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Toxicity to aquatic algae and cyanobacteria

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The conduct of an toxicity study on aquatic algae with the target substance titanium oxychloride itself is being waived, as the substance is highly unstable in water and produces insoluble oxide after rapid hydrolysis. Nevertheless, based on the information available it can be concluded that neither the parent compound titanium tetrachloride, nor the target compound titanium oxychloride nor the final hydrolysis transformation products (namely titanium dioxide) exhibit acute toxicity to aquatic algae.

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The conduct of a chronic toxicity study on aquatic algae with the target substance itself is being waived, as the substance is highly unstable in water and produces insoluble oxide after rapid hydrolysis. Thus the aquatic hazard assessment is to be based on the transformation products. As pH effects are not true toxic effects and not relevant for assessment and as the chlorides are present in high natural background concentrations, the assessment bases on titanium dioxide.

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 oxychloride is likely to sink and adsorb to the sediment. Notwithstanding all the above mentioned possible artefacts 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 concluded that neither the target compound titanium oxychloride, nor parent compound titanium tetrachloride, nor the final hydrolysis transformation products titanium dioxide and hydrochloric acid (in its neutralised form) exhibit effects to aquatic algae at the level of their water solubility and no threshold concentrations can be derived.

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