LC50 is defined as:

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LC50 represents the concentration of a pesticide in the environment (air or water) that will kill 50% of the exposed animals under a defined exposure period. It focuses on how much of the substance is present in the medium, not the amount taken per body weight. A lower LC50 means the chemical is more toxic because a smaller concentration is enough to cause death in half the population. This is distinct from LD50, which is about the lethal dose per body weight, usually for ingestion or dermal exposure. The other statements mix up dose versus concentration or specify ingestion, which is not what LC50 measures—the key point is the concentration in the environment that leads to 50% mortality under defined conditions. For example, if a pesticide has an LC50 of 2 mg/L in water for fish, exposing fish to 2 mg/L for the specified time would be expected to kill about half of them.