OZONE CHEMISTRY AND TECHNOLOGY

School of Aviation Medicine, U.S. Air Force,. Department of Physiology-Biophysics, Randolph Air Force Base, Tex. Ozone is found at high altitudes in s...
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Toxicity of Ozone in High Altitude Flight H. G. C L A M A N N and R. W.

BANCROFT

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School of Aviation Medicine, U.S. Air Force, Department of Physiology-Biophysics, Randolph Air Force Base, Tex.

O z o n e is found at high altitudes in such concentration that, pressurized in a cabin to ground level or near ground level pressure, it could exhibit harmful effects on man and material. Protecting factors, such as heating in the compressor, decomposition in contact with various substances, a n d use of oxygen masks, lessen such harmful effects considerably. But the existence of such a hazard has to be known. Studies on the toxic effect of ozone on man indicate that such effect is restricted to the respiratory tract. Man seems to be more sensitive than the usual laboratory animals. In sensitive persons, concentrations as low as 2 p.p.m. may cause severe irritation within less than 1 hour.

T h e presence of ozone i n t h e a t m o s p h e r e , k n o w n since ozone w a s first d e t e c t e d a n d n a m e d b y S c h o e n b e i n i n 1840, h a s b e e n i n v e s t i g a t e d w i t h e v e r - i n c r e a s i n g i n t e r e s t . T h e d e v e l o p m e n t of s p e c i a l s p e c t r o p h o t o m e t e r s , c a r r i e d a l o f t b y b a l l o o n s a n d i n recent y e a r s b y r o c k e t s , h a s m a d e i t possible t o s t u d y n o t o n l y i t s t o t a l a m o u n t b u t also i t s v e r t i c a l d i s t r i b u t i o n i n t h e a t m o s p h e r e . C l a s s i c a l studies a r e those of G o e t z , M e e t h a m , a n d D o b s o n (8). I n the past t e n years measurements were c a r r i e d out b y Regener (IS), J o h n s o n , P u r c e l l , a n d T o u s e y (10), a n d P a e t z o l d (13), a m o n g o t h e r s . A s these a r e a l l b a s i c a l l y m e a s u r e m e n t s of u l t r a v i o l e t a b s o r p t i o n of l a y e r s of a c e r t a i n t h i c k n e s s , t h e ozone c o n c e n t r a t i o n is u s u a l l y expressed as t h i c k n e s s of a l a y e r of a i r — f o r e x a m p l e , c e n t i m e t e r s of ozone p e r k i l o m e t e r of a i r . U s u a l l y these v a l u e s a r e r e f e r r e d t o as u n d e r c o n d i t i o n s of s t a n d a r d p r e s s u r e a n d t e m p e r a t u r e . T o c o n v e r t these u n i t s i n t o u n i t s t h a t a r e m o r e m e a n i n g f u l t o t h e t o x i c o l o g i s t , s u c h as p a r t s p e r m i l l i o n b y v o l u m e , t h e y have t o be m u l t i p l i e d b y t h e proper density ratio, considering temperature a n d p r e s s u r e a t specific a l t i t u d e s . S u c h v a l u e s f o r v a r i o u s g e o g r a p h i c a l l a t i t u d e s a r e a v a i l a b l e i n t h e f o r m of t a b l e s (9). W h e n t h e v a l u e s f o r ozone f r o m t h e a b o v e - m e n t i o n e d s t u d i e s a r e a v e r a g e d , t h e ozone c o n c e n t r a t i o n is s m a l l e r t h a n 1 p . p . m . b e l o w 33,000 feet, reaches a p e a k of 6 p . p . m . a t 80,000 feet, a n d f a l l s b e l o w 1 p . p . m . a g a i n a b o v e 114,000 feet. B o t h t h e l o c a t i o n of t h e p e a k a n d t h e c o n c e n t r a t i o n a r e s u b j e c t t o c o n s i d e r a b l e fluctuation, so t h a t m u c h greater peak concentration m a y occur at various altitudes depending o n l a t i t u d e , season, a n d w e a t h e r c o n d i t i o n s . C o m m e r c i a l a i r p l a n e s b e g i n t o p r e s s u r i z e t h e i r c a b i n s a t a l t i t u d e s b e l o w 10,000 feet. A b o v e t h i s a l t i t u d e c a b i n s h a v e t o be p r e s s u r i z e d , i f t h e passengers do n o t use a d d i t i o n a l o x y g e n s u p p l y . W i t h o u t o x y g e n , a p r e s s u r e of a b o u t 10 p.s.i., c o r r e s p o n d i n g 352

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t o 10,000 feet of a l t i t u d e , has t o b e m a i n t a i n e d i n t h e c a b i n regardless of flying a l t i t u d e , to m a i n t a i n t o l e r a b l e r e s p i r a t o r y c o n d i t i o n s . B e c a u s e t h e c o m p r e s s o r n o t o n l y p r e s s u r i z e s b u t also v e n t i l a t e s t h e c a b i n , t h e r e is a l i m i t o n a l t i t u d e f o r t h e p r e s s u r i z e d c a b i n . A b o v e 80,000 feet a c o m p r e s s o r becomes i n e f f e c t i v e ; i t is n o t able t o m a i n t a i n p r e s s u r e a n d v e n t i l a t i o n a t t h e l o w d e n s i t y of t h e a t m o s p h e r e . A b o v e t h i s a l t i t u d e lies t h e r e a l m of t h e sealed c a b i n (17). W e d o n o t k n o w h o w m u c h ozone m a y a c t u a l l y b e p r e s e n t i n a p r e s s u r i z e d c a b i n of f u t u r e a i r c r a f t , as o t h e r f a c t o r s , s u c h as h e a t i n g of t h e a i r p a s s i n g t h e c o m p r e s s o r o r c o n t a c t w i t h v a r i o u s substances, m a y d e s t r o y p a r t o f t h e ozone a n d use of o x y g e n m a s k s w o u l d p r e v e n t i n h a l i n g of a m b i e n t a i r e n t i r e l y ; s t i l l , t h e p o s s i b i l i t y of i n h a l i n g ozone exists. T h e use of ozone as a r o c k e t o x i d i z e r (H) m a y a d d to such a possi­ bility. T h e second f a c t o r t h a t m u s t be k n o w n is t h e t o x i c i t y of ozone t o m a n a t g r o u n d l e v e l c o n d i t i o n s . F r o m s u c h v a l u e s t h e t o x i c i t y of ozone a t o t h e r t h a n g r o u n d l e v e l conditions c a n easily be derived. A l t h o u g h t h e t o x i c i t y of ozone t o a n i m a l s h a s been s t u d i e d r e l a t i v e l y o f t e n , s t u d i e s on h u m a n s are few. E x t e n d e d reviews of such t o x i c i t y studies have been compiled b y T h o r p (19) a n d S t o k i n g e r (16). T h o r p (20) also suggested t h a t t h e presence of n i t r o g e n oxides, w h i c h m a y be g e n e r a t e d i n c e r t a i n o z o n i z e r s , m a y a g g r a v a t e t h e t o x i c i t y of ozone. W h i l e s t u d i e s o n t h e influence of o t h e r gases o n t h e t o x i c i t y of ozone a r e m o s t i n t e r e s t i n g , t h e t o x i c i t y of p u r e ozone m u s t b e k n o w n first. N i t r o g e n oxides do n o t seem t o exist i n t h e a t m o s p h e r e w i t h ozone, b u t r a t h e r a r e p r e s e n t a t c o n s i d e r a b l y h i g h e r a l t i t u d e s i n t h e s o - c a l l e d D l a y e r (S). A s t h e r e is m u c h c o n f u s i o n i n t h e l i t e r a t u r e o n t h e a c t u a l t o x i c i t y of ozone, e x p e r i m e n t s o n a n i m a l s were c o n d u c t e d a t A r m o u r R e s e a r c h F o u n d a t i o n u n d e r c o n t r a c t w i t h S c h o o l of A v i a t i o n M e d i c i n e , U S A i r F o r c e . T h e r e s u l t s of these studies o n a c u t e a n d c h r o n i c e x p o s u r e t o ozone a r e r e p o r t e d here a n d b y M i t t l e r a n d c o ­ w o r k e r s (12). T h e r e s u l t s i n d i c a t e g r e a t differences i n t h e LD rate for various laboratory a n i m a l s . O n t h e basis of these r e s u l t s i t w a s d e c i d e d t h a t o n l y s t u d i e s o n m a n c o u l d p r o d u c e r e l i a b l e i n f o r m a t i o n o n t h e t o x i c i t y of ozone t o m a n . S u c h s t u d i e s were c o n d u c t e d b y t h e S c h o o l of A v i a t i o n M e d i c i n e , u t i l i z i n g t h e e x i s t i n g f a c i l i t i e s of A r m o u r Research Foundation. 50

Procedure a n d

Methods

A g r o u p of five subjects w a s selected, r a n g i n g i n age f r o m 19 t o 54 y e a r s . Chest x - r a y pictures a n d E C G recordings were t a k e n before a n d after t h e 2-week p e r i o d of e x p e r i m e n t s . B e f o r e a n d a f t e r t h e e x p o s u r e t o ozone, t h e f o l l o w i n g r e c o r d ­ ings were c a r r i e d o u t : Circulation. B l o o d pressure, pulse rate (pulse rate recorded also d u r i n g exposure at 15-minute i n t e r v a l s ) . Blood. R e d b l o o d cell count, h e m a t o c r i t , h e m o g l o b i n i n grams per 100 m l . of b l o o d , w h i t e cell count, differential count, t o t a l serum p r o t e i n . Respiration. R e s p i r a t i o n rate (recorded also d u r i n g exposure at 15-minute i n t e r v a l s ) . R e s p i r a t i o n f u n c t i o n a l test : t i d a l v o l u m e , v i t a l capacity, m a x i m a l b r e a t h i n g capacity, r e s i d ­ u a l capacity, a n d diffusion coefficient for oxygen ( D 0 ) expressed i n cubic centimeters of oxygen per m i n u t e p e r pressure of oxvgen at 1 m m . of m e r c u r y . Tests of Taste and Smell. Subjective Symptoms. 2

U s u a l c l i n i c a l l a b o r a t o r y m e t h o d s were u s e d f o r c i r c u l a t i o n a n d b l o o d . W i t h a n o r m a l s p i r o m e t e r f o r t h e d e t e r m i n a t i o n of t h e r e s i d u a l c a p a c i t y , t h e m e t h o d of F e n n , O t i s , a n d R a h n (6) w a s u s e d f o r r e s p i r a t i o n . N i t r o g e n c o n c e n t r a t i o n w a s d e t e r m i n e d w i t h the L i l l y - A n d e r s o n nitrogen meter, which was calibrated w i t h correction for d i s c h a r g e c u r r e n t , p r e s s u r e , a n d c a r b o n d i o x i d e ( 1 ).

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T h e p u l m o n a r y d i f f u s i o n coefficient w a s d e t e r m i n e d b y t h e c a r b o n m o n o x i d e m e t h o d of K r o g h (5, 11). D e v i a t i n g f r o m t h e o r i g i n a l m e t h o d , a m u c h s m a l l e r c o n c e n t r a t i o n of c a r b o n m o n o x i d e w a s u s e d , 0 . 0 0 4 % i n s t e a d of 1 . 0 % . T h i s m a d e i t possible, a f t e r f u r t h e r d i l u t i o n , t o d e t e r m i n e t h e c a r b o n m o n o x i d e c o n c e n t r a t i o n b y means of i n d i c a t o r tubes ( M i n e Safety A p p l i a n c e s C o . ) , t h e color of w h i c h was c o m p a r e d w i t h c a l i b r a t e d s t a n d a r d s (4,21). T a s t e w a s t e s t e d b y offering t h e s u b j e c t aqueous s o l u t i o n s of sucrose (2 t o 1 6 % i n steps of 2 . 0 % ) a n d s o d i u m c h l o r i d e (1 t o 4 % i n steps of 0 . 5 % ) , i n a n i r r e g u l a r p a t t e r n of c o n c e n t r a t i o n s , i n w h i c h t h e s u b j e c t h a d t o s a y i f t h e taste w a s t h e s a m e , s t r o n g e r , o r w e a k e r t h a n t h a t o f t h e s a m p l e offered before. F o r t e s t i n g t h e sense of s m e l l a t h r e s h o l d m e t h o d w a s a d o p t e d . T h r e e s o l u t i o n s were p r e p a r e d — A , B , a n d M . A l l t h r e e s o l u t i o n s h a d 7 0 % aqueous e t h y l a l c o h o l as c a r r i e r . A w a s a b l a n k ; Β c o n t a i n e d 0 . 0 2 % of a m y l acetate ( p l e a s a n t o d o r ) ; a n d M c o n t a i n e d t h e same a m o u n t of l a u r y l m e r c a p t a n ( u n p l e a s a n t o d o r ) . T h e s u b j e c t h a d t o d i s t i n g u i s h b e t w e e n t h e f a i n t s m e l l o f a l c o h o l a n d t h e a d d i t i o n a l s m e l l of t h e p l e a s a n t o r u n p l e a s a n t substances. T h e c o n c e n t r a t i o n s w e r e chosen so t h a t u n d e r n o r m a l c o n d i t i o n s a l l subjects m a d e n o t m o r e t h a n t w o e r r o r s i n 15 p r e s e n t a t i o n s . T h e s u b j e c t i v e s y m p t o m s w e r e a r b i t r a r i l y classified s o m e w h a t a l o n g t h e c l a s s i f i c a ­ t i o n of T h o r p (19) as s y m p t o m a t i c , i r r i t a n t , a n d severe i r r i t a n t . S y m p t o m s a r e n a m e d s y m p t o m a t i c w h e n t h e s u b j e c t experiences t h e first sensations, s u c h as i r r i t a t i o n of t h e t h r o a t a n d t i c k l i n g i n t h e nose. W h e n t h e s y m p t o m s b e c o m e p e r m a n e n t a n d u n p l e a s a n t , t h e y a r e n a m e d i r r i t a n t , as w e l l as w h e n o c c a s i o n a l c o u g h i n g i s o b s e r v e d . T h e s y m p t o m s a r e l a b e l e d severe i r r i t a n t w h e n c o u g h i n g is p r o d u c e d b y deep i n s p i r a ­ t i o n , p r e s s u r e o r p a i n i n t h e chest a p p e a r s , b r e a t h i n g becomes l a b o r i o u s a n d m o r e f r e q u e n t , a n d a c o n s t a n t s h a r p p a i n i n t h e t h r o a t is f e l t . F o r e x p o s u r e t o ozone, a s p e c i a l c h a m b e r , 4 feet w i d e , 7 feet h i g h , a n d 6 feet long, constructed b y A r m o u r Research F o u n d a t i o n , was used. U s u a l l y one, b u t s o m e t i m e s t w o , s u b j e c t s were p l a c e d s i m u l t a n e o u s l y i n t h i s c h a m b e r . A n e x h a u s t f a n p r o v i d e d a c o m p l e t e a i r change i n t h e c h a m b e r a b o u t once e v e r y m i n u t e , t h u s a v o i d i n g a n y a c c u m u l a t i o n of c a r b o n d i o x i d e a n d w a t e r v a p o r . C o n t r o l w i t h a thermometer a n d a n A s s m a n n psychrometer showed that average r o o m temperature a n d h u m i d i t y were n e v e r exceeded. T h e h i g h e s t ozone c o n c e n t r a t i o n a p p l i e d w a s 6 p . p . m . f o r 1 h o u r , a n d t h e longest e x p o s u r e t i m e w a s 2.5 h o u r s a t 1.2 p . p . m . T o d e t e r m i n e i n d i v i d u a l s e n s i t i v i t y , a l l subjects were first e x p o s e d t o a b o u t 1.2 p . p . m . f o r a m a x i m u m of 2.5 h o u r s . S u b j e c t s w h o e x h i b i t e d i r r i t a n t s y m p t o m s w e r e n o t a d m i t t e d t o h i g h e r c o n c e n t r a t i o n s b u t w e r e exposed r e p e a t e d l y t o a b o u t t h e s a m e concentration. U n l e s s s t a t e d o t h e r w i s e , c o n c e n t r a t i o n s of ozone a r e p r e s e n t e d i n p a r t s p e r m i l l i o n by volume. Results T h e findings o n a s m a l l g r o u p o f five p e o p l e d o n o t h a v e t h e c o n c l u s i v e significance of a s t a t i s t i c a l e v a l u a t i o n o f a l a r g e g r o u p . H o w e v e r , as e a c h s u b j e c t s e r v e d as i t s o w n c o n t r o l a n d a l l subjects were e x p o s e d r e p e a t e d l y , t h e r e s u l t s i n d i c a t e t h e g e n e r a l t e n d ­ encies of t h e p h y s i o l o g i c a l effects of ozone o n m a n . B e g i n n i n g w i t h t h e s u b j e c t i v e s y m p t o m s , t h e r e s u l t s a r e p r e s e n t e d i n F i g u r e 1. T h e s y m p t o m s a r e i n d i c a t e d as f o l l o w s : A n e m p t y figure m e a n s s y m p t o m a t i c ; a figure filled h a l f b l a c k m e a n s i r r i t a n t ; a n d a t o t a l l y b l a c k figure i n d i c a t e s severe i r r i t a n t . T h e s e figures a r e p l a c e d i n a d i a g r a m p l o t t i n g ozone c o n c e n t r a t i o n a g a i n s t e x p o s u r e t i m e i n a d o u b l e l o g a r i t h m i c calibration. T h e s u b d i v i s i o n of t h e d i a g r a m i n regions of v a r i o u s degrees of t o x i c i t y is t h a t u s e d b y T h o r p (19). I n general, the d a t a correspond to T h o r p ' s diagram. H o w e v e r , the measuring

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