Toxicity of herbicides
Pesticides usually have several toxicity ratings. They are oral, dermal, acute and chronic.
Oral toxicity
The oral toxicity of a herbicide is determined by laboratory testing at various doses. From these trials the LD50 value is calculated. This is the amount of chemical tested in animals, expressed as mg of active ingredient per kilogram of body weight, required to kill 50% of the test group (usually rats or mice). The lower the LD50 number, the more toxic is the chemical.
| Caffeine | DDT | Aspirin | Penicillin | Salt | Petroleum oils |
|---|---|---|---|---|---|
| 150mg/kg | 420mg/kg | 750mg/kg | 1000mg/kg | 3000mg/kg | 1000– 10 000mg/kg |
| Trade name | Active ingredient | Oral LD50mg/kg | Dermal LD50mg/kg |
| 2,4-D | 2,4-D | 639–764 | >1600–2400 |
| 2,4-DB | 2,4-DB | 700 | n/a |
| Ally®/Brush-off® | metsulfuron methyl | >5000 | >2000 |
| Amitrole | amitrole | 1100–24 600 | >2500–10 000 |
| Atrazine | atrazine | 1869–3090 | >3100 |
| Basta® | glufosinate | 2000 | >4000 |
| Broadstrike™ | flumetsulam | >5000 | >2000 |
| Bromicide® | bromoxynil | 190-270 | >2000 |
| Casoron® | diclobenil | 2700-6000 | >2000 |
| Diuron | diuron | 3400-3700 | >2000 |
| DSMA | DSMA | 1800-2800 | >10 000 |
| Eclipse® | metosulam | >5000 | >2000 |
| Garlon™ | triclopyr | 713 | >2000 |
| Glean®, Lusta™ etc | chlorsulfuron | 5545 | >2500 |
| Gramoxone® | paraquat | 112-150 | 911 |
| Hoegrass® | diclofop-methyl | 481–693 | >5000 |
| Hyvar® X, Bromacil | bromacil | 2000 | >5000 |
| Kamba, Banvel™ | dicamba | 1707 | >2000 |
| Linuron | linuron | 1000-4000 | >2000 |
| Logran® | triasulfuron | >5000 | >2000 |
| Londax® | bensulfuron | >5000 | >2000 |
| Lontrel™ | clopyralid | >4300 | >2000 |
| MCPA | MCPA | 800 | >4000 |
| MCPB | MCPB | 4700 | >2000 |
| Propon | 2,2-DPA | 3860-9330 | >2000 |
| Ramrod® | propachlor | 1200 | >20 000 |
| Reglone® | diquat | 230–440 | >793 |
| Roundup® | glyphosate | 5600 | >5000 |
| Simazine | simazine | 500–10 000 | >2000 |
| Spinnaker® | imazethapyr | >5000 | >2000 |
| Spray.Seed® | paraquat + diquat | 150 | 911 |
| Starane™ | fluroxypyr | 2450 | >5000 |
| Terbutryn | terbutryn | 500–2500 | >2000–20 000 |
| Tigrex® | diflufenican | >2000 | >2 000 |
| Tordon™ 75D | 2,4-D + picloram | n/a | n/a |
| Tordon™ Double Strength | triclopyr + picloram | n/a | n/a |
| Tordon™ granules | picloram | 8200 | >2000 |
| Tribunil® | methabenzthiazuron | >5000 | >5000 |
| Trifluralin | trifluralin | >5000 | >5000 |
| Velpar® | hexazinone | 1 690 | >5278 |
* The above acute LD50s for herbicides commonly used in Western Australia were extracted from 'The Pesticide Manual: a world compendium' (12th edition) 2000, the British Crop Protection Council.
Although the toxicity of some herbicides varies with the route of entry into the body (oral, inhalation, dermal), in general, the acute oral LD50 figures gives a good indication of the relative toxicity of the herbicide. The poison schedule is dependent on other factors as well as LD50 of the product. For example, all arsenics are carcinogenic and hence are placed in the S7 category.