How plastics are making us infertile — and could even lead to human extinction

In an interview, Dr. Shanna Swan explains how sperm counts are dropping every year thanks to plastic pollution

By Matthew Rozsa

Staff Writer

Published April 4, 2021 7:00AM (EDT)

Plastic pellets and sperm count (Photo illustration by Salon/Getty Images)
Plastic pellets and sperm count (Photo illustration by Salon/Getty Images)

Climate change is rightly cited as an environmental crisis that could lead to human extinction. Yet there is another pollution issue, indirectly related, that could make it literally impossible for human beings to reproduce.

I am talking, of course, about plastic pollution.

Dr. Shanna Swan, a professor of environmental medicine and public health at Mount Sinai School of Medicine in New York City, has a new book out called "Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race." In it she describes how various chemicals commonly found in plastic products are leading to a decline in fertility. The most striking example of this is in dropping sperm counts; if you have fewer than 15 million sperm per milliliter of semen, you are considered to have a low sperm count. Human beings are rapidly reaching that point, as Swan demonstrates in her book.

Salon spoke with her about this issue over the phone; as always, this interview has been edited for length and clarity.

What is the thesis of your book?

The thesis of my book is that reproductive health in men and women has been declining dramatically at least over the past 40 years, and that a major part of that decline is linked to everyday exposure to chemicals in the environment that can affect our hormone system. There's a lot in there and we can spread that all out, but that's the overall thesis. There has been this downfall, if you will, a decline in reproductive health in many aspects. It impacts men and women. And if you look to the causes, a major cause — although not the only cause — is the presence in our daily lives of chemicals that are hormonally active. 

What is an endocrine disruptor and what are the tangible effects that we have seen it have on, for instance, sperm counts or important aspects of female reproductive health?

First of all, an endocrine disruptor is a chemical that impacts the body's endogenous natural hormone function. And by impact, it could be increases, slows, or interferes with in various ways. The most profound way they do that is by disturbing prenatal development so that the exposure to the pregnant woman early in pregnancy is going to have the biggest impact on later reproductive health and function in the offspring.

I know that there has been a drop in sperm counts since the 1970s. Could you elaborate a little more on the data there? 

It took two years of seven people working pretty hard on this to get the simple fact that sperm concentration dropped between 1973 and 2011 from 99 million per milliliter to 47 million per milliliter. That's the work that went into that one sentence. Those kind of data are not available for any other outcomes. They're just not. It's just this combination of consistency of method. And by the way, that's the numbers for Western men.

I should say that we divided the studies further into four categories. One of them was geographic. One of them was the kind of man it was. So we separated Western men from non-Western men. And Western was Europe, North America, Australia, New Zealand — all this is in the paper, of course. 

And the reason we did that is because the studies from other countries were different in many ways, including when they were published. Statistically it was more appropriate to separate them. When we did that, we saw there were very few studies in non-Western countries, not enough to really draw any conclusion. So what I told you with those numbers, that's Western studies. And the other countries, as I say, the numbers are too small to draw a conclusion.

Then we further divided the men into two big categories. One is, were they partners of pregnant women? Were their partners pregnant, or had they fathered a child? Those are the fathers, that's the group we called fertile men. And the reason we separated them is because they cannot demonstrate the same kind of decline because if their count was sufficiently low, they would not be fathers. So just being a father selects you into a certain category as sperm count.

We also see declines in testosterone in several studies around the world. We see increases in erectile dysfunction. We see increases in rates of genital abnormalities. There is quite a lot of data on that. We see increases in testicular cancer rates. We see increases, on the female side, in diminished ovarian reserve, which means that a woman does not have as many eggs left when she gets older as she might need to conceive. An increase in miscarriage, but perhaps the most important after sperm count is fertility.

Fertility is a complicated metric, but what's usually thought of as fertility and what's published by the World Bank is the number of children that a couple has, simply the number of children born. And that number has dropped 50% between 1960 and 2018 . . .

So then you ask, what could be causing this? And before I go to the chemicals, I want to say, we're not dismissing the many, many lifestyle factors that can influence reproduction and sperm count. There are things like smoking, binge drinking, obesity, stress, poor diet, et cetera.

Those things would not entirely explain this decline because they haven't been increasing at overall at the same rate, whereas the production of chemicals — and particularly the production of plasticizers and plastic products — has been actually even faster than the 1% per year [decrease in fertility]. So it's actually been exponential.

Let's turn to those chemicals. So why did I look at the chemicals I looked at? I looked at phthalates particularly, and bisphenols secondarily, and then other chemicals that other people are looking at.

The reason I focus on these chemicals was, like I told you, these chemicals have a direct action on the steroid hormones, and the steroid hormones are critical for proper development during pregnancy.

So I have to talk a little bit more about the science, because otherwise it doesn't make any sense. So in utero, in the womb, the fetus is developing first from obviously a few cells. And then pretty soon there is something called the genital ridge. It's, what's going to become the genital tract. It's just a single ridge. It's the same in boys and girls, not differentiated. So that's the undifferentiated state of the genitals. Then how does it become male typical and female typical? Well, it needs testosterone in the male. So the male has to have enough testosterone at a certain time, a delicately programmed time, by the way, genetically programmed, which is in the first trimester. And then when the testosterone is present made by the fetal testes, then the male genitals starts to develop in the male typical way that we expect.

That's what's expected in an XY individual in a genetic male, and that male will develop it as usual, and then if all is good, he'll have adequate sperm count and he'll be fertile and he'll not have genital birth defects and he'll not develop testicular cancer and all these things that can happen when there isn't enough testosterone. And the female, by the way, is going along her programmed route, developing in the female typical way, but she doesn't need testosterone for that because she's just going along with her tract and doesn't have a lot of testosterone. If she sees too much testosterone, then she will start getting a development that's more male typical.

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So phthalates are, first of all, everywhere. They're in everybody. The CDC has shown that since about 2000 over 95% of the population has one or more phthalates [in their bodies], and many of them are measured regularly by the CDC. So they're all pervasive. You don't know how much you have. I don't know. The only way we can know is to get our urine tested. And what it's tested for is a urinary metabolites, because phthalates are thankfully short, they're called non-persistent, they're only in the body for a short time. So the half-life is four hours. So these things come into the body and then leave quickly. And that's great. What's not so great is that they're coming in all the time because there's so many sources of exposure. So major sources of exposure for phthalates are food. That's probably the primary source. And that seems kind of counterintuitive. How would they get in the food? They get in the food in every way you can think of from the time the food is grown, because they're actually in pesticides, to when it comes on our plate. So if you will, farm to fork, they can get in anywhere along that path.

Another thing that phthalates do is they make cosmetics and personal care products more useful because they increase absorption into the skin. They increase the retention of color, which is great for nail polish and lipstick. And they hold odor, so anything fragrant has phthalates. We showed that by asking women, "what products did you use in the last 24 hours?" We got that information, looked at the phthalates in their urine, and sure enough, there was correlation between what products they use and what was in their urine. So it's definitely coming from personal care products.

Similarly, you can show it's coming in cleaning products — it's coming from the floor coverings that have polyvinyl in them, because it's a major contaminant of polyvinyl chloride. Wall coverings. Your garden hose, which is made him polyvinyl chloride. A soft shower curtain. Anything in your home that is soft plastic or polyvinyl chloride, which is not soft, will emit phthalates.

So you can see that we can't escape them. They're not labeled, we can't shop our way out of this by avoiding them because we don't know where they are. So this is what we say this is an everywhere, every time chemical.

Other chemicals that people should worry about. . .  I talked about phthalates, which makes plastic soft. Bisphenols make plastic hard. There's this Bisphenol A, there is Bisphenol S, there are many of them, and these are a class of chemicals that make plastics hard. They also are used for many other purposes. Like lining tin cans. They're in a majority of a cash register receipts. They're in various kinds of paper products, such as pizza boxes. They're also unavoidable and they have a different property. They have the property of being estrogenic. They apparently increase estrogen in the body, and that has a lot of reproductive effects as well.

What kind of policies could actually reduce the damage that has already been done, remove these plastic products from our lives, and then prevent us from being exposed to other dangerous chemicals in the future?

Well, that's an enormous agenda, isn't it? I think the first step to get this accomplished, which I think has to be accomplished, is that people have to be aware of the problem — which by the way, if you look at the analogy to climate change, that hadn't happened for a long time. This hasn't happened for a long time.

This book, and this paper, the 2017 paper, were a wake-up call. And the book is being widely recognized as talking about a problem that we have to consider now. And I think opening people's eyes on their own, to the urgency of this and making this relevant to everybody, is the first step. Because if people don't feel impacted, why should they do anything? And for a long time, people didn't recognize an impact at all.

As with climate change, there is the possibility that citizens can bring pressure on governments to start taking action. Those actions I see are twofold. One is that, as I mentioned, the chemical industry has to change what they are producing. They won't do that without being forced to, so there will have to be regulations that are implemented. There's many that are not properly implemented. And new ones have to be made to ensure that we do not produce hormonally active chemicals, particularly those that are harmful at low doses.

Is it even realistic to believe that we can beat this? Because there is a ticking clock and although we've been aware of the climate change crisis for decades, we have done nowhere near enough to address it. We're only now becoming aware on a wide scale about this crisis. And we only have a few decades in which to address it. Is it even realistic? Is it possible that we need to go through a grieving process and recognize that our species is about to become extinct? 

Well, I don't want to minimize the seriousness of this. I think it's absolutely critical that we turn around the declines that we're seeing, but I don't think it is impossible. And the reason is that we have an option for continuing our species, which is a different kind than the options for climate change, which is that we have technology now to reproduce even in the face of very severe decline. We have all kinds of all manners of assisted reproduction that allow us to have healthy children.

Then this becomes one of those class differences, because people with more money are likely to have more access to this than people with less money. 

That's right. This whole story has a huge social impact. The differential impact, depending on social class, is a social justice issue behind all of this.

Let me just say that people who are disadvantaged have higher exposures — there's a lot of data on that — to these endocrine disrupting chemicals. They have a greater impact on their health from these endocrine disrupting chemicals at the same levels, and they have less access to the kinds of things that would improve their health and then minimize their exposure. For example, organic food obviously minimize your exposure to processed foods. There are many neighborhoods in New York — I live in New York — where people can't even walk to a grocery store that has fresh vegetables. So, yes, there is a huge social justice issue here. And I think that part of the movement that has to happen now among people is to address that.

Dr. Swan's book, "Count Down," is on sale now from Scribner. 

By Matthew Rozsa

Matthew Rozsa is a staff writer at Salon. He received a Master's Degree in History from Rutgers-Newark in 2012 and was awarded a science journalism fellowship from the Metcalf Institute in 2022.

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Infertility Interview Men's Health Plastics Pollution Reproductive Health Women's Health