Heavy metal pollution is of major concern due to its potential threat to ecosystem safety and human health. To give a valuable insight into the status of heavy metal pollution in a sewage irrigation region in northwest China, this paper thoroughly studied the spatial distribution and possible source of heavy metals in soils under different land uses.
Materials and methods
Soil samples were collected from arable lands (maize field, orchard, and paddy field) and nonarable lands (village and barren hill) from a sewage irrigation region, northwest China. The concentrations of Cd, Cr, Cu, Mn, Ni, Pb, and Zn in the soils, together with soil pH, soil organic matter (SOM), and soil particle size distribution, were detected. GIS-based approach was employed to construct the spatial distribution maps of heavy metals, and multivariate analysis was used to identify their possible source.
Results and discussion
Although elevated concentrations of Zn, Pb, and Cu are detected, Cd is the priority pollutant in the soils. Land use, location, and SOM are crucial factors affecting metal distribution in the soils. Metal concentrations in different land uses arrange in the order of orchard > paddy field/maize field > village > barren hill. The area within the basin of Dongdagou stream presents the most pollution, whereas the northeast side far from the stream is the least. Irrigation water both from Dongdagou stream and the Yellow River are deemed as primary sources of Cd, Zn, Pb, and Cu. Besides, agrichemical application particularly contributes to metal accumulation in orchard soils, and Cd and Zn partially derive from atmospheric deposition. Nickel and Mn predominately originate from the soils.
When studying metal pollution in soils, land use should be taken into account because of its important roles in determining metal concentrations. In the study area, arable lands are more likely to be polluted by Cd, Zn, Pb, and Cu than nonarable lands via sewage irrigation; moreover, agrichemical application and atmospheric deposition also should be held responsible for metal accumulation in the soils.