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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The hydrolysis transformation products of titanium tetrachloride do not exhibit acute or chronic effects.

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Titanium tetrachloride rapidly hydrolyses in water resulting in the formation of titanium dioxide (CAS 13463-67-7) and causing an increase in acidity. Titanium dioxide is very poorly soluble in water at neutral pH (< 0.1 µg/L); excess titanium dioxide will be present as insoluble matter. Aquatic toxicity data for the titanium dioxide give no evidence of true toxicity however the secondary effect shading resulted in a dose response curve (Sloman 2006). This is considered irrelevant as shading is occurring only under artificial conditions, i.e. stirring, and when loading of more than three orders of magnitude above the water solubility is applied. It has been evidenced by Hund-Rinke & Simon (2006) that undissolved technical anatase titanium dioxide of 25 nm diameter particle size may cause photocatalytical effects on algal growth rate if precipitation is hampered. Again this represents an artificial situation as due to the density difference (algae ca. 1 versus titanium dioxide ca. 4) this hydrolysis product of titanium tetrachloride is likely to sink and adsorb to the sediment. Moreover the relevant eventual modification seems to represent the rutile rather than the anatase modification (Fisk et al 2010) and it seems unlikely that nanoparticles of well defined crystallinity get formed under environmental conditions. Notwithstanding all the above mentioned possible artifacts and the inclusion of secondary effects no 50% level was reached in these studies with titanium dioxide and the no effect level (NOELR) was always > 1 mg/L.

It is thus concluded that the hydrolysis transformation products of titanium tetrachloride do not exhibit acute or chronic effects to aquatic algae and no threshold concentrations can be derived.