Potassium aluminium silicate amorphous glass fibres

Carcinogenicity

Description of key information

a long term carcinogenticty test carried out for AES fibres, no evidence of increased cancerous incidents occurred and as such the fibre is not considered carcinogenic. The results from the existing 90 day and 2 year inhalation studies for Alkaline Earth Silicate fibres linked to the short term bio-persistence study with the Potassium Alumino Silicate fibres provide reliable evidence as to the lack of toxic potential for Potassium Alumino Silicate fibres. This is supported by the lack of effect on the lungs of the rats used in the biopersistence studies. With this background we do not believe that further animal testing can be justified.

Key value for chemical safety assessment

Carcinogenicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24th May 1988 to 14th November 1990

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

GLP Compliant, no justifcataion for the dose used, which was assumed to be the MTD. read across study from AES fibres,the results from these existing 90 day and 2 year inhalation studies for Alkaline Earth Silicate fibres linked to the short term bio-persistence study with the Potassium Alumino Silicate fibres provide reliable evidence as to the lack of toxic potential for Potassium Alumino Silicate fibres. This is supported by the lack of effect on the lungs of the rats used in the biopersistence studies. With this background we do not believe that further animal testing can be justified.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

yes

Principles of method if other than guideline:

lifetime inhalation with serial sacrifice for inflammatory and fibrotic effects in lung

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Kingston, Stone Ridge, N.Y., USA
- Age at study initiation: 8 weeks
- Weight at study initiation: 130-150g
- Housing: during exposure and beginning of recovered, stainless steel wire cages, during major part of recovery period Macrolon Cages Type IV with standard softwood bedding
- Diet (e.g. ad libitum): pelleted standard Kliba 343, rat/mouse maintenance diet
- Water: ad libitum
- Acclimation period: 18 days from day of delivery

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20
- Humidity (%): 30 - 70
- Air changes (per hr): 10 - 15
- Photoperiod (hrs dark / hrs light): 12hrs

IN-LIFE DATES: From: 24th May 1988 To: 14th November 1990

Route of administration:

inhalation: aerosol

Type of inhalation exposure (if applicable):

nose only

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: flow -past nose-only design
- Method of holding animals in test chamber: makrolon tubes
- System of generating particulates/aerosols: fibres were aerosolised using a stepping motor and stainless steel brush to bring them into the tangential air stream, following aerosolisation the fibres passed through a Nickel63 charge neutraliser to reduce electrostatic charge
- Temperature, humidity, pressure in air chamber: 22degC, 30-70%
- Air flow rate: 0.9 litre/ airport/min
- Method of particle size determination: fibre size measurements carried out by SEM

TEST ATMOSPHERE
- Brief description of analytical method used: mass concentration (gravimetric), fibre number concentration, fibre size measurements and impactor sampling.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

samples of the aerosol were collected on membrane filters , these were weighed for gravimetric analysis and fibres counted by SEM

Duration of treatment / exposure:

104 week

Frequency of treatment:

6hrs/day, 5days/week

Post exposure period:

91 to 26 weeks depending on length of exposure see table 1 below for more details.

Remarks:

Doses / Concentrations:
29.93 mg/m3 ± 5.87
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
174 WHO f/ml ±72
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
47 fibres >20µm/ml ±23
Basis:
analytical conc.

No. of animals per sex per dose:

140

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: 30mg/m3 had been found to be the maximum tolerated dose for another fibre in a 56 day study, it was assumed that this dose was the MTD for all man-made fibres.

Positive control:

NIEHS Intermediate Length Chrysotile Asbestos - Plastibest-20
Dose: 10mg/m3 ± 3, WHO Fibres 10,600 f/ml ± 11,400

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily, prior and following exposure and once daily on non-exposure days

BODY WEIGHT: Yes
- Time schedule for examinations: Each animal was weighed once during the acclimation period, weekly during the first 13 weeks of exposure and at least monthly thereafter

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table in "any other information on materials and methods incl. tables")
HISTOPATHOLOGY: Yes (on all necropsied animals)

Other examinations:

neoplastic tissues were sampled and sent frozen in liquid nitrogen to CIIT North Carolina 27709.
Special procedure for Lungs, examined under dissection microscope for detection and identification of small macroscopic lesions
lungs were inflated with formaldehyde photographed and sections taken for histopathology.
After sacrifices at 13, 26, 39 and 52 weeks lungs were instilled with Karnowski's fixative and sampled

Statistics:

Body weight and organ weight were analysed using Dunnett test, age specific survival rates were calculated with Kaplan-Meier non-parametric estimates, statistical evaluations for the neoplastic lesion was performed according to Peto et al..

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY clinical signs were comparable in all groups including air controls in their nature, incidence, time of onset, severity and duration. Therefore they were considered not to be directly related to fibre exposure. The Kaplan Meier survivor function showed no intergroup difference reaching a statistical level of significance of 0.05, it was however shown that there was a marginally delayed mortality in the x607 exposure group during the second year of exposure and the initial part of the recovery period. This difference was considered to lie within the limits of normal biological variations and was assumed not to be treatment related. However it is not excluded that this may have a marginal influence on the incidence and/or intensity of some pathological changes.

BODY WEIGHT AND WEIGHT GAIN during the first year of exposure the mean body weight was minimally lower than the control group whereas body weight gain was marginally higher. during the second exposure year mean values were statistically higher than that of the controls, with the maximum mean body weight reached during the study being 2-3% higher than the control group and occurred approximately 10 weeks later. these differences are believed to essentially reflect the slightly delayed mortality of the x607 exposure group

ORGAN WEIGHTS lung and lung accessory lobe weights.
In the x607 group there was no relevant difference observed from the control group at any sacrifice time point, however in the positive control group (chrysotile exposed) the mean lung weight and the mean lung to body weight ratio were moderately to markedly higher than the controls at the same sacrifice time point, there was a trend to increasing difference from control values as the study progressed at least until the end of exposure.

HISTOPATHOLOGY: NON-NEOPLASTIC only cellular changes were seen in the rat lungs and these are typical of physiological response to inhaled dust, no fibrosis was seen and all effects regressed when exposure terminated, the maximum Wagner score did not exceed 2 see table 3

HISTOPATHOLOGY: NEOPLASTIC the tumours seen consisted of one adenoma and one adenocarcinoma, these are felt to be background for this strain of animal, see table 5

Relevance of carcinogenic effects / potential:

no carcinogenic effects were observed during this two year inhalation study

Dose descriptor:

NOAEC

Effect level:

> 174 other: WHO f./ml

Based on:

test mat.

Sex:

male

Remarks on result:

not determinable

Remarks:

no NOAEC identified. Effect type:carcinogenicity (migrated information)

Table 1: Fibre Concentrations and Dimensions

	Concentration (mg/m^3)			Fibres (/ml)				nonfibrous Particles/ml <3µm		Dimensions (µm)^b
Fibre	Target		Actual	WHO^a		>20 µm Length				Length	Diameter
A. Aerosol Averages of exposure period
Chronic Study, 2 years
x607	30		30 ± 6	174 ± 72		47 ± 23		117 ± 77		11 ± 4	0.9 ± 0.3
RCF1	30		29 ± 6	187 ± 53		101 ± 15		307 ± 99		16 ± 3	0.8 ± 0.2
Chrysotile	10		10 ± 3	10,600 ± 11,400		0		0		1.2 ± 0.3	0.08 ± 0.01
Deposition Study 6 h
x607	60		57	247 ± 7		46 ± 4		182		8 ± 2	0.9 ± 2
RCF1	60		60	237 ± 7		69 ± 5		283		11 ± 3	1.0 ± 2
B. Lung Burden following termination of exposure
		Dimensions(µm)^b					Fibres (x10^3)^c
Fibre		Length			Diameter		WHO^a		>20 µM
Chronic Study, 2 years
x607		6 ± 0.4			0.5 ± 0.02		187 ± 31		4 ± 4
RCF1		8 ± 0.7			0.5 ± 0.05		275 ± 63		48 ± 10
Chrysotile		1.6 ± 0.2			0.07 ± 0.00		2800 ± 800		0
Deposition Study 6 h
x607		7 ± 1.7			0.6 ± 1.6		24 ± 3		2.4 ± 0.3
RCF1		8 ± 0.9			0.6 ± 1.8		9 ± 1		2.0 ± 0.3

 

^aWho Fibres are respirable fibres as defined by the World Health Organisation as being 5µmin length and >3µmin diameter and having a length/diameter ration >3.

^bDimensions are the geometric mean of all (total) fibres±the geometric SD

^cValues are means±SD per dry lung weight (n=6-10 animals) at termination of exposure

 

Table 2: Lung Burden after Exposure and after Exposure Plus Recovery

Exposure/recovery Weeks	WHO (fibres/lungs)			Fibres (>20 µm /lung)
	Exposure (x10^6)^a	Recovery (x10^6)^b	Percent retained after recovery	Exposure (x10^6)^a	Recovery (x10^6)^b	Percent retained after recovery
X607
13/91	nd	0.2 ± 0.1	nd	nd	0	0
26/78	nd	0.7 ± 0.1	nd	nd	0	0
52/52	62 ± 6	2.0 ± 0.2	3 ± 0.3	1 ± 0.2	0.03 ± 0.03	6 ± 6
78/26	81 ± 4	13.3 ± 2	16 ± 2	2 ± 1.9	0	0
104/23	58 ± 6	15.0 ± 4	26 ± 7	1 ± 0.5	0.10 ± 0.03	8 ± 2
RCF1^c
13/91	39 ± 4	5.8 ± 2	15 ± 6	3 ± 0.6	0.16 ± 0.04	5 ± 1
26/78	56 ± 6	7.6 ± 3	14 ± 6	6 ± 1.0	0.32 ± 0.16	5 ± 3
52/52	119 ± 19	21.0 ± ^c	18^d	20 ± 2.4	1.66 ± 0.00	8 ± 0
78/26	173 ± 51	87.7 ± 20	51 ± 11	21 ± 2.7	6.89 ± 2.54	33 ± 12
104/23	143 ± 10	61.0 ± 5	43 ± 4	25 ± 3.0	6.73 ± 1.20	27 ± 5
Chrysotile^c
13/0	250 ± 40	nd		nd	nd	nd
26/0	180 ± 83	nd		nd	nd	nd
52/0	1020 ± 178	nd		nd	nd	nd
78/0	853 ± 228	nd		nd	nd	nd
104/23	1600 ± 458	216 ± 60	14 ± 4	0	0	0

 

Note: nd, not done, no data. X607 lung samples were stored in liquid fixative causing lung fibres to degrade.

^aLung burdens for those animals euthanize within 24h of cessation of exposure

^bLung burdens for animals that were exposed and then held in recovery for the number of weeks indicated in the column Exposure/recovery

^cMast et all (1995)

^donly one animal in the 52/52 exposure/recovery week RCF1 recovery group survived. Data for all other time points are averages of three to six animals ± SD

 

 

Table 3: Pulmonary Change: Mean Wagner Score^a

Exposure/Recovery (weeks)	Air control (exposure only)	X607		RCF1^b		Chrysotile^b
		Exposure	Recovery	Exposure	Recovery	Exposure	Recovery
13/91	1.3	2.0	1.3	3.5	3.0	4.0	nd
26/78	1.0	2.0	1.0	4.0	4.0	4.0	nd
39/65	1.0	2.3	1.0	4.0	4.0	4.0	nd
52/52	1.0	3.0	2.5	4.0	4.0^c	4.0	nd
65/nd	1.0	3.0	nd	4.0	nd	nd	nd
78/26	1.0	3.0	2.0	4.3	4.0	4.0	nd
104/23	1.0	2.8	2.7	4.0	4.5	4.0	4.0

Note: For exposure animals, n=3-6; for 104 ± 23 week time point, n=>10; for interim recovery groups; n=2-4 due to decreasing survivals. Nd, not done,

^aScores according to Wagner, 1983. Scale 1, no lesion; 2, macrophage aggregation; 3, cellularity; 4 fibrosis (irreversible); 5, linking fibrosis

^bMast et all (1995)

^cScore of one surviving animal.

 

Table 4: Inflammation and Collagen Deposition in the Lung and Pleura during the Chronic Inhalation Study

Fibre	Exposure/Recovery (weeks)	Alveolar macrophage aggregation^a		Alveolar bronchiolization^a		Microgranulation^a		Bronchioalveolar collagen^a		Pleural collagen^a
		Exposure	(+) Recovery	Expos	(+) Recov	Expos	(+) Recov	Expos	(+) Recov	Expos	(+) Recov
X607	13/91	1.0	1.3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	26/78	1.3	0.3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	39/65	2.0	1.0	0.3	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	52/52	2.0	1.5	1.2	0.5	0.0	0.5	0.0	0.0	0.0	0.0
	78/26	2.3	2.0	2.0	0.0	2.0	0.5	0.0	0.0	0.0	0.0
	104/23	2.1	2.1	1.0	0.8	1.2	1.5	0.0	0.0	0.0	0.0
RCF1	13/91	2.0	0.5	1.0	0.5	2.0	0.0	0.7	0.5	0.0	0.0
	26/78	2.7	2.0	2.0	1.3	2.0	1.0	1.7	1.3	0.0	0.7
	39/65	3.0	2.0	2.7	1.0	2.7	2.0	2.7	2.0	1.0	0.5
	52/52	3.0	2.0	2.3	2.0	2.5	2.0	2.2	2.0	1.5	1.0
	78/26	3.0	2.5	2.7	1.8	2.3	2.0	2.3	2.3	1.0	0.5
	104/23	3.0	2.9	2.0	2.9	2.0	1.9	2.3	2.4	0.5	1.3
Chrysotile Asbestos	13/91	2.0	-^b	1.7	2.0		1.0		0.0
	26/78	2.0		2.0		2.0		2.0		0.0
	39/65	2.0		2.0		2.0		2.3		1.0
	52/52	2.0		2.0		2.3		2.2		0.2
	78/26	2.0		2.0		2.0		2.3		0.0
	104/23	2.7	2.5	2.7	2.4	2.0	1.9	2.7	2.7	0.0	0.0

Note: Level of severity of lesions observed at time points during 2 year exposure period and 6 month recovery period was graded as follows: Grade 0, normal; 1, minimal; 2, mild; 3, moderate; 4, marked; 5, massive. Each grade is a mean of 3-10 animals. Boldface values are scores of 2 or higher

^aExpos. Indicates animals had exposure but not recovery time: recov. Indicates animals had exposure + recovery

^bRecovery data for chrysotile pathology was determined for 12 month exposure/6 month recovery only

 

Table 5: Pulmonary and Mesothelial Proliferative Lesions during the Chronic Inhalation Study

Exposure	n^b	Hyperplasia (bronchioalveolar)^a	Lung Cancer^a			Mesothelioma (pleural)^a
			Adenoma	Carcinoma	Total lung cancers
Air	130	5 (3.8)	2 (1.5)	0	2 (1.5)	0
x607	121	6 (4.9)	1 (0.8)	1 (0.8)	3 (1.6)	0
RCF1^c	118	17 (14.0)	8 (6.6)	7 (5.6)	15 (12.4)	2 (1.7)
Chrysotile^c	69	13 (18.8)	6 (8.7)	6 (8.7)	12 (17.4)	1 (1.4)

Note: Values in boldface are significantly different from air controls

^aValues are the total number of X. Values in parentheses are percentages

^bNumber of animals at risk for tumour formation (at risk defined as surviving until at least the 12 month time point, after first tumour appeared)

^cMast et al (1995b)

Conclusions:

X607 was neither fibrogenic nor tumorigenic and induced only minimal lung cellularity that reversed after exposure was terminated.

Executive summary:

Since X607 is an AES fibre this is key evidence for the importance of low bio-persistance and relates to the read across case in section 7.5.2 for using read across for the 90 day sub chronic inhalation study.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Justification for classification or non-classification

no evidence of carcinogenicity by read across in conjunction with low bio-persistence testing according to note Q criteria.

Additional information

Justification for selection of carcinogenicity via inhalation route endpoint:
read across from 2 year inhalation study carried out on AES Fibres. The 2 year inhalation studies for Alkaline Earth Silicate fibres linked to the short term bio-persistence study with the Potassium Alumino Silicate fibres provide reliable evidence as to the lack of toxic potential for Potassium Alumino Silicate fibres. This is supported by the lack of effect on the lungs of the rats used in the biopersistence studies. With this background we do not believe that further animal testing can be justified.