00:00:08 Because we edit this thing totally,

00:00:11 as we just take bits and pieces.

00:00:13 Sometimes we might have your voice over a shot of, say, a hazardous waste site,

00:00:18 and you're describing something that has to do with that site.

00:00:21 Sometimes it might be just you on camera,

00:00:24 and we'll just pick and choose, and they're called bites.

00:00:27 I just want to say that you say that we have...

00:00:32 I'll ask you, if you would, please, to move just a little to your right.

00:00:37 Right there?

00:00:39 Yeah.

00:00:53 So, at the end, there is a text written,

00:00:56 somebody that underlies the whole...

00:00:59 That's right. The text has not been started yet.

00:01:01 So, that's why this thing is going to take forever to get on the air.

00:01:05 It won't be on the air for another year.

00:01:07 We'll finish the program, the television program,

00:01:10 this fall, October, supposedly.

00:01:14 But the text will still have to be written.

00:01:16 Then it has to be coordinated with colleges and universities.

00:01:19 We're going to use it.

00:01:20 So, it'll probably be the fall semester of 89.

00:01:23 So, it is for colleges and universities?

00:01:26 Freshman campus.

00:01:27 A little to your left.

00:01:28 One more.

00:01:29 Go back one more.

00:01:30 Okay, great.

00:01:32 I thought it was for high school students.

00:01:35 What does that say?

00:01:36 EFC camera.

00:01:39 Saw focus look anywhere?

00:01:41 You can tell it, huh?

00:01:42 Yeah, I noticed.

00:01:49 You're not going to...

00:01:50 I don't want you to watch it when we...

00:01:52 No, I was just curious how the colors look.

00:01:58 Well, I'm glad I didn't wear red, because with this background, it would be not...

00:02:04 That actually matches very well.

00:02:07 Yeah, I like that font.

00:02:10 Red is really forbidden.

00:02:13 Interesting.

00:02:14 It just smears horribly.

00:02:16 I think there's a pain in there.

00:02:19 Have you seen that?

00:02:20 It's like this black woman walking down the steps of somewhere, a building in Rome or somewhere.

00:02:26 She's got this brilliant red.

00:02:29 Have you seen that?

00:02:30 It just smears.

00:02:31 I don't know why they did it.

00:02:33 Okay.

00:02:39 I'm sure you have more.

00:02:43 Okay.

00:02:48 Do you think there's too much shadow on it?

00:02:52 I like that.

00:02:53 I like that, but it depends on how you've been doing things and if it's...

00:02:59 I like a contrast.

00:03:00 Could you put a little more light there?

00:03:02 Sure.

00:03:10 Do you want to look at me?

00:03:12 Yeah.

00:03:13 It's fine.

00:03:14 Good.

00:03:15 Good.

00:03:25 Looks nice.

00:03:28 Now, if you would just go in and out on my question.

00:03:31 That's a wide shot.

00:03:32 That's a good shot.

00:03:41 Where are you going?

00:03:45 Great.

00:03:46 Okay.

00:03:47 We're rolling already?

00:03:48 We're rolling, yes.

00:03:57 Let's start off just by talking about what we did earlier, and that is, just what do

00:04:01 we mean when we say something is toxic?

00:04:03 And if you would just describe to me the things you did earlier about dosage, basically, or

00:04:09 total quantity being the main determinant, if that's expressed accurately.

00:04:14 Well, let me first define the science of toxicology.

00:04:19 Okay.

00:04:20 Toxicology is a science that concerns itself with harmful effect of chemicals on biological

00:04:27 systems.

00:04:28 Now, those harmful effects can be described in several ways.

00:04:34 They can be described by...

00:04:39 I'm too uptight.

00:04:40 That's okay.

00:04:41 Let's just stop.

00:04:42 I'm too uptight.

00:04:43 That's okay.

00:04:44 Could we move the monitor around here?

00:04:47 Let me see the close before we...

00:04:53 You want to tell me what...

00:04:59 Okay.

00:05:02 Toxicity is a qualitative as well as quantitative term.

00:05:07 Qualitatively, when we say that substance is toxic, we usually talk about adverse health

00:05:13 effects that the substance can produce when it's administered to a biological system.

00:05:19 In other words, it can cause liver toxicity, kidney toxicity, can be adverse to the central

00:05:26 nervous system, to the blood-forming system, reproductive system, and so on and so forth.

00:05:32 It's the nature of the adverse effects that it causes that represents the qualitative

00:05:39 aspect of the term toxicity.

00:05:42 But toxicity also is a quantitative term.

00:05:46 And when I say quantitative, I mean that just about every chemical can be toxic at some

00:05:55 dose, and with the exception of cancer-causing chemicals, at least, can be harmless at some

00:06:02 other dose.

00:06:05 Could you give me an example of something?

00:06:08 Milk or whatever you'd like to pick as something that's maybe even beneficial at a low dose

00:06:15 but at a higher dose is harmful.

00:06:17 A classic example of substances that are beneficial at low doses and harmful at high doses are

00:06:25 certain trace metals.

00:06:27 As you probably know, a number of metals are essential to the normal functioning of the

00:06:34 body.

00:06:35 Example, iron, zinc, calcium.

00:06:39 However, too high doses of those metals will cause adverse health effects.

00:06:44 So, toxicology will concern itself with defining the level, the threshold at which these adverse

00:06:52 health effects begin to manifest themselves, as well as the shape of the dose-response curve

00:07:01 which will describe the relationship between the amount administered and the adverse health

00:07:08 effect that will occur.

00:07:11 Would you feel comfortable with saying that all substances are toxic at some dose level

00:07:17 and that really toxicity is a measure of, it really depends on the amount?

00:07:23 If you feel comfortable, would you say that?

00:07:25 Yes, I would say that.

00:07:27 That actually is a premise of the whole science of toxicology that dates back to the early

00:07:33 days of toxicology, sometime in the 16th century, where a definition was made that

00:07:41 sounds something like that.

00:07:43 The dose makes a poison.

00:07:45 Any substance can be harmless at low enough dose and can be harmful at high enough dose.

00:07:52 So, to say that a substance is toxic is really incorrect.

00:07:57 When one says that a substance is toxic, one needs to say what is the nature of that

00:08:03 adverse health effect and at what dose that effect was observed.

00:08:10 That's in addition to defining in what biological system that occurred and under what conditions

00:08:18 of exposure it happened.

00:08:21 Because different animals will react differently to exactly the same dose of a particular chemical

00:08:30 and different routes of exposure can lead to a whole different spectrum of adverse health

00:08:36 effects and once again, qualitatively and quantitatively.

00:08:42 Could you give me an example of, let's say, a route of exposure and how that would affect

00:08:49 the toxicity of something, a specific substance and a specific route of exposure?

00:08:55 Metals are a very good example of substances that will have entirely different adverse

00:09:00 health effects when ingested or when inhaled.

00:09:05 For example, let's take a chemical such as chromium.

00:09:09 Chromium is known to cause respiratory and lung cancer among workers.

00:09:15 And it's an effect that's fairly well documented by now.

00:09:19 Nasal cancers and lung cancers.

00:09:22 When ingested, it's fairly harmless.

00:09:26 And when I say fairly harmless, I mean it takes very large doses to produce any kinds

00:09:32 of adverse health effects and no cancer at all has been ever observed.

00:09:39 Instead of saying ingested, would you mind saying, you mean eaten?

00:09:43 Yes.

00:09:44 Okay.

00:09:45 Should I say eaten?

00:09:46 If you wouldn't mind.

00:09:47 Okay.

00:09:48 Because that's something that...

00:09:49 Stop.

00:09:50 Take a second.

00:09:51 That's the sort of thing that, once again, people know what the word means probably,

00:09:53 but they have to stop and think about it.

00:09:55 Okay.

00:09:56 By the time they've said, oh, okay, eating or is that smelling or...

00:09:59 Okay, so inhaled and eaten.

00:10:01 Yeah.

00:10:02 Okay.

00:10:03 But otherwise, it was great.

00:10:04 It was a perfect kind of example.

00:10:05 Okay.

00:10:06 So should I explain that again?

00:10:07 If you wouldn't mind.

00:10:08 Because actually, chromium is a very interesting case.

00:10:09 Yeah.

00:10:10 I'll give you a signal.

00:10:11 So this is the point that you made earlier about all these other effects that have to

00:10:16 occur simultaneously and why we can...

00:10:20 We can...

00:10:21 Change shot?

00:10:22 Yeah.

00:10:23 Okay.

00:10:30 Development of cancer is a probabilistic process.

00:10:33 It starts with the first event, which we presume to be a mutation, a chemical change in the

00:10:39 DNA, which can be inherited or can be caused by a chemical exposure to a chemical.

00:10:46 In order for cancer to develop, several other events have to take place.

00:10:52 Those are events that involve perhaps more mutations or perhaps some other changes in

00:10:59 the cell or in the surrounding tissue.

00:11:03 When the probability of...

00:11:06 This is going to be difficult.

00:11:15 When the...

00:11:16 Why don't you just start talking and say anything, and then maybe it will just come to you in

00:11:21 midstream, so to speak.

00:11:23 Okay.

00:11:24 When we have very few mutations, the probability that the other events will take place is very

00:11:32 low.

00:11:33 No, that doesn't come...

00:11:34 Why am I...

00:11:35 Oh, I have trouble with this.

00:11:39 Just keep trying.

00:11:40 I think it will come out eventually.

00:11:45 Okay, stop.

00:11:46 Yeah, yeah.

00:11:47 No, no.

00:11:48 Well...

00:11:54 Okay.

00:11:56 Body has a very clever mechanism of dealing with foreign substances that it encounters.

00:12:04 When a chemical enters the body, it has to be, of course, first absorbed, then it is

00:12:11 distributed between different tissues, and then very frequently is metabolized.

00:12:19 Why are chemicals metabolized?

00:12:22 Metabolism is a detoxification mechanism.

00:12:26 What's needed in order to get rid of the chemical is to make it more soluble so it could be

00:12:33 excreted through the urine.

00:12:34 Urine is the predominant method of excretion of foreign chemicals, toxic chemicals, from

00:12:40 the body.

00:12:42 The metabolism means chemical transformation of a substance, and body is very well equipped

00:12:49 to do so.

00:12:50 What happens with a chemical, for example, which is poorly soluble in urine?

00:12:55 That means it cannot be excreted easily, it will not dissolve, and it cannot be filtered

00:13:00 out of the blood in the kidneys into the urine.

00:13:04 In that case, the body is going to transform that chemical, make it more chemically reactive.

00:13:12 We call that chemical intermediates.

00:13:17 And those chemical intermediates then can be bound chemically with certain highly soluble

00:13:25 biological molecules, which will essentially carry that chemical out into the urine and

00:13:31 excrete it.

00:13:32 The process that I describe is called metabolism, two stages of metabolism.

00:13:39 The first stage is make the chemical more reactive.

00:13:43 Stage two, bind that with certain biological molecules, highly soluble in water, which

00:13:50 can be excreted via urine.

00:13:53 Those two stages are called metabolic transformation of a chemical.

00:13:58 A typical chemical such as benzene, for example, once it enters the body, is going to be transformed

00:14:05 into benzene epoxides, so-called epoxides, which are very chemically reactive, and it's

00:14:13 going to bind to glucuronides and excrete it.

00:14:19 So metabolism is a very efficient detoxification mechanism.

00:14:25 There is a problem.

00:14:27 The problem is that some of the intermediates, some of those results of the chemical transformation

00:14:33 turns out to be more toxic than the original compound.

00:14:37 And here a very good example is alcohol.

00:14:40 Alcohol per se is not particularly toxic.

00:14:44 Once it enters the body, it's going to be transformed into an aldehyde, which is much more toxic than the benzene.

00:14:53 Okay, let me start again with that one.

00:14:58 Hold it a second.

00:14:59 Let's change the shot here.

00:15:01 You don't need to change it.

00:15:02 Probably change tapes is what I'd say.

00:15:04 Okay.

00:15:05 Well, let's see.

00:15:06 How much time do we have?

00:15:07 Four.

00:15:08 Let's finish this phrase.

00:15:09 Okay, fine.

00:15:11 And we'll just start back with alcohol as a good example.

00:15:14 Okay.

00:15:15 Ready?

00:15:17 Alcohol is a very good example of detoxification mechanisms making things worse rather than better.

00:15:24 Alcohol per se is not particularly toxic.

00:15:27 When ingested, when swallowed by an oral route, alcohol is metabolized into an aldehyde.

00:15:35 That aldehyde is much more toxic than the alcohol itself,

00:15:39 and it's the aldehyde that produces toxicity to the liver,

00:15:44 especially over a long period of time when the ingestion takes place.

00:15:50 Another example—

00:15:52 Excuse me.

00:15:53 I'm going to stop you there.

00:15:54 Change shot again.

00:15:56 Could we talk about alcohol as being a cause of cancer as well?

00:15:59 Not really, no, because—no.

00:16:06 Let's start by saying another example.

00:16:08 Another—ready?

00:16:10 Yeah.

00:16:11 Another example of the adverse effect of detoxification mechanisms, which metabolism is,

00:16:19 is benzoylpyrin.

00:16:21 Benzoylpyrin is a common byproduct of incomplete combustion.

00:16:26 We see it every day when we charcoal a steak.

00:16:31 The dark material that we see there is a mixture of compounds, polycyclic aromatic hydrocarbons.

00:16:38 Benzoylpyrin is a very common member of the large class of chemical compounds.

00:16:44 Benzoylpyrin is very poorly soluble in water, and it's rather chemically unreactive.

00:16:50 What that means is that if it goes through the system unchanged,

00:16:56 it's very difficult to filter it into the urine.

00:16:59 It's not soluble in water.

00:17:02 It is also chemically unreactive, so it cannot be bound with those biological molecules,

00:17:08 which could make it more water-soluble.

00:17:12 So benzoylpyrin presents a problem in terms of excretion, unless it's changed chemically.

00:17:21 And benzoylpyrin is changed chemically through the phase I metabolism.

00:17:28 It's made into reactive intermediates, which then can be bound chemically with biological molecules

00:17:37 and fairly easily excreted in urine.

00:17:42 Now that's where the catch is.

00:17:45 It's the reactive intermediates, the products of this phase I metabolism,

00:17:52 which is intended to detoxify the chemical and remove it from the body as efficiently as possible.

00:18:00 These chemical intermediates are also capable of reacting with other constituents of the cell,

00:18:07 most notably proteins and DNA.

00:18:11 And it is believed that that chemical reactivity

00:18:15 Intermediate with DNA is the fundamental event that ultimately leads to benzoylpyrin being carcinogenic.

00:18:28 It is the binding, chemical binding, of that reactive intermediate to DNA that causes mutation.

00:18:38 Okay. Good timing.

00:18:46 We'll take...

00:18:51 Should I...

00:18:52 I'll tell you when.

00:18:54 Do you have a question before we start?

00:18:56 No, I think...

00:18:57 Okay.

00:19:05 Benzoylpyrin is a member of a larger class of chemicals known as polycyclic aromatic hydrocarbons.

00:19:12 Polycyclic aromatic hydrocarbons are products of incomplete combustion, and we often find them in everyday life.

00:19:19 For example, when we charcoal broil steak, the dark material that forms when the fat is burned incompletely is...

00:19:33 Just start from the beginning.

00:19:34 Yes.

00:19:35 Benzoylpyrin is a member of a larger class of chemicals known as polycyclic aromatic hydrocarbons.

00:19:42 These chemicals are commonly found in daily life.

00:19:45 For example, when we charcoal broil a steak, the dark material that we see has polycyclic aromatic hydrocarbons,

00:19:54 and benzoylpyrin is one of many of those substances.

00:20:00 Benzoylpyrin is probably the most studied carcinogen of all the chemical carcinogens that we know.

00:20:07 It's been studied for around a century by now, its chemistry and the mechanism by which it causes cancer.

00:20:17 It is a highly water-insoluble chemical.

00:20:21 So, in a usual manner, the body deals with it by transforming it chemically into a much more chemically reactive species,

00:20:31 the reactive intermediate, in order to be able to excrete it much easier through the urine.

00:20:39 Now, the byproduct of that process is that the chemical intermediate is capable of reacting chemically with the components of the cell,

00:20:52 namely proteins and nucleic acids, the DNA.

00:20:58 It's that chemical reaction between DNA and the reactive intermediate of benzoylpyrin that leads to a mutation.

00:21:08 Mutation is a chemical change in the DNA.

00:21:12 In this case, it's a formation of a chemical bond between benzoylpyrin metabolite and a site on the DNA.

00:21:24 That's a mutation.

00:21:27 This event, single molecular event, can ultimately lead to cancer.

00:21:37 Now, if you ask me now, can a single mutation cause cancer?

00:21:43 I would answer to it, in theory, a single mutation can cause cancer.

00:21:49 In practice, it may be such a rare event.

00:21:53 In other words, it would happen with such low probability that in practice, we would not be concerned about that.

00:22:02 In other words, very improbable that it would happen, although possible.

00:22:08 Why is it so improbable?

00:22:11 We don't understand everything about the process of cancer formation, but we do understand that it's a multistage process.

00:22:22 Probably the initial event that takes place is a mutation on DNA.

00:22:29 It could be caused by exposure to a chemical carcinogen, such as benzoylpyrin, for example,

00:22:37 or benzene, or vinyl chloride, or a host of other chemicals known to induce cancer.

00:22:45 Or that initial mutation may be inherited and not caused at all by exposure to chemicals.

00:22:53 Or, perhaps, it may be caused by oncogenic virus.

00:22:57 In either case, it is the initial event, the mutation, that, as it's believed currently,

00:23:05 leads to a series of changes in the cell that will ultimately lead to cancer.

00:23:11 Now, in order for cancer to develop, several additional events must take place.

00:23:18 Some of them are better understood than others.

00:23:21 But if there is only a single mutation, the probability of all the events taking place

00:23:30 in the right order that is required for this ultimate transformation of normal cell into malignant cell

00:23:40 are very improbable.

00:23:43 Each event has a limited probability, so if we combine several events,

00:23:48 each of them of very low probability, including this single mutation,

00:23:53 we come up with an event which is very, very unlikely.

00:23:58 That's why a single mutation, although in theory capable of leading to cancer,

00:24:06 is very unlikely to lead to cancer simply because the probability of it happening is very, very low.

00:24:14 Does that explain it?

00:24:16 Yeah, that was very good.

00:24:17 Let's see if we can go from that.

00:24:19 And you're doing a great job, Pam.

00:24:22 I'm still trying to relate it to a standard.

00:24:29 In other words, what I'm trying to get at is, you know,

00:24:32 there are people who say we should have zero, that certain carcinogens we should have zero tolerance for.

00:24:39 They should not be present, say, in our drinking water.

00:24:41 And I'm trying to say, given this arbitrary nature of things, not arbitrary,

00:24:46 but given this decreasing probability and, practically speaking,

00:24:50 the unlikelihood of cancer being caused, can we justify that it's a certain percentage

00:24:58 or a certain amount of a substance in our food or in our drinking water?

00:25:02 Is it okay?

00:25:04 I can say that where the rule of thumb is that people consider risks below one in a million to be insignificant

00:25:14 and risks greater than one in 10,000 to be significant.

00:25:19 In other words, we as a society have determined this gray area of cancer risks

00:25:25 of between one in 10,000 and one in a million.

00:25:28 So we really as a society believe that once the risks are lower than one in a million,

00:25:32 it's nothing to worry about.

00:25:35 But it's not by any scientific analysis.

00:25:40 It's by practicing it that way.

00:25:46 And what goes into that?

00:25:48 In other words, what other factors go into making this decision?

00:25:52 You are not taping it now, are you?

00:25:55 I actually, that last statement, I thought she was saying what she was going to say,

00:26:00 so I'm sorry a little bit right in the middle.

00:26:02 Okay.

00:26:03 It was good.

00:26:04 Let's do it again.

00:26:05 Yes.

00:26:07 Can you repeat what you just said?

00:26:10 Yes.

00:26:11 As the dose of a carcinogen gets smaller, the risks associated with it get smaller.

00:26:17 It never reaches zero, but it can become very, very small,

00:26:21 such as one in 100,000, one in a million, one in a billion.

00:26:27 You can go on and on and on into infinitely small doses and infinitely small risks,

00:26:34 although they will never be zero,

00:26:38 based on our current understanding of the carcinogenic process.

00:26:42 Now, what value of risk should we consider to be so small that we shouldn't worry about that?

00:26:50 Well, that's a matter of debate.

00:26:53 In practice, when we look at the government regulations of carcinogenic substances,

00:26:59 we see that in most cases when the risks are one in a million or smaller,

00:27:05 no action is taken by the government.

00:27:08 When the risks are greater than one in 10,000,

00:27:13 usually regulatory action is taken by the federal government.

00:27:17 So what we have defined by practicing it, not by any particular debate or analysis,

00:27:24 we have defined that risk of one in a million or smaller is an insignificant risk.

00:27:31 We have also defined a significant risk of one in 10,000 or greater,

00:27:38 but we have left this large gray area which spans two orders of magnitude,

00:27:44 hundredfold, where sometimes the action is taken, sometimes the action is not taken.

00:27:51 And that particular gray area is where all the debate takes place

00:27:58 and where different individuals and different organizations interpret the risk differently.

00:28:05 Sometimes it's significant, sometimes it's not significant.

00:28:10 You're fired.

00:28:14 Quiet, please.

00:28:16 Okay, we're talking about the gray area between the 10,000, one in 2,000, one in a million.

00:28:21 So I'd like you to say, if you would, that since we have this wide range,

00:28:27 there are other factors coming into play, such as, I think, give us some examples.

00:28:32 When the carcinogenic risks are in that gray area between one in 10,000, one in a million

00:28:44 is when other factors not related to risk and not necessarily related to the scientific concerns that are—

00:28:56 When the risks are in that gray area—

00:28:59 Start again.

00:29:00 Okay.

00:29:01 When the carcinogenic risks are within that gray area somewhere between one in 10,000 and one in a million

00:29:08 is when other concerns are included in the debate at what level to regulate.

00:29:15 And those include costs of the regulation, feasibility of enforcing that regulation,

00:29:22 technology available to remove a carcinogenic substance from circulation,

00:29:28 or technology available to measure it.

00:29:32 If no measurement can be made, no enforcement of the regulations can be made.

00:29:38 So there is a host of other considerations that will affect where, ultimately, the standard will fall.

00:29:46 And it will fall anywhere, as based on our past experience, anywhere in this range of two orders of magnitude.

00:29:56 What kind of considerations will be included also depends on what the law requires.

00:30:03 Carcinogens are regulated in many environmental statutes.

00:30:07 An example, Safe Drinking Water Act deals with carcinogenic risks in drinking water.

00:30:14 Clean Air Act addresses carcinogenic substances in ambient air, outdoor air.

00:30:21 Clean Water Act addresses carcinogens in surface waters, and so on and so on.

00:30:28 Several environmental statutes.

00:30:30 The statutes also have very specific requirements of what considerations have to be included in setting a standard.

00:30:40 So, for example, the Safe Drinking Water Act specifically requires that EPA,

00:30:47 in developing a drinking water standard, looks into the carcinogenic and other adverse health effects,

00:30:58 but it also looks into feasibility and cost of that particular regulation.

00:31:04 And that's exactly what EPA does when it sets the drinking water standard.

00:31:10 Clean Air Act does not make specific requirements that costs have to be considered

00:31:17 in setting ambient air standards for toxic chemicals, including carcinogens.

00:31:24 FIFRA, for example, which regulates pesticides, makes a specific requirement, once again,

00:31:32 that cost-benefit analysis is performed before a chemical is, for example, banned,

00:31:39 a pesticide is banned, or the registration of a new pesticide is given or is denied.

00:31:46 So those are the considerations that routinely have to be considered

00:31:51 when a standard is set for a carcinogenic substance.

00:31:56 Okay, fine. That was good.

00:31:58 Now, let's talk a little bit about...

00:32:07 If we could just say fairly, in a fairly short way,

00:32:11 the difference between non-carcinogenic and carcinogenic substances,

00:32:15 in terms of the fact that we can set a definite level, say a definite level below which no harm will be done,

00:32:23 whereas that we can carcinogenic, without going too far along in the explanation of the probability.

00:32:28 Okay.

00:32:31 Still rolling?

00:32:32 Yeah.

00:32:33 Go ahead.

00:32:34 The fundamental difference between carcinogenic and non-carcinogenic effect

00:32:40 is that it is believed that there is a threshold for non-carcinogenic effect below which no...

00:32:49 No, this is all wrong. Okay, I'll start again.

00:32:52 Start again.

00:32:55 For non-carcinogenic effects...

00:33:03 I'm thinking. Yeah, I'm thinking how to phrase the question.

00:33:06 I'll take a second.

00:33:18 For a substance that does not cause cancer, such as, for example, methanol or ozone or carbon dioxide or aspirin,

00:33:29 there is a level below which no adverse effect would be expected.

00:33:35 That dose differs with the individual chemical.

00:33:40 It also differs among people.

00:33:44 But we can, at least in principle, find a level below which the population as a whole

00:33:50 will not suffer any adverse health effects if exposed to that chemical.

00:33:56 No such level can be assumed for carcinogenic substances

00:34:01 because, in principle, a single molecule of a carcinogen increases a risk of cancer.

00:34:10 That may be a very, very small risk, but a risk nonetheless which is greater than zero.

00:34:17 So for carcinogenic substances, we don't say that we have to come up with a dose

00:34:24 below which no harmful effect will be observed.

00:34:28 Instead, we relate a dose to a risk.

00:34:33 So in other words, for benzene, for example, one part per billion in drinking water

00:34:40 may be associated with a risk of, for example, one in a million.

00:34:46 Ten parts per billion in water will be associated with a risk ten times higher of, in this case, one in 100,000.

00:34:57 These are illustrative numbers.

00:34:59 They are not much different from the real ones, but I do not remember what the real ones are.

00:35:05 What that creates from a regulatory viewpoint and from the perception viewpoint

00:35:11 is that an agency cannot come out and tell the public, you are safe.

00:35:19 We have reduced the exposure to the level that nobody will suffer any adverse health effects.

00:35:25 That can be said for ozone, but it cannot be said for benzene, which causes cancer.

00:35:32 The best that the agency can say is we have reduced the levels of benzene in ambient air

00:35:39 so that the risk of cancer is no greater than a particular number.

00:35:46 It may be a very small number, but the word safe cannot be used by an agency.

00:35:53 And that, of course, produces a serious problem of interpretation and perception

00:36:00 because people would like to know that they are safe.

00:36:05 That is the fundamental question, am I safe?

00:36:08 And the agency, when dealing with carcinogens, cannot ever say you are safe.

00:36:14 All that the agency can say, the risks are very small or they are above a certain level

00:36:20 or they are below a certain level.

00:36:22 And that is at the center of the controversial debate over carcinogenic risks.

00:36:30 Let's see if we can relate this to our interviews.

00:36:52 This question has two separate scientific components.

00:36:56 The first one is, can we document scientifically

00:37:01 that the population that claims that suffers from elevated rates of cancer

00:37:06 indeed has elevated rates of cancer?

00:37:09 In other words, do they have more cancers than we should expect

00:37:14 of a group of people with their particular socioeconomic characteristics,

00:37:20 their age distribution, their income, and so on and so forth.

00:37:24 That's the first question.

00:37:26 The second question is, suppose we can show that they indeed have more.

00:37:30 If we did have more cancer than we would expect of a group of people like that,

00:37:37 can we attribute that increase to the site?

00:37:43 Each of those scientific questions has its own problems.

00:37:48 The first one, demonstrating that there is an elevated rate of cancer,

00:37:54 has a problem of sensitivity.

00:37:56 It is done through epidemiologic studies.

00:37:59 Epidemiology is a very insensitive science.

00:38:04 Maybe I should explain what epidemiology is.

00:38:07 Well, let's stop for a second.

00:38:09 Or a health study.

00:38:27 Does the population have higher rate of cancer that we would expect of a population like that?

00:38:35 How do we answer that question?

00:38:37 We answer it by comparing the rate of cancer in that population with some other group of people

00:38:43 who are hopefully very similar to this group in all respects,

00:38:49 and look at the rates of cancer in that other group.

00:38:54 We'll call them control population.

00:38:57 The problem with doing that is that in order to see a difference between the two populations,

00:39:07 the rate in our study population would have to be at least two times higher

00:39:15 than the rate in control population in order for us to believe the results from a scientific viewpoint.

00:39:24 Two times higher rate is a significant increase, and we may not see it.

00:39:30 We may, for example, see 50% increase over the control.

00:39:35 Is it a significant difference?

00:39:37 Enough for us to conclude that they indeed suffer higher rate of cancer.

00:39:42 It's hard to tell.

00:39:44 There is large uncertainty in those results.

00:39:48 Now suppose that we show that this population really does have an elevated rate of cancer,

00:39:54 two or three times what we would expect otherwise,

00:39:58 based on national statistics or based on a comparison with some control population

00:40:03 which is well matched with this population.

00:40:06 Then the question comes, can we attribute that increase to the dump?

00:40:12 In other words, can we find a causal relationship between living in the vicinity of the dump

00:40:20 and elevated rate of cancer?

00:40:23 Now this question can never be answered beyond any doubt.

00:40:31 All we can do is present a set of evidence.

00:40:39 Is that an English set of evidence?

00:40:42 Set of arguments, right?

00:40:45 Okay, I will go back to the...

00:40:55 Okay, so I'll go back to...

00:40:57 Can I go now?

00:40:59 Yeah.

00:41:01 Suppose we document...

00:41:09 Suppose we document that the population in question

00:41:13 indeed has a rate of cancer which is higher than we would expect otherwise.

00:41:18 How can we attribute that to the dump?

00:41:24 That's the second question.

00:41:26 That question cannot be answered beyond a reasonable doubt.

00:41:31 All we can do is present a set of arguments,

00:41:35 a set of pieces of data that will either make that hypothesis strong or weak.

00:41:44 For example, if chemicals that have been detected at the dump

00:41:49 clearly are known to cause cancer, that strengthens the argument.

00:41:55 If it can be demonstrated that the population in the vicinity of the dump

00:42:01 has actually been exposed to those chemicals,

00:42:05 either by inhaling the air or by drinking contaminated water

00:42:11 or by using that site as a playground for the families or for the children,

00:42:19 that will strengthen the argument.

00:42:22 If we can show that the appearance of cancer

00:42:28 chronologically followed appearance of the dump,

00:42:34 that again strengthens the argument.

00:42:36 If cancer seems to have occurred, elevated cancer,

00:42:41 only in the last year or two,

00:42:44 has there been enough time to develop cancer?

00:42:48 Cancer requires a decade or two to develop.

00:42:51 If the dump has been there only for two years

00:42:54 and now we are observing cancer,

00:42:56 it is less likely that it's the dump that's causing the cancer.

00:42:59 So there is a whole set of arguments that one would have to make

00:43:05 in order to consider that there may be a causal association

00:43:11 between the existence of the dump and the elevated rates of cancer.

00:43:16 It will not be proven, but it can be demonstrated quite closely.

00:43:24 That was wonderful.

00:43:34 If the people who live in the neighborhood of a dump

00:43:38 inhale fumes of carcinogenic chemicals

00:43:42 such as tetrachloroethylene, trichloroethylene,

00:43:46 vinyl chloride, or PCBs,

00:43:49 it is possible that an elevated cancer rate will take place there.

00:43:57 It is possible.

00:43:59 Unfortunately, we will always be left to theoretical predictions.

00:44:05 Science cannot distinguish between the background levels of cancer

00:44:12 and those additional cancers that may occur

00:44:16 as a result of inhalation of carcinogenic chemicals.

00:44:20 Suppose, for example, that there are 10,000 people

00:44:23 living downwind of a site.

00:44:26 And suppose further that as a result of inhaling the air

00:44:30 contaminated with some volatile solvents,

00:44:34 carcinogenic solvents that emanate from the site,

00:44:37 suppose that those chemicals increase the risk of cancer

00:44:42 by, say, 1 in 10,000 in that population.

00:44:47 That means that upon a lifetime of exposure to these fumes

00:44:53 among 10,000 people, with the risk of 1 in 10,000,

00:44:58 we are going to observe one additional cancer attributed to that site.

00:45:05 Could we detect that above the existing background levels of cancer?

00:45:10 No, we could not.

00:45:12 Even if there were 10 cancers in addition to the existing background,

00:45:18 the science would not be able to distinguish

00:45:22 between the background levels and the additional levels of cancer.

00:45:27 That's why we are left with this hypothetical methodology

00:45:32 of risk assessment in predicting

00:45:36 what the magnitude of the risk may be at those sites.

00:45:40 But we have no tools to prove that, to test that hypothesis experimentally.

00:45:47 So we are left with a great deal of uncertainty,

00:45:50 and all we can do is assume that our theoretical predictions are correct

00:45:56 and act upon them as though they were correct.

00:45:59 But we cannot test them experimentally.

00:46:02 When you say assume that our theoretical assumptions are correct

00:46:05 and act upon them, what are you referring to?

00:46:08 Just a moment.

00:46:14 The theoretical predictions are calculations of risks

00:46:20 based on some presumed dose.

00:46:23 And these calculations of risks are based on what we know

00:46:28 the risks of chemicals are.

00:46:32 No, I will start again. This is getting convoluted.

00:46:35 I wonder if we could just say something like,

00:46:37 if we know that certain substances can cause cancer,

00:46:39 then we just try to eliminate the exposure or something?

00:46:43 That's right. Yes.

00:46:48 The theoretical predictions are what we know about chemicals

00:46:52 based on animal...

00:46:58 Theoretical predictions are what we know about chemicals

00:47:02 on the basis of tests with animals.

00:47:05 If... Okay, I'll do it again.

00:47:23 Theoretical predictions are what we know about properties of a chemical

00:47:31 based on some previous studies that were performed on it,

00:47:35 usually with animals, sometimes with humans.

00:47:39 If we know that the chemical is likely to cause cancer,

00:47:43 then we would like to reduce the exposure to it.

00:47:47 If we know that it causes cancer at relatively low doses,

00:47:54 in other words, it has high risk at low doses,

00:47:58 we would like to reduce the exposure to very low levels.

00:48:02 And especially if we can calculate that risk

00:48:09 on the basis of what we know about the chemical...

00:48:12 This is not going very well.

00:48:14 No, I don't like what I am doing.

00:48:16 Yeah, okay.

00:48:17 What if we could say something very simply,

00:48:19 like if we know that there are carcinogenic chemicals

00:48:22 being given off on the stump, then...

00:48:24 Well, there is more to it.

00:48:26 When I talk about theoretical prediction

00:48:28 is that we can actually calculate how many additional...

00:48:31 Okay.

00:48:41 If we know that these chemicals

00:48:44 will cause a significant number of additional cancers,

00:48:47 we simply want to reduce the exposures or eliminate them at all.

00:48:53 Okay.

00:48:54 How about AC noise?

00:48:56 Yeah, it just came in.

00:48:58 Can you try once more?

00:49:01 Oh, okay.

00:49:04 That's why people build studios,

00:49:06 so they don't have to worry about this.

00:49:08 Is it on now?

00:49:09 Yeah, but it's constant now, so it's all right.

00:49:11 So go ahead.

00:49:12 Okay.

00:49:13 If we know that exposure to the chemicals emanating from the dump

00:49:17 is going to cause a significant number of additional cancers,

00:49:22 even though we cannot demonstrate it experimentally,

00:49:26 we want to reduce the exposure or eliminate it altogether.

00:49:31 That's good.

00:49:32 That's very good.

00:49:33 Let me ask you one thing.

00:49:35 Your flight isn't at risk.

00:49:45 When a scientist looks at the risk,

00:49:47 which is one in 100,000,

00:49:50 they look at it and say,

00:49:52 this is indeed a very small risk,

00:49:54 not to worry about or certainly not a great concern.

00:49:59 When a person who lives downhill...

00:50:03 Okay, I have to change that.

00:50:06 You might even start with a person who lives downwind of a...

00:50:10 When a person who lives downwind from a site

00:50:14 and is exposed to carcinogenic substances

00:50:17 looks at the risk and sees a risk of one in 100,000,

00:50:22 they ask several questions.

00:50:24 They'll ask, risk of what?

00:50:28 Dreadful disease, cancer.

00:50:31 How well do scientists really understand this disease?

00:50:36 Not that well.

00:50:38 How sure are they that it's one in 100,000

00:50:41 and not one in 10,000 or one in 1,000?

00:50:45 It turns out there is a great deal of uncertainty.

00:50:48 Who caused this risk?

00:50:52 Chemicals dumped by a reckless company.

00:50:55 What if that one in 100,000 is my child?

00:50:58 In other words, this risk acquires a lot of dimensions

00:51:03 and many of them are personal dimensions.

00:51:07 Certainly this is not an abstract number of one in 100,000.

00:51:11 It's a very personal issue.

00:51:14 And it's an issue which has consequences

00:51:19 to the life of the person and their loved ones.

00:51:22 That's why the perception is entirely different

00:51:25 than a lay person will have of a risk versus the scientist.

00:51:29 The scientist will look at the number

00:51:31 and say probability of one in 100,000,

00:51:34 well, that's indeed a very low probability event,

00:51:37 very unlikely to happen.

00:51:39 What is the big problem?

00:51:41 Why is everybody getting upset?

00:51:43 And that difference in perception,

00:51:46 the personal multidimensional view of risk

00:51:50 that the lay person has

00:51:52 and the purely analytical view of risk

00:51:56 in terms of probability of an event

00:51:59 is what creates the tremendous gap between...

00:52:11 You have a great cheeto?

00:52:15 The grape is gone.

00:52:22 Okay, so start on that subject anywhere you'd like.

00:52:30 When an average person looks at the risk of cancer

00:52:33 that says you have a risk of cancer

00:52:36 which equals one in 10,000,

00:52:40 they ask several questions.

00:52:43 They don't stop at the number.

00:52:45 They ask, what is the source of it?

00:52:50 The answer in this case will be the chemicals

00:52:53 which were recklessly dumped by some company.

00:52:56 What is the disease that we are talking about?

00:52:59 Cancer, dreadful disease, disease that everybody fears.

00:53:04 What if that risk of one in 10,000

00:53:07 means that it's my child is going to get sick?

00:53:11 It's not an abstract concept anymore.

00:53:13 It's an extremely personal concept.

00:53:16 Therefore, there is a big gap

00:53:19 between how a lay person who is exposed to chemicals

00:53:24 which they have nothing to do with,

00:53:27 how these people perceive the risk versus a scientist.

00:53:32 A scientist will look simply at the probability

00:53:35 and say one in 10,000, that's a very low risk.

00:53:39 There is no reason to get all upset about that.

00:53:42 There is a tremendous gap between how people

00:53:46 who are affected by the exposure

00:53:48 to these environmental carcinogens perceive the risk

00:53:51 and how a scientist will perceive the risk.

00:53:54 A scientist will simply try to understand

00:53:56 what it means, one in 10,000,

00:53:59 and the answer will be it's a very low probability.

00:54:03 A lay person will look at all the human dimensions,

00:54:07 personal dimensions of that risk,

00:54:10 and that speaks an entirely different language

00:54:13 than the scientific language.

00:54:15 The lack of understanding of this different perception

00:54:19 between the scientists and the lay people

00:54:22 has led to a lot of problems in communicating risks

00:54:28 between the agencies or the scientists and the lay public

00:54:33 because simply the perceptions were quite different.

00:54:46 Ideally, of course, we would like to eliminate all carcinogenic substances from our environment

00:55:01 and reduce the risk of cancer to zero, at least cancer caused by those chemicals. And

00:55:08 in many ways, we are going very far in that direction. When you look at how much money

00:55:14 we are spending on cleanup of hazardous waste sites in this country, hazardous waste sites

00:55:20 on a whole are a relatively small risk to the population in terms of their effects on

00:55:28 health. They are not an insignificant risk, but compare, for example, with the risks of

00:55:36 cancer from indoor radio, or compare with the risks of cancer from… Oh, that's a

00:55:48 problem. I can't think of another. Okay. I'll start again. Okay.

00:56:02 Once again, the sort of encapsulation of why we have to make these cold decisions.

00:56:12 Of course, ideally, it would be very nice to get rid of all the chemical carcinogens

00:56:17 from the environment and say, do whatever it takes. Eliminate them. There is no need

00:56:24 to have carcinogens in drinking water, air. They have no business being there. But then

00:56:30 it boils down to money. Unfortunately, it takes tremendous resources to reduce the levels of

00:56:38 exposure in the environment to carcinogens, especially when you get to very low levels.

00:56:43 Reducing it by another order of magnitude may take millions of dollars per one hazardous

00:56:48 waste site. And the pie is not unlimited. There is only that much resources that we have. So,

00:56:55 it really boils down to how much money, as a society, can we spend on this particular hazard

00:57:03 in a sea of many other hazards from carcinogens and from any other products of our everyday life.

00:57:10 That's good. Let's talk about some of the other things. For example, the points that Ames mentions,

00:57:20 where we get carcinogens in our food. I guess we want to include, no, we don't want to include smoking in here now.

00:57:29 Carcinogens from our food. Things that we're inadvertently exposed to that we more or less

00:57:33 have to be exposed to, at least until we can do something about it. Am I shining? No, you're good so far.

00:57:40 Okay, so just comment on what he said. Yeah, don't mention my name or anything, but we just want to make

00:57:50 a comparison between. There are all these other problems, all these severe, I don't want to say severe.

00:57:57 Are we stopped? Yeah, we're stopped. We want to compare the amount of exposure we get normally

00:58:11 from foods, even radon in some cases, to the very low levels that we're trying to establish in

00:58:19 carcinogens from synthetic chemicals, and say something to the effect of, what is his point, that should we spend as much money?

00:58:38 Well, his point is that we are really, that we are implicitly accepting risks from carcinogens in food, and don't worry about it,

00:58:51 and those risks may be much higher than the risks from carcinogens in the environment.

00:59:00 If we are accepting those, why shouldn't we accept the additional risks from chemicals?

00:59:07 Can you pose that question and then give your viewpoint on that? Let's do it that way, because you started off very well.

00:59:12 And don't refer to him, which might even say, some people say, or something like that, or sometimes it's argued.

00:59:22 Well, there are trace amounts of carcinogens naturally.

00:59:28 No, just as you said, in other words, some people say or it's argued that we accept a lot of risk from carcinogens, making his point,

00:59:39 without looking at him by name, and going on to give your view of it.

00:59:43 Okay, let's roll. I turned it off, but it kept rolling, so we're on. Okay, go ahead.

00:59:52 Some people argue that we are implicitly accepting significant cancer risks from natural products.

00:59:59 Food, there are a lot of trace carcinogens naturally occurring in the food chain.

01:00:06 The fact that we charcoal broil our steaks, and we don't worry about that.

01:00:11 The fact that we eat a lot of fats, which are associated with breast cancer.

01:00:17 So we are really implicitly accepting certain amount of risk of cancer,

01:00:23 and Americans are not really changing their eating habits much, not in terms of carcinogenic risks.

01:00:32 So the argument goes, why shouldn't we expect, so the argument goes, why shouldn't...

01:00:40 Let's just change the shot there. Okay.

01:00:46 So the argument goes, we could accept certain amount of additional risks of cancer from synthetic chemicals.

01:00:58 I don't know what to say about that. We could.

01:01:05 Well, let's stop tape for a second.

01:01:08 So you don't want me to repeat what I said, or do you want me to repeat?

01:01:12 No, you only have to start from... I forget what you ended with.

01:01:19 Do you recall your last sentence? That's all you need, really.

01:01:22 If we accept those risks, why can't we accept small risks from chemical carcinogens in the environment?

01:01:32 It's a valid argument.

01:01:35 But then there is, of course, the counter argument.

01:01:38 The counter argument is, we cannot do much about trace amount of carcinogens that are present in the food.

01:01:46 Why should we add to this burden that we already have by increasing the level of exposure to carcinogens?

01:01:55 That's also a valid argument.

01:01:57 And once again, it boils down to how much effort can we as a society put into reducing those additional risks?

01:02:06 Once again, how many ways can you cut the pie?

01:02:10 It is not enough.

01:02:14 So could we then move on to talk about the political considerations or some of the other considerations that come into then making these decisions?

01:02:24 Is there a logical extension of that thought into that area?

01:02:31 Let's stop tape.

01:02:32 Not really. This is a sort of...

01:02:45 People argue that we as a society are accepting a significant risk of cancer by eating everyday diet.

01:02:54 There are trace amount of naturally formed carcinogens in a variety of foods.

01:03:00 One can make a list of dozens of naturally occurring carcinogenic substances,

01:03:05 which are present in fruits, in vegetables, in health foods, in grains, and so on and so forth.

01:03:13 If we are accepting these risks, and we are implicitly by not going after these natural substances

01:03:21 and not trying to extract them and eliminate them out of the food,

01:03:25 why can't we accept small risks from synthetic chemicals?

01:03:31 Well, I think we can.

01:03:34 Of course, the argument then is how high is high and how low is low.

01:03:42 And once again, that brings us to the interpretation of what is the acceptable level of risks.

01:03:48 And we can't set the definite level.

01:03:51 But I believe that small amounts of chemicals are not a big problem.

01:04:01 Okay.

01:04:02 I can't fly.

01:04:12 There is a general perception among the population that somehow everybody is dying of cancer

01:04:18 and cancer is on the increase.

01:04:20 The fact that cancer is a very common cause of death,

01:04:24 in this country it's a second leading cause of death, only second after heart disease, it's true.

01:04:31 But we have to look historically at how it came to be.

01:04:36 When you look at the leading causes of death 100 years ago,

01:04:40 you find that the leading causes of death then were infectious diseases.

01:04:45 Over the years, we have eliminated infectious diseases.

01:04:49 We have also increased the lifespan of the population.

01:04:54 So in relative terms, cancer has become among the leading causes of death.

01:05:01 It's not necessarily that we are increasing the risks of cancer.

01:05:07 Maybe we are, maybe we aren't.

01:05:09 But when we eliminate other causes of death,

01:05:14 cancer, which was maybe number five or six on the list, has become number two.

01:05:21 That's good. That's very good.

01:05:23 What about the element of just the increased lifespan?

01:05:28 Well, let's back up a minute.

01:05:38 Overall, in the last 30 or 40 years,

01:05:41 despite tremendous technological advances and growth of chemical industry

01:05:48 and use of technology in everyday life and chemicals,

01:05:52 the rate of cancer remained more or less the same.

01:05:56 The most significant growth has been in lung cancer,

01:06:01 which is greatly attributed to smoking.

01:06:04 For other cancers, overall the rate remained pretty much the same in the last 30 or 40 years.

01:06:11 So there is no strong indication, based on these statistics,

01:06:16 that increased use of chemicals in everyday life

01:06:20 increased the cancer mortality in this country.

01:06:25 Okay. And just so you don't sound like you're a spokesman for the Chemical Manufacturers Association,

01:06:32 if you feel comfortable saying it, let's say something in effect,

01:06:37 but nevertheless we should try to eliminate these causes to the extent we can,

01:06:42 and we can afford to, if you have sort of maybe a stock statement that you could say along those lines.

01:06:50 All right.

01:06:51 Go ahead.

01:06:52 That is not to say that we should not worry about chemicals in the environment.

01:06:59 I think that carcinogens have no business being in drinking water

01:07:04 and have no business being in air,

01:07:07 and to the extent that it's possible, we should reduce those risks.

01:07:12 Okay. I think we might have just lost it.

01:07:14 You kind of swallowed your words there, but just say that in your lesson again, if you will.

01:07:17 Okay.

01:07:19 That doesn't mean that we should accept chemicals in the environment

01:07:24 and cancel risks associated with them.

01:07:27 I think that carcinogens have no business in drinking water.

01:07:31 They have no business being in the air,

01:07:34 and I think to the extent that it's possible, we should eliminate them from the human environment.

01:07:43 Okay. Good.

01:07:44 Now, let me actually be able to wind this up now.

01:07:56 Many organic compounds disposed in an environment get biodegraded.

01:08:01 Biodegradation means chemical transformation to simpler chemicals by microorganisms.

01:08:09 Microorganisms use these chemicals as their source of carbon

01:08:14 and in the process reduce them to simpler and simpler molecules

01:08:18 until they get completely mineralized.

01:08:22 It's a slow process but effective.

01:08:25 Some of the synthetic chemicals that have been produced in recent years

01:08:30 are quite foreign to those microorganisms.

01:08:34 PCBs are a case in point.

01:08:36 The carbon-chlorine bond, it's quite foreign in nature and it's difficult to break.

01:08:46 Many of the microorganisms simply don't have enzyme systems that can easily break these bonds.

01:08:54 As a result, PCBs have not been biodegraded.

01:09:01 They have been quite persistent in the environment for that reason.

01:09:07 PCBs have another property.

01:09:10 They are very poorly water-soluble and therefore they are very soluble in fatty tissues.

01:09:18 So not only have they persisted over the years,

01:09:21 but they have been incorporated into the organisms, terrestrial organisms, aquatic organisms

01:09:30 and stored in the fatty tissues of those organisms.

01:09:35 As the organisms get eaten by larger species in the food chain

01:09:40 and those get eaten by even larger species,

01:09:44 the PCBs which have been accumulating in the bodies and very, very slowly degraded and excreted

01:09:54 accumulate through this food chain and increase to concentrations

01:10:00 which end up being 10,000 times, for example, higher than in the water from which they came.

01:10:10 So the fish may have concentrations in their bodies 10 times higher

01:10:16 than the concentration in the water in which they swim.

01:10:31 Carbon-chlorine bond is quite foreign in nature

01:10:34 and microorganisms that would be involved in biodegradation of organic compounds in the environment

01:10:41 have a difficult time breaking these bonds.

01:10:45 Their enzyme systems that usually break chemical bonds

01:10:50 and therefore make the molecules smaller and simpler, biodegrade them,

01:10:57 are not very well suited for breaking those carbon-chlorine bonds.

01:11:02 Therefore, PCBs have been quite persistent in the environment.

01:11:07 They have not been effectively biodegraded by microorganisms.

01:11:11 It's worth noting that in the last few years the scientists have found natural new strains of bacteria

01:11:20 which are quite efficient in utilizing PCBs as their source of carbon.

01:11:26 The reason is that the random process of mutations has produced new strains of bacteria

01:11:34 which are quite well suited to utilizing the PCBs.

01:11:38 And of course, in an environment which has a lot of PCBs,

01:11:42 these microorganisms have an advantage.

01:11:45 They have a source on which they can thrive.

01:11:48 So they have a competitive advantage over other bacteria which cannot utilize this source of food.

01:11:54 And therefore, they have grown.

01:11:57 And the scientists have been able to identify them and collect them

01:12:02 and are currently using these bacteria to destroy environmental deposits of PCBs.

01:12:11 Good. Excellent. You saved me the trouble of writing that.

01:12:15 Okay. This will be, what, 30 seconds of room tone?

01:12:21 Let's go.

01:12:51 Close. Okay.