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EC number: 236-675-5
CAS number: 13463-67-7
Data available for uptake of micro- and nanosized TiO2 by
different plant and earthworm species indicate an absence of a
bioaccumulation and biomagnification potential.
In a reliable study by Caille et al. (2005), BSAF values of
titanium range from 0.0002 to 0.0008 kg/kg for leaves of 3 different
plant species (rape, cabbage and red fescue) grown for 54 days on
dredged sediment in the laboratory containing 3040 +/- 210 mg Ti/kg dw.
Hence, Ti has a low potential for bioaccumulation in plants.
Additionally, in a supporting study by Gogos et al. (2016), uptake
of E171 TiO2 bulk particles (primary particle size: 92 ± 31 nm) by
Trifolium pratense (red clover) and Triticum spp. (spring wheat) after
14 and 12 weeks of exposure, respectively, was not significantly changed
with exposure concentrations up to 1000 mg TiO2/kg soil (nominal)
compared to the control.
This low uptake of Ti in plants is assumed to be due to the low
solubility of microsized TiO2 at environmentally relevant conditions.
According to the recent ECHA guidance on aquatic bioaccumulation
(Appendix R 7-2 Recommendations for NM applicable to Chapter R7c) it is
not possible to predict the bioaccumulation of nanomaterials from the
log Kow or solubility. Hence, BCF/BAF values have to be experimentally
determined. Further, for nanomaterials that undergo dissolution it is
recommended to obtain information on the form of the substance as
present in the animal tissue. Since nano-TiO2 does not to dissolve under
environmentally relevant conditions, a potential uptake is unlikely to
be associated with the uptake of dissolved Ti forms. Thus, nanosized
TiO2 (if any) could potentially only be taken up of via adsorption to
biological surfaces, direct penetration, or endocytic processes such as
via phagocytosis, pinocytosis, and caveolae-dependent or
Furthermore, according to ECHA
guidance on terrestrial bioaccumulation of NM (Appendix R 7-2
Recommendations for NM applicable to Chapter R7c, 2017), estimates based
on “partitioning” may underestimate exposure in soil and sediment
environments while overestimating exposure in water in the case of
nanoparticles. Since estimation methods are not available, BCF/BAF
values have to be determined experimentally.
In several laboratory bioaccumulation studies with TiO2-NP and
plants and earthworms exposed to spiked soil, accumulation kinetics were
not addressed and it was not always clarified if steady-state conditions
Three studies on the
bioaccumulation of TiO2 nanoparticles in terrestrial plants are
In a reliable study by Gogos et
al. (2016), uptake of titanium by Trifolium pratense (red clover) and
Triticum spp. (spring wheat) during 14 and 12 weeks of exposure,
respectively, did not significantly increase with nominal exposure
concentrations up to 1000 mg/kg soil TiO2 nanoparticles (P25, primary
particle size: 29 ± 9 nm) compared to the control, indicating a low
bioaccumulation potential in plants. Additionally, TEM imaging coupled
with EDX analysis did not detect a significant number of Ti-containing
nano-sized particles inside plant root cells.
Bakshi et al. (2019, supporting
study) investigated uptake and translocation of nano-TiO2 in tomato
plants (Solanum lycopersicum) grown on soil containing sludge from a
pilot wastewater treatment plant. Micro- and nano-TiO2 in the well
characterized sludge (XANES, µXRF, ICP-MS) with average Ti concentration
of 819±62 mg/kg (approx. 10 % nanoparticles) originated from
wastewater. Compared to control uptake, Ti concentrations of leaves,
flowers and fruits were not elevated after 120 days of cultivation.
Titanium concentrations of aboveground plant tissues were < 2.59 mg/kg
dw, indicating a very low potential for Ti root/shoot translocation at
realistic nano-TiO2 concentrations of the substrate.
In a supporting study by
Klingenfuss (2014), wheat was grown in sandy soil spiked with TiO2-NP
for 84 d. TiO2 NPs were not found in wheat roots, suggesting that TiO2
nanoparticles were not taken up. Results on the translocation of Ti to
the wheat grain at elevated TiO2 soil concentrations are, however,
Earthworms (Eisenia fetida) were
exposed to 10 - 1000 mg/kg of different TiO2-NP (rutile/anatase, rutile,
anatase) in artificial substrate for 28 days. After a depuration period
of 24 h, whole body burdens were determined. For the different
nanomaterials, median biota-soil accumulation factors range from 0.08
-0.15 kg soil/kg earthworm and median biota-food accumulation factors
range from 0.09 -0.11 kg food/kg earthworm indicating that earthworms do
not bioaccumulate TiO2-NP via soil or food. Further, titanium in the
earthworms could not be localised and an adsorption of TiO2-NPs to the
cuticle of earthworms cannot be excluded (Hund-Rinke & Klawonn, 2013).
In sum, data available for the uptake of TiO2-NP or titanium by
different plant species and earthworms indicate a low bioaccumulation
and biomagnification potential.
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