Evaluation of potential pollution risk and source analysis of heavy metals in paddy soil and rice

Abstract: The characterization and spatial distribution of the content and source of heavy metals in soils are necessary to assess the potential threat of heavy metals to food safety and human health. In order to investigate the origin of heavy metals in paddy soils and rice in the Duyun city, 110 sampling sites were set in this study. The soil samples in arable layer of paddy and rice were collected, the contents of Cd, Hg, As, Pb and Cr were measured, and the data were analyzed by the multivariate statistical technique. A geographic information system (GIS) was used to explore the variety of spatial distributions for 5 heavy metals. Single factor pollution index, Nemero comprehensive pollution index and potential ecological risk index were applied to evaluate the degree of soil heavy metal contamination. Our results showed that the average contents of Cd, Hg, As, Pb and Cr in soils in the Duyun were (0.45±0.48), (0.23±0.29), (11.94±10.86), (36.95±32.98) and (60.80±31.73) mg/kg, respectively. The average contents of Cd, Hg, As, Pb and Cr in rice were (38.91±86.50), (5.82±2.96), (113.26±27.18), (89.42±24.87) and (175.92±82.12) μg/kg, respectively. The proportion of Cd, Hg, As, Pb and Cr contents more than the background values of the Guizhou province were 14.55%, 40.00%, 16.36%, 22.72%, 13.64%, respectively. Anthropic activities caused the enrichment of Hg in paddy soils. Only 3.64% of all rice samples exhibited Cd content exceeding the threshold level (20 μg/kg) in the Chinese national guidelines for cereals, and the other elements were below the national limit. Distribution maps of heavy metal content were generated using the Kriging interpolation method to identify their distribution trends. The results show that the influence of smelting activities, transport services and coal combustion on the spatial distribution. These suggested that the impacts of human activities on soil heavy metals in Duyun had exceeded the impact of natural source. Multivariate and geostatistical analysis suggested that soil Cr had a lithogenic origin. The correlation analysis and principal component analysis suggested that Cd, Hg, As and Pb could be attributed to anthropogenic inputs. The accumulation of Cd, Hg and As in soils was mostly affected by lead-zinc smelting, coal combustion and agronomic practices, and the main sources of Pb were lead-zinc smelting, industrial fume, coal burning exhausts. The current study confirmed that the environmental quality could be seriously threatened by heavy metal contaminants from the smelter and industrial activity. Therefore, the use of fossil fuels (coal and oil), fertilizers and the "three wastes" emissions from the key industrial enterprises in this area should be strictly controlled.