Spatial variability and affecting factors of Pb, Cd and As in farmland soils irrigated by swine wastewater

To study Pb, Cd and As (heavy metals) in soils affected by long-term irrigation of swine wastewater, 52 soil samples in the plough horizon (0~20 cm) of groundwater-irrigation farmland soils and sewage-irrigation farmland soils were collected and the total and bio-available contents of heavy metals in soils were measured respectively. And sewage-irrigation farmland soils were irrigated with swine wastewater for eight years from Jing’an swine farm in Hebei Province. Spatial variability of heavy metals was studied using Geographic Information System (GIS) technique and geostatistical analysis. The aim was to explore the affecting factors and accumulation contributions of Pb, Cd and As due to swine wastewater application. The results indicated that the spatial variability of total contents of Pb, As and Cd and bio-available contents of Pb and As in soils were dominated by random factors and structural factors together, whereas bio-available content of Cd in soils was primarily controlled by structural factors because of high self-correlation. According to the analysis of background investigated, the variogram analysis, and the correlation analysis among pH value, the contents of heavy metals and soil nutriments in soils, it could be known that the Cd and As were associated with swine wastewater and fertilizer, whereas Pb was associated with fertilizer. The enrichment factor showed that the contribution of swine wastewater for Cd and As was little, and the contribution of fertilizer for Pb was large correspondingly. Attention should be paid to the pollution risk of Pb, Cd and As because pH value in soils would decrease and the bio-available concentrations of Pb, Cd and As would increase after swine wastewater was irrigated.