Tetra-n-butyl titanate, polymer with water

Endpoint summary

Additional information

Tetra-n-butyl titanate, polymer with water is a viscous organometallic liquid which is hydrolytically unstable. The hydrolytic stability was tested in buffered aqueous solutions at pH 4.0, 7.0, and 9.0 at 25°C for 9 hours. Based on the results, half-life of substance was less than 2 hours at all pH @ 25 deg. C (Brekelmans 2013). The progress of the hydrolysis was followed by monitoring n-butanol, 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 (n-butanol) of this substance. This was demonstrated by the aquatic toxicity studies (daphnia and algae) conducted for the analogue category member titanium tetraisopropanolate CAS no. 546-68-9 (Goodband 2010 and Vryenhoef & Mullee 2010).

The category justification is presented in the Annex I of this CSR, and the results of this analogue category member are included to the weight of evidence approach to evaluate the aquatic toxicity of titanium tetrabutanolate (see section 7.1 of CSR).

This analogue substance (titanium tetraisopropanolate), grouped with the target substance into the category of highly water reactive titanates, hydrolyzed immediately in aqueous test media releasing isopropanol 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 isopropyl alcohol and not parent test item. Therefore, the toxicity to the freshwater invertebrates and algae were investigated based on the measured isopropyl alcohol concentrations only. Based on these study results it is justified to conclude that the ecotoxicity of tetra-n-butyl titanate, polymer with water is related to the toxicity of n-butanol released, and testing of this substance is unnecessary. Instead the read-across data from the main degradation product (n-butanol) was used as a key value in CSA (see section 7.1 of CSR). The toxicity results 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 (n-butanol) is also known to be readily biodegradable (> 82 % in 20 days, Price et al. 1974).

The transport and distribution of titanium tetrabutanolate was evaluated based on its reactivity. Because of instability in water, 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. The vapor pressure of the target substance cannot be determined as it decomposes during testing (OECD 104, Brekelmans 2013). If released to air, this substance will release n-butanol. A vapor pressure of < 10 hPa at 20 ˚C and Henry's law constant of 1.16 Pa m³/mol indicate that n-butanol will be volatile in the ambient atmosphere. Vapor-phase n-butanol 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 46 hours. (HSDB 2012).

Based on the composition of this titanate and the properties of the main degradation product, this substance 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. The adsorption coefficient of n-butanol (Koc value of 3.471 L/kg), estimated by using KOCWIN v.2.00 is used in CSA for the target substance (US EPA 2012). N-butanol released from this substance is expected to have very high mobility based upon an estimated Koc. In addition, the water solubility of n-butanol (63.2 g/l, CHemIDplus Lite 2012) 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 1.16 Pa m³/mol of the main decomposition product (n-butanol). It is expected to volatilize from dry soil surfaces based upon its vapor pressure.

If released into water, a complete hydrolysis of this titanate will take place with no significant reaction products other than n-butanol and hydrated titanium dioxide (Brekelmans 2013). Again, n-butanol is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is expected based upon the Henry's Law constant. Biodegradation is the most important fate process of n-butanol.

Tetra-n-butyl titanate, polymer with water has no strong binding behaviour to soil particles as the partition coefficient of n-butanol (log Kow 0.84) is well below 4. Since the target substance is highly water reactive, 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 n-butanol and TiO₂ are released to water compartment. Because of this mechanistic reasoning for read-across, the relevant properties of n-butanol, 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 (n-butanol) and non-toxic to environment. Undirect 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 highly hydrolytically unstable substances and they have structural similarities, two group categories have been 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 the data matrices are presented in the Annexes of the CSR.