Quantitative analysis of inorganic particulate burden in situ in tissue sections

Quantitative information on tissue particulate burden is essential for investigation of relationships of particulates to several aspects of disease, such as exposure, physiology, radiology and pathology. We have developed a method for quantitative analysis of inorganic particulate burden in situ in tissue sections using scanning electron microscopy (SEM) with backscattered electron (BSE) imaging and energy dispersive x-ray analysis (EDXA) or the ion microprobe mass analyzer (IMMA). Our data show reproducible results for concentrations above 10(6) particles per cm3 of tissue. Samples of less than one microgram can be analyzed. Standard 5 microns paraffin sections of formalin fixed tissue are mounted on carbon discs, deparaffinized and examined in the SEM under standardized conditions. Fields of view comprising 10,000 microns3 are searched and all particles visible in the BSE image are counted and individually analyzed by EDXA. Location, number, size and types of particles are tabulated. Previous work showed correlation of quantitative SEM/EDXA with bulk analysis for Ni (r = 0.64), and IMMA with bulk analysis for Be (r = 0.999). Analytical results on exogenous and endogenous particles in 40 lungs (greater than 6000 fields searched and greater than 5700 particles analyzed), and the pathology observed in the tissue, may serve as baseline for future studies on all types of inorganic particles in normal and abnormal lungs. Observed concentrations ranged from 3 X 10(6) to 2 X 10(9) exogenous particles per cm3 of tissue.