Stephen Vantassel here wildlife control consultant. Wanted to talk today about L.D. 50 and understanding LD 50 as motive. Many of you know I’m involved in vertebrate control so the role of pesticides to control vertebrates raises a lot of issues and concerns about the relative toxicity of some of these toxic loans fume against that are being used to control unwanted pest vertebrates. So let’s back up a little bit and talk about the relationship between notions of risk and harm.
Now on another podcast I would kind of been deep in the notion of risk here, I’m not gonna go as far deep into that as before but I do want to give you concept to help you understand the difference between understanding risk and understanding what harm is. Because these are two different concepts. Risk is the probability or the potential for a negative event or the probability of harm that something bad is going to happen harm.
The concept of harm is what is the actual effect of that negative event so risk is the potential.
The likelihood that something bad is going to happen harm is it is an analysis or discussion of what that actual negative event actually is. So when we’re talking about LD 50. We really focusing in we’re drilling down on this notion of harm. What is this. What is the harmful
Effects of this particular toxic and or fumigate or many of your cases because many of you deal with bugs of this particular pesticide. So let’s kind of drill into that a little bit now if you’re heard by other podcast you would have heard me talk about how hazard or risk is exposure times toxicity.
And so we’re going to be focusing not on the exposures side but we’re going to be focusing on the toxicity side. That’s that that harm element of this particular toxicity. How lethal is this particular element. And even under toxicity we have to be breaking it down a little bit more. Our focus is going to be on its lethality not the toxicity in terms of its persistence. That’s a different question. We’re looking at the acute effects of the problem not the long term effects. Now acute effects are typically defined in pesticide use as what the effect of a pesticide is that occurs within twenty four hours
Long. The long term effects are beyond 24 hours in some cases some pesticides may have effects for years. But when we’re dealing with LV 50s we’re looking at acute toxic effects. All right so let’s kind of talk about
Understanding relative toxicity. Now L.D. 50 which stands for Lethal Dose 50 percent it’s symbolized as capital L capital D with a subscript number of 50 Five 0. That’s typically how it sits it’s so we call it L.D. 50 Lethal Dose 50 percent. Now what it is it’s a a formulaic way to give a number to how potentially lethal this particular product is and it’s often given in the sense of milligrams per kilogram. How much is needed to kill 50 percent of the test subject. So if you have 20 animals how many how much of the dose at a 50 milligram per kilogram rate do you need to kill 50 percent of those animals which would be in this case 10 so let’s talk about milligrams and kg so a milligram is one millionth Of a kilogram. Now if you’re trying to we know we’re not we don’t really use metric much in the United States but I think that’s probably changing over time.
So let’s kind of look at that a little bit closer. KG is about two point two pounds so if you’re dealing with a if I told you the LDA 50 was 10 milligrams per kilogram in the dog you’re looking at it for this is for dogs and your dog was forty eight pounds fifty pounds well then you would have to take your kg and say how many kilograms is that dog. Divide that by two point two and you’re getting somewhere around twenty two kilograms so you would need that dog would need to consume somewhere in the vicinity of what two hundred milligrams of the active ingredient to kill to have a 50 percent chance of killing that dog. Dogs are probably a poor illustration but I want to give you a nail and you know an animal you’re doing up now for dealing with mice for instance mice are not even a kilogram.
There was an ounce two ounces. So if if a kg two point two pounds. Well that gives you something in the vicinity of. Thirty six thirty eight ounces how small the doses are going to need to kill that mouse. Right. So you can see that we’re talking with some very very small fraction. So the rule is the larger the first number that that MG side the larger that first number the less toxic that product is. So if I told you something was ten thousand or excuse me let me let me go. If I told you it was you know sixty thousand milligrams per kilogram that is significantly less toxic than something that was one milligram per kilogram for the LDP fifty k. So the bigger the MG number the less toxic the product is on an elder 50 percent out. Why is this important.
Because you need to kind of get an understanding of what it takes when you’re reading some of these labels and trying to help clients understand risk and relative toxicity that the amount of poison needed to kill a mouse is significantly less than what the amount of poison that will need to kill that dog or their cat. So are there secondary poisoning issues with you with anticoagulants. Absolutely there are however. The dog would have to be eating a fair amount of animals over a long period of time to get the toxic dose needed to kill the dog or to even get that dog to play sick. The bigger the animal the more it’s going to have to consume because again lv 50 is based on a relationship of milligrams to weight. Right.
So weight based assessment so what. The one problem with LDA 50 as important of a measurement that it is is that it’s it doesn’t tell us two things.
First it doesn’t tell us what it takes to kill 100 percent of the animals because remember I said the LD 50 was the lethal dose needed to kill 50 percent of the test subjects. So if I have 20 mice in my study once I kill 10 once they kill 10 of those mice that’s my LD50.
The problem is that your client doesn’t want just 50 percent of the pest left. They often want zero of the past left.
So when lv 50 gives you a notion of what it takes to kill half fully half of the population. But it may take a whole lot more toxic and to kill the rest of the population but maybe not. That brings us to our second problem. And that is lv 50 is not is a static number. But that doesn’t mean the toxic end is static in its effect. What I mean by that is that we don’t always have a linear relationship of one to one relationship.
That is if we as we add more toxic end that we’re going to get an incrementally higher kill rate and one of the challenges when we’re dealing with Americans is that we always believe more is better if the label says we’re supposed to use a teaspoon of the product per gallon of water.
We think well we want to really kill this animal so we’re going to use you know a teaspoon and a half or maybe two teaspoons. Even though the label says the maximum dose is one teaspoon per gallon we think oh it’ll just be that much better but not necessarily because sometimes some toxins when you get to that LD 50 if you add just a fraction more. The toxicity of the product can go up exponentially not linearly. In other words it may not become 51 percent more effective it may become 80 percent more effective. Just have my new amount and that could put non target animals at risk. And sometimes you’re actually doing overkill because your product has already been designed to have a huge kill so you may be adding much more than what is necessary to get your hundred percent kill and so you’re ultimately wasting money and violating the label and potentially putting your clients in non targets at risk so when we look at LDA 50 lv 50 gives us a snapshot of what it takes to kill 50 percent of that population.
But understand that adding a little bit more in your product may be not a good idea may be legal. Again I’m assuming you all know that it’s illegal to violate the label because you’re labeled minority. Tell you what you need to kill to get that 80 percent kill or 90 percent kill or even 100 percent kill and then you’re adding a little bit more you’re ultimately increasing that toxicity in an exponential manner which is then putting other organisms at risk that may be why the label is written in such a way so that you don’t put those products at last. Remember labels are written to do two things to be said to be to provide that balance between efficacy and safety. So when you tweak the label you find out you may find out that you may get great success in a kill rate but you may be doing other things you haven’t even thought about and put other organisms at risk or you may be just wasting a whole lot of money. For something that because you didn’t understand how that product worked.
So when we talk about elders 50 with your clients and they want to use safe her products help them understand respect but particularly when dealing with rodents sides for instance that when you’re using first generation anticoagulants you can provide a significant margin of safety to non target animals by using a first generation anticoagulant now a first generation anticoagulant to remind those of you may not be familiar with it. First generation anticoagulants are known as multiple feed those products are those active ingredients are warfarin chloride fast known in die fast no so you may your power company policy may be well we’re going to be using second generation all the time because we want really you know hit these rodents with an H bomb basically using these second generation products in the second generation products were great but oftentimes that can be overkill and because they’re not necessary use.
Now if you’re in an area with high with a lot of competing food sources and your client just isn’t able to control the available food availability around for those rodents then yeah you’re probably going to need to use a second generation anticoagulants because you may only have one one chance for that rodent to try your bait but chances are the vast majority of you don’t have that particular right you’re not you’re not trying to control you know around granaries for instance or there’s tons of spilled food all over the place chances are you’re in more residential areas we don’t they don’t have an infinite amount of food available for mice and so there you have your first generation anticoagulant so you’re able to provide your clients with an ability to control a lot of these species these mouse species without necessarily using the hot what we call the hotter products.
Now I don’t want to be banning these hotter products.
Some states one state in particular is looking to ban these products, But if you look at the LV 50 of those it’s a significantly less than your first generation products because they’re that much more toxic so Ellen understand that LDA 50 it’s a good way of helping you compare products one to another but they don’t tell the whole story. They don’t tell you how relative how how relative that toxicity is as you increase or decrease the dose. It’s not always a clean line from the lower and lower left corner to the upper right corner. Sometimes it goes almost straight up faction that when you add a little bit more you get an incredibly high risk high increases in effect and other times it may flatline. We’re adding a little bit more as basically wasting money and violating the label for no benefit.
Not that you should ever be violating the label. Well people realize that I can’t speak for other things but I can tell you for the vertebrate labels the labels are designed to work follow the label and you will be fine. It’s what happens is when people tweak that label they think that they know something the manufacturer doesn’t know you don’t. The labels are designed to work if they’re not working it means you have failed to either use the product correctly or you have failed to control the habitat modification necessary or the exclusion or you haven’t identified the pest properly.
Hope that helps you understand a little bit about L.D. 50 and toxicity because that’s a concept that we want to be sure we understand that we have a better understanding of the products that we’re using so that we can use them effectively and more safely because these products don’t use themselves. They are used because of what you bring to the table.
That’s what you’re being paid for your clients can go out and buy a lot of these products right over the counter you need that you’re bringing your expertise so that you are using these products with the best effect but in the safest way for your client and for the wider environment. I’m Steven Van Tassel wildlife control consultant. Back to you. Frank.