Acute Exposure Guideline Levels for Selected Airborne Chemicals Volume 8 (2010) / Chapter Skim
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9 Sulfur Dioxide
9 Sulfur Dioxide
Pages 393-448
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From page 393... ...
Both the document and the AEGL values were then reviewed by the National Research Council (NRC) Committee on Acute Exposure Guideline Levels.
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From page 394... ...
Although the AEGL values represent threshold levels for the general public, including susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses, it is recognized that individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL. SUMMARY Sulfur dioxide is a colorless gas at ambient temperature and pressure.
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From page 395... ...
Exposure to concentrations at the level of derived AEGL-1 values is expected to have no effect in healthy individuals, but the concentrations are consistent with the definition of AEGL-1 for asthmatic individuals. AEGL-2 values were based on the weight-of-evidence from human asthmatic data suggesting that 0.75 ppm induces moderate respiratory response in exercising asthmatics for exposure durations of 10-min to 3-h (Hackney et al.
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From page 396... ...
. Sulfur dioxide is produced by burning sulfur or iron pyrites in air and is used in the production of sodium sulfite, sulfuric acid, sulfuryl chloride, thionyl chloride, organic sulfonates, disinfectants, fumigants, glass, wine, industrial and edible protein, and vapor pressure thermo-meters.
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From page 397... ...
AEGL-1 0.20 0.20 0.20 0.20 0.20 NOEL for (Nondisabling) ppm ppm ppm ppm ppm bronchoconstriction in (0.52 (0.52 (0.52 (0.52 (0.52 exercising asthmatics mg/m3)
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From page 398... ...
The eyes had severe conjunctivitis and superficial corneal burns and the pharyngeal mucosa was hyperemic but free of ulcerations. Pulmonary function tests performed at regular intervals showed that one survivor was asymptomatic, one survivor developed asymptomatic mild obstructive and restrictive disease, and the third survivor developed symptomatic severe airway obstruction unresponsive to bronchodialators.
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The lung function of the survivors was followed for 4 years. The largest decreases in forced vital capacity (FVC)
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Occupational Exposure Lung function and sputum cytology were compared between copper smelter workers chronically exposed to 0.3 to 4 ppm SO2 and a control group of mine repair shop workers (Archer et al.
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2.2.2. Community Exposure: Ambient Air Pollution Many studies concerning the relationship between SO2 exposure in polluted air and human health have been conducted; however, these studies are confounded by the presence of particulate matter and other air pollutants.
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Since it would not be feasible to include all available human SO2 data, the studies summarized below are considered sufficient to be quantitatively representative of data describing effects from acute exposure to SO2. Selected data from controlled exposures to SO2 in non-asthmatic individuals are presented in Table 9-3 and data from asthmatic individuals are presented in Table 9-4.
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From page 403... ...
1989c 5.0 ppm activity. Concentration-related up to 8 8.0 ppm ppm, no further increase at 1 ppm 11.0 ppm 1.0 ppm 4h 20 22.2 ºC, 60% RH, exercise No effects on lung function parameters.
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From page 404... ...
1964 Resting; exposures to SO2 4-6 ppm alone or in combination with ↑ Pulmonary flow resistance 14-17 ppm 18 mg/m3 NaCl ↑ Pulmonary flow resistance 15 ppm 10 min 11 Compared nose breathing vs ↑ Pulmonary flow resistance Frank et al. 1964 29 ppm mouth breathing 15 ppm: 3% Nose; 20% mouth 29 ppm: 18% Nose; 65% mouth 0.55 ppm 10 min 11 No nasal or eye irritation Dautrebrande and Capps 1950 1 ppm 6h 15 Resting No effects Andersen et al.
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From page 405... ...
TABLE 9-4 Selected Data from Exposure of Asthmatic Humans to Sulfur Dioxide Concentration Duration Subjects Exposure Parameters Effect Reference 0.2 ppm 5 min 8 23 ºC, 85% RH, exercise 48 L/min None Linn et al. 1983b 0.25 ppm 10-40 min 10 23 ºC, 70% RH, exercise 35 L/min None Schacter et al.
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TABLE 9-4 Continued 406 Concentration Duration Subjects Exposure Parameters Effect Reference 0.5 ppm 50 min 10 22 ºC, 75% RH, 30 min rest + 20 min exercise Nasal resistance ↑30% Koenig et al. 1985 43 L/min face mask FEV1 ↓16% Vmax-50 ↓26% Vmax-75 ↓26% 0.5 ppm 50 min 10 22 ºC, 75% RH, 30 min rest + 20 min Nasal resistance ↑32% Koenig et al.
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1985 1.0 ppm 30 min 10 26 ºC, 70% RH, exercise 41 L/min (3-10 min periods SRaw ↑172% Kehrl et al. 1987 separated by rests of 15 min)
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Only parameters related to air flow resistance were significantly affected by SO2 exposure, although spirometric parameters exhibited a similar trend. At the end of the first hour of exposure, airway resistance (SRaw)
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ages 20 to 35 years-old to filtered air or 1 ppm SO2 for 4 h. Each subject served as his own control and exercised for 15 min at both 1 and 3 h into the exposure period.
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Pulmonary flow resistance increased maximally at 10 min and was approximately 20% for 15 ppm mouth breathers, 65% for 28 ppm mouth breathers, 3% for 15 ppm nose breathers, and 18% for 28 ppm nose breathers. Cough or chest irritation was common in mouth breathers and rare in nose breathers.
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In exercising asthmatics exposed to 0.75 ppm SO2, effects were observed in airway resistance (150% increase) , forced expiratory volume in one second (mean -8%)
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From page 412... ...
Bronchoconstriction, as indicated by increases in SRaw, increased over baseline with increasing exposure time and concentration. SRaw was increased 46% after exposure to 0 ppm for 5 min, and 34%, 173% and 234%, after exposure to 0.5 ppm for 1-min, 3-min, and 5-min, respectively.
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From page 413... ...
Mean SRaw was increased 238% after the exposure period. Bethel et al.
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SRaw was increased two- and three-fold after exposures of 0.5 and 1.0 ppm, respectively. Increases were greatest after the first 10 min exercise periods and less after the latter two 10-min periods (with the exception of one subject whose bronchoconstriction increased with increasing exercise and who was unable to complete the protocol)
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From page 415... ...
Total mean SRaw was increased 172% after the first exercise, 137% after the second exercise, and 106% after the third exercise. A separate portion of the study involved exposure to SO2 at 0 or 1.0 ppm for a continuous 30 min period while exercising, with mean SRaw increasing 233% at the end of the 30-min exposure period.
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From page 416... ...
Seven of the subjects then similarly inhaled 0.5 ppm SO2 and 1 mg/m3 sodium chloride droplet aerosol via a face mask. No pulmonary function effects were noted.
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2.5. Genotoxicity Genotoxicy studies regarding acute human exposure to SO2 were not available.
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. Median lethal exposure time (Lt50)
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Maternal diet or SO2 exposure influenced liver GSH concentrations. GSH was lower in livers of rats exposed to the 120 g casein/kg maternal diet than in the 180 g/kg diet controls.
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TABLE 9-6 Increased Airway Resistance in Guinea Pigs Exposed to Sulfur Dioxide for 1 Hour % Increase in Airway Resistancea SO2 Concentration Number of Animals 2.6 ppm 16 20% 20 ppm 18 25% 100 ppm 10 70% 200 ppm 30 140% 750 ppm 13 300% a Approximate values estimated from graph.
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before being fixed for microscopic examination 1 and 6 h postexposure. Tracheal epithelial damage was not observed in any controls, but was observed in all dogs exposed to SO2.
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3.4. Genotoxicity Genotoxic studies regarding animal exposure to SO2 were not available.
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During inhalation, SO2 may react with water in the respiratory tract to form sulfurous acid or may be oxidized to form sulfur trioxide. Sulfur trioxide reacts rapidly with water to form sulfuric acid.
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From page 424... ...
These, and other data presented in Tables 4 and 5, suggest that a major portion of the SO2-induced bronchoconstriction occurs within 10-min and increases minimally or resolves beyond 10-min of exposure. Furthermore, there is no evidence that any other effect is relevant at low sulfur dioxide concentrations; the respiratory response is a first-level, sensitive response to SO2 exposure.
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From page 425... ...
examined the effect of concurrent exposure of SO2 and sulfuric acid mist or inert sodium chloride aerosol on guinea pigs and found that particle size was a factor in the magnitude of response. When animals were exposed to 0.8μ sulfuric acid mist particles and SO2, a synergistic response was observed with regard to bronchoconstriction; however, when 2.5μ sulfuric acid particles were administered with SO2, no synergism was observed.
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From page 426... ...
. No uncertainty factors will be applied because the weight of evidence approach utilized studies from a sensitive human population, that of exercising asthmatics.
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From page 427... ...
. No uncertainty factors will be applied because the weight of evidence approach utilized studies from a sensitive human population, that of exercising asthmatics.
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From page 428... ...
An uncertainty factor of 3 was applied for interspecies variability; this factor of 3 was considered sufficient because no deaths were reported in guinea pigs exposed to 750 ppm SO2 for 1 h (Amdur 1959) , in dogs exposed to 400 ppm SO2 for 2 h (Jackson and Eady 1988)
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A weight-of-evidence approach from studies in exercising asthmatics was used to derive AEGL-1 (NOEL for bronchoconstriction) and AEGL-2 (moderate respiratory effects)
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The ERPG-1 for SO2 is based on increased airway resistance in exercising asthmatics. The ERPG-2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 h without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual=s ability to take protection action.
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h TLV-STEL (American Conference of Governmental Industrial Hygienists, Threshold Limit Value - Short Term Exposure Limit, American Conference of Governmental Industrial Hygienists)
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1985. Effect of 0.25 ppm sulfur dioxide on airway resistance in freely breathing, heav ily exercising, asthmatic subjects.
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. Assessment of New Findings on Sulfur Dioxide Acute Exposure Health Effects in Asthmatic Individuals.
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1980. Acute effects of inhaled sulfur dioxide plus sodium chloride droplet aerosol on pulmonary function in asthmatic adoles cents.
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1983. A comparison of the pul monary effects of 0.5 ppm versus 1.0 ppm sulfur dioxide plus sodium chloride droplets in asthmatic adolescents.
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2001. Standing Operating Procedure for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.
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2005. Occupational Exposure Limit Value and Measures against Air Contaminants.
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Pp. 115-150 in Recom mended Health-based Occupational Exposure Limits for Respiratory Irritants.
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From page 439... ...
Therefore, AEGL-1 values for SO2 will be held constant across all time points. Uncertainty factors: None: subjects were exercising asthmatics 10-min, 30-min, 1-h, 4-h, and 8-h AEGL-1 = 0.20 ppm Derivation of AEGL-2 Key study: Weight-of -evidence approach suggests 0.75 ppm induces moderate respiratory response in exercising asthmatics for exposure durations of 10-min to 3-h ppm (see table below)
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From page 440... ...
Uncertainty factors: None: subjects were exercising asthmatics 10-min, 30-min, 1-h., 4-h, and 8-h AEGL-2 = 0.75 ppm 0.75 10-40 10 23 ºC, 70% RH, SRaw ↑150% Schacter et al. ppm min exercise 35 L/min FEF ↓22% 1984 FEV1 ↓8% 0.75 3h 17 22 ºC, 85% RH, SRaw ↑: Hackney et al.
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From page 441... ...
3 × 4 h = 752530068 ppmh C1 × t = k (573 ppm) 1 × 4 hr = 2292 ppmh Uncertainty factors: 10 for intraspecies variability 3 for interspecies variability 10-min AEGL-3 1-h AEGL-3 value adopted as 10-min value because asthmatic humans are highly sensitive to sulfur dioxide at short time periods 30-min AEGL-3 1-h AEGL-3 value adopted as 30-min value because asthmatic humans are highly sensitive to sulfur dioxide at short time periods C3 × 1 h = 752530068 ppmh 1-h AEGL-3 C3 = 752530068 ppm C = 909 1-h AEGL-3 = 909 ppm/30 = 30 ppm 4-h AEGL-3 4-h AEGL-3 = 573 ppm/30 = 19 ppm C1 × 8 hr = 2292 ppmhr 8-h AEGL-3 C1 = 287 ppm C = 287 8-h AEGL-3 = 287 ppm/30 = 9.6 ppm
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From page 442... ...
1983b ↓10% 0.5 ppm 10-40 min 10 23 ºC, 70% RH, None Schacter et exercise 35 L/min al. 1984 AEGL-2 VALUES 10 min 30 min 1h 4h 8h 0.75 ppm 0.75 ppm 0.75 ppm 0.75 ppm 0.75 ppm Weight-of -evidence approach suggests 0.75 ppm induced moderate bronchoconstriction in exercising asthmatics.
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From page 443... ...
1985 intermittent 1.0 ppm 30 min 10 26 ºC, 70% RH, SRaw ↑172% Kehrl et exercise 41 L/min SRaw ↑137% al. 1987 (3- 10 min periods SRaw 106% separated by rests of 15 min)
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From page 444... ...
Effects: Concentration: Mortality 224 ppm 0/8 593 ppm 0/8 965 ppm 3/8 1168 ppm 5/8 1319 ppm 8/8 Uncertainty Factors/Rationale: Total uncertainty factor: 30 Intraspecies = 10: due to the wide variability in response to SO2 exposure between healthy and asthmatic humans. Interspecies = 3: considered sufficient because no deaths were reported in guinea pigs exposed to 750 ppm SO2 for 1 h (Amdur 1959)
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From page 445... ...
APPENDIX C Category Plots for Sulfur Dioxide Chemical Toxicity - TSD Human Data Sulfur Dioxide-Asthmatic Humans 100 AEGL-3 No effect 10 Discomfort ppm Disabling AEGL-2 AEGL 1 AEGL-1 0 0 60 120 180 240 300 360 420 480 Minutes FIGURE C-1 Category plots for sulfur dioxide for asthmatic humans.
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From page 446... ...
446 Chemical Toxicity - TSD Human Data Sulfur Dioxide- Healthy Humans 100 No effect AEGL-3 10 Discomfort ppm Disabling AEGL 1 AEGL-2 AEGL-1 0 0 60 120 180 240 300 360 420 480 Minutes FIGURE C-2 Category plots for sulfur dioxide for healthy humans.
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From page 447... ...
Chemical Toxicity - TSD Animal Data Sulfur Dioxide 100000 10000 No Effect 1000 Discomfort Disabling 100 ppm AEGL-3 Partially Lethal 10 Lethal AEGL-2 1 AEGL AEGL-1 0 0 60 120 180 240 300 360 420 480 Minutes FIGURE C-3 Category plots for sulfur dioxide for animals.
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