In this video I want to give an introduction to environmental toxicology. And first, the reason I started with a bee on this first slide is because something that it is hard not to hear about in today's world is declining honeybees and the concern about both native and European honeybees and other pollinators right now and a huge reason, or I should say threat, to a lot of pollinators right now appears to be certain classes of pesticides that are harmful and are causing, in some cases, colony collapse disorder and in other cases, other problems for pollinators. And when I hear about these pollinator declines and specifically the honeybee declines, It sounds so familiar to me. It sounds so much like what we read about in Silent Spring. And we only read a short excerpt from this book.
And I wanted you to read it so that you could get a sense for Rachel Carson's writing and for what this book is like that really was very powerful and essentially catalyzed. the public debate in the United States about synthetic chemical use. So what was Rachel Carson's primary message?
Well, essentially, her primary message was that DDT and other synthetic pesticides are hazardous to people's health, they're hazardous to the health of wildlife, they're hazardous to entire ecosystems, and that we should be more conservative in their use. So not that we should totally abolish them, but that there is harm that's coming from them. and remember this is the early 1960s, and that we should be more conservative about their use.
So I wanted to, oh first I'll mention one of the reasons why this book played such an important role in the public debate, not just a you know a debate in academia or debate in industry, is that parts of this book were published as pieces in the New Yorker magazine over a series of over a period of time. And then eventually, the completed book, the compiled book was published, and Carson's message reached an even broader audience. But audiences were able to get a taste for what she was talking about through the New Yorker articles that kind of introduced the book to the American public. So a little bit of historical context about when Rachel Carson was preparing this book and then writing this book, Silent Spring was written at a time, so, you know, mid to late 1940s, 1950s, early 1960s, when pesticides were widely used and virtually untested for health impacts on either wildlife or human beings. And large amounts of pesticides were being sprayed indiscriminately over public areas.
You may have seen pictures of DDT being sprayed out the back of trucks in neighborhoods and little kids biking behind the spray, kind of like we've all played in sprinklers. But DDT is much more harmful than water. But this is happening not because people are malicious, but because people didn't know. We didn't know the danger of these chemicals at the time. DDT was also recommended for use in the household.
This is a real government ad. This is not. This is not a fake.
And this is saying, yeah, use DDT in your kitchen to reduce all sorts of insects that you don't want in your kitchen cabinets. People used it in their backyard garden and it led to respiratory problems and other sicknesses and death for people as well as what we call non-target wildlife. So unintended effects on the ecosystem. So all of this of course was happening on the assumption that chemicals that were intended for pests would do no harm to other animals or to including humans And during the same time bird populations were declining including many species of raptors so like hawks and eagles and Falcons like this peregrine falcon in the picture right here and osprey and at first it wasn't Clear exactly why this was happening So people weren't finding a lot of dead birds around.
It was just that the populations were not growing as quickly. They were declining. And it turned out that they weren't growing not because adults were being affected, but because the babies were being affected.
And not even the babies. It was that eggs weren't even hatching in many cases. So eventually it was discovered that the eggs were breaking under the weight of the adults that were incubating them because DDT was preventing the females from creating a certain protein that made the eggshells hard enough to withstand the weight of the parents sitting on the nest.
And so the eggs would crack under the weight of the adults who were trying to incubate them. And so there were very few... chicks that were able to hatch and enter the adult population.
And so why were peregrine falcons and other raptors affected more than other species? Well, part of this has to do with biomagnification, right? They are at the top of the food chain.
And so we'll return back to biomagnification in a future lecture, but you've already read a little bit about that concept. Okay. So What was the response to the publication of Silent Spring?
Well, the general public largely was intrigued, interested, and somewhat worried about the potential health effects for humans. And industry gave a lot of pushback, challenged Carson's book quite a lot, and made personal attacks against. Rachel Carson as well. The American Chemical Society released various statements trying to discredit Rachel Carson and saying that there was no founding for what she was saying. Monsanto magazine, which I didn't even know existed until a few years ago, actually published a parody of Silent Spring, so an article called The Desolate Year.
And it's... It's written in kind of the same language that Rachel Carson writes in, and it's about a world being overrun by insects in the absence of DDT and other industrial chemicals. And unfortunately, that didn't work, because ultimately, DDT was essentially nearly banned in the United States by 1972. So 1970 is when the Environmental Protection Agency started, and shortly thereafter, DDT was mostly banned in the United States. And incidentally, the banning of DDT is considered one of the first major successes in the American environmental movement. When I say near total ban, we continue to produce DDT and sell it to other nations, and I'm not sure if we do anymore.
But this was a problem because one of the nations we used to sell it to was Mexico, which is really close to where we are. And so animals were moving back and forth across the border. As we'll talk about later, pesticides can, of course, move through the atmosphere. So that probably was still harming some of the wildlife, potentially humans, in the United States.
But why did we continue to sell it to other nations? Well, some other nations... are really struggling and still today use DDT because they are struggling with incredibly high rates of malaria infection. And malaria can kill millions of people, does.
And so I wanted to bring this up because a lot of people hear that we banned DDT mostly, but that we kept selling it to other nations, like some African nations in South America. We look at that as a bad thing, and I kind of do too, but you can understand why. It's a really hard ethical decision when people are dying from mosquito bites, from getting malaria in certain nations. You kind of have to think maybe the risks of DDT outweigh millions of your citizens dying from malaria.
So it's really, it's not such a straightforward ethical call. A lot of complexity in everything we're talking about. Okay, so why was Rachel Carson's book so successful? I think it was successful, like I said before, because people got introduced to it in small doses in The New Yorker, and then the book was published.
But also, more importantly, Carson was a scientist with the USGS, the United States Geological Survey, and she was also a wonderful writer. Her writing is not like normal scientific writing. You have read this week.
Some of Rachel Carson's writing and then some of a textbook on environmental toxicology. And I think we can all agree that Rachel Carson's book is a lot easier to read and a lot more digestible. Her writing is lyrical and it was enjoyable and, like I just said, accessible to the general public.
And also she wrote about connections between what we were seeing happen with bird populations in nature and also the potential implications for the human population. So she had the credibility of... you know, being on staff with USGS, and she was a really good accessible writer.
And that's a powerful combination. And we'll see another example of that in a future lecture. So I really think it's important to start with Rachel Carson as kind of the beginning of our environmental toxicology unit, because she's really the beginning of, in a lot of ways, like I said, she really catalyzed us moving towards banning certain chemicals and really just re-evaluating how we should be using chemicals in our environment and kind of what we call the non-target effects, the side effects that chemicals can have that are unintended. So what is environmental toxicology?
What are we talking about in this unit? Environmental toxicology is the study of poisonous or toxic substances that come from or are discharged into the environment. And it's also the study of the effects of those chemicals, those toxic substances on the health of humans, wildlife, and ecosystems. Something I'm going to, a word I'm going to throw around a little bit, and then we'll address what it really means later, is toxicity. And so for right now, we just want to think of toxicity as the degree of harm that a certain substance can inflict on humans or non-human animals or ecosystems.
So the degree of harm that can be inflicted by a toxic substance. So you may have heard some of these quotes before. They're pretty famous. All substances are poisons. There is none that is not a poison.
The right dose differentiates a poison and a remedy. The more common one that you probably have heard of is the dose makes the poison. Absolutely true. I mean, everything, every substance can be poisonous, right?
Water can be toxic. Water can kill a person if ingested, if imbibed in too high a quantity and too fast, right? It can tax our kidneys.
You've probably heard of people in water drinking contests who died. um, from drinking too much water in a short time. Um, things like aspirin, uh, are another example in a really small dose. Aspirin can be good, right?
It can make a headache go away. It can, um, keep, uh, people, uh, keep heart disease, um, or, um, you know, heart problems, uh, from happening, but in large quantities, you know, if you, a whole bottle of Tylenol could kill a person. So everything, even oxygen, too much oxygen, uh, in the air. could be deadly.
So it's really true that everything can be a toxin and it's important to keep that in mind. Another thing that we often hear in the realm of toxicology is the solution to pollution is dilution. And this, on the other hand, is not true.
In some cases, it might be true that diluting something can reduce its impact, but there are some really important cases and we're going to talk about some of them. in a future lecture, where diluting a chemical, having exposure to only a small amount of a chemical can be a really dangerous thing. This essentially is an excuse when you hear this, is essentially an excuse to like dump things in the ocean and dump things in a river because like, oh, it's just a really small amount of oil, no big deal.
It'll get diluted in the larger scheme of things. But we know now. that small amounts and dilutions can actually be incredibly harmful to humans and non-humans. All right. So one thing I want to talk about, two more things in this introduction.
One thing is toxins versus toxicants. So toxins are natural. They come from the earth or from living things on the earth. So natural toxins... are produced by algae.
We have toxic cyanobacteria, fungi, plants, toxic plants, animals like venomous snakes, venomous spiders, and of course viruses and bacteria. Radon gas is a really important, especially was for a really long time, a major indoor air pollutant. And oil, right? Fossil fuels come from the earth, but they can be toxic.
So these are kind of the natural category. And if you're interested in this, there's a course in the Natural Resources Department, an inquiry course, an NR444, that's all about kind of venomous and poisonous things in nature. So check that out. But what we're going to talk about in this class is toxicants.
And toxicants are the synthetic toxic substances, so synthetic chemicals, and that's what we're going to focus on. So many of these toxicants, these synthetic chemicals, have found their way into soil and water and air, and they really are ubiquitous in our environment. I know this was a long time ago, and it probably has gotten worse since then because because we have even more synthetic chemicals in the environment. But a 2002 USGS study found that 80% of US streams contained at least trace amounts, so small amounts, of 82 different wastewater contaminants, including antibiotics and detergents and drugs and steroids and perfumes and like plasticizers and other solvents. And this one I think is really kind of eye-opening.
A 2005 study showed that 287 different synthetic chemicals were present in the umbilical cord blood of newborn babies. So these are babies that have not had any exposure to the outside environment. They're only interacting with things from their mother. And almost 300 different synthetic chemicals were present in their cord blood.
So we are being exposed to this stuff before we ever get out of the womb. So we really, really, truly, toxicants are ubiquitous and we should learn what some of their more obvious and subtle impacts are. Okay, so the last thing I want to talk about here is how we classify toxicants.
So the different categories that we put toxicants into. And so the first category, oh, and incidentally, what I want you to take away from this is First of all, how we classify toxicants. So how do we put them in these categories?
I don't need you to memorize what category different things fall into. So I just want you to get the bigger picture here. So corrosives is one category.
Corrosives are substances that react directly with tissue and destroy it. So things like acids and lye, bleach, things like that. Next we have asphyxiants, and you've probably heard of these. These are chemicals that deprive tissues of oxygen and cause suffocation, so carbon monoxide is a really common one, cyanide, things like that.
Next we have carcinogens, which I'm sure we've all heard of. So carcinogens cause cancer. So I have a bunch of examples here including BPA and benzene, asbestos, formaldehyde, arsenic, stuff like that. Next we have mutagens.
So mutagens cause mutations in DNA. And so something that you've probably started to notice here is another major idea that I want you to take away from the classification of toxicants piece, which is that a substance doesn't just get put into one category necessarily, it gets put into all of the categories that apply. And so we've already seen here that benzene and PAHs fall into both of these categories, right?
Because. A lot of mutagens, and this is probably true of a lot of things, because a lot of mutagens end up causing cancer. So you don't have to just put a chemical in one category. Next is teratogens.
And teratogens are things like thalidomide that you've probably heard of that affect the development of human embryos and cause birth defects. And again, probably a lot of mutagens and teratogens fall into both categories. Next is allergens, which is kind of interesting.
I don't know if we normally think of allergens as toxicants, but they are included as a category of toxicants. And these are, of course, substances that affect the immune system and increase respiratory problems like asthma. Next is neurotoxins.
So neurotoxins impact our nervous system, and a lot of heavy metals end up falling into the neurotoxin category. And then finally, our last category is endocrine disruptors. And these interfere with our hormones, with the function of our endocrine system. And some examples that we're going to talk about are atrazine and BPA.
We'll talk about a couple of other examples as well. And what we're going to do from here on out in a future lecture is focus a little bit on endocrine disruptors. Endocrine receptors are an example of chemicals that in diluted amounts, in very small amounts, can cause big problems.
So this is one of the major reasons that you will be able to walk away from this module and know that the solution to pollution is not dilution, right? Because endocrine receptors are a big example of miniscule amounts can make massive problems.