## 3 Results and Discussion
### BCF of Metal(loid)s in Corn and Wheat  
The bioconcentration factor (BCF) is the ratio of the concentration of metal(loid)s in crops and soil (Equation (6)) and is a crucial index to measure the degree of absorption of metal(loid)s by plants. BCF values are shown in Figure 4. Through statistical analysis of the BCF, the enrichment ability of agricultural products to metal(loid)s in soils and agricultural products was evaluated. Higher BCF values indicate a stronger migration ability of metal(loid) elements into plants. BCF is a common parameter often used in the study of environmental contamination [62; 63]. Zn had the highest average BCF for wheat and corn, with values of 0.446 and 0.297, respectively, which explains the high Zn concentration in these plant samples. [PERSON] et al. (2008) also found that the BCF of Zn was highest in wheat [48]. [PERSON] et al. (2013) reported that the BCF of Zn had a higher accumulation in grain than Cu [64]. The study also showed that the BCF of Cu in wheat and corn is lower than that of Zn, at about 0.195 and 0.059, respectively. The BCF of wheat is higher than that of corn in the study area and is similar to values found by [PERSON] et al. (2008) and [PERSON] et al. (2013) [48; 64]. [PERSON] and [PERSON] (2001) reported that corn's ability to move Zn [65], which is the most bioavailable metal in contaminated soils, from roots to other parts of the plant was greater than for Cu. The BCF of wheat Cd is greater than corn Cd, yet similar to BCF of Zn, resulting in three wheat samples that exceeded the national food standard. [PERSON] et al. (2008) showed that the BCF of Cd was higher than for the other metal(loid)s tested [47], which would harm human health. In comparison, the BCF of As (0.003 for wheat and 0.0015 for corn) was lower than the other metal(loid)s in this study and also significantly lower than the values reported by [PERSON] et al. (2005). [PERSON] et al. (2008) also found that the crop BCF of As was significantly lower than the values for Cd, Zn, Cu, and Pb [47; 66]. The corn BCF values for Cu, Zn, and Cd were higher than the BCF value for Hg (0.080 and 0.045, respectively), both of which are higher than the BCF values reported by [PERSON] et al. (2008) for wheat (0.0176). Importantly, the Hg concentrations of three grain samples exceeded the Chinese standard limits of 0.02 mg/kg. Previous studies have shown that Hg pollution is caused by emissions from coal-burning and large applications of phosphate fertilizers containing Hg, which increases soil and crop Hg levels. The BCF values for Ni and Cr were lower than for Pb, and also lower than the BCF values reported for carrots [47; 67; 68]. These results agreed with the findings of [PERSON] et al. (1996), who found that Cr, Ni, and Pb are less mobile in corn and wheat plants [69]. However, the Pb concentrations of five grain samples exceeded the Chinese tolerance limits of 0.2 mg/kg. Variations of Pb concentrations in corn and wheat grains were considerably higher than those in soil. In general, the order of average metal(loid) BCF values in corn was Zn (0.297) \(>\) Hg (0.08) \(>\) Cu (0.059) \(>\) Cd (0.026) \(>\) Ni (0.008) \(>\) Pb (0.002) \(>\) As (0.0015) \(>\) Cr (0.0004). For wheat, this order was Zn (0.446) \(>\) Cd (0.195) \(=\) Cu (0.195) \(>\) Hg (0.045) \(>\) As (0.003) \(>\) Pb (0.002) \(>\) Cr (0.0004) \(>\) Ni (0.00004). The crop BCF values for Zn were greater than for the other metal(loid)s. Additionally, the BCF values for Cd and Cu were also larger than the values for Ni, Pb, As, and Cr. The large BCF values for Zn, Cd, and Cu indicate that the three metal(loid)s have strong migration abilities in crops. The strong enrichment capacity of Zn and Cu indicates that the ability of Zn and Cu to migrate from the soil to the edible parts of the crops is significantly higher than for other elements, especially in wheat, which is consistent with the results found by [PERSON] et al. (2018) [PERSON] et al. (2018) [PERSON] et al. (2018).