In short
Pesticide toxicity classes group active substances by acute hazard to people.
The WHO scheme sorts them into Ia, Ib, II, III and U from the rat LD50 by mouth and on skin. The class describes short-term poisoning risk, not harm to bees, soil or water, and the registered product label always wins. Planva has fields for the toxicity class and the bee isolation period in its crop protection catalogue. The class is a four-step field, 1 to 4, not the WHO scale.
What a toxicity class measures
The WHO classification looks at acute risk: the risk to a person handling a product from a single exposure or several exposures over a short time. It is built on the LD50, the dose in milligrams per kilogram of body weight that kills half of a group of test animals. The rat is the default animal. A lower LD50 means a smaller dose is enough to do harm, so the class is more hazardous.
Chronic effects are a separate question, and the WHO class does not cover them. A substance can sit in a low acute class and still raise long-term concerns.
The WHO classes and their limits
| Class | Name | Oral LD50, mg/kg | Dermal LD50, mg/kg |
|---|---|---|---|
| Ia | Extremely hazardous | Below 5 | Below 50 |
| Ib | Highly hazardous | 5 to 50 | 50 to 200 |
| II | Moderately hazardous | 50 to 2000 | 200 to 2000 |
| III | Slightly hazardous | Over 2000 | Over 2000 |
| U | Unlikely to present acute hazard | 5000 or higher | 5000 or higher |
Active ingredient or finished product
The WHO tables classify technical grade active ingredients. They are a starting point. The final class of a product is meant to be set for the formulation, ideally from toxicity data the manufacturer measured on that formulation. Only when those data are missing does WHO give a calculation that extends the active ingredient value to the product.
Two routes are checked. The oral value is used unless the dermal value puts the substance in a more hazardous class, and the stricter result decides. This is why two products with the same active ingredient can carry different classes.
What the class means on a label
- Classes Ia and Ib. WHO says the label should carry a symbol for a high degree of hazard, usually a skull and crossbones, and a signal word such as POISON or TOXIC.
- Poisoning information. For Ia and Ib the label should also give symptoms and immediate treatment.
- Precautions in every class. WHO notes that even substances listed as unlikely to present acute hazard need the precautions used with any chemical.
The WHO text is a reference scheme. Protective equipment and handling come from the registered label and local rules. Your national register may use its own wording or the GHS categories, so read the class next to the product, not from memory.
What a class does not tell you
- Bees and other non-target species. Bee hazard and isolation periods are set per product on the label.
- Chronic and long-term effects. The WHO class is about acute toxicity.
- Dose and use. The class says nothing about the rate, the spray volume or the waiting period for a given crop.
How this works in Planva
- Catalogue. Crop protection products with active substances, a toxicity class and a bee isolation period.
- Class scale. The toxicity class is a four-step field, 1 to 4, that you select for a product. It is not the WHO Ia to U scale, and the field is optional.
- Registered products. Products added from the state register carry the registration number and the regulations: crop, pest, rate, spray volume and waiting period.
- What Planva does not do. It stores the class from the product data. It does not assign a class or tell you which product to use.
To see how product, rate and field come together in a record, read the guide to spray records. For the work that comes before the spray decision, see crop pest monitoring.
Sources
Common questions
They are groups of pesticides ranked by acute hazard to people. In the WHO scheme the classes are Ia, Ib, II, III and U, set from the rat LD50 by mouth and on skin.
The real Planva interface, shown with test data.
