| In recent years, the events that farmlands are contaminated by heavy metals have often occurred. The agricultural products, always contaminated by heavy metals, make a threat to human health through food chains. Nowadays, it is still difficult to avoid using the contaminated soil, which challenges the food security seriously. The components of heavy metals in soil are complex and hard to remove. At present, the repair for the farm-lands, contaminated by heavy metals, mainly focuses on the single heavy metal, for ex-ample, it ignores As when we deal with Cd contamination. So it is necessary to study the contamination characteristics of complex heavy metals, especially of Cd and As, as well as the transfer characteristics and influencing factors of Cd and As in the soil-rice system, and then put forward to countermeasures to reduce or avoid agricultural product contam-ination around the industrial and mining areas. In this study, both of rice plant samples and corresponding soil samples (red soil and purple soil) were collected from the industrial and mining areas in central Hunan prov-ince. In order to provide a theoretical basis for Cd management in paddy fields, the con-tamination characteristics of Cd and As in paddy soil and rice plant, along with the trans-fer characteristics in paddy soil-rice system, and influencing factors of Cd and As in rice seeds, were researched.The main results were listed as follows:(1) The survey by grid method sampling showed that paddy soils were seriously contaminated by Cd and As. With regard to Cd, All collected paddy soil samples (n=94) were seriously polluted, while for As,80.3% of total soil samples were polluted with dif-ferent extents, and the pollution of Cd was more serious than As. Paddy soils (2011, n=94) and brown rice (2012, n=48) were also heavily contaminated by Cd and As. Polluted samples accounted for 96.21% and 100%, respectively of total collected samples, and pollution of Cd was more serious than As. It existed potential health risk to the local in-habitants through food chains with the sort of seriousness:Cd> As.(2) The mean contents of total Cd in red soil (n= 54) and purple soil (n=40) were 12.87 mg kg-1 and 13.24 mg kg-1, respectively, while the mean contents of available Cd were 8.27 mg kg-1 and 7.94 mg kg-1, respectively. Moreover, the mean contents of total As were 79.64 mg kg-1 and 103.46 mg kg-1, respectively. Both of the concentration of Cd and As in Red Soil were lower than that in Purple Soil (P>0.05). There was a significant linear correlation between the content of available Cd and total Cd for Red Soil and Pur-ple Soil, the percentage of available Cd out of the total Cd was 64.26% in red soil, while 59.97% for Purple Soil. There was no significant difference between the content of vari-ous As forms of red soil and purple soil (P>0.05), and iron-arsenic (37.69%) and residual arsenic (37.68%) increased with the degree of As contamination increased. Moreover, both total Cd to total As and available Cd to total As in Red Soil and Purple Soil showed a certain degree of positive correlation. Cd content would decreased as the As content decreased. The correlation between Cd and As in Purple Soil was better than that in Red Soil.(3) Most of Cd and As were accumulated in 0-20 cm in Red Soil and Purple Soil. The Cd contents in 0-100 cm in both soils were higher than the standard limits, while in red soil profile (0-30 cm) and purple soil profile (0-50 cm), the As contents were greater than the standard limits. It was necessary to consider the feature of vertical distribution to control the pollution of Cd and As in soil by the method of soil replacement.(4) There were some differences in the aspects of enrichment, migration and accu-mulation characteristics between Cd and As in rice plant. The content of As in rice roots was 12.30 times as much as Cd, while the content of As and Cd in stems and leaves, glumes, and brown rice differed slightly. The content and enrichment coefficients of Cd and As in different rice organs in Red Soil and Purple Soil in 2011 and 2012 were ar-ranged in the order of:rice roots> stems and leaves> glumes> brown rice. The content and enrichment coefficient of Cd in different rice organs in red soil was more than that in purple soil in 2011 and 2012 (P>0.05). About 2/3 of Cd was accumulated in rice stems, and about 1/5 of Cd in rice roots, and about 1/20 of Cd in brown rice; while about 2/3 of As was accumulated in the roots of rice, and about 1/3 of As in rice shoots, and about 1/50 of As in brown rice. The migration coefficients of Cd in different rice organs were arranged in the order of:stems and leaves>rice roots> glumes> brown rice, while the order for As was:rice roots> stems and leaves> glumes> brown rice. Cd content in brown rice accounted for 6.35% of total Cd in whole rice plant, while As content in brown rice accounted for 1.93%. Compared with As, Cd was easier accumulated in brown rice(5) The impact factors of Cd and As in brown rice were analyzed by multivariate linear regression and correlation analysis, it showed that the main factors were soil total Cd, soil organic matter for Res Soil, while the main factors for purple soil were soil total Cd, organic matter and clay content (<0.002 mm). There was a certain correlation be-tween inorganic arsenic content in brown rice and soil physic-chemical properties, total As, As various forms content. And the moisture content of red soil reached a significant level (P<0.05). Cd content in brown rice (Red Soil, Purple Soil) showed a positive cor-relation with total soil As, as well as the inorganic As content in brown rice with the total Cd and available Cd content in soils. |
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