Metals in Traditional Chinese medicinal materials (TCMM): A systematic review

Traditional Chinese medicine has become an important pillar of "Healthy China" and the national medical system in recent years. Due to the wide range of raw materials in traditional Chinese medicinal materials (TCMM), the issue of metals has attracted more and more attention. In this paper, a comprehensive review of public reports on metals in TCMM in recent decades was conducted. From a total of 1969 reported articles, a total of 296 research reports on metals in TCMM were screened. The 296 reports involved 255 species in 85 families, with a total of 274 medicinal materials. These TCMM were divided into taproot-type, leaf-type, flower and fruit-type, herba-type, stem-type and bark-type medicinal materials according to the medicinal parts. The content of five metals lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As), chromium (Cr) in these TCMM was noted, and the distribution rules for metals were analyzed. The results showed that: (1) For the distribution of metals in different medicinal parts, Pb was mainly distributed in leaves; Cd was mainly distributed in flowers and fruits, stems and leaves; Hg was mainly distributed in barks; As was mainly distributed in stems; Cr was mainly distributed in stems, flowers and fruits. (2) The areas with the highest risk of metal residues were the Qinghai-Tibet Plateau, south China, and southwest China. (3) Among all types of TCMM, herba-type medicinal materials had the highest risk of metal content. (4) Combined with the pharmacopoeia metal limit standards implemented in 2019, the exceeding rate of Pb in TCMM was the highest, with a maximum value of 37.67%; among the six major types of TCMM, the medicinal materials with the highest exceeding rate were herba-type medicinal materials, among which Hg had the highest exceeding rate of 23.08%; in terms of medicinal parts, the highest exceeding rate of metals was in leaf-type medicinal materials, among which Pb had the highest exceeding rate of 37.67%. On the whole, the situation in regard to metal residues in TCMM was acceptable, but it cannot be ignored. It needed to be paid attention to in the industrialization and management of TCMM.