Chrome antimony titanium buff rutile

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the physicochemical properties of the substance indicate that it can be expected to have a low potential for adsorption

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Column 2 of Information Requirement 9.3.1., Annex VIII, Commission Regulation (EU) 1907/2006, “The study does not need to be conducted if: — based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g. the substance has a low octanol-water partition coefficient).”

“Adsorption/desorption measurements are used in fate modelling to indicate which compartment in the environment will be exposed the most or might need to be considered in hazard and risk assessment. These measurements help to determine in which environmental compartment (e.g. soil, sediment or water) the substance is most likely to end up and whether it is likely to be mobile or immobile in the environment. For instance, high adsorption to soil would show that both soil and sediment are highly relevant environmental compartments to be considered in hazard assessment (ECHA, 2017)”.

According to ECHA (2008), “The distribution of metals between the aqueous phase and soil / sediment / suspended matter should be preferentially described on the basis of measured soil / water, sediment / water and suspended matter / water equilibrium distribution coefficients”, since:

“(i) The Kow and Koc concept is not applicable for inorganic compounds.

(ii) Sorption is not controlled only by organic matter, but also by other solid phase constituents like clay minerals and oxides.

(iii) The distribution of metals over the solid and liquid phase is not only controlled by pure adsorption / desorption mechanisms. Other processes like precipitation or encapsulation in the mineral fraction also play a role.

(iv) Environmental conditions (pH, redox conditions, temperature, ionic strength) and the composition of the liquid and solid phase have a strong effect on the Kd of inorganic substances. As a result a wide range of Kd values have been reported (ECHA, 2008).”

Chrome antimony titanium buff rutile can be considered environmentally and biologically inert due to the characteristics of the synthetic process (calcination at a high temperature of approximately 1000°C), rendering the substance to be of a unique, stable crystalline structure in which all atoms are tightly bound and not prone to dissolution in environmental and physiological media. This assumption is supported by available transformation/dissolution data (Klawonn, 2017) that indicate a very low release of pigment components. According to ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017), “Where the acute ERV for the metal ions of concern is greater than 1 mg/L the metals need not be considered further in the classification scheme for acute hazard”. Further, “Where the chronic ERV for the metal ions of concern is greater than 1 mg/L, the metals need not be considered further in the classification scheme”. Accordingly, titanium was not considered in the T/D assessment as it does not have an aquatic hazard potential as confirmed by ecotoxicity reference values of > 100 mg Ti/L listed in the Metals classification tool (MeClas) database. Transformation/dissolution tests of chrome antimony titanium buff rutile for 24 h at a loading of 100 mg/L (24 h-screening test according to OECD Series 29) resulted in mean dissolved antimony concentrations of 1.859 and 2.139 µg Sb/L and dissolved chromium concentrations of 0.029 and 0.193 µg Cr/L at pH 6 and 8, respectively. The release of antimony and chromium ions from chrome antimony titanium buff rutile in aqueous media is highest at pH 8, and pH 8 is considered as pH that maximises dissolution. Metal ion release at the 1 mg/L loading and pH 8 resulted in dissolved antimony and chromium concentrations of 0.766 µg Sb/L and 0.071 µg Cr/L after 7 days and 1.027 µg Sb/L and 0.050 µg Cr/L after 28 days, respectively. Thus, the rate and extent to which chrome antimony titanium buff rutile produces soluble (bio)available ionic and other antimony- or chromium-bearing species in environmental media is limited. Hence, the pigment can be considered as environmentally and biologically inert during short- and long-term exposure. The poor solubility of chrome antimony titanium buff rutile is expected to determine its behaviour and fate in the environment, including the partitioning in soil, sediment and water.

The assessment of the partitioning of antimony, chromium and titanium in environmental media is based on Kp values derived from monitoring data for elemental concentrations in water and corresponding sediments provided by the FOREGS Geochemical Baseline Mapping Programme that aimed to provide high quality, multi-purpose homogeneous environmental geochemical baseline data for Europe.

A total of 735 (Sb), 734 (Si) and 739 (Ti) paired samples, i.e. samples with the same coordinates for the sampling location of stream water (filtered to < 0.45 µm) and sediment (wet sieved in the field to < 0.15 mm) were processed for EU-27 countries plus UK and Norway, and results correspond to steady-state conditions of antimony, chromium and titanium, independent of speciation. Sampled stream water and sediments cover a wide range of environmental conditions. Water parameters such as pH, hardness and organic carbon concentrations cover several magnitudes (Salminen et al. 2005).

Antimony is a chalcophile element and as such has an affinity for a sulfide phase. In stream sediment, antimony ions are present primarily in detrital sulphide minerals, which may weather relatively rapidly under acid, oxidising conditions. Further remobilisation of antimony is rather limited due to the tendency of antimony ions (Sb3+) to form insoluble basic salts and to be adsorbed by secondary hydrous oxides of Fe, Al and Mn at pH levels in the range 4.0–8.0 (Salminen et al. 2005 and references therein). According to the monitoring data provided by the FOREGS dataset, dissolved antimony water levels range from 0.01 to 2.5 µg Sb/L with 5th, 50th and 95th percentiles of 0.01, 0.07 and 0.3 µg Sb/L, respectively. Sediment concentrations of antimony range from < 0.02 (< LOQ) to 34.1 mg Sb/kg with 5th, 50th and 95th percentiles of 0.2, 0.6 and 2.9 mg Sb/kg, respectively. The 95th percentile of 0.31 µg Sb/L can be regarded as representative background concentration for dissolved antimony in European surface waters and the 95th percentile of 2.9 mg Sb/kg as representative background concentration of antimony in European stream sediments. Regarding the partitioning of antimony in the water column, stream water/sediment partition coefficients range from 280 to 1,706,000 L/kg, and the 50th percentile log Kp for antimony across Europe was determined to be 3.99.

Chromium is naturally abundant in sediments and a significant fraction of the total chromium is associated with the solid phase (e.g., bound to particulate phase, precipitation of insoluble inorganic complexes). In sediment, trivalent chromium will be converted rapidly to insoluble Cr(III)-species and therefore has a low mobility in this compartment (Salminen et al. 2005 and references therein). According to the FOREGS dataset, dissolved chromium water levels range from < 0.01 (< LOQ) to 43.03 µg Cr/L with 5th, 50th and 95th percentiles of 0.06, 0.38 and 1.81 µg Cr/L, respectively. In the sediment, chromium concentrations range from 2.0 to 1,748.0 mg Cr/kg with 5th, 50th and 95th percentiles of 6.0, 21.0 and 63.0 mg Cr/kg, respectively. Taking into account the high quality and representativeness of the data set, the 95th percentile of 1.8 µg Cr/L can be regarded as representative background concentration for dissolved chromium in European surface waters and the 95th percentile of 63.0 mg Cr/kg as representative background concentration of chromium in stream sediments. Regarding the partitioning of chromium in the water column, stream water/sediment partition coefficients range from 1,080 to 4,800,000 L/kg, and the 50th percentile log Kp for chromium across Europe was determined to be 4.75.

Titanium ions have very low mobility under almost all environmental conditions, mainly due to the high stability of the insoluble oxide TiO2 under all, but the most acid conditions, i.e., below pH 2. Some titanium may dissolve in stream water through the weathering of ferromagnesian minerals and authigenic phases, such as anatase, but dispersal is generally restricted by adsorption to clays. Titanium may further be removed from water column by flocculation of colloidal material, adsorption and scavenging by precipitation of Mn and Fe oxides. Titanium exists only in a fully hydrated form, TiO(OH)2, in water above pH 2, and is therefore transported in a colloidal state rather than as a dissolved ion. A large proportion of titanium in stream sediments is held in minerals, such as rutile, ilmenite and sphene, all of which are relatively insoluble (Salminen et al. 2005 and references therein). According to monitoring data provided by the FOREGS dataset, dissolved titanium water levels range from 0.1 µg Ti/L (< LOQ) to 16.8 µg Ti/L with 5th, 50th and 95th percentiles of 0.1, 0.9 and 4.2 µg Ti/L, respectively. In the sediment, titanium concentrations range from 95.9 to 29,919.2 mg Ti/kg with 5th, 50th and 95th percentiles of 1,354.5, 3,871.8 and 8,067.2 mg Ti/kg, respectively. The 95th percentile of 4.2 µg Ti/L can be regarded as representative background concentration for dissolved titanium in European surface waters and the 95th percentile of 8,067.2 mg Ti/kg as representative background concentration of titanium in stream sediments. Regarding the partitioning of titanium in the water column, stream water/sediment partition coefficients range from 182,527 to 119,329,171 L/kg, and the 50th percentile log Kp for titanium across Europe was determined to be 6.57.

Based on the European median log Kp values of 3.99, 4.75 and 6.57 derived for the sediment-water partitioning of antimony, chromium and titanium, respectively, a similarly high potential to partition into the sediment (or other solid phases) may be assumed for poorly soluble chrome antimony titanium buff rutile.

Based on the poor solubility, its potential for adsorption can also expected to be low. Thus, in accordance with Column 2 of Information Requirement 9.3.1., Annex VIII, Commission Regulation (EU) 1907/2006, a study on adsorption/desorption does not need to be conducted.

References:

ECHA (2008) Guidance on IR & CSA, Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds. July 2008.

ECHA (2017) Guidance on IR & CSA, R. Appendix R7-1 for nanomaterials applicable to Chapter R7a, V. 2.0, May 2017.

Salminen et al. (2005) Geochemical Atlas of Europe - Part 1: Background information, Methodology and Maps. EuroGeoSurveys.

Cross-reference

Reason / purpose for cross-reference:

data waiving: supporting information