Study on the Difference in the Contribution of Soil Particle Sizes to Heavy Metal Exposure of Children Around Smelting Area

This study focused on children residing near a smelter in Baiyin, and investigated the impact mechanism of different soil particle sizes on children's exposure to heavy metals. By analyzing the distribution pattern of concentrations and bioaccessibilities of typical heavy metals (Cd, Cr, Cu, Ni, Pb) across four particle size fractions (<63 μm, 63-150 μm, 150-250 μm, 250-352 μm), and incorporating the size-selective adherence characteristics of children's hand-loaded dust, this research quantitatively assessed the contribution of each particle size fraction to children's health risks from oral exposure. The results showed that fine particle size soil (<63 μm) exhibited both higher concentration and bioaccessibility of heavy metals, which were 1.3-1.9 times and 1.1-2.2 times higher, respectively, than those of the coarsest fraction (250-352 μm). The proportion of particles < 63 μm in children's hand-loaded dust (64.3%) was significantly higher than that in ambient soil, demonstrating selective adherence towards finer particles during children's exposure. Due to the particle size-selective effects on metal concentration, bioaccessibility, and actual child exposure, fine soil particles constituted the primary source of heavy metal exposure risk via oral ingestion in children. Soil particles with a size of <63 μm contributed 48-60% to the total exposure risk of the five heavy metals. Therefore, in the health risk assessment of soil around smelting plants, the influence of particle size on the occurrence characteristics of metals, bioaccessibility, and children's actual exposure behavior should be considered concurrently to enhance the accuracy and targetability of assessment and control measures.