How Does Glyphosate Weed Killer Affect the Environment?

Dec 05 2022

Glyphosate-based herbicides like Roundup are some of the most popular formulations used for agricultural weed control. As increasing amounts of glyphosate are sprayed on crops every year, scientists and environmentalists have begun to ask, “Is glyphosate bad for the environment?”

Since glyphosate was introduced in 1974, farmers have sprayed 1.6 billion kilograms (3.52 billion pounds)[1] of the herbicide on feed and food crops. Its use has risen 300-fold[2] to at least 280 million pounds per year,[3] in part due to the introduction of glyphosate-resistant (”Roundup Ready”) crops, which can tolerate the herbicide without dying. These types of crops now account for 56% of glyphosate use worldwide.[4] Glyphosate is also used as an off-label desiccant to dry some non-tolerant crops before harvesting.[5]

Although glyphosate is generally considered safe, widespread application may impact environments in and around treated fields. The science isn’t settled, but there is an increasing concern about how glyphosate weed killer affects soil, water, and wildlife.

glyphosate application

Glyphosate and Soil Health

When scientists consider how glyphosate impacts soil health, a key question is how long the herbicide remains in soil after it’s sprayed on crops. Glyphosate’s half-life—how long it takes for half of the herbicide to break down—depends on a range of environmental conditions, including:[6,7]

  • climate
  • soil mineral content
  • soil type and composition
  • the types of microbes in the soil

Variations in these conditions can cause the half-life of glyphosate to range anywhere from two days[8] to three years. The herbicide may persist for longer in acidic soils that contain a lot of organic matter like leaves or manure.[9]

Glyphosate, plants, and microbes

After glyphosate is applied, plants appear to take up at least 45% of the herbicide from the soil.[8] Glyphosate kills plants that aren’t bred to tolerate it by interfering with a mechanism called the shikimate pathway, which is involved in producing amino acids necessary for plant growth.[11]

In glyphosate-resistant crops, the herbicide can accumulate in plant roots and be released back into the rhizosphere, an area around the roots where plants and soil microbes interact. Microbes in the rhizosphere help plants grow and stay healthy by controlling pathogens and improving access to nutrients.[12,13] Many of these microbes also have a shikimate pathway and therefore may be affected by glyphosate.

Not all studies show that glyphosate harms soil microbe communities: some research indicates increased microbial activity after glyphosate application. This may be because microbes break down the herbicide to access carbon, nitrogen, and phosphorus they can use as fuel.[14] Overall effects on microbes appear to be minor and short-lived. However, repeated glyphosate use may reduce the number of microbial species in the soil over time[15] and potentially impact plant health.

Glyphosate in soil may affect plant growth

Glyphosate weed killer can directly affect plants outside of treated fields. Up to 10% of glyphosate sprayed on resistant plants can drift to untreated areas. Studies show this exposure may:[16,17]

  • interfere with root growth and health.
  • cause fruit damage or leaf discoloration.
  • prevent plants from protecting themselves against disease.
  • make fruit mature, ripen, and drop of trees faster than it should.
  • block plants from absorbing minerals, resulting in nutrient-deficient crops.

Widespread glyphosate use has also led to the rise of 38 weed species resistant to the herbicide, which can pose a threat to food crops if they spread.[18]

Glyphosate and Water Contamination

Soil runoff can carry glyphosate herbicide out of fields and into waterways. This is more likely in soils with high phosphate content because glyphosate and phosphate bind to the same minerals. Fertilizers can increase soil phosphate content and either prevent glyphosate from binding to minerals or displace glyphosate already bound in the soil and leave it free to wash away.[19]

When glyphosate enters the water, it dissolves and releases phosphorous compounds that spur plant growth. This can cause an explosion of algae that reduces oxygen levels and suffocates other aquatic life.[20]

Environmental conditions, such as rainfall amounts and soil mineral levels, affect how much glyphosate enters the water. Further investigation is needed to understand how glyphosate use may affect waterways and aquatic ecosystems.

Glyphosate Weed Killer and Wildlife

Glyphosate may impact insects and animals that live in treated or contaminated environments. Some of these effects may be direct, such as DNA damage;[21] others may result alterations in the microorganisms these species rely on for health.[22] Although all the mechanisms of action aren’t clearly understood, some studies have shown troubling disruptions in environments where glyphosate is present.

Bees and other insects

Bees can pick up glyphosate as they gather nectar and pollen from treated plants. Even at low concentrations, the herbicide may impair the bees’ ability to navigate, making it more difficult for them to find food or remember the return journey to their hives.[23] Glyphosate can also make bees more susceptible to disease by disturbing the balance of gut bacteria that protect them from getting sick.[24]

Image by Erik Karits from Pixabay

The herbicide’s impact isn’t limited to bees. In a study on mosquito larvae, glyphosate interfered with the ability to learn the difference between predators’ shadows and normal shadows that occur in the environment. This caused the larvae to react in panic and dive under the water too often, which can result in reduced numbers and affect animals that rely on the larvae for food.[25]

Aquatic animals

Aquatic animals like fish, shellfish, and frogs can be exposed to glyphosate through contaminated water or food sources. This may result in:

  • reproductive and developmental abnormalities.[26]
  • damage to cell structure.
  • impaired ability to learn important information from the environment, such as how to find food, escape from predators or attract mates.[9]

More research is needed to determine if chronic exposure to the levels of glyphosate commonly found in the environment produces the same effects seen in laboratory settings.[28]

Land animals

Glyphosate herbicide may interfere with enzymes and minerals essential to estrogen and testosterone production in animals. This could affect fertility and sexual development in both males and females.[8]

Some research also suggests that glyphosate can cause genetic damage with negative effects across generations. Despite the herbicide having little or no observable effect on parent or grandparent generations, later generations may develop obesity, reproductive abnormalities, and increased susceptibility to disease without direct glyphosate exposure.[30] Because these changes were observed in rats, it’s uncertain whether glyphosate may have the same effects on humans.

Does Science Say that Glyphosate is Bad For the Environment?

It can be difficult to know how many of these observed environmental effects are due to glyphosate itself, since herbicide formulations include other compounds called adjuvants that enhance its effects. Some research suggests these compounds may pose a higher risk of toxicity than glyphosate itself.[31]

Disparities in application may also influence glyphosate’s impact. For example, there can be as much as a 10-fold variation in the amount of glyphosate that two different people use when spraying the weed killer by hand. This can increase environmental concentrations to levels that harm non-tolerant plants.[32] More research is needed to determine how long glyphosate persists in the environment and whether it routinely builds up to toxic levels.

Image by Erich Westendarp from Pixabay

It’s also unknown how or whether glyphosate in the environment can affect human health. Safe intake levels were set based on studies in rats, mice, rabbits, and dogs, which may not always be accurate for predicting effects in people.[33] Existing studies suggest the herbicide could be a concern for immunity, hormone function, and gut health. Further research will be required to determine if glyphosate can cause health problems or genetic changes below levels generally accepted as safe.[34]

Going glyphosate free

While scientists work to better understand the impacts of glyphosate on the environment, there are steps you can take to minimize environmental exposure to the herbicide. Purchasing glyphosate-free products is one option to ensure that what you eat contains no glyphosate residue from drift, runoff, or desiccation. When you choose glyphosate free, you vote with your dollars for a healthier environment for you, your family, and future generations.