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Industrial Hqgiene Recent works on inhaled dusts, the irritant action of ozone, and the composition of nitrous fumes are contributions to basic research in industrial toxicology
YSUOW IWmTUTI
I.uutl.ta1HygSene Feluulatiom W. C. L. Hemeon, Engineering Director
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recent papers on industrial toxicology are of special interest because they contribute to subjects which have been controversial owing to the lack of pertinent information. These articles deal with the retention of dust and the physiological effects of oxides of nitrogen and ozone. In the first of theae, “Influence of Particle Size upon the Retention of Particulate Matter in the Human Lung” [Am.J . Pub. HmZth, 40, No.4,450-8 (1950)], J. H. Brown, K. M. Cook, F. G . Ney, and Theodore Hatch have described the basis and objective of their work as follows: HREE
The fraction of an inhaled dust which is retained in the respiratory system and the de th to which the dust penetrates before deposition are Bemitivet related to its particle size. Thm the size factor is a primary one ,in determining the magnitude of hazard aasociated with the inhalation of particulate matter. Specifically, in the case of silicosis and other ulmonary dust diseases interest is limited to that portion of t t e total inhaled materiai which is deposited in the alveoli. In order, therefore, to relate levels of atmospheric exposure for different size particles to actual pulmonar dosages, a quantitative relationship is required between size a n l t h e amount of dust so deposited.
calculated from the carbon dioxide content in each fraction of exhaled air. Figure 2 shows that the optimum particle size for reaching the alveoli and sthying there is about 1 micron. The existence of an optimum stems from the fact that large particles which have high rates of sedimentation have smaller chance of reaching the alveoli and vice versa. This fundamental work is important to studies of dust diseases, aerosol inhalation therapy, and community air hygiene; it should also be of interest to chemists and engineers concerned with characteristicsof aerosols.
The human lung is analogous to a d&bcollection system consisting of air “ducts” (bronchi and bronchioles) leading to a central “scrubber” (the alveoli, several million terminal air sacs measuring 0.1 to 0.2 mm. each), in which dust is deposited in the duck as well as in the scrubber (Figure 1). Design of experiments for measuring separately the amounts of dust deposited in the conveying ducts aa well as in the scrubber waa complicated became the ducts that carry dusty air to the scrubber serve also in alternate periods of time to conduct clean scrubbed air to the exterior of the system. The methods employed were based on engineering thinking and methods.
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Human subjects were caused to inhale especially prepared dust suspensions whose particle sizes and concentrations were accurately known. On each exhalation the issuing air stream over a period of about 2 seconds could be split into seven fractions by an ingenious rotary valve operating with splitsecond precision, and the dust content of each fraction could be measured. In thu way dusty air that originally penetrated only part way into the duct system, before reversal of flow, was collected separately from air which had reached the scrubber. As in a boiler test, where stoichiometric calculations permit estimation of flue gas rates from carbon dioxide determination, 80 in this work the proportion of each fraction that had passed through the scrubber could be
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2 3 4 PARTICLE DIAMETER, MICRONS Figure 2. Dust Collector Effioiency of Human Lung in Relation to Particle Size
BELLOWS ACTION AIR WMP
Figure 1. Human Respiratory Tract as Dust Collector
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The strongly irritant propertiesof ozone gas, when inhaled, have long been recognized, although to laymen the word may connote a healthful, invigorating atmosphere. Electric ozone-generating machines have been promoted from time to time for use in connection with ventilating systems. The claim that the ozone oxidizes carbon monoxide to dioxide and is thus beneficial in repair garages has long been disproved. Ozone generators have been advocated for use also in conjunction with air-conditioning systems on the basis that the gas destroys odors. Since dilution of body odor is usually the criterion determining the volume of ventilation required in auditoriums and the like, there could be a resultant economy by reduced air flow. It ia generally agreed that perception of odors is reduced in the presence of small concentrations of ozone, but it haa been demonstrated that t’ie effect is the result of a reduced sensitivity (perhaps temporary paralysis) of the olfactory organs due to ozone rather than to any action of oxidation on the odorous molecules in the air. Ozone i s encountered in rooms housing high voltage rectifier8 (Cottrell precipitator systems), in electric insulation breakdown test rooms,and similar places where high voltage electric arcs occur. For many years industrial hygienists have appraised the health hazard in such atmospheres on the ( C o n t h e d on puae 76 A ) 75 A
Industrial Hygiene basis that concentrations in eof 0.5 to 1 p.p.m. by dume may be harmful-the ckxw&eri&ic odor is apparemt below 0.1 p.p.m. C. E. Thorp mviews the literature and offers a brief report [“Toxicity of Ozone,” Znd. Med., 19, 50-7 (1950)l on some experimentid work, which leads to his conclusion that the toxicity of onane is much leas than is represented by these concentratiom 5igum. ,Nitrogen oxides, which have a lung irritant action like that of ozone, are simdtaneously generated in ozone machines in some circumstances, particularly where a high current d e d y is employed. Thorp, therefore, explains apparent discrepmwks En the lung irritant action of the gases from ozonizers by a n d m of the conditions of onone formation and whether these are 513immbktothe formation of nitrogen oxide. He suggests that the hvogrrsestogether have a more intense irritant action than similar aowmhtions of either gas alone. Thorp’s discmion provides m bitensting contribution to the literature because heretofore the pmwxx-8 of nitrogen oxides mixed with ozone has not been pimen, cumidemtion. On the baais of exposures of humans 5c!r p& up to 10 minutes, Thorp defines two regions of expointensity: One, the “nontoxic irritant” region, is based on omhnmmexposure for 1 minutetoaconcentrationof about250p.pm~hryvoEumeanda10minute exposure up to 40 p.p.m. by volume: The mthor’suse of in view of the the term, nontoxic, to describe these exporeactions described is questionable, as is hie use 08 “temporary toxicity” region, the term applied to the nasttl hi&m exposure, wherein one human was exposed to 15,0001 ppm. by volume for 1.2 seconds and the other to 3000 p.p.m. for B ; d . These exp o s resulted ~ in acute inflammation of %b PEPmembranes and several days were required for recovery. A m d i n g to the author’s tolerance chart, no worse than the .&owmight be expected from an exposure of 100 minutes to a m m m b t i o n as high aa 150 p.p.m. None of the experimental wwk is described, and there is, therefore, no basis for critical a p p a i d of the results. As to tolerance concentrations for long gaFisaS of exposure that result in no symptoms, he refers to the wonk of E.V. Hill. Hill’s results confirm the validity of the conamhtion levels for prolonged exposure currently in use by indhms%aislhygienists. Attempts to m a s the toxicity of oxi& of nitrogen that may arise from the action of nitric acid on &ah, ozone machines, arc welding, oxyacetylene torches, and expdcsions of nitroglycerin have always been complicated by a swies; of anomalous fatalities in which a consistency was lacking bebmen measured concentrations of the gas and the severity of theevent. Theexplanation may lie in differences in the proportions 0%dtmgen oxide and nitrogen dioxide in different circumscances. Nitrogen dioxide is believed to be a severe lung irritant above concentrations of about 1 6 p.p.m, The toxicity of nitric &de is relatively insignificant. Analytical methods in common use do not distinguish between these two forms. Recently there have been valuable contributions to the litemture on this subject: ‘‘Composition of Nitrous Fumes from Industrial Processes,” by H. A. Wade, H. B. Elkins, and B. P. W. Ruotolo [Arch.Ind.Hyg.&Occ.Med., 1,81(1950)], withpertinent references. These authors employed s new air-sampling methcd (by Flagg and Lobene) that depends on the adsorption of nitrogen dioxide by,silica gel while nitric oxide passes through; they made rough measurements of the rate of oxidation of nitric oxide to dioxide. The rate of reaction is expressed by dc/dt = Kct. The theoretical value of K is 2.8 X when e is in p.p.m. by volume. Their experiments showed ranges of 1.1 X to 5.4 X with an average of 3.0 X lo-’. The composition of nitrous fumes from various industrial processes are reported, and the percentages of the total nitrous fumes, which may be inferred to be the irritant nitrogen dioxide, are given as: carbon arc fumes, 9%; fumes from oxyacetylene shrinking torch, 8%; Diesel exhaust gases, 35%; dynamite fumes, 52%; fumes from combustion of cellulose nitrate, 19%; acid (concentrated nitric) dip fumes, 78%. 76 A
