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G. V. Alexeeff, K. K. Deng, R. L. Broadwin, A. G. Salmon

Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, CA

 

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Purpose

To evaluate the application of the USEPA benchmark dose (BMD) methodology to acute inhalation exposure risk assessment using human data.– To refine BMD methodology.– To inform the standard method: no

observed adverse effect level (NOAEL) divided by uncertainty factor (UF)s

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• Approaches to describe human risks and/or reference levels from acute inhalation exposures have been developed by: – American Conference of Governmental Industrial Hygienists

Inc. (ACGIH) short-term exposure limits (STELs) and Ceiling values (ACGIH Worldwide, 2006).

– National Research Council /USEPA acute emergency guidance levels (AEGLs) (NRC, 2000).

– USEPA acute reference exposures (Strickland et al., 2002).

– California acute reference exposure levels (Collins et al., 2004).

Background

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• Traditional NOAEL or LOAEL approach – empirically analyzes effects at discrete concentrations – does not infer about the exposure group response rates. – Usually is described as follows (Collins et al., 2004):

Reference value = NOAEL (or LOAEL) / (UFA x UFH x UFother) • LOAEL refers to lowest observed adverse effect level

• UF refers to uncertainty factor and may or may not be explicit

– Remains the predominant methodology due to data available.

Background (cont.)

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• BMD methodology is generally seen as an improvement of the NOAEL/LOAEL approach since: – reflects the shape of the dose-response curve– is not an artifact of the choice of experimental

concentration. – takes into account some variability in the test population.

• e.g., the choice of a 95% lower confidence limit (LCL).

– increases the minimum quality of an acceptable study.

Background (cont.)

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• BMD methodology

– considers data consistency over a range of exposures – estimates a concentration at a defined response level– provides an estimate of toxicological response that could

replace the NOAEL as the point of departure (POD) in health risk assessments.

– described as follows (Collins et al., 2004):

Reference value = POD/ (UFA x UFH x UFother) • POD (point of departure) could be BMD, NOAEL, or LOAEL • UF refers to uncertainty factor and may or may not be explicit

Background (cont.)

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• BMD methodology requires the user to input the desired response rate. Usually the response rate chosen is 1, 5 or 10 %.

• In 1999 we published a paper evaluating 100 acute inhalation lethality datasets using a BMD approach (Fowles et al.). From this analysis we decided on some preferred approaches for use in BMD evaluation. – Use of the probit model– Use of a 5% response rate– Equate the 5% response rate with the NOAEL

• While we may deviate from these approaches, they generally represent our starting point.

Background (cont.)

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• Caveat:– The Fowles et al. analysis is based on acute

inhalation animal lethality evaluations. – There is little acute inhalation exposure

information regarding • human endpoints or• non-lethal animal endpoints

• The USEPA BMD software has a wide range of models to consider.

• We considered whether other models may be superior to the probit model for a default approach.

Background (cont.)

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Approach

• Literature search of all hazardous air pollutants to identify data sets reporting – mild acute effects (Alexeeff et al., 2002)– NOAEL– LOAEL – sufficient information to conduct a BMD

analysis

• Relevant NOAEL and LOAEL information was identified for 70 chemicals.

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Acetaldehyde Acetophenone Acrolein

Acrylic acid Acrylonitrile Allyl chloride

Aniline Benzene Benzyl chloride

Beryllium compounds Butadiene Cadmium compounds

Carbon disulfide Carbon tetrachloride Chlorine

Chloroform Chloromethyl methyl ether Chloroprene

Cobalt compounds Cumene Diazomethane

Dichloropropene Dimethylformamide Dimethylhydrazine (1,1-)

Dioxane (1,4-) Epichlorohydrin Epoxybutane(1,2-)

Ethyl acrylate Ethylbenzene Ethyl chloride

Ethyl dichloride Ethyleneimine Ethylene oxide

Formaldehyde Glycol ether Hexachloroethane

Hexamethylene 1,6-diisocyanate Hexane Hydrogen chloride

Hydrogen fluoride Isophorone Methanol

Methyl bromide Methyl chloride Methyl chloroform

Methyl hydrazine Methyl isobutyl ketone (MIBK) Methyl isocyanate

Methyl methacrylate Methyl tert-butyl ether Methylene chloride

Methylene diphenyl diisocyanate Nickel compounds Nitrophenol

PCBs Phenol Phosgene

Phosphine Phosphorus compounds Propionaldehyde

Styrene Tetrachloroethylene Toluene

Toluene diisocyanate (2,4-) Trichloroethylene Triethylamine

Vinyl acetate Vinyl chloride

Vinylidene chloride Xylenes (m, o, p-isomers)

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Table 1. Studies Identified from the Literature

Search for Evaluation

SpeciesNumber of Studies

IdentifiedNumber of Studies with Multiple Doses

Human 60 15

Mouse 60 19

Rat 120 34

Other* 39 11

TOTAL 279 79

*Other refers to animal studies consisting of: baboon (N= 2), dog (N= 4), guinea pig (N= 19), hamster (N= 4), monkey (N= 1), prairie dog (N=2), and rabbit (N= 6), and rock dove (N=1).

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Table 2. Studies Identified Sorted by Endpoint

Category EndpointCategory

Number of Studies Identified

Number of Studies with Multiple Doses

Alimentary 41 11

Eyes 49 6

Nervous 79 26

Respiratory 77 27

Other* 34 11

TOTAL 311 81

*Other refers to ratios based on endpoints of: cardiovascular (N= 4), hematologic (N=18), immune (N= 12), and reproductive (N=1). Total N> 279 because some studies showed multiple effects.

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Human Studies Identified• 60 human studies contained data which met

the criteria of mild acute effects and reported NOAEL and LOAEL values. – 15 studies reported multiple doses.

• For this BMD analysis, we focused on those studies based on dichotomous (quantal or effect/no effect) responses.

• Eight data sets, for seven chemicals, met the additional criteria: dichotomous with at least three dose levels for BMD analysis.

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Table 3. Study Description of Acute Inhalation Human Studies Identified

ChemicalStudy duration/

Mean sample sizeHealth Effects References

Acetophenone 40 minutes/ 3Increased

sensitivity to lightImasheva, 1963

*Formaldehyde 150 minutes/ 16Conjunctival irritation and discomfort

Anderson & Molhave, 1983

*Formaldehyde 180 minutes/ 14 Eye irritation Kulle et al., 1987

Methanol Missing/ 5Affected alpha

rhythm amplitudeUbaydullayev, 1968

MIBK 2 hours/ 8 Headache Hjelm et al., 1990

*Vinyl Acetate 2 minutes/ 9Eye, nose, &

throat irritationUnion Carbide

Corporation, 1973

Vinyl Chloride 5 minutes/ 6Intoxicating

effectsLester, 1963

*Mixed Xylenes 15 minutes/ 6Eye irritation/

tearsCarpenter et al.,

1975

*Human irritants

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Data Analysis

• We analyzed and compared each data set using seven different BMD models for dichotomous data: – Probit– Quantal linear– Multistage– Weibull– Logistic– Quantal quadratic– Gamma

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Data Analysis (cont.)

• For each data set, comparisons among the BMDL and BMD values made at 1%, 5%, and 10% response rates are shown on the following slides.

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Figure 1. BMD Analysis for Formaldehyde Exposure at 5% Response Rate

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3

Fra

ction A

ffecte

d

dose

Probit Model with 0.95 Confidence Level

12:25 03/01 2006

BMDL BMD

ProbitBMD Lower Bound

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Figure 2. BMD Analysis for Mixed Xylenes Exposure at 5% Response Rate

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 100 200 300 400 500 600 700

Fra

ctio

n A

ffe

cte

d

dose

Probit Model with 0.95 Confidence Level

13:52 07/28 2006

BMDL BMD

ProbitBMD Lower Bound

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Table 4. Comparing BMD01 (Top Line) and

BMDL01 (Bottom Line) for Various BMD Models Chemical Probit Multistage Logistic

Quantal Linear

QuantalQuadratic

Weibull Gamma

Acetophenone(mg/m3)

8.8 x 10-3

2.4 x 10-3

1.2 x 10-3

7.1 x 10-5 8.0 x 10-3

1.8 x 10-3 1.2 x 10-4

5.7 x 10-5

1.2 x 10-3

7.7 x 10-4

8.1 x 10-3

8.5 x 10-4 5.8 x 10-3

6.4 x 10-4

Formaldehyde(ppm)

0.240.097

0.0300.014

0.140.010

0.0210.014

0.210.16

0.0670.015

0.110.015

Formaldehyde(ppm)

0.510.26

0.320.039

0.420.17

0.0260.019

0.210.18

0.360.13

0.440.16

Methanol(mg/m3)

1.00.84

0.140.014

0.92/0.74

0.0179.5 x 10-3

0.140.10

0.930.65

0.650.44

MIBK(mg/m3)

2816

5.42.6

5.91.9

5.42.6

3021 NA NA

Vinyl Acetate(ppm)

1.70.93

1.40.17

1.20.15

0.370.16

1.50.99 NA NA

Vinyl Chloride(ppm)

59003000

4400310

54002400

160100

14001100

46001700

55002300

Mixed Xylenes(ppm)

9758

329.9

528.1

209.8

11069 NA NA

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Table 4a. Comparing BMD01 (Top Line) and BMDL01

(Bottom Line) for Various BMD Models Chemical Probit Multistage

Acetophenone(mg/m3)

8.8 x 10-3

2.4 x 10-3

1.2 x 10-3

7.1 x 10-5

Formaldehyde(ppm)

0.240.097

0.0300.014

Formaldehyde(ppm)

0.510.26

0.320.039

Methanol(mg/m3)

1.00.84

0.140.014

MIBK(mg/m3)

2816

5.42.6

Vinyl Acetate(ppm)

1.70.93

1.40.17

Vinyl Chloride(ppm)

59003000

4400310

Mixed Xylenes(ppm)

9758

329.9

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Table 5. Comparing BMD05 (Top Line) and BMDL05 (Bottom Line) for Various BMD Models

Chemical Probit Multistage LogisticQuantal Linear

QuantalQuadratic

Weibull Gamma

Acetophenone(mg/m3)

9.2 x 10-3

3.6 x 10-3

2.6 x 10-3

3.6 x 10-4

8.8 x 10-3

3.2 x 10-3

6.3 x 10-4

2.9 x 10-4

2.6 x 10-3

1.7 x 10-3

8.9 x 10-3

2.1 x 10-3

7.0 x 10-3

1.7 x 10-3

Formaldehyde(ppm)

0.430.19

0.150.074

0.330.055

0.110.074

0.470.36

0.230.074

0.290.074

Formaldehyde(ppm)

0.730.44

0.640.20

0.690.39

0.130.094

0.470.40

0.670.35

0.690.37

Methanol(mg/m3)

1.070.92

0.31 0.073

1.000.87

0.0850.049

0.310.24

1.00.82

0.790.60

MIBK(mg/m3)

5532

2813

2710

2813

6746

NA NA

Vinyl Acetate(ppm)

3.21.8

3.30.86

3.000.76

1.90.82

3.362.23

NA NA

Vinyl Chloride(ppm)

72004300

66001600

72004100

820530

32002500

68003600

71003900

Mixed Xylenes(ppm)

190 110

14051

16042

10050

250160

NA NA

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Table 6. Comparing BMD10 (Top Line) and BMDL10 (Bottom Line) for Various BMD Models

Chemical Probit Multistage LogisticQuantal Linear

QuantalQuadratic

Weibull Gamma

Acetophenone(mg/m3)

9.5 x 10-3

4.4 x 10-3

3.8 x 10-3

7.5 x 10-4

9.2 x 10-3

4.2 x 10-3 1.3 x 10-3

6.0 x 10-4

3.8 x 10-3

2.5 x 10-3

9.3 x 10-3

3.2 x 10-3 7.7 x 10-3

2.6 x 10-3

Formaldehyde(ppm)

0.580.28

0.290.15

0.490.12

0.220.15

0.670.51

0.390.15

0.460.15

Formaldehyde(ppm)

0.870.59

0.860.40

0.870.56

0.270.19

0.680.57

0.870.54

0.870.54

Methanol(mg/m3)

1.100.97

0.450.15

1.00.93

0.170.010

0.450.37

1.10.90

0.870.54

MIBK(mg/m3)

7946

5727

5521

5728

9666

NA NA

Vinyl Acetate(ppm)

4.62.6

4.81.8

4.51.6

3.81.7

4.83.2

NA NA

Vinyl Chloride(ppm)

81005300

45002600

83005300

17001100

45003600

81004900

81005000

Mixed Xylenes(ppm)

280160

260100

26089

210100

350220

NA NA

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Reviewing Model Results

• Data analyses via Weibull and Gamma dichotomous models were eliminated due to calculation failure for one or more chemicals.

• For each data set, we considered whether the Chi-square p-value indicated that the fitted model adequately described the data, using a 0.05 rejection criterion. The quantal linear, multistage, and quantal quadratic models did not fit the data sets in all cases.

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Reviewing Model Results (cont.)

• Remaining models (probit and logistic) were compared using the goodness-of-fit statistics presented in the analsyis of deviance table. In almost all cases, there was little difference in the parameters evaluated.

• The probit model yielded an adequate fit overall for all the data sets, particularly in the low dose region. We concluded that it served as useful default approach, particularly in light of extensive experience with the model in acute toxicology.

• The remaining evaluations use the probit model.

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Table 7. Comparison of BMD to BMDL at 1%, 5%, and 10% Response Rates using the Probit Model

ChemicalBMD01

BMDL01

BMD05

BMDL05

BMD10

BMDL10

Acetophenone 3.7 2.6 2.2

*Formaldehyde 2.5 2.2 2.1

*Formaldehyde 2.0 1.6 1.5

Methanol 1.2 1.2 1.1

MIBK 1.8 1.7 1.7

*Vinyl Acetate 1.8 1.8 1.8

Vinyl Chloride 2.0 1.7 1.5

*Mixed Xylenes 1.7 1.7 1.7

Note: * = Human irritants MIBK = Methyl Isobutyl Ketone

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Relationship of BMC 95% Confidence Limits to Maximum Likelihood Estimates

(Fowles et al., 1999)

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Table 8. NOAEL and LOAEL Values, Compared to BMDL-BMD

Concentrations, for 1%, 5% & 10% Response Rates, Using the Probit Model . NOAEL 1 % Response 5 % Response 10 % Response LOAEL

Acetophenone(mg/m3) 0.007

0.0024 - 0.0088

0.0036 - 0.0092

0.0044 - 0.0095

0.01

Formaldehyde1

(ppm) 0.50 0.097 - 0.24 0.19 - 0.43 0.28 - 0.58 1

Formaldehyde2

(ppm) 0.51 0.26 - 0.51 0.44 - 0.73 0.59 - 0.87 1.01

Methanol(mg/m3) 1.01 0.84 - 1.0 0.92 - 1.07 0.97 - 1.10 1.17

MIBK(mg/m3) 10 16 - 28 32 - 55 46 - 79 100

Vinyl Acetate(ppm) 1.3 0.93 - 1.7 1.8 - 3.2 2.6 - 4.6 4

Vinyl Chloride(ppm) 4000 3000 - 5900 4300 - 7200 5300 - 8100 8000

Mixed Xylenes(ppm) 110 58 - 97 110 - 190 160 - 280 230

Note: Numbers in % response columns read as BMDL-BMD concentrations.1: Anderson & Molhave, 1983; 2: Kulle et al., 1987

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NOAEL and LOAEL Values Compared to BMDL-BMD Concentrations

• The relationship among the NOAEL, LOAEL, BMDL and BMD values were evaluated at the 1%, 5% and 10% response rates.

• The 1% and 5% BMDL-BMD range is more closely associated with the NOAEL than the 10% range.

• The 10% BMDL-BMD range may be associated with the LOAEL.

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Relationship of NOAEL and LOAEL to BMDL

RatioResponse Rate

1% 5% 10%

NOAEL to BMDL

2.1 1.3 0.93

LOAEL to BMDL

4.6 2.6 1.9

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Relationship of BMC to NOAELs & LOAELs from Acute Lethality Data – Probit (Fowles

et al., 1999)

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Table 9. NOAEL and LOAEL Values and BMDL Response Rates

NOAEL % Response LOAEL % Response

Acetophenone(mg/m3)

0.007 1.0 x 10-7 0.01 34

Formaldehyde1

(ppm)0.50 8.0 1 28

Formaldehyde2

(ppm)0.51 1.0 1.01 16

Methanol(mg/m3)

1.01 0.42 1.17 49

MIBK(mg/m3)

10 0.042 100 15

Vinyl Acetate(ppm)

1.3 0.45 4 7.8

Vinyl Chloride(ppm)

4000 0.018 8000 9.4

Mixed Xylenes(ppm)

110 1.4 230 7.2

1: Anderson & Molhave, 19832: Kulle et al, 1987

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Estimating a Reference Level from the BMDL

• Assuming that the BMDL05 represented the identified POD, we estimated a reference exposure level using a default 10-fold interindividual uncertainty factor (UFH) for each of the data sets.

• BMDL response rates were calculated at the estimated reference exposure level.

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Table 10. Estimated REL and BMDL Response Rate Using the Probit Model

ChemicalBMDL05

10Response Rate

CAREL

Comment

Acetophenone(mg/m3) 3.6 x 10-4 1 x 10-7 NA NA

*Formaldehyde1

(ppm) 0.019 4 x 10-5 0.076

Used Kulle et al, 1987

*Formaldehyde2

(ppm) 0.044 2.5 x 10-6 0.076

Used Kulle et al, 1987

Methanol(mg/m3) 0.092 1 x 10-7 28

Different study, endpoint, and exposure.

MIBK(mg/m3) 3.2 4 x 10-5 NA NA

*Vinyl Acetate(ppm) 0.18 4 x 10-5 NA NA

Vinyl Chloride(ppm) 430 6 x 10-9 72 Study with longer exposure

*Mixed Xylenes(ppm) 11 4 x 10-5 5 Study with longer exposure

CA REL = Reference 1-hour exposure level; NA= not available; Note: * = Human irritants1: Anderson & Molhave, 1983; 2: Kulle et al, 1987 MIBK = Methyl Isobutyl Ketone

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Estimating a Reference Level from the BMDL Results

• All of the estimated risk levels were at or below 4 x 10-5.

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Estimating the BMDL Response Rate at the AEGL

• We identified relevant AEGL-1 levels for four of the seven substances from: http://www.epa.gov/oppt/aegl

• AEGL-1 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

• We calculated the BMDL response rate at the AEGL-1.

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Table 11. BMDL Reported Rates for Acute Emergency Guideline Levels (AEGLs)

 Chemical AEGL-1 (ppm)

BMDL Response Rate (%)

*Formaldehyde 0.9 242 - 461

*Vinyl Acetate 6.7 39

Vinyl Chloride 450 9 x 10-7

*Xylene 130 6.5

 Note: * = Human irritants1: Anderson & Molhave, 19832: Kulle et al, 1987

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Estimating the BMDL Response Rate at the AEGL Results

• Expected risk levels from the AEGL-1 values appear to be significant for the irritants vinyl acetate and formaldehyde.

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Discussion and Conclusion• The probit model consistently provides an adequate fit

for these dichotomous acute human exposure data; this is consistent with the results for acute inhalation lethality animal data (Fowles et al., 1999).

• Among 1%, 5% and 10% response rates, 5% overall is more closely associated with the NOAEL; therefore,

human inhalation data sets at BMDL05 are considered to

be similar to a NOAEL in estimating a concentration associated with a low level of risk. This is consistent with the results for acute inhalation lethality animal data (Fowles et al., 1999).

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Discussion and Conclusion (cont.)

• The BMD 10% response rate may be associated with the LOAEL. This may require consideration of an additional uncertainty factor if the 10% response level is assumed.

• The average ratio of the BMD to the BMDL was fairly constant across chemicals. This indicates that no significant divergence between the BMD and BMDL for most chemicals in the 1% to 10% range. This is consistent with the results for acute inhalation lethality animal data (Fowles et al., 1999).

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Discussion and Conclusion (cont.)

• BMD approach provides a more consistent basis for estimating a point of departure. The estimated response rates at the NOAEL and LOAEL can vary substantially.

• At the LOAEL, response rates above 25% can occur.

• At the NOAEL, response rates are generally very low, although several in the 1% to 10% range were calculated.

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Discussion and Conclusion (cont.)

• Using the BMD approach to estimate of the response rate of a guidance level may provide useful insight to the level of protection of the guidance level.

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Contributors

OEHHA Staff• George V. Alexeeff• Rachel Broadwin• James F. Collins• Melanie A. Marty• Andrew Salmon

Support Staff• Laurie Bliss

Students• Kitty K. Deng• Dora Wang• Melisa Masuda

Other Contributors• Jefferson R. Fowles

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References• ACGIH Worldwide. 2006. 2006 TLVs and BEIs, Based on the

Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices. Cincinnati, OH: ACGIH Worldwide.

• Acute Emergency Guidelines Levels (AEGLs). (2005). U.S. Environmental Protection Agency (EPA). http://www.epa.gov/oppt/aegl/chemlist.htm

• Alexeeff, G.V., Broadwin, R., Liaw, J., and Dawson, S.V. (2002) Characterization of the LOAEL-NOAEL Uncertainty Factor for Mild Adverse Effects from Acute Inhalation Exposure. Reg. Toxicol. Pharmacol. 36:96-105.

• Anderson, I., Molhave, L. (1983). Controlled human studies with formaldehyde. Formaldehyde Toxicity. Chapter 14, 154-164.

• Carpenter, C. P., Kinkead, E. R., Geary, Jr., D. L., Sullivan, L. J., King, J. M. (1975). Petroleum hydrocarbon toxicity studies. V. Animal and human response to vapors of mixed xylenes. Toxicology Applied Pharmacology. 33, 543-558.

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References (cont.)• Collins, JF Et Al. (2004). Development of Acute Inhalation Reference

Exposure Levels (RELs) to Protect the Public from Predictable Excursions of Airborne Toxicants. Journal of Appl Toxicol. 24, 155-166.

• Fowles, JR Et Al. (1999). The Use of Benchmark Dose Methodology with Acute Inhalation Lethality Data. Regul Toxicol Pharmacol 29, 262-278.

• Hjelm, E.W, Hagberg, M., Iregren, A., and Lof, A. (1990) Exposure to methyl isobutyl ketone: toxicokinetics and occurrence of irritative and CNS symptoms in man. Int Arch Occup Environ Health 62:19-26.

• Imasheva, N.B. (1963) The Substantiation of the Maximal Permissible Concentration of Acetophenon in the Atmospheric Air. Hyg Sanit 28:57-63

• Kulle, J. T., Sauder, L. R., Hebel, J. R., Green, D., and Chatham, M. D. (1987). Formaldehyde dose-response in healthy nonsmokers. J. Air Pollution Control Assoc. 37, 919-924.

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References (cont.)• Lester, D., Greenberg, L. A., and Adams, W. R. (1963). Effects of

single and repeated exposures of humans and rats to vinyl chloride. Am. Ind. Hyg. Assoc. J. 3, 265-275.

• NRC. 2000. Acute Exposure Guideline Levels for SElected Airborne Chemicals. Washington, DC: National Academy Press.

• Smyth, H.F. and Carpenter, C.P. (1973) Vinyl Acetate Single Animal Inhalation and Human Sensory Response. Special Report 36-72. Union Carbide Corp. Danbury, CT.

• Strickland, J.A. Et. Al. (2002). US EPA’s Acute Reference Exposure Methodology for Acute Inhalation Exposures. The Science of the Total Environment. 288, 51-63.

• Ubaydullayev, R. (1968). A study of hygienic proper ties of methanol as an atmospheric air pollutant. USSR Lit. Air Pollut. Relat. Occup. Dis. – A Survey. 17, 39-45.