1. Behavior of titanium dioxide nanoparticles in the presence of the common contaminant
BPAZia Klocke1, Lindsay Denluck2, Bryan Harper2, Stacey L. Harper1,2,3
1School of Chemical, Biological and Environmental Engineering, 2Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis OR, 3Oregon Nano science and
Microtechnologies Institute, Eugene OR
Results
Acknowledgements
We would like to thank the Sinnhuber Aquatic Research
Laboratory for providing the zebrafish embryos. We
would also like to thank the Johnson Undergraduate
Internship Program for the support of ZK, the NIEHS
Training Grant under award numbers T32ES00760 and
ES017552-01A2 at OSU for the support of LD, and the
support of the Harper Laboratory.
Discussion
• The presence of anatase and rutile particles in BPA exposures had an
antagonistic effect on mortality in 120 hpf zebrafish.
• The lack of change in the malformation rate, even at 16 mg/L BPA
where mortality was decreased by anatase and rutile particles,
supports a similar mechanisms of toxicity.
• Our exposures were conducted under simulated light, thus the
breakdown of BPA via photocatalytic oxidation from free radicals
generated by TiO2 following UV exposure in water is possible.
• The anatase particles were smaller and are typically more reactive
to light than the rutile TiO2, yet no differences in toxicity existed
which suggests some other mechanism is driving the toxicity shift.
• The direct adsorption of BPA onto the surface of the TiO2 particles
would be expected to increase with increased particle surface area,
yet the toxicity shift was independent of agglomerate size.
• The linear relationship between the anatase rates of size change may
indicate an ordered interaction at the surface of the particle.
• The lack of linearity for the rutile rate of HDD change may indicate
a distinct lack of order between the association of BPA and the
rutile crystal structure.
Conclusions
• Interactions are occurring between BPA and TiO2 that are dependent
to the crystals structure of TiO2 .
• The concentration-dependent interaction between BPA and anatase or
rutile particles may reduce the toxicity of BPA to aquatic species,
supporting the use of TiO2 for water remediation.
• Continued investigation into the specific types of interactions
occurring between BPA and TiO2 nanoparticles is warranted.
Introduction
• Titanium Dioxide (TiO2) is the nanoparticle investigated and is commonly
used for water remediation and detecting water contaminants, preserving
food as an antimicrobial, providing color and texture to cosmetic products
and for UV protection for sunscreens and foods.
• Titanium Dioxide also has photocatalytic properties, which makes it valuable
for possible water treatment.
• Below is a basic diagram displaying how TiO2 can break up harmful
chemicals by utilization of UV light and freed electrons.
• There are three different crystal structures of TiO2 each having different
surface properties. These structures are known as rutile, anatase and
brookite. Only anatase and rutile TiO2 are examined in this study.
• Bisphenol A (BPA) was selected as our chemical contaminant because it is
commonly found in surface or ground water and it is a contaminant that
could be targeted for this chemical breakdown.
• BPA is a known endocrine disruptor that is used in plastics and epoxy resins
found in consumer products.
UV
Light
Photocatalytic
TiO2 NP
+
+
+
+
-
Electron hole
electron
OH-Bond
OH-
Radical
Harmful
chemical
“Hopefully”
harmless
breakdown
product
Figure 1. Process of UV light exposure to TiO2 NP
Figure 2. Chemical structure of bisphenol A.
Methods & Materials
Characterization
• Hydrodynamic diameter (HDD) and zeta potential of
the NPs in the presence of BPA was determined by
Dynamic Light Scattering (DLS).
• Samples were taken from suspensions prepared in
filtered (0.22 μm) fish exposure solution and measured
at 0, 4, 8, 12, and 24 hours.
• The TiO2 concentration was held constant at 10 mg/L
in the solutions and BPA concentrations were varied at
0, 10, and 20 mg/L.
10mg/L NP in exposure fish water
No BPA 10mg/L BPA 20mg/L BPA
Figure 3. Schematic of
solution size measurements
using Dynamic Light
Scattering
Developmental Zebrafish Assay
• Zebrafish embryos were from group spawns of wild-
type (5D) fish.
• At 8 hours post-fertilization (hpf) embryos were
dechorionated and exposed to BPA alone or mixtures of
BPA /NP at varying concentrations.
BPA alone BPA & 10 mg/L NP
Figure 4. Schematic of ZF embryos into 96
well plates
Nanomaterials
• Anatase (≤25 nm), and rutile (≤100 nm) powders were
obtained from Sigma-Aldrich; P25 (≤25 nm) powder
from Evonik Industries.
• TiO2 solution were prepared fresh and ultrasonicated
for 10 minutes immediately prior to the time 0 reading.
• TiO2 concentration was held constant at 10 mg/L and BPA concentration varied at 0,
2, 6, 10, 16, and 20 mg/L.
• Plates were kept at 28.6 C under 14 h light/10 h dark simulated natural light.
• Mortality was assessed daily and sublethal responses were evaluated at 24 and
120hpf.
Concentration BPA (mg/L)
0 10 20
ZetaPotential(mV)
-16
-14
-12
-10
-8
-6
-4
-2
0
0 hours
4 hours
8 hours
12 hours
24 hours
**
*
*
*
*
*
Figure 5. Zeta potential of 10 mg/L
P25 and BPA over 24 hours. (*)
indicates significant difference from
hour 0 measurement (Two-Way
ANOVA, p ≤ 0.05)
• The presence of BPA altered the rate of
size change for all particles (Figure 8).
• The relationship between anatase rate
and BPA concentration is linear
(R2=0.98).
• Anatase agglomerates are decreasing in
size at a decreasing rate in the presence
of increasing BPA concentrations.
• P25 agglomerates are decreasing in size
at an increasing rate in the presence of
increasing BPA concentrations.
Concentration BPA (mg/L)
0 10 20
Size(r.nm)
0
500
1000
1500
2000
2500
3000
3500
0 hours
4 hours
8 hours
12 hours
24 hours
*
* * *
Figure 6. Hydrodynamic diameter of
10 mg/L P25 and BPA over 24 hours.
(*) indicates significant difference
from hour 0 measurement (Two-
Way ANOVA, p≤0.05)
Figure 8. Rate of change in HDD during
first 8 hours.
Nanomaterials
(10mg/L)
Concentration of
BPA
PDI Initial HDD
(r.nm,0 hour)
Final HDD
(r.nm, 24
hour)
Rutile 0 .693 2061.0 2199.7
10 .854 2509.3 2613.7
20 .822 2935.3 2485.3
Anatase 0 .791 1282.3 1295.7
10 .785 1275.0 1358.6
20 .797 1347.0 1346.7
P25 0 .497 1371.0 1381.0
10 .510 1997.0 1902.0
20 .530 1519.0 1537.0
• Nanoparticle agglomeration occurred in the fish exposure solution (Table 1).
• HDD and zeta potentials were dynamic over the measurement period (Figures 5, 6).
Table 1. Polydispersity index (PDI) as well as initial and final HDD of each nanomaterial measured by DLS.
Figure 7. Zebrafish mortality at 120 hpf.
(*) indicates significant difference from
exposure to BPA alone. (Fisher’s exact test,
n=16 for each exposure, p < 0.0001).
Toxicity
• Coexposure of BPA and rutile or anatase
TiO2 resulted in differential toxicity in
zebrafish when compared to BPA alone
(Figure 7).
• P25 had no influence on BPA toxicity.
• No significant differences in any of the 19
assessed sublethal responses were noted
following any of the coexposures.