Pesticides applied directly to the soil may be washed off the soil into nearby bodies of surface water, may evaporate into the air, or may percolate through the soil to lower soil layers and groundwater. Pesticides may enter surface waters when applied for weed control, or indirectly as a result of leaching from boat paint, runoff from soil or other routes. The properties of pesticides determine their fate and behavior in the environment. The important properties are persistence, volatility, and solubility in water. The persistence of a pesticide is its ability to remain unchanged.
Persistence is measured by half-life.
The half-life is the time it takes for half of the initial amount of a pesticide to breakdown. When the pesticide is broken down, this usually leads to the formation of less harmful products. However, in some instances the products can be more toxic than the original pesticide. Pesticides that are easily broken down generally move the shortest distance and have the least adverse affects on people or other organisms. Persistent pesticides generally move the longest distances and have the greatest potential to accumulate in living organisms.