Document OE777YdnR7nJZjEkbXZDXomZp

<8: P. F. Holt and D. K. Youno persons who bad lived in Paris or Dear to a large factory manufacturing brake linings in which asbestos is used. The asbestos bodies in the lungs of persons not normally handling asbestos are presumably derived from fibres present in the urban atmosphere but the widespread reports suggest that most atmospheres are contaminated. We obtained samples oC dust from the air of several cities by drawing about 50 1. of air through a millipore filter (type VF) by means of an Austin diaphragm pump. The filters were used face downwards to prevent large particles from settling on the membrane. Tbe specimens were transferred to grids by forming a carbon deposit about 200 A thick over the dust, transferring small pieces (1-5 X 1-5 mm) cut from the filter onto the grids, carbon downwards, then dissolving the filter away with acetone. The dust was left on the carbon membrane on the grid. A careful search of these specimens was made with the electron microscope. Blank millipore filters treated in the same way were examined to ensure that the filters themselves were not contaminated. The sampling points chosen were well above street level and, so far as could be ascertained, away from any direct source of contamination. In London samples were taken from the top of a five-storey buildmg, in Reading from the top of a two-storey, building situated in a park and also inside the building. Sampliog positions well above street level were also chosen in Rochdale, England, in Bochum and Diisseldorf in Germany, in Prague and Pilsen in Czechoslovakia, in Johannesburg, South Africa, and in Reykjavik, Iceland. Only Rochdale, which has the largest asbestos textile factory in Europe, can be regarded as having an important asbestos industry. A cartful search of some of the grids revealed no true fibres, but on other gridsC there were fibres or agglomerates of fibres. It was seldom that more than one or two windows of a grid revealed fibres. Usually the fibres were single, but occasionally large agglomerates were observed. Some appeared to be coated with soot or other > material. Fibres were present in the specimens from every sampling point but no'- fibre was found on any blank filter. Cbrysotile is the most widely used variety of asbestos- The chrysotile crystal has ar7 characteristic appearance in the electron microscope. Tbe lattice is in the form of a. tube that may be hollow or filled with amorphous material and the ultimate fibril has . a diameter of about 0-0J-0-06 pm. Electron diffraction studies made on some fibres'-- baving this appearance confirmed that they were in fact chrysotile asbestos. Other; fibres were identified as amphibole asbestos. Amphiboie asbestos was identified in the; air of Bochum and Johannesburg. t. Compared with other contaminants the amount of asbestos is very smalL A put of^ grid as seen in {be electron microscope is showB in Flo. 1. Many similar fields con- * tain no fibres. There appears to be no way in which the concentration of fibres can be expressed satisfactorily. Rickajux and Badam (1971) found chrysotile asbestos, in tbe air of Rochdale and attempted to estimate the mass concentration by an X-ray. technique based on the measurement of the integrated area under the (002) peak. They were able to determine only the upper limit which was 100 r*g of chrysotile m"* of air. Gadsden, Parker and Smith (1970) described an infra-red technique for the measurement of tbe mass concentration of asbestos dust in air but they found the ' concentration too low for the application of their method even in a car park with a foundation of asbestos waste and a tip used for dumping asbestos waste. They did 1 however, detect fibres on their millipore filters by electron microscopy. * $000 1393 I m^ * " * * . '* '/ -V- - ` nr.tfhWi (____ __ 01 p m Fig. 2. A single fibre dorf. Ment fibres apj iFacutf p. 4S2) PRODUCED BY food