This page discusses the LD50, a key metric for assessing chemical toxicity, defined as the dose needed to kill 50% of test animals. A lower LD50 signifies higher toxicity, but results can vary by admi...This page discusses the LD50, a key metric for assessing chemical toxicity, defined as the dose needed to kill 50% of test animals. A lower LD50 signifies higher toxicity, but results can vary by administration method and species differences. Ethical concerns about animal testing have led to ongoing efforts since 2000 to replace LD50 testing with alternatives that minimize animal deaths.