By Morgan Chamberlin



Genetically modified (GM) crop technology was widely adopted for commercial use in 1996 and is mainly used in corn, soybean, cotton, and canola crops.  In 2018, 48% of the global plantings of these four crops utilized biotechnology.1  The main traits conferred to these crops through this technology are insect resistance (GM IR) and herbicide tolerance (GM HT).  These traits help produce high crop yields and lend themselves well to the monocropping farm techniques used for these commercial crops.2  While GM technology is less commonly used in specialty crops, it presents an opportunity to address the global food crisis if used in this manner.  The current global food system is not sustainable.1  A rapidly increasing world population, climate change, and crop pests such as insects and weeds present a significant challenge to the global food system.  The field of dietetics practices at the intersection of nutrition, health, and sustainability.  As such, it is critical to understand the current state of the global food system and the practices and technologies that influence it.

Genetically modified crops are thoroughly evaluated for environmental effects before they become commercially available.  They are assessed not only by the developers of GM crops but also by a variety of regulatory bodies.  In the United States, these regulatory agencies include the U.S. Food and Drug Administration (FDA), the U.S. Environmental Protection Agency (EPA), and the U.S. Department of Agriculture (USDA).3  The risk assessment includes considerations for interactions with the environment and unintentional effects.  Despite these safeguards, the use of GM technology in crop production has incited much debate regarding its impact on the environment.    

Research indicates that GM crop technology can result in a net increase in herbicide use and can foster the growth of herbicide resistant weeds.1  In addition, there is concern that the use of GM crops may negatively impact the agriculture ecosystem.  While these negative impacts are of concern, conflicting research studies abound making it difficult to interpret results.  By considering the aggregate global impact of GM technology on the environment, the overall trend of GM crop use can be more clearly deciphered.  When looking on a global scale since the widespread adoption of GM technology in 1996, research indicates that GM technology is not inherently dangerous to the environment.1,2  In fact, GM technology has positively impacted the environment in several ways1,4 making it a useful tool in the development of a sustainable food system.    

GM IR and HT Technology

Perhaps the most conflicting research surrounding GM crops concerns their effects on herbicide use and the subsequent environmental impact.  Some countries have experienced a net decrease in herbicide use associated with the adoption of GM crops.  For example, in Canada, the use of GM HT soybeans has resulted in a decrease of herbicide use compared to use on the conventional equivalent every year from 1997-2018.  However, in other countries, the average amount of herbicide active ingredient applied to GM crops compared to their conventional equivalent represents a net increase. For example, from 2007 – 2014, GM HT soybean crop use in Brazil resulted in an average increase of 4,940,262 kilograms (kg) of herbicide.  However, from 1997 – 2006, and from 2015 – 2018, the average volume of herbicides used in Brazil represented an average decrease.  This comparison stresses the importance of examining the aggregate impact of herbicide use over the entire time span of GM crop use.  In this example, the aggregate global impact of GM HT soybeans represents a 0.1% increase in the change of active ingredient used, corresponding to an increase of 5 million kg used.  Unlike this increase, the aggregate global amount of herbicide used on GM cotton, corn, and canola decreased from 1997-2018.1,4

The adoption of GM technology has resulted in a shift from the use of a wide variety of selective herbicides to the use of one or two broad-spectrum herbicides.  As a result, the comparison of herbicides used on GM crops versus conventional crops must include more than net amount used to determine overall environmental impact.  The environmental impact quotient (EIQ) is a method used to measure the impact of individual pesticides on the environment, making it an important factor to consider when discussing environmental impact.  Significantly, the EIQ values of herbicides frequently used on GM crops are commonly better than those used on the conventional equivalent.  For example, even though there was a 1.7% increase in the amount of herbicide used on GM HT soybean crops in Brazil from 1996 – 2018, the EIQ values over the same time period represent a 7.2% improvement compared to the conventional improvement.  It is also important to examine the aggregate global impact of herbicide use on crops in addition to effects seen in individual countries.  Even though the aggregate impact of the top ten soybean growing countries from 1996 – 2018 shows a 0.1% increase in the amount of herbicide used, the overall environmental impact, as measured by EIQ, improved by 12.9%.1,4 

Even more so than GM HT crops, GM IR crops have had a significant positive impact on the environment.  The use of GM IR technology effectively replaces the use of insecticides to control key crop pests.  This is particularly evident in cotton as intensive treatment protocols are traditionally used to control bollworm/budworm pests.  From 1996-2018, the aggregate impact of all countries growing GM IR cotton resulted in a net savings of 331 million kg of insecticide and a 34.2% improvement in EIQ.  GM Soybeans and corn have also had similar positive environmental impacts on a global scale.1,2

This research clearly shows that GM technology has had a positive environmental impact through a significant reduction in insecticide and herbicide use.  Globally, since 1996, the use of pesticides (herbicide and insecticide combined) on GM crops has fallen by 8.3% which represents a savings of 775.4 million kg of active ingredient relative to the amount expected if the same crop area had been planted conventionally.  As measured by EIQ indicator, this corresponds to an 18.5% improvement.1,4

GM Herbicide Resistance

While the shift in the type of herbicide used on GM crops represents a net improvement as measured by EIQ, the dominant use of one or two herbicides has resulted in broad spectrum herbicide resistant weeds.  Specifically, the use of glyphosate tolerant crops has resulted in glyphosate resistant weeds which have created major problems in some regions.  Countries with a high production of GM crops such as the US, Brazil, and Canada have a number of resistant weed species; 17, 9, and 6 respectively.  In the United States, some resistant species are widespread; an estimated 50-75% of the total area devoted to corn, cotton, and soybeans being affected annually.1,4 

However, this problem is not due to the inherent nature of GM HT crops.  Research indicates that these effects, at least in part, may be attributed to how glyphosate was originally used on GM crops.  Specifically, they were used as the sole method of weed control during first five years of GM crop use.  Over the last 15 years, GM growers have been advised to use other herbicides with complementary and different modes of action in combination with glyphosate.  In addition, growers are encouraged to integrate other farming practices such as reduced-tillage systems to aid in weed management.2

In addition, it is important to examine weed development in conventional farming practices over the same time period.  All weeds have the potential to develop resistance to herbicides and there are hundreds of resistant weed species confirmed.  As of March 2020, there were 48 weed species resistant to glyphosate worldwide.  Of these species, many were not associated with GM crops.  For example, some of the first glyphosate resistant weeds developed in the mid 1990’s in Australia before GM technology was adopted in the region.  In addition, two of the 17 glyphosate resistant weeds in the US are not associated with GM crops.  Furthermore, herbicide resistant weeds pre-date the use of GM HT crops by decades.1,4 

GM Insecticide Resistance

As with any environmental management tactic, there is concern that GM crops may cause adverse effects on non-target species.  Species of concern include parasitoids and arthropod predators of crop plants.5,6  For example, in 1999 a published study raised concerns that a Bacillus Thuringiensis (Bt) insect resistant corn crop was negatively impacting Monarch butterfly larvae.7  While the results of this study were concerning, the study itself took place in a laboratory.  As one of the study author’s indicated: “Our study was conducted in the lab and, while it raises an important issue, it would be inappropriate to draw any conclusions about the risk to Monarch populations in the field solely on these initial results”.7  In 2001, a follow up study published in Proceedings of the National Academy of Sciences (PNAS) concluded that the impact of Bt corn on Monarch butterfly populations is negligible.8

Over the 22 years of GM technology use, extensive laboratory and field-study research has been conducted to identify the non-target effects of IR crops.  The vast majority of studies demonstrate that the insecticidal proteins utilized in IR seed production cause no unintended adverse effects to natural enemies.  Furthermore, the replacement or reduction of chemical insecticide use associated with GM IR crops creates an environment supportive of the conservation of species in the agriculture ecosystem.  When used as part of an overall integrated pest management (IPM) strategy, GM IR crops can contribute to more effective biological control of both target and non-target pests.5

Greenhouse Gas Emissions

Of great significance to the environment, changes in agricultural practices associated with GM crop use are associated with a reduction in fuel use and a concomitant decrease in greenhouse gas emissions.  This impact is due primarily to a reduction in spray runs in GM IR crops and a switch from conventional tillage to reduced or no tillage farming systems facilitated by GM HT crops.  Both of these agricultural practices result in a decrease in the active time of fuel-dependent farm equipment.  In 2018, these practices reduced fuel use by 920 million liters, corresponding to a saving of 2,456 million kg of carbon dioxide.  The cumulative reduction in fuel use from GM agriculture equates to approximately 12,799 liters of fuel and 34,172 million kg of carbon dioxide.  This amount of fuel savings corresponds to taking 22.65 million cars off the road for a year.1

The adoption of reduced tillage or no tillage practices associated with GM crops has also contributed to a reduction in greenhouse gas emissions.  This effect is due to the slower breakdown of plant residues associated with less soil tilling.  Because the breakdown process is less rapid, more carbon is sequestered in the soil instead of being released to the atmosphere as carbon dioxide. The estimated amount of soil carbon sequestered as a result of GM crops since 1996 is equivalent to 302,364 million kg of carbon dioxide.  In addition to reducing gas emissions and improving soil carbon content, research indicates that reduced tillage practices also reduce soil erosion.1,4


While there are many regulations in place to prevent GM crops from harming the environment, there is still potential for this technology to have a negative impact.  Research does show that GM technology has led to the creation of HT weeds and is associated with a net increase of herbicide use on some crops in some regions.1,4  In many cases, these effects are due to human error in the application of this technology, not the technology itself.1,4  In order to accurately determine the environmental impact of GM crops, it is important to look at the aggregate global impact.  When examining the global environmental impact of GM crops, research clearly indicates that GM crops are not inherently dangerous to the environment.  On a global scale, GM crops have actually had a positive impact on the environment.  The widespread adoption of GM crops and the agricultural practices associated with their use have resulted in aggregate reductions in herbicide and insecticide volumes as well as an improvement in the EIQ profile of these chemicals.  In addition, a reduction of fuel use associated with GM crops has led to a significant reduction of greenhouse gas emissions and a concomitant increase in soil quality.1,2,4,5,7,8  The positive environmental impacts and increased crop yields associated with GM crops validate the use of this technology in the development of a sustainable food system.    


  1. Brookes G, Barfoot P. Environmental impacts of genetically modified (GM) crop use 1996-2018: impacts on pesticide use and carbon emissions. GM Crops Food. 2020;11(4):215-241.
  2. Meftaul IM, Venkateswarlu K, Dharmarajan R, et al. Controversies over human health and ecological impacts of glyphosate: Is it to be banned in modern agriculture? Environ Pollut. 2020;263(Pt A):114372.
  3. Carvalho FP. Pesticides, environment, and food safety. Food and Energy Security. 2017;6(2):48-60.
  4. Klumper W, Qaim M. A meta-analysis of the impacts of genetically modified crops. PLoS One. 2014;9(11):e111629.
  5. Romeis J, Naranjo SE, Meissle M, Shelton AM. Genetically engineered crops help support conservation biological control. Biological Control. 2019;130:136-154.
  6. Lu Y, Wu K, Jiang Y, et al. Mirid Bug Outbreaks in Multiple Crops Correlated with Wide-Scale Adoption of Bt Cotton in China. Science. 2010;328:1151-1154.
  7. Losey J, Raylor L, Carter M. Transgenic pollen harms monarch larvae. Nature. 1999;399:214.
  8. Sears MK, Hellmich RL, Stanley-Horn DE, et al. Impact of Bt corn pollen on monarch butterfly populations: A risk assessment. Proceedings of the National Academy of Sciences. 2001;98(21):11937 - 11942.