| The Pearl River Delta region is a typical migration-type high heavy metal background value region.The heavy metal element Cd mainly undergoes long-distance migration and transformation in the form of river handling,and is enriched in regional soils and crops,which seriously threatens local ecological security and human health.Based on the urgent need of prevention and control of heavy metal pollution in China's high geological background,this study carried out research on the characteristics and influencing factors of Cd distribution in soil-rice system in the typical area of Cd pollution in study area.This paper firstly explored the distribution characteristics of Cd content in the soilrice system of the study area.And then discussed the factors affecting the distribution of Cd by attribution models.Finally,the degree and risk of soil and rice Cd pollution were evaluated.The specific research results are as follows:(1)The data characteristics and spatial distribution characteristics of soil Cd content,available Cd content and rice Cd content in the study area showed that all three variables were normally distributed,indicating the dominant factors affecting the Cd content in the soil-rice system were natural factors rather than human influences.Soil Cd content and available Cd content had a spatial positive correlation,the hot spots were distributed in the northern soil,and the parent material of the area was river alluvial;The cold spot was distributed in the southern soil,and the parent material of this area was detrital sediment.The global Moran's I of rice Cd content was close to 0,and the spatial distribution was random,which was quite different from the distribution characteristics of Cd in soil.(2)The factors affecting the Cd content in the soil-rice system were analyzed.The soil Cd content,the effective partition coefficient(EPC)of Cd and the rice absorption rate(RAR)of Cd were dependent variables,the soil physical and chemical properties,river network density,metal elements,and distance from pollution sources are independent variables.Based on the results of influence size,spatial autocorrelation and spatial distribution of influence,it was found that the Cd content in the soil-rice system is greatly affected by natural factors such as pH value,river network density and metal elements,and is less affected by human activities such as mining,transportation and built-up areas.Among them,the density of river and metal elements networks had strong explanatory power and spatial correlation to soil Cd content.Combined with the spatial distribution of the parent material,it was speculated that the high Cd content in the northern soil was due to the fact that the sediments in the upstream which rich in Cd and other metal elements are migrated with the water system to the study area and were continuously enriched.(3)The evaluation results of soil and rice heavy metal pollution degree and risk showed that the Cd pollution index in soil did not exceed 2.0,the potential ecological risk level was mainly high potential ecological risk,and the northern pollution level was higher than that in the south.The over-standard rate of Cd content in rice is 10%,and the risk to human health exceeds the threshold,so it should focus on it.Finally,based on the results of pollution assessment and influencing factors identification,suggestions for prevention and control of farmland Cd pollution in high background areas were proposed.This study can provide a reference for quantitative analysis of the spatial distribution characteristics and influencing factors of Cd content in soil-rice system,and provide scientific and technical support for pollution assessment,control and farmland safety production in high-energy background. |
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