Abstract
This study reports urinary levels of glyphosate, an herbicide sprayed onto genetically modified crops, among participants in the Rancho Bernardo Study of Healthy Aging between 1993 and 2016.
The herbicide Roundup is sprayed onto genetically modified crops and applied as a desiccant to most small non–genetically modified grains. Use of this herbicide has increased since 1994 when genetically modified crops were introduced in the United States. Glyphosate, the primary ingredient in the herbicide, is found in these crops at harvest.1 Environmental exposure through dietary intake of these crops has potential adverse health effects and can be assessed by measuring urinary excretion.2,3,4 We measured excretion levels of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) in participants from the Rancho Bernardo Study (RBS) of Healthy Aging.
Methods
The RBS, established in 1972, is a prospective study of 6629 adults older than 50 years residing in Southern California.5 As of 2016, approximately 1000 participants were active (the primary reason for loss to follow-up was mortality). Of those 1000 participants, 112 had routine morning spot urinary biospecimens obtained at each of 5 clinic visits that took place from 1993 to 1996 and from 2014 to 2016. One hundred of these 112 were randomly selected for this study, which was approved by the University of California, San Diego, institutional review board. All participants gave written informed consent.
Samples were analyzed using high-performance liquid chromatography coupled with mass spectrometry. Limits of detection (LOD) were 0.03 μg/L for glyphosate and 0.04 μg/L for AMPA; assays were linear up to 50 μg/L. Analyses were normalized to each sample’s specific gravity, thereby accounting for dilution or concentration effects due to variability in water intake and age-related or other differences in renal function. Changes over time in the proportion of samples above the LOD were assessed using generalized estimating equation models to account for the dependency of observations in repeated measures. A 2-sided significance threshold was set at less than .05. Statistical analyses were performed using R (R Foundation), version 3.3.2.
Results
Among the 100 participants in this study, the mean age in 2014-2016 was 77.7 years (SD, 6.6) and 60% were women. These values were not different from the 112 with urine specimens but were older than the entire group of 1000 active participants in the RBS (mean age, 71.7 years [SD, 12.0]) (P < .001).
The mean 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 LOD (Table 1). Mean 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.
Table 1. Urinary Excretion Levels of Glyphosate and AMPA Among Rancho Bernardo Study Participants Sampled Between 1993 and 2016.
| Years | Glyphosate, μg/L | AMPA, μg/L | ||||
|---|---|---|---|---|---|---|
| All Participantsa (N = 100) | Participants Above LODb | All Participants (N = 100) | Participants Above LODb | |||
| Mean (95% CI), μg/L |
No. of Participants | Mean (95% CI), μg/L |
Mean (95% CI), μg/L |
No. of Participants | Mean (95% CI), μg/L |
|
| 1993-1996 | 0.024 (0.010-0.039) |
12 | 0.203 (0.151-0.255) |
0.008 (0.001-0.016) |
5 | 0.168 (0.114-0.222) |
| 1999-2000 | 0.053 (0.033-0.074) |
30 | 0.179 (0.136-0.222) |
0.044 (0.020-0.069) |
15 | 0.295 (0.205-0.384) |
| 2001-2002 | 0.110 (0.075-0.146) |
43 | 0.257 (0.197-0.317) |
0.112 (0.071-0.154) |
43 | 0.262 (0.185-0.339) |
| 2004-2005 | 0.111 (0.070-0.152) |
38 | 0.292 (0.213-0.370) |
0.091 (0.057-0.124) |
40 | 0.227 (0.164-0.290) |
| 2014-2016 | 0.314 (0.235-0.394) |
70 | 0.449 (0.352-0.547) |
0.285 (0.217-0.352) |
71 | 0.401 (0.319-0.482) |
Abbreviations: AMPA, aminomethylphosphonic acid; LOD, limit of detection.
Participants with levels below the LOD had values set at 0.
The LOD was 0.03 μg/L for glyphosate and 0.04 μg/L for AMPA.
The prevalence rates of glyphosate samples above the LOD increased significantly over time, from 0.120 (95% CI, 0.064-0.200) in 1993-1996 to 0.700 (95% CI, 0.600-0.788) in 2014-2016 (Wald statistic = 80.5; P < .001) (Table 2). The prevalence of AMPA samples above the LOD increased significantly from 0.050 (95% CI, 0.016-0.113) in 1993-1996 to 0.710 (95% CI, 0.611-0.796) in 2014-2016 (Wald statistic = 103; P < .001).
Table 2. Urinary Excretion Prevalence Rates of Glyphosate and AMPA Among Rancho Bernardo Study Participants Sampled Between 1993 and 2016.
| Years | Prevalence Rate (95% CI)a | |
|---|---|---|
| Glyphosate | AMPA | |
| 1993-1996 | 0.120 (0.064-0.200) |
0.050 (0.016-0.113) |
| 1999-2000 | 0.300 (0.212-0.400) |
0.150 (0.086-0.235) |
| 2001-2002 | 0.430 (0.331-0.533) |
0.430 (0.331-0.533) |
| 2004-2005 | 0.390 (0.294-0.493) |
0.400 (0.303-0.503) |
| 2014-2016 | 0.700 (0.600-0.788) |
0.710 (0.611-0.796) |
Abbreviation: AMPA, aminomethylphosphonic acid.
P value was less than .001.
Discussion
Mean glyphosate and AMPA levels and the proportion of samples with detectable levels increased over time. A 2015 review of nonfarmer US and European adults reported mean urinary glyphosate levels of 1.35 μg/L and 0.215 μg/L, respectively.6 The values observed in this study fall within this range and were higher than in European adults. Animal and human studies suggest that chronic exposure to glyphosate-based herbicides can induce adverse health outcomes.3 Animals consistently fed an ultra-low dosage of the herbicide with a 50-ng/L glyphosate concentration show hepatotoxicity consistent with nonalcoholic fatty liver disease and its progression to steatohepatosis.4 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.
Limitations of this study include that the cohort lived in Southern California, which might have different exposures than other states, only a subset of RBS participants were studied, urinary levels represent recent exposure, urinary-specific gravity is reduced with age, and data on clinical outcomes were not evaluated. Future studies of the relationships between chronic glyphosate exposure and human health are needed.
Section Editor: Jody W. Zylke, MD, Deputy Editor.
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