01
|
<0.005
|
<0.001
|
0.002
|
<0.0001
|
<0.004
|
<0.01
|
4
|
8.2
|
0.15
|
0.05
|
0.18
|
0.01
|
<0.005
|
<0.001
|
<0.001
|
<0.0001
|
<0.004
|
<0.01
|
5
|
8.1
|
0.12
|
0.05
|
0.18
|
<0.01
|
<0.005
|
<0.001
|
<0.001
|
<0.0001
|
<0.004
|
<0.01
|
6
|
6.4
|
<0.10
|
<0.03
|
<0.05
|
0.04
|
<0.005
|
<0.001
|
0.001
|
<0.0001
|
<0.004
|
<0.01
|
7
|
6.4
|
<0.10
|
<0.03
|
<0.05
|
0.04
|
<0.005
|
<0.001
|
0.001
|
<0.0001
|
<0.004
|
<0.01
|
GB3838 (Chinese EPA, 2002)
|
Class I
|
6~9
|
≤0.02
|
≤0.15
|
≤1.0
|
≤0.05
|
≤0.01
|
≤0.001
|
≤0.001
|
≤0.00005
|
≤0.01
|
≤0.01
|
Class Ⅱ
|
≤0.1
|
≤0.5
|
≤1.0
|
≤1.0
|
≤1
|
≤0.005
|
≤0.005
|
≤0.00005
|
≤0.01
|
≤0.05
|
Class Ⅲ
|
≤0.2
|
≤1.0
|
≤1.0
|
≤1.0
|
≤1
|
≤0.005
|
≤0.005
|
≤0.0001
|
≤0.01
|
≤0.05
|
Class Ⅳ
|
≤0.3
|
≤1.5
|
≤1.5
|
≤2.0
|
≤1
|
≤0.005
|
≤0.005
|
≤0.001
|
≤0.02
|
≤0.05
|
Class Ⅴ
|
≤0.4
|
≤2
|
≤1.5
|
≤2.0
|
≤1
|
≤0.01
|
≤0.01
|
≤0.001
|
≤0.02
|
≤0.1
|
Table 3 Shallow groundwater quality test results
Shallow groundwater
|
Sampling
sites
|
pH
|
NO2-
(mg/L)
|
SO42-
(mg/L)
|
NH4+
(mg/L)
|
Fe
(mg/L)
|
Zn
(mg/L)
|
Mn
(mg/L)
|
Cr
(mg/L)
|
Cd
(mg/L)
|
Pb
(mg/L)
|
1
|
9.2
|
0.154
|
25
|
0.3
|
4.91
|
0.6
|
0.06
|
<0.005
|
<0.001
|
0.003
|
2
|
6.9
|
<0.004
|
21.4
|
<0.04
|
0.03
|
<0.01
|
<0.01
|
<0.005
|
<0.001
|
<0.001
|
3
|
7
|
<0.004
|
32.3
|
<0.04
|
0.08
|
<0.01
|
0.03
|
<0.005
|
<0.001
|
<0.001
|
4
|
6.8
|
<0.004
|
30.6
|
<0.04
|
0.04
|
<0.01
|
0.02
|
<0.005
|
<0.001
|
0.002
|
5
|
7.3
|
0.132
|
25.3
|
0.26
|
0.22
|
0.28
|
0.1
|
<0.005
|
<0.001
|
0.005
|
6
|
7.3
|
<0.004
|
22.6
|
0.1
|
2.51
|
0.03
|
0.09
|
0.008
|
<0.001
|
0.004
|
7
|
6.5
|
0.006
|
12
|
<0.04
|
0.28
|
0.06
|
0.02
|
<0.005
|
<0.001
|
<0.001
|
8
|
6.5
|
<0.004
|
17.1
|
0.12
|
0.45
|
0.01
|
0.04
|
<0.005
|
<0.001
|
0.005
|
9
|
7.6
|
0.118
|
29.7
|
0.12
|
0.13
|
0.01
|
<0.01
|
0.005
|
<0.001
|
<0.001
|
10
|
6.8
|
<0.004
|
21.4
|
<0.04
|
0.05
|
0.03
|
<0.01
|
0.016
|
<0.001
|
0.002
|
11
|
7.4
|
0.004
|
31
|
0.04
|
0.27
|
0.03
|
0.01
|
0.01
|
<0.001
|
0.001
|
GBT 14848 (Chinese AQSIQ, 2017)
|
Class I
|
6.5≤pH≤8.5
|
≤0.01
|
≤50
|
≤0.02
|
≤0.1
|
≤0.05
|
≤0.05
|
≤0.005
|
≤0.0001
|
≤0.005
|
Class Ⅱ
|
≤0.1
|
≤150
|
≤0.1
|
≤0.2
|
≤0.5
|
≤0.05
|
≤0.01
|
≤0.001
|
≤0.005
|
Class Ⅲ
|
≤1.0
|
≤250
|
≤0.5
|
≤0.3
|
≤1.0
|
≤0.1
|
≤0.05
|
≤0.005
|
≤0.01
|
Class Ⅳ
|
5.5≤pH<6.5 8.5<pH≤9.0
|
≤4.8
|
≤350
|
≤1.5
|
≤2.0
|
≤5.0
|
≤1.5
|
≤0.1
|
≤0.01
|
≤0.1
|
Class Ⅴ
|
pH<5.5 or pH>9.0
|
>4.8
|
>350
|
>1.5
|
>2.0
|
>5.0
|
>1.5
|
>0.1
|
>0.01
|
>0.1
|
3.3 Soil quality linked to health
According to the analysis results of soil geochemical samples (Chinese MEE, 2018), we conducted the environmental quality evaluation of soil in the Anji area, and detected the total elements in 473 samples.The analysis of elements in the soil is divided into beneficial and harmful elements through geological background investigation and analytical testing of full and effective state samples of the soil, and the average value lacks accuracy due to the presence of outliers in the data. Therefore, we used the median value for comparison with the background value in Zhejiang Province (Table S5). Except for As, the median values of the remaining elements are less than the background value, and previous work in this study area found that As poses a slight ecological risk in the soil (Li et al., 2022). The frequency distribution shows the frequency of the data, wherein more concentrated distributions were observed for As and Cd (Fig. S2). The spatial distributions of hazardous elements in the study area (Fig. 3) also show that the distribution of As and Cd were concentrated in the southern part of the study area, which belongs to the Lower Cambrian Hetang Formation, and As and Cd are easily enriched in the black shale of its stratum (Yu et al., 2014; Zhang et al., 2021). Based on the prediction of geostatistical models, this study uses Kriging interpolation with uniform regional sample data coverage, followed by the continuous estimation of its results (Goovaerts, 2014). Although the median values of Se and I were higher than the background values, and the distribution of I was more uniform across the whole area (Fig. 4), the I values were evaluated at level 3. Alternatively, the values of F and Mo were not higher than the background values, and the distribution of Mo was more concentrated (Fig. S3), which was unsuitable for the distribution of beneficial elements across the whole area. Therefore, only Se was selected as the dominant element. The distribution of Se-rich soil and soil Se content is restricted by the geological background. The spatial distribution map clearly shows that the Se content is higher in the southern region, and previous studies have also proved that the strata in the southern region are rich in Se (Armstrong et al., 2019). The results of the region-wide soil evaluation score are shown in Fig. 5. Notably, the scores of most soil indicators in the region are above 85 points, and that of a small part of the southern region is less than 85 points, this is because the strata here belongs to the Cambrian Lower Unified Hetang Formation, whose black shale is not only rich in Se, but is also accompanied by the presence of Cd, and the Cd in the soil is positively correlated with the bioaccessible concentration of Cd in rice (Yang et al., 2021). Heavy metals in soil can also be a significant source of heavy metals in tea (Tao et al., 2021). Soil contamination by Cr and Pb elements poses a relatively lesser health risk (Yang et al., 2014).
3.4 Health geology zoning
In this study, we used the AHP method to combining the evaluation of each level of indicators to derive a comprehensive evaluation result. Previously, researchers used AHP models to delineate the groundwater potential zone in the study area based on seven hydrogeological factors, including the geology, geomorphology, slope, drainage, rainfall, soil and land use, and land cover (Ghosh et al., 2020). In this study, the appropriate weights of factors were determined according to the degree of influence of individual factors on the health geological zoning, and the evaluation results of each level of indicators were superimposed using the spatial calculation of ArcGIS (Fig. 6a). Some studies also analyzed the spatial distribution of toxic metals in different soil layers after superimposing the evaluation results (Zeng et al., 2022). The overall score of the study area is good, and mainly comprises two levels, namely, 89.6-90 and 90-96.5, wherein levels 2 (89.6-95) and 1 (95-96.5) accounted for 80.4 and 19.6%, respectively (Fig. 6b). The areas with lower terrain and non-polluted soil generally scored higher. Additionally, the results of sanitary conditions and GDP per capita in the auxiliary indicators show that the GDP and GDP per capita in Zhejiang Province have increased exponentially in the last 20 years (Liao et al., 2022). According to the statistical bulletin on national economic and social development in the study area, the annual GDP was 48.706 billion yuan, and the basic health insurance participation rate was 99.82%. The indicators of the study area are better, thus, further corrections to the consolidated results are not required.
Fig. S3 shows that the Se content in soil samples is generally between 0.175-0.6 mg/kg, accounting for 63.7%; only 1% of samples showed an Se content of 2-3 mg/kg, and 72.2% of primary indicators of elemental Se showed a value of 0.4-3.0 mg/kg. The spatial distribution of Se content in the study area is shown in Fig. 4, and the distribution of soils with high Se content is consistent with the distribution characteristics of the rock stratum with high Se content. Near the distribution area of coal seams of vanadium-bearing rock, the soil Se content is high can easily result in selenium-rich agricultural products; further away from the coal seams, the soil Se content decreases rapidly (Wang, 2021). These results also illustrate the basic concept of medical geology. The elements in water, soil, and food are derived from the geological environment. These elements are beneficial or harmful to humans or other life (M. LI. L, 2019).