What is the difference between LC50 and EC50?

LC50 (Lethal Concentration 50%) is the average concentration of drug or chemical which is required to kill half of the exposed population of animals or cells in specific conditions.
LC values usually refer to the concentration of a chemical in the air but in environmental studies, it can also mean the concentration of a chemical in water.
Agonists EC50 value is taken into consideration which is plasma concentration to achieve 50% of the maximum effect. EC50 is the effective dose of Agonist that half-maximally activates the channel/enzyme. You establish an EC50 by applying increasing amounts of Agonist to your system and you measure the responses for each dose until you reach saturation - i.e. the point at which increasing the concentration of agonist does not increase the magnitude of the response.