The presence of the herbicide glyphosate and its metabolite increased between 1993 and 2016 in older adults living in Southern California.
Glyphosate, the primary ingredient in a herbicide sprayed onto genetically modified crops, is found in these crops at harvest. Genetically modified crops were introduced in the United States in 1994. Environmental exposure through dietary intake of these crops has potential adverse health effects and can be assessed by measuring urinary excretion.
Paul J. Mills, Ph.D., of the University of California, San Diego, and colleagues measured excretion levels of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) in participants from the Rancho Bernardo Study of Healthy Aging.
The researchers found that the average glyphosate level increased from 0.024 µg/L in 1993-1996 to 0.314 µg/L in 2014-2016, and reached 0.449 µg/L in 2014-2016 for the 70 participants with levels above the limits of detection (LOD).
Average AMPA levels increased from 0.008 µg/L in 1993-1996 to 0.285 µg/L in 2014-2016, and reached 0.401 µg/L in 2014-2016 for the 71 participants with levels above the LOD.
The prevalence rates of glyphosate samples above the LOD increased significantly over time, from 0.120 in 1993-1996 to 0.700 in 2014-2016. The prevalence of AMPA samples above the LOD increased significantly from 0.050 in 1993-1996 to 0.710 in 2014-2016.
The authors write that animal and human studies suggest that chronic exposure to glyphosate-based herbicides can induce adverse health outcomes. In July 2017, in accordance with the Safe Drinking Water and Toxic Enforcement Act of 1986, the state of California listed glyphosate as a probable carcinogen. "Future studies of the relationships between chronic glyphosate exposure and human health are needed."