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

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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

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�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

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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

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chlo

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0

1

2

3

4

5

6

7

8

9

10

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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

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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

• troy.bauder@colostate.edu• http://waterquality.colostate.edu