CORE Ch7 Study Guide: Pesticides in the Environment

Learning Objectives

After studying this chapter, you should be able to:

Describe how pesticide applications affect the environment.
Prevent pesticide drift, runoff, and movement to nontarget areas.
Identify sensitive areas that could be harmed by pesticides.
Prevent pesticide residue accumulation at mixing, loading, and cleanup sites.
Know when to adjust or delay applications to minimize environmental impact.

The Three Key Questions

Before every application, an applicator must ask:

Where will the pesticide go after it leaves the container?
What effects could it have on nontarget sites it may reach?
What can I do to minimize harmful effects?

Pesticide Characteristics

Four properties determine how a pesticide interacts with the environment:

Solubility: Ability to dissolve in water. Highly soluble = moves easily with water in runoff or through soil.

Adsorption: Binding to soil particles. Oil-soluble and positively charged pesticides adsorb more tightly (especially to clay and organic matter). Higher adsorption = less offsite movement.

Persistence: Length of time active before breakdown, measured in half-life. Longer half-life = more persistent. Leftover chemical = residue.

Volatility: Tendency to turn into gas/vapor. Increases with heat, wind, and low humidity.

🎯 Trick Spot: High solubility + low adsorption + high persistence = worst case for leaching and runoff. Adsorption and solubility pull in opposite directions.

Breakdown Processes

Chemical degradation — non-living chemical reactions (often with water).
Microbial action — fungi and bacteria in soil.
Photodegradation — sunlight.

Warm, wet conditions speed breakdown; cool, dry conditions slow it.

How Pesticides Move in the Environment

In Air — Drift

Movement by wind or air currents is drift. Indoor ventilation and forced-air systems also move pesticides. Three forms:

Spray drift — small droplets on air currents. Most common.
Vapor drift — gaseous movement of volatile pesticides.
Particle (dust) drift — solid pesticide particles or contaminated soil.

In Water — Runoff and Leaching

Runoff

Leaching

Surface movement off the site. Contaminates streams, ponds, drainage.

Downward movement through soil. Can reach groundwater.

Occurs when too much pesticide is applied, rainfall/irrigation is heavy, or a pesticide is highly water-soluble or persistent.

On or In Objects, Plants, or Animals

Contaminated PPE, clothing, or equipment brings residues home where they transfer to carpeting, furniture, pets, and people.

Preventing Spray Drift

Spray drift is the result of small droplets traveling offsite on air currents. Three primary factors affect it:

Droplet size — larger droplets drift less.
Wind direction
Wind speed — ideal: 3 to 10 mph.

Nozzle relationships: High pressure + small orifice = small droplets (drift-prone). Large orifice + low pressure = larger droplets (less drift).

ASABE Droplet Size Classifications (S-572.1)

Outdoor Drift Reduction

Spray in 3–10 mph wind.
Spray downwind from sensitive areas.
Use proper nozzles and pressures, and drift-control additives if appropriate.
Lower boom height (aim for 20–24 inches above target crop).
Leave an untreated buffer in the downwind target area.

Indoor Drift Reduction

Turn off fans and HVAC. Close vents. Use low-volatile or nonvolatile pesticides and low-pressure treatments.

Temperature Inversions — The Silent Drift

Temperature inversion: Air at ground level is cooler than air above it. Vertical mixing stops — almost all air movement is lateral. Small spray droplets stay suspended in the cool ground layer and can be carried more than a mile later when wind picks up.

🎯 Trick Spot: Low wind is not automatically safe to spray! Drift over long distances (more than a mile) is most often from applications made during a temperature inversion, not during windy conditions.

Recognizing an Inversion

Dust or smoke rises little from its source and hangs in the air.
Ground-level thermometer reads colder than an elevated thermometer.
Most common in early evening, intensifying through the night, often persisting until mid-morning.

⚠️ Exam Tip: The two most important factors for vapor drift are temperature and pesticide volatility. Many labels advise against application when temps are 85°F or higher.

Sources of Water Contamination

Point-Source

Nonpoint-Source

Specific, identifiable location: pesticide spill into a storm sewer, back-siphoning at a wellhead, repeated spills at mix/load sites, careless wash-water disposal, container disposal errors.

Widespread area: broadcast applications to fields, turf, or rights-of-way that move into streams or groundwater after rain.

🎯 Trick Spot: Back-siphoning at a wellhead = point-source (specific location). Leaching from a broadcast application = nonpoint-source. A "mixing area" spill is point-source.

Groundwater Facts

Provides 70% of public/private water for drinking, irrigation, industry.
Found in the saturated zone below the water table.
Geological formation yielding groundwater = aquifer.
Once contaminated, correction is difficult or impossible.

Soil Properties Affecting Leaching

More Leaching

Less Leaching

Sandy soil (fast water flow, few binding sites)

Clay/silt soil (slow flow, more binding sites)

Low organic matter

High organic matter

Shallow water table (less filter)

Deep water table

High permeability (gravel)

Low permeability (clay layers)

⚠️ Exam Tip: Sandy soil + low organic matter is the leaching worst-case. Organic matter holds water and adsorbs pesticide in the root zone where plants can take it up.

Macropores

Small cracks, wormholes, and root channels can let pesticide move through even clay soils. Soil structure (arrangement of particles) affects these pores — not just texture.

Best Management Practices (BMPs) for Water Protection

Use IPM Principles

Apply only when needed, only in amounts adequate to control pests.
Choose the least toxic effective product.
Calibrate equipment regularly.
Use spot or band treatments when possible.

Mixing and Loading

Mix and load at least 50 feet from wells, lakes, streams, rivers, and storm drains.
When possible, mix/load at the application site.
Consider a sealed mixing/loading pad.
Never dispose in sinkholes, storm drains, or ditches.

Prevent Back-Siphoning

Back-siphoning: Reverse flow of tank contents into the fill hose and back into the water supply. Starts with a drop in water pressure.

Simplest fix: maintain an air gap between hose end and pesticide surface. Keep gap at least twice the diameter of the discharge pipe.
Or use a backflow prevention device / check valve.

Timing the Application

Runoff risk is highest in the first few hours after application.
Do not apply to saturated or frozen ground.
Check label for wind/weather restrictions.

Land Use and Application Methods

Conservation tillage and crop residue reduce runoff.
Grass buffer strips trap sediment and pesticides.
Mulches help in ornamental plantings.
After granular applications, sweep or blow granules from sidewalks/driveways back onto the treatment area.

⚠️ Exam Tip: EPA requires all outdoor-use labels to include the statement: "Do not apply directly to water, or to areas where surface water is present, or to intertidal areas below the mean high water mark..."

Sensitive Areas

Outdoor Sensitive Areas

Schools, playgrounds, recreational areas
Habitats of endangered species
Apiaries, wildlife refuges, parks
Areas with domestic animals or livestock
Ornamental plantings, public gardens, sensitive crops

Indoor Sensitive Areas

Homes, workplaces, shops, hospitals, daycare centers
Food/feed processing and storage
Animal enclosures
Ornamental plant areas (malls, buildings)

Leave untreated buffer zones around sensitive areas whenever possible. Check label for special restrictions.

Protecting Bees and Beneficial Insects

Bees may travel up to 3 miles from the hive. Notify beekeepers before applying products toxic to bees.

Impact

On Bees

Insecticides

Generally toxic; some worse than others.

Herbicides

Unlikely to harm bees directly.

Fungicides

Don't seem to affect adults; may affect larval development.

Insecticide + Fungicide tank mix

May be more toxic to bees than either alone.

Bee Protection Principles

Check label for the bee hazard icon in "Directions for Use."
Do NOT apply insecticides to crops in bloom.
Apply in the evening or at night when bees aren't foraging. (Early morning may protect honey bees but wild bees forage at or before dawn.)
Don't spray when nearby weeds/plants are in bloom.
Keep pesticide out of attractive habitat and beehives.
Choose the least hazardous product, formulation, and method.

🎯 Trick Spot: "Apply in morning" is a classic wrong answer — wild bees forage at dawn. Evening/night is safer overall.

Fish, Wildlife, Livestock, and Endangered Species

Wildlife Risks

Fish kills — usually from insecticides, worst in small/low-flow waters.
Bird kills — ingesting granules/baits/treated seeds (birds mistake them for food), direct spray exposure, contaminated food or water, or eating poisoned prey.
Secondary poisoning — predators eat animals killed by pesticide residues.
Livestock poisoning — usually through contaminated feed, forage, or drinking water.

⚠️ Exam Tip: Granular/pelleted formulations are especially risky for birds and wildlife — they look like food. Liquid formulations may be safer where wildlife is near.

Endangered Species Protection Program

Endangered: On the brink of extinction across all or a significant part of its range.
Threatened: Likely to become endangered.

Each state implements the federal Endangered Species Protection Program with EPA. Pesticide products that might harm listed species carry a label statement directing you to consult a county bulletin for precautionary measures — buffer strips, reduced rates, timing restrictions, or prohibitions.

Key Terms Cheat Sheet

Solubility: Ability to dissolve in water. High = moves with water.

Adsorption: Binding to soil particles. High = stays put.

Persistence: How long it remains active. Measured as half-life.

Volatility: Tendency to become vapor. Worse with heat, wind, low humidity.

Residue: Pesticide remaining after application or spill.

Drift: Off-target air movement. Spray, vapor, or particle.

Runoff: Surface water movement off the site.

Leaching: Downward movement through soil, potentially to groundwater.

Temperature Inversion: Cool air below warm air. Drift can travel miles.

Point-source pollution: Specific, identifiable location (spill, back-siphon).

Nonpoint-source pollution: Widespread area (runoff from a field).

Aquifer: Geological formation yielding groundwater.

Water table: Boundary between saturated and unsaturated zones.

Saturated zone: Where all soil spaces are filled with water.

Macropores: Cracks, wormholes, root channels — allow pesticide flow through even clay soils.

Back-siphoning: Reverse flow of tank contents into water supply. Prevent with air gap (2× pipe diameter) or backflow device.

Air gap: Space between water discharge and pesticide surface — prevents back-siphoning.

Buffer strip / buffer zone: Untreated area protecting sensitive sites.

Secondary poisoning: Predator harmed by eating poisoned prey.

Phytotoxicity: Plant injury from chemical exposure.

County bulletin: EPA document listing pesticide restrictions to protect endangered species.

ASABE droplet size: XF, VF, F, M, C, VC, XC, UC (color-coded from purple to black).

Chapter 7 — Pesticides in the Environment