What is your understanding of LD50? Do you know its significance for evaluating a toxicant’s lethality? Do you know the limits and weaknesses of LD50? If you haven’t heard of LD50, it is an acronym for Lethal Dose 50%. Typically, LD50 is listed as milligrams per kilogram as in milligrams of the pure toxicant per kilograms of the animal’s weight. The lower the milligram number the more lethal the toxicant is. For example, an LD50 of 1000 mg/kg is less toxic than say 5 mg/kg.
How the LD50 is Determined
Researchers take say, 20 mice and feed them a dose of poison being careful to measure the amounts given. When 50% of the study population dies, then they determine how many milligrams were need per kilogram of mice to kill 50%. Keep in mind that LD50 is based on an acute dose. That means the finding is for a single event poisoning. LD50 does not refer to chronic poisoning or when a little amount of poison is given over a long-period of time. In other words, LD50 is based on how much poison would an animal have to eat in a single feeding to kill it?
Weaknesses of LD50
The weaknesses of LD50 are: 1. It is based solely on a single dose. While there is nothing inherently wrong with evaluating single dose toxicity, some toxicants, such as first generation anticoagulant toxicants are not single dose poisons. So it could be argued that the LD50 underestimates the true toxicity of first generation anticoagulants (e.g. warfarin, chlorophacinone and diphacinone) because first generation anticoagulants are actually more toxic when a little is taken daily over several days. In other words, it takes less first generation anticoagulant to kill a mouse if the mouse eats a little over several days than what the mouse would need to eat to kill it in a single dose. For example, a mouse may need to eat 20 mg of anticoagulant to kill it in one dose but only 5mg to kill it if it ate 1mg/day for five days.
The second problem with LD50 is that it is a snap shot. It doesn’t tell us if the toxicant is additional amounts of toxicant are more lethal in a linear mode or if its more toxic logorithmically. For example, a toxicant may have an LD50 of 5mg/kg and another toxicant may also have an LD50 of 5mg/kg. But if we looked at the research data, we might see that when 6mg/kg of toxicant A were given to mice, 75% of the study population died. Whereas with toxicant B giving 6 mg/kg only killed 55% of the study population. Notice how two products have the same LD50 but when evaluating their total toxicity, toxicant A is significantly more lethal when more is added. (This fact is why following the label is not only the law but ensures that the product is being used in as safe a manner as practical).
Bottom Line
Understanding LD50 is important to know as it is a useful way to compare the toxicity of different pesticides. However, it is not perfect. Understanding LD50 and its weaknesses will help you use toxicants more safely and effectively.
Stephen M. Vantassel, CWCP, ACE, is the owner of Wildlife Control Consultant, LLC. He helps people restore their balance with nature through publishing, training, consulting, and the internet. He has published numerous articles in trade and academic publications available at {Stephen’s Academia.edu Page} along with several books {WCC Store}). Listen to his podcast “Living the Wild Life” at {Pest Geek Podcast}. Please subscribe to {Stephen’s YouTube Channel} He is a sought after speaker and trainer. If you would like to have Stephen speak at your event or use his consultation services, send an e-mail to wildlifecontrolconsultant@gmail.com. Copyright All postings are the property of Stephen M. Vantassel and Wildlife Control Consultant, LLC. Text (not images) may be reprinted in non-profit publications provided that the author and website URL is included. If images wish to be used, explicit and written permission must be obtained from Wildlife Control Consultant, LLC.