Lead-contaminated lichens as a hazardous pathway in the global cassia spice supply chain

Lead (Pb) contamination in cassia spice products has garnered significant attention, necessitating stringent quality control within the global supply chain to ensure food safety. Our preliminary research suggests that Pb contamination is linked to atmospheric deposition, as evidenced by elevated Pb concentrations found in lichens on cassia trees. This study expands upon those findings, focusing specifically on evaluating Pb within the lichen communities of cassia ecosystems across Northern Vietnam-a region with expanding industrial and mining activities that accounts for approximately one-third of the global cassia spice supply. Lichens exhibited Pb levels from 0.4 to 52.6 mg kg^-1 (median, x̃=7.55 mg kg^-1), representing at least a 20-fold increase compared to the underlying bark and wood. The interwoven structure of photobionts and mycobionts effectively sequester Pb-tainted dust, creating a persistent Pb source. This highlights Pb-tainted lichens as hazardous biomaterials and urges the necessity of a pre-processing lichen removal to eliminate associated Pb before it enters the global food chain. Given the ubiquity of epiphytes in tropical regions coupled with deteriorating environmental conditions, this lichen-derived Pb sink represents a widespread challenge. Immediate international/regional interventions are urged to address this issue, thereby safeguarding cassia quality and mitigating health risks for global consumers.