What is the relationship between LD50 and toxicity?

Toxicity and LD50 value have an inverse relationship with each other. The lower the LD50 value, the more toxic the substance is. The higher the LD50 value, the lower the toxicity of the substance. 

LD50 represents the amount of a substance that is enough to cause the death of 50% of a test population. 

A lower LD50 value means it requires a smaller quantity of the substance to cause the death of 50% of the test population indicating that the substance is more toxic and poses a higher risk to that particular population.  

A higher LD50 value means it requires a larger quantity of the substance to cause the death of 50% of the population. This is generally because the substance is less toxic and poses a lower risk to that population.