Soil Heavy metals contamination of a typical calcium carbide slag dump 1 sites: source apportionment and risk assessment

: Source identification and risk assessment of heavy metals were the 7 necessary preliminary work for the contaminated sites remediation. In this report, the 8 As, Cd, Cr, Cu, Hg, Ni, Pb and Zn concentration in a typical calcium carbide slag 9 dump site of thirty-four soil samples were collected to test. The source of heavy 10 metals was analyzed by PMF model, and the apportionment of ecological risk and 11 health risk with different pollution sources were calculated. The results show that Hg 12 was the main polluted heavy metal in the site, with a maximum concentration of 13 112.19 mg.kg -1 , and the soil in the site was accompanied by As, Cu and Pb 14 co-contamination. The average Hg concentration in farmland samples was 0.13 15 mg.kg -1 , which also exceeded the local soil background values, indicating that soil Hg 16 contamination in the site had spread outwards. The sources of eight heavy metals 17 were divided into oil refinery waste water and parent material mixed source (As, Cr, 18 Cu and Pb), vinyl chloride waste source (Hg) and parent material source (Cd, Ni and 19 Zn), respectively. The average potential ecological risk of soil in the site was 20 22344.39 and vinyl chloride waste source contributed 99.85% to ecological risk. The 21 average CR of oil refinery waste-water and parent material mixed source for children 22 and adults were 9.06 × 10 -6 and 6.36 × 10 -6 , accounting for 99.9% and 99.48% of the 23 total average CR for children and adults, respectively. The average HI of vinyl 24 chloride waste source to children and adults were 0.6 and 0.38, accounting for 64.13% 25 and 52.34% of the average total HI of child and adult, respectively. This indicates that 26 children were more vulnerable to heavy metals. Compared with adults, the major 27 pollution sources were more harmful to children.


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With the increasing importance of soil environment, the treatment of industrial 32 pollution sites has gradually become a hot research topic of soil restoration in recent As are mainly from soil-based mother metals, Cu, Zn, Pb and Cd are mainly from 60 industrial smelting and traffic emission sources, and Cr is controlled by soil-based 61 mother metals and man-made pollution. Xie (2018) analysis shows that Pb, Cd, Cu, 62 Zn and As at a steel plant in western Fujian Province are mainly affected by pollutants 63 emitted by steel mills, and Cr and Ni are mainly affected by native mother quality. Silver City shows that coal combustion and other related activities are the most 75 influencing sources of soil heavy metals cancer risk and non-carcinogenic risk in the 76 region, and he believes that using pollution sources for human health risk assessment 77 is more meaningful than using only carcinogenic risk thresholds and non-carcinogenic 78 risk thresholds for human health risk assessment. Yang  Wu (2020) believes that the use of pollution sources for human health risk assessment 87 is also important to guide similar enterprises production activities.

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This study analyzed the degree and source of soil heavy metal pollution in 89 mercury-containing waste landfill sites, and calculated the ecological and human 90 health risks based on pollution sources. The aim are: first, to understand the soil 91 contamination of the site; second, to analyze whether the pollution in the site spread 92 outwards, and third, to identify the ecological and human risks of the greatest impact 93 on the source of pollution.

Study area and sample collection 96
The geographical coordinates of the study area are 123°53'53.70″ east longitude 97 and 47°08′46.98″ north latitude, 22km away from Qiqihar city ( Figure 1). The 98 northeast of the study area was the production enterprises of caustic soda, PVC, oil 99 refining, etc., and the southwest was farmland. The study area is about 28.57×10 4 m 2 .

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Since the 1950s, industrial sites have started production, and a large amount of 101 production waste was discharged into the research area in the form of waste water and 102 waste residue.

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In this study, the judgment method was used to sample the soil under the waste 104 residue in the site, and thirty-four sampling points were arranged in the study area.

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The soil 0.5m deep below the mercury-containing waste residue was collected for   where c is the content of the element and MDL is the method detection limit. 138

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The comprehensive potential ecological harm index RI ( Human health risk assessment 175 The human health risk assessment is carried out according to the methods

Correlation analysis 253
The correlation between elements was significant or extremely significant, it  The average concentration of As, Cr, Cu and Pb did not exceed the background values, 284 It shows that these four heavy metals were mainly derived from parent material 285 (Zhang et al.2017). However, the concentrations of As, Cu, and Pb at six, two, and six 286 sampling points respectively exceeded the local soil background value, indicating that 287 the soil has suffered man-made pollution, too. Analysis shows that the higher 288 concentrations of As, Cu and Pb in the site were mainly related to the waste-water 289 discharge in the northern industrial production area (Ma et al.2019). A large amount of 290 sulfide will be generated during the refining process in the industrial zone, which will 291 be discharged into the site through the sewage outlet. Therefore, factor 1 represents oil 292 refinery waste-water and parent material a mixed source. which was the main factor that causes the Hg concentration pollution in the site.

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Therefore factor 2 represents the vinyl chloride waste source.  Table S1. 345 sites, this contaminated site was industrial land and belongs to category I land, and the 347 heavy metal risk assessment considers adult and child carcinogenic and hazard index.
348 Figure 8A and Figure 8B shows the carcinogenic risk (CR) values of the three 349 exposure pathways of As, Ni, and Cd at thirty-four sampling points with child and 350 adult. The CR of three exposure pathways with As were all exceeded the acceptable 351 level (1×10 -6 ), but did not exceed the tolerance value (1×10 -4 ), among them, the 352 carcinogenic risk of oral ingestion was the highest. The CR of the three exposure 353 pathways of Cd and Ni did not exceed the acceptable level (1×10 -6 ). The CR of heavy 354 metals in children was generally higher than that in adults, indicating that children 355 were more vulnerable to soil heavy metals.

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The HI for the eight heavy metals in thirty-four borehole of three exposure 357 pathways with child and adult were shown in Figure 8C and Figure Figure 9A and Figure 9B. The total CR value of child was between 369 4.17×10 -6 and 2.08×10 -5 . The CR of heavy metals in all the sampling sites was greater 370 than the acceptable level (1×10 -6 ), but did not exceed the tolerance value (1×10 -4 ).

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The oil refining waste-water and parent material mixed source (As) and soil parent 372 material sources (Cd and Ni) of the average total CR of child were 9.06×10 -6 and 373 8.68×10 -9 , with CR contribution rates of 99.9 % and 1%, respectively. The oil refining 374 waste-water and parent material mixed source (As) and soil parent material sources 375 (Cd and Ni) of the average total CR of adult were 6.36×10 -6 and 3.3×10 -8 , with CR 376 contribution rates of 99.48 % and 0.52 %, respectively. The oil refining waste-water 377 and parent material mixed source was the main factor causing carcinogenic risk of 378 heavy metals in the site. Both sources increase the CR in children compared to adults.

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At the same time, the proportion of pollution sources that dominate the child CR (oil 380 refining waste-water and parent material mixed source) will increase compared to 381 adults.

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The HI of three pollution sources with child and adult was shown in Figure 9C 383 and Figure 9D. The total HI of thirty-four sampling points with child was between