THE LUNG AS AN AIR SAMPLER

The mineral content of human lungs is more often studied by the medical community than the geological community, and the majority of the time the medical community is only concerned with the types and amounts of asbestos found in occupationally-exposed individuals. Also, in general, the medical community uses only small sections of digested lung tissue that they examine with the aid of an electron microscope, typically equipped with an energy dispersive detector (EDS) to obtain semi-quantitative compositional data. A high magnification system of some type is necessary because the particles in the lung are less than 10 microns in size. From a geological perspective, it would be interesting to: 1) identify all the minerals that occur in the lung and 2) determine the total mass of minerals in the lung. The former is needed to better understand what minerals occur naturally in the lung, while the later is helpful to determine a background dose.

It is relativity easy to obtain animal lungs (e.g., from slaughter houses), and use them to model human lungs; the difficulty arises in isolating the minerals from the organic material. Several methods can be used to digest the organic matter, but care must be taken not to dissolve any of the minerals. Freeze-drying the lung to remove the liquid results in a large weight reduction making the digestion methods easier to perform; then crushing and mixing the dried residue results in an homogenous sample. Given the mineral-concentrate, the typical repertoire of analytical methods (i.e., PLM, SEM, XRD, etc.) can be used to identify and characterize the minerals. As an example, we obtained a pair of sheep lungs that weighed 765 grams; freeze-drying them resulted in 205 grams of material. Next hydrogen peroxide was used to remove the organic material. From this mineral concentrate we used SEM-EDS and found that approximately 50% of the minerals were feldspars (with three separate feldspar species: K-feldspar, Ca-rich plagioclase, and Na-rich plagioclase in decreasing amounts) and about 20% quartz, with the remainder being the other common rock-forming minerals (e.g., micas, amphiboles, and pyroxenes). Interestingly, amounts and compositions of the major minerals are similar to those found in dust collected in our region (i.e., Moscow, Idaho) and analyzed by Norton and Gunter (Am. Min. 1999).