Fate of Pesticides in the Environment and Protection of Water, Soil, Air and Non-Targets
After application a pesticide moves by drift, volatilization, leaching, runoff, adsorption and degradation. Learn three properties: half-life (persistence), water solubility, and soil adsorption (Koc). High solubility + low adsorption + long half-life = high groundwater leaching risk. Sloping, erosion-prone fields with heavy rain forecast = runoff risk to streams. Volatile products applied in hot, calm, sunny weather can move off-site by vapour drift hours after you leave.
Degradation routes: microbial breakdown (usually the largest), hydrolysis (faster at high pH and temperature) and photodegradation (sunlight). Fat-soluble, persistent compounds bioaccumulate and biomagnify up the food chain.
Protection measures: untreated vegetative buffer strips beside ditches, streams and wells; keep booms out of buffers; respect label buffer zones; avoid spraying when wind exceeds the label limit, before heavy rain, or when soil is saturated; use low-drift nozzles, lower boom heights and drift-reducing adjuvants; never mix or rinse near a well; contain spills so they cannot reach drains; apply rinsate to a labelled site, never to a ditch.
Non-target protection: pollinators - spray when the crop is not flowering and in the evening, avoid dusts near blossoms, warn beekeepers; aquatic life - many products are lethal to fish and amphibians at parts-per-billion levels; birds and mammals - granules, baits and spilled seed; beneficial insects - broad-spectrum sprays flare secondary pests.
Traps: "it rained, so it's gone" - many products bind to soil and stay active for months, and some leach; and treating buffer zones as advice - they are label requirements.
Worked example: a product with a 60-day half-life, solubility of 500 mg/L and very low Koc applied to sandy soil over a shallow aquifer is a poor choice, regardless of how well it controls the pest.