Agilent 7700 inductively coupled plasma mass spectrometer (Agilent Technologies, USA), the operating parameters were listed in Table 1; Milli-Q laboratory water purification system (Millipore, USA); MDS-10 high throughput microwave digestion instrument (Shanghai Sineo Microwave Chemistry Technologies, China).

Table 1

Table 1

Table 1 Operating parameters of ICP-MS Parameters Numerical Value RF power/W 1 550 Nebulizer gas flow/(L· min-1) 0.9 (0.6~1.0) Auxiliary gas flow/(L· min-1) 0.25 (0.3~1.0) Sampling depth/mm 8 (7~10) Peristaltic pump speed/rps 0.1 (0.1~0.3) Sample cone/mm 1.0 Skimmer cone/mm 0.7

Table 1 Operating parameters of ICP-MS

1 000 mg· L^-1 As standard solution (IERM, China); Multi-element mixed solution of internal standard (Agilent, USA); 65% HNO₃, 29%~32% H₂O₂, 40% HF (Sinopharm Chemical Reagent Beijing Co., Ltd, China); GBW 07403 (soil), GBW 07602 (vegetable) and GBW 0901 (hair) (National Standard Sample Study Center, China).

In this study, the nine villages (S₁— S₉) around a Pb-Zn mining area in Yunnan province were determined as study area, and the county town 20 km away from mining was selected as reference area (S₁₀). The samples including 76 cultivated soils, 306 crop/vegetable and 86 human hairs were collected, respectively (Fig.1). The crops/vegetables samples included 51 maize (crop, as a staple crop) and ten kinds of vegetables, which were leafy vegetables (24 Chinese cabbages, 16 pakchoi, 22 scallions, 17 garlic, 14 lettuces, 9 parsley, 17 tine peas and 16 spinach), tuber vegetables (96 potatoes) and root vegetables (24 radishes), respectively. The soil samples (0~10 cm depth) below the crop/vegetables were also collected. To characterize the exposure levels, 60 no colored or treated hair samples from local inhabitants and 26 hair samples from S_{20 km} area were collected.

Fig.1

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	Fig.1 Sampling sites of the study area

Hair samples were washed according to the procedure recommended by the IAEA Advisory Group (acetone, three times water, acetone) to remove surface dirt and grease. The collected crop/vegetables were dried in oven for 24 h at 70~80 ℃, and the soil samples were air-dried at room temperature and the washed hair samples were dried at about 50 ℃ to constant weight. The samples (0.1 g) of dried and ground soil, vegetable and the hair which were cut into pieces less than 1 cm long and were digested according to the conditions of Table 2, and the As contents were measured by using inductively coupled plasma mass (ICP-MS) spectrometry (Agilent Technologies, USA).

Table 2

Table 2

Table 2 Microwave digestion conditions of samples Sample type HNO3/mL H2O2/mL HF/mL Programming Temperature/Heating time Soil 6 1 2 120 ℃/6 min, 160 ℃/5 min, 200 ℃/5 min, 240 ℃/5 min Crop/vegetable 7 1 0 120 ℃/5 min, 150 ℃/5 min, 175 ℃/5 min, 240 ℃/5 min Hair 7 1 0 100 ℃/6 min, 130 ℃/5 min, 170 ℃/5 min, 200 ℃/5 min

Table 2 Microwave digestion conditions of samples

Contents of As in the soil and crops were assessed by single-factor pollution index (SFPI, Pi= CiSi), and definition and calculation were referred to Ref. [11].

The human health risk models including non-carcinogenic hazard and carcinogenic risk assessment for all the elements through ingestion (CDI_ing), inhalation(CDI_inh), diet (EDI), and dermal contact (CDI_der) raised by USEPA, which were expressed as the hazard index (HI) and total cancer risk (TCR) for individual elements in soil while the target hazard quotient (THQ) and the carcinogenic risk (CR), respectively. The definitions of symbols and parameters were referred to Ref. [12]

Quality assurance and quality control were assessed using the analysis of duplicate samples, method blanks and standard reference materials. Precision and accuracy for As analysis in different samples were verified using the standard reference materials [GBW 07403 (soil, China), GBW 07602 (vegetable, China) and GBW 0901 (hair, China)]. Accepted recoveries ranges were from 92.43%~112.23%, 97.88%~114.72%, and 91.44%~109.65% for soil, crop/vegetable and hair samples, respectively. The difference of ≤ 5% between the determined and certified values of As contents were considered acceptable.

2.2.1 The pollution levels of As in the soil and vegetables

In this study, the contents of total As (mg· kg^-1 dw) in the different samples were shown in Fig.2. The highest As content of soil was detected in S₁ sampling site (100.53 mg· kg^-1), because the S₁ was the nearest sampling site from mining area, and the mean content of As in the soil samples was 3.84 times higher than that of the background value in Yunnan province (18.4 mg· kg^-1). The single-factor pollution index (P_i) of As in soil varied from 2.22 to 3.26, which reached heavy pollution. The possible reason was that As was associated with Pb-Zn mines in nature, and the long-term Pb-Zn mining smelting caused the removal of arsenide, leading to As pollution and irrational use of pesticides and chemical fertilizers led to As pollution in the soil.

Fig.2

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	Fig.2 Statistical comparison of As contents (mg· kg-1, mean± SD), their respective Chinese National Quality Value (dotted line) and the background values of Yunnan province (solid line) in soil, leafy-vegetables, tuber-vegetables, root-vegetables and maize at different localities

As shown in Fig.2, the As contents varied from different vegetables (p< 0.05), and the As contents in tuber-vegetables and leafy-vegetables were higher than that in others, and the mean were 1.75 and 0.77 mg· kg^-1, respectively, followed by maize (mean value=0.52 mg· kg^-1) and root-vegetables (mean value=0.51 mg· kg^-1). The variation of As contents in all sorts of vegetables might be due to variable capabilities of absorption and accumulation of As, variations in growth period and growth rates. It was very interesting that As contents in tuber-vegetables were much higher than that in others, indicating that this vegetable (potato) had the potential bioaccumulation for As. The contents of As in crops were similar to that in S_{20 km}. Compared with the threshold values issued by the Chinese Ministry of Health and WHO/FAO (2007), the As contents in agricultural crops were beyond the limits of food safety and the exceeding standard rate was 80.64%, which suggested a potential risk in view of product quality and human health. In this study, As levels in the agricultural food crops was high because the soil was rich in As, coinciding with the result that the soil was seriously polluted by As mentioned above.

2.2.2 The exposure level of As in hair samples

The contents of As in different gender and age hair samples were detected for local and S_{20 km}. (Fig.3). The Kolmogorov-Smirnov test showed that the contents of As (p< 0.05) in local area samples appeared to a normal distribution and varied from 0.01 to 9.10 mg· kg^-1, with the mean value approximately 4.41 times higher than that in S_{20 km}. Therefore, the high As levels in hair showed that the people living in the exposure area might be at high risk of toxic chemical element exposure.

Fig.3

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	Fig.3 Box-plot diagram of As for the subjects by gender and ages Male (n=36), Female (n=24), ≤ 18 years (n=18), 19~40 years (n=28), ≥ 41 years (n=14). Middle band, box and whiskers represented the median, 25th and 75th percentile, and 5th and 95th percentile, respectively. Circles represented the mean value, whereas “ * ” represented extreme values

Results found that at local area, hair As contents were observed comparatively higher in the male populations (2.71 mg· kg^-1) than the females (0.89 mg· kg^-1), which was consistent with the study of Baker^[8]. Variabilities among individuals were based on their susceptibilities in As accumulation and genetic differences. The possible reason is that their occupational exposure in mining, smelting and welding activities where the As is irreversibly adsorbed on human hair.

In this study, based on the frequency and intensity of outdoor life and work for study population, the participants were divided into three groups (Fig.3): Group Ⅰ (≤ 18 years, n=18), Group Ⅱ (19~40 years, n=28) and Group Ⅲ (≥ 41 years, n=14). In local area, the As contents in hair observed that Group Ⅱ were higher than other groups, indicating that this group people were the main participants in mining and metallurgy activities, having more opportunity to accumulate As by inhalation and dermal contact. On the contrary, Group Ⅱ was the lowest contents in reference area (S_{20 km}) due to the difference of work types. Notably, the mean content of As in the hair samples of different age groups in the local area was higher than that of the corresponding age group in the S_{20 km} area, revealing that As was an important element to endanger the health for the residents.

Human exposure to As near the study mining area occurred directly through ingestion, dermal contact and inhalation in soil or consumption of locally grown vegetables and crops, and the health risks to residents through above pathways were assessed by estimating target hazard quotients (THQ) and cancer risk (CR). Table 5 summarized the results of the actual exposure assessment for adult and child exposed to As through four exposure pathways around mining area. When the THQ value was greater than 1, it indicated that a potential health risk might exist. The THQs of As in vegetables through diet (> 1) were the highest among all pathways, indicating that a potential non-carcinogenic risk might exist. The THQs of As from consumption vegetables was in the order of Chinese cabbages> spinach> scallions> radishes> pakchoi> lettuces garlic> potatoes> tine peas > parsley> maize. However, we found that the non-carcinogenic risks from soil by three pathways were relatively lower than diet through consumption of agricultural crops. The HI values of As (the sum of all THQs) through four main pathways for adult and child were 4.67 and 4.23, respectively.

Table 5

Table 5

Table 5 Non-carcinogenic and carcinogenic risk assessments for adult and child exposed to As through four exposure pathways around the mining area Media Pathways CDI/EDI (mg· kg-1 bw· day-1) HQ/THQ Total HQ/THQ CR TCR Adult Child Adult Child Adult Child Adult Child Adult Child Soil Ingestion 4.13× 10-5 8.48× 10-5 4.13× 10-2 8.48× 10-2 0.041 0.085 7.78× 10-5 3.03× 10-4 1.12× 10-4 3.37× 10-4 Dermal contact 1.69× 10-7 4.40× 10-7 1.69× 10-4 4.40× 10-4 7.56× 10-7 4.14× 10-7 Inhalation 1.73× 10-8 1.73× 10-8 1.73× 10-5 1.73× 10-5 3.34× 10-5 3.34× 10-5 Leafy-vegetables Diet 1.41× 10-3 1.02× 10-3 1.41 1.02 1.16 1.04 2.01× 10-3 1.96× 10-3 1.66× 10-3 2.00× 10-3 Root vegetables 5.82× 10-4 5.67× 10-4 5.82× 10-1 5.67× 10-1 1.12× 10-3 1.09× 10-3 Tuber vegetables 2.00× 10-3 1.94× 10-3 2.00 1.94 3.85× 10-3 3.75× 10-3 Maize 6.39× 10-4 6.22× 10-4 6.39× 10-1 6.22× 10-1 1.23× 10-3 1.20× 10-3

Table 5 Non-carcinogenic and carcinogenic risk assessments for adult and child exposed to As through four exposure pathways around the mining area

Concerning carcinogenic risk (CR) of As, the CR of vegetables and soil varied from 1.12× 10^-4 to 8.30× 10^-3(> 10^-4), indicating that the potential risk was not negligible both for adult and for child. Similar to non- carcinogenic risk, vegetables consumption played key role in As exposure and risk, and the order of CR value from vegetables was the same as THQ as well. Notably, the TCR of As (the sum of all CRs) for child was higher than that for adult, concluding that concern has particularly focused on child, because As could harm brain and nervous system development in childhood.

In soil and agricultural crops, the relative contribution of human health risk for As was compared between adult and child (Fig.4). The intake of tuber-vegetables was the major source of As exposure, accounting for 42.77%~46.24% of the estimated total risks in the study area. Interestingly, for cancer risk of As, soil ingestion, dermal contact and inhalation for child were a relatively important factor. The possible reason was that their hand to mouth activities and playing time increases the chance of exposure to contaminated soil. Among all the main exposure pathways, the most important exposure pathway for As appeared to be the diet of locally grown vegetables, with about several times as much as that through soil and maize.

Fig.4

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	Fig.4 Relative contribution profile of human (adult and child) health risk, including non-carcinogenic and carcinogenic risks. Relative contribution was derived by dividing the risk estimate from a given source by the total risk from all sources under investigation

These results indicated that the high As contents in vegetables were mainly due to enrichment from the soil, and the adult and child living around the mining area might experience adverse health effects based on the contribution of vegetables to the intake of As. The reducing the source of As to relieve soil pollution and controlling the intake of contaminated vegetables were the reliable ways to control the human health risk.