My name is Edward B aier, Deputy D irecto r of the N ational I n s titu te fo r O ccupational S afety and H ealth (NIOSH). I welcome th is opportunity to appear here today to discuss the e ffe c ts of occupational exposure to s u lfu r dioxide upon human h e a lth , including the re s u lts of recen t NIOSH sponsored stu d ie s. With me today a re : Dr. V ictor Archer, D ivision of S u rv eillan ce, Hazard. E valuations and F ield S tu dies; Dr. Kenneth B ndbord, O ffice of Extram ural C oordination and S pecial P ro je c ts; Dr. David Groth, D ivision of Biomedical and B ehavioral Sciences; D r. Douglas Smith, D ivision of C rite ria Documentation and Standards Development; William Wagner, Environmental In v estig a tio n s Branch; P a tric ia Gussey, T esting and C e rtific a tio n Branch; and Dr. Jan et H aartz, D ivision of P hysical Sciences and Engineering.
Records of worker com plaints of th e i r r i t a n t e ffe c ts of su lfu r dioxide (SO2 ) date from 1821. SO2 is an i r r i t a n t gas which has wide in d u s tria l use. I t is commonly tra n sp o rte d and stored as a liq u id under pressu re but is a gas a t atm ospheric p ressu re and room tem perature. Exposures of less than an hour to SO2 at le v e ls above ten p a rts per m illio n p a rts of a ir (10 ppm or 26 mg/m3) are i r r i t a t i n g to the nose and th ro a t, sometimes causing a choking sen sation followed by nasal discharge, sneezing, cough and increased mucus se c re tio n . Acute e ffe c ts have been thoroughly studied in both man and anim als. The NIOSH C rite ria Document has noted th a t some acute exposures have re su lte d in d eath , and oth ers have been follow ed by chronic d ise a se , such as chronic b ro n c h itis, emphysema, and shortness of b reath . S tudies rep orted in the l a s t th ree years have shown some chronic e ffe c ts such as chronic b ro n c h itis and lo ss of pulmonary fu n ctio n a t chronic exposures below the cu rren t Federal occupational standard of 5 ppm (13 mg/m3) as a tim e weighted average (TWA) co n cen tratio n . I t has been estim ated by the Department of Labor th a t approxim ately 600,000 American workers may be occupationally exposed to SO2 . Some of the h ig h est exposures occur when i t is a by-product, as in th e m etal sm elting in d u stry , and m the processing or combustion of high s u lfu r coal or o i l . Other exposures occur in m anufacture of s u lfu ric a c id , fum igating, food p re se rv a tio n , wine making and bleaching of many substances.
Im portant chronic re s p ira to ry d iseases are emphysema, chronic b ro n ch itis and pulmonary f ib r o s is . These are im portant causes of d is a b ility and death in th e U nited S ta te s . These lung d iseases cause over 14,000 d is a b ility retirem en ts of persons under age 65 each y ear. They d ire c tly cause 30,000 deaths each year and c o n trib u te to an a d d itio n a l 32,000 deaths each year. The q u a lity of l i f e is markedly reduced fo r many thousands of persons by shortness of breath asso ciated with chronic re sp ira to ry d isease. Because of the magnitude of the problem of chronic re sp ira to ry d ise a se , a small percentage increase re s u ltin g from SO2 exposure may have a profound e ffe c t on the to ta l number of people being a ffe c te d .
O ccupational exposure to s u lfu r dioxide was high on the o rig in a l NIOSH p rio r ity l i s t . A c r i te r i a document on SO2 was tran sm itted to the O ccupational S afety and H ealth A dm inistration (OSHA) on February 11, 1974. This document recommended, among o th er th in g s, th at the Federal environm ental lim it fo r occupational exposure to SO2 be se t at 2 ppm (5.2 mg/m3) as a TWA exposure fo r a 40 hour work week, w ith d aily exposures up to 10 h ou rs. This proposed standard was based on inform ation a v a ila b le at th a t tim e. The standard then was 5 ppm (13 mg/m3). Because of recent d a ta , NIOSH now b eliev es th a t Che standard of 2 ppm (5.2 mg/m3) recommended in 1974 would not provide adequate p ro te c tio n fo r the h e a lth of workers.
Chronic re sp ira to ry d isease asso ciated w ith SO2 exposure has been rep o rted m sev eral d iffe re n t epidem iological stu d ie s. Most of them have had severe lim ita tio n s fo r use in standard s e ttin g , however. In s p ite of the problems encountered in epidem iologic stu d ies of SO2 e ffe c ts , NIOSH is convinced th a t a l l a v a ila b le stu d ies must be used to provide data fo r standard s e ttin g . F ortu nately , the design and techniques used in epidem iology stu d ies are improving.
In the la s t th ree y e a rs , four epidem iological stu d ie s have been rep orted which used b e tte r techniques and rep o rted a c tu a l personnel exposures. The NIOSH study of Archer and Gillam was a c ro ss-s e c tio n a l study of 903 workers in which s t a t i s t i c a l l y s ig n ific a n t reductions in FVC and FEV^ were found as w ell as an in crease in symptoms of re sp ira to ry d isease which c o rre la te d w ell w ith days o ff fo r ill n e s s . The e ffe c ts of SO2 were seen m both smokers and non-sm okers. When workers smoked and were exposed to S02> the e ffe c ts of th e two agents were d ire c tly a d d itiv e . Among sm elter workers 18% compared to 6% of co n tro ls rep orted a sen sation of chest tig h tn e ss on th e ir f i r s t day back on the job a f te r sev eral days o ff. "A concom itant environm ental study by Smith, Wagner, e t a l . provided evidence th a t TWA exposures had been in the range of 0.4 to 4 ppm (1-10 mg/m3 ) w ith a mean of about 2 ppm fo r many y ears. S u lfa te , manganese and to ta l dust were approxim ately the same in th e breathing zones of workers used as c o n tro ls . Of these substances, only the su lfa te was considered s u ffic ie n tly abundant to have an e ffe c t on pulmonary fu n ctio n . C oncentrations of the o th er contam inants were much below th a t which is known to have any p h y sio lo g ical e ffe c t, with th e p o ssib le exception of a rse n ic , a carginogen. Although the s u lfa te might have had some e ffe c t on pulmonary fu n ctio n , i t was not considered to have influenced th e sig n ifican ce of the study conclusions, because the co n tro ls m th is study were exposed to an average of 0.09 mg/m3 (a s lig h tly higher le v e l).
The second re p o rt was th e NIOSH sponsored study of Smith, P e te rs, et a l. in a lo n g itu d in a l in v e stig a tio n of 113 workers using personal SO2 dosim eters. They found a s t a t i s t i c a l l y sig n ific a n t in crease in the annual FEVj_ and FVC mean decrements among workers whose SO2 TWA exposures were between 1 and 4 ppm (2 .6 -10 mg/m3) -when compared to those whose mean exposure was le s s than I ppm (2.6 mg/m3). From an an aly sis of v arian ce, using cross ta b u la tio n s of FEV^ decrem ents, re sp ira b le dust and SO2 exposures, i t was found th a t th e increased annual decrement was asso ciated only w ith SO2 , not w ith the d u st. This ind icated th a t copper, s u lfa te s , s u lf ite s and other elements in th e dust -were not involved in the increased decrement. A comparison of FEVjl values between p re -s h ift and p o s t-s h ift te s ts on th e sm elter workers found th a t 30% had a d eclin e of 100 ml or more. This suggests th a t 30% of workers may have had an acute re a c tio n to SO2 at about the 2 ppm (7.2 mg/m3 ) TWA range encountered m the sm elter.
The th ird epidem iological study by the M inistry of H ealth in Toronto, Canada in 1974, rep o rted s t a t i s t i c a l l y s ig n ific a n t in creases in re sp ira to ry disease and decreases in FVC and FEV^ among copper sm elter workers exposed fo r ten years or more. Average exposure to SO2 was reported as 2.5 ppm (6.5 mg/m^). Smoking was c o n tro lle d in the a n a ly s is. However, possible pulmonary e ffe c ts co n trib u ted by other a ir contam inants could not be ruled o ut.
The fo u rth study was done in the B ritish s te e l in d u stry by Lowe, et a l. Approximately 10,000 workers were studied fo r chronic e ffe c ts . Mean exposures to SO2 were about 0.35 ppm (0.9 mg/m^). No d e fin ite e ffe c ts were found at th is le v e l.
In ad d itio n to in v e stig a tio n s on w orkers, epidem iological stu d ies have also in d icated chronic re s p ira to ry disease in th e g en eral population to be asso ciated w ith SO2 . This includes both asthm atic a tta c k s and chronic b ro n c h itis. Decreases in pulmonary fu n ctio n were asso ciated w ith oxidant p o llu ta n ts (e .g ., ozone), reducing p o llu ta n ts ( e .g ., SO2 ) and w ith elevated tem peratures. Lawther, Brooks, et a l. Although substances o th er than S02f such as n itro g en oxides and su lfa te s undoubtedly have had some influence on th e re s p ira to ry e ffe c ts of polluted c ity a i r in these s tu d ie s , the fact" th a t SO2 has been pin-pointed as an im portant fa c to r by m u ltip le c o rre la tio n techniques in a number of d iffe re n t stu d ie s is in d ic a tiv e th a t 24 hour continuous exposure to SO2 at TWA lev e ls below 0.5 ppm (1.3 mg/m^) are probably in ju rio u s to the h ea lth of some in d iv id u a ls in the community.
Many experim ental stu d ie s have been performed on humans to in v e stig a te the acute e ffe c ts of SO2 . Since tra n s ie n t pulmonary changes re su ltin g from sh o rt-term SO2 exposures may be re la te d to chronic re s p ira to ry d isease, those rep o rted in th e l a s t th ree years w ill be review ed. Lawther, MacFarlane, e t a l . te ste d 25 h ealth y a d u lts and found increased airway resistan ce (determ ined in a body plethysmograph) at 5 ppm (13 mg/m^) 0f SO2 and a t hig h er le v e ls when b reathing normally fo r 10 m inutes, but not at lower le v e ls . A fter 25 deep b re a th s, as might occur in lab o rers doing hard physical work, th e su b jects had a s t a t i s t i c a l l y s ig n ific a n t in crease in airway re sista n c e at 1 ppm and a f te r 8 deep breaths a t 3 ppm. Andersen, et a l. rep o rted reduced n asal mucus flow ra te s in 15 young men a f te r inhaling 5 ppm (13 mg/m3) 5 0 2 fo r 6 h o u rs. Increased n asal c ro ss-s e c tio n a l area and reduced FEV^ were noted a t 1 and 5 ppm SO2 a f te r 6 hour exposures. W olff, e t a l . found that a f te r b reath in g 5 ppm (13 mg/m^) SO2 nine healthy non-smoking ad u lts had a red u ctio n in trach eo b ro n ch ial clearance at one hour (p = .05) follow ed by a retu rn to normal a t 3 hours and a reduction in the maximal m id-expiratory flow ra te (MMFR) (P -.01) a t th ree hours. In e a rlie r human experim ents, some research ers reported tra n s ie n t changes m pulmonary fu n ction between 0.5 and 5 ppm (1.3-13 mg/m3) of Sq 2 whereas o th er workers fa ile d to find any changes at those le v e ls . When su b jects breathed through the mouth g re a te r e ffe c ts were noted.
Experim ental animal stu d ie s reported m the la s t 3 years have extended our knowledge of the b io lo g ic a l e ffe c ts of SC>2 - H irsch, et a l, using 8 dogs exposed fo r 12 months at 1 ppm of SO2  measured Teflon disk movement in bronchi by means of bronchofiberscope, and found s t a t i s t i c a l l y sig n ific a n t slowing of mucus tra n s p o rt. Ferin and Leach using a titanium oxide dust technique, found a s lig h tly increased clearance ra te when 0.1 ppm (.3 mg/m^) SO2 was adm inistered to r a ts fo r 10 and 23 days, but a d e fin ite ly decreased clearance ra te w ith 1 ppm (2.6 mg/m^). Increased airway re sista n c e was noted m guinea pigs by M cJilton and Frank when th e anim als were exposed at 1 ppm (2.6 mg/m^) SO2 in the presence of high hum idity and a fin e sodium c h lo rid e aero so l.
S ulfur dioxide is known to in te ra c t w ith commonly occurring substances in the atmosphere such as w ater vapor and fin e p a rtic u la te s . Some of these in te ra c tio n s are chemical and oth ers a re physical in th a t they perm it a h ig h er percentage of SO2 to reach the low er p a rts of the lung.
At re la tiv e ly high le v e ls of acute or chronic exposure to SO2 , a number of p ath o lo g ic al changes have been observed in anim als. Chakrin and Saunders noted an increase in goblet c e lls near the ends of bronchi and b ro nch io les, and h y p erp lasia of b ronchial glands, w ith an excess of mucopurulent exudate in dogs. The anim als had been exposed to 500-600 ppm (1300-1560 mg/rn^) fo r two-hour periods tw ice weekly fo r 4 to 5 months. In th e data re fe rre d to above, i t i s apparent th a t both acute and chronic e ffe c ts of SO2 in man a re observable in the I to 5 ppm (2.6-13 mg/m^) range. The appearance of both types of e ffe c ts a t approxim ately the same le v e ls is not lik e ly to be coincidence. Indeed, acute e ffe c ts in workers exposed to MDI and TDI (iso cyan ates used in making polyurethane foam) have been found to be followed by chronic e ffe c ts (chronic b ro n c h itis, e tc .) sim ila r to th a t observed fo r SO2  The mechanisms fo r th is twin e ffe c t are not c le a r. Perhaps th e tra n s ie n t acute e ffe c t is merely an observable symptom of more permanent damage, or perhaps frequent bro nch oco nstrictio n im pairs the se lf-c le a n sin g a b ility of lungs so th a t in fe c tio n s re s u ltin g in chronic b ro n c h itis are more lik e ly .
The delayed p a r tic le clearance tim es which have been observed a t low le v e ls of SO2 exposure also in d ic a te an impairment of the lungs to cleanse them selves. This e ffe c t is more prominent with prolonged exposure to low con centratio ns than fo r sh o rt exposures to high concentrations as indicated by the work of Ferin and Leach. The lin k s between acute and chronic e ffe c ts argue th a t chronic e ffe c ts are ju s t as lik e ly to be due to chronic low lev e l exposures as to in te rm itte n t peak exposures.
In considering an app ro p riate le v e l fo r an SO2 occupational standard, we must add to our co n sid eratio n th a t h e a lth e ffe c ts have been observed among workers and experim ental su b jects in the 1-2 ppm range, the fa c t th a t 10 to 20% of persons a re e sp ec ially su sc e p tib le to SO2 e f f e c ts , the p o s s ib ility th a t sy n e rg istic e ffe c ts w ith other aerosols or gases may occur, the p o s s ib ility of increased fra c tio n s of SO2 reaching the lower lungs through mouth b reathing or because of rap id or deep b reath in g , th e p o s s ib ility th a t SO2 may act as a cancer promoting agent, the p ossib le enhancement of e ffe c ts by high hum idity, and the lik e lih o o d th a t degradation products (SO2 ). s u lf ite s and s u lfa te s ) w ill accompany SC^. A fter considering a l l these fa c to rs , NIOSH recommends th a t the SO 9 occupational exposure lim it be a time weighted average of 0.5 ppm (1.3 mg/m' ) fo r up to a 10-hour workday, 40-hour workweek. I t is a n tic ip a te d th a t adherence to th is lim it w ill confine excursions to about 2 or 3 ppm (3 .2 -7 .8 mg/m^).
Preplacem ent and annual medical exam inations should be done whenever TWA exposures exceed 0.25 ppm (0.65 mg/m^). These exam inations should be d irec te d toward com plaints of mucus membrane i r r i t a t i o n , cough and shortness of b re ath . They should a sc e rta in th a t n asal passages are open. Persons w ith a h is to ry of asthma or w ith subnormal pulmonary fu n ction should be watched clo se ly . Simple ex p ira to ry fu n ction te s ts should be a p a rt of the exam ination. They are u sefu l fo r several purposes: (a) determ ining whether or not a person is a su ita b le candidate fo r using re s p ira to rs ; (b) id e n tify in g " re a c to rs ," , i . e . , persons who may be most su scep tib le to th e e ffe c ts of S02- This can be done by comparing p re s h ift and p o s ts h ift te s ts ; (c) when done p e rio d ic a lly , they can be used to determ ine whether or not a p erso n 's ex p irato ry fu n ction s a re d eclin in g a t a f a s te r than normal r a te . Such determ inations a re much more se n sitiv e when pooled d ata from a number of in d iv id u als are used. The forced ex p ira to ry volume a t 1 second and the maximum m id-expiratory flow ra te appear to be the most u se fu l of the simple pulmonary fu n ctio n t e s t s .
NIOSH is in agreement w ith the OSHA proposals fo r employee inform ation, tra in in g and record keeping, w ith Lhe exception th a t medical records should be m aintained a t le a s t 30 years a f te r an in d iv id u a l's employment ^ends. Medical re p re se n ta tiv e s of th e Department of Labor and of the Department o f H ealth, Education and W elfare, of the employer, and of the employee or former employee s h a ll have access to th e medical re c o rd s.
NIOSH is also in agreement w ith the OSHA proposals w ith resp ect to the e ffe c ts of overtim e on exposure, dermal and eye contact w ith liq u id S0 2  determ ination and measurement of exposure and methods of com pliance. NIOSH is in f u l l agreement w ith OSHA th a t prim ary relian ce fo r co n tro l should be on engineering and work p ra c tic e s . When temporary situ a tio n s occur fo r which c o n tro ls are inadequate, such as maintenance or process changes, re sp ira to rs may be used. When re s p ira to rs a re used, they must be f itte d p ro perly , and an ap p ro p riate maintenance program fo r them should be conducted. In the p ast, i t has been a general p ra c tic e fo r workers to put on re s p ira to rs only when they encountered, or expected to encounter, le v e ls of SO2 which would be i r r i t a t i n g to th e eyes, nose and th ro a t. This p ra c tic e should be discouraged, as th ere is evidence th at chronic lung in ju ry occurs at le v e ls below those which cause marked mucus membrane i r r i t a t i o n . NIOSH recommendations on re sp ira to rs to be used a t various SC>2 con centrations is subm itted fo r the record.
NIOSH agrees w ith the OSHA proposal on the hydrogen peroxide method of measuring S02 However, one change m the d esc rip tio n is recommended fo r c la r if ic a tio n in item (j) of the A naly tical sectio n in Appendix D. This c la rifie d the sta n d a rd iz a tio n of barium p erch lo rate so lu tio n , w ith isopropanol, su lfu ric acid so lu tio n and endpoint t itr a tio n with Thorin as the in d ic a to r.
Since no in d u stry has tr ie d to co n tro l SO2 concentrations to lev e ls as low as 0.5 ppm (1.3 mg/m^) th ere is no docum entation as to i t s tech n ical f e a s ib ility .
Before clo sin g , I would lik e to l i s t the backup m aterial subm itted fo r the reco rd .