OBJECTIVETo observe the histopathological changes of the lung of rats which exposed to the suspension of PM(2.5) and detect the effect of silver staining showing dust particles deposited in the lungs.

METHODSThe dissociative PM(2.5) of Beijing city was collected to make suspension. The rats were divided into different groups and exposed to different dosage of PM(2.5) (0.3 mg/0.2 ml per rat, 0.75 mg/0.2 ml per rat, 2 mg/0.2 ml per rat) by intratracheal instillation every week. These rats were sacrificed at 4, 12 weeks and 24 weeks (total dosage: 7.2 mg per rat, 18 mg per rat, 48 mg per rat) after the treatment, and their lungs were sampled. The pathological varieties and the situation of these rats' lungs were observed macroscopically and using hematoxylin and eosin (HE) staining, Warthin-Starry (WS) silver stain, as well as the transmission electron microscope (TEM). The dust particles in these rats' lungs were observed by x-ray spectrum chemical element analysis (X-RSA). The granulomatous lesion in the lungs of the rats was counted, and the deposition degree, integrated optical density (IOD) value and integrated area density (IAD) value of the dust particles deposited in the lungs were measured. The variance, least significance difference, and the unitary linear related and regression were analyzed.

RESULTSThe number of the granulomatous lesion in the lungs of the rats became more and more with time. In WS staining the dust particles were dark brown and became clearer. The IOD and IAD value of these dust particles were much higher in WS staining than that in HE staining (P < 0.05). The IOD value of the dust particles was positively correlated with the number of the granulomatous lesion (R = 0.639, P < 0.01). The ultrastructure of the dust particles in the rats' lungs and the dissociative PM(2.5) was basically same in TEM. Their main compositions were similar, by X-RSA, and both of them were silicon.

CONCLUSIONThe suspension of PM(2.5) could result in the granulomatous lesion in the lung of rats. WS silver staining is a good method to show PM(2.5) phagocytized by macrophage, and is better than HE staining.