There are several characteristics of pesticides that affect
the likelihood of pesticides leaching towards the ground water:
- Water solubility:
- the tendency for a pesticide
to dissolve in water and, hence, be carried to surface and ground water. Water
solubility of greater than 30 ppm (parts
per million) has been identified as a
"flag" for the possibility of a pesticide
to leach.
- Soil adsorption:
- the tendency of a pesticide to
adhere to soil particles. The higher the
tendency, the less likely the pesticide
will leach to the ground water.
- Pesticide volatility:
- the tendency for a pesticide
to disperse into the air. Determined by dividing the pesticide's
vapor pressure by its water solubility.
The lower this tendency, the less likely the
pesticide will dissolve in water and leach
to the ground water.
- Soil half-life:
- the time, usually given in days,
required for the pesticide in the soil to
degrade to the point that its concentration
decreases by one-half. The greater the
half-life, the more likely the pesticide
will have time to leach to the ground water.