Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats

Table 1 Lung histopathology (left lobe) after exposure to AM or LA for 10 days

	Air control	AM	LA	LA	LA
Target mass concentration (mg/m³)	0.00	3.50	0.50	3.50	25.00
Actual mass concentration (mg/m³)	0.08 ± 0.18	3.67 ± 1.58	0.53 ± 0.11	3.59 ± 0.91	26.76 ± 9.11
Foreign Body^a	0	6*	2	6*	7*
Alveolus Inflammation^b	0	7 (1.0)*	6 (0.9)*	7 (2.0)*	7 (2.0)*
Focal Chronic Inflammation^c	3 (0.4)	3 (0.4)	5 (0.7)	1 (0.1)	0
Bronchiole Epithelial Hyperplasia	0	0	0	0	5 (0.7)*
Interstitial Fibrosis^d	0	4 (0.6)	0	3 (0.4)	7 (1.0)*

Rats were exposed to AM or LA 6 h/day, 5 days/week for 2 weeks and evaluated 4 days after final exposure. Mass concentration data shown are mean values ± SD of daily mass concentrations. Other values represent the number of animals with a finding in each group (n = 7 per group). Average lesion severity scores for all rats in each group (shown in parentheses) were graded as follows: 1 = minimal, 2 = mild, 3 = moderate, 4 = marked, and 5 = severe. *P < 0.05 vs. air control by Fisher’s Exact Test. ^aConsistent with fibers; not graded for severity. ^bPredominantly macrophages with lesser numbers of neutrophils and lymphocytes, often associated with foreign bodies. ^cSmall aggregates of alveolar macrophages, often subpleural; distinct from the predominantly centriacinar populations of mixed inflammatory cells observed with “alveolus inflammation”. ^dConfirmed on Masson’s trichrome stain

ISSN: 1743-8977