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Environmental Fate of Herbicides

Public Concerns. HealthQuality of LifeEnvironmentNuclear and Toxic WasteChemicals vs. NaturalRight-to-Know. Public Concerns" About Chemicals. Cause cancerNot well testedHarm animalsLast forever. Not natural"Used carelesslyContaminate waterAny amount is dangerous. Herbicide Concerns. Last foreverContaminate waterAffect human healthSterilize soilUse is not neededKill all desirable organismsDegrade the environment.

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Environmental Fate of Herbicides

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    1. Environmental Fate of Herbicides Tim R. Murphy, Ph.D. The University of Georgia Crop and Soil Sciences

    2. Public Concerns Health Quality of Life Environment Nuclear and Toxic Waste Chemicals vs. Natural Right-to-Know

    3. “Public Concerns” About Chemicals Cause cancer Not well tested Harm animals Last forever Not “natural” Used carelessly Contaminate water Any amount is dangerous

    4. Herbicide Concerns Last forever Contaminate water Affect human health Sterilize soil Use is not needed Kill all desirable organisms Degrade the environment

    7. Fate of Herbicides Original dose and ˝ 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

    8. 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

    9. Herbicide Fate in the Soil Herbicide Chemical Characteristics Soil Physical-Chemical Characteristics

    10. Herbicide-Chemical Properties Ionic State (cation, anion, basic or acidic) Water Solubility Vapor pressure Hydrophobic/hydrophilic Partition coefficient Chemical, photochemical, microbial sensitivity

    11. Soils - Solid Phase Sand - 0.2 to 2.0 mm Silt - 0.002 to 0.2 mm Clay - < 0.002 Organic matter - decaying plant and and animal residue

    12. 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

    13. Soils - Gas & Liquid Phase Gas - oxygen, carbon dioxide, others Liquid - water (with dissolved molecules, ions, etc.)

    14. Soils - Living Phase Microorganisms - bacteria, actinomycetes, fungi Algae Vertebrates and Invertebrates Microorganisms degrade herbicides

    15. 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

    16. 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

    17. Soil Factors Cation Exchange Capacity (CEC) soils ability to adsorb positively charged compounds fine-textured, high-organic matter soils have larger CEC’s than coarse, low-organic matter soils

    19. Soil Factors Organic Matter and Texture most important for soil applied herbicides Indirectly influences all processes that affect herbicides!! the greater the organic matter and clay content, the greater adsorption of herbicides

    20. Amount of atrazine required to reduce giant foxtail growth by 50% at varying OM levels.

    21. Water Movement Surface runoff Leaching Capillary action

    22. Factors That Affect Leaching

    23. Relative Movement of Herbicides

    24. Mobility of Preemergence Herbicides in Soil

    25. Mobility of Postemergence Herbicides in Soil

    26. Volatility Volatility - physical change of a liquid or solid to gas.

    27. Volatility Related to vapor pressure Increases at high air temperatures Increases under high soil moisture conditions Higher on coarse textured, sandy soils

    28. Preemergence Herbicide Water Solubility and Relative Volatility

    29. Postemergence Herbicide Volatility

    30. Photodecomposition Photodecomposition - Breakdown of the herbicide by sunlight (primarily UV portion).

    31. Herbicide Persistence - Soil

    32. Herbicide ˝ Life

    33. Preemergence Herbicides – Avg. t-1/2

    34. Preemergence Herbicides – Avg. t-1/2

    35. Postemergence Herbicides – Avg. t-1/2

    36. Postemergence Herbicides – Avg. t-1/2

    37. Postemergence Herbicides – Avg. t-1/2

    38. Herbicide Degradation

    39. 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

    40. HLP Index Low potential for leaching - > 10.1 Moderate potential - 1.0 to 10.0 High potential - < 1.0

    41. HLP Index – Preemergence

    42. HLP Index – Postemergence

    43. 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

    44. 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

    45. 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

    46. Herbicide Selection with HLP/SLP Matrix

    47. HLP/SLP Matrix Example Lakeland 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: high high – HAZARDOUS Atrazine: high moderate – RISKY MSMA: high low - SAFE

    48. 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

    49. 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)

    50. SU Herbicide Lateral Movement Griffin, GA Lateral runoff facility 5% uniform slope Wobbler irrigation heads 1.25 inches per hour Tifway bermudagrass 0.5 inch clip height

    51. SU Herbicide Lateral Movement Plots 25 ft. long Lower 10 ft. fall-seeded with perennial ryegrass Upper 15 ft. not overseeded January 22, 2004, applied to dormant bermuda Monument at 0.33 and 0.56 oz./acre Manor at 0.5 oz./acre TranXit at 2.0 oz./acre Kerb at 2.0 lbs./acre

    53. SU Herbicide Lateral Movement Before application Applied 2.5 inches irrigation (2 hrs), 37% saturation Waited ~ 1hr, until foliage dried Applied herbicides Waited ~ 1hr, until foliage dried Applied 2.5 inches irrigation (2 hrs) Applied 0.5 inch irrigation water 24 HAT

    54. SU Herbicide Lateral Movement WHAT HAPPENED?? Kerb – moved 8 ft. (76% injury) Monument 0.33 oz. – 0.7 ft (3%) Monument 0.56 oz. – 3 ft. (14%) Manor 0.5 oz. – 0.7 ft. (1) TranXit 2.0 oz – 0.6 ft. (1) NOTE: No significant injury occurred until 48 DAT

    56. Can SU Herbicides Move? Yes, if: Surface film of water present at application Irrigation or rainfall immediately after application Not watering after foliage has dried Dew re-suspends and can cause tracking (prevent by watering in) Improperly adjusted irrigation heads

    57. Atrazine Technical Facts (U.S. E.P.A) www.epa.gov/OGWDW/dwh/t-soc/atrazine.html Drinking water (U.S.A.) MCL: 0.003 mg/L 2nd most frequently detected pesticide in EPA National Survey of Drinking Water Wells DE, IL, IN, IA, KS, MI, MN, MO, NE, NY

    58. Atrazine Technical Facts (U.S. E.P.A) Degradation Microbial, chemical (hydrolysis at acidic pH) Adsorption Higher in muck and clay soils, than in soils with low clay and O.M. t-˝ = 60 d

    59. 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.

    60. 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.

    61. 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

    62. 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

    63. 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

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