Cadmium (Cd) accumulation in traditional Chinese medicine materials (TCMMs): A critical review

Traditional Chinese medicine (TCM) has accumulated a wealth of ecological wisdom and is regarded as an outstanding cultural and medical resource in China. However, in the context of serious environmental pollution, the potential harm caused by TCM materials (TCMMs) due to toxic heavy metals has seriously affected the sustainable development of TCM. Cadmium (Cd) is an internationally recognized heavy metal contaminant. In this paper, 270 reports on Cd in TCMMs were screened from 1969 publications covering 243 species in 81 families. According to the source of the TCMMs, the data were divided into the following categories: aboveground part, bark, flower and fruit, herb, leaf and rhizome. The temporal dynamics of the Cd content and its correlations with the habitats and categories (parts) of TCMMs were also studied. The results show that 22.05 % of the investigated TCMM samples exceeded the relevant domestic standards (Cd≤0.3 mg/kg), among which the maximum Cd content was 17.75 mg/kg. Myrtaceae and Syzygium aromaticum were the family and species with the highest mean Cd content, respectively. Regarding the source of TCMMs of great concern, the mean Cd content of TCMMs decreased in the order of herb > aboveground part > flower and fruit > leaf > rhizome > bark. In addition, in terms of the spatiotemporal distribution, the spatial distribution of the mean Cd content of TCMMs was significantly higher on the Qinghai-Tibet Plateau, followed by Southwest China. When comparing different times, more serious Cd pollution of TCMMs existed after 2000, and the highest mean Cd content was observed in 2000-2004. In summary, soil acidity must be decreased and the cultivation conditions of Cd-hyperaccumulators such as Ligusticum chuanxiong and Lonicera japonica must be modified, in conjunction with a scientific health risk assessment, to ensure the sustainable development of TCMMs.