Abstract
Particulate matter (PM) has become a severe environmental issue, and ultrafine PM particles such as PM2.5 or PM1 can cause various complications and respiratory diseases to human beings. In particular, heavy metals contained in PM particles can contaminate edible plants; for example, plant leaves are exposed to PM particle-laden raindrops. The contaminated edible plants can injure the human health by ingestion, so a detailed understanding on the accumulation of PM particles inside edible plants is essential. In this study, we investigate the infiltration of PM particles in plant tissues with a hypothesis that ultrafine PM particles are absorbed through stomatal pathways. As an edible test plant, Perilla frutescens is selected. Drops of gold nanoparticle (AuNP) suspension are deposited on a leaf of P. frutescens to simulate the scenario where PM particle-laden raindrops fall on patulous stomata of the test plant. To examine AuNP adsorption on the P. frutescens foliar surface and diffusional AuNP absorption through stomatal apertures, we investigate three physical dynamics of AuNPs suspended in a sessile drop: sedimentation, evaporation-driven convective flow, and shrinkage of the drop interface. Quantitative information on the 3D spatial distribution of AuNPs in plant tissues was measured by X-ray imaging and two-photon excitation microscopy.
Highlights
Particulate matter (PM) has become a severe environmental issue, and ultrafine PM particles such as PM2.5 or PM1 can cause various complications and respiratory diseases to human beings
The stomatal aperture indicated in the yellow box was open, and the AuNPs were distributed around the guard cells
Most AuNPs observed in the inset were single particles or small-scale aggregates composed of 2–5 particles due to the well-dispersed AuNPs by ultrasonication, but a few large-size aggregates comprising 10–30 particles were observed (Fig. 1c)
Summary
Particulate matter (PM) has become a severe environmental issue, and ultrafine PM particles such as PM2.5 or PM1 can cause various complications and respiratory diseases to human beings. PM particles are deposited on the respiratory system by inhalation, and they permeate into blood vessels[3] Food consumption is another important infiltration pathway of PM particles, and uptake of edible plants is one of the main infiltration r outes[4]. Previous studies revealed that the foliar uptake of PM particles occurs through stomatal and cuticular entrances[14]. Previous work hypothesized that only nanoparticles (NPs) much smaller than 100 nm can cross the cuticular e ntrance[16] For this reason, PM particles with submicro/micro sizes are mainly absorbed through stomatal pathways[9]. The foliar uptake of PM particles usually occurs in the industrial r egions[17] or kitchen g ardens[18]
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