The Soil-Plant Transfer Model Of Heavy Metals In Contaminated Area Based On Sampling Strategy And The Associated Damage Cost Assessment

With the rapid development of agricultural production and rural economy, the living standard of residents is raising, people’s awareness of security is also gradually enhanced, food safety and the associated health risk is now one of the major concerns worldwide. Soil is the carrier of agricultural production, while China is suffering from environmental quality degradation and soil contamination, environmental quality has become the key to ensure the safety of agricultural products. Therefore, it is very necessary to conduct some investigations on the contamination and relationship of heavy metals in the soil-rice system at a rice production region.The present research was conducted in rice-production areas located in Daxi Town, southeast of Zhejiang Province in China. Total of 71 coupled rice-soil samples were collected here at a distance of 100-m grid interval, then 32 and 19 coupled rice-soil samples at the distance of 140-m and 200-m grid interval were derived from the 100-m grid samples, respectively. The properties of rice and soil samples were further analyzed in the laboratory including total concentrations and available concentrations of 5 heavy metals elements (Cd, Pb, Cr, As, Hg) in soils, concentrations in rice grains, and soil physicochemical properties (pH, cation exchange capacity, soil organic matter, amorphous Fe oxides, available P and soil texture). Based on GIS technique and relevant spatial analysis methods, we studied the spatial characteristics of heavy metals in soil-rice system at rice-production areas, which mainly included heavy metal contaminations, spatial variance, soil-to-plant transfer models, soil threshold concentrations inversion, damage cost assessment. The main results were summarized as follows:(1) Soil heavy metals in the study area showed spatial variability and spatial patterns based on geostatistical analysis, and spatial variability is different with sampling distance.For each metal,the prediction accuracy was pretty stable in response of increasing sampling distance. The distribution patterns of soil Cd and Pb were similar at different sampling distances, displaying a northwest-southeast decreasing trend. The spatial distributions of soil Cr, As and Hg were more smooth in response of increasing sampling distance, with a more clear trend that decreased from northwest and southeast corner to the center. That is to say, with the increase of sampling distance, the spatial prediction accuracy of soil heavy metals basic consistent. This work provide a basic and incipient foundation for sampling strategy that a moderate longer sampling interval also have highly accuracy in comparison with short sampling interval. This study also evaluated the daily exposure ways of carcinogenic risk of heavy metals, the results show that children’s carcinogenic risk is higher than adults, diet was the dominated exposure pathway for local residents. Moreover, the spatial map determined some high cancer risk areas at the southeast and west corner of the study area.(2) Results of multiple regression analysis for derivation of soil-to-plant transfer model as a function of both available soil pools and total pools and soil properties for the heavy metals for which significant relationships could be derived by the logarithmic linear models (P< 0.01). Soil pH and organic matter play an important role on the model simulation. With the increase of sampling distance, the derivation model of Cd, Pb and Cr become better. Based on the SPT model, limit concentrations in food crops can be used to back-calculate soil threshold. The back-calculate soil threshold of Cd, Cr and As is lower than the secondary standard of soil environment quality standard (GB 15618-2008), the back-calculate soil threshold of Pb is higher than the secondary standard of soil environment quality standard (GB 15618-2008).(3) Through the questionnaire survey analysis, we found that heavy metal has affects people’s lives to a certain degree, people realized that their own consumption behavior make a contribution to heavy metal pollution. This study estimates the damage cost of soil heavy metal, the order of heavy metals damage cost is:Cr>As>Cd, Cd, Cr and As damage costs of Cd, Cr and As are 4399 RMB ha-1,5810688 RMB ha-1 and 25537 RMB ha-1,...