Study On The Characteristics And Main Controlling Factors Of Cadmium Accumulation In Soil-rice In High Geological Background Area Of Guangxi

From the geological perspective,taking the high cadmium content area of Guangxi as research target,240 soil-rice samples were collected.At the same time,the potting soil was collected for cadmium accumulative characteristics of different rice varieties.The soil pH,cadmium value,available cadmium content,organic matter content,cation exchange capacity and rice cadmium content were measured.Pollution evaluation of soil rice is used in single factor index method;evaluation of rice cadmium content is used for health risk assessment;at the same time use correlation analysis and main component analysis to study the main control factors of rice in rice in the region and establish a predictive model,the main results are as follows:1.Field survey results（1）The soil pH is 6.50,which is neutral soil;the organic matter content is 27.54 g/kg,in the third grade;the cation exchange capacity is 6.74cmol/kg,at a lower level;the cadmium value is 0.17～6.02mg/kg,distribution uneven,there is a high cadmium-enzymatic characteristic of coarse bone and lime soil,and the DTPA-Cd content ranges from 0.004 to 2.3 mg/kg,the average rate is 43%,with DTPA The effective state measured for the extractant is at a high level.（2）The rice cadmium content ranges from 0.002 to 0.364 mg/kg,the distribution is extremely uneven,and the rice cadmium content mean of four rice soils is sorted by red paddy soil>coarse-bone soil paddy soil>lateritic paddy soil>calcareous paddy soil,The value was 0.075 mg/kg,0.022 mg/kg,0.009 mg/kg,0.008 mg/kg,respectively.（3）The results of single factor pollution evaluation showed that in the soil samples,the proportions of non-polluted samples,slightly polluted samples,slightly polluted samples,moderately polluted samples and heavily polluted samples were 50%,22.3%,7.5%,5.8%and 13.3%respectively,and the average pollution index was 2.04,indicating that the soil was in a state of mild pollution as a whole.The cadmium content of coarse-bone paddy soil and calcareous paddy soil was higher,and the pollution index was 3.58 and 2.89,respectively.85%of the rice samples were uncontaminated,10%of the samples were slightly polluted and 5%of the samples were heavily polluted.The contaminated samples were mainly from the rice growing on the red paddy soil,and the rest of the rice was basically in the clean state.Cadmium health risk assessment showed that the cadmium content in rice in the study area did not cause harm to human health.2.Results of pot experimentFor the soil Cd content ranged from 1.54 mg/kg to 3.14mg/kg,the average Cd content of different kinds of rice was ranked as follows:high Cd accumulation variety（0.202mg/kg）>local dominant variety（0.121 mg/kg）>low Cd accumulation variety（0.075mg/kg）,Among them,the cadmium content of high-accumulation varieties is significantly over standard,while a few local dominant varieties exceed the standard,and all samples of low-accumulation varieties do not exceed the standard.Therefore,Wuyujing 3,Fenghuazan and Y Liangyou 2 can be promoted locally to reduce the risk of cadmium pollution in rice.3.Correlation and main controlling factors of cadmium accumulation between soil and rice（1）The results of correlation analysis showed that the BCF value of rice in the study area was significantly correlated with soil pH,cation exchange capacity and total cadmium at the level of 0.01,and with organic matter at the level of 0.05.The correlation coefficients were-0.589**,-0.477**,-0.613**,-0.223*.There was a significant positive correlation between rice BCF value and DGT-Cd at 0.01 level,and the correlation coefficient was 0.631**;DGT-CD has a good prediction effect on the bioavailability of cadmium in the study area,while DTPA-CD has a general prediction effect on the bioavailability of cadmium in the study area.（2）The results of principal component analysis showed that total soil Cd,pH and DGT-Cd were the main factors that caused the difference of BCF value in rice,that is,the bioavailability of soil Cd in the study area was mainly affected by these three factors.After regression analysis of the principal component and BCF values,the principal component regression equation was as follows:Z（BCF）=-0.282F₁+0.383F₂(R²=0.485^**);The determination coefficients R2 of the three models obtained from the multiple linear fitting analysis are significantly correlated at the level of 0.01,among which Model 3 has the best fitting effect.The model equation is as follows:lg（BCF）=2.509 lg（DGT-Cd）-0.845lg（Soil-Cd）-0.3144pH+1.950（R²=0.717**）4.Safe planting measures in geological high background areas（1）The characteristics of soil-rice Cd content in the study area showed that the soil Cd content was high but the rice Cd content was low.The rice polluted by Cd mainly came from the red paddy soil area,so it should be considered to plant rice varieties with low Cd accumulation or other crops with low Cd accumulation to reduce the risk of Cd pollution.On the other hand,the paddy rice growing on the lateritic soil,limestone soil and coarse-bone soil was basically in a clean state and could be planted continuously.（2）The cadmium content of some local dominant rice varieties exceeds the standard,so Wuyujing 3,Fenghuazan and Yliangyou 2,three varieties with low accumulation of cadmium,can be popularized to reduce the risk of cadmium pollution in rice.