Toxicity varies inversely with regards to LD50 values. LD50 refers to the quantity of a toxic substance that will kill 50% of test organisms. Higher LD50 values represent lower toxicity levels and vice versa. 

A higher LD50 value implies that a larger quantity of the toxic substance is required to kill 50% of the test organisms. This larger quantity is necessary because of the lower toxicity of the substance. 

A lower LD50 value implies that a smaller quantity of the toxic substance will kill 50% of the test organisms. This smaller quantity is sufficient because of the higher toxicity of the substance.