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Study area and field dataThe dataset was generated over NYC, located in the north-eastern United States (40.713° N, 74.006° W). NYC has a total area of 778.2 km2, which is composed of five boroughs, i.e. Brooklyn, Queens, Manhattan, Bronx, and Staten Island (Fig. 1). There were 296 field plots randomly sampled (Fig. 1a) and measured in the summer of 2013 over NYC following the i-Tree Eco protocols9 developed by the United State Department of Agriculture Forest Service (USFS). Each plot occupied a circular area of 404.7 m2. All the trees with a Diameter at Breast Height (DBH) larger than 2.54 cm were surveyed to record their tree height, species, DBH, and other structural attributes. Within all the 296 plots across NYC, there were 1,075 trees in 139 species surveyed. The species types with the top ten largest sample size were Acer platanoides (65 samples), Cedrus species (59 samples), Ailanthus altissima (58 samples), Sassafras albidum (56 samples), Quercus alba (51 samples), Betula lenta (42 samples), Robinia pseudoacacia (39 samples), Acer rubrum (38 samples), and Hardwood species (37 samples). Because the exact coordinates of individual trees were not collected, we mainly used the plot-level tree attributes (i.e. tree number, mean tree height, and maximum tree height) to validate LiDAR-derived products. Due to confidential requirements, the exact coordinates of field plots were not allowed to be released.Fig. 1The distribution of field plots across five regions in New York City (NYC) borough (a). The land cover map over the entire NYC with seven land cover types (b). The summary of identified trees from remotely sensed datasets across five regions (c), and the tree density map over each block group in NYC (d).Full size imageAerial image and land cover mapsA fine-resolution land cover dataset (0.91 m spatial resolution) provided via NYC OpenData (https://opendata.cityofnewyork.us/) was used to mask out non-vegetation areas. This land cover dataset was generated using an object-based image classification method5 from LiDAR data collected in 2010 and NAIP aerial imageries in 2009. This final land cover map includes seven classes, i.e., tree canopy, grass/shrub, bare earth, water, buildings, roads, and other paved surfaces (Fig. 1b). We regrouped the land cover map into vegetation (tree canopy and grass/shrub) and non-vegetation groups, and resampled the map into 1 m resolution to match with NAIP and LiDAR datasets. We also collected NAIP imagery in the summer of 2013 for tree structural estimation from the Google Earth Engine platform36. The NAIP image had a resolution of 1 m with four spectral bands (Red, Green, Blue, and Near Infrared). We further calculated the NDVI from the Red and Near Infrared bands of NAIP images for tree structural estimation.LiDAR data and processingThe LiDAR data were collected using a Leica ALS70 LiDAR system from two flight missions (https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4920/index.html). The first LiDAR flight was taken on August 5th, 2013 at 2,286 m above ground level with an average side lap of 30%. The LiDAR data from this flight had a nominal pulse spacing of 0.91 m. The second flight was taken between March and April, 2014 at 2,286 m above ground level with an averaged side lap of 25% and a nominal pulse spacing of 0.7 m. According to the ground control survey, the LiDAR scan had a root mean square error accuracy of 9.25 cm. With up to 7 returns per pulse, the final LiDAR dataset has a point density of 5.9 points/m2.The tree structural information was mainly generated from LiDAR-derived CHM. The CHM was the difference between Digital Surface Model (DSM) and Digital Terrain Model (DTM) generated from LiDAR point clouds using the Kriging interpolation method37. All the raster layers (CHM, DSM, DTM) were generated at 1 m resolution using the LiDAR360 software (GreenValley International). We generated a Tree Canopy Cover (TCC) map by masking out non-vegetation land cover types from areas with CHM values larger than 2 m. The TCC was a binary map with the value of one indicating tree cover and zero indicating non-tree cover at 1 m resolution. The non-vegetation areas were derived from the land cover map (Fig. 1b). The 2 m tree canopy height threshold was chosen by referencing a commonly accepted canopy height threshold38.Individual tree segmentation and feature estimationIndividual tree crowns were segmented from LiDAR-derived CHM using the Marker-controlled Watershed Segmentation algorithm. This algorithm was widely adopted for LiDAR-based tree crown segmentation25,26,29 because it takes the advantages of both region-growing and edge-detection methods39. Due to the relatively low LiDAR point density, the CHM contained abnormal pits even after masking out non-tree-canopy pixels. We applied a Gaussian filter with two standard deviations to smooth the CHM and fill these pits in CHM. Then the segmentation was applied with a 3 × 3 moving window. Both smoothing and segmentation were conducted using the System for Automated Geoscientific Analyses software40. To refine the segmentation results, we deleted small segments with an area smaller than 1 m2 (one CHM pixel), which was most likely to be noise in CHM. We also visually examined and manually re-segmented extremely large segments by assuming most tree crowns should not exceed an area of 200 m2. The final tree crown dataset only contains segments with a maximum CHM value no less than 5 m because vegetation with lower height was mostly likely to be non-tree. All the post-segmentation operations were conducted in ESRI ArcMap 10.8.We estimated five tree structural features for each individual trees, which include tree top height, tree mean height, crown area, tree volume, and carbon storage. Tree top height (m) characterizes the height from ground to tree top, estimated as the maximum CHM value within each tree crown segment. Tree mean height (m) indicates the average height of the tree crown surface, calculated as the mean CHM values within each tree segment. Tree crown area (m2) is the total area of each tree crown segment. Tree volume (m3) is the volume of 3D space occupied by the tree crown25, which was calculated as the volume difference between crown surface (defined by CHM) and crown base (Eq. 1). Because the tree crown base height was difficult to estimate for individual trees due to the relatively low LiDAR point density, we used the 2 m to approximate the averaged crown base height according to Ma et al.25. The sensitivities of crown volume to the selection of crown base height from 1 m to 5 m was presented in the Technical Validation section.$$Volume={sum }_{i=1}^{n}left(CHMi-crown;base;heightright)times 1{m}^{2}$$
(1)
Where CHMi is the CHM values of the ith pixels within a tree segment, n is the total number of pixels within a tree segment. 1m2 is the area of each CHM pixel.The carbon storage (ton) was defined as the total carbon stock in both above- and below-ground biomass of each tree. The carbon storage was estimated in two steps: (1) calculating tree biomass from field measurements using allometric equations41; (2) running a regression between field measured carbon storage and LiDAR-derived tree structural features42 and applying the regression model to individual trees. In step (1), we applied species-specific allometric equations from i-Tree Eco database. There are more than 50 species-specific equations in i-Tree Eco, which can be summarised into four main equation forms with different coefficient values (Eqs. 2–5).$$Biomass=exp left({beta }_{1}+{beta }_{2}ast LNleft(DBHright)+frac{{sigma }^{2}}{2}right)$$
(2)
$$Biomass=exp left({beta }_{1}+{beta }_{2}ast LNleft({{rm{DBH}}}^{2}ast {rm{H}}right)+frac{{sigma }^{2}}{2}right)$$
(3)
$$Biomass={beta }_{1}ast left(DB{H}^{{beta }_{2}}right)$$
(4)
$$Biomass={beta }_{1}ast left({left({{rm{DBH}}}^{2}ast {rm{H}}right)}^{{beta }_{2}}right)$$
(5)
Where β1 and β2 are species-specific coefficients, DBH is diameter at breast height, H is tree top height, σ2 is the variance of model errors, which is applied to correct the potential underestimations when back-transforming predictions from logarithmic scale to original scale. For other species that were not included in the i-Tree Eco database, the averaged results from the four equations were applied. These allometric equations (Eqs. 2–5) estimate the entire tree biomass including both above- and below-ground biomass, and the final carbon storage for each field plot was converted to carbon by a factor of 0.541.In step 2), we compared different regression models to simulate carbon storage at plot scale using LiDAR data and NAIP imagery. First, we compared the single variable regression for carbon storage from NAIP-derived NDVI, LiDAR-derived TCC, LiDAR-derived CHMmean and CHMmax, respectively. The four metrics were calculated at 1 m resolution, masked out non-vegetation areas, and aggregated over each field plot. TCC was calculated as the percentage area with tree cover (CHM >2 m). CHMmean and CHMmax were calculated as the mean and maximum of all CHM values within each plot. We compared different regression algorithms, including linear, exponential, and quadratic regressions. We also compared the modelling efficiency and accuracy between using single and multiple variables by combing all the attributes together using the Random Forest regression model. Using the optimal regression model, we generated a carbon density map at 20 m spatial resolution (each pixel size is similar to the plot size of 404.7 m2) by dividing the total carbon storage by the pixel size (400 m2) in the unit of ton/ha (Eq. 6). More details of carbon density estimation can be found in our previous publication42. The carbon storage for each tree was calculated as the product of crown area and crown density (Eq. 7).$$Carbon;densityleft(ton/haright)=0.5ast Biomass(ton)/left(400left({m}^{2}right)ast 0.0001left(ha/{m}^{2}right)right)$$
(6)
$$Carbon;storageleft(tonright)=Crown;arealeft(haright)ast Carbon;density(ton/ha)$$
(7)
Where Biomass is the total biomass for each pixel, which was 400 m2. ha is short for hectare, which is 10000 m2.We further quantified the uncertainty range in carbon storage estimation by propagating the potential error in carbon density regression to tree level carbon storage estimation. We first calculated the 95% confidence interval of the best carbon density regression model, and applied the confidence interval to carbon storage estimation for individual trees. The predicted the upper and lower values for individual tree carbon storage were given in the final dataset and summarized in Table 1.Table 1 A summary of the individual tree carbon storage prediction (Carbon) and their lower (Carbon_lower) and upper (Carbon_upper) values. The minimum (min), maximum (max), mean, standard deviation (std), first quartile (q25), median, and third quartile (q75) values of individual tree carbon storage are presented.Full size tableBlock group level tree structure distribution mappingThree sets of tree structural parameters were mapped at block group level, including tree density (the number of trees in each hectare), tree height (m), and carbon density (ton/ha). The mean values of tree density, tree top height, and carbon density within each block group of NYC. The block group boundary was downloaded from https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.2014.html, which includes a total of 6392 block groups.We also estimated the potential tree height and carbon density at the census block group level. We assumed the 95% of the tree height and carbon storage values within each block group at mapping time were their potential values, which most trees can achieve during their life time. Then, we calculated the difference in tree height and carbon density between potential values (95%) and mapping time values (mean) over each block group, and used them as the extra carbon storage that trees could achieve during their life time. It is to be noticed that in this study we did not consider the carbon loss by tree degradation or removal, or extra carbon gain through the tree planting and management. More

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Concentrations of PTEs in agricultural soil of oasesThe descriptive statistical results of 11 PTE concentrations in agricultural soils of the four oases are shown in Table 1. The concentration order of different PTEs in the four oases was different. In terms of mean values, the concentrations of Co, Cu, Ni, Pb, Sb, V and Zn in Kashgar Oasis agricultural soil were higher than those in the other three oases, and the concentrations of Sn and Tl in Hotan Oasis agricultural soil were the highest. The Cv value of As in the Hotan Oasis was the highest (0.31), indicating that compared with that in other oases and other PTEs, the As in Hotan Oasis soil was more likely to have external inputs other than natural sources59. According to the “Soil Environmental Quality · Agricultural Land Soil Pollution Risk Control Standard (Trial)” (GB15618-2018)60, the corresponding elements of oasis agricultural soil in the source region of the Tarim River did not exceed the pollution risk control standard. Compared with the soil environmental quality provisions in the “Environmental Quality Assessment Standard for Producing Areas of Edible Agricultural Products” (HJ332-2006)61, the corresponding elements in the soil of the four oases were also below the limits.Table 1 Descriptive statistics of PTEs of oasis agricultural soil in the source region of the Tarim River.Full size tableCompared with the PTE concentrations in the agricultural soil of oases in other arid areas, the concentrations of Cd, Cu and V in the soil of the study area were lower than those of the Bortala River Basin and Ili River Basin3 in the northern Tianshan Mountains, while the concentrations of Co, Ni, Pb and Zn were similar to those of corresponding elements in agricultural soil of the Bortala River Basin and Ili River Basin3. Compared with the concentrations of PTEs in agricultural soil of Wuwei and Jiuquan cities in the Hexi Corridor62,63, the concentrations of Cu, Ni, Pb and V elements in agricultural soil of the four oases in the study area were lower. Similarly, the concentrations of Cu, V and Zn in the study area were much lower than the corresponding concentrations in the agricultural soil of the Bahariya Oasis, Egypt64.Geochemical baseline values of PTEs in oasis agricultural soilsThe PTE concentration of the subsoil (60–80 cm) after logarithmic and reciprocal conversion passed the KS normal distribution test (p  > 0.05). The GBVs of PTEs in agricultural soils of the four oases in the source region of the Tarim River were calculated according to the cumulative frequency method, and the results are shown in Supplementary Figs. S1–4 and Table 2. The GBVs of PTEs in agricultural soils were very different among the four oases. For example, except for those of Ni, Sn, Tl and V, the GBVs of PTEs in agricultural soils of the Hotan Oasis were much lower than those of the other three oases (Table 2). There was also a large gap between the GBVs of PTEs in agricultural soil and the soil background values in China65, Xinjiang66,67 and Xinjiang agricultural land66. In particular, the GBV of Zn obtained in this study was 3.6–5 times the soil background value of Xinjiang agricultural land. Under the same land use type, there are differences in the abundance of environmental PTEs due to heterogeneity in the disturbance degree of human activities and the parent material and soil formation processes68. Therefore, there were some differences in the GBVs of each PTE among the four oases in this study when the land use types were all agricultural soils.Table 2 GBVs of PTEs in oasis agricultural soils of the source region of the Tarim River.Full size tablePollution characteristics of PTEs in agricultural soil of oasesAccording to the GBVs of the above elements, the PF, PLI and PN of PTEs in agricultural soil of the four oases were calculated, and the results are shown in Fig. 2. The results of PF showed that (Fig. 2a), except for As and Cd in the Hotan Oasis, the PTEs of agricultural soils in the four oases were at uncontaminated and slightly contaminated levels, indicating that the oasis agricultural soils in the source region of the Tarim River were affected by human activities to a certain extent. From the perspective of individual elements, the PF of Cd in agricultural soils of the four oases was higher than that of other PTEs. Among them, Cd in most soil samples from the Hotan Oasis (81.25%) showed mild contamination, while Cd in the remaining samples (18.75%) showed moderate contamination. Since Cd in soil is generally regarded as an indicator of agricultural activities involving fertilizer use, the results suggest that soil in oases (especially the Hotan Oasis) in the source region of the Tarim River may be seriously affected by agricultural activities.Figure 2Box-whisker plots of PF (a), PLI (b) and PN (c) of PTEs in oasis agricultural soils.Full size imageThe results of the pollution load index of multiple PTEs showed that the agricultural soils in the Yarkant River Oasis, Kashgar Oasis and Aksu Oasis were between uncontaminated and moderate contamination levels, and most soil samples in the Hotan Oasis were moderately contaminated. PN showed similar results. The reason for this result was the high PF values of As and Cd in the agricultural soil of the Hotan Oasis (Fig. 2a), which caused the high comprehensive pollution index in this area. It is worth noting that compared with those in the other three areas, most PTEs (As, Cd, Pb, Sb, V and Zn) in the agricultural soil of the Hotan Oasis had lower mean values, but their PLI and PN values were higher. This was closely related to the lower GBVs of PTEs in the Hotan area.Source apportionment and source specific risk assessment of PTEs in oasis agricultural soilSource apportionment of soil PTEsFactor analysis and correlation analysis were used to identify the main sources of PTEs in the main oasis agricultural soil in the source region of the Tarim River. The results are shown in Table 3 and Supplementary Fig. S5. Table 3 shows that PTEs in the agricultural soil of the Yarkant River Oasis had two principal factors. The first principal component F1, which explained 61.6% of the total variance, mainly described Co, V, Cu and Sb and moderately described Cd, Ni and Tl. The second principal component, F2, accounted for 21.8% of the variance and mainly described As, Pb and Sn. There were three main factors for PTEs in Kashgar Oasis agricultural soil. Factor 1, which explained 58.9% of the total variance, was mainly composed of As, Co, Cu, Ni, Pb, Sb, V and Zn; factor 2, which accounted for 24.8% of the variance, was mainly composed of Sn and Tl; and factor 3, which accounted for 7.9% of the variance, was composed of Cd. There were three main factors for the PTEs of Aksu Oasis agricultural soil. Factor 1 was mainly composed of Cd, Co, Cu, Ni, Pb, V and Zn; factor 2 was mainly composed of Sn and Tl; and factor 3 was composed of As and Sb. PTEs in agricultural soil of the Hotan Oasis had only one main factor, which was composed of all (11) elements. To verify the above results of PTE extraction from oasis agricultural soil by PCA, Spearman correlation analysis was performed on PTEs from the soils of the four oases. The results showed that the correlations between PTEs in agricultural soils of the four oases were consistent with the results of PCA, indicating the reliability of the PCA results.Table 3 Principal component analysis results of PTEs of oasis agricultural soil in the source region of the Tarim River.Full size tableTo further determine the specific sources and contribution rates of PTEs in oasis agricultural soil in the source region of the Tarim River, the PMF model was adopted for analysis, and the results are shown in Fig. 3. Overall, the classification results of PTEs in agricultural soils of the four oases by the PMF model were consistent with the results of PCA. According to the above results, eight environmental factors related to the source of soil PTEs were selected: distance from factory (DF), distance from road (DR), pH, soil type (ST), total nitrogen (TN), soil fine silty particle size percentage (Fine silty), soil silty particle size percentage (Silty), and soil coarse silty particle size percentage (Coarse silty). A Geodetector model of PTEs and environmental factors in soil was constructed, and the results are shown in Supplementary Table S5. Among them, the TN content in soil was considered to be an index related to the intensity of agricultural activities69. Since the particle composition of atmospheric dust in the study area is mainly silt70, the silty particle size content of soil was selected as the atmospheric dust index in this study.Figure 3PMF analysis results of PTEs of agricultural soils in the Yarkant River Oasis (a), Kashgar Oasis (b) and Aksu Oasis (c).Full size imageIn the Yarkant River Oasis, Co, Cu and Zn showed no pollution at most of the sampling points for the first source factor of PTEs in agricultural soil (Fig. 2), indicating that the levels of these elements in soil were less affected by human activities. Meanwhile, the results of the factor detector showed that ST was one of the factors explaining the spatial distribution of Co, Cu, Sb, V and Zn (Supplementary Table S5). The Geodetector results revealed TN as one of the strong drivers of Cd and Tl, the former of which is found in pesticides and fertilizers and the latter of which may also enter agricultural soil through sewage irrigation and fertilizers contaminated by industrial wastewater71,72. Therefore, it is inferred that F1 in the agricultural soil of the Yarkant River Oasis had a mixed source of natural resources and agricultural activities. The three elements in F2 (As, Pb and Sn) were closely related to fuel combustion and traffic factors, among which Pb is usually selected as an identifying element for traffic sources (including leaded exhaust gas, vehicle tires and brake pads)73. In the results of the Geodetector model, the best explanatory factors for Pb and Sn were Silt and DR, while the best explanatory factor for As was Slit. Therefore, F2 was inferred to be the source of road dust/atmospheric dust.The weights of F1 in Kashgar Oasis agricultural soil PTEs were mainly included As, Co, Cu, Ni, Pb, Sb, V and Zn; the weights of F2 were mainly included Sn and Tl; and F3 were mainly included Cd (Fig. 3b). Similar to the results observed for the Yarkant River Oasis, the factor detector results showed that F1 might have a mixed anthropogenic source, including transportation, industrial and other sources. Both Sn and Tl in F2 are widely used in industrial manufacturing, and Sn can be used as an additive to enhance the properties of steel or alloys74. Tl is used in many different industrial manufacturing and medical fields, and metal smelting, sulfuric acid production, coal burning, cement manufacturing and other industrial activities involving the use of Tl minerals are the main pathways by which this element enters the environment71. At the same time, the strongest explanatory factor for Sn and Tl in the results of the geographic detector was DF, so F2 was inferred to be an industrial source. F3 contained only Cd (related to agricultural activities), so F3 was inferred to be the source of agricultural activities (Supplementary Table S5).In the PMF results, the weights of F1 for the PTEs of Aksu Oasis agricultural soil were mainly included Cu, Ni, Cd, Zn, Co, V and Pb; the weights of F2 were mainly included Sn and Tl; and the weights of F3 were mainly included As and Sb (Fig. 3c). Similarly, from the factor detector calculation results, it was inferred that F1 in the Aksu Oasis was a mixed source. According to the results of Geodetector analysis, the best explanatory factors for Sn and Tl in the agricultural soil of the Aksu Oasis were TN and ST. Previous studies have also shown that Sn in soil may also come from agricultural practices (pesticides)75, so F2 was inferred to represent agricultural activities and natural sources (rock mineralization). Similarly, according to Supplementary Table S5, F3 was inferred to be the source of agricultural activities. Previous studies have also concluded that agricultural activities such as the application of phosphate fertilizer are also the main source of As and Sb in soil76,77, which was consistent with the results of the Geodetector model.The explanatory factors for the PTEs of agricultural soil in the Hotan Oasis were the total nitrogen content and the silty particle size percentage, indicating that the PTEs in agricultural soil in the Hotan Oasis mainly came from agricultural activities and atmospheric dust fall. The economy in the Hotan Oasis is dominated by irrigated agriculture, and since most oases border large deserts, wind and sand disasters are extremely serious (annual average dust days exceeding 220 days)78. The sources of PTEs inferred by the Geodetector model in this study were consistent with the reality.Source-specific ecological risk assessmentBased on the results of source analysis, the source-specific ecological risks posed by agricultural soil PTEs were evaluated in this study, and the results are shown in Fig. 4. The total ecological risks caused by PTEs in the agricultural soils in the Yarkant River Oasis, Kashgar Oasis and Aksu Oasis were null, while those at of all sampling sites in the Hotan Oasis were moderate risk. According to the results of the source-specific ecological risk of PTEs, there was no direct relationship between the contribution degree of source-specific risks to the total ecological risk and its contribution to the existence of PTEs in soil. In particular, the agricultural activity source (F3), which accounted for only 7.9% of the PTEs in Kashgar Oasis agricultural soil, contributed the most to the total risk, the mixed source (F1), which contributed the most to the existence of PTEs in soil, contributed the second most to the total risk, and the industrial source (F2) contributed the least. The reason for this result was that the toxicity factor of Cd (30) introduced by agricultural activities was significantly higher than that of PTEs released from other sources, which was consistent with the conclusion of other studies16,19 that the main source of highly toxic elements was more likely to cause ecological risks than that of low-toxicity elements.Figure 4Source-specific ecological risk boxplots of PTEs of agricultural soils in oases in the source region of the Tarim River.Full size imageTo explore the spatial distribution of ecological risks generated by PTEs from different sources, a distribution map of ecological risks posed by specific sources at each sampling point was generated (Fig. 5). The total ecological risk of the sampling sites near Awat County in the Aksu Oasis was higher than 40, indicating moderate risk. In addition, the total ecological risk at the other sampling sites was at a low level. However, the ecological risks caused by mixed sources (F1) and agricultural activities and natural sources (F2) were high in the southwestern Aksu Oasis and the sampling sites near Aksu city, resulting in high total ecological risks. The ecological risks at all the sampling sites in the two oases in Kashgar (Kashgar Oasis and Yarkant River Oasis) were low. Notably, the sampling sites near Kashgar city had high total ecological risks due to the high ecological risks caused by PTEs from mixed sources (F1) and agricultural activity sources (F3). The total ecological risk at all sampling sites in the Hotan Oasis was moderate. In particular, the sampling sites near Hotan city had the highest total ecological risk generated by PTEs from agricultural activities and atmospheric dust sources (73.71).Figure 5Spatial distribution of the ecological risks of PTEs from different sources in the four oases. The graphs were generated by QGIS 3.26.3 (https://www.qgis.org) and the land use data are from the ESA global 30 m resolution land use cover dataset (https://viewer.esa-worldcover.org/worldcover). The combination of graphs (a–d) was accomplished with linkscape 1.2.1 (https://inkscape.org).Full size imageSource-specific human health risk assessmentAccording to the proportions of different sources of each PTE obtained from the PMF model, the source-specific health risks of PTEs in agricultural soil in the four oases to the human body were calculated, and the results are shown in Tables 4 and 5 and Fig. 6. Although the results of noncarcinogenic risk caused by different sources of PTEs in agricultural soil in each oasis showed that adults and children were not at risk, the total THI values of PTEs for children in the four regions were all greater than 1, indicating that soil PTEs in the study area posed significant noncarcinogenic risks for children. In terms of carcinogenic risk, the total TCR values of PTEs for adults and children were on the order of 1E−05, within the range of 1E−06 and 1E−04, indicating that the carcinogenic risk of soil PTEs for the human body is acceptable in the study area. In general, the noncarcinogenic and carcinogenic risks of PTEs from different sources in children were higher than those in adults, which can be explained by children having more opportunities PTE contamination through hand-to-mouth ingestion and dermal contact than adults due to the areas where they play and unhealthy eating habits (e.g., children are more likely to suck their fingers)79. Therefore, different parameters were set when employing the health risk assessment model.Table 4 Specific noncarcinogenic risks of PTEs from different sources.Full size tableTable 5 Specific carcinogenic risks of PTEs from different sources.Full size tableFigure 6Human health risk proportions of PTEs from different sources in the Aksu Oasis (a), Kashgar Oasis (b) and Yarkant River Oasis (c).Full size imageIn terms of the proportion of human health risks caused by PTEs from different sources (Fig. 6), those from mixed sources, which were considered to have the largest contribution to PTEs in the Aksu Oasis, Kashgar Oasis and Yarkant River Oasis, were not the largest. This might be explained by the presence of more toxic elements, such as As and Tl, in other sources of the three oases contributing the most (Fig. 3), while their low RfD may explain their greater noncarcinogenic risk. PTEs from agricultural activities and natural sources accounted for the largest proportion of carcinogenic risk in the Aksu Oasis, while mixed sources accounted for the largest proportion of carcinogenic risk in the Kashgar Oasis and Yarkant River Oasis. This was mainly because the presence of As, Cd, Co, Ni and Pb elements with carcinogenic risk in the above two sources accounted for a large proportion (Fig. 3), thus posing a large carcinogenic risk. The results of the proportion of health risks attributed to different sources of PTEs to the human body showed that the control of human health risks of PTEs cannot be determined based on their concentration alone. Therefore, in view of the obvious noncarcinogenic risk of soil PTEs in the four oases to children, from the results of the contribution of different sources of PTEs to the noncarcinogenic risk to children, agricultural activities and natural sources, industrial sources and atmospheric dust fall were the priority control sources in the Aksu Oasis, Kashgar Oasis and Yarkant River Oasis, respectively. More

These authors contributed equally: Arjun Srivathsa, Divya Vasudev, Tanaya Nair, Jagdish Krishnaswamy, Uma Ramakrishnan.National Centre for Biological Science, TIFR, Bengaluru, IndiaArjun Srivathsa, Tanaya Nair, Mahesh Sankaran & Uma RamakrishnanWildlife Conservation Society-India, Bengaluru, IndiaArjun SrivathsaConservation Initiatives, Guwahati, IndiaDivya Vasudev & Varun R. GoswamiDivision of Biosciences, University College London, London, UKTanaya NairDepartments of Biology and Environmental Studies, Macalester College, Saint Paul, MN, USAStotra ChakrabartiWorld Wildlife Fund, Delhi, IndiaPranav Chanchani, Arpit Deomurari, Dipankar Ghose & Prachi ThatteDepartment of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USARuth DeFriesAmity Institute of Forestry and Wildlife, Amity University, Noida, IndiaArpit DeomurariWildlife Institute of India, Dehradun, IndiaSutirtha DuttaFoundation for Ecological Research, Advocacy and Learning, Bengaluru, IndiaRajat Nayak & Srinivas VaidyanathanNetwork for Conserving Central India, Gurgaon, IndiaAmrita NeelakantanWorld Resources Institute, New Delhi, IndiaMadhu VermaSchool of Environment and Sustainability, Indian Institute for Human Settlements, Bengaluru, IndiaJagdish KrishnaswamyAshoka Trust for Research in Ecology and the Environment, Bengaluru, IndiaJagdish KrishnaswamyBiodiversity Collaborative, Bengaluru, IndiaJagdish Krishnaswamy, Mahesh Sankaran & Uma Ramakrishnan More