The levels of inorganic As in edible plants are closely related to the toxicity of arsenic to human health . When data from all of field collected samples plotted together, a striking pattern can be observed that the concentration of inorganic As increased with increasing total As (r ¼ 0.720, P < 0.01) (Fig. 1a). The same pattern also appeared in data plot between inorganic As and total As in CHMs from markets or pharmacies (r ¼ 0.987, P < 0.01) (Fig.1b). This relationship between inorganic As and total As was also reported in rice grain samples by Xu et al. (2008) and Zavala et al. (2008).