Analysis: Glyphosate exposure trends demand a public health driven response
As more evidence emerges that glyphosate is building up in people, feds need to step up efforts to monitor, quantify risks, and regulate
A study out this month once again highlights the need for bolstered monitoring and regulation of pesticide use and risks—this time the alarm bells are ringing over the world's leading herbicide, glyphosate.
Over the last 20 years, global use of glyphosate-based herbicides has risen steadily, driven by the widespread planting of genetically engineered, so-called "Roundup Ready," corn, soybeans and cotton.
In 2001, glyphosate bypassed another herbicide, atrazine, to become the number one pesticide on the U.S. Environmental Protection Agency's list of most heavily applied pesticides, measured by total pounds of active ingredient applied. About 90 million pounds of glyphosate-based herbicides were applied in 2001, compared to 80 million pounds of the number two pesticide on EPA's list, atrazine.
By 2005, glyphosate herbicide use had spiked dramatically. About 160 million pounds of glyphosate-based herbicides were applied that year, compared to around 75 million pounds of atrazine, again number two in the EPA's ranking.
In 2017, there was enough glyphosate sprayed in the U.S. for about three-quarters of a pound of active ingredient to be applied on every acre of harvested cropland in the country. Worldwide, enough glyphosate was sprayed in 2017 to apply about two-thirds of a pound on every harvested acre on the planet.
Despite this widespread use, knowledge about the public health impacts of glyphosate-based herbicides remains limited. However, a JAMA study published this month reports data on the trajectory of residues of glyphosate, and its principle metabolite AMPA, in the urine of 100 older adults participating in a major, long-term study based at the Rancho Bernado retirement community in California.
The team tested frozen urine samples collected in five time periods. In the first set of samples tested (1993-1996), only 12 of 100 participants had detectable levels of glyphosate in their urine. The frequency of detections jumped to 30 percent in 1999-2000 and 70 percent in 2014-2016. Also worrisome, the mean level of glyphosate among those with detectable levels in their urine more than doubled from the 1993-1996 test period to the 2014-2016 test period.
So, in one decade, 2.5 times more people were exposed to glyphosate-based herbicides and the average level of glyphosate in their urine more than doubled.
These are troublesome changes. One key question looms large: Why the steeply upward trajectory of glyphosate residues in the U.S. population between the 2004-2005 and 2014-2016 periods? It is doubtful that the planting and spraying of Roundup Ready crops is the cause, since by 2004-2005, Roundup Ready technology had already gained high levels of market penetration, and overall glyphosate use has risen modestly since 2005.
The likely answer lies elsewhere. Around 2002, farmers in the U.S. started adopting pre-harvest, desiccation uses of Roundup, to speed the harvest of grain crops like wheat, oats, and barley, as well as edible beans and several other crops. Such "harvest aid" uses of glyphosate entail spraying fields about two weeks prior to harvest. The objective is to speed up the drying of grain crops so harvest operations can be started earlier, and hopefully completed before onset of wet weather.
But spraying a mature grain or bean crop so close to harvest with a glyphosate-based herbicide results in much higher residues than traditional, spring or early summer applications. Beginning around 2004 and over about the next decade, incrementally more acres were sprayed to speed up harvest in the U.S. It is nearly certain that residues from these applications were largely responsible for doubling the levels of glyphosate and its metabolite found in the urine of Rancho Bernado residents.
This paper raises a red flag and is testament to the enormous importance of measuring chemical residues in populations. Small doses over large populations do have effects—we have learned this from radiation exposures, lead, and other environmental pollutants, including pesticides.
In addition, there have been big, hard-to-explain shifts in the health of Americans over the last 30 years, with massive increases in obesity and the doubling of diabetes rates. In some states, adult diabetes affects more than 15 percent of the population. In the 1980s, pediatricians very rarely saw children with Type 2 diabetes yet now it is one of the most common challenges for young patients, their families, and care givers.
Sperm counts and health, and male fertility, have declined over the last two to three generations. Several cancers are becoming more common, and the frequency and severity of reproductive problems and birth defects are rising. Pregnant women and young children in farming areas face a particularly worrisome combination of rising herbicide exposures from their diet, drinking water, and the air and dust particles.
Such immense changes in population health must have causes, some of which are environmental. Chemicals in the environment are rarely the sole cause of health problems—biology does not work that way—but nevertheless they can be big contributors. The Rancho Bernado study provides important new insights on long-term exposure patterns.
Many of the important human-health risk factors identified in the last half-century have come out of such studies.
Both the nature and severity of human health impacts following exposures to glyphosate herbicides are unknown. Despite a 20-fold increase in use over the last two decades, there has been no systematic effort by U.S. research or public health agencies to answer lingering questions.
The reality is that glyphosate uses and exposures are way up. Glyphosate and metabolite residues concentrate in the liver and kidney, and both animal studies and human investigations have highlighted liver and/or kidney problems.
The International Agency for Research on Cancer has classified glyphosate herbicides as "probable human carcinogens," and litigation over the contribution of glyphosate use to Non-Hodgkin lymphoma is opening an unprecedented window on the quality of information available to regulators responsible for quantifying – and hopefully minimizing – pesticide-driven public health problems.
Surely, the time has come for the government to add glyphosate and AMPA to the Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey biomonitoring program, which would allow federal researchers to more accurately quantify both trends and exposure levels in different populations.
An intensified review of glyphosate toxicity by federal public health officials will provide some new insights, but there will undoubtedly be several new questions raised. The possible scope of public health impacts from glyphosate warrants a systematic, government-led, independent appraisal of the biological impacts of glyphosate.
And while the science supporting the regulation of glyphosate herbicides is deepened and improved, the pre-harvest use of the chemicals should be suspended, worldwide.
Richard Jackson is Professor at the Fielding School of Public Health at UCLA and former CDC NCEH Director, as well as the former State Public Health Officer for California. Charles Benbrook is a Visiting Scholar in the Bloomberg School of Public Health, Johns Hopkins University.
Both serve on the Science Team of the Children's Environmental Health Network's "Herbicides in the Midwest" project.