Nanoparticles composed of ZnO encapsulated
in a mesoporous SiO2 shell (nZnO@SiO2) with
a primary particle diameter
of ∼70 nm were synthesized for delivery of Zn, a micronutrient,
by foliar uptake. Compared to the rapid dissolution of bare nZnO (90%
Zn dissolution after 4 h) in a model plant media (pH = 5), nZnO@SiO2 released Zn more slowly (40% Zn dissolution after 3 weeks),
thus enabling sustained Zn delivery over a longer period. nZnO@SiO2, nZnO, and ZnCl2 were exposed to Solanum lycopersicum by dosing 40 μg of Zn
micronutrient (in a 20 μL suspension) on a single leaf. No Zn
uptake was observed for the nZnO treatment after 2 days. Comparable
amounts of Zn uptake were observed 2 days after ZnCl2 (15.5
± 2.4 μg Zn) and nZnO@SiO2 (11.4 ± 2.2
μg Zn) dosing. Single particle inductively coupled plasma mass
spectrometry revealed that for foliar applied nZnO@SiO2, almost all of the Zn translocated to upper leaves and the stem
were in nanoparticulate form. Our results suggest that the SiO2 shell enhances the uptake of ZnO nanoparticles in Solanum lycopersicum. Sustained and controlled micronutrient
delivery in plants through foliar application will reduce fertilizer,
energy, and water use.
Pesticide nanoencapsulation and its
foliar application are promising
approaches for improving the efficiency of current pesticide application
practices, whose losses can reach 99%. Here, we investigated the uptake
and translocation of azoxystrobin, a systemic pesticide, encapsulated
within porous hollow silica nanoparticles (PHSNs) of a mean diameter
of 253 ± 73 nm, following foliar application on tomato plants.
The PHSNs had 67% loading efficiency for azoxystrobin and enabled
its controlled release over several days. Thus, the nanoencapsulated
pesticide was taken up and distributed more slowly than the nonencapsulated
pesticide. A total of 8.7 ± 1.3 μg of the azoxystrobin
was quantified in different plant parts, 4 days after 20 μg
of nanoencapsulated pesticide application on a single leaf of each
plant. In parallel, the uptake and translocation of the PHSNs (as
total Si and particulate SiO2) in the plant were characterized.
The total Si translocated after 4 days was 15.5 ± 1.6 μg,
and the uptake rate and translocation patterns for PHSNs were different
from their pesticide load. Notably, PHSNs were translocated throughout
the plant, although they were much larger than known size-exclusion
limits (reportedly below 50 nm) in plant tissues, which points to
knowledge gaps in the translocation mechanisms of nanoparticles in
plants. The translocation patterns of azoxystrobin vary significantly
following foliar uptake of the nanosilica-encapsulated and nonencapsulated
pesticide formulations.
In this study, two bench-scale moving bed biofilm bioreactors (MBBRs), achieving soluble organic matter removal, were exposed to 10.9 and 109 μg/L polyvinylpyrrolidone (PVP)-coated AgNPs for 9 weeks (64 d). Distribution of continuously added AgNPs were characterized in influent, bioreactor and effluent of MBBRs using single-particle inductively coupled plasma mass spectroscopy (spICP-MS). Continuous exposure to both concentrations AgNP inf significantly decreased soluble chemical oxygen demand (S COD ) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. The release of significant mass of Ag via effluent (˂78%), dominantly in NP form due to the limited retention capacity of aerobic heterotrophic biofilm, provide new and useful insight into fate of AgNPs in biofilm-laden engineered biological systems and their corresponding inhibitory effects at environmentally representative NP concentrations maintained over an extended period. To our knowledge, this is the first study evaluating chronic inhibitory effect of AgNPs on attached-growth wastewater process efficiency and its microbial communities at representative environmental AgNP concentrations by combining biological response and NP characterization.
Bioremediation end
points for biodegradable hydrophobic compounds
in soil aggregates are regulated by bacterial accessibility to different
pore sizes. We evaluated the accessibility of the nonmotile hydrocarbon-degrading
bacterium Dietzia maris (d = 1 μm
in the stationary phase) to 0.4 μm pores. A significant fraction
(22%) of the pore volume of the clayey soil from which the bacterium
was isolated was associated with 0.4–1 μm diameter pores.
The entry of bacteria into the pores was observed by electron microscopy
and by monitoring mineralization of [14C]hexadecane placed
well above membranes with fixed pore sizes (0.4 or 3 μm), in
a bioreactor. The membranes were used as a surrogate for soil pores
of fixed diameters. When membranes were not wetted or were wetted
with nonbiodegradable heptamethylnonane, bacteria did not penetrate
pores even if they attached to the membrane. However, bacteria penetrated
pores when membranes were wetted with hexadecane, as growth on hexadecane
yielded a crowd of smaller rod-shaped cells (d
min = 0.54 ± 0.14 μm) in biofilms formed on the
membrane. A morphological progression with time from smaller, elongated
cells in the early growth phase to cocci-shaped cells was observed.
The results suggest proliferation accompanied by morphological changes
as a mechanism of bacterial migration in submicrometer pores and low-permeability
media.
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