Study on the Relationship between the Contents of Heavy Metals in Rice and Root Soils in Typical Townships in the Western Pearl River Delta

BACKGROUND: The environmental quality of farmland soil is closely related to the safety of edible rice. Studies have shown that under the influence of mining, transportation, and electronics industries, the Pearl River Delta has accumulated a large number of environmental problems. Pollution such as cadmium, mercury and arsenic is becoming more and more serious. The migration and transformation of heavy metals in the soil-rice system is affected by the interaction of their total content, physical and chemical properties of the soil, organic matter, and trace or major elements.
OBJECTIVES: To find out the factors influencing the migration of heavy metals in the soil-rice system in the typical towns of Gaoming District, Foshan City, Guangdong Province, and to provide a basis for the prediction of rice food safety.
METHODS: In the main farmland areas of Mingcheng Town and Genghe Town of Gaoming District, 151 groups of rice and corresponding root soil samples were collected. Inductively coupled plasma-optical emission spectrometry (ICP-OES), atomic fluorescence spectrometry (AFS) and other techniques were used to determine heavy metals in the soil, nutrient element content, physical and chemical indicators of the soil, and heavy metal content in rice. The characteristics of heavy metal content and its influencing factors were analyzed, and the quantitative prediction model of heavy metal content in rice was established and verified.
RESULTS: Results showed that the heavy metal content of the soil was lower than the average heavy metal content of the soil in Guangdong Province obtained by the first national soil pollution survey, and was lower than the soil risk control value in the national standard Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018), resulting in a low soil pollution risk. Except for the slight excess of Cd and Pb in rice, the content of other heavy metals was lower than the limit of food hygiene standards. Total heavy metals and physical and chemical properties (soil pH, soil texture, soil organic matter content, soil N, P, K, etc.) were the key controlling factors for the migration of heavy metals in the soil-rice system. According to the 130 sets of randomly selected data, the total amount of soil heavy metals and soil physical and chemical indicators were used as independent variables to establish rice As, Cd, Cr, Cu, Hg, Ni, Pb content multiple regression equation. All reached a significant correlation. After the verification of the remaining 21 sets of data, the median and average of the average error of the prediction equation were 31% at the maximum and 7.8% at the minimum. In general, the prediction effect was good, and the model can be used to predict the heavy metal content of rice in the Gaoming District and similar regions.
CONCLUSIONS: A large number of soil nutrient elements were introduced as the influencing factors when exploring the influence of physical and chemical properties of the soil, and provided a reference for studying the effect of nutrient elements on the migration of heavy metals in the soil to rice, and guidance for future scientific fertilization. The influencing factors of the soil-rice system element migration obtained at the same time provide a reference for carrying out heavy metal bioavailability research, paddy soil pollution remediation, and ecological risk assessment in similar areas. This article briefly discusses methods to reduce the bioavailability of heavy metals in the study area and measures to inhibit the migration of heavy metals and reduce the biological hazards of heavy metals. It also provides ideas for exploring the relationship between the migration characteristics of heavy metals and endemic and epidemic diseases.