REPOSITORY > RESULTS

Abstract

The purpose of this dissertation was to examine inadvertent food and edible plant exposures to nanoparticles (NPs) in the context of NP emission and deposition from air. This was investigated in terms of: 1) the emitted NP dynamics and characteristics of two types of incense sticks (Strawberry and African Violet) burned in an unventilated room setting and 2) the impact of foliar surface free energy (SFE), a quantitative measure of polar and dispersive forces which determine hydrophobicity/hydrophilicity, on the adhesion and translocation behaviors of arugula (Eruca sativa Mill.; low SFE) and escarole (Cichorium endivia L.; high SFE) plants after exposure to Pt NPs.
In the first part of this work, scanning mobility particle sizer results showed that the maximum total NP concentration at the end of the burning period was up to 30-fold higher than that of the initial background levels and that it remained up to six-fold higher 100 minutes after the conclusion of the burning period. Emitted incense particles decayed in a biexponential manner, with particles up to 100 nm in size decaying with lifetimes of several tens of minutes on account of fast agglomeration, while the particles with diameters of 100-1,000 nm had lifetimes of >100 minutes, as their removal mechanisms are slower. Slight distance-dependent effects were also observed, with the total NP concentration being higher at decreasing distances to the measurement inlet due to greater proportions of short-lived nucleation mode particles with size up to 100 nm.
In the second part of this work, soil-cultivated arugula and escarole plants were exposed to Pt NPs through either the leaves (5-500 mg/L for 5 days) or roots (one exposure to 20 mL of a 50 mg/L dispersion). Among foliar-exposed plants, inductively coupled plasma-mass spectrometry data showed that relative to escarole, arugula contained higher Pt concentrations in leaves (33, 31, and 14 times higher for 5, 50, and 500 mg/L exposures, respectively). For both plants, the proportion of Pt translocated from roots to leaves (99% and 28% for arugula and escarole, respectively) was higher than that from leaves to roots (<1% for both plants). Scanning electron micrographs of foliar-exposed leaves (500 mg Pt NPs/L) showed a much higher degree of Pt NP aggregation/agglomeration on arugula relative to escarole, in addition to stomata closure from likely shading effects on arugula. Analysis of foliar SFE results based on acid-base theory did not indicate any relationship between Pt NP exposure and changes to SFE.
The results of the incense experiments provide a model of NP air pollution in a typical indoor room setting, indicating that the inadvertent contamination of food with NPs is likely to be significant when placed alongside burning incense and other significant NP emitters (e.g., burning cigarettes). In outdoor settings, the results indicate that plants with low SFE are more susceptible to NP foliar exposures than plants with more hydrophilic surfaces.