Ashes (residues), rice husk

Acute Toxicity: other routes

Administrative data

Endpoint:

acute toxicity: other routes

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable publication providing basic information

Data source

Reference

Reference Type:

publication

Title:

Silicosis Caused by Rice Husk Ashes

Author:

Liu, S. et al.

Year:

1996

Bibliographic source:

J. Occup. Health 38:57-62

Materials and methods

Principles of method if other than guideline:

Rats were intratracheally given the test material once at a single dose and pathologically examined at intervals for up to 12 months.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Ashes (residues), rice husk

EC Number:

275-735-5

EC Name:

Ashes (residues), rice husk

Cas Number:

71630-92-7

Molecular formula:

SiO2

IUPAC Name:

silanedione

Details on test material:

- Name of test material (as cited in study report): rice husk ash (RHA)
- Analytical purity: no data

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 3-4 months
- Weight at study initiation: 150-180 g

Administration / exposure

Route of administration:

other: intratracheal

Vehicle:

physiological saline

Doses:

50 mg per animal (corresponding to ca. 277-333 mg/kg bw)

No. of animals per sex per dose:

36

Control animals:

yes

Details on study design:

- Duration of observation period following administration: 1, 3, 6, 12 months
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight,organ weights, histopathology

Results and discussion

Effect levels

Sex:

male

Dose descriptor:

LD0

Effect level:

277 - 333 mg/kg bw

Remarks on result:

other: no mortalities occurred; inflammatory responses at early stages and development of lung fibrosis and silicotic nodules at the end of the 12-month post-instillation period

Any other information on results incl. tables

Wet lung weight:

The wet lung weight means for each group was 3.80 ± 1.03 g in the rice husk dust, 3.56 ± 0.99 g in the 3500 °C group, 4.57 ± 1.60 g in the 650 °C group, 5.44 ± 1.96 g in the 1300 °C group, 2.28 ± 0.61 g in the saline group and 7.19 ± 2.45 g in the quartz group. The wet lung weight for all exposed groups was higher than that for the saline group. The wet lung weight for the rice husk group and 350 °C group were all significantly higher than that of the 1300 °C group (P < 0.01).

Gross observation:

At an early stage, the surface of the lung in all exposed groups was smooth and soft. At the 6th month after administration, both the hardness and volume of lung were increased, and this was most obvious in the 650 °C group and 1300 °C group. The pulmonary hilar lymph nodes at the 12th month were as large as green grams in the rice husk group and 350 °C group, as large as soybeans in the 650 °C group and larger than soy beans in the 1300 °C group. Microscopic examination: At early stage, interstitial pneumonia and histiocyte proliferation were the main changes in each exposed group. Dust foci, dust-cell foci and foreign body multi nuclear giant cells were observed in the rice husk and 350 °C groups, and cell nodules with proliferated reticular fibers were found in the 650 °C and 1300 °C groups. At a later stage, rice husk group revealed foreign body granuloma with the proliferation of reticular fibers. In the 350 °C group, dust focus formation was the main change, and lymph nodes at different stages from the 3rd month to the 12th month after adminstration had dust foci with proliferated reticular fibers. In the 650 °C group, proliferated and widened collagen fibers were noted. Compared with this group, extensive lung fibrosis and silicotic nodules could be seen in the 1300°C group. Following King's pathological grading of lung fibrosis, the rice husk group and 350 °C group were grade I at the stage of the 12th month after administration, the 650 °C group was grade I at the 3rd to the 6th month and grade II at the 12th month. The 1300 °C group was grade I at the 3rd month, grade II at the 6th month and grade III at the 12th month.

Electron microscopic examination:

At an early stage, vacuolar degeneration of the lamellar body of Type II pulmonary alveolus epithelium and proliferated Type II epithelial cells could be seen. At a later stage, hyperlastic fibroblasts were noted. In the 1300 °C group at the 3rd month after adminis tration and in the 650°C group at the 6th month after administration, cell proliferation and collagen fibers were observed. In the 1300 °C group at the 12th month after administration, obviously proliferated fibroblasts could be seen and collagen fibrosis was widely formed.

Applicant's summary and conclusion

Conclusions:

The induction of pulmonary fibrosis by rice husk ashes incinerated at 350°C, 650°C, and 1300°C was investigated in male rats intratracheally given 50 mg/animal of the experimental dust once. Quartz dust served as positive control. Groups rats in each exposure group were killed after the 1, 3, 6 and 12 months of the experiment for pathological examination. The results of pathological studies showed that the RHA heated at 1300°C could
cause diffuse interstitial fibrosis and silicotic nodules.