Characteristics of lead in lung and brain reveals respiration as a direct exposure way

Lead (Pb) is known as a neurotoxicant, posing a global public health threat. Although Pb exposure is reported to be associated with brain functional impairment, there remain gaps to directly clarify their links and how the environmental lead entry into brain is rarely known. This study explored the entry pathway of atmospheric Pb to brain and lung through comprehensive profiling of Pb characteristics (distribution, nanoparticle characterization and isotope ratio) in the biological and atmospheric samples collected from a typical pollution area. The Pb distribution showed the targeted accumulation of Pb in brain and its descending trend with distances in both tissues and atmosphere indicated the direct transportation of Pb to lung due to point emission of atmospheric Pb. Then the identical characteristics of Pb-containing nanoparticles (PbNPs) in the lung (two sizes: 35 ± 6 nm and 52 ± 24 nm) and atmospheric (37 ± 6 nm and 53 ± 24 nm inside the smelter) samples, which was identified to be the mixture of PbSO₄ and Pb₅[PO₄]₃Cl particles, suggested the origination of exogenous PbNPs in lung from atmosphere through direct respiration. Finally, the highly correlation of Pb isotope ratios in brain and lung, liver and kidney, and the significant difference between the two groups (p < 0.0001) indicated Pb in brain and lung was most likely directly inhaled after exposure to particulate pollution in atmosphere, but not from the liver through circulatory system. This is the first time to apply Pb isotopic characteristics in biological organs for investigating the Pb circulations and possible entry route to brain, which would provide direct evidence and a crucial link to understand the brain diseases caused by atmospheric Pb.