How are pesticides assigned toxicity categories?

Pesticides are assigned toxicity categories primarily based on their acute toxicity levels, which reflect the potential harm they can cause to humans and the environment upon short-term exposure. The acute toxicity is assessed using standardized laboratory tests that evaluate how easily a substance can cause adverse effects after a single dose or exposure. This assessment is usually indicated by the pesticide's LD50 value, which measures the lethal dose required to cause death in 50% of a test population, typically laboratory animals. The lower the LD50 value, the more toxic the pesticide is considered, leading to its classification in a higher toxicity category.

Other factors, such as the pesticide's formulation, route of exposure, and specific use conditions, also contribute to its toxicity categorization. However, the fundamental basis for classification rests on acute toxicity levels, making it a critical criterion in determining the safety and regulatory requirements for pesticide use.