Contamination characteristics and source apportionment of soil heavy metals in Lalin River basin

Abstract: China faces great challenges in protecting its soil from contamination caused by rapid industrialization and urbanization over the last three decades. In order to reduce the risk of heavy metals pollution, it is very essential to study soil heavy metal contamination characteristics and quantify the sources of soil heavy metals. The results of source apportionment can provide the scientific supporting for soil quality management in the specific region. In this study, a total of 173 soil samples at depth 0-20 cm were collected, and concentrations and spatial patterns of soil heavy metals (including cadmium, chromium, arsenic, mercury, lead, copper, zinc, nickel, manganese, cobalt, vanadium and selenium) in Lalin River basin were analyzed, which is one of the most typical agricultural areas in Northeast China. A Geographic Information System (GIS) was used to explore the variety of spatial distributions for 12 heavy metals. Geoaccumulation index and potential ecological risk index were applied to evaluate the degree of soil heavy metal contamination. Positive matrix factorization method was introduced to apportion the sources of soil heavy metals. Results demonstrated that the average concentrations of Cd, Cr, As, Hg, Pb, Cu, Zn, Ni, Mn, Co, V, and Se in soil samples were 0.13, 46.28, 10.12, 0.07, 23.38, 17.09, 54.06, 21.26, 575.4, 14.04, 62.11 and 0.158 mg/kg, respectively. The mean values of Cr, As, Pb, Cu, Zn, Ni, Mn and V did not exceed their respective soil background values, while the mean values for Co and Se were slightly higher than their background values in Lalin River. Concentrations of Cd and Ni in some soil samples were greater than the GradeⅡof the Standard according to the Soil Environmental Quality of China. The geostatistical interpolation results of heavy metal concentrations showed the spatial variations for these heavy metals were significant difference. According to the geoaccumulation index, the soils in Lalin River basin were mainly contaminated by Cd and Hg, with followed by As, with no or moderated contaminated level for the others. The geoaccumulation index values of 45.1% samples for Cd and 37.0% samples for Hg were greater than 0, while their mean values for the potential ecological risk index (RI) were 49.83 and 70.29, respectively. The range of RI was from 29.81 to 659.70, with a mean value of 140.18, indicating high ecological risk. Moreover, the potential ecological risk index on the left bank area was significantly higher than the right bank area of the Lalin River. A three-factor modeling resulting from PMF provided the most satisfactory results of soil heavy metals sources. Industrial activities, the application of pesticides and fertilizers were identified as the main anthropogenic sources for soil heavy metals in this study area, accounting for 29.4% and 32.6% of the total contribution, respectively. The remainder was the natural source, accounting for 38.0% of source contributions. The accumulation of Cd and Se in soils was mostly affected by agricultural activities, while Cr, Cu and Zn were also affected by some extent in this study area. For Hg and As, their content in soils was mainly associated with industrial activities. These suggested that the impact of human activities on soil heavy metals in Lalin River basin has exceeded the impact of natural source. Therefore, the use of pesticides and fertilizers and the “three wastes” emissions from key industrial enterprises in this area should be strictly controlled.