In the equation for probability of harm, which two factors are combined?

The correct answer is the combination of toxicity and exposure. In assessing the probability of harm, it is essential to understand both how toxic a substance is (toxicity) and the extent to which individuals come into contact with that substance (exposure). Toxicity indicates the potential severity of the effects that may occur from exposure to a chemical, while exposure refers to the frequency and level of contact with the chemical.

Combining these two factors allows for a comprehensive assessment of risk: a highly toxic chemical poses a greater risk if exposure levels are also high, while a less toxic chemical may present a relatively lower risk even with higher exposure levels. Understanding both elements helps in better predicting and managing the potential harmful effects associated with herbicide application.

Other options, though relevant to discussions of hazard assessment and risk evaluation, do not provide the specific combination necessary for calculating the probability of harm. Concentration and duration focus more on exposure metrics, while hazard and risk are broader categories rather than specific measurable factors. Effect and route of entry relate to the impact and manner of chemical ingress but do not directly quantitatively assess the probability of harm as toxicity and exposure do.