Titanium tetraisopropanolate

Endpoint summary

Additional information

Titanium tetraisopropanolate is an organometallic substance which is hydrolytically unstable having a half-life less than three minutes. The hydrolysis of the substance was determined according to the guideline OECD 111 (Scholz, T. 2010). The hydrolytic stability was tested in buffered aqueous solutions at pH 4.0, 7.0, and 9.0 at temperatures of 10°C, 25°C, and 50°C for 3 hours. Only hydrolyses at 10°C and pH 4.0 and 9.0 gave sufficient data, before equilibrium was reached, to calculate a reaction half-life. The progress of the hydrolysis was followed by monitoring isopropyl alcohol (IPA), the main degradation product of the substance. Titanium is a solid precipitate of the substance present as hydrated titanium dioxide in water after hydrolysis. This decomposition product (TiO2) is not classified hazardous to human health or the environment. Furthermore, Ti compounds are not expected to bioconcentrate in soils, sediments or aquatic organisms (WHO 1982). As an insoluble precipitate, it is also lacking bioavailability, and therefore not relevant to be considered further in CSA.

Because of the rapid abiotic degradation, water solubility, biodegradation and partition coefficient (Kow) cannot be determined for the substance itself. In addition, the intrinsic properties of aquatic toxicity are related to the main degradation product (IPA) of this substance. This was demonstrated by the aquatic toxicity studies (Daphnia and algae) conducted for this substance according to the OECD guidelines and in accordance with GLP (Goodband 2010 and Vryenhoef & Mullee 2010). The test item hydrolyzed immediately in aqueous test media releasing IPA with the hydrated titanium oxide precipitating out of the test solution. Due to the rapid hydrolysis, it was considered that any toxicity would be due to the presence of IPA and not parent test item. Therefore, the toxicity to the freshwater invertebrates and algae were investigated based on the measured IPA concentrations only. Based on these study results conducted for the substance, the short-term toxicity testing to other organisms (fish and micro-organisms) was considered scientifically unjustified. Instead supporting read-across data from the main degradation product (IPA) was used as a key value in CSA (see section 7.1 of CSR). The toxicity results of the target substance and the decomposition product do not indicate the need to classify this substance hazardous to the environment.

As the rapid hydrolysis is the driving force for the fate and pathways of this substance, the abiotic degradation can be used to demonstrate fast degradation for this substance. This is justified as all decomposition products have been identified. The most relevant degradation product (IPA) is also known to be readily biodegradable (> 70 % at 20-d biodegradation, Price et al. 1974) and not classified as hazardous to the environment. The information on the short-term aquatic toxicity of IPA, EC/LC50 values between 1050 mg/l to > 10 000 mg/l, was used as supporting data in CSA. The long-term aquatic toxicity was not necessary to be further considered for titanium tetraisopropanolate based on the low short-term toxicity level of the degradation products, and ready biodegradability of IPA.

The transport and distribution of titanium tetraisopropanolate was evaluated based on its reactivity. Because of rapid hydrolysis, most of the physical chemical properties of the target substance are not technically feasible to determine. Therefore, the fate and pathways are related to the main degradation product IPA. The vapor pressure of titanium tetraisopropanolate cannot be determined as it decomposes during testing (OECD 104, Brekelmans 2013). If released to air, this substance will release IPA. A vapor pressure of 60.2 hPa at 25 ˚C indicates that IPA will exist solely as a vapor in the ambient atmosphere. Vapor-phase IPA will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 3.2 days (HSDB 2012).

Based on the composition of titanium tetraisopropanolate and the properties of the main degradation product, this titanate in the atmosphere has no potential for stratospheric ozone depletion for structural reasons. It does not contain any halogens. Therefore there is no reason for any hazard classification under the CLP regulation 1272/2008 for atmospheric environment (the ozone layer).

If released to soil, because of soil moisture this titanate will decompose releasing isopropyl alcohol and hydrated titanium dioxide. The adsorption coefficient of IPA (Koc value of 1.53 L/kg), estimated by using KOCWIN v.2.00 is used in CSA of the target substance (US EPA 2012). Isopropyl alcohol released from this substance is expected to have very high mobility based upon an estimated Koc. In addition, the water solubility of IPA (miscible in water, Riddick et al. 1986) indicates high mobility in soil, while the other inorganic degradation product (hydrated titanium dioxide) is insoluble (O'Neil et al. 2006). Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 0.81 Pa m³/mol of the main decomposition product (IPA). IPA is expected to volatilize from dry soil surfaces based upon its vapor pressure.

If released into water, a complete hydrolysis of titanium tetraisopropanolate will take place with no significant reaction products other than isopropyl alcohol and hydrated titanium dioxide (Scholz T. 2010). Again, isopropyl alcohol is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is expected based upon this compound's Henry's Law constant. Biodegradation is expected to be an important fate process of IPA (HSDB 2012).

Titanium tetraisopropanolate has no strong binding behaviour to soil particles as the partition coefficient of IPA (log Kow 0.05) is well below 4 (Dillingham et al. 1973). Since the target substance is hydrolytically unstable, use of water is avoided in the use applications. Therefore, no emissions to a sewage treatment plant (STP) are expected. Discharge to STP is relevant only in one use application when the target substance is used as a catalyst in industrial esterification processes. In this use application, water is used to remove the catalyst from the process. The discharge to STP is related to the degradation products of this substance as the hydrolysis will take place, and isopropyl alcohol and TiO2 are released to water compartment. Because of this mechanistic reasoning for read-across, the relevant properties of isopropyl alcohol, instead of measured values of the target substance, are used as the key values for the exposure assessment (see sections 9 & 10 of CSR). Based on the decomposition and the properties of the degradation products, this titanate has neither persistence potential nor sorption potential. Therefore, the soil/sediment simulation testing does not need to be further considered in CSA. This substance is not fulfilling the criteria to be classified as a PBT or vPvB substance. Thus, CSA indicates that further testing of long-term aquatic effects or terrestrial toxicity testing is also unnecessary. In addition, testing is scientifically unjustified as the direct exposure to aquatic or terrestrial compartment is unlikely based on the exposure scenarios (see section 9&10 of CSR). Discharge to STP is only relevant in industrial esterification processes when water is used to remove the catalyst from the process. The possible spreading of STP sewage sludge as fertilizer to soil is expected to cause low hazard to soil organisms as the degradation products are readily biodegradable (isopropyl alcohol) and non-toxic to environment. Indirect emissions to environment are occuring only via atmospheric deposits. There are all together eight different organometallic titanates from the same manufacturer which are registered at the same tonnage band. As all these titanates are hydrolytically unstable and they have structural similarities, group of categories were formed. Because of behavioral similarities some properties of these titanates are evaluated by using read-across data from the category members as well as from the degradation products. The category and read-across justifications with data matrices are presented in the Annexes of this CSR.