| Objective:To investigate the content of heavy metals in water body, soil, crops, drinking water, and poultry from a downstream village of Dachang mine of Guangxi, and evaluate the potential health risks to the local residents.Methods:Three sampling sites, TJ, SH, and LS village, were selected in the downstream of the Dachang mine. The water body (river water and mountain spring water), farmland soils (paddy soil and vegetable garden soil), crops (rice and vegetables), drinking water, and poultry in the study area were collected, and the concentrations of five heavy metals, arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), and mercury (Hg), were determined. Based on the data, water body and soil environmental quality and rice, vegetable, drinking water, and poultry safety was evaluated by the single factor index, Nermero comprehensive pollution index, over standard rate, times of ultra standard, etc. Meanwhile, a health risk assessment model proposed by the United States Evironmental Protection Agency (USEPA) was adopted to quantitatively assess the non-cancarcinogenic and carcinogenic risk for adults and children by multiple exposure routes.Results:1. The concentrations of As, Pb, Cd, and Hg in the river water were significantly higher than that of the corresponding heavy metals in the mountain spring water (P<0.05). The single pollution index of Pb, Cr, and Hg in the river water were less than 1, while the single pollution index of As and Cd were achieved by 4.22 and 3.22. Five heavy metals in the mountain spring water were all less than 1. The single pollution index of Pb in drinking water was 1.21, while other 4 heavy metals were all less than 1.2. Except for Cr, the contents of other four heavy metals in soils exceeded the environmental quality standard for soils in China. The over standard rates of As, Pb, Cd, Cr, and Hg in paddy soils were 100% (28/28),39.3% (11/28),100% (28/28),25.0% (7/28), reapectively. And the over standard rates of As, Pb, Cd, Cr, and Hg in vegetable garden soils were 85.7% (6/7),14.3% (1/7),85.7% (6/7), 14.3% (1/7), reapectively. The Nemero comprehensive pollution index for paddy soil and vegetable garden soil were 4.12 and 2.50, respectively. In comparison with the vegetable garden soils, the levels of As and Hg in paddy soils were significantly higher (P<0.01).3. The concentrations of Cd in rice collected from TJ, SH, and LS villages were all higher than the national maximum permissible levels (MPL) in rice, and the over standard rates were 100% (15/15),92.3% (10/11), and 9.1% (1/11), respectively. The Nemero comprehensive pollution index of rice was 1.21.4. Compared with the national food safety limits,6.8% (4/59) and 13.6% (8/59) of the vegetable collected from the study area exceeded the MPLs for Pb and Cd, respectively. The concentations of As, Pb, Cd, and Cr in the leafy vegetables were significantly higher than those in the non-leafy vegetables (P<0.01). while the non-leafy vegetables contained significantly larger amount of Hg than the leafy vegetables (P<0.01).5. The results of correlation analysis showed that positive significant correlations between Cd and Hg concentrations in rice and paddy soil samples, with the values of coefficient correlations (rs) were 0.427 (P=0.024) and 0.401 (P=0.035); as well as there were positive significant correlations between Hg concentrations in vegetables and vegetable garden soil samples, with the values of rs was 0.453 (P=0.030).6. The total non-carcinogenic risks of heavy metals for adults and children were 9.43 and 14.22, respectively; and the total carcinogenic risks were 1.0*10"2 (adults) and 1.4 ×10-3 (children).7. Arsenic was the primary heavy metal posing non-carcinogenic risks, with the values of contribution rates were 56.0%～59.7%; while Cd caused the greatest carcinogenic risk, with the values of contribution rates were 75.6%～ 80.9% of contributions. The highest risk was associated with the pathway of consumption of rice for all the heavy metals.Conclusions:1. The river water in the study area was seriously contaminated with As and Cd, but mountain spring water was not polluted by any heavy metals yet. The drinking water from study area was lightly contaminated with Pb.2. The farmland soils in the study area were subjected to the varying degree pollution by As, Pb, Cd, and Hg, in which As and Cd pollution were the most serious.3. The rice collected from the studied area was mildly polluted by heavy metals, and the main contamination of heavy metals was Cd. Some vegetable samples were contaminated by Pb and Cd, while poultry samples were not polluted by any heavy metals.4. The total non-carcinogenic risk and total carcinogenic risk for adults and children exceeded the safety limits recommended by USEPA, suggesting that the local residents were at high risk of both non-cancer and cancer effect.5. Arsenic and Cd were the predominant contributors to the health risks. Therefore, the priority should be to take measures against these two kinds of heavy metals. The highest risk was associated with the pathway of rice consumption for all the heavy metals, thus strengthening the management of contaminated rice can greatly reduce the health risk to residents. |
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