Glass, oxide, chemicals

Additional toxicological data

Administrative data

Endpoint:

additional toxicological information

Type of information:

experimental study

Adequacy of study:

key study

Study period:

~53 weeks during 1997 and 1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study. Study conducted according to previously published methods in a peer-reviewed scientific journal. Test-material and methods are well described and the animal model is appropriate.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Unnamed

Year:

1998

Report date:

1998

Reference 2

Reference Type:

publication

Title:

Unnamed

Year:

1985

Reference 3

Reference Type:

publication

Title:

Unnamed

Year:

1999

Reference 4

Reference Type:

publication

Title:

Chronic Inhalation toxicity of size-separated glass fibers in Fischer 344 rats

Author:

Hesterberg TW; Miller WC; McConnel EE; Chevalier J; Hadley J; Bernstein DM Thevenaz P; Anderson R

Year:

1993

Bibliographic source:

Fundam Appl Toxicol. 20:464-476

Reference 5

Reference Type:

publication

Title:

An experimental approach to the evaluation of the biopersistence of respirable synthetic fibers and minerals

Author:

Bernstein DM; Mast R, Andserson, Hesterberg TW; Musselman R; Kamstrup O; Hadley J

Year:

1994

Bibliographic source:

Environ Health Perspect, 102:15-18

Reference 6

Title:

Biopersistence of man-made vitreous fibers and crocidolite asbestos in the rat lung following inhalation.

Author:

Hesterberg TW; Miller WC; Musselman RP; Kamstrup O; Hamilton RD; Thevenaz P

Year:

1996

Bibliographic source:

Fundam. Appl. Toxicol. 29:267-279

Reference 7

Reference Type:

publication

Title:

The evaluation of soluble fibers using the inhalation biopersistence model, a nine fiber comparison

Author:

Bernstein DM; Morscheidt C; Grimm HG; Teichert U

Year:

1996

Bibliographic source:

Inhal Tox, 8:345-385

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rats were exposed to fiber aerosol by nose-only inhalation for 6 h/day for 5 days. Aerosols were monitored daily for concentrations in fibers per cc and milligrams per cubic meters and twice every 5 days for fiber bivariate dimensions (length and diameter for each fiber). Rats were followed through one year following the termination of exposure. At 9 time points (post-exposure days 1, 2, 7, 14, 30, 60, 90, 180, and 365), 5–8 rats were euthanized to evaluate lung burdens (number of fibers per lung, fiber bivariate dimensions, and fiber surface morphology).

Aerosol Generation and Characterization
For each of the six fiber aerosols, mass concentrations were adjusted to a target of 150 fibers/cc >20 um (Tables 2 and 3). During animal exposure, samples of airborne fibers were collected on filters placed in animal exposure ports. Fiber mass concentrations were determined in two aerosol samples per day for each of the 5 exposure days. Aerosol fiber numbers and dimensions were analyzed using scanning electron microscopy. Total fibers were counted in each of five daily samples. Bivariate fiber dimensions were measured in two of the five daily samples according to the method outlined by the World Health
Organization (WHO, 1985) modified for an electronic monitor. Dimensions were measured at an on-screen magnification of 70003 in a minimum of 20
fields (approximately 27 3 27 um) for 400 fiber ends (representing measurements of at least 200 fibers). Magnification was adjusted for length measurements so that no lengths were truncated. Percentages of fibers in each of several fiber-size categories were determined in the two daily samples, then used to estimate the numbers of fibers in each size-category from the total fibers per cc counted in the samples from the remaining 3 days. WHO fibers per cc are reported to permit comparisons with previous studies that have used this category and because the World Health Organization has defined a respirable-size fiber as having a length >5 um, diameter< 3 um and an aspect ratio >=3 um (WHO, 1985).

Animals
Male Fischer 344/N rats (Charles River Breeding Laboratories, Raleigh, NC) were randomly divided into 6 fiber-exposure groups (74 animals/group) and an air control group (29 animals). When not being exposed, the rats were housed individually in polycarbonate cages containing hardwood bedding in rooms under negative pressure (220 mm H2O) with 12–15 air changes/h. Temperature was maintained at 22 6 3°C, with a relative humidity of 30–70%, on a 12-h light-dark cycle. The animals were fed pelleted standard Kliba 343 rat maintenance diet (Klingentalmuehle AG, 4303 Kaiseraugst, Switzerland) and filtered fresh water was available ad libitum.

Lung Burden Analyses
At various time points, 5 rats (post-exposure Days 1 and 2) or 8 rats (post-exposure Days 7, 14, 30, 60, 90, 180, and 365) were randomly selected from each fiber exposure group and euthanized. For determining background lung burden levels, the lungs of 21 air control animals (5 rats on Day 1 and 8 rats each on Days 30 and 365) were analyzed. The lungs from each animal (without the bronchi and trachea) were weighed and stored frozen (280°C). For fiber analysis, each lung was thawed, dehydrated in acetone, and dried to a constant weight. The dried lung was minced and a portion was plasma ashed in an LFE LTA 504 multiple chamber plasma ashing unit. The portion ashed was 10% on Day 1 and was gradually increased with time to 40% to ensure adequate fiber
numbers in the later samples. The ash from each lung was washed with prefiltered household bleach (alkaline hypochlorite solution) at 60°C and pH
9.5–10.5 for 20 min to digest organic debris, rinsed with filtered, deionized water, and passed through a Nuclepore filter, which was then applied to an
SEM stub and gold-coated. The bleach rinse was necessary in this study but not in previous studies because larger amounts of lung tissue were ashed in this study to increase the number of lung fibers in the final sample for SEM analysis. Analyses using energy dispersive and scanning electron microscopy
found no chemical or physical differences between fibers recovered from the lung on post-exposure Day 1 and aerosol fibers, thus demonstrating that the
bleach rinse did not change the characteristics of the recovered fibers.

Further details:
The methods of production of fibre aerosols and exposure of the rats was previously published by Bernstein et al. (1994) (An experimental approach to the evaluation of the biopersistence of respirable synthetic fibers and minerals, Environ Health Perspect, 102:15-18) and Hesterberg et al. (1993) (Chronic inhalation toxicity of size-separated glass fibers in Fischer 344 rats, Fundam. Appl. Toxicol. 20:464-476). The method has similarities to the method described in EC Guideline ECB/TM/26 rev 7. Test fibres were analysed according to methods outlined by World Health Organisation 1985.
Lung burden was analysed according to a method published by Hesterberg et al. 1996 (Biopersistence of man-made vitreous fibers and crocidolite asbestos in the rat lung following inhalation. Fundam. Appl. Toxicol. 29:267-279) and Bernstein et al. 1996 (The evaluation of soluble fibers using the inhalation biopersistence model, a nine fiber comparison. Inhal. Tox. 8:345-385).

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

E glass microfibre

IUPAC Name:

E glass microfibre

Constituent 2

Reference substance name:

MMVF32

IUPAC Name:

MMVF32

Details on test material:

- Name of test material (as cited in study report): MMVF32
- Substance type: man-made mineral glass fibre
- Physical state: solid
- Composition of test material, percentage of components: See details in Table 1.
- Produced by: Johns Manville Corporation
- Stability under test conditions: Stable
- Other: E glass fiber (MMVF32) is generally produced as a continuous filament with a diameter that exceeds the upper limit of respirability (the small diameter version of the fiber used in this study was formerly manufactured in small quantities for special applications by Johns Manville Corporation, but is not currently produced in the U.S. or Europe);

Results and discussion

Any other information on results incl. tables

Fibre dimensions were smaller in the fibres deposited in the lung tissue, than what was present in the aerosol.

Table 2: Aerosol and Lung Fibre Dimensions	Aerosol			Lung
	Concentration (mg/m3)^a	Dimensions^b (µm)		Dimensions^c (µm)
Test fibre		Diameter	Length	Diameter	Length
MMVF32 (E-Glass)	51 (11)	0.81 (1.98)	16.1 (2.4)	0.47 (1.71)	8.9 (2.2)

 ^a Aerosol mass data as mg/m3 are mean (and SD) of 10 samples (2/day).

^b Average geometric mean (average geometric SD) of 2 air samples; $200 fibers per sample were measured.

^c Lung fiber dimensions one day after cessation of 5-day exposure. Data are average geometric means (average geometric SD) of 2 animals/exposure group, $200 fibers per animal.

The fibre concentration and geometry in the aersol was characterized, and the concentrations of fibres > 20 µm were adjusted to a target of 150 fibres/cm3.

Table 3: Aerosol Fiber Concentrations (Fibres per cm3)
	Fiber length category, µm
Test fibre	<5	5-20	WHO (>5)	>20
MMVF32 (E-Glass)	38 (9)	176 (37)	316 (50)	146 (28)

 Note. Mean and SD; n 5 5 air samples. WHO fibers have lengths .5 mm, and length/width ratio $3 m (WHO, 1985).

Lung burdens were analyzed for the four fibre length categories (L < 5 µm, L=5-20 µm, WHO > 5 µm and L > 20 µm) at time intervals from the end of the 5 day exposure period (day 1) and up to 1 year after the end of exposure. Lung clearance of fibres (L > 20 µm) was characterized by two phases; relatively rapid clearance occurred from day 1-90 after end of exposure and a slow or undetectable clearance occurred between 90-365 days after exposure. For E-glass the number of fibres at day 90 post exposure was reduced to 33% and 30 % of the number of fibres at day 1 post exposure, for WHO fibres (L>5 µm, L/D >3) and long fibres (L > 20 µm) respectively. At 365 days after end of exposure the remaining number of fibres was 10% for both WHO fibres and long fibres.

Table 4: Lung Burdens during Post-Exposure Recovery for MMVF32
Day^a	F < 5 µm^b	SD	% Day 1^c	F 5-20 µm^b	SD	% Day 1	WHO^c	SD	% Day 1	F <20 µm^b	SD	% Day 1
1	19	4	100	44	12	100	57	13	100	13	3	100
2	31	3	165	56	5	128	70	8	123	14	4	106
7	19	3	101	43	7	99	55	9	96	11	2	88
14	8	2	42	28	4	63	35	6	62	8	1.5	59
30	14	1.5	74	28	5	63	33	5	58	6	1.6	43
60	8	1.5	44	24	6	55	30	8	53	6	1.5	46
90	6	1.3	29	15	1	33	19	2	33	4	0.6	30
180	7	0.8	34	13	2	30	17	2	29	4	0.4	27
365	2	0.7	12	4	1	10	6	1	10	1	0.4	10

Note. Fibers/lung 3 105 (SD 3 105). N 5 5 for Days 1 and 2; N 5 8 for all other timepoints.

^a Number of days after termination of exposure period.

^b F ,5 mm 5 fibers shorter than 5 mm; F 5–20 mm 5 fibers with lengths 5–20 mm; F ,20 mm 5 fibers longer than 20 mm.

^c WHO F 5 respirable fibers as defined by the World Health Organization to have aspect ratio $3 and length ,5 mm (WHO, 1985).

For modeling of lung clearance one- and two pool first-order kinetic models were used. On this basis a weighted half-life time for E-glass fibres (L > 20 µm) was estimated to be 79 days.

 

Table 5: Models of Lung Clearance of Fibres Longer Than 20 µm
	Faster Pool			Slower Pool		Weighted half-life times		90% clearance
Fiber	% of total	T½	95% CL	T½	95% CL	T½	95% CL	T½	95% CL
MMVF32	58	7	5-14	179	149-225	79	62-96	371	272-506

Applicant's summary and conclusion

Conclusions:

The biopersistence of E-glass microfibre was tested after 5 days of inhalation in rats. The recovery period was up to 12 months after end of the exposure period. The weighted half-time of E-glass microfibre (L > 20 µm) was 79 days. The pattern of reduction in the number of deposited fibers in the lungs were similar in WHO (L> 5 µm, L/D > 3) and long fibers (> 20 µm), whereas for the other fiber types (L< 5 µm and L=5-20 µm) were reduced more quickly.

Executive summary:

The biopersistence of E-glass microfibre was tested after 5 days of inhalation in rats. The study was conducted according to previously published methods in several peer-reviewed journals, and the test fibres were analysed according to the method described by WHO (1985).

Male Fischer rats (74 exposed/fibre type + 29 clean air-controls) were exposed to fiber aerosols (~150 fibres (L>20µm)/cm3) by nose-only inhalation for 6 h/day for 5 consecutive days. The rats were followed during a post-exposure recovery period for 1, 2, 7, 14, 30, 90, 180, and 365 days.

The weighted half-life time of E-glass fibres (L > 20 µm) was 79 days. The pattern of reduction in the number of deposited fibres in the lungs were similar in WHO fibres (L> 5 µm, L/D > 3) and long fibres (> 20 µm), whereas the other fibre types (L< 5 µm and L=5-20 µm) were reduced more quickly.