Zinc oxide nanoparticles, ZnO NPs, are used in a range
of commercially available products including sun tan
lotions and semiconductors. Increasing number of ZnO
NPs incorporated products will likely raise concentration
of this nanomaterial in the environment. Available
information suggests that ZnO NPs can easily enter soil
and water resources. ZnO NPs have adverse effects on
different components of the environment in particular
because of their toxicological impacts. Zinc oxide
nanoparticles are one of the most toxic nanomaterials
and could inhibit the root growth of plants and embryonic
development of some of marine species.
To better understand fate and behaviour of these
nanoparticles in the environment and their potential
pathways, determining in-situ concentration of these
nanomaterials is essential. We have recently used
Nano-DGT in combination with standard DGT devices
to determine available concentrations of zinc oxide
nanoparticle and its ionic species in soil samples spiked
with a range of concentrations from 100 mg/kg to 2200
mg/kg of ZnO NPs and Zn2+. The samples were aged
approximately for 80 Days after spiking. For each soil
sample a Nano-DGT and a standard DGT device were
deployed for approximately 20 hours (in triplicates).
The results showed that for the samples spiked with ZnO
NPs, available concentrations of zinc species measured
by DGT devices were notably higher than Nano-DGT
devices. Nevertheless considerably high concentrations
of available zinc were also measured by Nano-DGTs,
which could partly be attributed to dissolution of ZnO
NPs and released Zn2+ because of the soil pH (5.5). In
the soil samples spiked with ionic zinc the available
concentrations measured by Nano-DGT and DGT devices
were approximately 1.5X higher for the spiked samples
with 100, 225, 500 and 1100 mg/kg ZnO NP. This ratio
was more than twice for the soil samples spiked with
2200 mg/kg ionic zinc.
Nanoscience is facing a turning point, after years of
research it has entered commercialization stage and
a number of nanotechnology products are expected
to enter the market. Apart from environmental
impacts of emerging products there are a number of
nanomaterials that are already widely used in different
industries namely, ZnO, Ag and TiO2 nanoparticles.
These nanomaterials could enter into the environment
through different paths including the production stage,
waste management and recycling or accidents.
It is known that these nanomaterial have adverse
environmental impacts. However, a major challenge that
still exists is to better understand their fate and behaviour
in the environment, which is not possible without access
to proper and reliable sampling techniques.
Here we present application of a modified DGT device
known as Nano-DGT, which in combination with
standard DGT devices could provide a reliable approach
to measure available concentrations of zinc oxide, silver
and titanium dioxide nanoparticles in the environment.
In this research, as part of TINE (Transatlantic Initiative for
Nanotechnology and the Environment) collaborations,
soil samples were spiked with different concentrations
of ZnO, Ag and TiO2 nanoparticles and their respective
ionic forms were studied. For each soil sample a Nano-
DGT, with 1000 MWCO (molecular weight cut off)
dialysis membrane in the front of the diffusive gel layer,
and a standard DGT device (DGT Total) were deployed in
triplicates. The deployment times were approximately
As it has been difficult to obtain accurate diffusion
coefficients of those nanomaterials due to their variable
nature, average mass accumulated (M) by DGT was used
as a reliable measure to reveal differences between
available metals in their nanoparticle and ionic forms.
Among three different metals used in these studies,
ZnO NP and ionic zinc seem to be the most available
ones. Average concentrations of accumulated metal
(M) are significantly lower for TiO2 NP and its ionic form
followed by Ag NP and Ag+. This could be attributed
to retention of these metallic spices by active surfaces
in the soils samples (e.g. organic matter), which make
them less available for DGT measurements. Interestingly
the samples, even those that were spiked by ionic
metals only, showed considerably higher accumulated
metals for the DGT devices compared to Nano-DGT. This
indicates notable fraction of freely available ions formed
high molecular weight complexes in the soil.
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