What does a low LD50 value indicate about a substance?

A low LD50 value indicates that a substance is more toxic. The term LD50 refers to the lethal dose required to kill 50% of a test population, usually laboratory animals, under controlled conditions. When the LD50 value is low, it means that only a small amount of the substance is needed to cause death in a significant percentage of the population. This reflects a higher level of toxicity, as it suggests that the substance can have harmful effects at lower exposures.

In contrast, a high LD50 value implies that more of the substance is required to achieve the same lethal effect, indicating lower toxicity. Thus, understanding the significance of LD50 values is essential for evaluating the safety and risk associated with chemical substances, especially in agricultural settings where herbicide applicators must make informed decisions about the products they use.