Layout of file containing H2SO4 data 336 lines: 28 ss x 3 days x 4 times per day Each line contains, in order, ... Smoker 0 = Nonsmoker 1 = Smoker PtNo 1 - 14 within each smoker category Day 1 2 3 Hour 0 2 4 6 SGAW FRC FVC Forced Vital Capacity (liters) FEV1 Forced Expiratory Volume in 1 sec (liters) FEV3 Forced Expiratory Volume in 3 sec (liters) PHASEIII PHASEIV CLSTAT CLDYN48 RL data values are separated by spaces The last variables above were measured only once per day; the values are in the line corresponding to HOUR = 4, and the entries for hours 0, 2 an 6 are set to missing (.). ---------------------------- EFFECTS OF SULFURIC ACID AEROSOL ON PULMONARY FUNCTION IN HUMAN SUBJECTS: AN ENVIRONMENTAL CHAMBER STUDY * H D Kerr, T J Kulle, B P Farrell, L R Sauder J L Young, D L Swift and R M Borushok Environmental Research 26, 42-50 1981. Measurements of pulmonary function were obtained 2 hr into the exposure. immediately follo~ing exposure. and 2 and 24 hr postexposure. These measurements were compared with control values obtained at comparable hours on the previous day when the subjects breathed only filtered clean air in Ihe chamber. No significant dif~erences in pulmonary f~lnction were observed either during the exposure, immediately after exposure, or ' and 24 hr postexposure. INTRODUCTION Sulfuric acid (H2SO4) aerosol is an air pollutant formed from oxidation of atmospheric sulfur dioxide, with subsequent hydration. A more recent source of H2SO4 is the automobile catalytic converter. Sulfuric acid is a more toxic pollutant than SO2, and has been suggested as one of the irritants contributing to to the excess mortality and morbidity resulting from the London smog of 1962, where excessively high levels were presumed to occur (Lawther, 1963). In 1976, it was estimated that the peak U.S. urban atmospheric burden of H2SO4 was 20 micrograms/cubic meter,; however, it is anticipated that with increased use of high-sulfur fuel, and more widespread use of catalytic converter-equipped automobiles, the level could rise three- or fourfold. Animal studies (Amdur, 1958; Alarie et al., 1973, 1975) have revealed adverse pulmonary function effects to extremely high levels of H2S04 aerosol (> 2000 ug/m3). Amdur et al. (1952) reported adverse effects (decreased flow rates) in human subjects exposed by face mask to high concentrations of H2SO4 mist (350-500 ,ug/m3 of l-um particle size for 5-15 min). Sim and Pattle (1957) reported symptoms of respiratory tract irritation and increased airway resistance in human subjects exposed to high concentrations of H2SO4 acid mist (>3000 ,ug/m3 of l-um particle size for 10 min) in high humidity (90% RH). More recently, Avol et al. (1979) reported no effects on pulmonary function following exposure to lOO ug/m3 H2SO4 for 2 hr, and Sackner et al. (1978) found no effects following exposure of normal and asthmatic humans to 100 and 1000 um/m3 for 10 min. Utell et al. (1979) did find significant changes in flow rates and increased bronchial reactivity, following exposure to 1000 ug/m3 H2SO4 aerosol for 16 min. The purpose of this investigation was to determine if exposure of human subjects to levels of H2SO4 aerosol anticipated in the near future, in a realistic time frame, would have an adverse effect upon respiratory function. M A T E R I A L S A N D M E T H O D S Environmental Chamber This study was conducted in an environmentally controlled chamber permitting restriction of environmental effects to sulfuric acid. The chamber was designed so that air entering passed through high-efficiency particulate absolute (HEPA) filters and activated carbon filters, permitting cleanliness approaching class 100 (< 100 particles > 0.5,um/ft3 or 3534 particles > 0.5 um/m3). All air was exhausted to the outside, and no recirculation was permitted. The ventilation rate of 8.49 m3/min (300 ft3/min) in the 22.2-m3 (784 ft3) chamber enabled a complete change of air every 2.6 min. Temperature was maintained at 22.2 +/- 0.5C (72 +/- 1F) and relative humidity at 60 +/- 2%. A more detailed description of the environmental chamber was Dresented in a previous publication (Kerr, 1973). Aerosol Generation and Monitoring Aerosol was generated by the reaction of SO3 gas with water vapor similar to the method described by Scaringelli and Rehme (1969).Compressed cylinder air was dried by a molecular sieve column and passed through a glass-fiber filter to take out particulate matter. The air was then split, one airstream passing through temperature-controlled Erlenmeyer flask containing 250 ml of approximately 20% fuming sulfuric acid. This SO3-laden air was diluted by the second air stream and brought to the room's air inlet diffuser where rapid mixing occurred. The SO reacted with the room's water vapor immediately to form a submicronic aerosol Teflon tubing (0.48-cm i.d., 0.64-cm o.d.) and Type 316 stainless-steel Swagelok fittings were used throughout the system. The mass concentration of the acid in the room was adjusted by flow control valves and rotameters; flow through the system was approximately 500 cc/min (refer to Fig. 1). Aerosol samples were collected onto 47-mm-diameter Fluoropore filters having l-um pore size (Millipore Corp., Bedford, Mass.) held in a Millipore stainless steel filter holder. Each filter was flow calibrated before use. The volume of air sampled was at least 1 m3 and the amount of aerosol collected was 100 ug or more. Sampling was done every hour. After sampling, the filter was placed in a beaker containing 30 ml of distilled water, facedown. The beaker was covered with Parafilm M (American Can Co., Greenwich. Conn.) and sonified for 8 min in an ultrasonic cleaner (Mettler Electronic Corp., Anaheim, Calif.) to extract the collected acid. After extraction, the sample was analyzed twice in 10-ml aliquots for total soluble sulfate by titrating with 0.005 M barium perchlorate in an 80% isopropanol solution, using thorin as the endpoint indicator (NIOSH, 1974). The average of the two determinations was taken. Knowing the amount of sulfate (SO42-) collected and the volume of air sampled, the mass concentration of the acid in the room could be determined. Reference filter strips supplied by the EPA Quality Assurance Laboratory were analyzed using this method and good correlation was noted with EPA data. Instrumental Methods For each instrument, the signal output is an indication of the amount of aerosol present. However, because of difference in design, method of detection, and sensitivity to particle size and shape, the instruments were calibrated by comparing the instrument readouts with results from the wet chemical analysis of filter samples collected concurrently. (a) Meloy SA-285 Total Sulfur Analyser (Meloy Labs Ine., Springfield, Va.). The Meloy Analyser was a modified unit in which the aerosol goes directly from the inlet port to the flame photometric detection (FPD) burner block bypassing the solenoid valves. The unit was factory calibrated using sulfur dioxide gas. We have used the unit to give us information of the consistency of the mass concentration of the sulfuric acid aerosol in the environmental chamber. Calibration was by wet chemical sulfate analysis of filter samples. A preliminary study by Cobourn et al. (1978) had indicated little particle size dependence of the Meloy FPD in the size range 0.1-1.0 um, which formed the bulk of the aerosol generated in our chamber. (b) Electrical Aerosol Analyser (EAAÑThermo-Systems Inc., St. Paul, Minn. ). The EAA was used to provide data on particle size distribution and mass concentration of the H2SO4 aerosol. The instrument detects particles in the size range from 0.0042 through 0.75 um in diameter. Knowing the volume distribution and the particle density, a mass distribution can also be obtained. In the environmental chamber, where the relative humidity was maintained at 60% and temperature at 22.2C, the particle density was 1.3 g/cm3 or 0.38 g H2SO4/g solution. The H2SO4 aerosol in the chamber had a mass median diameter (MMD) of 0.14 um and a geometric standard deviation (ag) of about 2.9. The variability of the aerosol mass concentration was 98 +/- 9 ug/m3, and was within lO% of the mean value. Subjects The 28 subjects (14 smokers and 14 nonsmokers) selected for the investigation had no history of chronic respiratory or cardiovascular disease, and had normal findings on physical examination. They ranged in age from 18 to 45 years with a mean age of 24 years (Table 1). There were 19 males and 9 females, of which the nonsmokers included 8 males and 6 females. The subjects were studied singly or in pairs, and each served as his or her own control. The smokers were asked to refrain from smoking on the morning of the study, and were not permitted to smoke during the study. Chamber Procedure The studies were carried out on 3 consecutive days, at the same time each day. During the first and third days the subjects breathed only filtered clean air for a 6-hr period; on the second day, they breathed sulfuric acid aerosol at a concentration of 100 ug/m3 for 4 hr, and filtered clean air for an additional 2 hr. The second day was always the exposure day but the subjects did not know on which day they would be exposed. On each day pulmonary function tests, FVC, FEV1, FEV3, FRC, Raw, and SBNER, were performed immediately prior to exposure, and at 2-hr intervals thereafter. At 4 hr, quasistatic and dynamic compliance and pulmonary resistance were also measured. At 1 and 3 hr into the study on each day, bicycle ergometer exercise was TABLE 1: ANTHROPOMETRIC DATA FOR 14 SMOKERS AND 14 NONSMOKERS Smokers Nonsmokers Mean age (years) 24 24 Age range (years) 19-38 18-45 Mean height (cm) 175 175 Height range (cm) 152-185 160-183 Male 11 8 Female 3 6 performed at a work load at 100 W at 60 rpm for 15 min. The exercise was performed to morc closely simululate normal activity of urban dwellers, who would be expectcd to engage in some cxercise during thc course of the day. Physiological Tests Pulmonary function studies were timed so that measurements were made prior to exposure, 2 hr into exposure, immediately postcxposure, and 2 and 24 hr postexposure. These measurements were comparcd with the control day during which the subjects breathed only filtered clean air. Pulmonary resistance and compliance measurements were made only once a day to minimize subject discomfort. To ensure technically satisfactory subject performance, the subjects repeatedly executed each test in practice sessions before the study, except those involving the esophageal balloon. The forced vital capacity (FVC) was performed using a waterseal direct-writing spirometer. All volumes were expressed in liters adjusted to body temperature, pressure, saturated (BTPS). Airway resistance (Raw) and volume of thoracic gas (VTG) were measured by the whole-body pressure plethysmographic technique of DuBois and associates (1956) with some modifications (Kerr, 1973). The Raw was converted to specific airway conductance (SGaw = I/Raw/VTG). SGaw was expressed as l/cm H20 x second units. Tests of N2 elimination rate (SBNER) were calculated from an XY plot of expired N2 concentration versus expired volume from TLC to RV, after a full inspiration of lOO% O2 from RV to TLC. The rate of expiration was controlled so as not to exceed 0.5 liter/sec. Phase III was expressed as change in percentage of alveolar N2 concentration per liter per liter of expired volume, and was determined from the best-fit straight line of the alveolar sample midportion of the XY plot. Phase IV (closing volume) was measured from RV to the phase III junction with phase IV (Anthonisen, 1972). One reader performed all of the line-fitting procedures. Pulmonary resistance (RL) and compliance (CL) were determined by the electronic subtractor method of Mead and Whittenberger (1953). Dynamic compliance was performed at frequencies of 16 (CL dyn 16), 32, and 48 breaths/min in rhythm with an audio metronome while maintaining a tidal volume of 1 liter for 8 to 10 breaths at each breathing frequency. To stabilize volume history, each subject fully inflated his or her lungs to TLC before performing the quasistatic and dynamic compliance maneuvers. To determine CL dyn, a portion of the transpulmonary pressure proportional to airflow was substracted by manual potentiometer adjustment for the best- fit straight line XY oscilloscope display of this resultant pressure versus tidal volume. For RL, a portion of transpulmonary pres sure proportional to volume change was subtracted in a similar fashion, with straight line fitting of the XY plot of this pressure versus airflow. All subtractions and readings were performed on playback of analog tape recordings of airflow, volume change, and transpulmonary pressure. This procedure enabled rereading of the recordings to verify values and also to standardize the length of time each subject performed at the various breathing frequencies, thereby avoiding excessive alveolar ventilation from prolonged measurement. Pulmonary resistance was expressed as centimeters of H20 per liter per second, and was not corrected for the VTG at which it was measured. All compliance data were expressed as liters per centimeter of H20. Data Analysis Quasistatic compliance, dynamic compliance, and total pulmonary resistance for the group of 28 subjects were examined by the Student t test for paired observations. The postexposure measurements were each compared with control values. This type of analysis was suitable because these measurements were performed only once each day. The remaining physiological data were examined by analysis of variance for factorial design. This statistical parameter was employed because it was necessary to consider day-hour interaction. These data were also subjected to orthogonal polynominal analysis to determine if there were any significant trends. * This study was supported by Environmental Protection Agency Grant 803804-01.