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1
Pesticide Fate in The
Environment
Troy Bauder
Soil and Crop Sciences
Overview
� Pesticide properties
� Site interactions
� Pesticides in Colorado ground and surface water
�Application considerations
Pesticide Fate
Site Characteristics
ManagementPesticide
Characteristics
Environmental
Fate
What are the Pesticide Characteristics Influencing
Movement and Degradation?
�Volatility – moving with air
�Solubility – moving with water
�Adsorptivity – attached to soil
�Persistence and degradation (half-life)
Volatilization vs. Drift?
• Change of state vs.
physical movement
• Potential depends
upon chemical
properties and
conditions
2
Volatility of Common Pesticides
Trade Name Common Name Vapor Pressure (mm Hg)
Aatrex atrazine 2.89 x 10-7
Banvel dicamba 0
Tordon picloram 6.2 x 10-7
Roundup glyphosate 0
Weedone 2,4-D Acid 0.2
Weedar 2,4-D Amine 7.5 x 10-7
Pesticides in Soil System
Adsorption - Partitioning of a compound between
solid matter and water (Koc or Kd)
Physio-chemical process, Largely electrostatic “bonds”pH induced charges
Sorption Soil Adsorption of Common Pesticides
Trade Name Common Name Sorption index
(Koc)
Aatrex atrazine 100
Banvel dicamba 2
Tordon picloram 16
Roundup glyphosate 24,000
Weedone 2,4-D Acid 100
Comite Propargite 4,000
Soil factors affecting pesticide adsorption
Soil Properties
• Organic Matter
• Clay content
• pH
• moisture
Low OM High OM
Degradation Pathways
3
�Soil conditions�Temperature
�Moisture
�Organic matter
�Aeration
�pH
Persistence – Half Life
Half life = amount of time it takes for 50% of the pesticide to degrade.
Does that mean the pesticide is 100% degraded (no longer present) after two half-lives?
0
10
20
30
40
50
60
70
80
90
100
% Pesticide Remaining
0 1 2 3 4
Number of Half-Lives
0
0.05
0.1
0.15
0.2
0.25
0.3
0 2 4 6 8 10 12 14 16 18
Degradation Rate
Days
Optimum Above Optimum
Persistence (Half – Life)
• Affected by:
– Temperature
– Soil moisture
From: Guenzi and Beard, 1976
Soil Moisture and Half-life
125.9
33 27.6
572
23.1 19.7
0
100
200
300
400
500
600
Half-life (days)
Simazine Velpar
4%
10%
18%
From: Varcia-Valcarcel and Tadeo, 1999
Persistence of Common Pesticides
Trade Name Common
Name
Soil Half Life
(days)
Aatrex atrazine 60
Banvel dicamba 14
Tordon Picloram 90
Gramaxone paraquat 500
Treflan trifluralin 60
Pesticide Environmental Fate
Properties and Ratings
http://www.ext.colostate.edu/PUBS/CROPS/xcm177.pdf
4
Pesticides with Groundwater Advisories
Trade name Common name
Weed B Gone 2,4-D, salt
Lasso Alachlor
Temik Aldicarb
Aatrex Atrazine
Abound Azoxystrobin
Hyvar Bromacil
Furadan Carbofuran
Dacthal DCPA
Casoron Dichlobenil
Imidacloprid 4F Imidacloprid
Balance Isoxaflutole
Trade name Common name
Plateau Imazapic
Kilprop MCPP, DMA salt
Dual Metolachlor
Sencor Metribuzin
Solicam Norflurazon
Vydate C-LV Oxamyl
Tordon Picloram
Princep Simazine
Confirm 2F Tebufenozide
Sinbar Terbacil
Platinum Thiamethoxam
Bayleton 50 Triadimefon
Where Do You Find The Ground or Surface
Water Advisory?
Web information:
-http://www.cdms.net/manuf/manuf.asp
-http://extoxnet.orst.edu/
waterquality.colostate.edu
Pesticide Fate
Site Characteristics
ManagementPesticide
Characteristics
Environmental
Fate
Site Characteristics?
Leaching
� Overlying soil type
• Permeability
• Organic matter
� Depth to water table
� Geology
� Recharge rate (precipitation and irrigation)
Runoff
�Soil type
�Slope
�Soil conditions
� Irrigation
�Vegetation characteristics
�Other ground cover
Leaching Potential Factors
Soil characteristics Numeric guidelines*
sandy soil
low organic matter less then 1% OM
numerous macropores
Pesticide properties
long half-life greater then 21 days
low adsorptivity KOC less then 300-500
high solubility greater than 30 ppm
5
�Texture
�Sand, silt, clay
�Slope
�Structure
�http://www.nrcs.usda.gov/wps/portal/nrcs/site/soils/home/
PermeabilityDepth to Groundwater
• Time
– Opportunity for
adsorption and
degradation
– Dilution
http://coloradogeologicalsurvey.org
Geologic Conditions
http://coloradogeologicalsurvey.org/water/groundwater-atlas/
Potential for Recharge
N
S
W E100 km
(62 miles)
Ground Water Sensitivity to Pesticide Contamination in Colorado
Low Sensitivity
High Sensitivity
Moderate Sensitivity Non-irrigated BUT Shallow Water Table
Non-irrigated and No Shallow Water Table
• Aquifer present
• Depth to groundwater
• Soil Permeability & Slope
• Irrigation
Groundwater Monitoring
• Ag Chemicals and Groundwater Protection
Program
• 3,359 samples from 1281 wells
• Since 1992
• Analyze:
– Nitrate
– Other inorganic
– ~100 pesticide ai’s
6
https://erams.com/co_groundwater/ Pesticide Detections
BDL
73%
Detects
26%
> Std
1%
% of Wells
BDL
64%
Detects
36%
> Std.
<1%
% Samples
Pesticides Detected in Groundwater (61)2,4-D Dicamba Malathion
Acetochlor Dichlorvos MCPA
Acetochlor ESA Diflufenzopyr MCPP
Alachlor Dimethenamid ESA Metalaxyl
Alachlor ESA Dimethenamid OA Metolachlor
Alachlor OA Dimethoate Metolachlor ESA
Aldicarb sulfone Diuron Metolachlor OA
Atrazine Ethoprop Metribuzin
Azoxystrobin Fenamiphos Nicosulfuron
Bentazon Fenamiphos sulfone Oxydemeton methyl
Bromacil Hexazinone Phosphamidon
Chlorantraniliprole Hydroxy Atrazine Picloram
Chlorpyrifos Imazamethabenz acid Prometon
Chlorsulfuron Imazamox Propazine
Clopyralid Imazapic Quinclorac
Cyromazine Imazapyr Simazine
DCPA Imazethapyr Tebuthiuron
Desethyl Atrazine Imidacloprid Tetraconazole
Desisopropyl Atrazine Lindane Thiamethoxam
Diazinon OA Linuron Triazine (ELISA)
Long List a Concern?
• 27 compounds detected
above 1.0 µg / L (ppb)
• 30 compounds detected
fewer than five times
• Detection limits for some
compounds as low as
0.003 µg / L (ppb)
• Most detections < 0.10 µg
/ L (ppb)
• i.e. dose makes the
poison
Above Drinking Water Standard
• Unusual in Colorado
• Only 20 active ingredients have defined standard or health advisory level
• Often suggest possible spill in area
• All products with leaching characteristics
0
5
10
15
20
25
30
35
40
45
ug
/L
West Slope Detections
0
0.5
1
1.5
2
2.5
Ima
zap
yr
Ma
lath
ion
Ch
lors
ulf
uro
n
Ala
chlo
r E
SA
He
xazi
no
ne
Imid
acl
op
rid
Me
tola
chlo
r E
SA
Ima
zeth
ap
yr
Pro
me
ton
Ace
toch
lor
ESA
De
seth
yl
Atr
azi
ne
Ala
chlo
r O
A
pp
b
0
1
2
3
4
5
6
7
8
9
10
Ala
chlo
r E
SA
Ima
zap
yr
Me
tola
chlo
r E
SA
Ch
lors
ulf
uro
n
He
xazi
no
ne
De
seth
yl
Atr
azi
ne
Ala
chlo
r O
A
Ma
lath
ion
Imid
acl
op
rid
Ima
zeth
ap
yr
Pro
me
ton
Ace
toch
lor
ESA
# o
f H
its
7
Surface Water Sampling
• Less frequent and
coordinated as
groundwater
• Typically CDPHE,
USGS
• Generally focused on
basins with use
http://water.usgs.gov/nawqa/pnsp/pubs/pest-streams/
Surface Water Pesticides
0
2
4
6
8
10
12
14
16
18
Nu
mb
er
of
de
tect
ion
s
Number of pesticide detections
by basin South
Platte
North Fork
Gunnison
Arkansas
0
0.1
0.2
0.3
0.4
0.5
0.6
Co
nce
ntr
ati
on
(p
pb
=µ
g/L
)
Detected pesticide concentration by
basinSouth
Platte
North Fork
Gunnison
Monitoring Summary
Pesticide detection varies widely depending upon area of state .
Chemicals with leaching properties and higher rates are most frequently detected compounds.
Detections above drinking water standard are rare.
Application Considerations
� Awareness:
� Pesticide choice
� Site Characteristics
� Setback from water sources (Wells)
• Application
• Label setbacks
• Mixing and loading
� Application timing – pending irrigation or rain
See newly revised BMPs for Pesticide and Fertilizer Storage and
Handling:
http://www.ext.colostate.edu/pubs/crops/xcm178.pdf
Application Considerations
• Awareness
– Location:
• Nearby surface water
• Topography
– Low lying areas
– Slopes toward water
• Extremely sandy soils
• Avoid overspray onto impermeable surfaces!!
– Timing – incoming weather, irrigation
Most pesticide detections at higher levels(in Colorado) are likely due to point sources
• Poor mixing and
loading
• Uncontained spills
• Mixing near
wellhead
• Improper storage
and disposal
8
Agricultural Chemicals and
Groundwater Protection ProgramRequires secondary containment and
mixing and loading pads if you …..
� Store pesticide in bulk containers > 55 gal. (non-DOT approved or >660 gal)
� Mix more than 500 gal product at 1 site annually�Field mixing and loading is exempt
Other Resources
• RUP Recordkeeping
– Updated Excel Program
– http://waterquality.colostate.edu/p
estrecordbook.shtml
• Colorado RUP
Recordkeeping App (CRURA)
• Available on App Store soon
Summary
Certain Colorado waters are vulnerable to pesticide impacts, however …
�Site characteristics
�Chemical selection
�Application/ management practices
Determine actual impacts.
Contact Information
• Troy Bauder– Department of Soil and Crop
Sciences
– Colorado State University
– Fort Collins, CO 80523-1170
• (970) 491–4923
• [email protected]• http://waterquality.colostate.edu