Pesticides in The Environment Compiled by Shelley Mills

Understand How Pesticides Impact the Environment Chemical characteristics of pesticides Degradation methods Pesticide movements during and after application Special environmental considerations This presentation will help you understand the basic interactions of pesticides in the environment. You need to understand some chemical characteristics and how pesticides break down following an application. Once a pesticide is applied, you need to understand some of the dynamics of its movement in air, water, and soil. Lastly, we’ll discuss special assessment considerations to protect sensitive sites, pollinators, aquatic organisms and other animals.

Pesticide Characteristics: Solubility Adsorbtion Persistance A pesticide that readily dissolves in water is said to be water-soluble. Water-soluble pesticides are more likely to move with water. Water-soluble products can easily runoff with surface waters that don’t penetrate into the soil. For water that moves through the soil, water-soluble pesticides are carried downward into the soil profile. Once in the soil, the question becomes where does the water go and how fast does it take for the pesticide to degrade? Pesticides that are not water-soluble, don’t move readily with surface or subsurface waters. The adsorption characteristic is important to the fate of pesticides. Adsorption, that is A-D-sorption, is the physical binding of the chemical to the outside of soil particles and organic matter. Ad – means to add onto. Adsorption is different from Absorption. Absorption sucks material into something like a sponge sucking in water. Adsorption is binding to the outside, like lint stuck on your shirt. Pesticides that are oil-soluble or oil-loving tend to adsorb or bind to soil particles. Soil type is a key factor as to how much chemical is held by the soil particles. Clay and organic soils have many, many binding sites and adsorb a lot of pesticide. If pesticide is adsorbed or bound to the soil, it doesn’t move freely with the soil water and water contamination concerns are greatly reduced. Persistence is another important characteristic when assessing impacts on the environment. Persistence is the measure of how long a pesticide remains active before it degrades. If you want long-term pest control, seek out a pesticide that’s persistent and doesn’t readily degrade. But realize persistent pesticides don’t break down for some time and they can harm sensitive plants or animals. Persistent pesticides also pose concerns for illegal residues on rotational crops that can pick up the chemical because the product was not labeled for that rotational site and no tolerance was set.

CARRY OVER Soil characteristics can affect the persistence of a pesticide too. Here we have the Herbicide Huskie (Wolverine) that was more persistent in higher pH soils and had a visually devastating effect on lentils.

Fortunately the effect was more visual than agronomic and yields were not noticeably affected.

Pesticide Characteristics: Solubility Adsorbtion Persistance Volatility Temperature Wind Humidity = Higher Volatility Volatility is a characteristic of vapor pressure. Depending on the temperature and humidity, and in some situations wind, a chemical changes from a liquid or solid state into a gas or vapor. As a vapor it can move off-target with the air flow. Increases in temperature and wind increase the potential for volatility. Also, lower humidity levels increase the potential for volatility.

Pesticide Degradation Microbial Chemical Photodegradation Microbial degradation is a primary means for destroying pesticides in the soil. There are a number of microorganisms, like species of bacteria and fungi that use the pesticide as food. As the microbes feed on pesticides, they break them down. Soil conditions that favor microorganism reproduction increase the degradation process. So, soils that are warm, have adequate moisture and a favorable pH provide the right conditions for rapid pesticide degradation. Also, soils with a good mix of oxygen, sufficient fertility and with pesticide adsorbed onto the soil, have increased degradation. Simple chemical reactions occur in the soil. Something as simple as the mixing of water and the chemical can result in hydrolysis that causes chemicals to break down. Again, soil properties and conditions affect which chemical reactions take place and how quickly. The sun can cause chemical degradation. You’ve probably experienced the effect of photodegradation, where the sun is responsible for chemical breakdown, like when your nylon tarp wears out. Sunshine is very effective in breaking down chemicals. Remember, this is why you hang your laundered pesticide application clothing out to dry in the sun. Some chemicals break down so quickly they must be immediately incorporated into the soil. Others can only be used indoors where the sun doesn’t shine.

Pesticide Movement Vapor, particle, spray drift Surface runoff By air Vapor, particle, spray drift By water Surface runoff Movement through soil By other objects Residues on plants and animals

DRIFT

PARTICLE DRIFT

DROPLET DRIFT WSDA Spray drift is the movement of spray droplets in the air. The spray droplets are carried in the air beyond the application site. A concentrated dose of droplets that moves off-target can cause damage or leave illegal residues. To minimize off-target spray drift, labels state specific precautions. The label may require a mandatory no-spray buffer between the application site and a sensitive area. The label may stipulate exactly what size droplet classification can be used during the application. Wind speed conditions, both very low winds and high winds, may restrict applications. The label may require you apply a certain volume of spray. Aerial application may be restricted on some labels. Labels may have specific precautions listed for sensitive crops or sites, like schools and day cares.

Factors That Influence Drift Applicator attitude Droplet Size Viscosity of spray a liquid’s resistance to flow Weather conditions

Applicator Attitude Assess what sensitive sites are near the application area No-spray buffer necessary? Assess weather conditions: air stability, wind direction and speed Set up equipment with appropriate boom height, nozzles, and pressure Make decision to spray or not to spray It’s up to the applicator to make an assessment of the application site. He alone is responsible for off target movement of the chemical.

Droplet Size The Larger the Spray Droplet Size The Less Distance the Droplet Drifts Nozzle adjustment, pressure adjustment, greater viscosity (adding drift retardants or deposition aids), boom height,

Weather Conditions – Read the Wind What’s downwind? Direction How far will it move? Speed 0-3 mph: could be very stable with airflow, just not sure which direction the air is moving 3-7 mph: manage for off-target movement downwind >7 mph: carries more material off-target

Temperature Temperature and humidity affect the life of the droplet. As temperatures increase, droplets evaporate into smaller droplets. As humidity decreases, evaporation also increases. So you’d expect more ‘driftable’ droplets under conditions of high temperatures and low humidity. Humidity

Stable Air Conditions: Temperature Inversion air at ground has cooled (heavier air) warm air as risen (lighter air) result is stagnant, stable air = inversion long distance drift can result from applications made during inversions G.Thomasson and C. Ramsay, WSU

Temperature Inversion Can occur anytime Usually develops at dusk May continue through night Breaks up when ground warms up in morning It may appear ideal, but is not

Pesticide Movement in Water Pesticides can move into water from a identifiable occurrence or from general contamination Point Source identifiable source Non-point Source wide area contamination Maintain an Air Gap

Runoff is dependent on: grade or slope of the area soil texture vegetation soil moisture amount and timing of irrigation/rainfall pesticide characteristics

Leaching Sandy: fast percolation, few binding sites Geology – how permeable is the soil? Soil texture and structure Sandy: fast percolation, few binding sites Silt, clay or organic matter: slower percolations and many binding sites Depth to groundwater: shallow water tables pose a concern Amount and timing of rainfall or irrigation Again, pesticides that are water-soluble tend to leach through the soil. The contaminated soil water may move horizontally to nearby roots or it may move vertically through the soil profile down to the groundwater. Pesticides that tend to leach are those that are highly water-soluble, don’t readily adsorb onto soil particles, and don’t degrade quickly. Dependent on: Geology – how permeable is the soil? Soil texture and structure Sandy: fast percolation, few binding sites Silt, clay or organic matter: slower percolations and many binding sites Depth to groundwater: shallow water tables pose a concern Amount and timing of rainfall or irrigation

Leaching/Runoff & Groundwater Concern for leaching or the site is vulnerable select a product that does not pose a concern Little or no concern for leaching product selection is not a concern High Annual Precipitation Cool Soil Temperature Shallow Groundwater Sandy or Gravely Soil Soluble Pesticide

Special Environmental Concerns Protect sensitive areas Protect non-target organisms Pollinators, beneficials Fish, livestock, and wildlife Protect endangered and threatened species

Protect Sensitive Areas Schools, playgrounds, parks, hospitals Wildlife refuges, bee hives Yards, gardens, crop fields Indoors: homes, offices, stores, clinics, restaurants, factories, animal facilities Endangered/threatened species and their habitats Protect people and take special care when applying near children or places where there might be elderly or ill people. Consider locations that are inhabited by sensitive plants, animals, fish, or insects. Be careful when applying near yards and people’s gardens. Don’t contaminate adjacent crops. When making applications indoors, consider exposures to people and animals. Ventilation may be required. Know if there are listed endangered or threatened species in the vicinity of the application site.

Protect Non-target Organisms Hover fly H. Riedl Plants Bees, other pollinators Other beneficial insects Fish and other wildlife Humans Jerry Stein, Nev. DOW Virgin River Chub

READ THE LABEL

Which of the following techniques would reduce spray drift? Increasing the nozzle orifice size. Decreasing pressure. Lowering your booms. Increasing the viscosity of your spray All of the above.

You need to control aphids in a blooming alfalfa field and the label has a bee toxicity hazard. What application precautions can you take to reduce bee mortality? Apply mid morning when temperatures are warming. Apply a dust formulation instead of an EC. Use a systemic granule formulation Move the hives to greater than 300 yards from the field to be sprayed.

Temperature Inversions are the product of: Warm air trapped above colder denser air. Usually occur in mid-day Only occur in summer Are dependant on temperature and humidity Answer is a.

Teaching Environmental Fate Use examples from your own experience. Keep the concepts simple Use analogies Use brain science Use activity based learning

Questions??