Biopersistence of fibrous thermal insulations (AES fibers) after heat exposure using intratracheal instillation technique

Silva, D. G. M.; Ridgley, A. R.; Vasconcelos, W. L.

doi:10.1590/0366-69132019653732456

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Articles • Cerâmica 65 (373) • Jan-Mar 2019 • https://doi.org/10.1590/0366-69132019653732456 copy

Biopersistence of fibrous thermal insulations (AES fibers) after heat exposure using intratracheal instillation technique

Biopersistência de isolantes térmicos fibrosos (fibras AES) após exposição ao calor utilizando técnica de instilação intratraqueal

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Because refractory ceramic fibers (RCF) were classified as possibly pathogenic to humans, alkaline earth silicate (AES) wools have been used as a substitute product for high-temperature applications. All in vivo assays developed to evaluate its pathogenicity were assessed using as-received AES samples. The classification as a pathogen does not apply if the retention half-time for fibers longer than 20 μm is less than 40 days. Therefore, this work describes the evaluation of one AES sample after heat treatment, using the intratracheal instillation technique in rats. Over a three-month post-treatment period, the rats were dissected, and their lungs were examined. The half-time calculation for the retained fibers longer than 20 µm in the lungs was 56 days. Therefore, this AES sample after heat treatment could be presumed to have pathogenic potential for humans.

Keywords:
alkaline earth silicate fibers; biopersistence; biosoluble fibers; cristobalite; crystalline silica; man-made vitreous fibers

Table I General information of the tested fiber.

Type	Chemical composition (%)				Thickness (mm)	Bulk density (kg/m³)	Classification temperature (°C)
Type	SiO₂	CaO+MgO	Al₂O₃+ZrO₂+TiO₂	Other oxides	Thickness (mm)	Bulk density (kg/m³)	Classification temperature (°C)
AES	60-70	25-40	<6	<1	25	128	1200

Table II Number of animals per group and sacrifice dates.

Group	2 days	14 days	32 days	88 days	Sum
Study group	5	5	5	5	20
Negative control group	7	7	7	7	28

Table III Chemical composition (wt%) after ignition of the sample.

SiO₂	CaO	MgO	SO₃	Al₂O₃	Fe₂O₃	Na₂O	TiO₂	K₂O	Others*
65.9±0.3	27.8±0.1	5.50±0.11	0.21±0.02	0.19±0.01	0.10±0.01	0.04±0.01	0.02±0.01	0.02±0.01	trace

Table IV Fiber concentration in suspension.

Parameter	Day 0	Day 1	Day 2	Day 3	Mean
N° of fibers counted	414	411	411	410	412
All fibers (10⁶/1.2 mL)	64.8	55.2	57.0	60.6	59.4
WHO fibers (10⁶/1.2 mL)	36.3	32.9	37.4	42.1	37.2
Fibers (L<5 µm) (10⁶/1.2 mL)	28.5	22.3	19.6	18.5	22.2
Fibers (5<L<20 µm) (10⁶/1.2 mL)	29.6	27.4	29.8	33.9	30.2
Fibers (L>20 µm) (10⁶/1.2 mL)	6.65	5.47	7.61	8.20	6.98
Total length of the fibers (m/1.2 mL)	602.4	523.5	599.1	652.7	594.4
N° of particles counted	108	107	141	106	116
Particles (10⁶/1.2 mL)	263.2	259.4	341.4	257.0	280.2

Table V Gravimetric concentration in fiber suspension (mg/0.3 mL).

	Day of the instillation
	1	2	3	4	Mean
Beginning	0.49	0.50	0.51	0.51	0.50
Ending	0.44	0.48	0.48	0.47	0.47
Mean	0.47	0.49	0.50	0.49	0.49

Table VI Analyses of the fibers in the lung ash of individual animals.

Sacrifice date	Animal Id.	N° of fibers counted	Number of fibers (10⁶/lung)					Calculated mass of fibers (µg)	Length of fibers (µm)	Particles counted	N° of particles (10⁶/lung)
Sacrifice date	Animal Id.	N° of fibers counted	All fibers	WHO fibers	L≤5 µm	5<L≤20 µm	L>20 µm	Calculated mass of fibers (µg)	Length of fibers (µm)	Particles counted	N° of particles (10⁶/lung)
2 days	5001	404	54.5	31.4	23.2	26.3	5.104	751	497	106	231.0
	5002	402	31.2	17.9	13.3	15.7	2.236	496	261	113	89.4
	5003	412	63.9	35.0	28.9	30.1	4.895	940	550	103	193.3
	5004	405	33.5	17.3	16.2	15.5	1.807	364	261	111	103.6
	5005	407	55.2	34.0	21.2	30.3	3.699	761	479	102	149.1
14 days	5008	415	42.3	28.4	13.9	26.4	1.951	578	352	117	54.5
	5009	405	39.8	21.5	18.3	19.6	1.904	462	294	101	95.1
	5010	408	37.4	19.9	17.5	18.1	1.836	485	288	105	71.9
	5011	408	57.5	31.8	25.7	29.2	2.626	660	431	101	91.7
	5012	403	54.9	31.8	23.1	28.9	2.893	783	430	103	75.9
32 days	5015	401	39.9	21.7	18.2	20.5	1.244	392	276	102	36.4
	5016	407	52.6	29.9	22.7	27.9	2.026	587	395	108	74.2
	5018	383	22.3	12.4	9.9	11.5	0.958	252	162	101	38.4
	5019	404	43.9	25.1	18.8	23.2	1.953	622	343	102	90.8
	5020	405	35.4	21.7	13.7	20.3	1.475	496	272	110	70.0
88 days	5022	380	35.3	15.6	19.7	14.9	0.687	311	212	103	54.9
	5023	408	48.1	22.9	25.2	21.6	1.229	617	309	141	106.2
	5024	368	49.9	20.1	29.8	19.5	0.545	498	279	114	68.0
	5025	402	49.5	24.4	25.1	23.3	1.143	513	321	102	56.6
	5026	408	59.4	26.8	32.6	25.5	1.296	501	366	101	71.8

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