Ch.8: Pesticides in the Environment

2. The Five Pesticide Properties (drive movement)

• Degradation happens by chemical, physical, and biological processes. Biological breakdown = fungi, bacteria, and other microorganisms. Sunlight (radiation) breaks chemical bonds.

3. Water Contamination

• Precipitation during or soon after application greatly increases movement into surface water (runoff) or groundwater (leaching).
• "Rain fast" time (e.g., two hours) = after this, the pesticide is less likely to wash off.
• Groundwater = water in the cracks and pores of rocks underground. Contamination → tainted drinking water for people and livestock.
• Spring and fall = greatest recharge and highest water tables → highest groundwater risk. Heavy rains add risk anytime.
• Surface water contamination → injury/death to wildlife, including fish and waterfowl.
• Once groundwater is contaminated it's nearly impossible to fix — stop the source and wait. Prevention (follow the label) is the best solution.

4. Point vs. Nonpoint Source

• Point source = a specific, identifiable place or incident. Examples: a spill into a storm sewer/water body, back-siphoning into a well, repeated spills at mixing/loading sites, wash-water spills at cleanup, spills during transport/storage, improper disposal of containers/rinsate/excess.
• Nonpoint source = a widespread area with no easily identifiable source. Examples: runoff, leaching, and drift across a broad area over time.
• Back-siphoning = unwanted reverse flow from the spray tank into a well or water source (a point source).

5. Labels, Water & Vegetative Strips

• Water-contamination info is in the Environmental Hazards section (or elsewhere): toxicity to fish/aquatic life, leaching/groundwater warnings, buffer areas, vegetative buffer strips.
• Advisory vs. mandatory: "use caution when applying near water" = advisory; "Construct and maintain..." = mandatory.
• Example vegetative filter strip: at least 25 feet of grass/permanent vegetation between the field and down-gradient aquatic habitat.

6. Site Conditions — Soil & Terrain

• Key factors: soil type, terrain, drainage patterns.
• Retentive soil (holds pesticide until it degrades): deep, high organic matter, medium-to-fine texture (silt/clay), good structure and drainage.
• Greater depth to groundwater → more filtering → more chance to degrade first.
• Table 8.1 (soil):
  • Coarse (sand, rock, gravel): fast flow, high permeability, little adsorption.
  • Fine (clay, silt): slow flow, low permeability.
  • High organic content: more retention, less flow, greater adsorption.
• Terrain = the lay of the land (elevation and slope). Hills/slopes increase runoff and erosion carrying pesticide off site.
• Buffer = an edge area where you don't apply pesticide. Add one even if the label doesn't require it if runoff could reach a sewer, surface water, or sensitive area.

7. Drift vs. Overspray

• Drift = pesticide movement away from the site by wind or air currents. Three types:
  • Particle drift = movement as a granule, pellet, or dust.
  • Vapor drift = a volatile pesticide turns to gas and moves off site — hours or even days later; travels farthest (gasses are smaller than the smallest droplets → miles).
  • Spray drift = off-site movement during a liquid application. Key word: "during."
• Indoor applications are NOT immune — ventilation, fans, forced-air heating/cooling move pesticide.
• Overspray = direct application beyond the target boundary. It is ALWAYS applicator error (e.g., not shutting off the spray at a turn, over a property line, or crossing a stream).

8. Reducing Drift — Weather Factors

Two factor categories: weather-related and application-related.

• Wind direction matters, not just speed — always know what's downwind and protect sensitive sites.
• Very light winds (0–3 mph) are NOT ideal — variable surface winds; a sign of a possible temperature inversion.
• Labels often give a wind range (e.g., 3–10 mph) — don't spray above or below it.
• Higher wind speed → droplets travel farther and are likelier to leave the target.
• Temperature inversion = cooler air BELOW warm air. Stable, dense, cool near-ground air keeps droplets concentrated → move far horizontally (miles). Strongest after a hot day into a cool night; peaks in the early morning.
• Air stability: Stable air = dense/cool/near-ground, little mixing → droplets stay concentrated (more drift risk). Mixing air (sun-warmed, rising) → droplets spread apart and dissipate.
• Humidity/temperature: low humidity and/or high temperature → more evaporation → smaller droplets → more drift; small droplets can fully evaporate into a tiny drop of pure pesticide. Volatility rises as temperature increases and humidity decreases.

9. Reducing Drift — Application Factors

• Droplet size is the MOST important drift factor. Drift increases as droplet size decreases. Goal: coarsest spray that still works, minimizing small droplets.
• A micron = 1/1,000 of a millimeter. Droplets ≤100 microns are most prone to drift (barely visible, stay airborne).
• Spray pressure: higher nozzle pressure → smaller droplets. Exception: aerial application may need more pressure for speed.
• Nozzle coarseness: flood > flat fan > hollow cone. Large orifice / high flow rate → coarser droplets. Drift-reduction nozzles make fewer small droplets.
• Low-drift nozzles: coarser, fewer drift-prone droplets, but cannot eliminate drift, and coverage often drops (so not for every job).
• Nozzle height: keep booms/guns/wands as low as possible for good coverage, but not below the nozzle's recommended height; shorter tip-to-target = less drift.
• Label drift info is typically in the Directions for Use: nozzle types, droplet size categories, release heights, min/max wind speeds, buffer zones, drift-reduction adjuvants.

Key Vocabulary