Exposure sources, intake pathways and accumulation of lead in human blood

Lead (Pb) is a toxic heavy metal and its long-term accumulation in human bodies can lead to serious diseases. Investigation on Pb exposure provides an effective intervention opportunity to reduce the blood lead levels (BLLs) of the populations. Although the phase-out of the gasoline has been conducted in many developing countries (e.g., China), the BLLs of these populations are still higher than the alert BLL (5.0 μg/dL) set by World Health Organization (WHO) and Centers for Disease Control and Prevention of USA (CDC). Here, we reviewed the BLLs of the populations in different countries and summarized the sources and intake pathways of blood Pb which were associated with dietary Pb intake and non-dietary Pb intake. Extensive progress has been made in the studies of soil biogeochemistry and the plant biological processes, including the effects of soil pH, redox potential, Fe/Mn oxides, and organic matter on the availability of soil Pb, as well as the mechanisms regulating the Pb absorption by plant root and transport from root to shoot. The oral-nasal respiration and skin infiltration pathways have been specifically identified as the main causes of the increased BLLs of the populations exposed to different Pb sources. In the developing countries, complex dietary and non-dietary Pb intakes increase the BLLs, making intervention strategies to reduce BLLs difficult. This review provides a systematic understanding in the processes and mechanisms of Pb intake from environment to human blood and helps to guide safe strategies to reduce the BLLs and enhance human health.