Dichloride titanium oxide

Adsorption / desorption

Description of key information

Parent compound titanium tetrachloride hydrolyses in water fast via target compound titanium oxychloride, revealing eventually titanium dioxide (rutile), thus read across from titanium dioxide would be proposed. As no results are available for the adsorption/desorption of TiO2, read-across is proposed to Kp values based on available monitoring data for elemental Ti-concentration in water and corresponding sediment or suspended matter (no data are available for soil). These results reflect water/solid equilibrium conditions for Ti in the environment, regardless the speciation of Ti. The available log Kp data indicate that sediments and soils represent the relevant sink for the analogue materials and the target chemical. 

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

4.566

at the temperature of:

12 °C

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

2.36

at the temperature of:

12 °C

Additional information

Parent compound titanium tetrachloride hydrolyses in water fast via target compound titanium oxychloride, revealing eventually titanium dioxide (rutile), thus read across from titanium dioxide would be proposed. As no results are available for the adsorption/desorption of TiO2, read-across is proposed to Kp values based on available monitoring data for elemental Ti-concentration in water and corresponding sediment or suspended matter (no data are available for soil).

In order to assess the mobility of the solid transformation products, data from measurements of the sum of titanium were used. The available information is derived from monitoring of water and corresponding sediment or suspended matter. No soil data exist in the recent literature (until 2009). A median log Kd sed of 4.566 L/kg d.w. (solids-water in sediment, organic matter mean 3.9% with a range of 0.9-15.5%; Kd = 36’813, mean log Kd 4.61 L/kg d.w. with a range of 3.77-5.13, 5th, 10th, and 95th percentile 4.052, 4.265, and 5.106 L/kg respectively) was derived from the literature data (Roychoudhury & Starke 2006). The authors cite a world average reference value according to Li (2000) of 5.75 L/kg. A median log Kd susp of 2.36 L/kg d.w. (solids-water in suspended matter, Kd = 230) for samples from 54 rivers in 119 localities was reported (Veselý et al 2001).

The Kd reflects the total titanium concentration ratio in equilibrium for all titanium compounds under environmental conditions, where 12 °C are assumed. In the risk assessment and based on field observed values, the partition coefficients log Kp susp 2.36, log Kp sed 4.566 are used.

Concerning data interpretation of the resulting Kp values, one has to consider that in these studies dissolved and undissolved (i.e. solid particles) Ti species could not be distinguished in the above mentioned studies, while adsorption by definition is the accumulation of dissolved or air-borne gaseous substances to solid surfaces. Therefore, while the Kp data stated above clearly indicate that titanium species are accumulating in the sediment rather than remaining in the water phase, these data are of limited relevance only in terms of describing the actual adsorptive behaviour of titanium species. When interpreting monitoring data for elemental Ti-concentration in water and corresponding sediment or suspended matter, the resulting equilibrium also is much influenced by the fact that titanium species are insoluble, thus forming particles sedimenting to the ground.

Nevertheless all available data uniformly are pointing in one direction and clearly indicate that sediments and soil represent the relevant sink for the analogue materials and the target chemical.

Due to their high water solubility and hydrophilicity, both hydronium ions and chlorides are not subject to adsorption.

• Roychoudhury, Starke (2006). Partitioning and mobility of trace metals in the Blesbokspruit: Impact assessment of dewatering of mine waters in the East Rand, South Africa. Applied Geochemistry 21:1044-63
• Veselý et al (2001). Solid-water partitioning of elements in Czech freshwaters. Applied Geochemistry 16:437-50