The Decline in Male Fertility: An Existential Threat?

By 1960 it was obvious that something was killing birds and fish in startling numbers.  It would be Rachel Carson who would piece together the clues and unravel the science in order to indict pesticides, their manufacturers, and their users for these deaths.  Meehan Crist paid homage to Carson for her accomplishments and issued a warning that such threats continue in an article for the London Review of Books: A Strange Blight. 

Rachel Carson published Silent Spring in 1962.  Crist provides this perspective.

“Following the scattered clues wherever they led, Carson painstakingly pieced together an unassailable case against chemical pesticides, then being indiscriminately dumped over field and stream in white clouds, and in smaller but more intimately toxic loads by American housewives cultivating their gardens and moth-proofing their babies blankets.”

“Silent Spring demonstrated, with scientific rigour and in heart-thumping prose, that chemical pesticides were not just poisoning their intended insect or weed targets, but accumulating in living cells, where they altered essential cellular machinery, interacted in unpredictable ways, and mutated genes in a heritable waterfall of damage that was warping the entire ‘web of life’.”

This was accomplished without assistance from the scientific infrastructure and the vast datasets that are available today.

“The scientific achievement of Silent Spring is less often heralded. By making connections across disciplines Carson inferred the way chemical pesticides disrupt endocrine function and lead to tumour formation before any of this was established science.”

It would be her book that would drive the development of environmental science for succeeding generations.

“Rarely has the work of a single author – or, indeed, a single book – had such an immediate and profound impact on society. Silent Spring was the first book to persuade a wide audience of the interconnectedness of all life, ushering in the idea that ‘nature’ refers to ecosystems that include humans. It spurred the passage in the United States of the Clean Air Act (1963), the Wilderness Act (1964), the National Environmental Policy Act (1970), the Clean Water Act (1972) and the Endangered Species Act (1973). Perhaps most significant, it showed how human health and well-being ties in with the health of our environment, leading to the establishment of the Environmental Protection Agency in 1970. No wonder, then, that writers, activists and scientists concerned about the ongoing destruction of biodiversity and the catastrophic effects of climate change look to Carson with urgent nostalgia.”

Crist feels a need to remind us of what Carson, one person, had accomplished, perhaps wishing that a new champion might appear.  The environmental threat from continued use and misuse of ever more new chemicals is now accompanied by the environmental threats presented by a warming Earth.  Animal die-offs continue and while the mechanisms are not always well understood, it is clear the cause is human activity.  While considering the lack of progress in countering carbon buildup in the atmosphere, she casually lets this thought drop.

“But maybe humans won’t be around to see the effects of the changes we have wrought on the biosphere. The postwar chemical revolution that produced pesticides has also led to a dramatic drop in male fertility. Because we are all ingesting chemicals that mess with human hormones, sperm counts in men around the world have dropped by 50 per cent in the last four decades – men today are half as fertile as their grandfathers were. If this downward trend continues, as it seems to be doing, humanity may be incapable of unassisted reproduction within decades. The social consequences stagger the imagination. This trend towards male sterility is being driven by endocrine disruption at the cellular level, which Carson linked to toxic chemicals in Silent Spring. ‘Not all robins receive a lethal dose,’ she writes, ‘but another consequence may lead to the extinction of their kind as surely as fatal poisoning. The shadow of sterility lies over all the bird studies and indeed lengthens to include all living things within its potential range’.”

The notion that male sperm counts were falling in the wealthy societies of Europe and North America was well established.  More recently, data has emerged indicating the phenomenon is worldwide and it is continuing.  And it is not just the sperm count that is affected, it is also the motility of the sperm, its ability to move around, that has also been diminished.  Something is changing the very nature of the sperm, not just its concentration. 

Crist’s suggestion that this trend could be an existential threat is startling, but not unreasonable.  Humans and other mammals have the same organs and biochemistry.  If animal species are dying off and becoming extinct, there is no reason why humans wouldn’t be subject to the same threats.

Rachal Carson’s work did produce changes in behavior with chemicals that were beneficial at the time.  However, since that period many more new chemicals have come into use than can possibly be studied and evaluated, let alone try to understand how they might behave in concert.  And every chemical we use eventually ends up in our water systems.  Every shower we take washes chemicals that we have applied to our bodies or have just settled on us, into our waterways.  Every flush of the toilet sends residue from every pill, lozenge, liquid, and food item we have consumed into that same system.  Every rainstorm sweeps up the chemicals we dripped, poured, or sprayed onto the landscape into our water supply.  Our treatment systems are not designed to remove those chemicals, so they continue to build up and become more dangerous. 

There are plenty of indications that the chemicals that mess with or mimic hormones, endocrine disrupters, exist at a level that can harm fish.  This source provides this definition of endocrine disrupting chemicals (ECBs).

“Found in many household and industrial products, endocrine disruptors are substances that ‘interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for development, behavior, fertility, and maintenance of homeostasis (normal cell metabolism)’.”

We are not allowed to experiment on humans, but data on other animals tells us that this complex chemical stew we now find in our environment is dangerous.

“Studies in cells and laboratory animals have shown that EDCs can cause adverse biological effects in animals, and low-level exposures may also cause similar effects in human beings.  EDCs in the environment may also be related to reproductive and infertility problems in wildlife and bans and restrictions on their use has been associated with a reduction in health problems and the recovery of some wildlife populations.”

Not all the problems with EDCs are reproductive in nature.

“In 2015 the Endocrine Society released a statement on endocrine-disrupting chemicals (EDCs) specifically listing obesity, diabetes, female reproduction, male reproduction, hormone-sensitive cancers in females, prostate cancer in males, thyroid, and neurodevelopment and neuroendocrine systems as being affected biological aspects of being exposed to EDCs.”

And this is the most frightening aspect of EDCs.

“The critical period of development for most organisms is between the transition from a fertilized egg into a fully formed infant. As the cells begin to grow and differentiate, there are critical balances of hormones and protein changes that must occur. Therefore, a dose of disrupting chemicals may do substantial damage to a developing fetus. The same dose may not significantly affect adult mothers.”

Fish inhabit our water sources.  Since they are generally smaller than us but have the same biochemistry, one might expect their fate to be a harbinger of the fate of humans as the chemicals continue to build up in our waters.  The existence of “intersex” has become common in fish species.  This source provides a definition of that term.

“Intersex people are individuals born with any of several variations in sex characteristics including chromosomes, gonads, sex hormones, or genitals that, according to the UN Office of the High Commissioner for Human Rights, ‘do not fit the typical definitions for male or female bodies’.”

If intersex is becoming more common in fish, might one expect the same to be occurring in humans?  This study, The Increasing Prevalence in Intersex Variation from Toxicological Dysregulation in Fetal Reproductive Tissue Differentiation and Development by Endocrine-Disrupting Chemicals, provided by the National Institutes of Health seems to believe that is the case.

“An increasing number of children are born with intersex variation (IV; ambiguous genitalia/hermaphrodite, pseudohermaphroditism, etc.). Evidence shows that endocrine-disrupting chemicals (EDCs) in the environment can cause reproductive variation through dysregulation of normal reproductive tissue differentiation, growth, and maturation if the fetus is exposed to EDCs during critical developmental times in utero. Animal studies support fish and reptile embryos exhibited IV and sex reversal when exposed to EDCs. Occupational studies verified higher prevalence of offspring with IV in chemically exposed workers (male and female).”

This paper also suggests that EDC exposure of males can affect the development of a fetus, presumably by altering the quality of sperm produced.

It turns out that Canada has a lake it reserves for environmental experiments.  One of its recent studies involved exposing a species of fish to a level of EDCs found in our now polluted waterways to determine the effect on the evolution of that species.  The results are found in Collapse of a fish population after exposure to a synthetic estrogen.

“We conducted a 7-year, whole-lake experiment at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada, and showed that chronic exposure of fathead minnow (Pimephales promelas) to low concentrations (5–6 ng·L−1) of the potent 17α-ethynylestradiol led to feminization of males through the production of vitellogenin mRNA and protein, impacts on gonadal development as evidenced by intersex in males and altered oogenesis in females, and, ultimately, a near extinction of this species from the lake. Our observations demonstrate that the concentrations of estrogens and their mimics observed in freshwaters can impact the sustainability of wild fish populations.”

If the fish are beginning to go, can humans be far behind? 

Yes, we do face existential threats, and there is no Rachel Carson out there worrying about us.