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Chemical Sampling Information (CSI)
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General Description

Synonyms: Dursban®; O,O-Diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate; Phosphorothioic acid, O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) ester

OSHA IMIS Code Number: 0681

Chemical Abstracts Service (CAS) Registry Number: 2921-88-2

NIOSH Registry of Toxic Effects of Chemical Substances (RTECS) Identification Number: TF6300000

Department of Transportation Regulation Number (49 CFR 172.101) and Guide: 2783 152

NIOSH Pocket Guide to Chemical Hazards, Chlorpyrifos: chemical description, physical properties, potentially hazardous incompatibilities, and more

Exposure Limits

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 0.1 mg/m3 TWA - Inhalable fraction and vapor; Skin; Appendix A4 - Not Classifiable as a Human Carcinogen

National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 0.2 mg/m3 TWA; 0.6 mg/m3 STEL; Skin

Health Factors

Potential Symptoms: Wheezing, laryngeal spasms; salivation; bluish lips, skin (cyanosis); miosis, blurred vision; nausea, vomiting, abdominal cramps, diarrhea; sweating; dizziness, convulsions, unconsciousness

Health Effects: Cholinesterase inhibition (HE6); LD50 (oral, rat) 82 mg/kg

Affected Organs: Respiratory system, CNS, peripheral nervous system, plasma cholinesterase


  1. OSHA does not have a PEL for chlorpyrifos.
  2. Chlorpyrifos can be absorbed through the skin.
  3. A 1-year study of chlorpyrifos manufacturing workers found a 13% lower mean plasma butyrocholinesterase activity than in a reference group (p<0.002), but no persistent symptoms of weakness or sensory deficits were reported (Albers et al., 2004). In comparison, male human volunteers taking 0.1 mg/kg/day orally for nine days showed a mean inhibition of plasma cholinesterase of about 65% (EPA).
  4. Persistent sensory neuropathy with or without memory impairment was reported in cases of prolonged moderate exposure in enclosed sites fumigated with chlorpyrifos (Kaplan et al., 1993). Cases of deficits in grip strength measured seven weeks or more following hospitalization for chlorpyrifos poisoning have also been reported (Meggs, 2003; Miranda et al., 2002).
  5. Desulfuration by cytochrome P450 2B6 produces the biologically active oxon metabolite, whereas dearylation by cytochrome P450 2C19 detoxifies chlorpyrifos. Detoxification occurs more rapidly than activation in human liver microsomes (Sams et al., 2004).
  6. Urinary excretion of 3,5,6-trichloro-2-pyridinol has been used as a marker of occupational exposure to chlorpyrifos (Albers et al., 2004).

Literature Basis:

  • NIOSH Pocket Guide to Chemical Hazards: Chlorpyrifos.
  • International Chemical Safety Cards (WHO/IPCS/ILO): Chlorpyrifos.
  • US Environmental Protection Agency Integrated Risk Information System: Chlorpyrifos (CASRN 2921-88-2).
  • Albers, J.W., Garabrant, D.H., Schweitzer, S.J., Garrison, R.P., Richardson, R.J. and Berent, S.: The effects of occupational exposure to chlorpyrifos on the peripheral nervous system: a prospective cohort study. Occup. Environ. Med. 61(3): 201-211, 2004.
  • Kaplan, J.G., Kessler, J., Rosenberg, N., Pack, D. and Schaumburg, H.H.: Sensory neuropathy associated with Dursban (chlorpyrifos) exposure. Neurology 43(11): 2193-2196, 1993.
  • Meggs, W.J.: Permanent paralysis at sites of dermal exposure to chlorpyrifos. J. Toxicol. Clin. Toxicol. 41(6): 883-886, 2003.
  • Miranda, J., et al.: Onset of grip- and pinch-strength impairment after acute poisonings with organophosphate insecticides. Int. J. Occup. Environ. Health 8(1): 19-26, 2002.
  • Pohanish, R.P. (editor): Chlorpyrifos. Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens, Fourth Ed., Vol. 1. Norwich, NY: Noyes Publications, William Andrew Publishing, 2002, pp. 602-604.
  • Sams, C., Cocker, J. and Lennard, M.S.: Biotransformation of chlorpyrifos and diazinon by human liver microsomes and recombinant human cytochrome P450s (CYP). Xenobiotica 34(10): 861-873, 2004.

Date Last Revised: 05/18/2005

Monitoring Methods used by OSHA

Primary Laboratory Sampling/Analytical Method (SLC1):

  • sampling media: OSHA Versatile Sampler (OVS-2) - 13 mm XAD-2 tube (270/140 mg sections, 20/60 mesh) with Glass Fiber Filter enclosed
    maximum volume: 480 Liters
    maximum flow rate: 1.0 L/min
    current analytical method: Gas Chromatography; GC/FPD
    method reference: OSHA Analytical Method (OSHA 62)
    method classification: Fully Validated
    note: OSHA personnel may obtain sampling tubes from the Salt Lake Technical Center.

Wipe Sampling Method:

  • sampling media: Glass Fiber Filter

Bulk Method:

  • Limit the amount of bulk submitted to one gram or one mL.

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