| As urban and rural transition zone, the Peri-urban area is not only important food and vegetable production bases, but also sensitive, weak ecology and environment zone due to existence of multiple pollution sources. The environmental conditions of the Peri-urban area will give directly impact on local food quality and human health. So, it's very important and necessary to conduct a comprehensive and systematic investigation on accumulation and health risk of key pollutants in soil-water-crop system located in Peri-urban area. In this study, the easten suburb of Kaifeng City was selected as study area to make a systematic research on accumulation,transfer and health risk of As in soil-groundwater-crop system located in Peri-urban area.Based on the field investigationand grid sampling method, 247 topsoil samples were collected and their As contents were determined, then spatial distribution of total As in topsoils was analyzed. On the basis of the above analysis, the three representive profile sampling areas were selected,and they were P1(area along Huafei River), P2(the interaction polluted area of Huafei River and chemical fertilizer plant) and P3(control area). Here, 280 soil profile samples from 13 soil profiles were collected.At the same time, eight typical topsoils sampling areas were selected. They were T1(chemical fertilizer plant with zinc smelting factory and pharmaceutical factory of northeast radiation zone), T2(thermal power plant southwest), T3(Huafei River and zinc smelting factory/fertilizer plant interaction region), T4(Huafei River branch canal and railway along the interaction region) and T5(Huafei River and railway along the interaction region), T6(Huafei River canal and railway along the interaction region), T7(Huafei River Branch) and T8(The southern section of Huafei River), respectively. Here, 34 topsoil samples and 22 matched wheat samples were collected. In addition, the 26 groundwater samples were collected from different areas and depths.The As contents in soil, groundwater and crop samples were determined by Atomic Fluorescence Spectrometer, and the chemical fractions of As in soil samples were analyzed by Tessier sequential extraction method. At the same time, the physical and chemical properties of soil samples were analyzed.Then, the accumulation and transfer of As in soil-groundwater–crop system located in the study area were analyzed, their health risk was assessed using the improved Hakanson potential ecological risk index method.The main conclusions of this study are as follows:(1) Spatial variation of arsenic in the topsoils of the study area.The average content of arsenic in the topsoils was 7.13 mg/kg, which was 1.94 times as much as that in the control area(3.67 mg/kg), which was significantly higher than that in the control area(P<0.01).However, topsoil samples in the study area was only 25.91% more than the soil background value area(9.7 mg/kg). The average content of arsenic in the typical region was 19.19 mg/kg, equivalent to 5.22 times of the control area, about 1.97 times as much as that in Chinese aquic soil background value, of which 82.86% points higher than the background value.Obviously, the topsoils in the study area was polluted by arsenic in different degree, especially the pollution of the topsoils in the typical sample area.The spatial distribution of arsenic in the topsoils of the study area showed significant heterogeneity.The low value area was located in the the northern of study area(pharmaceutical factory to the North), the content of arsenic in the soil(0.45~9.7 mg/kg) lower than the background value; high value zone(21~29.8 mg/kg) there are two high value areas, one was located in chemical fertilizer plant/zincsmelter and Huafei River interactive aera, and another was located in the middle and lower reaches of the Huafei River; the second high value area(14.3 to 21 mg/kg) was located between the Huafei River canal(the Longhai Railway and the Xin Song Road).The content of soil arsenic in the study area was in the island state and the ring decreases. In general, the study area of arsenic pollution in soil showed high in the north and low in south, and the area of pollution was concentrated in the industrial and mining enterprises and the interactive areas along the river.The pollution of As showed a decreasing trend with the increase of the distance from the plant or the river.(2) Vertical distribution of arsenic contents in the soil profiles of the study area.In general, more close to the fertilizer plant/zinc smelting factory and other enterprises or Huafei River and irrigation canals,the soil profile soil of As accumulation and leaching was more significant.The P1 sample plot which is near to the fertilizer river(P1-A, P1-B) was the most serious pollution.Third sampling plot(P1-C) was far away from the Huafei River and was not contaminated by industrial,so profiles were relatively clean;P2 sample plot which was affected by sewage irrigation and some plots which were affected by sewage irrigation and zinc smelting plant and fertilizer plant, carbon plant cross contamination were showed the characteristics of As accumulation and leaching,because of far away from fertilizer and only affected by the carbon plant,plot(P2-C)was relatively light pollution;P3 sample plot was located near the thermal power plant and the content of As in soil near the power plant is lower than the background value which was far away from the river, so it was relatively light pollution.The three profile samples were all lower than the background values. Among them, the change of P3-A and P3-C was not very obvious. Because of rice planting in the P3-B plot, The law of vertical migration from arsenic was different from that of the other two plots.(3) Assessment of soil arsenic pollution in the study area.Nemero comprehensive pollution indexwas 2.24 in the topsoil samples in the study area, and the pollution level was moderately polluted;Potential ecological risk in the entire sample area was not in a strong and strong risk of the sample point, most of the sample point in a slight risk, only 1.21% of the sample was in a strong risk.Nemerow comprehensive pollution index for typical soil profile was 3.44 and pollution level was seriously polluted. The order of magnitude of each sample interval Nemerow pollution index for: P1(2.00) >P2(1.76) >P3(0.70).From a single point of view, there was no point in the entire section of the sample area was very strong risk, most of the sample point in a slight risk, only 0.71% of the sample was very strong risk.On each plot, 0 ~ 30 cm pollution level was overweight in P1 area. In medium or strong risk,0 ~ 40 cm pollution levels exceeding in P2 area, was in a medium or strong risk, P3 was clean in a slight risk level.(4) Total arsenic content and chemical speciation distribution in typical samples.The amount of soil arsenic high value area was Huafei River southern region,The low value area for chemical fertilizer plant and zinc smelting plant and pharmaceutical factory of northeast radiation zone, Huafei River south area mainly affected by irrigation.Obviously, the source of arsenic in the farmland soil was related to the sewage irrigation in the research area.The order of five kinds of chemical forms of the average percentage of the topsoil area of arsenic in soil from large to small: RE(71.34%) >FM(16.82%) >CA(6.68%) >EX(3.86%) >OR(1.29%).Huafei River branch area in ion exchangeable and carbonate bound highest;The southern region of Huafei River of iron and manganese oxidation state the highest fertilizer river;Huafei and River interactive area along the trunk railway organic fraction.Chemical fertilizer plant with zinc smelting factory and pharmaceutical factory of northeast radiation ion exchange state and the iron and manganese oxidation state minimum; thermal power plant in the southwest area of carbonate with thehighest state.Huafei River branch biological use of chemical fertilizer plant with zinc smelting factory and pharmaceutical factory of northeast area of radiation biology was the least effective.Huafei River in the southern area was located in the arsenic content of the high value area. Huafei River branch area was located in high value zone of annular descending region, chemical fertilizer plant with zinc smelter and radiation area of Northeast Pharmaceutical Factory and power plant in southwest are located in the arsenic content in the low value zone, sample interval of soil arsenic species showing different rules, may be associated with soil physical and chemical nature, the arsenic content in soil and with the factory or the river distance.From the point of view of morphology and distribution of arsenic in the soil profile, plots of soil arsenic in five chemical forms of average percentage content from big to small order: RE(85.73%) >FM(9.88%) >CA(2.17%) >EX(1.53%) >OR(0.69%).Except for the residual fraction, ion exchangeable,carbonate combination state and the iron and manganese oxidation state in the soil profile showing increased at first and then dropped in topsoils(0~20 cm), decreased in subsurface soils(20~ 40cm), tends to be stable in deep soils(40~110cm), stable after three forms of the average percentage of points don't:0.79%, 0.89% and 5.56%.Except for residual and organic bound, P1 area in the following 35 cm, P2 area in the following 45 cm, and P3 area in the following 25 cm form tends to be stable.Percentages of ion exchange,carbonate bound and Fe Mn oxidation state in P1 area were 1.07%, 1.03% and 5.94% respectively, and the P2 plot was 0.62%, 0.83% and 6.12%, and the P3 plot was 0.60%, 0.79% and 4.38% respectively.Three sample areas of various forms are in different depth tends to be stable, the main reason was P2 soil long-term wastewater irrigation and located at the high value area of arsenic in the surface layer, the soil polluted by arsenic pollution was more serious, in deeper tends to be stable, P1 area pollution degreeinferior to P2, so a stable state depth less than P2, the soil in P3 area wasn't affected by the effects of external contamination, so in the shallow was stable.(5) The contents of As in soil-water system and their health risk assessment.in the soil and wheat matching acquisition of the study area, Huafei River was high value area of soil wheat As content, but the southwest of the thermal power plant was the low value area.Although the branch canal of Huafei River area soil wheat arsenic content was relatively low, the soil As bioavailability, migration coefficient and wheat migration accumulation rate were the highest in this area.Therefore, the content of As in wheat grains in the sample plot was only next to that of the southern section of Huafei River.As content of groundwater was highest in the shallow(0.294 ?g/L)but lowest in the middle level90.021 ?g/L).The carcinogenic risk level of As in soil-wheat system was 1.78×10-4 a-1, which exceeded the standard value recommended by ICRP.The carcinogenic risk level of skin exposed soil was 1.76×10-6 a-1,and the risk level of edible wheat was 1.76×10-4 a-1.And arsenic in study area 95.45% wheat samples of individual cancer risk more than recommended by ICRP standard value, risk level of the highest Huafei River in the southern area, lowest for thermal power plant in the southwest area.The groundwater of urban and rural areas in Kaifeng City is the standard of water quality and the carcinogenic risk level of groundwater is 2.45×10-6 a-1, As health risk level of in shallow groundwater was highest but lowest in the middle, which lower than the recommended standard values for ICRP, so drinking and skin exposure did not have health risks. |
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