Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Aquatic

Titanium tetrachloride hydrolyses rapidly under environmentally relevant conditions in two steps to hydrogen chloride and titanium (IV) intermediates, which hydrolyze eventually to titanium dioxide. The transient formation of hydroxides (titanium hydroxide, titanium dihydroxide oxide), oxychloride and hydroxychloride is probable. The titanium dioxide eventually formed corresponds to the naturally occurring mineral rutile albeit in micro-disperse form. It is considered stable under environmental conditions. It will sink to the sediment due to its density where it will be bound as indicated by the Kp values. Hydrogen chloride gets readily dissociated in contact with water into hydronium ions (via the proton) and chlorides (OECD SIDS 2002 Hydrogen chloride SIAR). Studies on direct phototransformation in water are not available but it is assumed the substance and its transformation products are not degraded by direct photolysis due to its spectral properties. It is concluded, therefore, that abiotic processes do not contribute significantly to the depletion of the transformation products in the aquatic environment.

Biodegradation is not relevant as titanium dioxide and its transformation products are inorganic and thus a priori mineralized. No formation of organometallic species is assumed.

In conclusion the fate of titanium tetrachloride in the aquatic environment is rapid transformation to environmentally occurring inorganic inert compounds.

Atmospheric

With regard to the atmospheric fate of titanium tetrachloride its vapour pressure of 1200 to 1330 Pa at 20 °C indicates vaporisation. Nonetheless these values are not relevant as in the presence of any air humidity rapid hydrolysis forms the above mentioned transformation products. A particular intermediate, i.e. the volatile compound Ti(OH)2Cl2, occurs instantaneous in gas-phase hydrolysis. The latter compound forms very fine dusts which easily evolve into aerosols and has a half life of 6 h. The eventually formed particles have diameters of 400 nm or bigger and consist finally on titanium dioxide. Hydroxylation by indirect photolysis is considered an irrelevant reaction mechanism as no new chemicals would result. No vapour pressure measurement exists for titanium dioxide, which melts at 1843°C (rutile, CRC Handbook of Chemistry and Physics, 2007). On the basis of this value vaporisation is considered not a relevant process and titanium dioxide is assumed to fall down to soils and surface waters due to the particle size and density. Most of the titanium species present in the atmosphere will be bound to aerosols. Therefore, an extremely low value for the vapour pressure should be used to estimate the fraction bound to aerosol, e.g. 10^-20 Pa. This leads to a value for the aerosol-bound fraction almost equal to one. If a valid measured value becomes available for the aerosol-bound fraction, this value should be used. Volatilisation can be ignored for metal compounds, except for several organometallic compounds, whose formation is not likely. Therefore, the Henry coefficient should generally be set to a very low value. On the other hand hydrogen chloride is volatile and the vapour pressure is about 4723 kPa at 25 °C (Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis, 1989). Due to its physico-chemical properties hydrogen chloride distributed into the will enter airborne water droplets and dissociate there into waterbound ions, which enter the surface waters via rain.

In result titanium tetrachloride gets transformed in the atmosphere due to contact with air humidity water. The formed airborne solid particles or waterbound ions were quickly depleted from the atmosphere mainly by gravitational settling or by rain and enter the soil and aquatic compartments. It is assessed that the substance and/or its transformation products will neither stay in the atmosphere nor reach the troposphere in relevant amounts.

Terrestrial

In suspended matter, sediments and soils as well the contact with the present pore water will initiate rapid hydrolysis into the above mentioned solid and ionized compounds. The octanol-water derived partition coefficient is considered not an appropriate way to estimate the Kp values for metals and measured partition coefficients should be used instead. In order to assess the fate of the solid transformation products, data from environmental measurements of the sum of titanium were used. They were influenced by speciation and the speciation behaviour must therefore be accounted for in Kp. The reported Kp reflect thus the total titanium concentration ratio in equilibrium conditions for all titanium compounds under environmental conditions including speciation. In the risk assessment and based on field observed values, the partition coefficients log Kp, susp 2.36, log Kp, sed 4.61 are used. The measurements indicate that the solid transformation products, probably almost titanium dioxide, have to be considered as “immobile” or “non-mobile” in soils or sediments. On the other hand hydronium ions and chlorides belong to the “very high” or “very mobile” mobility class.

In conclusion the fate of titanium tetrachloride in environmental soils is rapid transformation to naturally occurring inorganic inert compounds.

Bioaccumulation is not likely to occur for titanium tetrachloride and/or its transformation products. Based on experimental BCF data after spiking water with titanium dioxide a metal-typical inverse relationship was established between water concentrations and the corresponding BCF (352 to 20 L/kg ww) and in consequence no bioconcentration is expected and the formation of organometallic compounds seems unlikely. Titanium is the ninth-most abundant element in the Earth's crust (0.63% by mass) occurring naturally as titanium dioxide in several modifications, whereof the corresponding one is called rutile. Although it is widely distributed no accumulation in wildlife biota is described in the literature. No accumulation of hydrogen chloride and/or its dissociation products in living organisms is expected due to its high water solubility and hydrophilicity (OECD SIDS 2002 Hydrogen chloride SIAR).

In conclusion titanium tetrachloride and its transformation products are rapidly depleted from the air to soils and surface waters. They represent naturally occurring inorganic inert compounds.

PBT/vPvB assessment

A PBT assessment is obsolete as the criteria for persistence are not applicable, no relevant bioaccumulation exist and (if any) only low toxicity threshold levels are known. No indication for the formation of organometallic compounds exist. According to REACH Annex XIII as of 31 December 2006 (Official Journal of the European Union, p. L 396/383) „A substance is identified as a PBT substance if it fulfils the criteria in Sections 1.1, 1.2 and 1.3. A substance is identified as a vPvB substance if it fulfils the criteria in Sections 2.1 and 2.2. This annex shall not apply to inorganic substances, but shall apply to organo-metals.“