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Ecotoxicological information

Toxicity to aquatic plants other than algae

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Reference
Endpoint:
toxicity to aquatic plants other than algae
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
Qualifier:
according to
Guideline:
OECD Guideline 221 (Lemna sp. Growth Inhibition Test)
GLP compliance:
yes
Remarks:
Range-finder was non-GLP
Details on sampling:
Will be submitted.
Vehicle:
no
Details on test solutions:
Will be submitted.
Test organisms (species):
Lemna minor
Details on test organisms:
Will be submitted.
Test type:
static
Water media type:
other: Will be submitted.
Limit test:
no
Total exposure duration:
7 d
Nominal and measured concentrations:
Range finder:
Nominal: 0 (control), 1, 10, 100 mg TiO2/L
Details on test conditions:
Range finder:
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
Further information on test conditions will be submitted.
Key result
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
Growth rate based on frond number, frond area and dry weight
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
Growth rate based on frond number, frond area and dry weight

Sedimentation of TiO2 nanoparticles was observed. However, roots of Lemna minor reached the bottom of the test vessel and are thus still in contact with the test material.

Particles in test medium were characterized with a Z-average size (d. nm) of 2329 nm, a polydispersity index of 0.364 (polydisperse) and a zeta potential of -16.5 (± 3.91) mV.

Table 1: Effect on frond number (range finder)

Nominal conc.  Growth rate 0-7 d Yield 0-7 d
[mg/L] G %I Y %I
Control 0.336 0.00 114.3 0.00
1.0 0.333 0.86 112.0 2.04
10.0 0.327 2.87 106.3 7.00
100.0 0.329 2.29 107.7 5.83

Table 2: Effect on total frond area (range finder)

Nominal conc.  Growth rate 0-7 d Yield 0-7 d
[mg/L] G %I Y %I
Control 0.357 0.00 1064.8 0.00
1.0 0.362 -1.38 1004.2 5.69
10.0 0.334 6.48 888.1 16.59
100.0 0.358 -0.31 970.1 8.90

Table 3: Effect on biomass (dry weight)

Nominal conc.  Growth rate 0-7 d Yield 0-7 d
[mg/L] G %I Y %
Control 0.350 24.30  
1.0 0.334 4.42 21.70 10.68
10.0 0.315 9.95 18.80 22.88
100.0 0.336 3.90 21.90 10.00
Validity criteria fulfilled:
yes
Remarks:
Range finder: doubling time (frond number) = 2.1 d, mean growth rate = 0.336/d
Conclusions:
In a 7-d range-finding test following OECD test guideline 221, dispersions of TiO2 nanoparticles (TiO2-uf-2) did not affect the growth rate of Lemna minor up to the highest tested concentration of 100 mg TiO2 NP/L (nominal) and a 7 d EC10 > 100 mg TiO2/L (nominal, growth rate) was determined. The growth rate was based on frond number, total frond area and biomass (dry weight). During the test, aggregation of TiO2 nanoparticles (z-average size: 2329 nm) and subsequent sedimentation of aggregated particles could be observed. To enable a continous exposure of the test organisms to TiO2 nanoparticles, dispersions were mixed daily. Furthermore, roots of Lemna minor reached the bottom of the test vessel and were still in contact with sedimented test material. Thus, it can be assumed that test plants were exposed to the test material for the entire test period.
Results from the definitive study will be submitted, when the final report is available.

Description of key information

In a 7-d range-finding test conducted in the course of a GLP guideline study following OECD test guideline 221, dispersions of TiO2 nanoparticles (TiO2-uf-2; primary particle size: 19 nm) did not affect the growth rate of Lemna minor up to the highest tested concentration of 100 mg TiO2 NP/L and a 7 d EC10 > 100 mg TiO2/L (nominal, growth rate) was determined (Schlich, 2017). The growth rate was based on frond number, total frond area and biomass (dry weight).

Furthermore, one supporting study on the toxicity of nanosized TiO2 to Lemna minor is available. Dispersed nano-TiO2 , i.e. Aeroxide P25, particle size: 27.6 ± 11 nm did not affect the growth rate of Lemna minor up to the highest tested concentration of 90 mg n-TiO2/L (nominal) under laboratory light conditions in a test performed according to ISO 20079. An unbounded 7 d NOEC value of ≥ 90 mg/L was determined. Since the test medium was not described, the respective results are considered supporting data.

Both studies indicate a low toxic potential of nanosized TiO2 to aquatic plants.

Key value for chemical safety assessment

Additional information