Residues of glyphosate in food and dietary exposure. John L. Vicini, Pamela K. Jensen, Bruce M. Young, John T. Swarthout. Comprehensive Reviews in Food Science and Food Safety, August 16 2021. https://doi.org/10.1111/1541-4337.12822
Abstract: Glyphosate is the active ingredient in Roundup® brand nonselective herbicides, and residue testing for food has been conducted as part of the normal regulatory processes. Additional testing has been conducted by university researchers and nongovernmental agencies. Presence of residues needs to be put into the context of safety standards. Furthermore, to appropriately interpret residue data, analytical assays must be validated for each food sample matrix. Regulatory agency surveys indicate that 99% of glyphosate residues in food are below the European maximum residue limits (MRLs) or U.S. Environmental Protection Agency tolerances. These data support the conclusion that overall residues are not elevated above MRLs/tolerances due to agricultural practices or usage on genetically modified (GM) crops. However, it is important to understand that MRLs and tolerances are limits for legal pesticide usage. MRLs only provide health information when the sum of MRLs of all foods is compared to limits established by toxicology studies, such as the acceptable daily intake (ADI). Conclusions from dietary modeling that use actual food residues, or MRLs themselves, combined with consumption data indicate that dietary exposures to glyphosate are within established safe limits. Measurements of glyphosate in urine can also be used to estimate ingested glyphosate exposure, and studies indicate that exposure is <3% of the current European ADI for glyphosate, which is 0.5 mg glyphosate/kg body weight. Conclusions of risk assessments, based on dietary modeling or urine data, are that exposures to glyphosate from food are well below the amount that can be ingested daily over a lifetime with a reasonable certainty of no harm.
7 DISCUSSION
Calculating dietary consumption of glyphosate can be done using two disparate methods. In the first method, residues are measured in individual food items and these are summed based on consumption data for the foods that people eat. This approach requires answering several questions to make reasonable assumptions used in the modeling such as: (1) what residue value for a food is used; (2) is the food processed or cooked; (3) what residue value is used when an analyte's concentration is < LOD; (4) are mean, median, or 90th percentile values used for consumption; and (5) what and how much do people eat? In the second approach, for a pesticide like glyphosate with the knowledge of absorption from the gut, lack of metabolism, and elimination from the body, sampling of urine is an accurate way to calculate ingestion and exposure within the body (Acquavella et al., 2004; Niemann et al., 2015). Regardless of which of the two methods is used, these values need to be compared to a safety standard, such as the ADI or RfD, which are regulatory-derived safety standards. Results of determining exposure to glyphosate by dietary modeling or urinary glyphosate are presented in Table 5, Table 6, and Figure 2. Modeling allows different scenarios using estimates of consumption and data derived from market surveys, whereas urine is a surrogate for estimating actual dietary exposure to glyphosate. The results from these two methods are in relatively close agreement. Dietary estimates range from 0.03% to 18% depending on assumptions. An especially critical assumption used is the residue levels that are used. Urinary glyphosate estimates of exposure are 0.02%–2.67% of the ADI, which do not require an assumption about residue on individual foods.
In spite of that, testing and publishing about glyphosate residues, whether in peer-reviewed journals, by internet postings or in the news media, has become somewhat common in the last decade. Unfortunately, many of the popular press reports are accompanied by value-judgment words like “high” or “contaminate,” or they make scientifically inappropriate comparisons to other standards (i.e., concentrations in urine vs. regulatory defined residue levels for drinking water). Furthermore, some of these reports imply that glyphosate residues were not known to exist previously in a given food or in urine, and, therefore the findings are regarded as novel. Recent publications, such as Winter and Jara (2015), Winter et al. (2019), and Reeves et al. (2019), have attempted to provide more information about the process for risk assessment of pesticides conducted by regulatory agencies. Moreover, timely communications from regulatory agencies, such as BfR responding to reports of residues in food, German beer, or urine (BfR, 2016, 2017), provide helpful information from what should be a trustworthy source in the face of widespread social media communications about food and agriculture (Ryan et al., 2020).
One statistic that is often encountered in publications that also might generate concern by consumers is reports of increased trends over time of usage of a pesticide, either by expanded adoption or as the result of new technology, such as herbicide-tolerant crops (Benbrook, 2016). These statistics intimate that pesticide use has exceeded safe levels established by the original regulatory assessments. In one residue study, the authors suggested that it appeared that MRL values were adjusted due to actual observed increases and not based on toxicity (Bøhn et al., 2014). This is precisely how MRLs are derived. It is important to highlight that alterations in the use of a previously approved pesticide, such as usage of glyphosate on newly approved GT crops, require new residue data to be submitted from the pesticide registrant(s) prior to regulatory approval. These new residue data are reviewed by regulators in order to ensure that the previous ADI or RfD is not exceeded. Additionally, MRLs or tolerances are derived from empirical data of real-world conditions and, once established, MRLs represent for any crop the agricultural practice that results in the highest residue. EPA (1996) stated in their guidance that pesticide use patterns, such as changes in the preharvest interval and/or postharvest treatment, are likely to require residue studies, and potentially another petition for a new tolerance. Expanded usage of a pesticide might change, but by conservatively assuming that 100% of a crop will use the agricultural practice with the highest residue, exposure remaining below the ADI is not subject to changes in commercial adoption. If a new exposure resulted in the sum of all exposures exceeding the ADI, there would need to be a restriction in some use. Moreover, since regulatory authorities use data collected prior to authorization of cultivation or import of the crop, combined with periodic testing to ensure that tolerances are not being exceeded, these media reports of residues do not necessarily provide unexpected data. When properly conducted, independent, peer-reviewed studies are published, they can be a corroboration of the accuracy of previously reported regulatory residue studies.
Putting pesticide residues into context by converting these values to percentages of the EFSA- or EPA-derived ADI or RfD helps one understand the margin of safety, but many consumers want food that is free of synthetic pesticides (Krystallis & Chryssohoidis, 2005). According to Currie (1999), many believe that with improved assays, a concentration of zero might be detected, but that is scientifically not feasible.
More than ever, as in other areas of science, transparency on residues of pesticides and their assessment by global regulatory authorities entrusted by the public to ensure food safety is needed to address complex scientific information (OECD, 2020). The scientific publication process that requires peer-review of the data and conclusions has largely provided the basis for science-based regulatory assessments for the past century (Codex, 2004) . Although peer-review is not a foolproof process, it is a process with the intent of ensuring that results and conclusions from published studies are based on well-conducted and documented scientific experiments. This is in sharp contrast to the essentially unreviewed environment of media and online publications. Adequacy of peer review is increasingly more confusing with predatory journals and electronic publishing (Kelly et al., 2014). Since the public lacks training to help them distinguish information from peer-reviewed journals and science-based regulatory authorities from information they see in media reports and predatory journals, this review has included results on glyphosate residues from both sources to provide them with a single-point reference for an informed discussion of this subject.
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