### U.S. Department of the Interior U.S. Geological Survey 

# Scientific Investigations Report 2005–5094 

# Summary of Significant Results from Studies of Triazine Herbicides and Their Degradation Products in Surface Water, Ground Water, and Precipitation in the Midwestern United States During the 1990s

1990 0 10 20 30 40 50 60Midwestern United States herbicide use, in million pounds per year

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 

### Atrazine

Cyanazine

Simazine

# S u mma ry of Sig n ifica n t Res u lts f r om St u dies of T r iazi n e He r bicides a n d Thei r Deg r adatio n P r od u cts i n S urface Wate r , G r o un d Wate r , a n d P r ecipitatio n i n the Midweste rn U n ited States D ur i n g the 1990s

By Elisabeth A. Scr ibne r , E. M. Thu r man, Donald A. Goolsby, Mi c hael T. Meye r , William A. Battaglin, and Dana W. Kolpin

U.S. Depa rtme n t of the I n te r io r U.S. Geological S urvey 

# S cientific Investigations Report 2005–5094

## U.S. Depa rtme n t of the I n te r io r Gale A. No rton, S e cr eta r y U.S. Geological S urvey Cha r les G. G r oat, Di r e c to r

U. S . Geologi c al S u r vey, Reston, Vi r ginia: 2005

For sale by U. S . Geological S urvey, Information S ervices Box 25286, Denver Federal Center Denver, CO 80225 For more information about the U S G S and its products: Telephone: 1-888-A S K-U S G S World Wide Web: ht tp://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U. S . Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material s contained within this report.

Suggested citation: S cribner, E.A., Thurman, E.M., Goolsby, D.A., Meye r, M.T., Battaglin, W.A., and Kolpin, D.W., 2005, S ummary of significant results from studies of triazine herbicides and their degradation products in surface water, ground water, and precipitation in the Midwestern United S tates during the 1990s: U. S . Geological S urvey S cientific Investigations Report 2005–5094, 27 p.

P r epa r ed by the U.S. Geological S urvey i n Law r e n ce, Ka n sas (http://ks.wate r . u sgs.gov)iii


# Co nte nts

Abst r a c t. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Int r odu c tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 T r iazine He r bi c ide Usage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Wate r -Quality Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 4 S u r fa c e Wate r
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 G r ound Wate r
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 6 P r e c ipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Chemist r y and T r anspo r t of T r iazine He r bi c ides in Wate r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Pe rsisten c e of T r iazine He r bi c ides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 18 S umma r y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Refe r en c es Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

# Fig ures 1. Map showing lo c ation of U. S . Geologi c al S u r vey Toxi c S ubstan c es Hyd r ology P r og r am study a r eas fo r t r iazine he r bi c ides in the Midweste r n United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 2. G r aph showing t r iazine he r bi c ide use in Midweste r n United States, 1990 to 2002. . . . . . . . . . . . . . . . . . . .4 3. Map showing lo c ation of study a r ea, hyd r ologi c units, and 147 st r eam sites sampled du r ing 1989–2002 in the Midweste r n United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 4. G r aphs showing c on c ent r ations in su r fa c e-wate r samples c olle c ted f r om 53 Midweste r n st r eams du r ing post-appli c ation r unoff in 1989, 1990, 1994, 1995, 1998, and 2002 fo r at r azine and c yanazine, p r opazine and simazine, and c yanazine amide, deethylat r azine, and deisop r opylat r azine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .7 5–8. Maps showing: 5. Lo c ation of 76 r ese r voi rs sampled fo r he r bi c ide analysis in the Midweste r n United States du r ing 1992 and 1993. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 6. Th r ee-dimensional c ompute r images of at r azine c on c ent r ations in Pe rr y Lake, no r theaste r n Kansas, du r ing 1992 p r e-appli c ation, fi rst flush, summe r, fall, and 1993 p r eappli c ation su r veys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .9 7. Lo c ation of wells in the U. S . Geologi c al S u r vey Midweste r n g r ound-wate r monito r ing netwo r k sampled du r ing 1991–94. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. Lo c ation of wells sampled in Iowa du r ing 1995–98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9. Diag r am showing deg r adation pathways fo r at r azine, c yanazine, p r opazine, and simazine to deethylat r azine and (o r ) deisp r opylat r azine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. Diag r am showing deethylat r azine-to-at r azine r atios fo r su r fa c e- and g r ound-wate r samples f r om Midweste r n United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 15 11. G r aph showing deethylat r azine-to-at r azine r atios fo r su r fa c e- and g r ound-wate r samples f r om Midweste r n United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 12–16. Diag r ams showing: 12. Con c eptual model and data fo r deethylat r azine-to-at r azine r atios in Pe rr y Lake, no r theaste r n Kansas, du r ing Ma rc h 1992–Ma rc h 1993. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 13. Mixed-mode model of so r ption fo r hyd r oxylated at r azine deg r adation p r odu c ts. . . . . . . . . . . . . 18 14. P r oposed models fo r the me c hanisms c ont r olling c on c ent r ations of hyd r oxylated at r azine deg r adation p r odu c ts in st r eams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18iv

15. Deg r adation pathways fo r at r azine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 16. Deg r adation pathways fo r c yanazine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

# Tables 1. Methods of analysis fo r t r iazine he r bi c ides and thei r deg r adation p r odu c ts . . . . . . . . . . . . . . . . . . . . . . . . .3 2. Pe rc entage of dete c tions of t r iazine he r bi c ides and deg r adation p r odu c ts in su r fa c e-wate r samples c olle c ted f r om sele c ted st r eams in the Midweste r n United States du r ing 1989 and 1990 . . .6 3. T r iazine he r bi c ides and thei r deg r adation p r odu c ts analyzed in samples c olle c ted f r om 76 Midweste r n r ese r voi r outflows, Ap r il 1992 th r ough S eptembe r 1993. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 4. S umma r y of analyti c al r esults fo r t r iazine he r bi c ides and thei r deg r adation p r odu c ts in g r oundwate r samples c olle c ted f r om wells in the Midweste r n United States du r ing 1991–93 . . . . . . . . . . . . . 10 5. S umma r y of analyti c al r esults fo r t r iazine he r bi c ides and thei r deg r adation p r odu c ts in samples c olle c ted f r om 131 Iowa wells du r ing 1995–98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. S umma r y of analyti c al r esults fo r t r iazine he r bi c ides and thei r deg r adation p r odu c t c on c ent r ations measu r ed in p r e c ipitation samples f r om 81 sites a cr oss the Midweste r n and No r theaste r n United States f r om Ma rc h 1990 th r ough S eptembe r 1991 . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. Physio c hemi c al p r ope r ties of t r iazine he r bi c ides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

# Co n ve r sio n Facto r s a n d Dat u m

Ho r izontal c oo r dinate info r mation is r efe r en c ed to the No rth Ame r i c an Datum of 1983 (NAD 83)

. M u ltiply By To obtai n foot (ft) 0.3048 meter (m) inch (in.) 2.54 centimeter (cm) microgram per liter ( μ g/L) 1 part per billion (ppb) microgram per square meter per y ear

[(μg/m 2 )/y r] 0.003276x10 -6 ounce per billion (ppb) mile (mi) l.609 kilometer (km) milligram per liter (mg/L) 1 part per million (ppm) milliliter per gram (mL/g) 0.007491 gallon per ounce (gal/oz) millipascal (mPa) 0.000208854 pound-force per square foot (lbf/ft 2 ) mole per liter (mol/L) 1 gram molecular weight liter pound (lb) 453.6 gram (g) pound active ingredient per acre per

y ear [(lb a.i./acre)/y r] 1.121 kilogram active ingredient per hectare per y ear [(kg a.i./ha) y r] pound per acre (lb/acre) 1.121 kilogram per hectare (kg/ha) square mile (mi 2 ) 2.590 square kilometer (km 2 )

# S u mma ry of Sig n ifica n t Res u lts f r om St u dies of T r iazi n e He r bicides a n d thei rDeg r adatio n P r od u cts i n S urface Wate r , G r o un d Wate r , a n d P r ecipitatio n i n the Midweste rn U n ited States D ur i n g the 1990s

By Elisabeth A. Scr ibne r , E.M. Thu r man, Donald A. Goolsby, Mi c hael T. Meye r , William A. Battaglin, and Dana W. Kolpin 

# Abstr act Nonpoint-source cont amination of water resources from triazine herbicides has been a major water-quality issue during the 1990s in the United States. To address this issue, studies of surface water, ground water, and precipitation have been carried out b y the U.S. Geological Surve y in the Midwestern United States. Reconnaissance studies of 147 streams were conducted to determine the geographic and seasonal distribution of atrazine, c y anazine, propazine, and simazine. These studies showed that high concentrations of herbicid es were flushed from cropland and transported through the stream s y stem as pulses in response to spring and summer rainfall. The studies also revealed the persistence of herbicides and their degradation products in streams. An investigation of 76 reservoirs showed that the occur

rence and temporal distribution of herbicides and their degrada

tion products in reservoir outflow could be related to reservoir and drainage-basin ch aracteristics, water and land use, herbi

cide use, and climate. Signifi cant findings showed that concen

trations of atrazine and its degradation products remained elevated all summer and into th e fall and that recentl y applied atrazine mixed with atrazine applied the previous y ear as water moved through a reservoir. Reconnaissance studies of 303 ground-water wells were completed to determine h y drogeological and seasonal occur

rence, concentration, and distribution of herbicides and their degradation products. Samples collected from across the Mid

western United States consistentl y revealed that triazine herbi

cide degradation products commonl y were found more fre

quentl y than their parent herbicide and that ground-water age could be an important factor in explaining variations in herbi

cide contamination. A final stud y investigated precipitation in the Midwestern United States, northeas t to the Atlantic O cean, and northward to the Canadian border. It found that the highest herbicide concen

trations in precipitation occurred following herbicide application to cropland. Atrazine was detected most often, fol

lowed b y deeth y latrazine, c y anazine, and deisopropl y atrazine. Mass deposition of herbicides b y precipitation was greatest in areas where herbicide use was in tense and decreased with dis

tance from the Midwest. Findings of the 1990s studies include an improved under

standing of the occurren ce, persistence, chemistry , and trans

port of triazine herbicides and their degradation products in the h y drologic environment. A significant increase in knowledge of triazine herbicides and develo pment and improvement of ana

l y tical methods were accomplished in the past decade. The results produced are not onl y significant for the present (2005) but provide an important data set for future use. 

# I ntrod u ctio n The U.S. Geological Surve y (USGS) Toxic Substances H y drolog y (Toxics) Program provides unbiased scientific information on the behavior of toxic substances in the Nation’s h y drologic environments. The ob jectives of the program include development and quantifi cation of methods to measure contaminants and thei r degradation products at levels low enough to understand the fate and transport in h y drologic s y s tems. Investigations are focused on identif y ing persistent pesti

cides and their degradation products in surface water, ground water, and precipitation. The research involves developing methods to measure these pestic ides in water samples at lowlevel concentrations. Re sults then are used b y manufacturers, farmers, regulators, researchers, and the public (Buxton, 2000).Throughout the 1990s, a series of regional-scale waterquality studies were conducted b y the Toxics Program in the Midwestern United States. The stud y area extended across parts of 12 States (fig. 1) and was select ed because it is the largest and most intensive area of row-crop agriculture in the country . This area often is referred to as th e Corn Belt (Thurman and others, 1991; Infoplease, 2004). Most of the agricultural application of triazine herbicides in the United States is to crops in this region.2 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

The major Midwestern row crop s include corn, sorghum, and so y beans, to which more than 52.8 million lb of triazine herbi

cides, such as atrazine, c y anazine, propazine, and simazine, were applied during 1997 (Gianessi and Marcelli, 2000). The regional-scale studies included reconnaissance of Midwestern streams, reservoirs, and ground water. Other studies were con

ducted to investigate herbicides dispersed b y air currents, rain

fall, snow, and dry deposition. Field-dissipation studies were conducted to examine the chemistry , fate, and transport of the tr iazine herbicides atrazine, c y anazine, propazine, simazine, a nd their degradation products in greater detail. These studies resulted in an improved under

standing of the geochemical fate and transport of triazines and degradation products in h y drologic environments (Mills and Thurman, 1994a,b; Thurman and others, 1994). USGS has emphasized anal y tical methods development to compliment studies of pesticide fate and transport. The USGS Organic Geochemistry Research Laboratory was established in 1987 in Lawrence, Kansas, to develop anal y tical methods and conduct research on the fate and tr ansport of pesticides and their degradation products. Anal y tical methods developed for triaz

ine compounds during the 1990s (table 1) included solid-phase extraction (SPE; Thurman and others, 1990; Mills and Thur

man, 1992; Me y er and others, 1993; Thurman and Mills, 1998; Ferrer and others, 1999; Thurman and Snavel y , 2000), gas chro

matograph y /mass spectrometry (GC/MS; Zimmerman and Thurman, 1999; Kish and others, 2000), high-performance liq

uid chromatograph y (HPLC; Hostetler and Thurman, 2000), liquid chromatograph y/mass spectrometry (LC/MS; Ferrer and others, 2000; Thurman and others , 2001; Lee and others, 2002), and enz y me-linked immunosorbent assa y (ELISA; Thurman and others, 1990; Aga and Thurman, 1993; Pomes and others, 1996, 1998; Schraer and others, 2000). Anal y tical methods con

tinue to be developed at the Organic Geochemistry Research Laboratory to measure concentrations of pesticides and their degradation products (Scribner and others, 2000b). The purpose of this report is to provide a summary of tri

azine herbicide usage and water-quality effects, persistence, chemistry , and transport in h y drologic environments of the Midwestern United States using significant results from USGS studies conducted during the 1990s. The report also includes an extensive bibliograph y of publications resulting from these studies. 

# Tr iazi n e He rbicide Usage Modern agricultural practices in the United States often involve widespread use of herbicides for production of crops. Because of concern about wate r contamination, several manu

facturers voluntaril y reduced the recommended application rates or, in other cases, remove d herbicides from the market during the 1990s. Monitoring the effects of these usage changes is important in understanding the occurrence, persistence, chemistry , and transport of these he rbicides and their degrada

tion products. The historical use of atrazine, c y anazine, and simazine in the Midwestern United States is shown in figure 2. In 1990, the Playa Study area

lake study 

## C 

## o 

## r 

## n B e l t

0 500 KILOMETERS 500 MILES 0 CANADA

MEXICO

Fig ur e 1. Lo c ation of U. S . Geologi c al S u r vey Toxi c S ubstan c es Hyd r ology P r og r am study a r eas fo rt r iazine he r bi c ides in the Midweste r n United S tates.T r iazi n e He r bicide Usage 3 Table 1. Methods of analysis fo rt r iazine he r bi c ides and thei rdeg r adation p r odu c ts. [SPE, solid-phase extraction; GC/MS, gas chromatograph y/mass spectrometry ; HPLC/DAD, high-perform ance liquid chromatograph ywith diode array detection; LC/MS, liquid chromatograph y/mass spectrometry ; ELISA, enz y me-linked immunosorbent assay ; x, method used; NA, not applicable]
T r iazine c ompounds Method S PE GC/M S HPLC/DAD LC/M S ELI S A Pa r ent c ompounds Atrazine x x NA x x C y anazine x x NA x x Propazine x x NA x x Simazine x x NA x NA Deg r adation p r odu c ts Deeth y latrazine x x NA x NA Deisoprop y latrazine x x NA x NA Deeth y lh y drox y atrazine x NA x NA NA Deisoprop y lh y drox y atrazine x NA x NA NA H y drox y atrazine x NA x x NA
C y anazine acid x NA NA x NA C y anazine amide x x NA x NA Deeth y lc y anazine x x NA x NA Deeth y lc y anazine acid x NA NA x NA Deeth y lc y anazine amide x x NA NA NA
H y drox y simazine x NA NA x NA
manufacturer of atrazine voluntaril y reduced the maximum rec

ommended application rate on corn and sorghum (U.S. Envi

ronmental Protection Agenc y, USEPA, written commun., January 23, 1990). In 1992, the maximum recommended appli

cation rate of atrazine on corn and sorghum was reduced again b y the manufacturer to a range of 1.6 to 2.5 (lb a.i./acre)/y r (pounds active ingredient per acre per y ear) depending on soil organic residue and erosion potential. As much as 0.50 (lb a.i./acre)/y r could be used in subsequent applications (USEPA, written commun., March 8, 1993), with the total of all applica

tions not to exceed 2.5 (a.i./acre)/y r (Scribner and others, 2000a). As seen in figure 2, the use of atrazine decreased from about 47 million lb in 1991 to 39 million lb in 1995, fluctuating to 52 million lb in 2001, then declining sharpl y to 42 million lb in 2002. Besides voluntary reductions in application rates, her

bicide use fluctuates in response to annual changes in planted corn and so y bean acreage and the introd uction of new herbicide products (U.S. Department of Agriculture, 1991–2003). C y anazine was historicall y one of the most intensivel y used herbicides in the country since its introduction in 1972. However, in 1996, the manufacturer of c y anazine voluntaril y began reducing the maximum recommended application rate from 6.5 to 5 (lb a.i./acre)/y r to 3 (lb a.i./acre)/y r b y January 1, 1999. The manufacture of c y anazine was discontinued on December 31, 1999, with distribution of ex isting supplies terminated in September 2002 (Ton y Catka, Dupont, oral commun., September 14, 2000). As shown in figure 2, approx

imatel y 20 million lb of c y anazine were used in the Midwestern United States in 1990, peaking at 26 million lb in 1994, then steadil y declining to about 0.05 million lb usage b y 2002 (U.S. Department of Agriculture, 1991–2003). Simazine is applied to corn, primaril y in Illinois, Indiana, Kentucky , Ohio, and on to the eastern seaboard. As can be seen in figure 2, simazine usage in the Midwestern United States increased from 0.80 million lb in 1990 to approximatel y 1 mil

lion lb in 2002 (U.S. Department of Agriculture, 1991–2003). Propazine was voluntaril y removed from the market b y the manufacturer before 1990. However, there were man y sorghum farmers who confirmed that propazine was still a necessary product in their region, and the manufacturer agreed to continue marketing the product to States that applied for U.S. Environ

mental Protection Agenc y (USEPA) Section 18 Emergenc y Exemption. For the 1993–97 growing seasons, USEPA granted Section 18 Emergenc y Exemptions for the use of propazine on sorghum to one or more of the following States: Colorado, Kan

sas, New Mexico, Oklahoma, and Texas (U.S. Environmental Protection Agenc y , 1998). As a result of USEPA Section 18 Emergenc y Exemption grants, propazine usage during 1993 was approximatel y 100,000 lb, increasing to approximatel y 360,000 lb in 1994, with a sharp decline in 1997 to 40,000 lb (Jim Bone, Griffin, L.L.C, written commun., 2005).4 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts



# Wate r-Qu ality Stu dies
S ur face Wate r

Since 1989, USGS has conducted periodic reconnaissance studies of streams located in th e Midwestern United States to determine the occurrence, distribution, and concentrations of herbicides. The studies also in cluded measuring concentrations of herbicide degradation products in surface-water samples to gain information about the transport and fate of herbicides in the environment (Battaglin, 2002). Sampling sites were selected at 147 USGS streamflow-gaging stations during 1989 to ensure geographic and seasonal distribution and regional-scale inter

pretation of the data (fig. 3). The streams were sampled before application of herbicides, during the first major runoff period after application, and during low-flow conditions in the fall when most of the streamflow was derived from ground water. A follow-up sampling at 53 sites of the 147 sites (fig. 3) was conducted in 1990 because of increased concern about the findings of high post-application concentrations of herbicides in 1989. The distribution of major herbicide concentrations detected in these streams was essentiall y the same in 1989 and 1990 for both the pre- and post-application samples. Subse

quent studies in 1994, 1995, 1998, and 2002 indicated that the flush of herbicides following application is an annual occur

rence (Goolsb y and others, 1991a, 1991b; Thurman and others, 1991, 1992; Scribner and others, 1993, 1994, 1998, 2000a, 2003; Goolsb y and Battaglin, 1995; Battaglin and others, 2003, 2005). The most striking feature of these reconnaissance data was that high concentra tions of herbicides and their degradation products are mobilized b y rainfall, then transported to streams with runoff. The majority of this transport takes place during the first rainfall or runoff after the application of herbicides. Subse

quent runoff tends to produce le sser peaks in concentration. Because of these flushes, the det ections of herbicides in larger Midwestern streams tends to be seasonal with higher percent

ages of detections in spring and earl y summer and lower per

centages in fall and winter (table 2). Measurable amounts of atrazine, the most frequentl y detected herbicide, occurred in 91 percent of the pre-application samples and 76 percent of the harvest samples, providing an indication of its persistence in surface water. Also, deeth y latrazine, a triazine degradation product, occurred more frequentl y in pre-application, postapplication, and harvest samples than did deisoprop y latrazine, also a triazine degradation produc t (table 2). These findings are significant because the y indicate that some of the parent herbi

cides persist from y ear to y ear in soil and water, and that degra

dation products, such as deeth y latrazine, both persist and are mobile. Results of studies of water samples collected from streams in eastern Iowa during the 1990s further substantiate these findings (Kalkhoff and others, 2003; Schnoebelen and others, 2003). Herbicide concentrations inMidwestern streams were expected to change between 1989 and 2002 as a result of changein herbicide use. In 1994, 1995, 1998, and 2002 postapplication runoff samples were coll ected at approximatel y 50 of the 147 sites sampled in 1989 (fig. 3). These samples were collected to assist in determini ng if changes in the application rates recommended b y the manufacturer of atrazine had resulted in a decrease in atr azine concentrations in postapplication runoff (Scribner and others, 1998, 2000a). The percentage of samples with herbicides detected at or above the anal y tical reporting limit of 0.05 μg/L was greater in 1995 than in 1989 for c y anazine and propazine, but less in 1995 than in 1989 for simazi ne. The detection frequenc y for atrazine was 100 percent for ever y y ear. The frequenc y of detection of deeth y latrazine was the same in 1989 and 1995, but the fre

quenc y of detection of deisoprop y latrazine was greater in 1995 than in 1989 (Battaglin and Goolsb y , 1999; Scribner and others, 2000a). The distribution of concentr ations for surface-water sam

ples collected during post-application runoff in 1989, 1990, 1994, 1995, 1998, and 2002 is shown in figure 4. Nondetections are plotted at the reporting limit of 0.05 μ g/L. The use of atra

zine and c y anazine was approximatel y the same in 1989 and 1995; however, the median concentrations of both herbicides were higher in 1989 than in 1995 or 2002. Although herbicide concentrations in Midwestern st reams are quite variable during post-application runoff, the data suggest that changes in herbi

cide use do affect herbicide con centrations in streams (Battaglin and Goolsb y , 1999; Scribner and others, 2000a). Studies during 1998 and 2002 of surface water inthe Midwestern United States confirmed that herbicide degradation products were found to occur as frequentl y or more frequentl y and at concentrations 1990 0 10 20 30 40 50 60Herbicide use, in million pounds per year

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Atrazine

Cyanazine

Simazine
Fig ur e 2. T r iazine he r bi c ide use in the Midweste r n United S tates, 1990 t o 2002 (data f r om U. S . Depa rtment of Ag r i c ultu r e, 1991–2003).Wate r -Q u ality St u dies 5

EXPLANATION Drainage area sampled in 1989 Drainage area of site sampled in 1990, 1994, 1995, 1998, 2002 Stream sampling site Base from U.S. G eological Survey digital data,1:2,000,000, 1972 Albers Equal-Area C onic Projection Standard Parallels 39°30’ and 43°30’, central median -90°30’ 40° 45° 95° 85°

0 100 200 MILES 0 100 200 KILOMETERS

Fig ur e 3. Lo c ation of study a r ea, hyd r ologi c units, and 147 sites sampled du r ing 1989–2002 in the Midweste r n United S tates.

that were frequentl y higher than the parent herbicides (Battaglin and others, 2003, 2005; Scribner and others, 2003). In the summer of 1993, a persistent wet-weather pattern resulted in flooding in the upp er Mississippi River Basin. Con

centrations of selected herbicides were measured at several locations on the Mississippi River during this flood and in adja

cent shallow wells after the floo dwaters receded. These studies determined that record flooding did not dilute the concentra

tions of herbicides as expect ed. Instead, con centrations of herbicides such as atrazine were si milar to those seen during normal spring and summer flows (Goolsb y and others, 1993; Kolpin and Thurman, 1995). Surface-water reservoirs in the Midwestern United States were also the focus of USGS studies as the y are an integral component of the suppl y , management, and quality of water resources in the United States. Man y reservoirs are designed to catch and retain spring and earl y summer runoff for recreation, water suppl y , flood control, or irrigation use. Regional studies have shown that this water contai ns elevated concentrations of herbicides and their degradation products for several months of the y ear (Leonard, 1988; Baker and Richards, 1989; Pereira and Rostadt, 1990; Thurman and ot hers, 1991, 1992; Squillace and Thurman, 1992; Goolsb y and others, 1996; Battaglin and Goolsb y , 1998). USGS designed a monitoring network of 76 h y drologicall y representative reservoirs (fig. 5) in the Mid

western United States described in Scribner and others (1996). Reservoir outflows were sampled eight times from April 1992 through September 1993 for a total of 608 samples. The timing6 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

and frequenc y of sampling made it possible to determine approximatel y when maximum and mini mum concentrations of herbicides occurred in the reservoir outflows (Stamer and oth

ers, 1998a). One of the most significant findings from this stud y is the abundance and persistence of triazine herbicides and their deg

radation products in reservoirs. In man y reservoirs, concentra

tions of atrazine and its degrad ation products remained elevated all summer and into the fall (Stamer and Zelt, 1992; Thurman and Fallon, 1996; Stamer and others, 1998a). As shown in table 3, atrazine occurred at the highest frequenc y (82.1 per

cent) and in the highest detectable concentration with a mean of 1.36 μg/L, whereas c y anazine was detected in onl y 47.2 percent of samples with a mean detectab le concentration of 0.61 μg/L (Stamer and others, 1998a). As reported b y Goolsb y and others (1996), atrazine, deeth

y latrazine, and deisoprop y latrazine were detected in more than one-half of the reservoirs during the fall sampling, whereas onl y atrazine was detected in more than one-half of the streams sam

pled in the fall of 1989. Another notable difference between the occurrence of herbicides in re servoirs and streams was the much greater frequenc y of detection of c y anazine and deisopro

p y latrazine in reservoirs. Neither c y anazine nor deisoprop y la

trazine was detected in stream s during the fall because these compounds were no longer present in significant amounts on the agricultural fields where the y were applied. A detailed study of Perry Lake in northeast Kansas (fig. 5) was completed during 1992–93 b y Fallon and others (2002). Water samples were collected monthl y from four locations upstream and downstream from the reservoir, as well as within the reservoir throughout the y ear and from runoff during April to August (Thurman and Fallon, 1996; Fallon and others, 2002). Three-dimensional images of the distribution of atrazine concentrations in Perry Lake during 1992 showed that recentl y applied atrazine mixed with atrazine applied the previous y ear as water moved through the re servoir (fig. 6). Relations between atrazine and the degradation product, deeth y latrazine, indicated whether the atrazine inthe reservoir had been flushed off the fields immediatel y prior to sampling or from the preced

ing y ear. Changes in atrazine con centrations in the reservoir resulted from several factors, including herbicide application, which fueled and reset the s y stem, and precipitation, which drove the s y stem b y flushing atrazine into the reservoir and determining the residence time of water in the reservoir. Con

centrations varied between the main inflow and the public water suppl y intakes located at the opposit e ends of the reservoir. The concentration range in the outflow varied much less than con

centrations in the upstream part s of the reservoir because of mixing (Fallon and others, 2002). The frequenc y of occurrence, con centrations, both annual average and peak, and loads of pes ticides in streams or reservoir outflows is related to the magnitude of the herbicide use in the upstream drainage areas. In mostcases, the annual loss of her

bicides to streams represents less than 5 percent of the amount applied. Pesticide losses are also affected b y soils, climate, land cover, other basin characteristics, and management or applica

tion techniques. These studies de monstrate the strength of rela

tions between the use of herbic ides and their occurrence in streams and reservoirs (Battaglin and Goolsb y , 1995, 1997, 1998; Clark and others, 1999; Clark and Goolsb y , 2000). 

## G ro un d Wate r During the 1990s, the Midweste rn United States was also the focus of research on agricultu ral chemical contamination in ground water. A series of studies b y USGS began in 1991 to investigate the occurrence of ag ricultural herbicides in nearsurface aquifers of the Midwestern United States. To improve understanding of the movement and distribution of agricultural chemicals in ground water, USGS designed (Kolpin and Burkhart, 1991) a reconnaissance network that was geographi

call y and h y drogeologicall y representative of near-surface aquifers in the corn- and so y bean-producing region of the Mid

western United States (Burkart and Kolpin, 1993; Kolpin and others, 1994, 1996b; Thurman and others, 1998). The objectives of the study were to determine the h y dro

geological and seasonal distribution of herbicides in nearsurface aquifers, determine the statistical relations of agricultural herbicides to natural factors, and obtain data on agricultural herbicide concentrations in ground water from geo

graphic areas where few data existed (Burkart and Kolpin, 1993; Kolpin and others, 1994, 1996a). The report that sets the stage for these studies is Kolpin and others (1993a), which describes locations, detailed land use, and local features sur

rounding 303 wells sampled in the Midwestern United States during 1991 (fig. 7). During the summer of 1992, additional water samples were collected from 101 of the 303 wells to Table 2. Pe rc entage of dete c tions of t r iazine he r bi c ides and deg r adation p r odu c ts in su r fa c e-wate rsamples c olle c ted f r om sele c ted st r eams in the Midweste r n United S tates du r ing 1989 and 1990 (f r om Thu r man and othe r s, 1991). [n= total number of samples anal y zed; <, less than]

T r iazine c ompound Pe rc entage of dete c tions P r eappli c ation

samples

(n=53) Postappli c ation

samples (n=132) Ha r vest samples (n=145) Pa r ent c ompound Atrazine 91 98 76 C y anazine 5 63 0 Propazine 0 40 <1 Simazine 7 55 3 Deg r adation p r odu c t Deeth y latrazine 54 86 47 Deisoprop y latrazine 9 54 0Wate r -Q u ality St u dies 7198919901994199519982002200219891990199419951998 0.01 0.10

1.0 10 100 1,000

Atrazine Cyanazine198919901994199519982002198919901994199519982002

0.01 0.10

1.0 10 100

Propazine Simazine1994199519982002198919901994199519982002198919901994199519982002 0.01 0.10

1.0 10 100

Cyanazine amide Deethylatrazine Deisopropylatrazine 

### A. Atrazine and cyanazine

B. Propazine and simazine

C. Cyanazine amide, deethylatrazine, and deisopropylatrazineConcentration, in micrograms per liter EXPLANATION O u tlier more than 95th percentile

O u tlier less than 5th percentile 95th percentile 75th percentile

Median 25th percentile 5th percentile

Fig ur e 4. Con c ent r ations in su r fa c e-wate r samples c olle c ted f r om 53 Midweste r n st r eams du r ing post-appli c ation r unoff in 1989, 1990, 1994, 1995, 1998, and 2002 fo r (A) at r azine and c yanazine, ( B) p r opazine and simazine, and (C) c yanazine amide, deethylat r azine, and deisop r opylat r azine (data fo r1989–98 f r om Scr ibne rand othe r s, 2000a; data fo r2002 f r om Battaglin and othe r s, 2003).

examine the occurrence of triazineherbicides and their degrada

tion products not anal y zed in 1991 (Kolpin and others, 1993b, 1995). Herbicides and their degradation products were detected in water samples from 28.4 percent of the 303 wells sampled during 1991. During 1992, herbicides and their degradation products were detected in 62 percent of the 101 wells sampled. The greater frequenc y of detection during 1992 was due prima

ril y to the increased number of herbicide degradation products examined and a more sensitive anal y tical method that was avail

able (Kolpin and others, 1993b, 1995, 1996b). Although numerous studies were conducted during the earl y 1990s to investigate the o ccurrence of herbicides in ground water, few had considered the degradation products of these herbicides. Information on degradation products is essen

tial to full y understand the fate and occurrence of the parent herbicides and to determine the complete consequences of her

bicide use on human health and the environment (Kolpin and others, 1995). Triazine degradation products, deeth y latrazine and deisoprop y latrazine, commonl y were found in shallow aquifers across the Midwestern United States. As shown in table 4, during 1991, deethy latrazine (21.4 percent) was detected more frequentl y than its parent compound atrazine (20.8 percent) even though deeth y latrazine had a higher report

ing limit than atrazi ne, whereas deisoprop y latrazine was8 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

Table 3. T r iazine he r bi c ides and thei rdeg r adation p r odu c ts analyzed in samples c olle c ted f r om 76 Midweste r n r ese r voi r outflows, Ap r il 1992 th r ough S eptembe r1993 (f r om S tame rand othe r s, 1998a). [μg/L, micrograms per liter; n, number of samples; <, less than]

He r bi c ide o rdeg r adation p r odu c ts Repo rting limit (μg/L) Pe rc entage of samples with

dete c tions Median c on c ent r ations (μg/L) Mean of samples with dete c table c on c ent r ations (μg/L) He r bi c ides (n=608) Atrazine 0.05 82.1 0.43 1.36 C y anazine .05 47.2 <.05 .61 Propazine .05 4.1 <.05 .10 Simazine .05 19.7 <.05 .21 He r bi c ide deg r adation p r odu c ts (n=511) C y anazine amide .05 49.3 <.05 .43 Deeth y latrazine .05 71.6 .17 .39 Deisoprop y latrazine .05 61.8 .08 .26 Deeth y lc y anazine .05 25.2 <.05 .14 Deeth y lc y anazine amide .05 2.0 <.05 .62 100 0 0 100 200 KILOMETERS 200 MILES Base from U.S. G eological Survey digital data 1:2,000,000, 1972 Albers Equal Area C onic Projection Standard Parallels 39 ° 30' and 43 ° 30', central meridian -90 ° 30' Iowa North Dakota

South Dakota

Nebraska

Kansas Perry Lake site Missouri Minnesota CANADA

Michigan Michigan

Ohio Indiana Illinois

37° 43 ° 49° 100 ° 94°

88 °

82 ° Wisconsin

Fig ur e 5. Lo c ation of 76 r ese r voi r s sampled fo rhe r bi c ide analysis in the Midweste r n United S tates du r ing 1992 and 1993 (f r om Scr ibne rand othe r s, 1996).

detected in 7.6 percent of the sa mples. In 1992 (table 4), deeth

y latrazine was detected in 31 per cent, atrazine in 43 percent, and deisoprop y latrazine in 18 percent of the samples collected. The reporting limits for atrazine and deeth y latrazine were lower in 1992 than in 1991. The fact that deeth y latrazine was detected more frequentl y than deisoprop y latrazine supports conclusions from field-dissipation studies during the 1990s that deeth y lation is the more stable, biotic degradation pathway (Adams and Thurman, 1991; Kolpin and others, 1994). C y anazine was used extensivel y during the earl y 1990s but was detected in onl y 1.3 percent of the water samples in 1991 and 3.0 percent of the water samples in 1992 (table 4). A method for c y anazine amide, a degr adation product of c y ana zine, was used to anal y ze water samples collected during 1992.Wate r -Q u ality St u dies 9

(A) Pre-application survey, March 30 to April 10, 1992 (B) First flush survey, June 16 to 25, 1992

(C) Summer survey, August 3 and 4, 1992

(E) Pre-application survey, March 25 to 29, 1993 (D) Fall survey, September 16 to 22, 1992

Greater than 15 10 to 15 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Less than 0.5 Triazine concentration, in micrograms per liter EXPLANATION

Fig ur e 6. Th r ee-dimensional c ompute rimages of at r azine c on c ent r ations in Pe rr y Lake, no rtheaste r n Kansas, du r ing (A) 1992 p r e-appli c ation, (B) fi r st flush, (C) summe r , (D) fall, and (E) 1993 p r e-appli c ation su r veys (f r om Fallon and othe r s, 2002).10 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

Table 4. S umma r y of analyti c al r esults fo rt r iazine he r bi c ides and thei rdeg r adation p r odu c ts in g r ound-wate rsamples c olle c ted f r om wells in the Midweste r n United S tates du r ing 1991–93 (f r om Kolpin and othe r s, 1993b, 1994; Kolpin and Thu r man, 1995).

[μg/L, micrograms per liter; NA, not applicable]

T r iazine c ompound 1991 1992 1993 Pe rc entage of dete c tion Maximum c on c ent r ation (μg/L) Repo rting limit (μg/L) Pe rc entage of dete c tion Maximum c on c ent r ation (μg/L) Repo rting limit (μg/L) Pe rc entage of dete c tion Maximum c on c ent r ation (μg/L) Repo rting limit (μg/L) Pa r ent c ompound Atrazine 20.8 2.1 0.05 43.0 1.0 0.005 23.6 1.8 0.05 C y anazine 1.3 .68 .05 3.0 .02 .008 3.6 .88 .05 Simazine 1.6 .27 .05 13.0 .07 .005 NA NA NA Deg r adation p r odu c t C y anazine amide NA NA NA 9.3 .55 .05 NA NA NA Deeth y latrazine 21.4 2.3 .05 31.0 1.8 .015 23.6 1.7 .05 Deisoprop y latrazine 7.6 1.2 .05 18.0 .28 .05 13.6 .48 .05 Base from U.S. G eological Survey digital data 1:2,000,000, 1972 Albers Equal Area C onic Projection Standard Parallels 39 ° 30' and 43 ° 30', central meridian -90 ° 30' Iowa North Dakota

South Dakota

Nebraska

Kansas Missouri Minnesota CANADA

Wisconsin Michigan Michigan

Ohio

Indiana Illinois

37 ° 43 ° 49 °

100 0 0 100 200 KILOMETERS 200 MILES 100° 94 °

88°

82°

Fig ur e 7. Lo c ation of wells in the U. S . Geologi c al S u r vey Midweste r n g r ound-wate rmonito r ing netwo r k sampled du r ing 1991–94 (f r om Kolpin and othe r s, 1995).

As shown in table 4, c y anazine amide was detected in 9.3 percent of the samples with a maximum concentration of 0.55 μg/L (Kolpin and others, 1995). This greater frequenc y of detection suggests an increase in degradation product mobility to ground water after transformation from c y anazine. C y ana zine may degrade to deisoprop y latrazine b y the loss of a c y anoisoprop y l group (Me y er, 1994; Thurman and others, 1994; Me y er and others, 2001). Simazine was detected in 1.6 percent of the samples in 1991 and 13 percent in 1992 (table 4). A study b y Mills and Thurman (1994a) showed that atrazine, c y anazine, and simazine also can degrade to deisopro

p y latrazine. The dealky lation of simazine to deisoprop y latra

zine contributes to the amount of deisoprop y latrazine as it may degrade b y two pathway s to deisoprop y latrazine (Mills and Thurman, 1992). Water samples were collectedduring September and Octo

ber from 110 wells during the historic 1993 flooding in the Mississippi River Basin (Goolsb y and others, 1993; Kolpin and others, 1996b). There was a direct relation between increases in total herbicide concentration (between pre-flood and post-floodWate r -Q u ality St u dies 11 samples) and the occurrence of stream flooding near wells (Kolpin and Thurman, 1995; Kolpin and others, 1996b). More than 60 percent of the wells that had at least a 20-percent increase in total herbicide concentration in water samples were located in areas that alsowere affected extensivel y b y stream flooding. Water in shallow wells more quickl y reflected changes in water quality in response to changes in recharge from the 1993 flooding than did deeper wells (Kolpin and oth

ers, 1996b). Of the 110 wells sampled, 30 were reported to be unaffected b y flooding or intense rainfall, 45 were affected b y stream flooding, and another 35 were affected b y standing water from rainfall. Results from these samples were compared with those samples obtained during 1991 and 1992 from the same wells. As shown in table 4, there was no statisticall y significant differ

ence in either the frequenc y of herbicide detection or total her

bicide concentration between the previous samples and those collected for the 1993 stud y (Kolpin and Thurman, 1995). An additional stud y during Jul y to August 1994 of samples col

lected from 38 wells showed thatherbicides and their degrada

tion products were detected in water from 76 percent of the wells (Kolpin and others, 1996b). An investigation of samples collected from 131 municipal wells completed in all the major aquifer ty pes in Iowa (fig. 8) from 1995 to 1998 was made to compare the occurrence of her

bicide degradation products in ground water with that of their parent compounds. An important finding of this stud y was the high frequenc y with which degradation products were detected in ground water (Kolpin and others, 1997, 1998, 2000). During 1995, more than one herbicide compound was detected in sam

ples from 44 of the wells, with as man y as nine compounds being detected in a single sample (Kolpin and others, 1997). Table 5 summarizes anal y tical results from 1995 through 1998. Atrazine is the onl y herbicide for which the parent compound was found more often than an y of its degradation products. This could be because of the gr eater environmental stability of atra

zine compared to the other parent compounds under investiga

tion. Although herbicides commonl y were detected, their frequencies of detection and concentrations varied significantl y among the major aquifer ty pes samples. These differences were much more pronounced when herbicide degradation products were included (Kolpin and others, 2000). Aquifer ty pes pre sumed to have the most rapid recharge rates were those most likel y to contain detectable concentrations of herbicides, indi

cating that ground-water age coul d be an important factor in explaining these variations in herbicide contamination (Kolpin and others, 2000). This stud y demonstrated that obtaining data on herbicide degradation products is critical for understanding the fate of herbicides in the hy drologic s y stem (Kolpin and others, 2000). A large-scale investigation of the occurrence of c y anazine and its degradation products, c y anazine acid, c y anazine amide, deeth y lc y anazine, and deeth y lc y anazine acid in samples from 64 Iowa wells was conducted during 1999. C y anazine was detected in onl y 3.1 percent of wells sampled. but its degrada

tion products were commonl y detected, deeth y lc y anazine acid (32.8 percent), followed b y c y anazine acid (29.7 percent), c y anazine amide (17.2 percent), and deeth y lc y anazine (3.1 per

cent) (Kolpin and others, 2001). The more frequent presence of c y anazine acid and c y anazine amide compared to c y anazine is in agreement with the re ported greater stability of these degra

dation products after transformation from c y anazine (Ferrer and others, 2000; Kolpin and others, 2001). Thus, the results of the stud y emphasized that data on the c y anazine degradation prod

ucts are critical for understanding its fate and transport in the h y drologic s y stem (Kolpin and others, 2001). As a continuation of the Iowa stud y , ground-water wells were sampled and anal y zed for 21 herbicides and 24 herbicide degradation products during 2001. The frequenc y of detection increased from 17 percent when onl y herbicide parent 96°

43°

42°

41° 95° 94° 93° 92°

91°

50 0 0 50 100 KILOMETERS 100 MILES Iowa

EXPLANATION W ell samp led du rin g 1995−98 Fig ur e 8. Lo c ation of wells sampled in Iowa du r ing 1995–98 (f r om Kolpin and othe r s, 2000). Table 5. S umma r y of analyti c al r esults fo rt r iazine he r bi c ides and thei rdeg r adation p r odu c ts in samples c olle c ted f r om 131 Iowa wells du r ing 1995–98 (f r om Kolpin and othe r s, 2000). [μg/L, micrograms per liter]

T r iazine c ompound Pe rc entage dete c tion Maximum c on c ent r ation (μg/L) Repo rting limit (μg/L) Pa r ent c ompound Atrazine 37.4 2.1 0.05 C y anazine 6.1 .51 .05 Simazine 0 0 .05 Propazine 0 0 .05 Deg r adation p r odu c t C y anazine amide 19.8 .64 .05 Deeth y latrazine 32.1 .59 .05 Deisoprop y latrazine 21.4 1.1 .05 H y drox y atrazine 11.4 1.3 .2012 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts compounds were considered to 53 pe rcent when both herbicide parent compounds and degradation products were considered. A significant difference in resu lts among the major aquifer ty pes was apparent when both herbicide parent compounds and their degradation products were considered (Kolpin and others, 2004). The ground-water samples collected across the Midwest

ern United States and in Iowa from 1991 through 2001 consis

tentl y revealed that triazine he rbicide degradation products commonl y were found more frequentl y than their parent herbi

cide, the frequenc y of herbicide detection was, in part, affected b y a more sensitive anal y tical method, and ground-water age could be an important factor in explaining variations in herbi

cide contamination (Kolpin and others, 1994, 1996a, 2000, 2004). 

## P recipitatio n During the late spring and summer of 1990 and 1991, another USGS stud y focused on herbicides transported in the atmosphere b y various processes. In the atmosphere, these com

pounds can be dispersed b y air currents and redeposited on the land surface, lakes, and streams b y rainfall, snow, and dry dep

osition, often at considerable di stances from their source areas. Triazine herbicides were reported in precipitation in the Mid

western United States b y Goolsb y and others (1997), which highlighted the major findings of this stud y . The report that describes the location of the stud y area, background areas, and sampling sites is Goolsb y and others (1995). Herbicide concentrations exhibited distinct geographic and seasonal patterns. The highes t concentrations occurred in the Midwestern United States following herbicide application to cropland. The highest concentr ations occurred following her

bicide application to cropland. Rainfall-weighted concentrations of 0.20 to 0.40 μ g/L for atrazine were ty pical throughout the Midwest, and weighted concentrations as large as 0.60 to 0.90 μ g/L occurred in precipitation at several sites. Concentrations of 1.0 to 3.0 μ g/L were measured in a few indi

vidual samples. Atrazine was det ected most often, followed b y deeth y latrazine, c y anazine, and deisoprop y latrazine. Table 6 contains a summary of the concentrations of triaz

ine herbicides detected in 6,2 30 precipitation samples screened b y enz y me-linked immunosorbent assay and then confirmed in 2,085 of the samples using gas chromatograph y/mass spectrom

etry (Pomes and others, 1998). The most frequentl y detected herbicide was atrazine, which was present in 30.2 percent of the samples anal y zed b y gas chromatograph y /mass spectrometry , followed b y deeth y latrazine at 17.4 percent. C y anazine was detected in 7.2 percent of the samples. Although herbicides were detected in a significan t number of samples, concentra

tions were relativel y small (Goolsb y and others, 1997; Stamer and others, 1998b; Thurman and Cromwell, 2000). Because of the large temporal and spatial variation in the amount of rainfall, it is difficult to make meaningful compari

sons of herbicide concentrations among sites or over time on the basis of individual samples. Instead, comparisons were made with rainfall-weighted concentrations. Overall, the spatial pat

terns of the weighted atrazine concentrations in 1990 and 1991 were similar and generall y reflected the intensity of the use of atrazine. The total amount of atrazine deposited annuall y in pre

cipitation in the stud y area represented about 6 percent of the atrazine applied annuall y to crops in the stud y area (Goolsb y and others, 1997). The stud y showed that the occurrence of atrazine in rain

fall is highl y seasonal. The detection frequenc y began to increase in mid-April following application of herbicides to cropland and peaked in late Ma y or earl y June. Atrazine was detected in low concentrations at sites remote from cropland, such as Maine and Isle Ro y ale in northern Lake Superior (Stamer and others, 1998b; Thurman and Cromwell, 2000).

Table 6. S umma r y of analyti c al r esults fo rt r iazine he r bi c ides and thei rdeg r adation p r odu c t c on c ent r ations measu r ed in p r e c ipitation samples f r om 81 sites a cr oss the Midweste r n and No rtheaste r n United S tates f r om Ma rc h 1990 th r ough S eptembe r1991 (f r om Goolsby and othe r s, 1997). [ELISA, enz y me-linked immunosorbent assay ; GC/MS, gas chromatograph y/mass spectrometry ; n, total number of samples anal y zed; μg/L, micrograms per liter; <, less than; --, not determined]

T r iazine c ompound Pe rc entage of dete c tions Con c ent r ation ( μ g/L) fo rindi c ated pe rc entiles 1

1 Reporting limits are 0.10 μg/Lfor triazine compounds anal y zed b y ELISA and 0.05 μg/L for all compounds anal y zed b y GC/MS. 75th 90th 95th 99th 100 (maximum) ELI S A analysis (n=6,230) Triazine compounds 25.5 0.10 0.24 0.42 1.3 16 GC/M S analysis (n=2,085) Atrazine 30.2 .07 .23 .40 1.0 11 C y anazine 7.2

-- <.05 .07 .27 2.0 Deethy latrazine 17.4 <.05 .11 .15 .39 .75 Deisoprop y latrazine 2.6

-- -- <.05 .17 1.2 Simazine 1.5

-- -- <.05 .07 1.5Chemist r y a n d T r a n spo rt of T r iazi n e He r bicides i n Wate r13 

# Chemistr y a n d Tr a n spo r t of Tr iazi n e He rbicides i nWate r Degradation pathway s may be followed from herbicide application on the soil to its en trance into an aquifer. These deg

radation pathway s depend on the characteristics of the transport pathway (Adams and Thurman, 1991). Herbicides derived from point and nonpoint sources can be transported to streams b y runoff from agricultural and urban areas, discharge from reser

voirs and aquifers, and precipitation (Goolsb y and others, 1993). The ph y siochemical properties of the triazine herbicides as well as the soil half-lif e and such factors as intensity of use, application methods, timing, intensity , duration of rainfall, and antecedent soil moisture conditions are also important in deter

mining the amount of herbicides that can be transported into streams. Ph y siochemical properties sh own in table 7 indicate that soluble and mobile herb icides, such as atrazine, c y anazine, propazine, and simazine are transported primaril y in the dis

solved phase. Water solubility determines how easil y herbicides wash off soil and crop residues and leach through the soil. Herbicides with solubilities greater than about 30 mg/L are likel y to wash off the soil, whereas those with solubilities less than 1 mg/L are likel y to remain on the soil su rface during storms (Becker and others, 1989). The soil sorption coefficient (K oc ) is a measure of the tendenc y of a herbicide to sorb to soil particles. The larger the K oc value, the more strongl y the herbicide will be adsorbed to soil particles. Those herbicides with K oc values less than about 500 mL/g tend to be transported primaril y in the dissolved phase, whereas K oc values greater than 1,000 mL/g are trans

ported primaril y on suspended-sediment particles (Becker and others, 1989; Goolsb y and others, 1993). Half-life in soil is the length of time required for herbicides to degrade in the soil to one-half of their previous con centration. The longer the soil half-life, the more persistent the herbicide is, and the longer it will be available to wash off in storm runoff. Once herbicides are in surface water, the half-life generall y is much longer than in soil because surface water contains much less organic matter and fewer microorganisms to de grade the herbicides (Goolsb y and others, 1993). The water solubility of deeth y latrazine is 670 mg/L and for deisoprop y latrazine is 3,200 mg/L. The water solubilities of triazine degradation products increase as carbon atoms are removed b y dealkl y ation (Mills and Thurman, 1994a). The result is that the degradation products are more sol

uble and mobile than the parent compound. A stud y of selected triazine herbicides and their degrada

tion products was designed to define the relative rates and trans

port mechanisms of four parent triazine herbicides—atrazine, c y anazine, propazine, simazine—andtwo triazine degradation products—deeth y latrazine and deisoprop y latrazine—in the unsaturated zone and in surface runoff (Me y er, 1994; Mills and Thurman, 1994a; Thurman and others, 1994; Me y er and Thur

man, 1996). This choice of parent herbicides was used because each degradation product had two parent herbicide sources, each source requiring the removal of either an ethy l or an isoprop y l side chain. As shown b y figure 9, atrazine and pro

pazine degrade to deeth y latrazine b y deeth y lation and deisopro

p y lation. Similarl y , atrazine, c y anazine, and simazine can all dealky late to deisoprop y latrazine b y removal of an isoprop y l and eth y l side chain. Differences inthe concentration of the dealky lated degradation product fromthe two different sources should indicate an y preferential removal of eth y l versus isopro

p y l side chain. Furthermore, because deeth y latrazine and deiso

prop y latrazine have different side chains remaining, their relative rate of removal should provide additional information on the stability of the eth y l side chain versus an isoprop y l side chain (Thurman and others, 1994). The dealky lation field study found the preferential removal of an eth y l side chain from atrazine relative to the removal of an isoprop y l side chain. The high ratio of deeth y la

trazine to atrazine, referred to as the DAR, in shallow soil is evidence that simazine may degrade more rapidl y to deisopro

p y latrazine (eth y l side chain removal) than propazine to deeth

y latrazine (isoprop y l side chain removal). Furthermore, deeth y lation rates of atrazine and simazine are comparable, and approximatel y two to three times more rapid than the rates of deisoprop y lation from atrazine and propazine. This indicates that the removal of an eth y l side chain is pref erential over an isoprop y l side chain, regardless of parent triazine compound. Continued dealky lation of the degradation products in the unsaturated zone, where the parent compound is removed, also shows a preferential removal of eth y l side chains over isoprop y l side chains, as deisoprop y lation can occur to a significant

Table 7. Physio c hemi c al p r ope rties of t r iazine he r bi c ides (f r om Goolsby and othe r s, 1993). [mg/L, milligrams per liter; mL/g , milliliters per gram; pKa, negative logarithm of the acid dissociation constant; mPa, millip ascal]
T r iazine he r bi c ide Wate rsolubility (mg/L) S oil so r ption c oeffi c ient (K o c , mL/g) pKa S oil half-life (days) Vapo rp r essu r e (mPa) Atrazine 33 100 1.7 60 0.04 C y anazine 170 190 1.7 14 .0002 Propazine 5 154 1.7 45 .004 Simazine 6.2 138 1.6 75 .00081014 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

N
N N
NH Cl

C 2 H 5 NH C 2 H 5 

### Simazine Cyanazine N
N N
NH Cl

C 2 H 5 NH C CH 3 CH 3 C N C N
N N
NH Cl

H NH CH CH 3 CH 3 2 5 

### Atrazine N
N N
NH Cl

CH NH CH CH 3 CH 3 CH 3 CH 3


### Propazine

N
N N
NH Cl

C 2 H 5 NH 2 

### Deisopropylatrazine (DIA) N
N N
NH 2 Cl

NH CH CH 3 CH 3 

### Deethylatrazine (DEA) Fig ur e 9. Deg r adation pathways fo rat r azine, c yanazine, p r opazine, and simazine to deethylat r azine and (o r ) deisp r opylat r azine (f r om Thu r man and othe r s, 1994). degree in the unsaturated zone. Therefore, the small concentra

tions of deisoprop y latrazine commonl y reported in the environ

ment do not result purel y from a smaller production of the degradation product but also to the more rapid removal of the isoprop y l group once produced. The substantial turnover rate of deisoprop y latrazine in the environmen t is evidence for the pres

ence of a didealk y lated degradation product in the unsaturated zone. The data supporting these conclusions are presented in Mills and Thurman (1994a). To understand the geochemistry of the deeth y latrazine-toatrazine ratio (DAR) as an indicator of su rface-water and ground-water interaction, it is valuable to compare the degrada

tion product deeth y latrazine to atrazine. The resulting ratio is called the DAR and is defined b y Adams and Thurman (1991): . (1) The DAR may be a valid indicator of soil-mediated trans

port of atrazine to an aquifer. A DAR of unit y (1.0) or greater could be an indicator of nonpoint-source contamination of an aquifer (Adams and Thurman, 1991), whereas a small DAR may be an indicator of point-source contamination of an aqui

fer. In clay - and silt-loam plots, the average concentrations of atrazine in the soil were about four times higher than the aver

age concentrations of deeth y latrazine. The concentrations of deeth y latrazine, however, were significantl y higher than the concentrations of atr azine in soil-water l y simeter samples col

lected at about the same time as the cores were collected (Adams and Thurman, 1991). Th ese results indicate that atra

zine is absorbed more strongl y than deeth y latrazine in clay - and silt-loam soils. Thus, the recharging ground water has a higher concentration of deeth y latrazine than atrazi ne giving rise to DAR values greater than 1.0 (Adams and Thurman, 1991). The conversion of atrazine to deeth y latrazine is primaril y the result of the metabolic activity of soil bacteria and fungi. In the case of nonpoint-source cont amination, soil microorgan

isms can convert sign ificant quantities of atrazine to deeth y la

trazine, thereb y increasing the DAR. Conversel y , point-source contamination resultin g from direct entry of atrazine into an aquifer b y a natural or artificial conduit would not involve prolonged contact of the applied atr azine with soil microorgan

isms. In such a point-source-co ntamination occurrence, soil microorganisms would have little opportunity to degrade to deeth y latrazine. Therefore, in th e case of point-source contam

ination, the DAR may be expected to be much less than unity ; that is, the concen tration of deeth y latrazine would be less than that of atrazine in the aquifer (Adams and Thurman, 1991). The DAR h y pothesis is predicated on the assumption that atrazine degrades slowl y in an aquifer because of low organic carbon concentrations, small mi crobial populations, and anaer

obic conditions. This is substantiated b y Wehtje and others (1983) who determined that, under aquifer conditions, atrazine did not undergo deeth y lation or deisoprop y lation and onl y slowl y underwent abiotic degradation to deisoprop y lh y drox y atrazine. Adams and Thurman (1991) foundthat atrazine transport through the unsaturated zone gaveDAR values greater than 1.0, whereas atrazine transported off the field b y surface runoff had DAR values much less than 1.0. Deisoprop y latrazine was rap

idl y degraded in the unsaturated zone but was an important per

sistent degradation product in surface runoff fromthe fields. Thus, the DAR may be an indicator of ground-water recharge b y atrazine-laden water. Figure 10 shows that the DAR deethylatrazine, mol/L [ ] atrazine, mol/L [ ] ---------------------------------------------------------- =Chemist r y a n d T r a n spo rt of T r iazi n e He r bicides i n Wate r15
Pre-application DAR = 0.3 Deisopropylatrazine = 9 percent detections

Harves

Land surface Land surface Land surface

t DAR = 0.4 Deisopropylatrazine = 0 percent detections

Post-application DAR = less than 0.1 Deisopropylatrazine = 54 percent detections SW input (small)

SW input (small) SW inpu t (large) G W input (large)

G W input (large) G W

G W G W

SW SW Stream

Stream

Stream 

### EXPLANATION W ater table Gro u nd w ater S u rface w ater

Fig ur e 10. Deethylat r azine-to-at r azine r atios (DAR) fo rsu r fa c e- and g r ound-wate rsamples f r om Midweste r n United S tates (f r om Thu r man and othe r s, 1992). pre-application samples had a high DAR of 0.3 but also con

tained a few detections of deisoprop y latrazine (9 percent). These results suggest both a surface-water and a ground-waterorigin of herbicides during this sampling period. The postapplication samples collected during this period had a low DAR (less than 0.1) and the highest number of detections of deisopro

p y latrazine (54 percent), which indicate that surface runoff was the major contributor of herbicides. Finall y , the post-harvest sampling during low streamflow had the highest DAR of 0.4 and detections of deisoprop y latrazine, which indicate that allu

vial ground water was likel y the major source of herbicide (Thurman and othe rs, 1992). Following the surface-water reconnaissance of Midwestern streams, Thurman and others (1992) reported DAR values less than 0.1 in streams shortl y after herbicide application, whereas DAR values generall y were 0.3 or higher in the fall at harvest during base-flow conditions. As shown b y figure 11, the median DAR values obtained from USGS ground-water reconnaissance for both sampling periods were about 0.7. The DAR ranged from about 0.1 to 8.4. These results indicate that most of th e atrazine detected in ground water was derived from nonpoint sources and had infiltrated the soil slowl y (Kolpin and others, 1994). Further field-dissipation studies of atrazine and c y anazine demonstrated that about 6 percen t of the atrazine degraded to deeth y latrazine and about 3 per cent degraded to deisoprop y la

trazine (Adams and Thurman, 1991; Mills and Thurman, 1994a). C y anazine degraded onl y to the common degradation product, deisoprop y latrazine. Thus, the ratios of deisoprop y la

trazine to deeth y latrazine (D 2 R) and atrazine to c y anazine (ACR) were used to differentiate the nonpoint source of deiso

prop y latrazine to surface water. Me y er and others (2001) successfull y tested the D 2 R discrimination diagram in two basins with very different application rates of atrazine and c y anazine to check the validity of the D 2 R. The D 2 R also was used to show that c y anazine contributed a considerable amount (40 percent) of the deisoprop y latrazine that was transported during flooding of the Mississippi River in 1993. The D 2 R is a useful water-quality monitoring tool to measure nonpointsource contributions of deisoprop y latrazine (Me y er and others, 2001). A regional study of nine streams in the Midwestern Corn Belt confirmed that deeth y latrazine and deisoprop y latrazine occur frequentl y in surface water that has received storm runoff containing two parent triazine herbicides, atrazine and c y ana zine (Scribner and others, 1994; Pomes and others, 1996). The concentrations of deethy latrazine and deisoprop y latrazine in surface water varied with the h y drologic conditions of the basin and the timing of runoff, with maximum concentrations16 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

34 44

114 69 50

10 5.0

1.0
0.50

0.05

0.01 0.10Pre-applicationPost-applicationPost-applicationHarvest G round-water reconnaissance Surface-water reconnaissanceRatio of deethylatrazine to atrazine concentration EXPLANATION N u mber of samples 90th percentile
75th percentile
Median 25th percentile 10th percentile 34

Fig ur e 11. Deethylat r azine-toat r azine r atios (DAR) fo rsu r fa c eand g r ound-wate rsamples f r om Midweste r n United S tates (f r om Kolpin and othe r s, 1994).
reaching 5 μ g/L (deethy latrazine plus deisoprop y latrazine). Earl y rainfall, followed b y a dry summer, delay ed the maximum concentrations, giving a second flush of triazine degradation products to surface water. Replicatedfield-dissipation studies of atrazine and c y anazine indicated that D 2 Rs varied from 0.4 + 0.1, when atrazine was the ma jor triazine co mpound present, to 0.6 + 0.1 when significant amounts of c y anazine were present. A comparison of transport time of deethy latrazine and deisoprop y latrazine from field plots to their appearance in sur

face water indicated that storag e and dilution were occurring in the alluvial aquifers of the nine stream basins (Thurman and others, 1994). In a study b y Thurman and Fallon (1996), a conceptual model was presented to explain how the DAR could be used to follow runoff through Perry Lake in northeast Kansas (fig. 12 A ). In the model, the reservoir alread y contained water with atrazine and deeth y latrazine present fr om the previous y ear’s runoff. The arrows show th e direction of the flow with the dam at the downstream end of the reservoir. Near the dam, the water has been in the reservoir longer and contains water and herbicides from the previous summer, whereas the upstream water contains herbicides that had entered the reservoir during the fall and winter. Therefore, the DAR values were higher at the upstream e nd of the reservoir. The actual DAR values for each time peri od are shown in figure 12 B . The concept of the DAR proved to be a useful tool in the ability to follow water movement through a reservoir. In the precipitation study described earlier (Goolsb y and others, 1997), deeth y latrazine and deisoprop y latrazine were detected in 17.4 and 2.6 percent, respectivel y , of the samples anal y zed. Deeth y latrazine was present in more than one-half of the samples that contained atrazi ne and was the third most fre

quentl y detected compound. The me dian DAR value calculated for the 352 rainfall samples th at contained both atrazine and deeth y latrazine was 0.5. All of these DAR values were determined for rainfall samples collected from May through Jul y of 1990 and 1991 when the median DAR values for streams in this area were less than 0.1 (Thurman and others, 1992). Considerabl y more deeth y latrazine than atrazine was present in rainfall compared to streams draining the Corn Belt. There are several possible explan ations for this observation. One is that deeth y latrazine evaporates from the soil into the atmosphere faster thanatrazine, resulting in a higher DAR value in rainfall. Another is that the high DAR value in rainfall is from atrazine transformed to deethy latrazine in the atmosphere b y photochemical processes. Thus, it is possible that the high median DAR value of 0.5 in rainfall reflects the photocatal y zed degradation of atrazine in the atmosphere (Goolsb y and others, 1997). Finall y , other important degradation products of atrazine that provide evidence of surface-water/ground-water interac

tion are h y drox y lated atrazine degradation products (HADPs), which include hy drox y atrazine, deeth y lh y drox y atrazine, and deisoprop y lhy drox y atrazine. In general, HADPs are strongl y bound to soil b y two sorption mechanisms , cation exchange and hy drophobic interaction, which occur simultaneousl y . This is referred to as a mixed-mode m odel of sorption as shown in fig

ure 13. Evidence of this model is provided b y chromatographic studies, using solid-phase extraction and reverse-phase liquid chromatograph y, as well as soil-extraction studies that showChemist r y a n d T r a n spo rt of T r iazi n e He r bicides i n Wate r17

0 1 2 3 4 5 KILOMETERS 0 1 2 3 4 5 MILES North Pre-herbicide application 

## (A) Conceptual model

(B) Data from Perry Lake March 1992 pre-application High DAR = 0.22 to 0.29 Low DAR = 0.18 to 0.21 June 1992 post-application High DAR = not present Low DAR = 0.09 to 0.17 Post-herbicide application

Hi g h DARs Lo w DARs Direction of flo w EXPLANATION

Dam

Dam Dam Dam Water with high DARs enters reservoir in pre-application inflow Water with low DARs enters reservoir in post-application runoff, pushing water with higher DARs farther downstream

Fig ur e 12. Con c eptual model and data fo rdeethylat r azine-to-at r azine r atios (DARs) in Pe rr y Lake, no rtheaste r n Kansas, du r ing Ma rc h 1992–Ma rc h 1993 (modified f r om Thu r man and Fallon, 1996, fig. 5).18 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts

the release of HADPs bound b y mixed-mode sorption (Lerch and others, 1997). As shown b y figure 14 A , during runoff conditions, a com

bination of dissolved-phase transport b y surface runoff and desorption from suspended stream sediment is the source of HADPs, whereas during base-flow conditions, the primar y source of HADPs is desorption from bed sediments in the stream, as shown in figure 14B . Dissolved-phase transport of h y drox y atrazine b y surface runoff has been measured directl y in end-of-field samples from a north-central Missouri field treated with atrazine in 1994. Surface runoff from precipitation 6 to 7 day s after atrazine application showed h y drox y atrazine concentrations of 3.3 to 5.4 μ g/L in flow-weighted samples collected throughout the course of the precipitation. Thus, sur

face runoff has the ability to extract or deso rb a fraction of the hy drox y atrazine present in the soil. In addition, continuous monitoring of h y drox y atrazine in Goodwater Creek, also located in Missouri, showed that hy drox y atrazine mass flux was directl y related to streamflow, indicating that increased hy drox y atrazine mass flux during runoff resulted from dis

solved-phase transport (L erch and others, 1998). 

# Pe r siste n ce of Tr iazi n e He rbicides Another important finding of USGS research during the 1990s was the persistence of triazine herbicides in surface water. Once applied to soil and crops, triazine compounds begin to degrade through biotic and abiotic reactions . Much of the research on the fate of triazine compounds prior to the late1980s addressed onl y the parent herbicide because most of the triazine degradation products were assumed not to be effective herbi

cides and, therefore, were not of particular interest to the agron

omists. During the 1990s, there was an increased focus on Clay mineral Organic matter coating Hydrophobic interaction

Cation exchange HN
N HN
NH O

NH C−COO +

N N N

H H NH

O

H 2 N Si—O +

Fig ur e 13. Mixed-mode model of so r ption fo r hyd r oxylated at r azine deg r adation p r odu c ts (f r om Le rc h and othe r s, 1997).

Stream water containing dissolved-phase HA and suspended sediment Older bed sediment Surface runoff Surface runoff 

### (A) Runoff conditions

Stream

Stream water containing dissolved-phase HA
Older bed sediment Newer bed sedimentcontaining dissolvephase HA 

### (B) Base-flow conditions

Stream

G round water G round water Fig ur e 14. P r oposed models fo rthe me c hanisms c ont r olling c on c ent r ations of hyd r oxylated at r azine deg r adation p r odu c ts (HADPs) in st r eams. The figu r e depi c ts the cr oss-se c tional view of a st r eam c hannel. (A) Du r ing r unoff c onditions, hyd r oxyat r azine (HA) is t r anspo rted p r ima r ily f r om at r azinet r eated fields to the st r eam in the dissolved phase. An additional sou rc e of HA in st r eams is suspended sediment de r ived f r om e r osion of HA- c ontaminated soil. (B) Du r ing baseflow c onditions (that is, g r ound wate ras the sou rc e of st r eamflow), HA is deso r bed by g r ound wate rflowing th r ough the HA- c ontaminated sediment deposited in the st r eambed (f r om Le rc h and othe r s, 1998).Pe r siste n ce of T r iazi n e He r bicides 19 accounting for the ultimate fate of triazine degradation products (Adams and Thurman, 1991; Thurman and others, 1994). These studies found that the frequenc y of detection, or apparent order of stability , of triazine herbicides and their deg

radation products was atrazine, deeth y latrazine, deisoprop y la

trazine, and c y anazine. It was also found that temporal trends in the number of detections in both pre-application and postharvest samples, and in the range of the distribution during sampling periods, of various herbicides was significant. In a stud y b y Thurman and others (1991, 1994), measurable amounts of atrazine, the most frequentl y detected herbicide, occurred in 91 percent of the pre-application samples, 98 percent of the post-applicatio n samples, and 76 percent of the harvest samples. The atr azine degradation product, deeth y latrazine, was found in man y pre-application, postapplication, and harvest samples that contained atrazine. Substantial evidence exists that another major biotic deg

radation process, dealky lation for atrazine b y both bacteria and soil fungi, does occur. Several bacteria and fungi species have been shown to prefer deeth y lation, whereas others prefer deiso

prop y lation. The presence of deeth y latrazine in surface and ground water is ascribed almost exclusivel y to the degradation of atrazine b y the removal of an eth y l group. Atrazine degrada

tion pathway s are shown in figure 15. Deeth y latrazine is the most important degradation product found in water-quality studies throughout the Midweste rn United States. Deisoprop y l

atrazine is formed b y the removal of an isoprop y l group and also may occur from the degradation of c y anazine and simazine (Mills and Thurman, 1994a; Me y er and others, 2001). It may be degraded further to didealky latrazine b y removal of an eth y l group (fig. 15). Both the production of deeth y latrazine and the degradation of deisoprop y latrazine proceed b y removal of an eth y l group. Therefore, the high er concentrations of deeth y latrazine and the smaller concentrations of deisoprop y latrazine during atrazine dealky lation may be a reflection of the greater ease of deeth y lation versus deisoprop y lation. These studies also show that concentrations of deeth y latrazine and deisoprop y la

trazine in surface water vary with h y drologic conditions in the basin and the timing of runoff, with maximum concentrations reaching 5 μ g/L (deeth y latrazine plus deisoprop y latrazine) (Mills and Thurman, 1994a; T hurman and others, 1994, 1998). Earl y studies of atrazine degradation products focused on the chlorinated atrazine degrad ation products because of their greater water solubility , lower soil adsorption compared to the parent compound, and the fact that they are more amenable to gas chromatography /mass spectrometry anal y sis than the hy drox y degradation products. However, hy drox y lated atrazine degradation products, particularl y hy drox y atrazine, are the major degradation products of atrazine in most soils. H y drox y lated atrazine degradation products (HADPs), which include hy drox y atrazine, deeth y lh y drox y atrazine, and deisoprop y lh y drox y atrazine, are a major class of atrazine degradation prod

ucts that form in the environment through chemical, biological, and photochemical h y drol y sis of atrazine or dealky lated atra

zine degradation products, resu lting in replacement of chlorine with a h y drox y l group at the two-position of the triazine ring. In soil or water, the rate of h y drol y sis is enhanced b y extremes in pH, dissolved organic matter, sorption to soil colloids, and the presence of photosensitizing compounds. HADPs have been shown to be more persistent in soil than atrazine and humic acids (Lerch and others, 1998). Studies b y Me y er (1994), Me y er and Thurman (1996), and Me y er and others (1996, 2001) suggest that c y anazine is more stable in the aquatic environmen t compared to the soil environ

ment. The studies also showedthat the half-life of c y anazine in the soil varied from 14 to 21 day s (Me y er and Thurman, 1996). However, degradation products of c y anazine have been identi

fied in the soil as long as 4 y ears after application (Me y er and Thurman, 1996). The c y anazine degradation pathway is shown in figure 16. The degradation process for herbicides generall y increases the water solubility and the polarity of the compound. The increase in solubility is caused b y the loss of carbon, the incorporation of ox y gen, and the addition of carbox y lic-acid functional groups. For every carbon atom that is removed, the water solubility will increase from tw o to three times (Me y er and Thurman, 1996). A stud y b y Me y er (1994) showed that atrazine and c y ana zine were dissipated in the top 12 in. of the soil and the y were not detected below 18 and 24 in. Deeth y latrazine was the pri

mary dealky lated compound produced from the degradation of atrazine. Stable production of deeth y latrazine and deisoprop y l

atrazine in the shallow soil was marked b y relativel y constant D 2 R of about 0.4 throughout the growing season. In the deeper soil where the parent compound, atrazine, was diminished, the D 2 R was generall y less than 0.2 or nonexistent due to the absence of deisoprop y latrazine. The s y stematic decrease in the concentrations of deisoprop y latrazine relative to deeth y latra

zine with depth was determined to be from the preferential removal of the eth y l group from deisoprop y latrazine and not from the preferential transport of deeth y latrazine (Me y er, 1994; Me y er and others, 2001). It was found that c y anazine amide dissipated rapidl y and was not readil y transported through the shallow soil (fig. 16). The concentration of c y anazine amide often was greater than c y anazine in both soil and pore water, and b y mid-season, con

centrations indicated that c y anazine amide was more readil y transported through the unsaturated zone than c y anazine (Me y er, 1994; Me y er and others, 1996). The deeth y lated c y ana zine degradation products, deeth y lc y anazine and deeth y lc y anazine amide, were identified onl y in the earl y season when the concentrations of c y anazine and c y anazine amide were high. The y dissipated rapidl y and were not transported at detect

able levels deeper th an 12 in. The primary degradation product of c y anazine that was measured with depth was deisoprop y la

trazine. It was detected as deep as 30 in. at concentrations greater than deeth y latrazine (Me y er, 1994; Me y er and others, 2001). The high DAR values showed that atrazine was not responsible for the deisoprop y latrazine found in the soil-core samples in the c y anazine field plots. Also, deisoprop y latrazine generall y was detected later in the growing season and at deeper20 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts



### Cyan u ric acid

Rin g cleav a g e CO 2

### + NH 3 

### + H 2 

### O Fig ur e 15. Deg r adation pathways fo rat r azine.Pe r siste n ce of T r iazi n e He r bicides 21

N
N N Cl

NH C C H 3 C

CH 3 NH 2 N



### Deethylcyanazine

N
N N Cl

NH C C H 3 C

CH 3 NH CH 3 CH 2 O OH 

### Cyanazine acid

N
N N Cl

NH C C H 3 C

CH 3 NH 2 O OH


### Deethylcyanazine acid N
N N Cl

NH CH 3 CH 2 NH 2 

### Deisopropylatrazine N
N N Cl

NH NH C C H 3 2 C

CH 3 NH CH 3 CH 2 O 

### Cyanazine amide N
N N Cl

NH C C H 3 C

CH 3 NH CH 3 CH 2 N 

### Cyanazine

N
N N Cl

NH C C H 3 C

CH 3 NH 2 NH 2 O 

### Deethylcyanazine amide

N
N N Cl

H N

2 NH 2 

### Didealky latrazine Fig ur e 16. Deg r adation pathways fo r c yanazine.

levels than either c y anazine or c y anazine amide. Thus, the detection of deisoprop y latrazine at depth is probabl y the result of the degradation of another c y anazine degradation product that is rapidl y transported through the unsaturated zone, c y ana zine acid. C y anazine amide and c y anazine acid both have modified isoprop y l moieties that may be removed b y microbial degradation. The rapid dissipation of c y anazine amide suggests that c y anazine acid is formed rapidl y . Furthermore, because c y anazine acid is ionic at normal pH, it may be preferentiall y leached through the soil. As it is leached, it also ma y undergo deeth y lation and deisoprop y lation (Me y er and others, 1996, 2001). As previousl y shown in figure 9, simazine also degrades to deisoprop y latrazine. However, as alread y stated, about 15 to22 S u mma r y of Sig n ifica n t Res u lts F r om St u dies of T r iazi n e He r bicides a n d Thei rDeg r adatio n P r od u cts
20 times more atrazine than simazi ne was applied in the United States during the earl y 1990s (Gianessi, 1992), which is wh y the presence of deeth y latrazine and deisoprop y latrazine in surface and ground water is ascribed almost exclusivel y to the degrada

tion of atrazine. Finall y , propazine has not been so ld since 1990 , except to States that requested a USEPA Section 18 Emergenc y Exemp

tion; however, it still occurred routinel y in water because it was a contaminant present in atrazineat about 1 pe rcent (Thurman and Fallon, 1996). Propazine is very persistent in the soil. It is broken down primaril y b y microbial action and, therefore, will persist longer in dry , cold conditions or in other conditions that inhibit microbial activity . In a study of play a lakes in the High Plains of Texas (fig. 1), atrazi ne and propazine were detected frequentl y (Thurman and others, 2000). Because propazine has a longer soil half-life (35 to 231 day s) than atrazine (45 to 60 day s), it is thought that atr azine was responsible for the majority of the deeth y latrazine. Commonl y , propazine was detected at much smaller concen trations than atrazine, perhaps because of little use during the 1990s. However, it is apparent from these data that propazine was still being used in Texas dur

ing the 1990s. Figure 9 also shows the structures of propazine and its respective dealky lation reactions to deeth y latrazine b y the removal of an isoprop y l group (Thurman and others, 2000). 

# S u mma r y
Triazine herbicides in surf ace water, ground water, and precipitation have been a major water-quality concern throughout the United States. The herbicides described in this report include atrazine, c y anazine, propazine, and simazine. Modern agricultural practices in the United States often require extensive use of these herbicides for crop prod uction. Because of public concern about possible water contamination, several manufacturers have voluntaril y reduced the recommended application rates and, in some cases, have removed herbicides from the market. During the 1990s, numerous studies were conducted in the Midwestern United States as part of the USGS Toxic Sub

stances H y drolog y Program to document the usage of triazine herbicides and formation of their degradation products in the h y drologic environment. Studies showed that changes in application rates affected the frequenc y of detection of some of the triazine herbicides and their degradation products and revealed that herbicide use also fluctuated in response to annual changes in planted corn and so y bean acreage as well as intro

duction of new herbicide products to the market. Monitoring the effects of these changes are important to understanding the occurrence, fate, and transport of these herbicides and their degradation products in surface water, ground water, and precipitation. The first major source studied was surface water. A recon

naissance stud y of 147 stream sampling sites was conducted during 1989 with subsequent studies during 1990, 1994, 1995, 1998, and 2002 of about 50 of the 147 stream sampling sites to determine the geographic and seasonal distribution of herbi

cides. Results showed that large amounts of triazine herbicides and their degradation products were flushed into streams with runoff. Much of this transport took place during the first runoff period after application of herbicides. Subsequent runoff tended to produce lesser con centration peaks. Herb icide detections in larger Midwestern streams tendedto be seasonal with higher percentages in spring and earl y summer and lower percentages in fall and winter. The use of atrazine and c y anazine was approximatel y the same in 1989 and 1995; however, the median concentrations of both herbicides in stream samples were higher in 1989 than in 1995 or 2002. Although herbicid e concentrations in Midwest

ern streams were quite variable during post-application runoff, the data suggest that changes in herbicide use affected herbicide concentrations in streams. Thes e studies also confirmed that herbicide degradation products were found to occur as fre

quentl y or more frequentl y and at concentrations that were often higher than the parent herbicides. In 1993, a stud y during flood

ing in the upper Mississippi River Basin determined that flood

ing did not dilute the concentrations of herbicides but rather concentrations were similar to those seen in no rmal spring and summer flows. A stud y of 76 reservoirs in the Midwestern United States reported an abundance and persistence of triazine herbicides and their degradation products in reservoirs. Significant find

ings showed that concentrations of atrazine and its degradation products remained elevated all su mmer and into the fall. A fur

ther stud y of the distribution of atrazine in Perry Lake (Kansas) during 1992 showed that recentl y applied atrazine mixed with atrazine applied the previous y ear as water moved through the reservoir. The reservoir studi es demonstrated the relation between herbicide use and thei r occurrence in streams and reservoirs. The second major source studied was ground water. Reconnaissance studies of 303 ground-water wells in the Mid

western United States began in 1991 with additional water sam

ples collected from 101 of the 303 ground-water wells in 1992 to examine the occurrence of tr iazine herbicides and their degradation products. Triazine degradation products, deeth y l

atrazine and deisoprop y latrazine, commonl y were found in ground water. During 1991, deeth y latrazine was detected more frequentl y (21.4 percent of the samples) than its parent com

pound atrazine (20.8 percent of the samples) even though deeth

y latrazine had a higher reporting limit than atrazine, whereas deisoprop y latrazine was detected in 7. 6 percent of the samples. During 1992, the reporting limits for atrazine and deeth y latra

zine were lowered, and deeth y latrazine was detected in 31 percent of the water samples while atrazine was present in 43 percent, and deisopropl y atrazine was found in 18 percent of the samples collected. Samples collected from 110 wells during the historic 1993 flooding in the Mississippi River Basin showed that there was a direct relation between increases in total herbicide concentra

tion in ground water (between pre-flood and post-floodRefe r e n ces Cited 23 samples) and the occurrence of streamflooding near wells. Results from these samples were compared to those samples obtained during 1991 and 1992 from the same wells. There were no statisticall y significant differences in either the fre

quenc y of herbicide detection or total herbicide concentration between the previous samples an d those collected for the 1993 flood stud y . However, water from about 63 percent of the wells that had at least a 20-percent in crease in total herbicide concen

tration also were severel y affected b y stream flooding. An important finding of an investigation of samples col

lected from 131 municipal wells in Iowa was the high frequenc y with which degradation products were detected in ground water. Ground-water samples collected from across the Mid

western United States and in Iowa from 1991 to 2001 consis

tentl y revealed that triazine he rbicide degradation products commonl y were found more frequentl y than their parent herbi

cide, the frequenc y of herbicide detection was affected b y a more sensitive anal y tical method, and ground-water age could be an important factor in explaining variations in herbicide contamination. The third major source studied was precipitation. This stud y area included the upper Midwest (where the use of herbi

cides is most intense), the Northeast to the Atlantic Ocean, and northward to the Canadian bord er, a total of 26 States. The results identified the occurren ce and temporal distribution of triazine herbicides and their degradation products in the Mid

west. Because of the large temporal and spatial variation in the amount of rainfall, it is difficult to make meaningful compari

sons of herbicide concentrations among sites or over time on the basis of individual weekl y samples. Comparisons can best be made with rainfall-weighted concentrations. The highest con

centrations occurred following herbicide application to crop

land. Rainfall-weighted con centrations of 0.20 to 0.40 μ g/L for atrazine were ty pical throughout the Mi dwest, and weighted concentrations as larg e as 0.60 to 0.90 μ g/L occurred in precip

itation at several sites. Concentrations of 1.0 to 3.0 μ g/L were measured in a few individual samples. Atrazine was detected most often, followed b y deeth y latrazine, c y anazine, and deiso

prop y latrazine. The large ratio (about 0.50) of deeth y latrazine to atrazine in precipitation was greatest in areas where herbicide use was intense and decreased wi th distance from the Midwest. Other important findings of the 1990s USGS studies included the chemistry , transport, and persistence of triazine herbicides and their degradatio n products in surface water and ground water. A number of field-dissipation studies were car

ried out for atrazine, c y anazine, propazine, and simazine in the unsaturated zone and in surf ace runoff. These dissipation studies resulted in outlining the structure and transport of man y degradation products of triazine herbicides in the aquatic envi

ronment. A dealky lation field stud y found the preferential removal of an ethy l side chain from atr azine relative to the removal of an isoprop y l side chain. The high ratio of deeth y l

atrazine to atrazine (referred to as the DAR) in shallow soil was evidence that simazine degraded more rapidl y to deisoprop y l

atrazine than propazine to deeth y latrazine. Furthermore, deeth y lation rates of atrazine and si mazine were comparable. This indicates that the removal of an eth y l side chain was preferential over an isoprop y l side chain, regardless of parent triazine com

pound. It was also found that atrazine transport through the unsaturated zone gave DAR values much greater than 1.0, whereas atrazine transported inrunoff had DAR values much less than 1.0. Deisoprop y latrazine was rapidl y degraded in the unsaturated zone but was an important degradation product in surface runoff from the fields. An additional finding of US GS research was the persis

tence of triazine herbicides an d their degradation products in surface water. Studies found that the frequenc y of detection, or apparent order of stability , was atrazine, deeth y latrazine, deiso

prop y latrazine, and c y anazine. The temporal trends in the num

ber of detections of various herbicides were also significant for several reasons. First, the y indicated that some compounds per

sisted from y ear to y ear in soil and water. Second, degradation products, such as deeth y latrazine, were both persistent and mobile in water. Third, the data showed that the DAR, which has been proposed as an indicator of nonpoint-source contami

nation of ground water, might be us ed also as a tracer of groundwater discharge to streams. Once it was applied, atrazine began to degrade through the action of soil microbes and abiotic losses and chemical reactions. Findings of the 1990s studies b y the USGS include an improved understanding of the occurrence, persistence, chem

istry , and transport of triazine herbicides and their degradation products in the h y drologic environment. A significant increase in knowledge of triazine herbicides and development and improvement of anal y tical methods were accomplished in the past decade. The result s produced are not onl y significant for the present but provide an important data set for future use. 

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illary -column gas chromatograph y /mass spectrometry with selected-ion monitoring: U.S. Geological Surve y Open-File Report 98–634, 21 p.Printed on recycled paperScribner and others—Summary of Significant Results from Studies of Triazine Herbicides andTheir Degradation Products in Surface Water, GroundWater, and Precipitation in the Midwestern United States During the 1990s—USGS/SIR 2005–5094 N
N N Cl

NH C C H 3 C
CH 3 NH 2 N



### Deethylcyanazine

N
N N Cl

NH C C H 3 C
CH 3 NH CH 3 CH 2 O OH 

### Cyanazine acid

N
N N Cl

NH C C H 3 C
CH 3 NH 2 O OH


### Deethylcyanazine acid N
N N Cl

NH CH 3 CH 2 NH 2 

### Deisopropylatrazine N
N N Cl

NH NH C C H 3 2 C
CH 3 NH CH 3 CH 2 O 

### Cyanazine amide N
N N Cl

NH C C H 3 C
CH 3 NH CH 3 CH 2 N 

### Cyanazine

N
N N Cl

NH C C H 3 C
CH 3 NH 2 NH 2 O 

### Deethylcyanazine amide

N
N N Cl

H N

2 NH 2 

### Didealkylatrazine