The mineral dust load of human lungs.

Studies of the dust content of lungs from non-industrially exposed city dwellers have shown that many people build up during life a total dust load of 2 grammes or more. This dust load may include up to 17 X 10(6) mineral fibres large enough to be visible with the light microscope and 360 X 10(8) fibres visible only by electron-microscopy. All lungs examined contained a small percentage of fibres that appeared structurally similar to chrysotile asbestos. It was found that the total dust content and content of light microscope sized mineral fibres was much lower in a non-industrialised city than in one with a high level of heavy industry, but levels of electron-microscope sized fibres did not differ markedly between the two groups. It would appear that these very small fibres are part of a general mineralogical background rather than resulting from industrial atmospheric pollution. This was further indicated by the fact that many of the dust particles, including large numbers of the fibrous ones proved to be derived from diatom skeletons.