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(Nano)-Titanium dioxide (Part III): Environmental effects

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Institute of Technology Assessment
of the Austrian Academy of Sciences NNoo.. 003355eenn DDeecceemmbbeerr 22001122
Introduction
Titanium dioxide (TiO2) has been industrial-
ly produced and used for over 100 years
(see NanoTrust Dossier 033en); this makes
nano-titanium dioxide (nano-TiO2) the best
investigated of all nanomaterials. Its abun-
dance also raises the question of risks to
the environment from TiO2both in its reg-
ular and nano-form. Numerous in-vivo and
in-vitro studies have been conducted to de-
termine the environment-related risks. This
dossier provides a brief overview. Details,
compilations of studies as well as in-depth
risk assessments are available from a num-
ber of international bodies (EU, IARC, OECD,
FDA, CDC).
Environmental effects
of nano-TiO2
As already reported in detail in the Dossier
Environment1, the impacts of nano-TiO2
are the best investigated among nanoma-
terials. Many animals and plants as well
as the media water and soil (aquatic, ter-
restrial) have been studied. One criticism
is that the results of the studies are not com-
parable because the respective NPs (and
therefore their properties) vary from man-
ufacturer to manufacturer2. Moreover, the
presence and distribution of synthetic na-
noparticles in the environment are almost
completely unknown3, with the exception
of a few modeling studies in which environ-
mental concentrations were calculated4; 5.
Nonetheless, experimental approaches pro-
vide evidence for harmful effects both in
aquatic and terrestrial ecosystems, although
such impacts were demonstrable only at
very high doses. An industrial accident,
however, could release such concentrations
of nano-TiO2and pose a risk to algae,
plankton and fishes6. The US Environmen-
tal Protection Agency EPA7has compiled
an overview of research results on TiO2-
NPs on the aquatic environment8; 9:
For algae, which serve as the basis of
marine food chains, values exceeding
30 mg/l are harmful. 30 mg/l photocat-
alytic and 90 mg/l photostable nano-
TiO2impede growth.
For water fleas (Daphnia magna, Fig-
ure 1), which are accepted test organ-
isms and indicators for environmental
impacts, damage was caused by photo-
catalytic particles at concentrations from
5.5 to 10 mg/l (LC50 see also10). For coat-
ed nano-TiO2, an LC50-value of 100 mg/l
was determined.
For fish (rainbow trout, Oncorhynchus
mykiss as an aquatic test organism) an
LC50-value of 100 mg/l photostable
TiO2-NPs was determined. In the case
of chronic exposure to photocatalytic
particles, a value of 0.1 mg/l already led
to oxidative stress and altered organ
structure. The accumulation in the or-
gans, however, apparently does not im-
pair their function (see also11; 12).
Summary
Nano-titanium dioxide (nano-TiO2) is the
nanomaterial produced in the greatest
amounts and is already a component in
many products, both in its regular and
nano-scale size. This also makes it the
best-investigated nanoparticle. Many in-
vivo and in-vitro studies have been con-
ducted to test for potential environmen-
tal risks. Nonetheless, the possible long-
term effects remain unknown. Short-term
exposures to high doses showed dam-
age both in aquatic and in terrestrial
ecosystems. No specific regulations for
nano-TiO2are currently in place.
1
* Corresponding author
(Nano)-Titanium dioxide (Part III):
Environmental effects
Myrtill Simkó*,
René Fries
Figure 1:
The water flea (Daphnia magna)17
NNoo.. 003355eenn DDeecceemmbbeerr 22001122
One study experimentally simulated a run-
ning water system and added photocatalyt-
ic nano-TiO2(5 mg/l water) in order to in-
vestigate the effects on the microbial com-
munities under natural conditions13. Both
TiO2-NPs as well as larger natural agglom-
erates significantly damaged the microor-
ganisms. The authors concluded that the mi-
crobial communities reacted very sensitive-
ly to NP concentrations that can be expect-
ed in the environment. The resulting impacts
on the ecosystem itself remain unknown.
A further study reported on the effect of UV
light on the toxicity of photoactive nano-
TiO2(1 mg/l)14. Laboratory measurements
showed that even the very low UV intensi-
ties that occur near the ocean surface can
trigger significant toxic damage to aquatic or-
ganisms (phytoplankton). The authors there-
fore identify the need to consider the pho-
toactive (toxic) properties of nanomaterials.
It remains unknown how TiO2-NPs behave
along food chains. Does a transfer of the
particles take place from animal to animal
or from plant to animal through food up-
take? A first study shows that this is experi-
mentally possible. Daphnia fed with TiO2-
NPs were subsequently fed to zebra fishes
(Danio rerio) and the particles were found
in the fishes. The long-term effect of such
particles on these fishes and on other food
chains is not known.
Effects on sewage
treatment plants
The issue of accumulation of TiO2-NPs is rel-
evant not only for the environment but also
for sewage treatment plants, where an ac-
cumulation can actually take place. Two stud-
ies4; 5 came to the conclusion that risks for
aquatic organisms through nano-TiO2in
waste streams in all regions considered (USA,
Europe, Switzerland) could not be excluded.
This pertained both to surface waters as well
as to the wastewater in sewage treatment
plants. The calculations are based on a sce-
nario using current estimated values (no ex-
trapolation into the future was undertaken
because the uncertainty of such data was too
high). The simulations involved both a re-
alistic as well as a so-called „worst case sce-
nario” based on generally accepted values
(see Table 1). Since 2006 it is no longer per-
missible to spread sewage sludge on agri-
cultural land. This has minimized soil con-
tamination with nano-TiO2. If this ban did
not exist and sewage sludge was applied on
50 % of such land, this would yield the high-
er values (marked with KS)4in Table 1. The
second study5 simulated material flows for
different regions (Europe, Switzerland and
the US). The data for surface waters and for
treated wastewater represent the actual val-
ues in 2008. In contrast, the data for soils
consider the annual increase in the NP con-
centration and separately treat soils with (KS)
and without (noKS) fertilization with sewage
sludge. This makes the newer simulation
more precise (Table 2). Interestingly, the con-
centrations of nano-TiO2in treated waste-
water and in soils are lower than in the ear-
lier study.
Another study investigated the purification
effect of the sewage treatment facilities in
greater detail. The results show that a good
biological wastewater treatment retains
more than 98 % of the TiO2-NPs from the
wastewater flows and that the use of micro-
filtration is more effective than the common-
ly used settling tanks15. The remaining con-
centration of Ti in the treated wastewater typ-
ically lies between 2 and 20 µg/l.
One study focused on the question of what
effects TiO2-NPs have on those bacterial
colonies in sewage treatment plants that de-
compose nitrogen and phosphorus com-
pounds. Over the short term (1 day), TiO2
concentrations of 1 or 50 mg/l showed no
effects. It required a long-term period (70
days) with a very high TiO2concentration (50
mg/l) to significantly reduce nitrogen decom-
position from 80 % to 24 %. A more detailed
DNA study of the bacterial strains showed
that this was caused by a strongly reduced
microbial diversity16.
Effects on soils
Similar results were obtained in studies on
soil samples from meadows (California,
USA), where TiO2-NPs were applied at dif-
ferent concentrations (0, 0.5, 1.0, and 2.0
mg/g soil) and times (15 days and 60 days)
(see also6). The effects on the natural soil
bacteria communities were investigated. The
authors determined that both amount of mi-
croorganismic biomass and its diversity
changed over time. The impacts were dose-
dependent and already present at the low-
est dose applied (0.5 mg/g soil). The authors
point to model calculations5that predict the
annual amount of TiO2-NPs spread by sew-
age sludge to be 0.09 mg/kg soil, under-
lining the potential risks to the environment.
2
rs ... realistic scenario
ws ... worst case scenario
KS ... with sewage sludge application
noKS ... without sewage sludge application
Table 1:
Different scenarios for
nano-TiO2concentrations in wastewater, sewage sludge and soil
Study Concentration of nano-TiO2
In treated wastewater
(in µg/l)
In sewage sludge
(in mg/kg)
In soil
(in µg/kg)
MUELLER 200840.7 (rs) to 16 (ws) no data 0.4 (rs) to 4.8 (ws), 120 (KS)
GOTTSCHALK
20095
3.5 (Europe)
1.8 (USA)
4.3 (Switzerland)
136 (Europe)
137 (USA)
211 (Switzerland)
Europe (annual input):
1.3 (noKS) to 89 (KS)
USA (annual input):
0.5 (noKS) to 42 (KS)
Switzerland (annual input):
0.3 (noKS)
NNoo.. 003355eenn DDeecceemmbbeerr 22001122
Notes and References
1NanoTrust Dossier, 027en.
2Menard, A., Drobne, D. and Jemec, A., 2011,
Ecotoxicity of nanosized TiO2. Review of in vi-
vo data, Environ Pollut 159(3), 677-84.
3Peralta-Videa, J. R., Zhao, L., Lopez-Moreno,
M. L., de la Rosa, G., Hong, J. and Gardea-
Torresdey, J. L., 2011, Nanomaterials and the
environment: a review for the biennium 2008-
2010, J Hazard Mater 186(1), 1-15.
4Mueller, N. C. and Nowack, B., 2008, Expo-
sure modeling of engineered nanoparticles in
the environment, Environ Sci Technol 42(12),
4447-53.
5Gottschalk, F., Sonderer, T., Scholz, R. W. and
Nowack, B., 2009, Modeled environmental
concentrations of engineered nanomaterials
(TiO(2), ZnO, Ag, CNT, Fullerenes) for differ-
ent regions, Environ Sci Technol 43(24), 9216-
22.
6Zhang, R., Bai, Y., Zhang, B., Chen, L. and Yan,
B., 2012, The potential health risk of titanium
nanoparticles, J Hazard Mater 211-212, 404-
13.
7EPA (U.S. Environmental Protection Agency),
2010, State of the Science Literature Review:
Nano Titanium Dioxide Environmental Matters.
Scientific, Technical, Research, Engineering and
Modeling Support (STREAMS) Final Report, Nr.
EPA/600/R-10/089, August 2010.
8Adams, L. K., Lyon, D. Y., McIntosh, A. and Al-
varez, P. J., 2006, Comparative toxicity of na-
no-scale TiO2, SiO2and ZnO water suspen-
sions, Water Sci Technol 54(11-12), 327-34.
9Hund-Rinke, K. and Simon, M., 2006, Ecotox-
ic effect of photocatalytic active nanoparticles
(TiO2) on algae and daphnids, Environ Sci Pol-
lut Res Int 13(4), 225-32.
10 NanoTrust Dossier 028en.
11 Federici, G., Shaw, B. J. and Handy, R. D.,
2007, Toxicity of titanium dioxide nanoparti-
cles to rainbow trout (Oncorhynchus mykiss):
gill injury, oxidative stress, and other physio-
logical effects, Aquat Toxicol 84(4), 415-30.
12 Ramsden, C. S., Smith, T. J., Shaw, B. J. and
Handy, R. D., 2009, Dietary exposure to tita-
nium dioxide nanoparticles in rainbow trout,
(Oncorhynchus mykiss): no effect on growth,
but subtle biochemical disturbances in the
brain, Ecotoxicology 18(7), 939-51.
13 Battin, T. J., Von der Kammer, F., Weilhartner,
A., Ottofuelling, S. and Hofmann, T., 2009,
Nanostructured TiO2: Transport Behavior and
Effects on Aquatic Microbial Communities un-
der Environmental Conditions, Envir Sci Tech-
nol 43(21), 8098-8104.
14 Miller, R. J., Bennett, S., Keller, A. A., Pease,
S. and Lenihan, H. S., 2012, TiO2nanopar-
ticles are phototoxic to marine phytoplankton,
PLoS One 7(1), e30321.
15 Westerhoff, P., Song, G., Hristovski, K. and Kiser,
M. A., 2011, Occurrence and removal of tita-
nium at full scale wastewater treatment plants:
implications for TiO2nanomaterials, J Environ
Monit 13(5), 1195-203.
16 Zheng, X., Chen, Y. and Wu, R., 2011, Long-
term effects of titanium dioxide nanoparticles
on nitrogen and phosphorus removal from
wastewater and bacterial community shift in
activated sludge, Environ Sci Technol 45(17),
7284-90.
17 Lovern, S. B., Strickler, J. R. and Klaper, R.,
2007, Behavioral and Physiological Changes
in Daphnia magna when Exposed to Nanopar-
ticle Suspensions (Titanium Dioxide, Nano-C60,
and C60HxC70Hx), Envir Sci Technol 41(12),
4465-4470.
3
Conclusions (Parts I to III)
TiO2is a widely distributed substance that is currently incorporated in many different prod-
ucts including sunscreens and foods. This explains why TiO2is so well studied, even if no
long-term studies on nano-TiO2are available. In epidemiological studies, regular TiO2showed
no TiO2-specific effects related to cancer incidence. Nonetheless, based on animal exper-
iments, international bodies have classified this material as “possibly carcinogenic in hu-
mans”. Although specific studies conducted by the FDA clearly point to an extremely low
risk, the remaining uncertainties and discrepancies lead to the recommendation to use cau-
tion when applying nano-TiO2-containing cosmetics to injured skin.
Many studies have been conducted to describe the potential environmental effects of nano-
TiO2. As most of these studies involved extremely high doses, any definitive statements on
the environmentally relevant risks remain speculative. Nonetheless, the consensus is that
small amounts represent a rather low risk to the environment, whereby the long-term ef-
fects with low doses of nano-TiO2remain unclear. There are currently no actually meas-
ured data on environmental exposure; another unclarified issue is how TiO2-NPs behave
in food chains. Whether a transfer of the particles takes place from animal to animal or
from plant to animal through feeding also remains unclear. We have no information about
the effects that the particles may exert over the long term on aquatic and terrestrial ecosys-
tems. This calls for urgent and targeted research in this field.
MASTHEAD:
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www.oeaw.ac.at/ita
Mode of publication: The NanoTrust Dossiers are published irregularly and contain the research
results of the Institute of Technology Assessment in the framework of its research project NanoTrust.
The Dossiers are made available to the public exclusively via the Internet portal “epub.oeaw” :
epub.oeaw.ac.at/ita/nanotrust-dossiers
NanoTrust-Dossier No. 035en, December 2012: epub.oeaw.ac.at/ita/nanotrust-dossiers/dossier035en.pdf
ISSN: 1998-7293
This Dossier is published under the Creative Commons
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licence: creativecommons.org/licenses/by-nc-nd/2.0/at/deed.en
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