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Review of Chlorpyrifos - Chemistry Assessment
Interim review -
NRA Review Series 00.5 - September 2000
Section 2
CONTENTS
- 1. OVERVIEW
- 2. DECLARATION OF COMPOSITION (DOC) FOR CHLORPYRIFOS TGAC
- 3. ACTIVE CONSTITUENT
- 3.1. Chemical Identity
- 3.2. Physical and Chemical Properties
- 3.3. Chemistry Aspects
- 4. FORMULATION OF END-USE PRODUCT
- 5. DECLARATION OF COMPOSITION
- 6. CONCLUSION
- 7. BIBLIOGRAPHY
1. OVERVIEW
Chlorpyrifos is an organophosphorus insecticide used for the control of Coleoptera, Diptera, Homoptera and Lepidoptera in soil or on foliage in a wide range of crops. Crops include fruit (pome, stone and citrus fruit, strawberries, figs, bananas), nuts, vines, vegetables (potatoes, asparagus), grains (rice, cereals, maize, sorghum), cotton, mushrooms and ornamentals. The mode of chlorpyrifos action is non-systemic, and exposure of insects to the active (via contact, ingestion and/or inhalation) affects the nervous system by inhibiting the activity of acetyl cholinesterase.
Chlorpyrifos is included in Schedule 6 of the SUSDP, although formulations containing chlorpyrifos concentrations of 5 % or less are included in Schedule 5.
The physico-chemical properties of chlorpyrifos are given in Appendix 1, along with the relevant chemistry details.
There are 13 chlorpyrifos TGAC manufacturers currently approved in Australia. The chemistry aspects (synthetic process, quality control procedures, batch analysis results and analytical methods) were evaluated previously and found acceptable.
2. DECLARATION OF COMPOSITION (DOC) FOR CHLORPYRIFOS TGAC
Details of the 13 chlorpyrifos TGAC manufacturers are tabulated below. Also included in the table are details of: (i) the purity of chlorpyrifos; (ii) the specification limit for the toxic micro-contaminant sulfotep (O,O,O,O-tetraethyldithiopyrophosphate); and (iii) an indication of whether all impurities which could be present at a concentration of 1 g/kg or more are listed in the DoC.
| Licensed Chlorpyrifos Manufacturer | TGAC Approval No. | Chlorpyrifos purity | Sulfotep levels | Other Impurities listed in DoC |
| Dow Chemical Company, Michigan, USA | P44112 | NLT 990 g/kg | NMT 0.3 g/kg | 3 |
| P44113 | NLT 990 g/kg | NMT0.3 g/kg | 3 | |
| P44160 | NLT 970 g/kg | NMT 2 g/kg | 3 | |
| Dow AgroSciences Ltd, Norfolk UK | P44111 | NLT 970 g/kg | NMT 2 g/kg | 3 |
| P49340 | NLT 180 g/kg | * | N/A | |
| Luxembourg Industries (Pamol) Ltd, Tel-Aviv, Israel | P46670 | NLT 940 g/kg | NMT 2 g/kg | 3 |
| P48643 | NLT 990 g/kg | NMT 0.3 g/kg | 3 | |
| Lupin Agrochemicals Inc, India | P46796 | NLT 940 g/kg | NMT 2 g/kg | 3 |
| Makhteshim Chemical Works Ltd, Israel | P44005 | NLT 970 g/kg | ** | 3 |
| Ficom Organics Ltd, India | P46642 | NLT 940 g/kg | NMT 2 g/kg | 3 |
| Gharda Chemicals Ltd, India | P46888 | NLT 980 g/kg | NMT 2 g/kg | 3 |
| Hubei Sanonda Company Ltd, China | P47254 | NLT 940 g/kg | Not detectable | 3 |
| Aimco Pesticides Ltd, India | P48459 | NLT 940 g/kg | NMT 2 g/kg | 3 |
| 3M Canada Inc, Ontario | P49124 | NLT 190 g/kg | * | N/A |
| Excel Industries Ltd, Bombay, India | P47155 | NLT 960 g/kg (965 g/kg) | NMT 2 g/kg | 3 |
| Mitsu Industries Ltd, India | P48077 | NLT 940 g/kg | NMT 2 g/kg | 3 |
| Cheminova Agro A/S, Denmark | P48521 | NLT 960 g/kg | NMT 2 g/kg | 3 |
NLT: Not Less Than; NMT: Not More Than; N/A: Not Applicable
*The manufacturing concentrate is prepared using chlorpyrifos TGAC that has a maximum sulfotep concentration of 2 g/kg. Hence, the levels of impurities in the manufacturing concentrate will not exceed those present in the technical material.
**Sulfotep was not listed on the DoC. However, the manufacturer tested for the presence of the impurity, and determined that it was not detected.
Chlorpyrifos purity: The FAO Specification Limit for chlorpyrifos technical is 940 g/kg minimum. The NRA approved sources of chlorpyrifos TGAC have minimum chlorpyrifos limits of between 940 g/kg and 990 g/kg.
Impurities: All impurities that could be present in the chlorpyrifos TGAC (at concentrations of 1 g/kg or more) were listed in the DoCs. The specification limit for O,O,O,O- tetraethyldithiopyrophosphate (sulfotep) was 2 g/kg maximum, with the highest purity (99%) chlorpyrifos TGACs specifying a sulfotep limit of 0.3 g/kg maximum.
Toxic Impurities: It is considered that other compounds of toxicological significance (N-nitrosamines, halogenated dibenzo-pi-dioxins, or halogenated dibenzofurans and PCBs) are not expected in chlorpyrifos TGAC due to the raw materials and synthetic route used.
Manufacturing concentrates: There are two approved sources of chlorpyrifos manufacturing concentrates, containing a minimum of 180 to 190 g/kg chlorpyrifos. In manufacturing concentrates, the chlorpyrifos is present in a micro-encapsulated form (0.5 µm polyurea coating) that is suspended in an aqueous mixture. The capsule wall protects the chlorpyrifos from any physical damage, enabling the concentrate formula to withstand the effects of strong acids and bases. Since the manufacturing concentrate is prepared using the chlorpyrifos TGAC, any impurities present will not exceed those present in the technical material.
3. ACTIVE CONSTITUENT
3.1. Chemical Identity
Chlorpyrifos is a broad-spectrum organophosphorus pesticide, displaying insecticidal activity against a wide range of insect and arthropod pests. Technical chlorpyrifos has a minimum purity of between 940 and 990 g/kg. Manufacturing concentrates contain a minimum of 180 to 190 g/kg chlorpyrifos.
| Common name: | Chlorpyrifos |
| UPAC Name: | O,O-diethylO-3,5,6-trichloro-2-pyridyl phosphorothioate |
| CA Name: | O,O-diethylO-(3,5,6-trichloro-2-pyridinyl) phosphorothioate |
| CAS Registry No.: | 2921-88-2 |
| Empirical formula: | C9H11Cl3NO3PS |
| Molecular weight: | 350.6 |
| Structural formula: |  |
3.2. Physical and Chemical Properties
| Physical and chemical properties of the pure active constituent | |
| Colour | white/colourless crystalline solid |
| Odour | odourless |
| Physical state | crystalline solid |
| Melting point | 41 to 43.5 oC |
| Octanol/water partition coefficient (Log P) 4.70 (McDonald et al., 1985) | |
| Vapour pressure | 1.87 x 10-5 mm Hg (2.5 mPa) at 25 oC (Brust, 1964) |
| Density/specific gravity | 1.38 g/cm3 at 46 oC |
| Dissociation constant | Chlorpyrifos does not contain any readily dissociable groups |
| Solubility in water | 2 mg/L at 23 oC (Hummel and Crummet, 1964); 1.39 mg/L at 25 oC (Drummond, 1986) |
| Solvent solubility | Benzene - 7900 g/kg; acetone - 6500 g/kg; chloroform - 6300 g/kg; carbon disulfide - 5900 g/kg; carbon tetrachloride - 3100 g/kg; chloroform - 6300 g/kg; diethyl ether - 5100 g/kg; ethanol - 630 g/kg; ethyl acetate - >2000 g/kg; isooctane - 790 g/kg; methanol - 450 g/kg; methylene chloride - 4000 g/kg; propylene glycol - 40 g/kg; toluene - 1500 g/kg; trichloroethane - 4000 g/kg; triethylene glycol - 50 g/kg; xylene - 4000 g/kg (Drummond, 1986; Hummel and Crummet, 1964); |
| Stability | Chlorpyrifos is stable in air (non-volatile) and is not sensitive to UV radiation. It is stable to neutral and weakly acidic solutions, but is hydrolysed by strong bases. Chlorpyrifos is thermally sensitive to temperatures over 50 oC, and undergoes violent exothermic decomposition above 130 oC. The half-life of the aqueous methanolic solution at pH 6.0 is 1930 days. |
| Hydrolysis | The rate of chlorpyrifos hydrolysis increases with both pH and temperature. At 25 oC, pH 8 t½ = 23 days
At pH 7.0, 35 oC t½ = 12 days
|
| Corrosiveness | corrosive to copper and brass |
| Hazchem code | 2WE |
| Fire and explosion hazard | Unknown |
| Extinguishing media | Dry chemical, water spray or regular foam |
| Hazardous combustion products | Thermal decomposition may release toxic and/or hazardous gases |
| Physical and chemical properties of the TGAC | |
| Colour | White to light yellowish-brown crystalline solid |
| Odour | mild mercaptan odour |
Other characteristics are as listed above for the pure active constituent.
3.3. Chemistry Aspects
The chemistry aspects (manufacturing process, quality control procedures, batch analysis results, and analytical methods) of chlorpyrifos TGACs were evaluated and found acceptable.
4. FORMULATION OF END-USE PRODUCT
Chlorpyrifos is used in a formulated form as a broad spectrum insecticide for the control of Coleoptera, Diptera, Homoptera and Lepidoptera in soil or on foliage in a wide range of crops. Crops include fruit (pome, stone and citrus fruit, strawberries, figs, bananas), nuts, vines, vegetables (potatoes, asparagus), grains (rice, cereals, maize, sorghum), cotton, mushrooms and ornamentals. The chlorpyrifos formulations are available as emulsifiable concentrates (EC), baits, granules, ultra-low volumes (ULV), liquid concentrates (LC), wettable powders (WP) and dusts. The mode of chlorpyrifos action is non-systemic, and exposure of insects to the active (via contact, ingestion and/or inhalation) affects the nervous system by inhibiting the activity of acetyl cholinesterase.
5. DECLARATION OF COMPOSITION
The FAO monograph specifications for the Technical chlorpyrifos are listed below:
| Chlorpyrifos content: | not less than 940 g/kg |
| Impurities: | Water: 1 g/kg maximum |
| Acetone insolubles: | 5 g/kg maximum |
Chlorpyrifos TGACs from 13 approved sources comply with the FAO specifications for the content of the active constituent (the minimum chlorpyrifos limits are between 940 g/kg and 990 g/kg).
Toxic Impurities
The specification limit for the toxic impurity sulfotep (O,O,O,O-tetraethyldithiopyrophoshate) is 2 g/kg maximum. All of the approved chlorpyrifos TGAC sources comply with this sulfotep specification, and the highest purity chlorpyrifos TGACs (99%) specify a sulfotep limit of 0.3 g/kg maximum. The levels of sulfotep in the Manufacturing Concentrates do not exceed those present in the technical material, since the Manufacturing Concentrates are prepared using the chlorpyrifos TGAC.
Other compounds of toxicological significance (N-nitrosamines, halogenated dibenzo-pi-dioxins, or halogenated dibenzofurans and PCBs) are not expected in chlorpyrifos TGAC due to the raw materials and synthetic route used.
6. CONCLUSION
The NRA will introduce a compositional standard for all chlorpyrifos TGACs which is based on the latest FAO specifications for this chemical. In addition, the level of sulfotep should be ≤2 g/kg.
7. BIBLIOGRAPHY
Brust H.F. (1964) A summary of chemical and physical properties of O,O-diethyl-O-(3,5,6-trichloro-2-pyridinyl)phosphorothioate. DowElanco, Indianapolis, IN (unpublished report).
Drummond J.N. (1986) Solubility of chlorpyrifos in various solvents. DowElanco, Indianapolis, IN (unpublished report).
Hummel R.A. and Crummet W.B. (1964) Solubility of ethel O,O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothioate in various solvents. DowElanco, Indianapolis, IN (unpublished report).
McDonald I.A., Howes, D.A. and Gillis, N.A (1985) The determination of the physicochemical parameters of chlorpyrifos. DowElanco, Indianapolis, IN (unpublished report).