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by Jennifer Hsaio
figures by Krissy Lyon

Summary: Pesticides are ubiquitous. Because they are used in agriculture and food production, pesticides are present at low levels in many of our diets.  Less obvious is the fact that many people use pesticides around their homes, and even on their skin (i.e. in the form of insect repellents). According to the NIH, the health effects of pesticides are still not well understood [1]. Potential effects include cancer and damage to the nervous, endocrine, and reproductive systems. Genetically modified organisms (GMOs) are often engineered to be more resistant to pesticides or produce pesticides themselves. How are GMOs changing the landscape of pesticide usage in our crop fields, and ultimately, the pesticide dosage in our dinners?

Pesticides are substances used to repel, kill, or control animals (insecticides) or plants (herbicides) that are considered to be pests.  There are different types of pesticides, which include synthetic pesticides and biopesticides (Figure 1).  Pesticides are used extensively in agriculture and they are also used at a lower scale in our homes and on ourselves.  According to the National Institutes of Health (NIH), the health effects of pesticides are not well understood, but their use has been associated with conditions such as cancer, diabetes, and neurological effects.  GMOs have been changing the way that pesticides are used in agriculture.  Herbicide-tolerant genetically modified (GM) crops have led to an increase in herbicide usage while insecticide-producing GM crops have led to a decrease in insecticides. To understand whether GMOs make us better or worse off in our interaction with pesticides, let’s explore the relationship between pesticides and GMOs in some detail.

Figure 1. Pesticides are grouped under several classes. 

The Upside of Pesticides

According to the US Environmental Protection Agency (EPA), pesticides are often the only effective way to control disease organisms [2].  As a result, their use has become deeply entrenched in our lives. We as consumers often reap the benefits of pesticide use with lower costs and a wider selection of food and clothing.  As a way of conserving food supply and lower food costs, they also help to combat hunger and related problems in various parts of the world (see this article).  Pesticides can protect our homes and buildings from structural damage by creatures such as termites. They can protect our health, too – disease outbreaks are prevented by controlling insect and rodent populations.  Pesticides can even disinfect our drinking water and medical instruments [2].

The Downside of Synthetic Pesticides

Despite their agricultural, economic, and safety , pesticides can also have negative impacts on our health.  Many conventional pesticides are synthetic materials that kill or inactivate the pest directly.  These chemical pesticides include compounds such as organophosphates, carbamates, pyrethroids, and sulfonylureas.  Short-term exposure to a large amount of certain pesticides can result in poisoning.  Exposure to large amounts of pesticides is usually more likely for people such as farmers who may frequently touch and/or breathe in pesticides. The effects of long-term exposure to small amounts of these pesticides are unclear, but studies have linked them to a variety of chronic health conditions such as diabetes, cancer, and neurological defects (for more detailed information, the EPA has an extensive table of health effects of different pesticides).   Specifically, carbamates and organophosphates are known to affect the nervous system by disrupting a neurotransmitter called acetylcholine [3].  Studies have shown preliminary evidence that chronic, low-dose exposure to pesticides increases the risk of cognitive impairments and diseases such as Alzheimer’s and Parkinson’s later in life [4].  A study of 50 pesticides and more than 30,000 licensed pesticide applicators linked exposure of seven pesticides that contain chlorinated compounds (including two herbicides, two organophosphate insecticides, and two organochlorines) to increased risk of diabetes [5].  Exposure to pesticides has also been associated with increased infertility in women and developmental problems in children [6].

Natural Pesticides and GMOs

Biopesticides are derived from natural materials such as plants, animals, bacteria, and minerals. There are three main categories of biopesticides: 1) microbial pesticides, which are microorganisms (e.g. bacteria, fungi, viruses, or protozoa) that have relatively specific pest targets; 2) biochemical pesticides, which are naturally occurring substances that control pests using nontoxic mechanisms (e.g. mimics of insect sex hormones that interfere with their mating); and 3) plant-incorporated-pesticides (PIPs), which are pesticides that the plants themselves produce after genetic material has been added to them.  An example of a PIP is Bacillus thuringeinsis (Bt) crops.

Bacillus thuringiensis (Bt) is a naturally occurring bacterium in the soil that produces proteins specifically active against certain insects.  Some crops such as corn, cotton, and soybeans have been genetically engineered to express the Bt genes that act as insecticides (see this article).  Bt corn is designed to control corn pests such as the European corn borer, corn earworm, and southwestern corn borer, and Bt cotton effectively controls cotton pests such as the tobacco budworm, cotton bollworm, and pink bollworm [7].  The use of Bt crops has led to a reduction in conventional synthetic insecticide use [8] (Figure 2).  The EPA has analyzed Bt crops and found that they do not pose any significant risks to human health [7].  Specifically, the EPA has done studies showing that the Bt protein in GM plants behaves as would be expected for a dietary protein, is not structurally related to a known food allergen or protein toxin, and does not show toxicity when administered orally at high doses [7].

Figure 2. Timeline of the introduction of Bt corn into cornfields and the concurrent reduction of insecticide usage in these fields. The two quantities are strongly anti-correlated, suggesting that this Bt crop has made synthetic insecticides unnecessary. 

Roundup tolerance and the development of herbicide resistance

GM herbicide-tolerant crops enable farmers to use certain herbicides that will kill weeds without harming their crop. The prime example of GM herbicide-resistant crops is the suite of “Roundup-resistant” GMOs, which are designed to tolerate the herbicide glyphosate, an ingredient in the weed killer Roundup (see this article).  Glyphosate is the most widely used herbicide in the world by volume [9].  It is employed extensively in agriculture and can be found in garden products in many countries.

The use of these herbicide-tolerant crops has allowed farmers to switch from traditional herbicides to glyphosate (Figure 3). The good news is that glyphosphate is thought to be less toxic and less persistent than traditional herbicides, which means that it carries fewer health risks for humans [10].

However, the World Health Organization recently announced that glyphosate is a probable carcinogen, so we still need to be cautious [11] (for more information, the EPA also has a list of other pesticides and their carcinogen status).  Although studies have shown conflicting conclusions about the link between glyphosate and cancer in humans, glyphosate has been linked to cancer in rats and mice and experiments in human cells have shown that exposure to glyphosate can cause DNA damage [9].

Plants may develop resistance to herbicides over time [12].  Weeds that have developed resistance to herbicides such as glyphosate may require higher amounts of glyphosate and perhaps other herbicides to keep them in check, and this means that herbicide-tolerant crops will be exposed to higher levels of herbicides as well.

Figure 3. Timeline of glyphosate-based herbicide use on corn, cotton, and soybean in response to the growing popularity of their GMO versions. Since the introduction of Roundup-tolerant crops, herbicides have experienced a significant increase in application. (Adapted from [15])

Ways to reduce pesticide exposure

The lack of conclusive evidence ruling out negative effects of chronic exposure to low doses of pesticides may mean that we should still work to minimize exposure to pesticides when possible.  It is especially important to limit the pesticide exposure of more susceptible groups of people such as pregnant women and growing children.  Pesticide use should be regulated in a way that will limit development of herbicide and insecticide resistance in their target organisms.  This can help prevent an increase in the amount and toxicity of pesticides used.  Making sure that farmers are aware of the best ways to limit unwanted pesticide resistance will also be essential.

Fortunately, pesticide use is studied, monitored, and regulated by organizations such as the EPA and the World Health Organization. The EPA regulates pesticides in food by evaluating every new pesticide for safety and every new use before it is registered [13].  The EPA evaluates hundreds of scientific studies on pesticides to ensure their safety to humans.  After a pesticide is registered, the EPA reevaluates its safety every 15 years [13].  Before the EPA allows a pesticide to be used on crops, it sets a maximum legal residue limit (called a “tolerance”) for each treated food, and if that residue limit is exceeded, government action will be taken [13].

Furthermore, it is essential to strike a balance in pesticide usage: we want to minimize the consequences induced by the toxicity of synthetic pesticides, while maximizing their beneficial effects for crops. GMOs have played a mixed role in this development, helping reduce pesticide use in some cases (e.g. with Bt crops) while increase pesticide use in other cases (e.g. with herbicide-resistant weeds).  Thus, their use has not resolved our pesticide conundrum. Encouragingly, research is ongoing to find synthetic pesticides that have high specificity for their target pests. Alternative, non-chemical forms of pest control that are less toxic to humans and other organisms are also being studied [14].  Chances are good that these efforts will become part of the permanent solution.

Jennifer J. Hsiao is a Ph.D. candidate in the Biological and Biomedical Sciences Program at Harvard University

This article is part of the August 2015 Special Edition, Genetically Modified Organisms and Our Food.

References

1. Pesticides.  (24 March 2015).  NIH.  https://www.niehs.nih.gov/health/topics/agents/pesticides/
2. Benefits of Pesticide Use.  (27 June 2012).  Environmental Protection Agency.http://www.epa.gov/oecaagct/ag101/pestbenefits.html
3. Human Health Issues.  (17 October 2014).  Environmental Protection Agency.  http://www.epa.gov/pesticides/health/human.htm
4.  Kamel, Freya.  Paths from Pesticides to Parkinson’s. (16 August 2013).  Science.
5. Long-term pesticide exposure may increase risk of diabetes.  (4 June 2008).  National Institute of Environmental Health Sciences.  http://www.niehs.nih.gov/news/newsroom/releases/2008/june04/
6. Sanborn M, Kerr KJ, Sanin LH, Cole DC, Bassil KL, Vakil C.  Non-cancer health effects of pesticides. (October 2007). Can Fam Physician.  53: 1712-1720.
7. Mendelsohn M, Kough J,Vaituzis Z, Matthews K. 2003. Are Bt crops safe? (September 2003). Nat. Biotechnol. 21:1003–9.
8. Malakof D. and Stokstad E. Pesticide Planet (infographic).  (16 August 2013).  Science.
9. Cressey D. Widely used herbicide linked to cancer.  (24 March 2015). Scientific American.http://www.scientificamerican.com/article/widely-used-herbicide-linked-to-cancer/
10. Fernandez-Cornejo J,  Wechsler SJ, Livingston M. Adoption of genetically engineered crops by U.S. farmers has increased steadily for over 15 years.  (4 March 2014). USDA. http://www.ers.usda.gov/amber-waves/2014-march/adoption-of-genetically-engineered-crops-by-us-farmers-has-increased-steadily-for-over-15-years.aspx#.VasdfEVExLQ.
11. International Agency for Research on Cancer (IARC). IARC monographs volume 12: evaluation of 5 organophosphate insecticides and herbicides. (20 March 2015).  World Health Organization.
12. Barfoot P and Brookes G.  Key global environmental impacts of genetically modified (GM) crop use 1996-2012. (3 November 2014). Landes Bioscience.
13. Food and Pesticides.  (20 March 2015).  Environmental Protection Agency.  http://www2.epa.gov/safepestcontrol/food-and-pesticides
14. Agricultural Pesticides. (27 June 2012).  Environmental Protection Agency. http://www.epa.gov/oecaagct/ag101/croppesticideuse.html

 

Featured image by the Global Water Partnership and licensed by Creative Commons.

17 thoughts on “GMOs and Pesticides: Helpful or Harmful?

    1. Monsanto has kept the use of glyphosate (Roundup) on the market by hiding behind the fact that glyphosate on interrupts the PLANT metabolic pathway (shikimate pathway). Since humans DON’T have the shikimate pathway, no harms…Well Monsanto fails to mention that human gut bacteria DO have the shikimate pathway and are interrupted in such a way causing harmful bacteria and their wastes to affect our brain chemistry (Autism, Alzheimers, appetite out of control).

      Watch the interview the the MIT researcher linking glyphosate to Autism, Alzheimers, obesity – http://articles.mercola.com/sites/articles/archive/2013/06/09/monsanto-roundup-herbicide.aspx

      1. I can find no evidence that human gut bacteria are significantly affected by the traces of glyphosate in our diet. (One study estimated that typical exposure was of the order of 1 microgram per kilogram body weight—a microgram is about 1/1000 the weight of a mosquito).

        Don’t forget that salt, sugar, alcohol and vinegar all affect the growth of bacteria: what matters is the combination of dose and inherent antimicrobial potency.

        (BTW Jerry, mercola is a website that sells products and “remedies”. I have never found it to be an accurate source of scientific information).

        1. Dr. Mercola does have a substantial background in traditional medicine, regardless of what his website has on it. I’d be interested to know what study you are referring to, Dr. Olins, that mentions the effects of glyphosate in our diet. I’m doing a research paper about GMO’s and their safety.

    2. Yes, Laura,
      Your link shows how surfactants (i.e. soaps) can be more toxic to cultured animal cells than the pesticides that accompany them. Don’t you find this encouraging? !

      There are very few people on earth who do not use surfactants on a daily basis, and I’m sure you are no exception.

      1. The benefits of GMO crops are largely speculative. We don’t know if they will turn out to handle bad weather better, or if they will end up delivering more vitamins per piece of fruit, or if they will end up having more yield per acre. Even the best studies touting these advantages are unconvincing. This study she posted suggests that Pesticides like Glysophate, the most used pesticide ROUND UP in GMO farming is more dangerous than previously thought. Also, 2,4+D was recently removed from the market by the EPA. And neoniconoids have been found in tests to disorient and ultimately kill the bees on a massive scale. These are very bad things to put in our food and there are non-pesticide ways of controlling insects which work just as well. No one has a problem with organic local farming done without pesticides and herbicides. It’s great for the local economies. It’s responsive to consumers. It’s healthier according to recent studies. And it’s what people actually want. GMOs tend to be supporting global corporate profiteering, factory farming, and INCREASED pesticide usage. If you look at pesticide use over 20 years, it has INCREASED. We were told it would DECREASE. Nature is unpredictable. We don’t need to add a corporatist profiteer model over growing our food. People don’t want it. And it’s unnecessary. ANY additional health risk because of pesticides, herbicides and even monocultures is unacceptable. Even a tiny risk when it’s applied to 1/3 of the planet’s food supply is too big of a risk. The tech our way out of the problem only solution is failing as pesticide usage is rising. We need to return to weeding and crop rotation and local organic farming.

        1. How many acres have you weeded in your lifetime?

          Can you be more specific about the “we” when you say that “…we need to return to weeding.”? Do you have a plan to incentivize all these weeders, or do you think a voluntary program will be sufficient?

        2. Steve, You mix so many things into your brew of fear , it is hard to respond. But consider- like the national debt is still increasing it is growing slower than it would if not for budget controls. Similarly, crop acreage has increased substantially in the past decades – so we would expect pesticide use to increase. But is has grown at slower rate and for many crops has decreased on a per/acre basis.
          You can rant about corporations & we will join to some extent but is irrelevant to the discussion of this paper.
          Again and again organic produce has been demonstrated to be no better tasting, not more nutritional, and no better for the environment- just more expensive. A triumph of style and marketing over sound science.

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  2. Jennifer, thanks for this article. The graph showing the use of insecticide on Bt corn (shown dropping to zero) was dated 2013. I’m wondering if that effect is holding up, given the growth of Bt-resistant strains (as discussed, for example, in this article: http://www.nature.com/nbt/journal/v31/n6/full/nbt.2597.html).

    Also, Dr. Olins, it would be nice if you could cite the research you reviewed on the impact of glyphosate on gut bacteria. The research literature on GMO effects on food safety is notoriously thin–any academic research in this area would be very interesting.

      1. Sorry that you are having trouble! Can you please tell me where comments appear to be blocked so that I can fix the issue? We have to manually approve all comments to eliminate spam, so that’s why they are sometimes slow to appear. E-mail us at: sitnbostonblog[at]gmail[dot]com.

        Thanks!

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