Expert response from Wayne Parrott
Professor, Crop Breeding and Genetics, University of Georgia
Friday, 01/04/2016 20:24
Pesticides such as herbicides, fungicides, and insecticides vary in the amount of time they break down in the environment by the specific pesticide, the rate applied, and environmental conditions. We measure how long pesticides persist in the environment by a measure called half-life or how long it takes the original material to be reduced by 50%. Under most situations we would encounter in an agricultural setting, a pesticide half-life can range from a few hours to 4-5 years. Most pesticides are broken down by microbes in the soil, so environmental conditions that reduce microbial activity (cold, dry conditions) will extend pesticide remaining in the soil. In general, the trend is for the newer pesticides to last far less than those used decades ago (eg, DDT). In some parts of the world, copper-based fungicides are still used, and these will last forever in the soil, for all practical intents and purposes.
Here is a graph from the USDA-ERS that should be helpful:
How Do GMOs Benefit The Environment?