Environmental Protection and Pesticide Fate
Where pesticides go
After application a pesticide may adsorb to soil particles, leach, run off, volatilize, be broken down by sunlight (photodegradation), by water (hydrolysis), or by microbes, or be taken up by plants. Half-life measures persistence; long half-life plus high water solubility plus low soil binding equals groundwater risk.
Soil and water
High organic matter and clay increase adsorption and reduce leaching; sand, low organic matter, sinkholes, and shallow water tables increase it. Runoff carries soil-bound pesticide to surface water; leaching moves dissolved pesticide to groundwater. Nonpoint source losses are diffuse and hard to trace - the main route for agricultural pesticides.
Drift
Particle drift is droplets moving off target; vapor drift is volatilization after deposit, favored by high temperature and volatile formulations such as esters. Reduce both with coarse low-drift nozzles, lower pressure, lower boom height, drift-reduction adjuvants, buffer zones, and spraying when wind is roughly 2-10 mph and the air is not stable (no inversion).
Nontarget and special cases
Protect pollinators by avoiding applications to blooming crops and spraying in late evening. Read the label's bee, aquatic, and endangered species statements. Bioaccumulation is buildup within one organism; biomagnification is increasing concentration up the food chain, as with DDT in raptors.
Worked example
Two fields: one sandy loam with 0.8% organic matter over a shallow aquifer, one clay loam with 4% organic matter. The sandy field carries far higher leaching risk for a mobile herbicide, so use lower rates, splits, or a less mobile product there.