Migration, accumulation, and risk assessment of potentially toxic elements in soil-plant (shrub and herbage) systems at typical polymetallic mines in Northwest China

Abstract

In grassland systems of the semi-arid mining area, migration, accumulation and bioavailability of potentially toxic elements (PTEs) are important ecological and health risk issues. 38 pairs of topsoil (0-20 cm) and plant samples were collected around Baiyin city and in Dongdagou stream valley to investigate the migration of PTEs in soils, transfer of PTEs in soil-plant (shrub and herbage) systems and assess the risk in soils and plants. The total concentrations of PTE (Hg, As, Cu, Zn, Cd and Pb) were analyzed following digestion in mixture acid solution and bioavailable PTE was extracted with a strong chelating agent (DTPA-TEA-CaCl 2 ). The transfer factor (TF) and bioaccumulation factor (BCF) were calculated to examine the migration of PTEs in soil-plant. Hazard quotient (HQ) and total hazard index (THI) were calculated to assess the risk and migration of PTEs in soils. The results showed that PTEs in soils and plants of study area exceeded the soil background value and Hygienic Standard for Feeds. Correlation among the total Hg, As, Cu, Zn, Cd and Pb in soils of Dongdagou stream valley were signi cant at p < 0.01. A good correlation was exhibited between PTEs in root/aboveground parts of plants and DTPA-soil extractable. Difference of TF and BCF were existed between Dongdagou stream valley and around Baiyin city. Hg, Cu, Zn, Cd and Pb were mainly accumulated in soils near the mining area. The calculated THI was exceeded 1, and As and Pb were the major risk factors. The ability to absorb and transfer Hg, As, Cu and Pb of plants was lower in more serious polluted area. As had a stronger migration capacity in study area.PTEs in soils had an adverse health effect for residents and PTEs in plants may cause toxicity to cattle and sheep.

Risk Assessment and Attribution Analysis of Potentially Toxic Elements in Soil of Dongdagou, Baiyin, Gansu Province, China

“…Table 5 shows that the average content of As, Cu, Hg, and Pb in the 1.00-1.50 m soil layer of Dongdagou farmland in Baiyin City is the highest, while the average content of Cd and Zn in the 0.50-1.00 m soil layer is the highest, which are 1.65 ± 0.64 (1.35-1.65), 18.88 ± 9.44 (10.05-18.88), 2.72 ± 2.77 (1.59-2.72), 3.51 ± 1.46 (1.89-3.51), 4.09 ± 1.84 (3.09-4.09), and 2.37 ± 0.62 (1.86-2.37) times the background value of the soil in Gansu Province, respectively. The average contents of As, Cu, Hg, Pb, Cd, and Zn in each soil layer were 1.45 ± 0.50 (0.82-4.32), 13.80 ± 8.50 (1.58-43.60), 1.89 ± 1.14 (0.88-8.19), 3.07 ± 1.24 (0.73-8.04), 3.64 ± 1.32 (1.32-8.56), and 2.13 ± 0.76 (1.09-6.03) times higher than the background values of soil in Gansu Province [14], respectively, indicating that the contents of all six metals in the farmland soil of Dongdagou in Baiyin City are higher than the soil background value (Figure 2). In terms of the vertical distribution of potentially toxic elements in soil, As, Cu, and Pb all have the highest mean concentrations at depths of 1-1.5 m, while Cd and Zn have the highest mean concentrations at depths of 0-1.0 m. This indicates that except for Hg, which hardly changes with depth, the concentrations of other potentially toxic elements increase with soil depth.…”

“…The EPA PMF 5.0 model was used to analyze and plot the contribution rate. [14], respectively, indicating that the contents of all six metals in the farmland soil of Dongdagou in Baiyin City are higher than the soil background value (Figure 2).…”

“…The prevailing wind direction in this area is typically from the northeast. Additionally, the study area is predominantly characterized by a calcareous soil composition [14] (Figure 1). Baiyin City is situated in the arid region of the upper Yellow River, serving as a hub for the extraction of non-ferrous metals such as copper, lead, zinc, and their respective minerals.…”

“…where in Formula (1), C f i represents the pollution coefficient of potentially toxic element i; C d i represents the measured content of potentially toxic element i in the sample, mg/kg; and C r i is the environmental background value of potentially toxic element i in the soil of Gansu Province [14], mg/kg.…”