Titanium dioxide

Long-term toxicity to aquatic invertebrates

Description of key information

Dispersed microsized TiO2 is not chronically toxic to freshwater invertebrates, such as Daphnia magna, up to at least 10 mg/L (EC50: > 10 mg/L, nominal). Considering the low solubility of microsized TiO2, it is further concluded that microsized TiO2 is not toxic up to its solubility limit. Several guideline studies of dispersed nanosized TiO2 indicate that the chronic toxicity to aquatic freshwater invertebrates is also low with NOEC values ranging from > 1 mg/L to ≥ 100 mg/L.

Additional information

Microsized TiO2:

Campos et al. (2013) tested dispersions (1 and 10 mg/L, nominal) of the TiO2 bulk material (Tiona AT 1, 200 nm, anatase) the age at first brood, size of first brood, cumulative fecundity, body length of adult females after 21 d and body length of adults at first maturity, and the population growth rate of Daphnia magna were not affected in a semi-static chronic toxicity tests according to OECD 202 (1981, and OECD 211). Derived unbounded 21 d NOEC values for these endpoints amounted ≥ 10 mg/L (nominal) and ≥ 2.33 when based on measured concentrations of Tiona AT 1. Results of additional non-standardised tests by Campos et al. (2013) are not relevant for the hazard assessment of TiO2 because the tests were performed under depleting food conditions, which are expected to enhance daphnia sensitivity, or for a shorter test period than recommended in OECD 211. One supporting study by Beim et al. (1982) on the chronic toxicity of microsized TiO2 to Daphnia magna reveals some toxic effects on the reproduction (30 d NOEC: ≥ 5-<10 mg/L) and survival (30 d NOEC: 70 mg/L) of daphnids. However, since limited information on test performance was provided, results from the study by Beim et al. (1982) are considered supporting data.

Furthermore, transformation/dissolution data of different microsized TiO2 materials indicate a low solubility in environmental media as dissolved Ti concentrations after 28 d were below the respective LOD/LOQ (< 0.11 / < 0.34 µg Ti/L). Hence, chronic invertebrate tests with dispersed microsized TiO2 were performed at TiO2 concentrations several magnitudes above the solubility limit. Thus, it is further concluded that microsized TiO2 is not chronically toxic to freshwater invertebrates up to its solubility limit.

Data on marine organisms does not exist.

Nanosized TiO2:

Campos et al. (2013) tested dispersions (1 and 10 mg/L, nominal) of the nanosized TiO2 materials NM 103 (20 nm, rutile, hydrophobic coating), NM 104 (20 nm, rutile, glycerin coating), and P25 (21 nm, rutile-anatase) and the age at first brood, size of first brood, cumulative fecundity, body length of adult females after 21 d, and the population growth rate of Daphnia magna were not affected in semi-static, chronic toxicity tests according to OECD 202 (1981); the respective 21 d NOEC value amounted to ≥ 10 mg/L (nominal) for all materials and ≥ 2.80, 3.12, and 2.70 mg/L when based on measured dispersed concentrations of NM 103, NM 104 and P25.
The body length of adults after 21 d was not affected at 10 mg/L NM 103, NM 104 or P25 compared to control organisms whereas the body length of adult organisms at first maturity was reduced at 10 mg P25/L (nominal). However, the endpoint body length of adults after 21 d is the standardised endpoint recommended in OECD 211 to assess effects on growth of D. magna. Furthermore, the observed effects of P25 on body length of adults at first maturity do not influence age at first brood, survival of adult organisms, and cumulative fecundity, and fitness measurements such as population growth rate, i.e. endpoints that are typically the most sensitive and also the most critical chronical endpoints according to OECD 211 and ECHA Guidance on IR & CSA, Chapter R. 7b (Version 3.0; February 2016). Thus, the respective 21 d NOECs of NM 103, NM 104 and P25 for reproduction and growth of Daphnia magna amount to ≥ 10 mg/L (nominal dispersed). Results of additional experiments performed in this study are not considered for the hazard assessment of nano-TiO2 because the tests were performed under depleting food conditions, which are expected to enhance daphnia sensitivity, or for a shorter test period than recommended in OECD 211.

Results of the study of Hund-Rinke et al. (2013) confirm that dispersed nano-TiO2 is not chronically toxic to daphnids up to 5 mg/L (nominal). In this study, daphnids were exposed to 1 and 5 mg/L (nominal) dispersed n-TiO2 (P25, 21 nm) in five independent semi-static limit tests (OECD 211) and the media were renewed daily or three times per week. Unbounded 21 d NOEC values of ≥ 5 mg/L (nominal) were determined for mortality, mobility and body length in all 5 experiments. Unbounded 21 d NOEC values of ≥ 5 mg/L for reproduction were derived in three of five experiments. However, reproduction was reduced by 10-16% at 5 mg/L in two experiments resulting in a LOEC of 5 mg/L (nominal). A NOEC should nevertheless not be derived from the latter two experiments since the separation factor should not exceed 3.2 according to OECD 211. Based on results of all five experiments by Hund-Rinke et al. (2013), the toxic potential of nano-TiO2 is low for daphnids with the NOEC being > 1 mg/L up to ≥ 5 mg/L. 

In addition, a multigeneration study was performed by Hartmann et al. (2019) according to OECD Guideline 211 to assess the long-term toxicity of TiO2-NPs (NM-105) on Daphnia magna over several subsequent generations. Daphnids were exposed to three concentrations (0.025, 0.05, 0.1 mg Ti/L) of pristine TiO2 NPs dispersed in ASTM reconstituted hard water as well as three concentrations of wastewater effluent containing Ti (originating from model STPs operated for 6-10 days in accordance with OECD 303a). Neither pristine nor wastewater-borne TiO2 NPs caused any significant effects on the reproduction (mean number of offspring), adult mortality, body length and time to first brood of Daphnia magna, and thus a NOEC ≥ 0.1 mg Ti/L (corresponding to ≥ 0.17 mg TiO2/L) was derived for all six generations. Tested concentrations were however selected based on environmental relevance, and testing was not performed at the limit concentration of 10 mg/L (as specified in OECD TG 211).

 

Evaluating the available data of all five tests by Hund-Rinke et al. (2013) as well as the results obtained by Hartmann et al. (2019), and considering that Campos et al. (2013) did not observe effects on reproduction at concentrations of 10 mg/L n-TiO2 (nominal, dispersed), one may conclude that the long-term toxic potential of nano-TiO2 is low for daphnids.

 

Two studies on the chronic toxicity of nano-TiO2 to the epibenthic and endobenthic freshwater organisms Chironomus riparius and Lumbriculus variegatus exposed via the water phase, further indicate that the long-term toxic potential of nano-TiO2 is low for aquatic invertebrates. Although these tests are sediment tests, the organisms were exposed via the water phase so that the respective results are relevant for freshwater assessment. Schaefers et al. (2013) exposed Lumbriculus variegatus to dispersions of the nanosized TiO2 material P25 (21 nm) by direct addition to the overlaying water in a chronic sediment toxicity test according to OECD guideline 225. The derived 28 d NOEC values for biomass and reproduction of Lumbriculus variegatus were ≥ 100 mg/L (nominal). Furthermore, Hund-Rinke et al. (2013) tested the chronic toxicity of dispersions of the nanosized TiO2 materials P25 (anatase, rutile, 21 nm) and Homibkat UV 100 (anatase, 8 nm) applied to the overlaying water in a chronic sediment toxicity test according to OECD 219. Emergence and development rate of Chironomus riparius were not affected resulting in 28 d NOEC values of ≥ 100 mg n-TiO2/L (nominal). One supporting study on the chronic toxicity of nanosized TiO2 to the freshwater clam Corbicula fluminea additionally indicates that nanosized TiO2 is not chronically toxic up to 1 mg/L to freshwater invertebrates. However, only one concentration was tested and the organisms were not fed during the test so that results from this study are supporting data. 

 

Data for marine organisms are not available.

 

In sum, dispersions of microsized TiO2 material are not chronically toxic to freshwater invertebrates, such as Daphnia magna, up to 10 mg/L (nominal). Considering the low solubility of microsized TiO2, it is further concluded that microsized TiO2 is not chronically toxic up to its solubility limit. The long-term toxic potential of dispersed nano-TiO2 is also low for freshwater invertebrates with NOEC values ranging from > 0.2 mg/L to ≥ 100 mg/L.