Titanium dioxide

Toxicity to terrestrial plants

Description of key information

 Chronic toxicity data are available for the effect of upgraded ilmenite (>80% TiO2) to barley and lettuce. Significant effects were not observed up to the highest concentration tested, resulting in an unbounded NOEC of >= 100,000 mg/kg dw. With regard to the phytotoxicity of nanoforms, the application of TiO2 NPs up to 100 mg/kg did not affect germination and root growth of Avena sativa, Phaseolus aureus and Sinapis alba, but fresh shoot weight of Avena s. was slightly lower at 100 mg/kg. However, nominal concentrations of up to 1000 mg/kg soil of micro- and nanosized TiO2 did not result in toxicity to Triticum spp. but in an increase of above-ground biomass. In sum, toxicity data from standard toxicity tests seems to indicate that micro-and nanosized TiO2 has a low potential for toxicity to mono- and dicotyledon plant species. 

Additional information

Microsized TiO2:

Chronic toxicity data are available for the effect of upgraded ilmenite (>80% TiO2) to a monocotyledon and dicotyledon species (barley and lettuce, respectively). Significant effects were not observed up to the highest concentration tested, resulting in an unbounded NOEC of >= 100,000 mg/kg dw. Upgraded ilmenites (UGI) consist primarily (> 80%) of titanate, i.e., TiO2 with Fe, Al, Si, Mg and other metals, and are poorly soluble and not biodegradable.

The transformation/dissolution of 3 UGI products at loadings of up to 100 mg/L over 28 d did not result in any significant release of titanium (Skeaff and Hardy, 2007). Bulk and nano-TiO2 forms are also poorly soluble in environmental media (Brouwers, 2009; Klawonn, 2017 a-f). Based on similarity in composition and the same poor solubility of UGI and TiO2, read-across of ecotoxicological data from UGI to TiO2 is justified.

Furthermore, Klingenfusss et al. (2014) observed that nominal concentrations of 1000 mg/kg soil of TiO2 bulk did not reduce plant growth of Triticum spp. (wheat), including plant height, chlorophyll content of leaves, area of the flag leaves, lengths of upper and lower culms, number of tillers and ears, shoot to root ratio, root biomass, number and phosphorous concentration of grains, on a soil-sand mixture in a long-term (84 d) study. On the contrary, an increase in above-ground biomass by TiO2 bulk was observed.

Nominal concentrations of up to 1000 mg/kg soil of E171 bulk TiO2 (92 ± 31 nm) did not affect plant growth of Triticum spp. (spring wheat), based on shoot and root dry weight, chlorophyll content of leaves as well as number and dry weight of ears, in a soil-sand mixture in a long-term (84 d) study. 84 d-NOEC values ≥ 1000 mg/kg soil dw were derived for all endpoints (Moll et al., 2017).

Nanosized TiO2:

With regard to the phytotoxicity of nanoforms, nominal concentrations of up to 1000 mg/kg soil of two types of TiO2 NPs (i.e., anatase and anatase/rutile with ratio 3-4:1) did not affect plant growth of Triticum spp. (wheat) – a monocotyledon species, including height, chlorophyll content of leaves, area of the flag leaves, lengths of upper and lower culms, number of tillers and ears, shoot to root ratio, root biomass, number and phosphorous concentration of grains, on a soil-sand mixture in a long-term (84 d) study by Klingenfuss (2014). On the contrary, an increase in above-ground biomass by both types of TiO2 NPs was observed. In a study by Moll et al. (2017), nominal concentrations of up to 1000 mg/kg soil of P25 TiO2 NPs (29 ± 9 nm) did not affect plant growth of Triticum spp. (spring wheat), based on shoot and root dry weight, chlorophyll content of leaves as well as number and dry weight of ears, in a soil-sand mixture in a long-term (84 d) study. 84 d-NOEC values ≥ 1000 mg/kg soil dw were derived for all endpoints. Application of TiO2NPs (rutile) via powder up to 100 mg/kg and via suspension up to 20 mg/kg did not affect germination and root growth of three species (Avena sativa, Phaseolus aureus and Sinapis alba), a monocotyledon and two dicotyledons, in a sandy soil in a study according to OECD 208 (2006) by Hund-Rinke et al. (2013). Further, phyto-pathological symptoms were not observed at any application. The EC50 values for fresh shoot weight of Avena sativa, Phaseolus aureus and Sinapis alba are > 100 mg/kg. However, shoot weight may be sensitive as fresh shoot weight of Avena s. was slightly lower at 100 mg/kg when applied via powder. Unfortunately, dry weight of shoots as the more reliable measure of plant growth was not measured in this study by Hund-Rinke et al. (2013). Considering the stimulation of above-ground plant growth in the long-term study by Klingenfuss (2014), these slight effects on fresh shoot weight should not be over-interpreted.

In sum, toxicity data from standard toxicity tests seems to indicate that micro-and nanosized TiO2 has a low potential for toxicity to mono- and dicotyledon plant species.