We are a chemically-addicted society. I am not talking caffeine, alcohol, or painkillers–although there is plenty of that–but chemicals designed to kill. Of the nearly 37 million pounds of antibiotics used in the United States each year, some 7 million pounds are ingested or injected, aimed at whatever ails us: staph, strep, salmonella, syphilis. The rest is used by the agricultural industry.
But that’s a pittance compared with the more than 600 million pounds of pesticides directed at plants and animals infesting farmlands, backyards, and homes. I imagine a pile of these so-called pests: the boll weevils, corn borers, gypsy moths, bed bugs, horseweeds, pigweeds, fish, rats, and mice poisoned over the past 60 or 70 years, our golden age of pesticides, and conjure an image of a great pyramid. Then add all the bacteria, harmful and beneficial alike, killed by antibiotics.
As a toxicologist, I am fascinated by the relationship between toxic chemicals and evolutionary processes. Recently, I’ve been thinking about chemicals, death, and the resilience of life, particularly in those species we try hardest to control. And so next to that pyramid of death, I imagine another smaller, but growing, pyramid of all things resistant. Like beings from some alternate toxic universe, these are descendants of species specifically targeted for obliteration by insecticides, herbicides, and antibiotics. I imagine them feasting upon our farm fields, indulging on the arms and legs of children, and threatening to return us to the pre-antibiotic era.
On corn, soy, and wheat fields across the country, in hospitals, hotels, and homes in our communities, life is evolving. Rapidly. This is life sprung from the trap of chemical death. Nature is schooling us big time. We would do well to take note.
In little over a century, we have squandered one of our most valuable defenses against pathogenic bacteria, namely antibiotics, and there is plenty of blame to go around. Many people contribute to the rise of antibiotic-resistant superbugs, whether they are doctors pacifying anxious parents, those of us who don’t follow doctor’s orders, the agricultural industry preventatively treating disease and encouraging growth in livestock, or hospitals fending off recalcitrant infection. The most infamous outcome of this unbridled chemical warfare is the evolution of methicillin resistant staph, or MRSA: the poster-bug for resistance. Of the roughly 80,000 Americans who become infected with MRSA each year, an estimated 11,000 will die. Likewise, a once-curable pneumonia recently killed seven patients at a well-regarded national hospital. Totally drug-resistant tuberculosis has surfaced in India, Italy, and Iran. Gonorrhea is on the verge of shaking free from its vulnerability to antibiotics. Each of these new superbugs ought to strike fear into all of us, because one way or another we are all within their reach.
Bacteria may be among the most primitive life forms on earth, but they have proven to be formidable opponents with an impressive arsenal of detoxification genes spread around their collective genome. Even bacteria collected deep within caves well beyond the reach of industrial or pre-industrial age chemicals harbor genes for detoxifying our modern antibiotics. Since the majority of our antibiotics are derived from nature, these are chemicals with which bacteria have had a long history.
Penicillin, derived from mold, became one of the world’s first miracle drugs. Yet just a couple of years after its introduction, it began to fail. But those were the booming days where industrialized countries enjoyed “Better things for better living…through chemistry” thanks to DuPont and other chemical industry giants. There was certain to be a technological fix. A new antibiotic would be developed or the chemical structure of penicillin could be tweaked. Man would not be conquered by Nature. In hindsight it is not surprising that new antibiotics, many cut from the same biological cloth as penicillin, eventually succumbed to resistance; it had been lurking in the bacterial gene pool for millennia. We simply hit them with a dose of their own medicine. Resistance was predictable, and perhaps even avoidable had physicians and the public alike heeded early warnings. More than six decades into the Golden Age of Antibiotics despite ongoing research and development, physicians, and public health scientists warn that we are heading toward a pre-antibiotic future. And antibiotics aren’t the only industrial age chemical rendered useless by Mother Nature.
DDT was another miracle chemical, controlling lice, fleas, mosquitoes, and bed bugs in an age when there were few options to prevent deadly insect-borne diseases. Giddy with the promise of synthetic chemicals, one early twentieth century zealot envisioned the day when pesticides like DDT would banish “…all insect-borne disease from the earth.” By 1972, over one billion pounds of the chemical had been applied to homes, gardens, wetlands, and millions of acres of US cropland. Books like Silent Spring andWho Really Killed Cock Robin revealed to the general public the pesticide’s toxicity to birds, while houseflies, lice, mosquitos, and agricultural pests were evolving resistance.
The rise of resistance is far from unique to bugs and bacteria though. Another post-world war savior was the herbicide 2,4-D, which targeted broad-leaved plants, leaving grasses like corn alone. Yet, a little over 10 years after 2,4-D went to market, weeds resisted. Today there are over 100 different herbicides, and over 200 resistant weed species. In 2010, weeds resistant to just one herbicide infested over 33 million acres of crop land in the U.S. Today the percentage has more than doubled. By the time you read this, the acreage of cropland infested with herbicide resistant weeds will likely be higher. If there is an herbicide, you can bet there are resistant weeds.
“Agriculture,” wrote plant scientist Jonathan Gressel back in 2009, “is the largest evolution laboratory presently on earth today with herbicides as the most ubiquitous man-made artificial selector for evolution on the planet.” In 2012, herbicide resistance loomed so large that the National Academy of Sciences, the premier scientific organization in the U.S., gathered together the top agricultural scientists for a summit on herbicide resistance. One goal was to prevent the herbicide Roundup, the “once in a century herbicide,” from going the way of penicillin.
If there is somewhat of a silver lining to these toxic clouds, it may be that rapid evolution isn’t just for pests and pathogens. Bacteria, insects, plants, and even vertebrate species are evolving in response to chemical pollutants, including metals, PCBs, and road salts. Fish, frogs, and salamanders have all been found living and breeding, while not necessarily thriving, in highly contaminated ponds and rivers. Recently, after a presentation about environmental contaminants and evolution an audience member asked, “If we can’t rein in all of these chemicals, why bother? Why not let nature take its course?” I should have said “Because we just don’t want to live in that kind of world. I don’t want my kids and their kids to live in that world. We can, we must, do better.” Instead I gave some impersonal scientific answer about disrupting the web of life. Later, I asked a couple of evolutionary biologists what they thought about the rapid evolution of wild species in response to human activity. “I think it’s sort of hopeful,” one quipped. “Populations will survive no matter what we do.” The other agreed that it was sort of like Nature thumbing her nose at us. But the truth is, we know very little about the long-term implications of evolution in response to pollution.
Evolutionary dogma holds that, like cash-strapped cities, there is very little excess energy in life’s budget. Should there be any, it is put into reproduction and development, thus optimizing fitness. When a population adapts, whether to sudden shifts in available food or to pollutants, energy may be diverted from reproduction to defense, which burns through valuable energetic resources. So some species take a different tact. Consider the yellow perch inhabiting metal contaminated lakes in the Rouyn-Noranda region of Quebec. Decades of copper smelting left the lakes contaminated with toxic metals like zinc, cadmium, and copper. Studies show that over the course of some 50 years, populations of yellow perch evolved. Yet, rather than spending precious energy on detoxification–populations survive by maturing young and spawning early. In other words, these perch live fast and die young.
Piles Creek, New Jersey offers another scenario. Contaminated with mercury along with a hefty load of other industrial pollutants, it is a system that upon first glance seems normal, and it is perhaps even comforting that life can indeed survive even in such a grossly-polluted site. There are killifish, crabs, and shrimp as one might expect in a tidal creek. Yet the system is anything but normal. Instead, it has become a topsy-turvy world full of chemically-addled survivors. The shrimp, normally hunted by the killifish, are fat and happy, once-predatory crabs now feed on detritus, mud, and algae. Meanwhile the hunters are more easily hunted, as killifish from the creek have become less efficient at capturing prey and avoiding predators. It is an ecosystem that is resistant yet sickly.
There are secondary impacts too. For all those species that adapt to their polluted environment, there is very likely a predator that has not. So while fodder fish have apparently evolved free of cost, as is the case for PCB and dioxin-adapted killifish and tomcod, their predators–the bluefish, kingfisher, and mink–are picking up the bill. Along the banks of PCB-contaminated waters, mink populations in particular carry around enough of the organochlorine to cause reproductive failure.
As a toxicologist, I used to focus on the toxic effects of chemicals. Did they kill? Reduce reproduction? Slow growth? Over the past half-century, toxicity testing has managed to flag some of the most egregious toxicants. And, we are in a far better place today than we were in the 1960’s when our chemicals drove raptor population towards extinction. But now I see some of the more insidious effects of toxic chemicals. Over the course of 3.5 billion years, life made its peace with the countless naturally occurring toxic chemicals. Yet in the blink of an eye, we have added hundreds of thousands of new chemicals to the mix and continue to do so at an alarming rate: antibiotics, pesticides, and industrial chemicals. We are challenging Nature to a game of evolve or die, and it is a game we will surely lose. In the closing paragraphs of Silent Spring, Rachel Carson lamented that insecticides were, “As crude a weapon as the cave man’s club, the chemical barrage has been hurled against the fabric of life–a fabric on the one hand delicate and destructible, on the other miraculously tough and resilient, and capable of striking back in unexpected ways.”
We cannot turn back the clock, nor would most of us want to return to pre-industrial, pre-antibiotic days (and Carson did not advocate this either). But we must learn how to live in balance with the rest of life: to manage pests without creating superbugs, to protect individuals from disease without inviting epidemics, to benefit from technology without threatening the health of future generations. Our chemicals are powerful. They can influence the course of evolution in wild and unpredictable ways–often not to our benefit. It is time we reduce the pressure. Our lives and the lives of those we hold dear, may well depend upon it.