Physicochemical and Mineralogical Characterization of Test Materials used in 28-Day and 90-Day Intratracheal Instillation Toxicology Studies in Rats

Figures & data

TABLE 2  Physical properties of instillation materials for the 2001 and 2004 Fraunhofer rat studies

	2001 Rat study			2004 Rat study
	Quartz Isolate	Reference Quartz	Clay	Quartz Isolate	Reference Quartz
Property	2001	2001	Isolate	2004	2004
Mineralogy^a:
Quartz	62	87	0.04	60	87
Undefined silica	13	13	0	8	13
Montmorillonite	23	0	99.9	30	0
Analcime	2	0	0	2	0
Calcite	<1	0	0	0	0
Crystallinity:
Quartz crystallinity index	1.6	6		1.6	5
Quartz XRD domain size (μ m)	0.085	0.16		0.076	0.19
Scanning electron microscopy:
Mass mean geometric diameter, (μ m)	3.69	1.31		3.58	3.01
Surface area:
EGME (m^2/g)	173.7	16.01	479.5	213.0	5.6
Nitrogen BET (m^2/g)	3.2	1.51	6.4	21.2	3.7

^aIn weight percent. Quartz, analcime and calcite concentrations were determined by x-ray diffraction analysis. NIST SRM 1878a was used as the standard reference for quartz. Montmorillonite concentrations were estimated by subtracting the chemical contributions of the non-montmorillonite mineral phases from the total chemical analysis and then fitting a chemical formula matching that of the montmorillonite unit cell to the remaining chemical values following the method of Ross and Hendricks (1945). Excess SiO₂ is identified here as undefined silica.

TABLE 1  Chemistry of instillation materials used in the 2001 and 2004 Fraunhofer rat studies

	2001 Rat study			2004 Rat study
	Quartz Isolate	Reference Quartz	Clay	Quartz Isolate	Reference Quartz
Element^a	2001	2001	Isolate	2004	2004
SiO2	87.61	99.39	65.00	87.88	99.30
Al2O3	7.79	0.10	22.53	7.58	0.00
Fe2O3	1.33	0.04	4.67	1.39	0.04
MnO	0.01	0.00	0.01	0.00	0.00
Na2O	1.05	0.16	4.00	0.78	0.21
K2O	0.23	0.05	0.00	0.75	0.05
MgO	0.76	0.04	2.51	0.79	0.00
CaO	0.88	0.14	0.44	0.19	0.00
TiO2	0.08	0.05	0.11	0.08	0.02
P2O5	0.05	0.02	0.02	0.04	0.02
F	0.07	0.00	0.14	0.07	0.02
S	0.01	0.01	0.36	0.01	0.01
Total C	0.12	0.00	0.11	0.39	0.33

Note. Chemical composition of the instillation test materials was determined using standard lithium metaborate/tetraborate fusion methods for inductively coupled plasma (ICP) analysis. Trace element chemistry data is available from the authors.

^aIn weight percent. Expressed as oxides.

FIG. 1  SEM photomicrograph of Reference Quartz 2004 (15,000×).

FIG. 2  SEM photomicrograph of Quartz Isolate 2004 (20,000×).

TABLE 3  Electron spin resonance of Quartz Isolate 2004 and Reference Quartz 2004

	Wet^a
			Dry^b unground	Dry^c ground
	Si radicals	OH• radical quartet	Si radicals	Si radicals
Test material	peak height	peak height	peak height	peak height
Fenton reaction: FeSO4 + H2O2 control	None	Very strong^d	—	—
Min-U-Sil 5 crushed quartz	None	65	21	32
Reference Quartz 2004	None	65	31	44
Quartz Isolate 2004 before filtration	Very low	50	90	131
Quartz Isolate 2004 after filtration^e	None	50	—	—

^aTests conducted using 10 mg samples in aqueous suspension. DMPO added for ESR signal generation.

^bTests conducted using 40 mg dry powder samples.

^cTests conducted using 40 mg dry powder samples that had been crushed in a Fritsch IEC centrifugal ball mill for 10 min immediately prior to testing.

^dNot specifically defined but on the order of 100× greater than the values for the test materials.

^eSamples filtered through 0.45-μ m nitrocellulose filter to remove quartz particulate material.

FIG. 3  Zeta potential of instillation test materials at pH 4, 6, and 8.

FIG. 4  (a) SEM photomicrograph of quartz isolate before instillation in rat lung (5000×). (b) SEM photomicrograph of quartz isolate recovered from rat lung after 90 days by low-temperature plasma ashing (5000×).

FIG. 5  (a) SEM photomicrograph of reference quartz before instillation in rat lung (5000×). (b) SEM photomicrograph of reference quartz recovered from rat lung after 90 days by low-temperature plasma ashing (5000×).

FIG. 6  Recovered Quartz Isolate 2004 particle diameter distribution vs. stock material. Median diameter: stock particles, 2.6 μ m; recovered particles, 2.3 μ m.

FIG. 7  Recovered Quartz Isolate 2004 particle mass distribution vs. stock material. Median diameter: stock particles, 3.8 μ m; recovered particles, 3.8 μ m.

FIG. 8  Recovered Positive Control 2004 particle diameter distribution vs. stock material. Median diameter: stock particles, 0.5 μ m; recovered particles, 0.5 μ m.

FIG. 9  Recovered Positive Control 2004 particle mass distribution vs. stock material. Median diameter: stock particles, 3.1 μ m; recovered particles, 3.4 μ m.

TABLE 4  EDS chemical analysis of stock Quartz Isolate 2004 and Quartz Isolate 2004 recovered from rat lungs after 90 days by plasma ashing

Sample	Na2O	MgO	Al2O3	SiO2	K2O	CaO	Fe2O3
EDS analysis results
Stock Quartz Isolate 2004	0.81	1.28	5.94	89.71	0.21	0.61	1.46
Recovered Quartz Isolate 2004 (Average of 6 animals)	0.88	1.3	6.17	89.41	0.51	0.32	1.42
Wet chemical analysis results
Stock Quartz Isolate 2004	0.79	0.78	7.63	88.44	0.19	0.75	1.4

C. S. Ross, and S. B. Hendricks. Minerals of the montmorillonite group, their origin, and relation to soils and clays.. U.S. Department of the Interior, Geological Survey, WashingtonDC, (1945) Professional Paper 205-B.

 Google Scholar