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Traits in Agriculture » Herbicide Tolerance

Title: Health Impacts of Glyphosate May Include Driving Antibiotic Resistance
Publication date: December 20, 2017
Posting date: December 20, 2017

THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE                                                                

Dear Friends and Colleagues

Health Impacts of Glyphosate May Include Driving Antibiotic Resistance

The herbicide glyphosate, N-(phosphonomethyl) glycine, is a biocide with broad spectrum activity that was introduced for weed control in 1974. Glyphosate products are used primarily before planting of agricultural crops and after planting of genetically modified (GM) glyphosate-resistant crops such as soybean, cotton, canola and corn. In 2012, about 127,000 tons of glyphosate were used in the USA and 700,000 tons worldwide.

Although quite resistant to degradation, decomposition of glyphosate takes place in living plants as well as in soils; the first decomposition product often is aminomethyl phosphonic acid, AMPA. So both glyphosate and AMPA residues can be found in plant products. Due to the large scale and intensive use of glyphosate and its accumulation in the environment and edible products, several major concerns have arisen in recent years about harmful side effects of glyphosate and AMPA for soil and water quality, and plant, animal and human health. The World Health Organization reclassified glyphosate as probably carcinogenic to humans in 2015.

A review of scientific literature on glyphosate and AMPA has found that:

  • Glyphosate and its degradation product AMPA have accumulated in the environment.
  • Chronic low dose effects on animals and humans have been documented recently. In particular, the high proportion of people and farm animals with glyphosate in their urine is cause for concern. Sufficient data has accumulated regarding the chronic toxic effects of glyphosate formulated products on aquatic and terrestrial animals and humans to warrant reconsideration of the tolerable residue levels of glyphosate and AMPA in plant and animal products and the environment.
  • Shifts in microbial community composition in soil, plants and animal guts were documented. These may have contributed to the proliferation of plant and animal pathogens.
  • Glyphosate and antibiotic resistance have arisen in fungi and bacteria in parallel. Glyphosate may serve as one of the drivers for antibiotic resistance. Management of weeds with multiple glyphosate applications could result in microbiomes that are relatively glyphosate and antibiotic resistant. The authors hypothesise that the selection pressure for glyphosate-resistance and the associated resistance to antibiotics in the soil microbiome result in transfer of antibiotic resistant bacteria from soil to plants, animals and humans through the food web, even in urban and hospital environments.

The sequence of events outlined, namely introduction of glyphosate resistant crops, intensification of glyphosate use, emergence of glyphosate-resistant weeds and microorganisms, changes in microbiomes and disease resistance, deteriorated plant and animal health, and increased antibiotic resistance, could serve as a harbinger for events to follow the introduction of genes conferring resistance to other herbicides such as dicamba and 2,4-D.

In conclusion, the authors suggest that the problems associated with the large scale and intensive use of glyphosate (and other herbicides in the future) are much more encompassing than originally anticipated by the regulatory agencies. They recommend additional interdisciplinary research on the associations between low level chronic herbicide exposure, distortions in microbial communities, expansion of antibiotic resistance and the emergence of animal, human and plant diseases. Independent research is needed to revisit the tolerance thresholds for glyphosate residues in water, food and animal feed taking all possible health risks into account. A global effort will be needed to collect appropriate high quality residue and health data across the range of settings in which glyphosate and other herbicides are used; these are needed to design, develop and implement strategies to counter further escalation of the problems associated with the use of glyphosate and other herbicides.


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Third World Network
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ENVIRONMENTAL AND HEALTH EFFECTS OF THE HERBICIDE GLYPHOSATE

Van Bruggen, A.H.C. et al.
Elsevier
Science of the Total Environment 616–617 (2018) 255–268
Nov 2017
https://www.sciencedirect.com/science/article/pii/S0048969717330279

Abstract

The herbicide glyphosate, N-(phosphonomethyl) glycine, has been used extensively in the past 40 years, under the assumption that side effects were minimal. However, in recent years, concerns have increased worldwide about the potential wide ranging direct and indirect health effects of the large scale use of glyphosate. In 2015, the World Health Organization reclassified glyphosate as probably carcinogenic to humans. A detailed overview is given of the scientific literature on the movement and residues of glyphosate and its breakdown product aminomethyl phosphonic acid (AMPA) in soil and water, their toxicity to macro- and microorganisms, their effects on microbial compositions and potential indirect effects on plant, animal and human health. Although the acute toxic effects of glyphosate and AMPA on mammals are low, there are animal data raising the possibility of health effects associated with chronic, ultra-low doses related to accumulation of these compounds in the environment. Intensive glyphosate use has led to the selection of glyphosate-resistant weeds and microorganisms. Shifts in microbial compositions due to selective pressure by glyphosate may have contributed to the proliferation of plant and animal pathogens. Research on a link between glyphosate and antibiotic resistance is still scarce but we hypothesize that the selection pressure for glyphosate resistance in bacteria could lead to shifts in microbiome composition and increases in antibiotic resistance to clinically important antimicrobial agents. We recommend interdisciplinary research on the associations
between low level chronic glyphosate exposure, distortions in microbial communities, expansion of antibiotic resistance and the emergence of animal, human and plant diseases. Independent research is needed to revisit the tolerance thresholds for glyphosate residues in water, food and animal feed taking all possible health risks into account.

Discussion and Conclusions

Due to the almost exponential increase in glyphosate use and the slow decomposition of glyphosate and its breakdown product AMPA in soil, water and sediment, the accumulation of glyphosate in the environment, plant products and animal organs has become quite worrisome
(Myers et al., 2016; Shehata et al., 2014). In particular, the high proportion of people and farm animals with glyphosate in their urine is concerning, even though the concentrations are still low (Niemann et al., 2015). Although the acute toxic effects of glyphosate on fish and mammals are low, the formulated products often are more toxic than glyphosate itself, and concerns have emerged about chronic effects of the formulated products on human and animal diseases, in particular various forms of cancer and mental disorders (Fortes et al., 2016; Mesnage et al., 2015a, 2015b; Swanson et al., 2014). Although conclusions regarding possible carcinogenicity and other health effects of glyphosate remain controversial, we feel that sufficient additional data has accumulated regarding the chronic toxic effects of the formulated products on aquatic and terrestrial animals and humans to warrant reconsideration of the tolerable residue levels of glyphosate and AMPA in plant and animal products and the environment. The recent reclassification of glyphosate as probably carcinogenic by the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) was based primarily on research with the main formulated product Roundup® (IARC, 2015; Séralini et al., 2014). Additional research is needed to come to a definitive conclusion on the chronic health effects of the various formulated products containing glyphosate.

In addition to the possible chronic direct health effects of glyphosate on a variety of aquatic and terrestrial animals and humans, we documented shifts in microbial communities in soil, plants, water and intestinal tracts and the association with specific plant and animal pathogens (Ackermann et al., 2015; Priestman et al., 2005; Sanogo et al., 2000, 2001). The shifts in microbiomes resulting from intensive glyphosate use can affect resistance mechanisms and have severe impacts on plant, animal and human health (Hoffman et al., 2015). These complex, indirect effects of glyphosate need to be taken into account by regulatory agencies.

Other indirect health effects can come about through the recently documented cross resistance to glyphosate and clinically important antibiotics (Kurenbach et al., 2015). The surge in antibiotic resistance has been attributed primarily to the increased use of antibiotics by human patients and farm animals (Smith et al., 2005; Stine et al., 2007), but antibiotic resistance is also widespread in agricultural soils that were not exposed to high antibiotic concentrations (Udikovic-Kolic et al., 2014). Considering that subsets of the microbiomes in soil transfer to plants, fresh plant products, animal and human intestinal tracts (Berg et al., 2014), and then to excrements that return to soil and water, we suggest that there are microbial cycles that are characteristic for particular  management systems. Management of weeds with multiple glyphosate applications could result in microbiomes that are relatively glyphosate and antibiotic resistant. This leads us to the hypothesis that the selection pressure for glyphosate-resistance and the associated resistance to antibiotics in the soil microbiome result in transfer of antibiotic resistant bacteria from soil to plants, animals and humans through the food web, even in urban and hospital environments.

The sequence of events outlined here for glyphosate, namely introduction of glyphosate resistant crops, intensification of glyphosate use, emergence of glyphosate-resistant weeds and microorganisms, changes in microbiomes and disease resistance, deteriorated plant and animal
health, and increased antibiotic resistance, could serve as a harbinger for events to follow the introduction of genes conferring resistance to other herbicides. The recent addition of genes for resistance to the herbicides dicamba and 2,4-D to glyphosate resistant crops (Ruen et al., 2017) will likely result in additional increases in herbicide use and unintended side effects (Leon et al., 2016). Weeds with multiple herbicide resistance at multiple sites of action have been detected already (Bell et al., 2013). Similar to glyphosate, dicamba and 2,4-D have differential effects on microorganisms, and shifts in plant and animal microbiomes can be expected as a result of intensification of the use of dicamba and 2,4-D (Oleszczuk et al., 2014; Seghers et al., 2003). The mechanisms that convey resistance to herbicides in plants are largely similar to those conferring resistance to herbicides in microorganisms, and thus, insensitivity to herbicides other than glyphosate will likely also increase in microbial communities, possibly followed by increased antibiotic resistance. These wide-ranging consequences of intensive herbicide use have not been pointed out previously.

In conclusion, we suggest that the problems associated with the large scale and intensive use of glyphosate (and other herbicides in the future) are much more encompassing than originally anticipated by the regulatory agencies (EPA, 2013). We recommend additional interdisciplinary research on the associations between low level chronic herbicide exposure, distortions in microbial communities, expansion of antibiotic resistance and the emergence of animal, human and plant diseases. Independent research is needed to revisit the tolerance thresholds for glyphosate residues in water, food and animal feed taking all possible health risks into account. A global effort will be needed to collect appropriate high quality residue and health data across the range of settings in which glyphosate and other herbicides are used; only as such data become available will we be able to design, develop and implement strategies to counter further escalation of the problems associated with the use of glyphosate and other herbicides.
 

 


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