How are pesticides assigned to toxicity categories?

Pesticides are assigned to toxicity categories according to the highest measured toxicity. This approach ensures that the categorization reflects the potential risk that a pesticide poses to humans and the environment. Toxicity is typically assessed through standardized tests that measure acute toxicity (i.e., effects of a single exposure) and chronic toxicity (i.e., effects over time).

The highest measured toxicity is critical because it helps regulatory bodies and users understand which pesticides require more stringent handling and safety protocols. Pesticides with higher toxicity levels may need specific precautions during storage, application, and disposal to mitigate risks to humans, wildlife, and non-target organisms.

In contrast, the other methods mentioned, such as the lowest measured toxicity or the method of application, do not provide a comprehensive reflection of the inherent danger of a pesticide. Additionally, manufacturer preference is not a scientific basis for toxicity categorization, as safety and health risk assessment must be objective and based on empirical data. This objective methodology is essential for consistent regulations and guidelines that protect both applicators and the environment.