Since the 16th century, the guiding principle of the science of toxicology has been that “the dose makes the poison.” In other words, toxicology tells us what quantity (dose) of a substance will cause harm. This applies to the medicines used by Americans hundreds of millions of times a day to help relieve symptoms or treat illnesses’ for example, the right dose of aspirin or an over-the-counter cold remedy can be a therapeutic godsend, but consuming too much can be lethal. The principle even applies to foods: Large amounts of nutmeg and licorice are notoriously toxic.
This principle has led to understanding that the probability of injury – which we call “risk” — depends on two factors: the inherent ability to cause harm and exposure. Even some presumptive professionals seem not to grasp that, however. An example is the recent classification of the commonly used pesticide 2,4-D by the International Agency for Research on Cancer (IARC), a component of the UN’s World Health Organization, as “possibly carcinogenic to humans.”
IARC seems to be on a losing streak. As I wrote in March, the group classified glyphosate, another popular herbicide, as “probably” carcinogenic, a conclusion that conflicted with regulatory agencies around the world. And again more recently, not a single governmental agency has deemed 2,4-D a carcinogen. Earlier this year, the U.S. Environmental Protection Agency concluded, “[B]ased on weight of evidence consideration of the available data, 2,4-D would be classified as ‘Not Likely to be Carcinogenic to Humans.’” The European Food Safety Authority also recently concluded that “2,4-D, as currently manufactured, is unlikely to have a genotoxic potential or pose a carcinogenic risk to humans.”
These recent erroneous IARC classifications raise questions for farmers and consumers. Has commercial agriculture created unnecessary, significant risk by having used this herbicide for more than 70 years? Should homeowners change their approach to lawn care? The answer to both is, No! In making its determination, IARC failed to consider the probability that the chemical will cause cancer in real-world use. Its “expert” panels only assess whether a chemical is capable of causing cancer, not if it actually will cause cancer.
The result of this flawed paradigm is that IARC previously concluded that aloe vera, acrylamide (a substance created by frying foods, such as French fries and potato chips), cell phones, working night shifts, Asian pickled vegetables and coffee are “probable” or “possible” carcinogens. But the critical question is, how great would your exposure need to be actually to cause harm? In the case of coffee, you would have to drink more than 50 cups a day, day after day. Thus, the dose makes the poison.
Saying that 2,4-D is a cancer risk to humans ignores the entire body of extensive research and analysis conducted by health authorities worldwide, including the UN’s own WHO/FAO Joint Meeting on Pesticide Residue (JMPR). The JMPR examines pesticides such as 2,4-D in a comprehensive way and considers various aspects of real-world exposure, including the amounts in soil and nearby water; exposure to as animals that may pass through a field sprayed with 2,4-D; and direct human exposure.
In all of its reviews beginning in 1970, the JMPR has found that when applied according to guidelines for use, the exposure from 2,4-D does not pose a health threat to anyone or anything on land or water. As noted above, this has been affirmed by numerous government agencies, including the European Food Safety Authority, the U.S. EPA, USDA, Health Canada and others. In short, when all the evidence is examined and 2,4-D is applied according to the label instructions, the real-world use of 2,4-D does not pose a health risk. By contrast, during its panel meetings IARC “experts” are permitted access only to a narrow spectrum of selected publications.
IARC’s decisions on glyphosate, 2,4-D and other substances fuels activists’ headline-seeking, chemophobic, out-of-context warnings about important chemicals and encourages “regrettable substitutions” — misinformed bans or limitations on the use of certain products, even when the alternatives pose uncertain or greater risks or do not provide the same benefits.
Unwarranted concern over the spurious IARC classifications, which activist groups have already stirred up, will do nothing to benefit health and the environment, but can cause considerable harm. 2,4-D is not used only by farmers. There are more than 100 prescribed uses, including the control of invasive weeds on lawns, along highways, power line corridors and rail lines; in forestry; and in recreational applications.
If products such as glyphosate and 2,4-D were no longer available, users of them would be forced to resort to other methods to control weeds. The regrettable substitutions would include the use of less effective, more toxic chemicals and increased tillage, which would result in more soil erosion, increased CO2 emissions to the air, decreased crop yield, and higher production costs and consumer prices.
Because IARC’s flawed decision-making is harmful and has wide exposure, by definition it poses risk. Let’s get rid of it.
Henry I. Miller, a physician, is the Robert Wesson Fellow in Scientific Philosophy and Public Policy at Stanford University’s Hoover Institution. He was the founding director of the Office of Biotechnology at the FDA.