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Sediment toxicity

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Sediment toxicity tests reveal that microsized TiO2 is not chronically toxic to sediment organisms up to concentrations of at least 100,000 and 14,989 mg/kg dw (nominal) in freshwater and marine sediment, respectively. Two sediment-spiked toxicity tests and three water-spiked sediment toxicity tests further point to a low toxic potential of nanosized TiO2 for freshwater epi- and endobenthic organisms, with NOEC values of ≥ 851.1 mg/kg dw (measured, initial) as well as EC10, EC50 values > 1000 mg/kg dw (nominal) for sediment-spiked tests and NOEC values ≥ 100 mg/L (nominal) for water-spiked tests, respectively.

Key value for chemical safety assessment

Additional information

Microsized TiO2:

Data are available for freshwater and marine sediments. A 28 d exposure of upgraded ilmenite (>80% TiO2) up to 100,000 mg/kg dw did not affect survival and growth of Hyalella azteca in freshwater sediment (Arcadis et al. 2008).

The 10 day exposure of the marine amphipod Corophium volutator to a sediment spiked with microsized TiO2 in a non-standardized toxicity assay under GLP conditions did not affect its survival resulting in a 10-d NOEC of 14,989 mg/kg dw (nominal) (Hudson, 2007).

In a freshwater mesocosm study (Jovanovic et al. 2016), rated as supporting, autoclaved natural sediment was spiked with 25 mg/kg titanium dioxide E171 and incubated for 100 days (July to November) in the original pond. Thereafter, the reinvasion of macroinvertebrates was analysed by evaluating the macroinvertebrate community structure by means of non-metric multidimensional scaling (NMDS), multivariate analysis of variance, and indicator value analysis after identifying all recovered organisms at the lowest possible taxonomic level. Czekanowski’s index was 0.61, meaning that 39% of the macroinvertebrate community structure was negatively or positively affected by TiO2. The absolute abundance of Chironomus luridus agg, Radix auricularia, Theodoxus transversalis, Lymnea stagnalis, Psectrotanypus varius, Trichoptera, Endochironomus tendens, Chaoborus sp., Baetis sp., Chironomus plumosus, and Asellus aquaticus was comparable to the abundance in controls. In contrary, the absolute abundance of the gastropods P. corneus and R. labiata was significantly lower in the TiO2 treatment compared to control, and the absolute abundance of the Ceratogonidae (Diptera) per tray was significantly enhanced in the TiO2 treatment compared with the control. Nevertheless, this study is only considered supporting, since reinvasion or avoidance is generally not considered as a relevant endpoint for the environmental hazard assessment. Furthermore, it is not possible to derive valid effect values, since only one concentration was tested, and sediment and water were not well characterized.

Nanosized TiO2:

Regarding the toxicity of TiO2-NP to sediment organisms, a GLP guideline study following OECD 225 revealed that the total number and biomass (worm dry weight) of Lumbriculus variegatus were not affected up to 851.8 mg TiO2/kg sediment dw (28 d NOEC ≥ 851.8 mg/kg dw, measured (initial)), when TiO2 NP (PC105, anatase, 19 nm) were directly spiked into artificial sediment (Simon, 2019). Due to the high background level of the artificial sediment in the test, effect concentrations were based on the mean measured background-corrected concentration at test start.

Additionally, no effects were observed after 28 d exposure of adult Lumbriculus variegatus to artificial sediment spiked with TiO2 nanoparticles (NM-104; 26 nm, rutile, Al-coated) in a chronic sediment toxicity test according to OECD TG 225 by Hund-Rinke et al. (2016). A 28 d EC10 and EC50 of > 1000 mg TiO2 NP/kg sediment dw (nominal) were derived for both survival/reproduction and growth (dry biomass).

Furthermore, reproduction and growth of Lumbriculus variegatus as well as emergence and development rate of Chironomus riparius were not affected up to 100 mg/L TiO2 (rutile/anatase, both tests: 28 d NOEC ≥ 100 mg/L) in water-borne exposure tests according to OECD 225 and OECD 219, respectively (Schäfers & Weil, 2013; Hund-Rinke & Klawonn, 2013).

One supporting sediment toxicity study is available and results indicate that nanosized TiO2 is also not chronically toxic to Hyalella azteca when applied via the sediment: In a chronic toxicity test according to EPA 600/R-99/064, Wallis et al. (2014) exposed Hyalella azteca (7-8 d old) to 20 and 100 mg/L of the nano-sized TiO2 material P25 (nominal) in a natural sediment under laboratory light and simulated solar radiation conditions resulting in 21-d NOEC values for survival and growth rate of ≥ 100 mg/L sediment (nominal). However, the applied natural lake water was not well characterized by Wallis et al. (2014) and thus results are considered as supporting data.

In sum, micro- and nanosized TiO2 appears to have a low potential for acute and chronic freshwater and marine sediment toxicity based on data available for insect, crustacean and annelid species.