Is there a risk of trace element contamination in herbal preparations? A test study on the lichen Cetraria islandica.

Lichens are a source of unique secondary metabolites, which have been proved to have many biological properties with possible pharmaceutical roles, including e.g. antioxidant, antimicrobial, antifungal or anti-inflammatory activities and to be worth of consideration for potential human use. However, lichens lack cuticolar tissues and are exposed to several atmospheric contaminants, including trace elements. This work aims at exploring the potential toxicity of herbal preparations derived by the lichen Cetraria islandica due to trace element contamination, testing whether different concentrations may be observed, depending on the origin of the raw material. Fourteen samples of C. islandica, as cut dried thalli occurring on the European market, have been bought from different providers. For each sample, the concentrations of As, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, V and Zn were measured on comminuted herbal substance and on the corresponding decoction, using atomic emission spectrometry (ICP-OES). The elemental concentrations in decoctions were significantly lower than those measured in raw materials, dropping down to levels of negligible health concern. Differences observed in raw materials were not observed anymore in the corresponding decoctions. Also, the elemental transfer rate from dried lichen to decoction was extremely element-specific, ranging from 2% for Cu to 95% for Zn.