Office of Environmental Health Hazard Assessment

Air Toxicology and Epidemiology

All OEHHA Acute, 8-hour and Chronic Reference Exposure Levels (chRELs) as of January 2014

Follow the links below to download documentation on the reference exposure levels.

Footnotes:
[1]REL types: A = acute, 8 = 8-hour, C = chronic. Exposure averaging time for acute RELs is 1 hour.  For 8-hour RELs, the exposure averaging time is 8 hours, which may be repeated.  Chronic RELs are designed to address continuous exposures for up to a lifetime: the exposure metric used is the annual average exposure.

[2]Species used in key study for REL development: D = dog; Gb = gerbil; GP = guinea pig: H = human; Ha = hamster; M = mouse; Mk = monkey; R = rat; Rb = rabbit

[3]These peer-reviewed chronic REL values were developed under the Toxic Air Contaminant (TAC) Program mandated by AB1807.

[4]REL based on benchmark dose (BMC) approach.

[5]REL developed using the revised methodology (OEHHA, 2008)].

OEHHA Acute, 8-hour and Chronic Reference Exposure Level (REL) Summary1

Substance

REL type[1]

Inhalation REL
(
ug/m3)

Oral REL
(
ug/kg BW-day)

Hazard Index
Target Organs

Species[2]

Acetaldehyde (75-07-0)

A

470[5]

 

Eyes; respiratory system (sensory irritation)

H

8

300[4,5]

 

Respiratory system

R

C

140[4,5]

 

Respiratory system

R

Acrolein  (107-02-8)

A

2.5[5]

 

Eyes, respiratory system (sensory irritation)

H

8

0.7[5]

 

Respiratory system

R

C

0.35[5]

 

Respiratory system

R

Acrylic Acid  (79-10-7)

A

6,000

 

Respiratory system; eyes

R

Acrylonitrile (107-13-1)

C

5[4]

 

Respiratory system

R

Ammonia (7664-41-7)

A

3200[4]

 

Respiratory system; eyes

H

C

200

 

Respiratory system

H

Arsenic (7440-38-2) & inorganic arsenic compounds (including arsine)

A

0.20[5]

 

Development; cardiovascular system; nervous system

M

8

0.015[5]

 

Development; cardiovascular system; nervous system; respiratory system; skin

H

C

0.015[5]

0.0035[5]

Inhalation & oral: Development; cardiovascular system; nervous system; respiratory system; skin

H

Benzene  (71-43-2)

A

1,300

 

Reproductive/ Development; immune system; hematologic system

R

C

60

 

Hematologic & nervous systems; development

H

Benzyl Chloride(100-44-7)

A

240

 

Respiratory system; eyes

M, R

Beryllium& beryllium compounds (7440-41-7)

C

0.007

2.0

Inhalation: Respiratory system; immune system Oral: Alimentary system (Gastrointestinal tract)

H

Butadiene (106-99-0)

A

660[4,5]

  Development

M

8

9[4,5]

  Reproductive system

M

C

2[4,5]

 

Reproductive system

M

Cadmium & cadmium compounds (7440-43-9)

C

0.02

0.5

Inhalation: Kidney; respiratory system
Oral: kidney

H

Carbon disulfide (75-15-0)

A

6,200

 

Reproductive/ Development; nervous system

R

C

800[4]

 

Nervous system; reproductive system

H

Carbon monoxide (630-08-0)

A

23,000

 

Cardiovascular system

H

Caprolactam (105-60-2)

A

50

 

Eyes (sensory irritation)

H

8

7

 

Respiratory system

R

C

2.2

 

Respiratory system

R

Carbon tetrachloride (56-23-5)

A

1,900

 

Alimentary system (liver); Reproductive/ Developmental; nervous system

R

C

40

 

Alimentary and nervous systems; development

GP

Chlorinated dibenzo-p dioxins and
dibenzofurans
 

Unspeciated mixtures treated as 2,3,7,8-tetrachlorodibenzo-p-dioxin (1746-01-6)

C

0.00004

1 x 10-5

Inhalation and Oral: Alimentary (liver) reproductive, endocrine, respiratory, hematologic systems; development

R

Chlorine (7782-50-5)

A

210

 

Respiratory system; eyes

H

C

0.2[4]

 

Respiratory system

R

Chlorine dioxide (10049-04-4)

C

0.6

 

Respiratory system

R

Chlorobenzene (108-90-7)

C

1,000

 

Alimentary system (liver); kidney; reproductive system

R

Chloroform (67-66-3)

A

150

 

Reproductive/ Developmental; respiratory system; nervous system

R

C

300

 

Alimentary system; kidney; development

R

Chloropicrin (76-06-2)

A

29

 

Respiratory system; eyes

M

C

0.4[4]

 

Respiratory system

M

Chromic trioxide (as chromic acid mist)

C

0.002

20

Inhalation: Respiratory system
Oral: Hematologic system

H

Chromium (hexavalent) (18540-29-9) & soluble hexavalent chromium compounds (except chromic trioxide)

C

0.2[4]

20

Inhalation: Respiratory system
Oral: Hematologic system

R

Copper and compounds

A

100

 

Respiratory system

H

Cresol mixtures (1319-77-3)

C

600

 

Nervous system

R

Dichlorobenzene (1,4-) (106-46-7)

C

800

 

Nervous and respiratory; alimentary systems (liver); kidney

R

Dichloroethylene (1,1) (75-35-4)

C

70

 

Alimentary system (liver)

GP

Diesel Exhaust

C

5[3]

 

Respiratory system

R

Diethanolamine  (111-42-2)

C

3

 

Respiratory and hematologic systems

R

Dimethylformamide (N,N-) (68-12-2)

C

80

 

Alimentary (liver) and respiratory systems

H

Dioxane (1,4-) (123-91-1)

A

3,000

 

Respiratory system; eyes

H

C

3,000

 

Alimentary system; kidney; cardiovascular system

R

Epichlorohydrin (106-89-8)

A

1,300

 

Respiratory system; eyes

H

C

3

 

Respiratory system; eyes

R

Epoxybutane (1,2-) (106-88-7)

C

20

 

Respiratory system; cardiovascular system

M

Ethylbenzene(100-41-4)

C

2,000

 

Alimentary system (liver); kidney; endocrine system; development

M, R

Ethyl chloride (75-00-3)

C

30,000

 

Development; alimentary system (liver)

M

Ethylene dibromide (106-93-4)

C

0.8

 

Reproductive system

H

Ethylene dichloride (107-06-2)

C

400

 

Alimentary system (liver)

R

Ethylene glycol (107-21-1)

C

400

 

Respiratory system; kidney; development

H

Ethylene glycol monobutyl ether (111-76-2)

A

14,000

 

Respiratory system; eyes

H

Ethylene glycol monoethyl ether (110-80-5)

A

370

 

Reproductive/ Development

R

C

70

 

Reproductive system; hemotologic system

Rb

Ethylene glycol monoethyl ether acetate (111-15-9)

A

140

 

Reproductive/ Development; nervous system

R

C

300

 

Development

Rb

Ethylene glycol monomethyl ether (109-86-4)

A

93

 

Reproductive/ Development

R

C

60

 

Reproductive system

Rb

Ethylene glycol monomethyl ether acetate (110-49-6)

C

90

 

Reproductive system

Rb

Ethylene oxide (75-21-8)

C

30

 

Nervous system

R

Fluorides (except Hydrogen Fluoride - listed below separately)

C

13[4]

40

Inhalation: Bone and teeth; respiratory system

Oral: Bone and teeth

H

Formaldehyde (50-00-0)

A

55[5]

 

Eyes (Sensory irritation)

H

8

9[5]

 

Respiratory system

H

C

9[5]

 

Respiratory system

H

Glutaraldehyde (111-30-8)

C

0.08[4]

 

Respiratory system

M

Hexane (n-)(110-54-3)

C

7000

 

Nervous system

H

Hydrazine  (302-01-2)

C

0.2

 

Alimentary system (liver); endocrine system

Ha

Hydrogen chloride (7647-01-0)

A

2,100

 

Respiratory system; eyes

H

C

9

 

Respiratory system

H

Hydrogen cyanide (74-90-8)

A

340

 

Nervous system

H

C

9

 

Nervous system; endocrine system; cardiovascular system

H

Hydrogen fluoride (7664-39-3)

A

240

 

Respiratory system; eyes

H

C

14[4]

40

Inhalation: Bone and teeth; respiratory system (See “fluorides” summary)

Oral: Bone and teeth

H

Hydrogen selenide (7783-07-5)

A

5

 

Respiratory system; eyes

GP

Hydrogen sulfide (7783-06-4)

A

42

 

Nervous system

H

C

10

 

Respiratory system

M

Isophorone (78-59-1)

C

2,000

 

Development; alimentary system (liver)

R, M

Isopropanol (67-63-0)

A

3,200

 

Eyes; respiratory system

H

C

7,000

 

Kidney; development

R, M

Maleic anhydride (108-31-6)

C

0.7[4]

 

Respiratory system

R,Ha, Mk

Manganese (7439-96-5) & manganese compounds

8

0.17[4,5]

 

Nervous system

H

C

0.09[4,5]

 

Nervous system

H

Mercury (7439-97-6) & inorganic mercury compounds

A

0.6[5]

 

Nervous system; development

R

8

0.06[5]

 

Nervous system; development; kidney

H

C

0.03[5]

0.16[5]

Inhalation & Oral: Nervous system; development; kidney

H

Methanol (67-56-1)

A

28,000

  Nervous system

H

C

4,000[4]

 

Development

M

Methyl bromide (74-83-9)

A

3900

 

Nervous system; respiratory system; Reproductive/ development

H

C

5

 

Respiratory system; nervous system; development

R

Methyl chloroform (71-55-6)

A

68,000

 

Nervous system

H

C

1000

 

Nervous system

Gb

Methylene chloride (75-09-2)

A

14,000

 

Cardiovascular system; Nervous system

H

C

400

 

Cardiovascular system; nervous system

H

Methylene dianiline (4,4’-) (101-77-9)

C

20

 

Eyes; alimentary system (liver)

GP

Methylene diphenyl isocyanate (101-68-8)

C

0.7[4]

 

Respiratory system

R

Methyl ethyl ketone (78-93-3)

A

13,000

 

Respiratory system; eyes

H

Methyl isocyanate (624-83-9)

C

1

 

Respiratory system; reproductive system

R

Methyl t-butyl ether (1634-04-4)

C

8,000

 

Kidney; eyes; alimentary system (liver)

R

Naphthalene (91-20-3)

C

9

  Respiratory system

H

Nickel & nickel compounds (except nickel oxide for chronic inhalation exposures) (Inhalation concentrations as µg Ni/m3: oral dose as µg Ni/kg-day)

A

0.2[5]

 

Immune system

M

8

0.06[5]

  Respiratory, immune systems

R

C

0.014[5]

11[5]

Inhalation: Respiratory system; hematologic system
Oral: Development

R

Nickel oxide (1313-99-1) (Inhalation concentration as µg Ni/m3: oral dose as µg Ni/kg-day)

C

0.02[5]

11[5]

Inhalation: Respiratory system
Oral: Development

M

R

Nitric acid  (7697-37-2)

A

86

 

Respiratory system

H

Nitrogen dioxide (10102-44-0)

A

470

 

Respiratory system

H

Ozone (10028-15-6)

A

180

 

Respiratory system; eyes

H

Perchloroethylene (127-18-4)
(syn. Tetrachloroethylene)[3]

A

20,000

 

Nervous system; respiratory system; eyes

H

C

35

 

Kidney; alimentary system (liver)

M

Phenol  (108-95-2)

A

5,800

 

Respiratory system; eyes

H

C

200

 

Alimentary system; cardiovascular system; kidney; nervous system

R

Phosgene (75-44-5)

A

4

 

Respiratory system

R

Phosphine (7803-51-2)

C

0.8

 

Respiratory system; alimentary system (liver); nervous system; kidney; hematologic system

M

Phosphoric acid (7664-38-2)

C

7[4]

 

Respiratory system

R

Polychlorinated biphenyls (PCBs)
Individual congeners evaluated using TEF methodology, relative to as 2,3,7,8-tetrachlorodibenzo-p-dioxin (see Appendix C in the TSD for Cancer Potency Factors – online at: http://oehha.ca.gov/air/hot_spots/tsd052909.html

C

-

-

Inhalation & oral: Alimentary (liver) reproductive, endocrine, respiratory, hematologic systems; development

R

Phthalic anhydride (85-44-9)

C

20

 

Respiratory system

H

Propylene(115-07-1)

C

3,000

 

Respiratory system

R

Propylene glycol monomethyl ether (107-98-2)

C

7,000

 

Alimentary system (liver)

R

Propylene oxide (75-56-9)

A

3,100

 

Respiratory system; eyes; reproductive/development

H

C

30

 

Respiratory system

R

Selenium and selenium compounds (other than hydrogen selenide)

C

20

5

Inhalation & oral: Alimentary system (liver); cardiovascular system; nervous system

H

Silica (crystalline, respirable)

C

3[4]

 

Respiratory system

H

Sodium hydroxide (1310-93-2)

A

8

 

Respiratory system; eyes; skin

H

Styrene (100-42-5)

A

21,000

 

Respiratory system; eyes; reproductive/development

H

C

900[4]

 

Nervous system

H

Sulfates

A

120

 

Respiratory system

H

Sulfur dioxide (7446-09-5)

A

660

 

Respiratory system

H

Sulfuric acid (7664-93-9) [& oleum, acute only]

A

120

 

Respiratory system

H

C

1

 

Respiratory system

Mk

Toluene (108-88-3)

A

37,000

 

Respiratory, nervous systems; eyes reproductive/development

H

C

300

 

Nervous system; respiratory system; development

R

Toluene diisocyanates (2,4- & 2,6-)

C

0.07

 

Respiratory system

H

Trichloroethylene (79-01-6)

C

600

 

Nervous system; eyes

H

Triethylamine  (121-44-8)

A

2,800

 

Nervous system; eyes

H

C

200

 

Eyes

R

Vanadium pentoxide(1314-62-1)

A

30

 

Respiratory system; eyes

H

Vinyl acetate (108-05-4)

C

200

 

Respiratory system

R, M

Vinyl chloride (75-01-4)

A

180,000

 

Nervous system; respiratory system; eyes

H

Xylenes: technical mixture (1330-20-7) and o-xylene (95-47-6), m-xylene (108-38-3) and p-xylene (106-42-3) isomers.

A

22000

 

Nervous & respiratory systems; eyes

H

C

700

 

Nervous & respiratory systems; eyes

H

 

 
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