Which term describes the effectiveness of a substance after repeated low-dose exposure?

Chronic toxicity refers to the harmful effects of a substance that occur after prolonged exposure, often at low doses. This term is particularly relevant in scenarios where an organism is exposed to a chemical or toxin over an extended period, which can lead to cumulative effects that may not be immediately apparent. Unlike acute toxicity, which is characterized by harmful effects resulting from a single, high exposure, chronic toxicity is more about the long-term implications of consistent exposure, even if each individual exposure may not cause immediate harm.

In the context of aquatic environments and pesticide application, understanding chronic toxicity is essential because many substances can persist in the environment and continuously affect aquatic organisms over time. Knowledge of chronic toxicity allows for better risk assessment and management strategies to protect aquatic ecosystems.

Other terms like acute toxicity and immediate toxicity focus on short-term effects, whereas residual toxicity relates to the activity of a pesticide remaining on surfaces after application, rather than the repeated low-dose exposure scenario described in the question. Thus, chronic toxicity is the most suitable choice for this situation.