“It’s Not Easy Being Green” Do weed-killers turn frogs into hermaphrodites? by William Souder In the summer of 1997, Tyrone Hayes, a biolo- Initially, Hayes was asked only to review the gist at the University of California, Berkeley, scientific literature for studies involving atra- accepted what seemed a harmless offer to join zine and frogs. The review turned up noth- a panel of eight other scientists investigating ing, so Hayes designed an experiment to test the safety of the common weed-killer atrazine. atrazine directly on the animals. “I honestly The panel had been commissioned by atrazine’s thought that the compound wouldn’t do any- inventor and primary manufacturer, the Swiss- thing,” Hayes says… based chemical giant then called Novartis and since renamed Syngenta. The company wanted The experiment was similar to ones Hayes had to know if its product threatened “non-target” performed many times before. Newly hatched organisms, including fish, reptiles, and amphib- tadpoles were reared in water containing atra- ians—creatures whose fate had remained zine in amounts ranging from .01 to 25 parts largely unexplored through the half century in per billion (ppb) until the animals completed which atrazine had become the metamorphosis. The test animal was the most heavily used herbicide in African clawed frog, a species known as the “lab he federally the United States as well as one rat of amphibians” and typically referred to by its generic name, Xenopus. Once used in human established of its most widespread environ- T mental contaminants. pregnancy testing, Xenopus is easier to rear than “safe” limit for native North American species, largely because atrazine in human Hayes himself was acutely it is entirely aquatic, can be readily force-bred, drinking water is interested in discovering the grows quickly through well-defined stages, and 3 ppb, thirty times causes of a global decline in will eat almost any commercial animal feed. the dose that frog populations that had Hayes gives his tadpoles Purina Rabbit Chow. worried scientists since the turned some of early 1990s. Many of the hor- In March 1999, Hayes and his students divided Hayes’ frogs into mones and genes that regulate 900 Xenopus tadpoles among thirty small hermaphrodites. reproduction and develop- aquariums. Half of the tanks contained atra- ment and metabolism in frogs zine; the rest—the control tanks—did not. All perform similar functions in the tanks were coded, so neither Hayes nor his people, making frogs important proxies for students knew which animals were swimming humans—nature’s test animals in a changing in what dose. Every three days, the tanks were world. Syngenta’s concern was different. The cleaned and the solutions replaced. After forty Environmental Protection Agency had been days, the tadpoles had become frogs. When ordered by Congress to “reregister” atrazine as Hayes examined the frogs, all the control ani- part of a program to subject a large number mals were normal. So were all the females. But of older pesticides to current safety testing, a among the males that had been exposed to atra- process that required considerable new data. zine at concentrations of 1 ppb or more, about Excerpted from the August 2006 issue of Harper’s Magazine. The original article goes on to describe how chemical manufacturer Syngenta challenged research it had supported and influenced the U.S. EPA to overlook the dangers of atrazine. William Souder has written A Plague of Frogs and was a finalist for the 2005 Pulitzer Prize for his biography of James Audubon. 12 PAN North America Magazine Fall 2006 80 percent had smaller than expected a plan to bury important laryngeal dilator muscles—puny voice data.” boxes… …He repeated the Xenopus Examining the frogs more closely, Hayes experiment two times, and was surprised to discover that about in April 2002 he pub- a third of the male frogs exposed to lished his findings in the atrazine also had abnormal reproductive Proceedings of the National organs. Some had malformed or multi- Academy of Sciences… ple sets of testes. Others had both testes and ovaries, sometimes in odd numbers. In his published articles, The cooccurrence of testes and ovaries Hayes argued that atra- is rare in vertebrates and rarer still in zine activates a gene that Xenopus. Yet in Hayes’s experiment this produces an enzyme called morphology had been elicited at con- aromatase, which converts centrations as low as 0.1 ppb, a tenth testosterone to estradiol, of the amount that altered their voice the strongest of the natu- boxes. Such a dose is equivalent to a rally occurring estrogens. Dr. Tyrone Hayes grain of salt dissolved in a ten-gallon Elevated levels of aroma- aquarium. To put it another way, the tase, he proposed, could federally established “safe” limit for atra- explain the males’ stunted voice boxes and multiple, zine in human drinking water is 3 ppb, mismatched sex organs—as well as the fact that atra- thirty times the dose that turned some zine appeared to have no effect on the females. Hayes of Hayes’ frogs into hermaphrodites… called the process “chemical castration and feminiza- tion.” He was not surprised that the abnormalities he Hayes says that he was naive about found were associated with extremely weak doses of how his findings would be received. atrazine; hormones, including testosterone and estra- After reporting his discovery to the diol, typically function at very low concentrations. “If other panelists studying atrazine, Hayes you’re a toxicologist, this is a low-dose effect,” Hayes argued with them and with Syngenta for says. “If you’re an endocrinologist, it’s a reasonable months about what to do next. There effect.” Chemical poisons tend to be more toxic as the were protracted discussions about the dose increases—the classic “linear” dose-response asso- statistical relevance of the voice-box ciation. But chemicals that affect hormonal systems data and disagreements over the pace sometimes operate in nonlinear ways: In women, for of follow-up studies. Hayes was asked example, estradiol is necessary to stimulate ovulation, for repeated revisions of the “final” but a large dose of estradiol—the amount contained report on his results. He saw all of this in the birth control pill—cancels this effect. as an effort to discourage him from publishing his findings. In November …According to Bruce Blumberg, an associate profes- 2000 he quit the panel. In his letter of sor of developmental and cell biology at the University resignation he complained that were he of California, Irvine, scientists who study endocrine to remain on the team, “recent history disruption often see dramatic biological effects when suggests that I will spend a great deal of they expose cell cultures to weak chemical concentra- effort preparing reports that will not be tions. Curiously, Blumberg says, research sponsored by finalized in a timely manner, let alone chemical companies rarely detects such effects. published.” He added, “It will appear to my colleagues that I have been part of ≈≈≈ PAN North America Magazine Fall 2006 13 Atrazine is among the world’s oldest and most effective herbicides—the aspirin of weed- kill- ers…. Syngenta, a company with roots dating back a couple of centuries that also gave the world DDT and LSD, introduced atrazine to the market in 1959… Syngenta does not divulge sales figures for individual products, but atrazine continues to contribute a signifi- cant portion of the company’s U.S. revenues from selective herbicides, which last year totaled $1.9 billion worldwide. …a fraction of the nearly 80 in their semen as their Minneapolis counter- trazine would million pounds of atrazine parts. Urine samples from the Columbia group still be found applied to crops in the United showed significantly higher herbicide residues. A States every year ends up Swan says few of the men in Columbia were in well water for contaminating surface water, decades even if use farmers and that she suspects their exposure to groundwater, rain, and even pesticides was through drinking water contami- of the pesticide fog…In 2003 the EPA reported nation. Reduced semen quality is correlated not were halted today. that a survey of more than only with reduced fertility but also with testicu- That very concern 14,000 water utilities, drawing lar cancer. One of the pesticides Swan detected led the European water from wells in twenty-one in the Missouri group was atrazine. states, had found that atra- Union to ban zine, where it previously had ≈≈≈ atrazine in the fall been detected, averaged about of 2003. 0.55 ppb—more than five …When confronted with evidence that a times the amount that caused pesticide has adverse effects, the EPA usually abnormalities in Hayes’s initial responds with a recommendation that the mat- experiment. Because water can take years to ter be studied further, and under the peculiar percolate down into aquifers, atrazine would logic of pesticide regulation, it is the manufac- still be found in well water for decades even turer and not the agency that is responsible for if use of the pesticide were halted today. That testing chemical products. (The EPA stipulates very concern led the European Union to ban what kinds of studies are necessary and requires atrazine in the fall of 2003. companies to submit raw data in addition to safety conclusions.) People, unlike frogs, don’t undergo critical developmental stages exposed to the elements, One way to maintain the perception that a and frogs may be particularly sensitive to pesticide is safe is to take a very long time water-borne chemicals. Still, in the same year reviewing information suggesting it is not. atrazine was banned in the European Union, an The EPA routinely reframes questions about American epidemiologist named Shanna Swan, the safety of pesticides in such a way that they then at the University of Missouri School of remain questions, and evidence of adverse Medicine, published research showing reduced effects usually results in a demand for more semen quality in men exposed to pesticides.