Upload
ferdinand-park
View
231
Download
2
Tags:
Embed Size (px)
Citation preview
Environmental Fate
of Pesticides in the Environment
What is Pesticide Environmental Fate?
• How and where a pesticide enters the environment
• How long it lasts• Where it goes.
Fate Processes
• Adsorption
• Transfer
• Degradation
Fate Processes• Adsorption• Transfer
– Volatilization – Runoff & leaching– Absorption– Crop Removal
• Degradation
Pesticide Losses at Application
• Method of application
• Rate• Timing• Number of
applications• Placement
Pesticide Characteristics
• Chemical characteristics of a pesticide will determine how it behaves in the environment.
• Four main characteristics:– Solubility– Adsorption– Half-life (aka. Persistence)– Volatility
Solubility• Amount of chemical
that can be dissolved into a solution
• Expressed as parts per million.
• > 30 ppm means high solubility = high tendency to leach or runoff.
• Tordon = 400- 430• 2,4-D = 890• Assert = 1370• Ally/Escort
– 1750 (pH 5)– 2790 (pH 7)– 213,000 (pH 9)
• Paraquat = 7000• Roundup = 15,700
– 900,000
Runoff vs. Leaching
Adsorption • The binding of a
pesticide molecule to a soil particle
• Mostly due to organic matter that coats the soil particle
• More organic matter = more binding by less-soluble pesticides
Measuring Adsorptivity - Koc
• Yardstick is the Koc or organic carbon partition coefficient - universal index
• Reflects how tightly a pesticide will bind to the organic matter in the soil.
Adsorptivity
• Binding of a pesticides to soil particles..OM
Koc of Common Pesticides
• Banvel – 2
• Stinger – 6
• Pursuit – 10
• Tordon – 16
• 2,4-D – 20
• Assert – 35 to 66
• 2,4-D Ester – 100
• MCPA – 110
• Broadstrike - 700
• Methyl Parathion – 5100• Lorsban - 6070• Treflan – 7000• Roundup – 24,000 *• Buctril – 10,000• Capture – 216,500• Paraquat – 1,000,000
* binds tight but also highly water soluble
Solubility & AdsorptionSome things to ponder
• Read the label! – Look for restrictions based on soil type.
Example – restrictions on loamy sand to sandy soils.
• Calibrate! Calibrate! Calibrate!• Do not over apply • Know the soil type in the area you are
spraying. Conduct a soil test….
Texturing your soils
Even a jar test will give you an idea!
• Degradation
– Microbes (#1)
– pH (#2)
– Sunlight
– Rate applied
• Degraded over time to produce CO2, H2O, N, P, Su,
• Expressed as “half-life.”
• Time required for that substance to degrade to one-half its previous concentration.
Persistence (Residual)
• Malathion - 1 • 2,4-D - 10• Banvel – 14• Ally, Amber – 30 • Stinger - 40• Assert – 45• Roundup - 47• Tordon – 90 to 180 • Spike - 360• Paraquat – 1000
Degradation values of some common pesticides (1/2 life in days)
pH• Measures the concentration of Hydrogen ions • A scale for measuring acidity & alkalinity• 0 - 14• pH 2 is strongly acid - batteries• pH 3-4 - citrus fruits• pH 5 - coffee• pH 7 - neutral • pH 8 – baking soda• pH 9-10; soaps• pH 11 - ammonia• pH 13; lye
* At a low pH, 2,4-D is an uncharged molecule * At a high pH, 2,4-D becomes anionic or negatively charged
H+
OH-
O-CH2-C-OH O-CH2-C-O-
OH indicates this is a weak acid. The H can be easily “pulled off” by pH effects
Pesticides and pH
Acid dissociation - (pKa)– pH at which the pesticide degrades – If pH > pKa …degradation begins– Tells only when degradation occurs..not the
rate of degradation.
Some common pKa’s
• Tordon – 2
• Banvel – 2• Curtail – 2
• 2,4-D – 3
• Roundup – 6
Low pH
• Acid Hydrolysis
• Sulfonyl Urea herbicides degrade in acidic environments.– Ally and Escort
• Most sulfonyl ureas are stable in pH > 7.9
Pesticide Drift• Physical drift
caused by small droplets– Improper
nozzles– Improper
pressure• Chemical drift
– Volatilization
Physical driftis a product of:
• droplet size that is produced by a nozzle orifice
• pressure produced by the sprayer that is measured in Pounds Per Square Inch (p.s.i)
• Weather – wind & relative humidity
Measuring Droplet Size
• All nozzles produce a wide range of drop sizes and not a single drop size.
• Volume Median Diameter” or VMD– diameter at which half the spray volume is in droplets
of larger diameter and half is in smaller droplets. – If a nozzle is producing droplets of 500 microns VMD,
it is producing 50% of the volume in larger drops and 50% in drops smaller than 500 microns.
• While 100 micron droplets are best for insects and mites, 200-500 microns is best to limit drift
Vapor Drift
• Pesticide changes from liquid or solid state in to a gas --the pesticid evaporates!!
• Moves from the target area• 2,4-D ester & MCPA ester can produce
damaging vapors readily at a given temperature
• Vapor pressure is just one chemical property of a pesticide that affects vapor drift.
Vapor Pressure
• Vapor pressures vary widely among pesticides.
• The least volatile pesticides:– salts and acids
• Pesticide more prone to volatize:– phenols and esters
Volatility• Conversion of a liquid or solid to a gas
• Lower vapor pressure = lower volatility
• EPTC – 3.4 x 10-2 mm Hg
• Fargo – 1.1 x 10-4 mm Hg
• 2,4-D ester = 13 mPa
• Banvel = 4.5 mPa (9x10-6 mm Hg)
• Banvel SGF = 1.6 mPa
• Tordon = 0.082 mPa (6x10-7 mm Hg)
• Roundup = 0.010 mPa (2x10-7 mm Hg
Volatility is also affected by:
• Weather
– High temperatures
• 2x more 2,4-D ester volatilizes at 70o than 80o
– Low humidity = more volatilization
– Air Inversions
Protecting Water Resources
Protect your wells!
Protecting Water Resources
• Practice IPM• Environmental considerations• Well Locations?• Calibrate and use only what is needed• Mix and load carefully• Prevent back-siphoning• Consider the weather• Select, store and dispose of pesticides carefully