Environmental health risks of heavy metal transfer from soil to cicadas via poplar trees: implications for safe cicada farming

Poplar trees possess dual functionality for soil heavy metal phytoremediation and cicada cultivation. However, the health risks associated with metal transfer along the soil-root-cicada pathway require further elucidation. Inductively coupled plasma optical emission spectrometry analysis of soil (n = 36), poplar root (n = 9), and cicada life stage (n = 27) samples revealed distinct heavy metal distribution patterns. Soil concentrations (mg·kg^-1) ranged as follows: Cd 0.03-5.67, Pb 2.50-433, Cu 11.25-37.73, Ni 27.00-65.50, Zn 58.33-141.50. Metal partitioning showed Cd (0.16-33.05 mg·kg^-1) and Cu accumulating in adult cicadas, while Zn (peak 609 mg·kg^-1), Pb (0.30-94.33 mg·kg^-1) and Ni were predominantly retained in exuviae. Notably, Zn exhibited particularly strong bioaccumulation from roots. Cd and Pb concentrations in edible cicada stages and Cd in exuviae exceeded safety limits, correlating with substantial root accumulation (Cd: 0.75-19.67, Pb: 4.32-85.33 mg·kg^-1). Risk assessment showed negligible non-carcinogenic risks (HQs < 1.0) at typical consumption rates, though adults presented higher Cd-related risks than nymphs. Soil Cd safety thresholds were established at 1.52 mg·kg^-1 (adults) and 3.97 mg·kg^-1 (nymphs). These findings demonstrate significant trophic transfer amplification of metal risks and provide crucial safety benchmarks for sustainable cicada production.