Assessment of Cd, Pb, Hg and As contamination in soils and plants in Isatis indigotica cultivated regions in Hebei Province

Concentrations of Cd, Pb, Hg and As in soils and plants in Isatis indigotica cultivated regions of Anguo City and Yuxian County in Hebei Province were analyzed and the bioconcentration factors of I. indigotica from different regions discussed. The study would provide data support and scientific basis for further studies of safe and rational development in crude Chinese drugs. The results showed that the contents of Cd, Pb, Hg and As in soil varied little in I. indigotica cultivated regions of Anguo City and Yuxian County in Hebei Province, with a range of coefficient of variation of 11.70%-97.65%. In the evaluation of the levels of soil contamination based on Class 1 standard for Cd, Pb, Hg and As of the Environmental Quality Standard for Soils (GB 15618-1995), and the Nemerow index background values of heavy metals were used as assessment standard. The range of Nemerow index of 45% soil samples from I. indigotica cultivated regions was 0.7-1.0, which suggested that the soils in the study areas were at an alarming level of pollution. When Class 2 quality standard was used, both the single pollution index and the Nemerow index did not exceed 0.7, which suggested that the investigated soils were generally safe for cultivation of I. indigotica. In addition, the average contents of Cd, Pb, Hg and As in shoots of I. indigotica were respectively 0.22 mg·kg^-1, 0.89 mg·kg^-1, 0.04 mg·kg^-1 and 0.25 mg·kg^-1, with accumulation capacity rank of Cd > Hg > Pb > As. The average contents of Cd, Pb, Hg and As in roots of the herb were respectively 0.14 mg·kg^-1, 0.57 mg·kg^-1, 0.04 mg·kg^-1 and 0.26 mg·kg^-1, with accumulation capacity trend of Cd > Hg > As > Pb. The concentrations of Pb, As and Hg did not exceed the safety limitation based on the Green Trade Standards for Import-Export of Medicinal Plants Preparations (WM2-2001). However, the contamination index of Cd in shoots of I. indigotica was higher than 0.7 and Cd level in 9.09% of the plant samples exceeded the safety limitation, indicating that the levels of Cd in the herbs in both regions were at an alarming level of pollution. It was therefore recommended to follow Class 2 standard of soil quality set in the Environmental Quality Standard for Soils. The accumulation characteristics of heavy metals in roots and shoots of I. indigotica should also be of significant concern in GAP (good agricultural practices) soil quality evaluation.