 You're watching FJTN, the Federal Judicial Television Network. The Federal Judicial Center presents Science in the Court Room, a series of programs for judges on science and scientific evidence with an introduction by Stephen Breyer, Associate Justice of the Supreme Court of the United States. Welcome to the Federal Judicial Center's series of science programs for judges. This series is a response to two significant developments. One is that as time goes on, an increasing number of cases on your dockets are turning upon the application of scientific principles. Another is that recent decisions of the Supreme Court have imposed new duties on you, gatekeeping and decision-making duties that require an enhanced understanding of the scientific methodologies at issue in your cases. The series seeks to help you fulfill these duties in several ways. First, by providing you with an understanding of the basic principles governing three discrete fields of pure science, microbiology, epidemiology and toxicology. Second, by examining methods of evaluating the reliability of evidence from those three fields of science. And third, by considering scientific evidence from these fields in the wider context of making rulings and management decisions in specific types of cases that is patent and toxic tort cases. As you know, after Markman v. Westview Instruments Inc., a patent case can turn almost entirely on your conclusions about the meaning of scientific terms in the patent claim. Because patent litigation increasingly involves questions of microbiology, the first three programs in the series will be devoted to an examination of the fundamentals of microbiology in the context of a patent case. The first two programs will be pure science lectures. In the third program, a panel of judges and attorneys will examine the Markman and related issues presented by microbiology evidence in the patent case. The series then turns to a consideration of scientific evidence in the arena of toxic tort litigation. As far as you're well aware, the parties often seek to present evidence from toxicologists and epidemiologists on the issue of causation, and Daubert and Joyner and Tkumo Tire require you to make rulings on this evidence that may determine the outcome of the case. As such, the fourth and fifth programs of this series will address the basic principles of toxicology and epidemiology. The sixth will be a discussion by a different panel of judges and attorneys focusing on methods of evaluating toxicology and epidemiology evidence for purposes of resolving Daubert and other issues in toxic tort cases. The goal, of course, is not to turn you into scientists. Still, as you encounter terms like recombinant DNA, antisense, or nucleotides, and phrases like no observable effect level and cohort study, you may find yourself thinking you were on a longer and more arduous journey into the realm of scientific inquiry than you'd like to take. I can only respond that I think it is a journey you must take, indeed that we all must take, to be effective judges in this day and age. Why? Because it will increase our knowledge about the science we can expect to encounter in our cases. And as such, increase our chances of achieving justice in them. And so, in the spirit of scientific inquiry and in the pursuit of justice, let us begin. Science in the Courtroom, Program 4, Basic Principles of Toxicology. This lecture is presented by Dr. Bernard D. Goldstein, Chairman of the Department of Environmental and Community Medicine at the University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School. My goal today is, my objective is to try to provide just the basics of toxicology, particularly as it relates to toxic torts. Most of what I say is going to be right from the Federal Judicial Center's Science Manual. There's much more detail there if you'd like to follow up on this. Toxicology basically is the science of poisons. It's an ancient science, an understanding of the toxicity of natural chemicals has been a part of human evolution, a successful human evolution. Toxicology has been practiced through the years, not only by scientists and by physicians, but also by government people, considered Lucretia Borgia, for instance. And a lot of toxicology has developed in terms of worrying about poisons and the potential for poisoning. Modern toxicology is really an interface science. We're sort of stuck between chemistry and biology, and it's exciting that way. We have to keep up with the newer advances in biology, which is just such an exploding and scientific field now, and of course with chemistry. The chemistry is particularly important to us because we have to understand the intrinsic basis of how chemicals react and how they fit into the niches that biology produces. And it's that interface which is really the challenge to toxicology. I will actually show you a few chemical structures, but only really to make you feel good about having entered what for most of you I know is sort of dangerous territory, and it's in a sense to appease my conscience that I really shouldn't give an hour lecture on toxicology without showing at least a little bit of chemistry. We can roughly divide the field of toxicology into three. Forensic toxicology is a field that has long been associated with the courts. Its practitioners are well aware of their role in the criminal justice system, and you are well aware of what they do. The complexity of the field has been greatly increased in recent years by DNA and other advanced approaches, which can be brought to forensics. And I emphasize this distinct nature of forensic toxicology because it is not necessarily true that expert toxicology and the other two, toxicologists rather, and the other two fields of toxicology will necessarily be expert in forensic toxicology or vice versa for that matter. These other two areas can loosely be called pharmacology, pharmacological toxicology, and environmental toxicology. Well, pharmacology is in many ways the parent discipline out of which toxicology has evolved. Therapeutic drugs always have some associated toxicity, which must be understood if the benefits are to be achieved and to be calculated. The toxicity of chemicals can also be a basis for development of a therapeutic agent. For example, there's an effective class of anti-cancer agents that came out of studying a West Indian tea. It was a tea that was made from a bush in the West Indies, and people believed there that it would help in cutting down on diabetes. And so it was tested to see if it decreased blood sugar in rats, and it didn't have any effect on blood sugar, but it destroyed white blood cells. Well, that isn't good for an anti-diabetic drug, but it's very useful for an anti-wukimic drug. So again, testing the toxicity of chemicals is a way to not only be careful about therapeutic agents, but it's a way to develop agents which can be of value. Environmental toxicology is the newest field of emphasis for toxicologists. It arises in large part from the need for experts to address concerns arising out of the use and abuse of chemicals, which is so prevalent in our modern chemical era. And it's concerns that often lead to toxic tort suits. My first overhead, and I'll be showing you lots of them, tries to list for you the three major laws of toxicology. I'm going to keep coming back to these laws, but let me first focus on the first one, the idea that the dose makes the poison. This really was developed, stated very clearly in the 15th century by Paracelsus. He's a bit of an alchemist and a bit of a fraud, sort of a bombastic renaissance type who was always one step ahead of the laws he wandered around Europe. But he very clearly pointed out that everything is poisonous. It's only a matter of dose. Even water can kill, it's a question of dose. And so we really have enshrined that as if you will, a law. Now, I don't mean a law in the sense of these are really scientific laws, and they're certainly not laws of the type that you're familiar with, but they are basic principles which govern our understanding of toxicology. Let me first define dose in terms of the dose makes the poison. Dose very simply is concentration times time. There's a related concept which sometimes gets confused with dose, and I will through this lecture be talking about areas which, in my experience at least, there seem to have been some confusion in legal cases and with the hopes of setting these straight. And that related concept is called dose rate. And that's the speed at which dose is delivered. So, but it isn't dose itself. And let me give you some examples, or at least one major one, which is let's assume that we were breathing 10 parts per million carbon monoxide for one hour. That's exactly the same dose as breathing one part carbon monoxide for 10 hours. But the dose rate is obviously greater in that first dose in the sense that we're delivering the dose much more rapidly. A dose rate can be very important in terms of toxicity, but I won't really discuss it in too much more detail beyond this. There are two major types of dose response curves, dose response relationships that we discuss in toxicology. This is a gross generalization. It's a simplification, but I think it's a very useful simplification because many laws are based upon this, and it does help in understanding these relationships. The two major types of dose response curves are one that has a threshold associated with it. And this is a dose level below which no adverse effects are observed or expected. It's believed to be applicable to all chemical impacts other than certain mutational effects. And it's the mutational effects that we are concerned about that we believe have a non-threshold relationship in that every molecule, at least theoretically, has the potential for an adverse effect. Further, the risk is directly proportional to the number of molecules in the dose. So even one molecule has some threat, some risk associated with it. There is no threshold below which there is no effect. And the mutational events are particularly believed to be important in terms of cancer, and I'll go through that in much more detail. Well, what do we mean in terms of a threshold and non-threshold dose response curve? And I thought what I would do to try to help explain this in more detail would be to go through and actually draw some of these curves. I hope that, in fact, if you'd like to, you might want to draw them along with me. It just is a pedagogic technique to help understand them a bit more. And what we're going to do is we're going to draw, we're going to plot two axes. The vertical axis is going to be the response. It's going to tell us how much response occurs. And this response can be anything. It can be the number of animals that die. It can be the amount your blood pressure goes up or down for that matter. It can be something not measurable in the direct way, but subjective. How much pain are you in based upon something happening to you, a scale of 1 to 10. 10 is the worst, 1 is the best, and you've got to give us some numbers. And we can plot that as a response. The other axis, the horizontal one, is going to be dose, where the greater the dose, the further the right we get. If we start over here, we start with a situation in which there's neither dose nor response. We're starting with zero with both. Well, as an example, let's take sulfuric acid being poured on your skin. If we start with pure sulfuric acid, there's no question that we will burn a hole right into your skin. We'll destroy the tissues. Let's call that the maximum response at a dose that's over here, and this is the maximum response, and we'll put a little mark there. But what's the minimum response? If I take some pure sulfuric acid, if I take one drop and I put it in 100 gallons of water, and I mix it thoroughly, and I take a jigger full of that and pour it on your skin, nothing's going to happen. That's too dilute. It's just simply no effect whatsoever. The level of acid in that would be far lower than we have in our body naturally, certainly much lower than you'd have if you eat some vinegar on your salad. The acid level is too low. You won't feel anything. That's a dose where nothing happens. There's no response. And I can keep doing that. I can put two drops in 100 gallons or four drops. I can get up to a gallon in 100 gallons, one gallon of sulfuric acid, 99 gallons of water, mix it well, pour it on you. Do you feel anything? At a certain point, you're going to start feeling something. At a certain point, you're going to get a burn there. At a certain point, as I go higher and higher in dose, I'm going to get more of an effect. But we start with what is a threshold. It's at this level where we first start seeing an effect. And as we draw these curves, we get what's generally seen as an S-shaped effect. In that, as you adding more and more sulfuric acid, higher, higher doses in that jigger-full, higher concentrations in that jigger-full of water that we're pouring on your skin, each time there's going to be a little bit more. And each time, we're finally going to get to a level which is an effect. And that's what we would call the threshold. Below that, there's no effect. Above that, there is an effect. There's a maximum level. You can't do any more than burning a hole through the skin or then killing someone. And you can do this with just about anything that affects people, affects animals. You can take a lead pipe. And I could just softly put it on top of someone's head in a way you can't feel it. And there'll be no observed effect. Till we finally get to the strength of putting that lead pipe on someone's head, we'll finally get to a threshold to feel it, to have pain. And then as we keep doing this, we'll end up with a level where we'll crush the skull. Now, what this does, what I've described to you, hides a little bit of something that's very important, which is that people have different susceptibility. Obviously, a baby's skin is going to be more susceptible to that acid than an adult's skin. If you've got a cut, so you can go from a time where you're more or less susceptible just by having a cut in your skin. And obviously, pour a little weak acid on that. If you've ever had a cut in your hand when you've got some vinegar on it, you'll notice that you feel some pain when you went otherwise. If I turned around to the camera, you'd see why I have, over the past 20 years or so, gotten more susceptible to a lead pipe in the back of my head than I was 20 years ago. People change in their susceptibility. I'm going to go through susceptibility to a large extent later, because it is a very important issue having to do with understanding toxicology and having to do with what happens in toxic tort suits. Who is susceptible? Why are they susceptible? And how important is susceptibility in these situations? One of the issues that we come up with as we look at these dose response curves, and actually, let me use the same one all over again because I think there's room to write it, is to understand how we go about making standards. And that's an important issue in terms of understanding whether or not people are particularly been affected. What is a standard for, say, a level of sulfuric acid in the skin or in air? What would you permit to have happen? And traditionally, in toxicology and in regulatory toxicology, we have taken this threshold level and put what we call safety factors. They're really protection factors. They don't make you completely safe, but they do protect. And these are protective factors that are based upon extrapolations from the laboratory animal where this study was done. We haven't really done this study in humans. We've done these in the laboratory animals. And we try to understand what would protect a human. So traditionally, the standard as it's been applied in the workplace and the general environment has been one which has been 1,000 fold lower than this particular no observed effect level. And that's the number which you may sometimes exceed. And we don't want people to exceed that number. We don't want people to be exposed to it. But just because you are, just because one day you happen to be exposed to a level that's just above the 1,000 fold safety factor, doesn't mean you are necessarily affected. It doesn't mean you are more likely than not affected. If we've done our job right as toxicologists, as regulators, just barely exceeding that allowable level, should we view completely safe? And we should be no harm whatsoever if we've done our job right. So that's where that standard comes from, and that's the general approach in toxicology. Well, I said there's two types of dose response curve. And the other we usually use for cancer. I want you to consider that we have a situation in which this dose causes this response, and the response is a 10-fold increase in cancer levels in a work group. I'll talk about benzene. Benzene causes acute leukemia in adults. Workers exposed to benzene at high levels of benzene have been found to have elevated levels of acute leukemia. So let's say this is a 10-fold increase in acute leukemia. That's the response at this dose. That's very high levels of benzene. There's benzene in this room right now. What's the effect? What's the implication of the level of benzene in this room? Benzene's a component of gasoline. It's in some ways a natural product. It's almost impossible to be anywhere in the world without some measurable level of benzene. The level of benzene in this room is very low compared to the level at which workers had an increased risk of leukemia. That was demonstrable. But how do we know it isn't causing an effect at this lower level? And the thing is that we think it might, theoretically at least, it could. And we say that because we don't think there's a threshold for the leukemia, for the cancer that's caused by a chemical. We think even one molecule has some risk. Well, why is that? It's simply because of the way we understand mutations. If there's a mutation that causes cancer, it can occur with just one change in the DNA bases that is basically our genetic code that codes for the information that the cell has. And if we change just that one base, that theoretically at least can be done by just one molecule. Now, there's a trillion molecules of benzene in every breath you're taking, roughly, right now. Don't stop breathing. The chance that any one molecule will do this is incredibly small. But we can't rule it out as being zero because if we think of cancer as being a single mutation that leads to a clone of cells that just keeps on dividing and dividing and dividing, well, then it could be done by any one molecule of a cancer causing chemical, at least theoretically. Basically, what we've done in our society from a regulatory point of view is to put the burden of proof, I'm using your language now, on the industry that's making the benzene or making whatever chemical it is to prove that the chemical has a threshold. And in some cases, you can. In some cases, there are good reasons why a chemical does not cause cancer in any one molecule. But the burden of proof is on industry and it's not easy to prove. And so what we have is a situation where we just assume that it's a straight line down to what we call the intercept. So that if this level of benzene causes this much leukemia risk, well, that level of benzene will cause that much leukemia risk. I'm going to go back to this because it's so key to so much of modern toxicology and so many of the arguments about it. Let me now talk about our second law of toxicology. And that's the law that says that toxic agents have specific effects. That I like to think of was first described by Dr. Paré. Dr. Paré was a very famous French surgeon from the 15th century. He's considered to be the father of modern experimental surgery. And the king of France, once came to him very excited because he had just purchased this very difficult thing to obtain. He'd gotten it from a Spanish nobleman who was something called a bezzouar. And a bezzouar is a concretion of the fact is a concretion, it's sort of a soft stone that comes out of the stomach of goats, particularly goats from Persia. And somehow this has been smuggled out of Persia. And the reason the king was so excited is this was supposed to be a universal antidote against all poisons. And Paré said to the king of France, nonsense. There is no such thing as a universal antidote against all poisons. It can't be because every single poison acts individually through a specific pathway. And each of these is different. And so no one antidote can help against all of these. Well, the king, of course, having invested all this money, decided he would do an experiment. And what he did was there was some poor cook who had been convicted of stealing the king's silver and was about to be hung. And they went to the cook and they said, well, instead of being hung, would you be willing to take this poison? We'll give you the antidote if it works. You'll go free. The cook took the opportunity. The cook died. Paré was right. Every chemical has a specific effect. There's a specific pathway by which it works, more or less based upon its own inherent chemistry, but also on pawn biology. Let me give you a couple of examples about specificity. And these come from being just basically going to a gasoline station and filling up your car. Gasoline's a mixture. It's got lots of chemicals in it. One of the chemicals, for instance, is benzene, which we just talked about, which may at low doses, perhaps even cause cancer. It's also got other compounds in it, which can cause effects. I'm going to talk about two different types of specificity related to this. Let me, in fact, talk about, since I've talked about benzene, let me talk about hexane and other straight chain alkanes. It's a very fancy word. It gives me a chance to show some chemistry. And really, I'll anchor it for you by pointing out that one of the straight chain alkanes is called octane. And we all know that octane is in our gasoline. And this is actually the end, stands for the fact that it's normal octane. It's a straight line of just eight carbons. These are hydrocarbons. I haven't shown you the hydrogens on there. And what I've done is I've drawn for you the pentane, which is five carbons, hexane, which is six, heptane, which is seven, octane, which is eight. The approach to metabolism by the body of these kind of compounds is similar to each one of these. You oxidize the internal carbon in each end of the chain. So this is an oxygen being added to these carbons. They were all added one carbon inside. And so you've got, in this situation, with eight carbons, you've got four carbons inside. You've got three carbons inside. You've got two here. You've got one there. It all looks the same, except this specific product of n-hexane causes peripheral neuropathy, causes damage to your peripheral nerves. None of the others does. And that's simply because of the fact that there's a niche in the peripheral nerves, which allows this particular size of four carbons with the two oxygens at the end to slip in there, cross-link that nerve in such a way that it stops functioning well. Doesn't happen if it's more, doesn't happen if there's less. See, here we have a very specific result, which is due solely to the fact that there's a biological niche, which allows that chemical to react and cause the effect. Well, that happened at the gas station. Absolutely not. Won't happen because there isn't enough n-hexane there. There's a threshold for this effect. Without getting to this level of n-hexane, it simply isn't a worry. We don't worry about the hexane that's in gasoline. We do worry about the benzene that's in gasoline. Now, as I pointed out in the previous overhead, benzene, the example of benzene is one in which there is a central nervous system effect, and the example of hexane in other straight chain alkanes is one in which there are central nervous system effects. You can get to high enough levels, very high levels, of these compounds in the pure sense that can make you drowsy. They're anesthetic-like. They can put you to sleep. In fact, people have died over vats of benzene in the workplace by just basically falling asleep and drowning. So these all have that same type of an effect. I can get a toxicology graduate student to give a very learned, at least the student better be able to do this, very learned discourse as to all the different alkanes as to which one will put you to sleep faster, which one you will recover from. The same thing with benzene and alkylbenzene. Alkylbenzene is a toluene, xylene, a whole bunch of other compounds, which are basically the benzene ring with just a small change and additional carbon added to it in various places. These compounds also have central nervous system effects. They'll put you to sleep. And again, the toxicology graduate student should be able to tell which one will more rapidly put you to sleep as compared to the other. Easily predictable. What I showed you about the n-hexane is not predictable in that way. It doesn't fall into what we call structure activity relationships that we could understand. We could not predict the peripheral neuropathy caused by n-hexane from knowing what pentane did and heptane did. It simply would not be predictable. And the same thing is true for the benzene toxicity. We cannot predict the bone marrow damage or the leukemia caused by benzene by understanding what happens to toluene and xylene and the other alkylbenzene. I can predict the central nervous system effects to some extent, not completely, but pretty well. But I can't predict the bone marrow toxicity. What I've described to you are two different types of toxicity in terms of direct acting or indirect acting. The central nervous system effects of benzene or of hexane or related compounds is a direct acting. It depends purely upon the actions of the compounds themselves, benzene, toluene, xylene, hexane, heptane, octane. The toxicity that I described in terms of the peripheral neuropathy due to n-hexane is not a direct effect of n-hexane. It's an effect of its metabolite. The same thing with benzene. It's not a direct effect of benzene to cause leukemia. It's an effect of its metabolite. Anything that changes metabolism can change the extent of these effects. So metabolism is something that we have to understand in order to be able to deal with toxicity. Well, I've talked a fair amount about these first two laws of toxicology. One of the reasons I did want to spend so much time on about it is that we see a fair amount of obfuscation on the part of defense and plaintiff's attorneys and sometimes confusion and judicial opinions between the two. And particularly when it gets the issues of general causation and specific causation. In essence, that first law of toxicology, the dose makes the poison, refers to specific causation. The second law, the specificity of effects, really refers to the general causation. It's almost the opposite. Specificity in specific causation refers to the dose responsible specificity in toxicology has to do with the general causation questions of whether or not a chemical can or cannot produce a specific adverse effect. You'll come across this, I'm sure. Let me talk now about toxicology methodology. How do we go about doing toxicology? We have three major approaches. One is that we will look in a test tube and try to develop what we call in vitro techniques that will allow us to predict what adverse effects might be. We would very much like to be able to replace animal toxicology with test tube studies, at least certainly in safety assessments so that we don't have to test as many animals to see whether a new cosmetic, a new drug, whatever is safe. So far, we've been not very successful in developing in vitro tests, developing test tube tests, which will really be predictive of animal effects. Animal studies are a major part of what we do in toxicology. I'll come back to them. Controlled human exposures are something that also occurs. People think of toxicology as not dealing with humans. You can, in fact, ethically expose humans to, for instance, to levels of compounds that are present when you go into a gas station. So as you understand what the metabolism and the effects are, many of the Clean Air Act rules and laws come out of studies in which humans are exposed in a controlled way to levels of pollutants that you might get outdoors anyhow. And this way you can understand which one of the pollutants might be responsible for an effect. But animal studies remain the major part of what we do in toxicology. As you saw in my first overhead, the third law of toxicology is that humans are animals. Toxicologists really do believe that. We really believe that we can understand so much about humans by understanding what happens to animals. We do know that there are differences. There's almost a bias built into the scientific literature about this. And I've seen this in legal documents or in the legal literature, where people have reviewed this and pointed out how poor animal studies are to be being predictive. You have to understand that I can write a paper and publish it. I can get a graduate student to do a PhD thesis on a difference between species. I can't do it on a similarity between species. Almost everything is similar. If something is different, though, it gives us an opportunity to understand why, to understand mechanism. For instance, we know that mice are more sensitive to benzene than our rats, in terms of the acute bone marrow toxicity. If we can understand why, that would help us understand which of the metabolites, which of that big list of chemical structures I showed you, is responsible. So it becomes something that's publishable. There's a mouse that's different than other mice in terms of its sensitivity to benzene. That's a publishable difference if it's different than a rat, if it's different than a hamster. But if it's the same, it just doesn't make any difference. I mean, we're not going to publish that. So there's a publication bias that sits in the literature having to do with toxicology in that you will find lots of examples that we really look for to show where species are different. So we can exploit this in understanding toxicology. Toxicology, this methodology, obviously, is different from epidemiology. It has the strength, as compared to epidemiology, of being able to carefully control the complete situation, except for just modify one thing. And that's the variable we're interested in in that variable. We usually be the dose of a chemical. So we can put an animal into a situation in which we have complete, the animals getting exposed are the same as the animals getting not getting exposed. They control animals in just about every way imaginable. As I said before, they're very often the littermates, they're identical twins, identical sex tuplets, and they've been carefully randomized to the different groups. They've also been brought up in a situation in which they had the same food, the same light, the same environmental issues for them. So they're really identical. And if you expose one group, you're really can deal with issues of causality. And I thought I'd talk about one aspect of a multi-year animal cancer study. And that's something called the maximum tolerating dose. This is routinely used in lifetime rodent exposure studies. It's usually the highest dose tolerated by animals in a short-term study. It's controversial because it uses doses much higher than those usual for human exposure and because it may lead to physiological changes that cause the cancer that wouldn't be applicable to humans. You may have heard of this in relationship to saccharin, where it was basically equivalent to 8,000 bottles of soda pop a day worth of saccharin was given to rats. And how relevant could that be? I want to describe in a simplified way why that's done and to some extent what the support is and what the problem is. Really, the reason for supporting this use has to do with statistical power and the goal of doing these tests. Let me give an example. Let's assume that there's a regulatory objective to protect the public against the chemical, which in its usual use, its usual exposure, we would be exposed to it, would cause cancer in one out of 1,000 individuals. That's not an unreasonable regulatory objective. In fact, sometimes we go much more stringent than that, one in a million or 100,000. And assume that there is this compound. I call it HMCW. That's a favorite toxicology compound. It stands for hexamethyl chicken wire. And this really would produce pancreatic cancer. So we've got a chemical. It's going to produce pancreatic cancer if we let it out there. And it's going to increase the, if we use the expected dose, which I gave initial white to over a lifetime, that cancer will occur. And let's assume that rats are similar to humans in response and that the background incidence of pancreatic cancer in humans and in rats is 20 in 1,000. And that it's going to cost about $2 million for this usual study where we're exposing 100 control rats and 100 exposed rats. And the question that comes up immediately is, well, OK, how many rats need to be exposed lifetime to the expected environmental doses to observe a statistically significant increase in pancreatic cancer incidence in these laboratory animals? And obviously, you can ask the question, well, the routine study is done with 100 animals in the expose and 100 in the control group. Could we expect to see this? And the answer is no. I mean, your background expected control incidence is 2 in 100. You do 100 rats. Sometimes it'll be 3. Sometimes it'll be 1. But the average will be 2. And 1 in 1,000 increase just brings it up to 2.1. Well, you can't get a 0.1. Either you get a 2 or you get a 3. But you're not going to be able to see that won't be any difference. Even if one time you got a 3 and the other time you got a 2, which would only happen one time out of 10, it wouldn't be statistically significant. You wouldn't know what to do with it. You really would not be able to say that this causes pancreatic cancer. What if we went and increased the number of rats in the study to 1,000? Using the usual expected dose, couldn't we find that then? It's a still no. What we would get, on average, is 20 out of 1,000 in the control group and 21 out of 1,000 in the exposed group, because there'd be a 1 in 1,000 more increased risk of cancer. That's not statistically significant. If you found that once, you'd say, well, maybe next time we'll go the other way. So you can't possibly protect the public using this animal cancer test if you're worried about a 1 in 1,000 risk. Well, you can if you make some additional assumptions. And then you make two. One is that, as we showed before, that the cancer risk is linearly related to dose. That's basically this curve over here. We're linearly related to dose. And the second assumption we're going to make is that rats can tolerate a 50 times higher than the anticipated lifetime dose with no real change in their health. And what we usually will do is we'll give a dose response study for 90 days in rats. We'll give lots of different doses. And we'll pick the dose where there's no weight loss. There's no change in the animal's life that we can tell through using a series of tests. And then we will go back and start all over again and use that as the maximum tolerated dose for two years in these laboratory animals. Well, if we do that, then we ask the question of can a statistically significant increase in pancreatic cancer incidents be observed with exposure of 100 rats to a lifetime dose 50 times higher than the anticipated dose? And he says yes. Because what we would see in those 100 control animals, again, it's two out of 100, but in the exposed animals, we do expect to see seven out of 100 to have pancreatic cancer. That would be statistically significant. It would say to us, well, if we're right about that being the cause of that if we're right about the linear response, again, if we're right, then we can just basically go down 50-fold on this and say, OK, here's the amount of cancer we would expect from 150th of that dose that we used. And that's an increase in 1 in 1,000. Of course, we get an increase in 50 in 1,000 out of the 50-fold higher dose. So what we have is a situation where, again, assuming linearity and assuming the rats like humans, we can make some regulatory approaches. But these are regulatory approaches. In doing toxicology, we focus a lot on the chemical pathways in the body. The chemical has to get into the body. It has to distribute within the body. It has to be metabolized within the body. It has to be excreted. These are important pathways, important to understand for each chemical what happens. Absorption is obvious. It can come through the skin. You can inhale it. You can get it through ingestion, through coming through the mouth. These are the major pathways. They all have different implications as to how rapid things will come up. If you breathe fine particles of lead, basically 100% of what you breathe comes into the body. If you eat lead in your diet, sometimes 10%, 20% will depend upon what you're eating with it, or what your basic status is, and I'll talk a bit about that. We'll only get into the body. So different pathways have different implications as to uptake. Distribution means how does something get around the body? There are certain chemicals which, because of their chemical structure, will pass what we call the blood-brain barrier and get into the brain. Others will not. Iodine in the body will go preferentially to the thyroid because it's thyroid hormone, which is really about the only major constituent that the body has, which we have iodine. Iodine's necessary for it. Well, when you get iodine into your blood, you take iodine into your body, the thyroid gland has a very specific pump which basically sucks out all the iodine or almost all the iodine that will go past the thyroid. Other tissues do not, so more iodine will distribute to the thyroid than to any other area. And again, understanding this is important to understanding toxicity. Metabolism, basically, how does the chemical change within the body? As I pointed out before, some of the changes are, if you will, good in that they detoxify, they get rid of the toxicity of the agent. Other changes actually make the agent into a toxic agent. And excretion is important to understand as well. What are the pathways of excretion? Some things come out through the urine, some through feces, some through just exhaling, some through our gallbladder. So there's a variety of different approaches that need to be understood. The responses can be acute, can be sub-acute, can be chronic. These responses are very often the time pattern of response along with the understanding of absorption, distribution, metabolism, and excretion can tell you a lot about toxicology and about toxicity. One of my favorite questions to toxicology graduate students is to tell them about the newspaper article about someone who had chronic headache for about five years and it decided that it must be coming from the mercury in their dental amalgams. And had the mercury removed from the dental amalgams and got up from the dentist chair and said, my headache is gone. And the question to the toxicology graduate students, what are your problems with that? And there's a couple of problems. First of all, mercury in the brain will build up in the brain if a high level of mercury exposure and can give you symptoms like headaches. So no question that can occur. But I would expect the toxicology graduate student to be a little concerned about, a little skeptical about how mercury in an amalgam gets up to the brain. I'd expect the toxicology graduate student to be, even if they could come up with a pathway while maybe some of it vaporizes and somehow gets through the pallet into the brain to say that, well, the dose won't be high enough to be equivalent to the kind of dose which we've observed in people who are mercury miners or gold miners using mercury and roasting mercury and getting lots of mercury exposure, high enough to cause chronic headache. But most importantly, that student would have to point out that the level of mercury, whatever level of mercury you have in your brain, the time at which it turns over, that kinetics of its turnover is such that it will take months for it to leave the brain. So you can't just get out of the dentist chair, immediately after having the mercury removed and say that the mercury got out of the brain and therefore the headache went away. If the headache went away, it had nothing to do with the mercury. These are the kind of decisions you can make if you understand the toxicology, if you understand the pathways, if you understand the time frames of these issues. Some chemicals stay in the body for lots, for a long, long time. Other chemicals basically get right out of the body. Understanding that and knowing that is very important. We also have to understand toxicological responses. What these responses can be for everything from altering the cell function or cell death, you can just basically kill a cell, but the cell can mutate and lead to cancer. If you have mutations of germ cells, you can end up with fetal changes, which are obviously very important. Scarring is a kind of long-term process. You can get scarring of the lungs from asbestos. You can get scarring of the liver from cirrhosis from drinking, that's what cirrhosis really is, is simply scarring of the liver from drinking too much alcohol. And again, dose response considerations are important. Alcohol, obviously, the dose rate is important. One drink every day for a month is not gonna be harmful, while 30 drinks in one day will cause a lot of acute damage to your liver and the healing process will very often be with scarring. And if you keep repeating that, you will end up with a lot of problems. And again, target organ toxicity. If there's radioactive, I mentioned iodine going to the thyroid. If there happened to be a nuclear power plant releasing a lot of radioactive iodine because something went wrong, it would put you at an increased risk of thyroid cancer because the radioactive iodine would go preferentially to the thyroid just as any other iodine would. If it was not radioactive iodine, it was radioactive C-zema, it would go somewhere else. In considering toxicological responses, we always have to remember about adaptation and repair. The body is able to adapt. Sometimes the adaptation is very good for a short-term problem, but very bad for a long-term problem so that an adaptation response to smoke, presumably developing from the time of living in caves with smoky fires, is that we produce more mucus. And that makes sense. If you breathe in a lot of smoke, the lung airway starts producing a lot more mucus. The mucus sort of cleans, gets rid of some of the smoke particles which gets on and protects the lung. What too much mucus production over a long period of time is the basis for chronic bronchitis and emphysema. So what we have with cigarette smokers is a situation where cigarette smokers make more mucus than non-smokers. What I started to say, you and I, I hope you're all non-smokers. And that cigarette smoke does manage to produce that, if you will, it's a protective response. But over time, you end up with so much mucus being produced by so many cells, it changes the characteristic of the lung. The mucus gets stuck down in the airways and you end up with chronic bronchitis. There's a lot of situations like that where acute responses, good acute responses, turn out to be the basis for chronic disease. These have to be understood. And certainly the mechanisms of susceptibility are increasingly important in toxicology. Obviously some reasons for differences among people are the inherited factors. We're genetically different and some of the genetic basis for this is being understood more and more with our new science, with unraveling the human genome. We will understand even more of this over time. I'll try to get back to that. Age and gender, I pointed out before about a lead pipe in the back of my head. That's an age-related change. Obviously male-female differences are great. Lifestyle factors will change dramatically how much at risk you are to chemicals. The benzene example I gave, benzene, we know that if we increase benzene metabolism, we will make things worse. We do know that alcohol induces, basically increases the amount of the metabolic machinery that's responsible for the metabolism of benzene. So we will end up with far more metabolite of benzene if we have alcohol at the same time. And health status factors, if you've already got emphysema and you're exposed to an air pollution, you're clearly gonna be at greater risk than if you have a normal lung function. So obviously these all play a role in toxicology. I thought though I would go back specifically to the toxicokinetics to basically the absorption of distribution metabolism and excretion to discuss with you a little bit more about susceptibility, about the things we're learning. The way susceptibility will often develop is through changes in how the kinetics of chemicals go through the body. We've all heard, read about the unfortunate situation in which the family of four is caught in a snowdrift, leaves the car motor running, when they're finally dug out, mom and dad are unconscious in the front seat and the two kids are dead in the back seat. That's carbon monoxide toxicity. And the reason the kids are more at risk is simply because children breathe more per unit body weight than do adults. It's partly because of their metabolism, it's partly because they just don't sit as still as you do. I mean if you're a bunch of first graders, you bounce around a lot and that causes an increased airway uptake. They simply will breathe more. So they breathe more carbon monoxide. So respiratory uptake is just one example of increased absorption. Another for susceptibility is the fact that lead uptake in through the stomach will increase if you're iron deficient. Inner city children who tend to have more lead around also tend to be more iron deficient. They just don't get as much iron as they should. So the very children who are iron deficient are the very children who are more likely to be exposed to lead and who are at higher risk because they're gonna absorb more of the lead. Simply because lead and iron have a similar absorption pathway and if you have not enough iron, you make more of this absorption pathway and so if there's a lead around more it gets taken into the body. Distribution, I mentioned the iodine going to the thyroid is a classic example of something that could make you susceptible. In the Chernobyl incident a lot of radioactive iodine came out and it came out into an area in central the old Soviet Union where there isn't much natural iodine and so these are relatively low iodine diet. Well the more iodine you have that's natural the more it's competing with the radioactive in terms of being taken up into the thyroid. In fact the way we've stockpiled around the country around nuclear reactors, we've stockpiled iodide. And if any time anything ever gets loose and there's radioactive iodine coming your way just grab some iodide because what you do is you put so much into your system the thyroid won't take it all up and it will take up much less of the radioactive than it would if you had very little iodine. Well these people were more at risk, these children particularly, because they had very low levels of iodide in their salt and in their natural food and so they ended up with being more susceptible to thyroid cancer and now are having a high level of thyroid cancer. Metabolism as a cause of susceptibility. We have inherited all sorts of different pathways of metabolism, there's differences among individuals. These are very often genetically determined as we learn more about genetics we're going to learn more about why people differ from each other. Why is it that only one out of every eight lung cancer, cigarette smokers gets lung cancer? To what extent is this determined by genetic predisposition? Have to do with metabolism of the chemical or other issues as well. Excretion obviously the same type of thing. If you've got kidney disease you are going to be much more likely to retain within the body a toxic chemical that otherwise would be excreted in the urine that will lead to higher levels and more likely to have an effect. So all of these things affect susceptibility and are going to become more and more important in understanding whether people have been affected by toxic agents. Let me switch now to talking a bit about how we go about practicing toxicology and what we really do. And to do that I thought I'd start by giving you the distinction between drug and environmental toxicology. As I mentioned these are two major parts of what we do in toxicology and just trying to understand those differences might help understanding what we do on a day to day basis. First of all, when you're looking at a drug if you're the manufacturer of a drug you really want something that's got a biological effect. I mean it's gonna decrease blood pressure it's gotta do something to the body or it's a placebo or it's a chivalroid. I mean it's no sense making it. If you're manufacturing an industrial chemical you got a new color of paint you got something to make the color of my tie a little sexier, you're hoping it has no biological effect at all. You just want it to do, you know, just change that color please, nothing else because you don't want any effects in humans. Now there's an in between thing. There are things that are sides, C-I-D-E-S those are the pesticides or odenticides. You're trying to kill, herbicides we're trying to kill something that's living whether it be a plant, that dandelion in a backyard or whatever. But we don't want to affect humans. So again, they're sort of in between things. But basically that's a major distinction. And that leads to also a distinction in exposure and dose. Exposure to a drug is limited to the individual using the medicine, we hope. And the appropriate dose is well defined. On the other hand, if you've got an industry or a consumer chemical, you're never quite sure where it's going to end up. You're never quite sure what a kid is going to sniff or who's going to paint when there's a bunch of babies around there, any of those other things. You have to be really concerned about these things rather than assuming that it's really predictable. The other, another difference is that an individual exposed to a pharmaceutical agent presumably has some potential for a direct benefit. So if there's toxicity, it's unfortunate, but at least it's related to the hope that there was some benefit. There's no reason whatsoever we should have any toxicity from painting something in our home or doing something with a consumer product. Or any effluent that comes out of an industry. If they're making some money on it, it shouldn't be contaminating the neighborhood. And this leads to a difference in the amount of information we have available, which is what will very often appear in a courtroom. How much information do we have available about this chemical? We require the manufacture of the drug to do all sorts of trials in laboratory animals before you go to humans and then do trials in humans before you go out and market these things. For a new chemical that's going to be used again for color of my tie, we really require a very minimal amount of information and that minimal amount of information is hardly enough to be able to predict what is going to happen. The way we get this information is by two means. One is through understanding mechanism, the kind of basic toxicology that I've spoken about to try to understand and predict how chemicals act. Another is through something we call safety assessment. This is a routine testing that is done in response to regulatory requirements. They range from prescribed tests in a test tube to see if say something might cause mutations in cells in a test tube to multi-year animal cancer studies. So let me stop here and again refer you to the Federal Judicial Center's scientific manual if you have other questions about toxicology. Thank you.