environmental fate of herbicides
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Environmental Fate of
Herbicides
Tim R. Murphy, Ph.D.
The University of Georgia
Crop and Soil Sciences
Public Concerns
Health Quality of Life Environment Nuclear and Toxic Waste Chemicals vs. Natural Right-to-Know
“Public Concerns” About Chemicals
Cause cancer Not well tested Harm animals Last forever
Not “natural” Used carelessly Contaminate water Any amount is dangerous
Herbicide Concerns
Last forever Contaminate water Affect human health Sterilize soil Use is not needed Kill all desirable organisms Degrade the environment
Fate of Herbicides
Original dose and ½ life Water solubility - the extent to which a pesticide will
dissolve in water Sorption by clay colloids and organic matter
• Adsorption - binding of a herbicide to the surface of a soil particle .
• Absorption - Penetrates into plant tissue Microbial degradation - influenced by herbicide
concentration, temperature, moisture, pH, oxygen, microbial population
Fate of Herbicides
Chemical degradation and photodecomposition Hydrolysis, oxidation, reduction, and photodecomposition under field conditions
Volatilization and evaporation - Loss due to an increase in temperature, vapor pressure, and wind movement.
Plant uptake and metabolism - roots, shoots, leaves
Soils - Colloidal Phase
Consists of clay and organic matter Huge surface area Negatively charged Anions (-charge) repelled Cations (+charge) attracted Primarily responsible for binding herbicides
Soils - Living Phase
Microorganisms - bacteria, actinomycetes, fungi Algae Vertebrates and Invertebrates
Microorganisms degrade herbicides
Microbial Degradation
Higher with high microbial populations May use as food source, or just degrade the
herbicide Faster under warm, moist conditions Slower under cool, dry conditions
Herbicide Adsorption
Soil texture• coarse, sandy soils have few binding sites
Permeability• highly permeable soils low in CEC have few binding
sites Soil OM and clay content
• increase binding Excessive moisture interferes with binding
Water Movement
Surface runoff
Leaching
Capillary action
Factors That Affect LeachingIncrease Decrease
Coarse soils Fine Soils
Low O.M. High O.M.
Water soluble Water insoluble
Non-binding Readily bind
High rainfall Normal rainfall
Relative Movement of Herbicides
Soil Type
Herbicide Silt loam ½ Loam + ½ Sand
Trifluralin 2 5
Simazine 14 27
Bromacil 55 88
Dicamba 91 95
Mobility of Preemergence Herbicides in Soil
None to slight
Low
Moderate
High
DNA’s Dimension
Ronstar Betasan Pennant Devrinol Rubigan
Aatrex Princep Sencor Prograss
Kerb
Mobility of Postemergence Herbicides in Soil
None to slight
Low
Moderate
High
Diquat Roundup MSMA
Buctril Acclaim Vantage Fusilade TranXit Revolver Certainty
Image Manage Corsair Metsulfuron Monument Katana
MCPP 2,4-D Vanquish Basagran Triclopyr Clopyralid Finale
Volatility
Volatility - physical change of a liquid or solid to gas.
Volatility
Related to vapor pressure Increases at high air temperatures Increases under high soil moisture conditions Higher on coarse textured, sandy soils
Photodecomposition
Photodecomposition - Breakdown of the herbicide by sunlight (primarily UV portion).
Herbicide Persistence - Soil
Usually expressed as the half-life (t1/2).
Herbicide ½ Life
Amount of time it takes a herbicideto reach one-half (t1/2) of the originallyapplied concentration. Expressed in days, wks,months, yrs..
1.0 lb. Ai/acre 0.5 lb. Ai/acre
Preemergence Herbicides – Avg. t-1/2
Herbicide
Soil Persistence t-1/2
Benefin Prodiamine Oryzalin Trifluralin Pendimethalin Dithiopyr Oxadiazon
40 d 120 d
20 - 128 d 45 d 44 d 17 d 60 d
Postemergence Herbicides – Avg. t-1/2
Herbicide
Soil Persistence t-1/2
MSMA Bentazon Imazaquin Glyphosate Glufosinate
180 d 20 d 90 d 47 d 7 d
Herbicide Degradation
0.0
0.2
0.4
0.6
0.8
1.0
lbs.
/acr
e
Herbicide Concentration
Herbicide Leaching Potential Index
HLP – developed by Warren and Weber, NCSU Factors considered include:
• Binding ability• Persistence (t-1/2)• Application rate• Amount that penetrates turf canopy and reaches soil• Soil pH, O.M., type
HLP Index
Low potential for leaching - > 10.1
Moderate potential - 1.0 to 10.0
High potential - < 1.0
HLP Index – Preemergence
Herbicide kg ai/ha HLP Index
Pendimethalin 3.4 65 - L
Dithiopyr 0.6 143 - L
Oxadiazon 3.4 9.2 – M-L
Bensulide 11.0 1.0 - M
Atrazine 2.2 1.5 - M
Simazine 2.2 1.9 - M
HLP Index – Postemergence
Herbicide kg ai/ha HLP Index
MSMA 3.4 39 - L
Glyphosate 4.5 112 - L
2,4-D 0.8 0.4 - H
Dicamba 0.6 0.48 - H
Imazaquin 0.6 3.6 - M
Soil Leaching Potential - SLP
Texture, O.M. and pH have greatest impact on herbicide leaching
Clays retard movement, sands increase High O.M. retards, low O.M. increases Acidic pH increases degradation Neutral to alkaline pH decreases degradation,
and can increase movement potential
SLP
S, LS, SL, L, SiL, L: 10 SCL, CL, SiCL: 6 SiC, SC: 3 C or muck: 1
S= sand, L = loam, Si = silt, C = clay
SLP
Can be calculated for each soil type• Based on texture and pH 0 to 91 cm• Based on O.M. in upper 15 cm
High soil leaching potential: > 131 Moderate: 90 to 130 Low: < 89
Herbicide Selection with HLP/SLP Matrix
Soil Leaching Potential (SLP) Rating
HLP Rating High Moderate Low
Groundwater Contam. Potential (GWCP)
High Hazardous Risky Safe
Moderate Risky Risky Safe
Low Safe Safe Safe
HLP/SLP Matrix ExampleLakeland Sand, low O.M. and clay, SLP = 134, High
Dicamba: HLP = 0.48 or high
Atrazine: HLP = 1.5 or moderate
MSMA: HLP = 39 or low
Dicamba: highhigh – HAZARDOUS
Atrazine: highmoderate – RISKY
MSMA: highlow - SAFE
Best Management Practices - BMPS
Use herbicides with low HLP Indices on high SLP soils
Train employees on proper application techniques
Spot treat if possible Follow label
• Be aware of any water advisory statements
BMPS (continued)
Consider mixing/loading pads, with spill containment
Do not mix or apply within 100 ft. of a well head Prevent back-siphoning Calibrate sprayer Establish buffer (non-treated areas)
Atrazine Label Precautions
Do not apply to sands and loamy sands where water table is close to surface.
Do not mix, load within 50 ft. of wells, sinkholes, etc. (unless pad with containment is used).
Do not mix, load within 50 ft. of streams, lakes, etc.
Atrazine Label Precautions
Do not apply within 66 ft. of where surface water run-off enters streams or rivers, or within 200 ft. of lakes and reservoirs.
On highly erodible land, use a 66 ft. crop or grass buffer strip.
0 Residue Ain’t Possible!!!
1 ppm = one second in 12 days 1 ppb = one second in 32 years 1 ppt = one second in 32,000 years 1 ppq = one second in 32,000,000 years
1.0 lb. Ai/acre = 1.0 ppm in upper 3 inches
Risk Communication
“Everything is Poison. There is nothing without poisonous properties. The dose differentiates a remedy from a poison.”
Philippus Aureolus Theophrastus Bombastus von Hohenheim 1493-1541 Better known a Paracelsus
Facts
30 yrs added to lifespan in 20th century 8 yrs added since use of pesticides only 37% of land farmed in 1950 is cultivated
today• Dennis Avery, Hudson Institute, Wall Street Journal, August 12, 1999
deer, turkey, geese populations increasing in GA
Thank you very much!!
georgiaturf.com
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