HEAVY METAL CONTENTS IN SOIL-CHINESE HERBAL MEDICINE SYSTEM IN XIBO RIVER BASIN, CHIFENG CITY, INNER MONGOLIA: Distribution Characteristics and Ecological Effect Evaluation

Based on the test data of topsoil, Chinese medicinal materials and root soil samples, the paper studies the contents, spatial distribution characteristics and pollution degrees of five heavy metal elements including As, Cd, Cu, Hg and Pb in the topsoil of Chinese medicinal materials planting area of Niujiayingzi Town in Xibo River Basin, Chifeng City, Inner Mongolia, as well as the accumulation characteristics of soil heavy metals by different Chinese medicinal materials and heavy metal pollution degree of herbs. The results show that the five elements in the topsoil of Chinese medicinal materials planting area share the same origin, mainly from the parent material, and in association, with the mean contents of 8.729×10^-6, 0.142×10^-6, 21.146×10^-6, 0.036×10^-6 and 23.651×10^-6, respectively. The variation coefficients of Hg and Cd are 0.639 and 0.472 respectively, reaching the intensity variation, for their low soil background contents and more susceptible to various factors. Both the single and comprehensive pollution indexes of the soil heavy metals are less than 0.7, which shows a clean level of soil quality and meets the soil environmental requirements for the GAP base construction of Chinese medicinal materials. The concentration coefficients or pollution indexes of heavy metals in the medicinal parts of platycodon grandiflorum, glehnia littoralis and achyranthes bidentata are all less than 0.50, with their contents much lower than the limit value of heavy metals in Chinese medicinal materials. The Chinese medicinal materials produced in the planting area of Niujiyingzi Town all meet the requirements of green standard.