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National Pesticide Information Center

npic@ace.orst.edu

1.800.858.7378

What Happens to Pesticides Released in the Environment?

cartoon chemicals in environment

Pesticides may become airborne, get into soil, enter bodies of water, or be taken up by plants and animals. The environmental fate of pesticides depends on the physical and chemical properties of the pesticide as well as the environmental conditions. The physical and chemical properties of the pesticide determine how likely it is to travel through soil (soil mobility), how well it dissolves in water (water solubility), and how likely it is to become airborne (volatility).

Once a pesticide has been released into the environment, it can be broken down by:

  • exposure to sunlight (photolysis)
  • exposure to water (hydrolysis)
  • exposure to other chemicals (oxidation and reduction)
  • microbial activity (bacteria, fungi, and other microorganisms)
  • plants or animals (metabolism)

What is the "half life"?

The "half-life" is the time required for half of the pesticide to break down in the environment.

  • 1 half-life = 50% remaining
  • 2 half-lives = 25% remaining
  • 3 half-lives = 12% remaining
  • 4 half-lives = 6% remaining
  • 5 half-lives = 3% remaining

Half-lives are only estimates and they can vary depending on environmental conditions. The amount of pesticide remaining after a half-life depends on the amount of pesticide originally applied. Some pesticide chemicals break down into other chemicals that can also be toxic.

Scientists do experiments to determine how long pesticides last in various environments. They apply pesticides to soils, leaves or other surfaces and measure the time it takes for half of the pesticide to break down, a measure called the half-life. After one half-life, half of the chemical may be broken down. Following another half-life, half of the 50% remaining may be broken down, leaving 25% of the original amount and so on. The half-life can be a useful measure of how long a pesticide may last, but studies have found a wide range of half-lives for the same pesticide under different environmental conditions.

For more information about pesticide behavior in the environment, see the additional resources below. If you have questions about the fate of pesticides in the environment, or any pesticide-related topic, please call NPIC at 1-800-858-7378 (8:00am - 12:00pm PST), or email at npic@ace.orst.edu.

Additional Resources:

Last updated October 23, 2012