Titanium dioxide

Monitoring data

Administrative data

Endpoint:

monitoring data

Type of information:

other: report

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Unnamed

Year:

2005

Report date:

2005

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

no guideline required

Principles of method if other than guideline:

Evaluation and summary of high quality environmental geochemical data for Europe, which is provided by the Forum of European Geological Surveys (FOREGS) and the European Geochemical Mapping of Agricultural and Grazing Land Soil (GEMAS), with respect to Ti concentrations in stream water, stream sediment, sub- and topsoil, as well as in agricultural soil and grazing land. In addition, an overview of titanium solubility, possible chemical species and their calculated areas of thermodynamic stability under environmentally relevant conditions is included.

GLP compliance:

no

Type of measurement:

other: Geochemical background and ambient Ti concentrations in environmental compartments across Europe

Media:

other: Natural stream water, stream sediment and soil (top- and subsoil), as well as agricultural and grazing land soils

Test material

Test material information

Constituent 1

Reference substance name:

Titanium dioxide

EC Number:

236-675-5

EC Name:

Titanium dioxide

Cas Number:

13463-67-7

Molecular formula:

O2Ti

IUPAC Name:

dioxotitanium

Test material form:

other: elemental concentrations

Details on test material:

naturally occuring titanium

Study design

Details on sampling:

FOREGS:
-The FOREGS sampling grid was based on GTN grid cells developed for Global Geochemical Baseline mapping. This grid divides the entire land surface into 160 km x 160 km cells covering an area of 4,500,000 km2.
- Sampling methodology, preparation and analysis are described by Salminen et al. (2005).
- A total of 808 stream water samples and 852 sediment samples were processed in the FOREGS-program, including 757 paired samples, i.e. samples with the same coordinates for the sampling location of stream water and sediment that are summarised below. However, Ti concentrations in six stream water samples were reported with “0.0” (five samples) or “-1.0” (1 sample), and respective samples were excluded from the analysis, resulting in a total of 751 paired samples summarised below. However, including these six samples with estimated concentrations of ½ LOD (=0.005 µg/L) does shift the summary statistics negligibly.
- The FOREGS dataset reports titanium concentrations as titanium dioxide concentrations for 845 topsoil and 788 subsoil samples sampled on a grid across Europe. Two different depth related samples were taken at each site: a topsoil sample from 0-25 cm (excluding material from the organic layer where present), and a subsoil sample from a 25 cm thick section within a depth range of 50 to 200 cm (the C soil horizon). Data from sampling locations with similar coordinates were selected to match subsoil with topsoil samples resulting in 782 paired samples.
- High quality and consistency of the obtained data were ensured by using standardised sampling methods and by treating and analysing all samples in the same laboratory of each country.

GEMAS:
- Samples from 33 out of 38 European countries were analysed to develop a suitable harmonised geochemical database for soils. The sampling started in the spring 2008 and the first four months of 2009.
- The whole GEMAS project area of 5,600,000 km2 was divided into a grid with 50 km x 50 km cells.
- To generate harmonised data sets, all project samples were processed by a central sample preparation facility in Slovakia.
- The GEMAS dataset reports titanium and titanium dioxide concentrations for 2108 samples (including field duplicates) from the ploughing soil layer (Ap-horizon) of agricultural land (arable land; 0 - 20 cm) and for 2023 samples (including field duplicates) from the topmost part soil on grazing land (soil under permanent grass cover; 0 – 10 cm) sampled on a grid across Europe.

Results and discussion

Any other information on results incl. tables

FOREGS DATABASE STREAM WATER/SEDIMENT:

- 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. Dissolved/dispersed titanium water levels range from < 0.1 to 16.80 µg Ti/L with 5^thand 95^thpercentiles of 0.10 and 4.21 µg Ti/L, respectively.

- The FOREGS dataset reports titanium dioxide concentrations of the sediment. Respective TiO_2-data were converted into titanium concentrations to enable comparison of sediment with dissolved/dispersed stream water concentrations. Sediment concentrations of Ti range from 0.01 to 2.99 % Ti with 5^thand 95^thpercentiles of 0.14 and 0.81 % Ti, respectively (Table 1).

- Taking into account the high quality and representativeness of the data set, the 95^thpercentile of 4.21 µg Ti/L can be regarded as typical background concentration for dissolved/dispersed titanium in European surface waters and the 95^thpercentile of 0.81 % Ti as typical background concentration of European stream sediments.

- Even though Ti concentrations of sediments can be as high as 3 %, dissolved/dispersed Ti concentrations in the water column of European stream waters are well below 20 µg/L. These monitoring stream water and sediment data provide strong evidence that Ti is sparingly soluble in a wide representative range of European stream waters.

Table1: Paired titanium and titanium dioxide concentrations of stream water, sediments and respective partitioning

	Parameter	#	Unit	Min.	Max.	Mean	STDEV	5^thp	50^thp	90^thp	95^thp
water	pH^1	743^2 731^4	-	9.8	4.5	6.6 6.6	5.85 5.84	8.5 8.5	7.7 7.7	6.5 6.5	6.1 6.1
water	Ca	751 739^4	mg/L	0.23	592.00	56.58 56.43	62.47 62.02	1.72 1.70	43.10 43.10	117.60 117.76	148.25 148.21
water	Cl	751 739^4	mg/L	0.14	4560.00	34.92 35.35	198.40 199.97	0.49 0.51	9.48 9.50	43.79 44.03	69.78 72.31
water	HCO3	749^5 737^4	mg/L	0.69	1804.42	156.11 156.12	145.92 146.41	5.96 5.84	134.00 131.67	335.72 335.91	372.40 374.55
water	K	751 739^4	mg/L	0.01	182.00	3.15 3.18	7.57 7.62	0.15 0.15	1.65 1.66	6.87 6.91	9.83 9.87
water	Mg	751 739^4	mg/L	0.05	230.00	11.74 11.75	19.60 19.71	0.48 0.49	6.25 6.25	26.55 26.52	38.37 38.80
water	Na	751 739^4	mg/L	0.23	4030.00	24.15 24.41	163.76 165.07	1.01 1.03	6.80 6.80	25.69 25.72	48.31 48.39
water	NO3	751 739^4	mg/L	0.02	107.00	9.38 9.47	13.67 13.75	0.02 0.02	3.10 3.19	29.03 29.08	39.80 39.90
water	DOC	746^3 737^4	mg/L	0.25	57.94	7.38 7.45	8.08 8.10	0.60 0.61	4.78 4.82	16.31 16.40	23.01 23.08
water	SO4	751 739^4	mg/L	0.15	2420.00	54.11 53.73	157.74 157.22	1.19 1.19	16.96 17.49	103.64 103.13	172.22 168.04
water	Dissolved/dispersed Ti	751 739^4	µg/L	0.10	16.80	1.46 1.47	1.96 1.97	0.10 0.10	0.90 0.90	2.90 2.90	4.25 4.21
sediment	Ti	751 739^4	%	0.01	2.99	0.42 0.42	0.24 0.24	0.14 0.14	0.39 0.39	0.63 0.63	0.80 0.81
Partitioning (Kd)	Ti (sed / water)	751 739^4	L/kg	182,527	119,329,191	8,922,560 8,862,395	14,215,816 14,182,762	747,891 733,573	3,792,985 3,695,949	21,616,304 21,348,598	40,635,455 40,084,060
Log Kd	Ti (sed / water)	751 739^4	-	5.26	8.08	6.62 6.62	0.51 0.51	5.87 5.87	6.58 6.57	7.33 7.33	7.61 7.60

¹Statistics are based on H⁺concentrations rather than pH.

²Removal of 2 outliers < pH 4.3 and 6 negative values.

³Removal of 1 outlier > 70 mg/L and 4 negative values.

⁴Values from Switzerland and Albania are not included.

⁵Removal of 2 outliers < 0.01.

FOREGS DATABASE STREAM TOP-AND SUBSOIL:

- Sampled soils cover a wide range of environmental conditions. Soil parameters, including pH and TOC, cover several magnitudes.

- Baseline titanium levels in topsoil range from 0.013 % Ti to 2.496 % Ti with 5^thand 95^th percentiles of 0.113 and 0.663 % Ti, respectively. In subsoil, concentrations of Ti range from 0.007 % to 1.881 % with the 5^thand 95^thpercentiles of 0.085 % and 0.645 % Ti, respectively (seeTable 2).

- Taking into account the high quality and representativeness of the data set, the 95^th percentiles of 0.663 and 0.645 % Ti can be regarded as typical background concentrations of titanium dioxide in top- and subsoils of EU countries, respectively.

Table 2: Concentrations of titanium dioxide in top- and subsoil samples

	Parameter	Unit	#	Min	Max	Mean	STDEV	5^thp	50^thp	90^thp	95^thp
topsoil	pH^1	-	756 747^2	7.55	3.38	4.85 4.85	4.54 4.54	4.28 4.28	5.45 5.45	4.44 4.44	7.26 7.26
	TOC	%	759 750^2	0.07	46.61	2.47 2.39	3.24 2.91	0.58 0.58	1.72 1.72	4.56 4.45	5.97 5.86
	TiO2	%	784 774^2	0.021	4.165	0.600 0.602	0.325 0.326	0.185 0.188	0.570 0.570	0.951 0.953	1.11 1.11
	Ti^3	%	784 774^2	0.013	2.496	0.360 0.361	0.195 0.195	0.111 0.113	0.341 0.341	0.570 0.571	0.663 0.663
subsoil	pH^1	-	759 750^2	7.86	2.89	5.05 5.05	4.22 4.21	4.53 4.34	5.79 5.80	4.74 4.74	7.56 7.56
	TOC^4	%	760 752^2	0.001	48.52	0.94 0.93	2.86 2.86	0.01 0.01	0.40 0.39	1.75 1.72	2.72 2.72
	TiO2	%	784 774^2	0.012	3.139	0.588 0.589	0.322 0.323	0.142 0.143	0.565 0.563	0.935 0.936	1.074 1.076
	Ti^3		784 774^2	0.007	1.881	0.353 0.353	0.193 0.194	0.085 0.085	0.338 0.337	0.560 0.561	0.644 0.645

¹ Statistics are based on H⁺concentrations rather than pH.

²Values from Switzerland and Albania are not included.

³Values converted from TiO₂.

⁴For 26 samples with a value of 0 has been replaced by DL/2 (DL=0.01%)

GEMAS DATABASE AGRICULTURAL AND GRAZING LAND SOIL CONCENTRATIONS:

- Baseline titanium levels in agricultural land range from < 0.01 to 2.45 % Ti with 5^thand 95^th percentiles of 0.11 and 0.60 % Ti, respectively (seeTable 3). In grazing land, concentrations of Ti range from 0.01 to 2.38 % with 5^thand 95^thpercentiles of 0.09 and 0.61 % Ti, respectively (see Table 4).

Table 3: Agricultural soil concentrations

Parameter	Unit	Method	#	Min	Max	Mean	STD	5p	50p	90p	95p
CEC	meq/100g	AAS	2108*^1 1867*^2	1.80	48.30	17.93 17.25	8.77 8.45	6.24 6.10	16.40 15.80	30.33 29.10	34.67 33.30
pH (CaCl2)	pH	pH-meter	2108*^1 1867*^2	3.32	7.98	5.88 5.85	1.10 1.12	4.18 4.14	5.77 5.71	7.36 7.37	7.45 7.45
TOC	%	IR	2095*^1 1854*^2	0.40	46.00	2.55 2.62	3.98 4.21	0.70 0.70	1.80 1.70	3.90 4.10	5.40 5.67
Ti	mg/kg	AR	2108*^1 1867*^2	2.50	7860.10	247.77 265.37	399.66 413.01	16.95 16.94	85.70 96.37	711.08 746.57	973.51 1,006.83
Ti^3	%	XRF	2108*^1 1867*^2	0.01	2.45	0.36 0.36	0.18 0.18	0.11 0.11	0.36 0.35	0.54 0.54	0.60 0.60
	mg Ti/kg		2108*^1 1867*^2	89.90	24,549.01	3,617.17 3,586.34	1,797.22 1,839.66	1,108.78 1,132.76	3,620.03 3,524.14	5,383.90 5,402.48	5,955.37 6,028.79
Ti	mg/kg	MMI	2108*^1 1867*^2	< 0.01	13.20	0.25 0.28	0.60 0.64	< 0.01 < 0.01	0.04 0.05	0.72 0.80	1.26 1.39
Ti	%	AR/XRF	2108*^1 1867*^2	0.05	52.12	6.70 7.22	8.08 8.33	0.52 0.50	2.89 3.40	18.62 19.73	24.72 25.24
Ti	%	MMI/AR	2107*^1+ 1866*^2+	< 0.01	42.40	0.27 0.28	1.34 1.40	< 0.01 < 0.01	0.05 0.05	0.49 0.52	1.05 1.05

*¹EU – ALB, BEL, MAL, MLD, ROM

*²EU-28 plus NOR without MAL

³Values converted from TiO2.

⁺one sample of MMI could not be paired

Table 4: Grazing land soil concentrations

Parameter	Unit	Method	#	Min	Max	Mean	STD	5p	50p	90p	95p
CEC	meq/100g	AAS	2023*^1 1781*^2	2.54	49.88	20.42 20.01	9.40 9.32	8.17 8.27	18.75 17.96	33.87 33.42	38.12 37.74
pH (CaCl2)	pH	pH-meter	2022*^1 1780*^2	3.26	8.06	5.68 5.63	1.16 1.17	4.04 4.03	5.45 5.38	7.33 7.33	7.45 7.45
TOC	%	IR	2022*^1 1780*^2	0.41	49.00	4.05 4.24	5.36 5.64	0.92 0.94	2.70 2.80	6.80 7.00	10.00 11.05
Ti	mg/kg	AR	2023*^1 1781*^2	2.50	10,420.82	213.14 229.53	413.52 432.49	15.21 15.35	73.71 77.70	594.94 642.45	859.47 910.45
Ti^3	%	XRF	2023*^1 1781*^2	0.01	2.38	0.35 0.35	0.18 0.19	0.09 0.09	0.36 0.35	0.54 0.54	0.60 0.61
	mg/kg		2023*^1 1781*^2	113.88	23,757.96	3,537.06 3,516.91	1,829.73 1,851.70	894.22 911.00	3,566.09 3,518.14	5,364.12 5,370.11	6,031.79 6,065.35
Ti	%	AR/XRF	2023*^1 1781*^2	0.05	56.22	5.91 6.39	7.67 7.99	0.43 0.42	2.69 3.04	16.25 17.41	22.58 23.81

*¹EU – ALB, BEL, MAL, MLD, ROM

*²EU-28 plus NOR without MAL

³Values converted from TiO2.

Speciation of TiO₂in stream water: Thermodynamic stability areas of Ti species as a function of pH

At typical environmental conditions (pH 4-10, elemental concentrations as reported in FOREGS stream waters), TiO₂constitutes the predominating solid species according to modeling approaches using Outotec Oyjs HSC8 software (v8.2.0, Eh-pH Diagrams Module) . Aqueous neutral Ti(OH)₄, the “hydrous” TiO₂species, is prevalent in the pH range 3 – 10, however at nanomolar levels, i.e. < 50 ng/L at 25°C, 100 mM NaCl₂, approx. 0.5 mg/L TiO₂loading, pH 3 ‑ 11 according to Schmidt & Vogelsberger (2009). In aqueous solutions, unhydrolysed Ti⁴⁺(aq) does not remain as a free ion. As solution pH increases, a series of hydrolysed titanium species is formed, of which Ti(OH)₄is the predicted predominant environmental aqueous species. This is in agreement with other studies which predicted that Ti(OH)₄ constituting the dominant aqueous species and estimated a solubility of TiO₂ - nanoparticles at environmentally relevant conditions in the nanomolar range. Based on the performed modelling approaches, TiO₂does not dissolve to any significant extent under environmentally relevant conditions and is thus not expected to be bioavailable. Major ions (Ca, Cl, H, K, Mg, Na, S, N) as found in European freshwaters do not appear to affect titanium solubility or speciation.

Applicant's summary and conclusion

Conclusions:

Typical baseline concentrations for titanium in various environmental compartments as derived from monitoring data are summarised below:

Compartment Typical baseline level (95th P)
Background stream water µ µg dissolved/dispersed Ti/L 4.21
Background stream water sediment % Ti 0.81
Background topsoil % Ti 0.663
Background subsoil % Ti 0.645
Agricultural soil % Ti 0.603
Grazing land soil % Ti 0.607

According to Salminen et al. (2005), titanium is a common lithophile metallic element that forms several minerals, including ilmenite FeTiO3, rutile, brookite, anatase (all TiO2) and sphene CaTiSiO5, but it also occurs as an accessory element in pyroxene, amphibole, mica and garnet.
Titanium has very low mobility under almost all environmental conditions, mainly due to the high stability of the sparingly soluble TiO2 under all, but the most acid conditions, i.e., below pH 2 (Brookins 1988 as referenced in Salminen et al. 2005), a pH typically not observed in the environment. Titanium minerals are resistant to weathering, they occur practically undecomposed in soil. Titanium is mobilised more readily in peats and podzols (Hutton et al. 1972), at low pH (<4.5) and in the presence of organic acids. Based on the FOREGS dataset, Ti concentrations of topsoils can be as high as 2.5 % but are typically below 0.7 % (95th P = 0.663 %). Typical Ti concentrations below 0.7 % were also measured in agricultural and grazing land (95th P = 0.6 %) with a maximum around 2.4 %. Total Ti concentrations of agricultural and grazing land soil of the EU28+Norway are 3,524 and 3,518 mg/kg. However, only 3.40 % (agricultural land) and 3.04 % (grazing land) of total titanium was extractable by aqua regia (all median values).
Some Ti may dissolve in stream water through 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 the water column by flocculation of colloidal material, adsorption and scavenging by precipitation of Mn and Fe oxides (Skrabal 1995 as referenced in Salminen et al. 1998).
Based on the FOREGS dataset, dissolved/dispersed titanium concentrations in European stream waters, can go up to 16.8 µg/L but are generally below 4.5 µg/L (95th P = 4.21 µg/L). Titanium exists only in a fully hydrated form, TiO2 * n H2O, in water above pH 2, and is, therefore, transported in a colloidal state rather than as dissolved ion (Skrabal 1995 as referenced in Salminen et al. 1998). This is further supported by thermodynamic stability data and speciation modelling, which suggests TiO2 * n H2O to consitute the dominating species within environmentally relevant pH values and within the ionic composition of stream waters as provided by the FOREGS dataset. Because of the propensity of TiO2 for hydrolysis, other titanium hydroxo complexes than TiO2 * n H2O are rare within a pH range of pH 4-10. According to Salminen et al. (2005), a large proportion of the Ti in stream water sediments is held in minerals, such as rutile, ilmenite and sphene, all of which are relatively insoluble. Based on the FOREGS dataset, Ti concentrations of sediments can be as high as 3 % but are typically below 0.9 % (95th P = 0.81 %).