CHLORPYRIFOS

Chemical Name : 0,0-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate

Category: Organophosphate

Physical Properties:

CAS Number: 2921-88-2
Description: Technical chlorpyrifos is an amber to white crystalline solid with a mild sulfur odor
Molecular formula: C₉H₁₁Cl₃N0₃PS
Molecular weight: 350.62
Melting point/Boiling point: 41.5-44 C
Solubility: water: 2 mg/L @ 25 C; Soluble in organic solvents.
Vapour Pressure: 2.5 mPa @ 25 C [13]

Usage:

Chlorpyrifos is a broad spectrum insecticide used on wide variety of crop types, for  the control of locusts  and is present in some cattle dips for the control of ticks and lice.

Chlorpyrifos is also used in domestic gardens; as indoor insect control, as a termiticide, and for pet products.

Regulatory Standards:

AUSTRALIAN GUIDELINES
TWA: 0.2 mg/m³
STEL: no guideline

OVERSEAS GUIDELINES
0.2 mg/m³ OSHA TWA (skin)
0.2 mg/m³ ACGIH TWA (skin)                                    (9)

The US EPA has established a 24-hour reentry interval for crop areas treated with emulsifiable concentrate or wettable powder formulations of chlorpyrifos unless workers wear protective clothing.(13)

HEALTH EFFECTS:

Acute Toxicity

Chlorpyrifos is very toxic to humans, between 1 teaspoon and 1 ounce may be fatal. (6)  Chlorpyrifos toxicity is considerably greater if administered orally compared to dermal exposure. (8)  Primary routes of exposure are inhalation, skin or eye contact.  Inhalation exposure to high concentration may cause upper respiratory irritation, central nervous system depression, headache, dizziness, increased sensitivity to epinephrine, irregular heartbeats, incoordination, muscle twitching, tremor, pinpoint pupils, blurred vision, tightness in chest, and convulsions.  Eye contact may cause pain, moderate irritation.(6)

Poisoning may impair Central Nervous System.  (2)

Chronic Toxicity

Continual absorption at intermediate dosage may cause an influenza-like illness which includes symptoms like weakness, anorexia and malaise.(2, 13) Other chronic exposure effects may include behavioural neurotoxicity and organo-phosphate induced delayed neuropathy. (8)

Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure. Other effects reported in workers repeatedly exposed include impaired memory and concentration, disorientation, severe depressions, irritability, confusion, headache, speech difficulties, delayed reaction times, nightmares, sleepwalking and drowsiness or insomnia. An influenza-like condition with headache, nausea, weakness, loss of appetite and malaise has also been reported (13).

Carcinogenicity

Chlorpyrifos is not considered to be a carcinogen by the National Toxicology Program, the International Agency for Research on Cancer, or the Occupational Safety and Health Administration.   (1)

Mutagenicity

US EPA classifies chlorpyrifos as not mutagenic, though mutagenic effects were observed in fruit flies given oral concentrations of 50 parts per billion of chlorpyrifos for 3 days (13).

Chlorpyrifos was also mutagenic in microbial inhibition assays.(5)

Teratogenicity and Reproductive effects

US EPA has determined that chlorpyrifos is not teratogenic. (2)

In one experiment developmental NOEL was 10mg/kg/day (13). 

An experimental teratogen (7)

US EPA has determined that chlorpyrifos does not adversely affect reproduction. In two studies reviewed by the US EPA, no effects were seen in the animals tested at dose levels up to 1.2 mg/kg/day (13).

Fate in Humans

Animal studies suggest that Chlorpyrifos is rapidly absorbed and metabolised to 3,5,6-trichloro-2-pyridinal (TCP) with the parent compound and metabolite being excreted in the urine. (2)

Yet, the metabolite 3,5,6-trichloro-2-pyridinol was detected in urine of 5.8% of 6990 samples from general population (1976-80) with a mean in urine of pest controllers in Texas of 5.6-8.3 ug/l.(10)

More recent sampling from the US Environment Protection Agency Preliminary Risk Assessment October 1999, reports “measurable concentrations of the primary metabolite, 3,5,6-trichloro-2-pyridinal (TCP) in the urine of 92% of adults and 89% of children tested. (14)

ACTION ON ANIMALS
Chlorpyrifos is very highly toxic to freshwater fish, aquatic invertebrates and estuarine and marine organisms and moderately to very highly toxic to birds. (2)

Aquatic and general agricultural uses of chlorpyrifos pose a serious hazard to wildlife and honeybees. (10)

Chlorpyrifos was detected in 1990 sampling of three eggs of Little Terns (0.06-0.36ppm), one liver sample from Little Terns (0.02ppm) and one Pelican egg (0.5ppm) from the Wallace Lake Colony, central coast of NSW.  (12)

When applied to freshwater ponds, cladocerans and copepods were killed and a 42% mortality rate in Mallard ducklings. (8)

Chlorpyrifos residues have been detected in the kidney and fat from cattle dipped once in a 0.025% emulsion. Fats of Australian cattle contained the breakdown product, 0,0-diethyl 0-(3,6-dichloro-2-pyridyl) phosphothioate after being treated with chlorpyrifos for cattle tick.(8)

Animal Toxicity Data 

Acute Oral     163mg/kg   Toxicity Category 11

Acute Dermal   1505mg/kg  Toxicity Category 11

Avian Oral      76mg/kg

Freshwater fish : Rainbow Trout    3ppm

Two studies carcinogenicity studies were submitted were to USA EPA, neither suggest

carcinogenicity. (2)

EPA evaluated 3 reproductive health studies and determined that Chlorpyrifos is not teratogenic at levels up to 25mg/kg. Chlorpyrifos does not produce reproductive effects at dose levels up to 1.2mg/kg/day.  (2)

Two assays in bacterial systems are weakly positive for DNA damage.  (3)

Action on Plants
Chlorpyrifos may be toxic to some plants, such as head lettuce. Residues remain on plant surfaces for approximately 10-14 days. Data indicate that this insecticide and/or its soil metabolites can accumulate in certain crops (13).

FATE IN THE ENVIRONMENT
US EPA considers that there is insufficient data to fully assess the environmental fate of Chlorpyrifos. (2) 

Chlorpyrifos is tightly adsorbed by soil and not expected to leach significantly. Volatilisation from soil surface will contribute to loss (10). Depending on soil type, microbial metabolism of Chlorpyrifos may have a half-life of up to 279 days.(2) Higher soil temperatures, lower organic content and lower acidity increases degradation of chlorpyrifos.

When applied to sandy soil, a 50% loss was noted after 2 weeks and when applied to high organic matter soil, a 50% loss was noted after 8 weeks. (8)

Chlorpyrifos inhibits nitrification and nitrogen fixation marginally, many bacterial strains were unable to degrade it but some micro-organisms can use chlorpyrifos as their only source of carbon and nitrogen.(8)

If released to water, chlorpyrifos partitions significantly from water column to sediments. Hydrolysis half-life at 25C in neutral conditions is 35-78 days. Photolysis half-life at water surface in mid-summer is approx. 3-4 weeks.  The desorption from sediment can contribute to long term residual concentration in water column. (10)

If released to air will react in vapor phase with photochemically produced hydroxyl radicals with half life 6.34 hours. Detected in 14/123 ambient air samples collected at 10 U.S. locations (1980) with maximum concentration of 100ng/m3 and mean of 2.1ng/m3. (10)

Air in 16 houses treated for subterranean termites according to label instructions average 1.38-3.07 ug/m3 one year after treatment and 1.32-1.82 ug/m3, 2 years after treatment. These were above the air equivalent of Acceptable Daily Intake set by New York Department of Health: 1.0ug/m3 (adult) and 0.49 ug/m3 (child). (11)

* Disclaimer: These sheets are designed as summary information and as such

are a guide only.

References:

1. Canadian Centre of Occupational Health Database - CCINFO 1991.

2. EPA Pesticide Fact Sheet, Chlorpyrifos 1984

3. EPA Chlordane, Heptachlor Aldrin & Dieldrin 1987 Technical Support

  Document.

4. Pesticides and Human Health, W.H.Hallenbeck&K.M.Cunningham-Burns School

  of Public Health, University of Illinois Chicago, Springer-Verlag   1985

5. Contemporary Issues in Pesticide Toxicology & Pharmacology, Dr Judith

  Marquis, Associate Professor of Pharmacology,Boston Uni. Karger 1986

6. Oil & Hazardous Materials - Technical Assistance Data System, US EPA

7. Irving Sax, N. & Lewis, R.J. “Dangerous Properties of Industrial Materials” Seventh Edition , Van Nostrand Reinhold 1989 N.Y. USA

8. Centre for Human Aspects of Science and Technology, Pub 1., Chlorpyrifos

9.  Exposure Standards for Atmospheric Contaminants in the Occupational Environment

    [NOHSC:3008(1995)] http://www.nohsc.gov.au/databases/exp/az/chlorpyrifos.htm

10. Handbook of Environmental Fate and Exposure Data for Organic Chemicals,

Ed. P.H.Howard  Lewis Pub. Michigan 1991

11. Dr Mary O'Brien , Chlorpyrifos, Journal of Pesticide Reform, Vol8 No4 1989

12. NSW Department of Agriculture, Pesticide Analysis No. CP90/633-635

   Re: Pelican Eggs, Little Tern - Wallace Lake Colony

13. E X T O X N E T, Extension Toxicology Network Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program available at

http://ace.orst.edu/cgi-bin/mfs/01/pips/chlorpyr.p93

14. Comments of New York State Attorney general Elliott Spitzer.  In re: United States Environmental Protection Agencies Preliminary Risk Assessment for Chlorpyrifos Reregistration Eligibility Decision, Docket Control Number 0PP – 34203, December 27, 1999, amended January 3, 2000.