| The development of industry, urban expansion and high intensity agricultural activities, often leaded to the heavy metals enrich in soil and accumulate in rice through various ways, and affected ecological environment and human health finally. So heavy metal pollution problem of soil and rice increasingly caused the attention of people. And the study of the heavy metals accumulation in the soil-rice system and influence factors, could provide important base material for the control of the heavy metal pollution. The samples of soil and rice were intensively collected in JiaXing City of the middle and lower Yangtze on the basis of taking into account the soil schemes and industrial enterprise distribution. Then, on the basis of determination heavy metals in soil and rice, we analyzed the heavy metal accumulation status and spatial variability, evaluated soil heavy metal pollution and grain heavy metal health risk, discussed influencing factors on accumulation of grain Cu, Pb, Zn and established the prediction model of the grain Cu, Pb, Zn. In addition, because the traditional determination methods for heavy metal were time-consuming and difficult to satisfy a large of samples batch determined, the application of Portable X-ray fluorescence (PXRF) for soil heavy metals rapid analysis was investigated with Suzhou and Jiaxing for instance. The main conclusions were as follows:1、Application of Portable X-ray fluorescence (PXRF) for Heavy metals analysis of soils in Agricultural fieldsIn this paper, the accuracy and precision of89agricultural soil samples collected from JiaXing city and SuZhou city were determined by the portable X fluorescence spectrometer method(PXRF). The research showed that the accuracy and precision of Pb, Cu, Zn and As in low content slightly exceed NY/T395-2000limit, but most of the their determination results could meet the requirements. Although the precision of Cr was preferably, the accuracy of almost all the determination results couldn’t meet NY/T395-2000limit. Compared with traditional method, the coefficients of determination between different methods were0.58above (p<0.01). But the contents of Pb, Cu, Zn and As were significantly different (p<0.0001) between using PXRF method and traditional method (AAS or AFS), among them the PXRF result of Pb and As increased24%and18%respectively, and Cu and Zn reduced7%and8%, respectively. In general, the PXRF method was simple, convenient, easy to operate, saving time and energy, appropriate for detecting the concentration of most heavy metals in farmland soils, such as Pb, Cu, Zn and As. Therefore, the heavy metal contents of soil in JiaXing City were all determined by the PXRF.2、The accumulation status and evaluation analysis of heavy metals in soil-rice systemStatistical results showed that the total content average of Cu, Pb and Zn in soil was36.51mg/kg,27.93mg/kg and91.27mg/kg and all did not exceed the secondary standard of bid (GB15618-1995), so indicated that there was no heavy metal pollution of soil in JiaXing City on the whole. From space distribution, soil Pb and Zn presented a northwest to southeast reduce trend; soil Cu present a northeast to southwest reduce trend. Under different soil types, soil Cu content was significantly higher than alluvial soil and Waterlogged paddy soil. Soil Cu and Pb collected from enterprise soil significantly were significantly greater than general enterprise and around the field.The average content of grain Cu, Pb, Cr and Zn was2.76mg/kg,0.27mg/kg,0.52mg/kg and17.02mg/kg. Grain Pb existed risk for beyond the GB2762-2005limits (0.20mg/kg), but the health risk analysis showed that heavy metal health risks mainly was affected by the Cr, which indicated that two kinds of method had no consistency. From space distribution, grain Cu high value area (>2.99mg/kg) mainly concentrated in eastern and centre; the distribution of grain Pb present a northeast to southwest direction gradually decrease trend; grain Cr present a center around to reduce trend; Zn performance for the northwest to southeast of lower trend. Under different soil type, there was significant difference for grain Cu and Pb. From sampling method, grain Pb collected polluting enterprise around was significantly higher than general enterprise and the field.3、Affect factors on rice grain heavy metal accumulation and the model of the grain heavy metal content predictionThe heavy metal contents of rice grain were directly related to the health of human body and produced harmfulness to the nervous system, the digestive system, the blood circulation system, etc., so it was necessary to analyze the influence factors on accumulation of heavy metals by rice grain. Therefore, on the one hand the influence of pH, soil organic matter(SOM) and soil heavy metals content to accumulation of heavy metals (Cu, Pb, Zn) by rice grain was discussed; and on the other hand the multivariate nonlinear statistical model of accumulation of heavy metals by rice grain was established. Multiple comparison analysis showed that sampling schemes all had a significant impact on rice grain Cu, Pb, Zn, which showed polluting enterprises> general enterprises> field. Regression analysis showed that along with the rise of pH, the reduction of SOM and soil heavy metals, the Cu, Pb, Zn of grain all presented a reduction tendency and the Cu, Pb, Zn of grain were significant correlated with pH, SOM and soil heavy metal contents. Through multivariate nonlinear regression analysis, the model of Cu, Pb, Zn of grain established were as follows:R-Cu=0.538EXP[1.463lgS-Cu-2.018lgpH+0.654lgSOM](r=529, p<0.0D, R-Pb=0.020EXP [3.840lgS-Pb-7.329lgpH+1.893lgSOM](r=0.563, p<0.01), R-Zn=21.455EXP[0.397lgS-Zn-1.939lgpH+0.359lgSOM](r=0.409, p<0.01). Residual analysis and regression analysis between prediction values and the real values showed that the statistical model Cu, Pb, Zn was effective. |
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