Cover photograph: 

The lower Clackamas River winds westward through agricultural, urban, and industrial land before flowing into the Willamette River 

downstream of Oregon City (photograph by Dennis Lynch, U.S. Geological Survey). 
U.S. Department of the Interior 

U.S. Geological Survey 

Pesticides in the Lower Clackamas River Basin, 

Oregon, 2000–01 

By KURT D. CARPENTER 

Water-Resources Investigations Report 03–4145 

Prepared in cooperation with the 

Clackamas River Water Providers and 

Clackamas County Department of Water Environment Services 

Portland, Oregon: 2004 
____________________________________________________________________________ 

U.S. DEPARTMENT OF THE INTERIOR 

GALE A. NORTON, Secretary 

U.S. GEOLOGICAL SURVEY 

CHARLES G. GROAT, Director 

The 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. 

For additional information: 	 	 Copies of this report may be 

purchased from: 

District Chief 

U.S. Geological Survey U.S.Geological Survey 

10615 S.E. Cherry Blossom Dr. Information Services 

Portland, OR 97216-3159 Box 25286, Denver Federal Center 

E-mail: info-or@usgs.gov Denver, CO 80225-0286 

Internet: http://oregon.usgs.gov Telephone: 1-888-ASK-USGS 

Suggested citation:
 


Carpenter, K.D., 2004, Pesticides in the lower Clackamas River Basin, Oregon, 2000–01: 
 


U.S. Geological Survey Water-Resources Investigations Report 03–4145, 30 p. 

ii 
CONTENTS


Summary.................................................................................................................................................................................... 1


Introduction................................................................................................................................................................................ 2


Study Design, Methods, and Data Quality Control ................................................................................................................... 4


Results and Discussion .............................................................................................................................................................. 6


Stream Conditions During Sampling................................................................................................................................. 6


Pesticide Detections........................................................................................................................................................... 6


Potential Pesticide Source Areas ..................................................................................................................................... 13


Pesticide Concentrations Relative to Water-Quality Standards and Suggested Guidelines to


Protect Human Health and Aquatic Life ................................................................................................................. 16


Potential Effects of Pesticides on Aquatic Life ............................................................................................................... 17


Potential Uses of Pesticides in the Clackamas River Basin............................................................................................. 21


Pesticide Management and Future Studies ...................................................................................................................... 23


Acknowledgments ................................................................................................................................................................... 23


References................................................................................................................................................................................ 24


Appendix.................................................................................................................................................................................. 27


FIGURES 

1. Map showing the locations of sampling sites, rain gages, and streamflow measurement locations


in the Clackamas River Basin, Oregon .......................................................................................................................... 3


2. Graphs showing precipitation and streamflow conditions during pesticide sampling in the Clackamas River Basin, 


2000–01.......................................................................................................................................................................... 5


3. Graph showing streamflow conditions during pesticide sampling in the lower Clackamas River Basin, Oregon, 


2000–01.......................................................................................................................................................................... 7


4. Graphs showing pesticide detections in the Clackamas River Basin, Oregon, 2000–01 ............................................. 11


5. Graph showing maximum concentrations of herbicides and insecticides in the Clackamas River Basin, 

May and October 2000................................................................................................................................................. 12 

6. Pie charts showing relative pesticide loads from the lower-basin tributaries, May and October 2000 ........................ 14


7. Pie charts showing relative pesticide loads in the main-stem Clackamas River and lower-basin tributaries,


May 2000 ..................................................................................................................................................................... 15


8. Pie charts showing relative pesticide loads in the main-stem Clackamas River and lower-basin tributaries, October


2000.............................................................................................................................................................................. 16


9. Graph showing pesticide toxicity index (PTI) values compared with EPT taxa richness for samples collected


from tributaries in the Clackamas River Basin, Oregon............................................................................................... 21


10. Pie chart showing top agricultural crops and commodities grown in Clackamas County, Oregon, 1997.................... 21


11. Pie chart showing percentage of total estimated pesticide applications to agricultural crops grown in 


Clackamas County, Oregon, 1997................................................................................................................................ 23


TABLES 

1. Pesticides detected in the Clackamas River Basin, Oregon, 2000–01, and commercial products containing them .....8


2. Summary of sampling regime and pesticide detections in the Clackamas River Basin, May 2000–August 2001 ....... 8


3. Pesticide concentrations in the main-stem Clackamas River, untreated, and treated drinking water, and


tributaries of the Clackamas River, May 2000–August 2001 .......................................................................................9


4. Pesticide loads from the main stem Clackamas River and lower-basin tributaries, May and October 2000 ..............14


5. Pesticide concentrations relative to human health standards and aquatic-life criteria ................................................18


6. Pesticide toxicity index (PTI) values for fish and benthic invertebrates for samples collected in the 


Clackamas River Basin, May 2000–August 2001 ......................................................................................................20


7. Potential uses of pesticides detected in the Clackamas River Basin, Oregon, 2000–01 .............................................22


iii 
Pesticides in the Lower Clackamas River Basin, 
 


Oregon, 2000–01 

By Kurt D. Carpenter 

SUMMARY 

In 2000–01, the U.S. Geological Survey 

sampled the Clackamas River and its major 

lower-basin tributaries for 86 dissolved pesticides 

and selected breakdown products during storm 

runoff conditions. In all, 27 compounds, including 

18 herbicides, 7 insecticides, and 2 pesticide 

breakdown products, were detected in 18 stream 

samples. The most commonly detected pesticides, 

in decreasing frequency, included atrazine, 

simazine, diazinon, metolachlor, and diuron, 

which occurred in 46–92% of samples collected 

from the tributaries. Of these, atrazine, simazine, 

and metolachlor, plus six other compounds, also 

were detected in the main-stem Clackamas River. 

Pesticides were consistently detected with 

greater frequency and at higher concentrations in 

the four lowermost tributaries (Deep, Richardson, 

Rock, and Sieben Creeks). In these streams, a total 

of 12 to 18 pesticides were detected per stream in 

samples collected during spring and fall. Pesticides always occurred with at least one other pesticide, and about half of the samples, including one 

sample from the Clackamas River in October 

2000, contained six or more pesticides. 

Nine pesticides—the insecticide diazinon 

and the herbicides 2,4-D, atrazine, dichlobenil, 

diuron, imazaquin, metolachlor, simazine, and 

trifluralin—were detected at relatively low 

concentrations in five samples of Clackamas River 

water. Despite these detections, no pesticides were 

detected in three samples of treated Clackamas 

River water used for drinking. 

Concentrations of six compounds—carbaryl, 

chlorpyrifos, diazinon, dieldrin, malathion, and 

the breakdown product of DDT (p,p’-DDE)— 

exceeded established or recommended criteria for 

the protection of aquatic life in some of the 

tributaries, sometimes for multiple pesticides in 

one sample. The greatest number of aquatic-life 

criterion exceedances occurred in Rock and 

Sieben Creeks, which drain both agricultural 

land and urban developments. Concentrations of 

three pesticides exceeded aquatic-life criteria in 

each of these streams, and concentrations of the 

organophosphate insecticides diazinon and 

chlorpyrifos exceeded their respective criteria by 

several-fold in both streams. Diazinon was 

detected in all of the four lowermost tributaries, 

at concentrations that exceeded the U.S. 

Environmental Protection Agency aquatic-life 

criterion (0.1 μg/L) in all five samples collected 

from Sieben and Rock Creeks. The highest 

diazinon concentration (0.160 μg/L measured in 

Sieben Creek in May 2000) exceeded the 

maximum concentration recommended by the 

National Academy of Sciences/National Academy 

of Engineering by a factor of 18. 

Such aquatic-life criteria consider only one 

pesticide at a time, and therefore do not evaluate 

the effects of multiple pesticides detected at once 

in a sample. To do this, a composite pesticide 

toxicity index (PTI) was used. The highest PTI 

values were found in samples collected from Rock 

and Sieben Creeks, where relatively fewer sensitive invertebrates were observed in other studies 

conducted in 1997–99. These two streams, with 

1 
the highest pesticide concentrations and greatest 

number of pesticide detections, supported fewer 

high-quality invertebrates (1–10 taxa) compared 

with other streams sampled (15–31 taxa). 

During the May 2000 storm, two tributaries—Deep and Rock Creeks—contributed most 

(65% and 15%, respectively) of the total measured 

pesticide load from the 6 tributaries sampled. Most 

(90%) of the total measured pesticide load during 

the October 2000 storm could be accounted for by 

inputs from Sieben Creek alone. Note, however, 

that because of the dynamic nature of precipitation, rainfall runoff, and streamflow during 

storms, instantaneous pesticide loads constitute 

best estimates, not precise calculations. 

Identification of pesticide sources in the 

Clackamas River Basin is difficult because of the 

diverse land uses in the basin and the multiple-use 

nature of many of the pesticides detected. Of the 

25 parent compounds detected, 22 have agricultural uses, 24 have urban uses, 16 are applied to 

golf courses, 11 are applied along roads and other 

right-of-ways, and 5 have or had forestry 

applications. Based on current available crop 

acreages for Clackamas County and best estimates 

of chemical application rates in the Pacific 

Northwest, most (49%) of the pesticide estimated 

to be applied to agricultural lands in Clackamas 

County (for those detected) is used for nursery and 

greenhouse crops. Lesser amounts, ranging from 4 

to 15%, are applied to pastureland, Christmas 

trees, alfalfa and hay fields, hazelnuts, and grass 

seed fields. Such estimates could be improved 

with more detailed pesticide use information. 

Although pesticide use data are available at the 

county level, such data are too coarse to identify 

particular areas with subbasins where pesticide 

contamination is occurring. Also, because only a 

small fraction of the thousands of pesticide 

products registered for use in Oregon were tested 

for during this study, pesticide use information 

would help ensure that high-use pesticides are 

included in future studies. 

INTRODUCTION 

Approximately 9,500 pesticide products are 

registered for use in Oregon to control brush, weeds, 

insects, fungi, rodents, nematodes, and other pests on 

agricultural crops, lawns, and landscaping in urban and 

industrial areas, home gardens, golf courses, forestland, 

and vegetation along right-of-ways such as roads, 

railways, and utility lines. Despite educational 

programs and regulations geared toward preventing 

pesticide contamination, studies have shown that a 

wide variety of these compounds are making their way 

into streams and ground water. A U.S. Geological 

Survey (USGS) study on pesticide occurrence in 

streams found 1 or more pesticides in 95% of 8,000 

streams across the country, and 50% of streams 

contained 5 or more pesticides (U.S. Geological 

Survey, 1999; Gilliom and others, 1999). Studies in 

Oregon have found numerous pesticides in streams 

(Anderson and others, 1997; Wentz and others, 1998; 

Rinella and Janet, 1998; Sandahl and Jenkins, 2002; 

Grange, 2002) and ground water (Hinkle, 1997), 

particularly in agricultural and urban areas, where most 

pesticide applications occur. The great diversity of 

crops grown in Oregon, particularly in the northern 

Willamette Valley, results in a wide variety of 

pesticides being applied and later detected in streams 

(Anderson and others, 1997). 

The Clackamas River in northwestern Oregon 

drains the western slope of the Cascade Range, 

descending from forested highlands into the Willamette 

Valley (fig. 1). Streamflows in the Clackamas River are 

typically sustained well into the dry season, making the 

river an important drinking-water supply for about 

200,000 people in the Portland area. Other designated 

beneficial uses for the Clackamas River include 

water-contact recreation, fishing, boating, as well as 

passage, spawning, and rearing habitat for fish, 

including resident cutthroat and rainbow trout, spring 

and fall Chinook and coho salmon, and summer and 

winter steelhead trout. Today, fish populations in the

Clackamas and other western rivers are declining 

(Nehlsen and others, 1991)—spring Chinook salmon 

and winter steelhead trout in the Clackamas Basin are 

listed as threatened on the Endangered Species List, 

and late-run Clackamas River coho salmon, the last 

remaining wild coho salmon stock in the Columbia 

River Basin, was listed as a candidate species in 1995 

(Taylor, 1999). 

2 
Figure 1. Locations of sampling sites, rain gages, and streamflow measurement locations in the Clackamas River Basin, Oregon. 

Streams in the lower Clackamas River Basin 

drain a diverse landscape of forest, agricultural areas, 

industrial land, and urban developments (see cover 

photograph). Based on the land use, the highest 

pesticide concentrations are likely to occur in the 

lower-basin tributaries, which drain areas where 

pesticide applications are most likely. Although 

specific information on pesticide use in the basin is 

limited, Hassanein and Peters (1998) reported use of at 

least 100 pesticides, mostly herbicides and insecticides, 

in the Clackamas River Basin. Anderson and others 

(1997) and Rinella and Janet (1998) found 36 and 50 

pesticides, respectively, in Willamette River Basin 

streams draining lands with a similar mix of uses as 

those in the lower Clackamas River Basin. 

The Clackamas River supports the last remaining wild coho 

salmon stock in the Columbia River Basin (photograph by 

Tim Shibahara, Portland General Electric). 

3 
As a drinking-water supply, the Clackamas River 

has been monitored for regulated pesticides since 1995, 

but none have been detected (Gordon McGhee, 

Clackamas River Water, written commun., 2000). This 

lack of detections is partly because of the relatively 

high laboratory detection limits for the pesticide 

analyses and because sampling has included only 

main-stem sites, where dilution reduces the chances of 

detecting pesticides. Previous pesticide sampling also 

has not targeted periods of storm runoff, when the 

highest pesticide concentrations typically occur 

(Anderson and others, 1997; Krastzer, 1998). To fill 

this data gap, the USGS began sampling for pesticides 

in the Clackamas River and its major lower-basin 

tributaries in 2000, using advanced laboratory 

methods that detect pesticides at parts-per-trillion 

concentrations. 

This report describes the pesticide sampling 

program, presents the data from the study as it relates 

to pesticide use, compares pesticide concentrations in 

the main stem to those in the tributaries, evaluates 

potential risk to aquatic life by comparing pesticide 

concentrations to protective toxicity criteria, and 

examines the relationship between the relative 

pesticide toxicity and the benthic invertebrate community using data collected during 1997–99. Data 

used in this report can be obtained from the Clackamas 

Basin Water-Quality Assessment Web page at 

http://oregon.usgs.gov/clackamas. 

STUDY DESIGN, METHODS, AND DATA QUALITY 

CONTROL 

Water samples were collected from the 

Clackamas River and six of its lower-basin tributaries: 

Eagle, Clear, Deep, Richardson, Rock, and Sieben 

Creeks (fig. 1) in May and October 2000 during 

periods of storm runoff (fig. 2). Three small tributaries, 

Goose, Foster, and Cow Creeks, which drain areas of 

agricultural, urban, and industrial land, were not 

sampled. Samples were collected using standard USGS 

protocols (Shelton, 1994) and sampling occurred 

following periods when pesticides are typically applied 

in the basin. Two rain gages located in or near the study 

area (fig. 1) were used to determine the timing of 

sample collection. Following the detection of two 

pesticides in untreated drinking water from the lower 

Clackamas River in May, additional samples of 

untreated and treated drinking water were analyzed in 

October 2000 (high flow), January 2001 (moderate 

flow), and August 2001 (low flow). 

Water samples were collected at equally spaced 

points along a transect across the stream channel using 

either a US DH-81 or US D-77 sampler (Edwards and 

Glysson, 1999) equipped with a 3-liter Teflon 

bottle-nozzle assembly. Individual samples were 

collected from the surface to the bottom at each point 

and composited into one bottle to form a representative 

sample. Samples of untreated and treated drinking 

water were obtained from taps at the treatment plants. 

Water samples were filtered through 0.7-micron 

glass-fiber filters and shipped to the USGS National 

Water-Quality Laboratory in Arvada, Colorado, where 

they were analyzed for 84 pesticides and 2 breakdown 

products using a C-18 solid phase extraction, gas 

chromatography/mass spectrometry (GC/MS) method 

(Crepeau and others, 1994; Zaugg and others, 1995). 

This sensitive method is compound-specific, meaning 

that when a pesticide is detected, there is a high degree 

of certainty (greater than 99% confidence) that the 

compound is present. Pesticides found at concentrations less than the detection limit, however, have a 

lower degree of statistical certainty regarding the actual 

concentration, and were therefore reported by the lab as 

estimates. Some of the pesticides that are widely used 

in the United States, but not tested for in this study, 

include the herbicides glyphosate (the active ingredient 

in RoundupTM, RodeoTM, and other brands), MSMA, 

and propazine; the insecticides cryolite, acephate, 

dimethoate, methomyl, and thiodicarb; the inorganic 

pesticides copper and sulfur; and biological pesticides. 

Streamflow was measured at sampling sites 

according to standard USGS guidelines (Rantz and 

others, 1982), and continuous streamflow data was 

obtained from the USGS gaging station in the 

Clackamas River at Estacada. In October, field 

parameters (water temperature, dissolved oxygen, pH, 

and specific conductance) were measured at each 

stream site using a Hydrolab Datasonde 3 multiparameter probe, and the turbidity of each pesticide 

sample was measured at the USGS Oregon District 

laboratory using a Hach 2001AN turbidity analyzer. 

Twenty-five percent of samples were submitted 

for quality control. Two equipment blanks and one 

laboratory blank sample were submitted to check clean 

techniques; two duplicate samples and one split sample 

4 
Figure 2. Precipitation and streamflow conditions during pesticide sampling in the Clackamas River Basin, 2000–01. (Clear Creek streamflow 

data provided by Kent Doughty, Duke Engineering; Data from Tower Drive rain gage, located just to the north of the Clackamas Basin, is 

shown because a longer period of record was available [data from the Clear Creek gage, in the Clackamas River Basin, was collected 

intermittently.]) 

5 
were collected to check laboratory variability; and one 

sample was spiked to measure the recovery of each 

compound (see table A-2 and associated evaluation of 

quality-control results in the appendix). 

RESULTS AND DISCUSSION 

Stream Conditions During Sampling 

The first samples of storm runoff were collected 

on May 11, 2000, following 3 consecutive days of 

about 0.5 inches of rain per day (total rainfall for this 

storm was about 1.75 inches) (fig. 2). Streamflow in the 

lower Clackamas River at Carver peaked at just over 

7,000 cubic feet per second during the May sampling 

(fig. 3). This storm was preceded by another storm 1 

month earlier that produced more than an inch of rain. 

In the fall, the first runoff-producing storm 

occurred in mid-October, when about half an inch of 

rain produced observable turbidity in Sieben Creek. At 

this time, however, streamflows in the other tributaries 

did not increase significantly, and those streams were 

therefore not sampled. Most streams, including Sieben, 

Rock, Richardson, and Deep Creeks were sampled 10 

days later, when a 1.2-inch storm produced observable 

runoff and high turbidity in Rock, Deep, and Sieben 

Creeks. Eagle and Clear Creeks, which continued to 

rise, were not as turbid, and were sampled the next 

day as their streamflows crested (see Clear Creek 

hydrograph, fig. 2). Streamflows during storm 

sampling were higher in May than in October at most 

of the tributary sites sampled, although a greater 

amount of runoff was observed in Sieben Creek in 

October (fig. 3). High levels of turbidity were observed 

during storms at most of the lower-basin tributary sites, 

particularly in October, when the turbidity in Rock 

Creek exceeded 1,000 NTU (nephelometric turbidity 

units), and Deep, Richardson, and Sieben Creeks 

ranged from 150 to 250 NTU. 

Pesticide Detections 

Twenty-seven compounds (18 herbicides, 7 insecticides, and 2 pesticide breakdown products) were 

Stormwater runoff produces high turbidity in Deep Creek, 

October 2000. 

detected in 18 samples collected from the Clackamas 

River and its tributaries (table 1, table 2, and table 3). 

Herbicides were detected more frequently and at higher 

concentrations than insecticides, making up about 80% 

of the pesticide detections. The most commonly 

detected pesticides, occurring in at least half of all 

samples collected from the tributaries, included the 

herbicides atrazine, simazine, diuron, metolachlor, and 

the insecticide diazinon (fig. 4). These results closely 

resemble those reported for other streams in the 

Willamette Basin (Anderson and others, 1997). 

Atrazine was detected at least once in each of the 

six lower-basin tributaries sampled, occurring in 92% 

of all samples collected from the tributaries, as well as 

in one of four samples collected from the main-stem 

Clackamas River. Atrazine concentrations were notably 

higher at all sites in May compared to October, 

probably indicating use during springtime. Atrazine 

and deethylatrazine (one of the atrazine breakdown 

products) were the only compounds detected in Eagle 

6 
and Clear Creeks during May, suggesting that the 

primary land use/crops in these watersheds—forestry 

and Christmas trees—may be an important contributing 

source of atrazine in these streams. 

Figure 3. Streamflow conditions during pesticide sampling in the 

lower Clackamas River Basin, Oregon, 2000–01. 

Certain pesticides showed seasonal patterns that 

may be related to the timing of their use or other 

factors, such as how quickly they break down in the 

environment. Detections of 2,4-D, an herbicide found 

in many weed and feed products that is applied in the 

spring to control broadleaf weeds on lawns, for 

example, occurred only in May and August. It was not, 

however, found in October (fig. 4), possibly because 

of the relatively short half-life of 2,4-D (10 days; 

appendix table A-1). Other pesticides, including 

the widely used herbicide metolachlor, and several 

insecticides, particularly chlorpyrifos, carbaryl, and 

dieldrin, were found more frequently in October (fig. 

4), possibly from applications during summer. 

Pesticide samples were collected during periods 

of storm runoff and likely represent conditions that 

occur at least twice annually if not more often. Several 

moderate rain storms occurred in the weeks prior to 

sampling, however, which may have produced even 

higher concentrations in the streams than those 

reported here. Further, because pesticide samples were 

filtered, and because some pesticides adhere strongly to 

sediment (those in appendix table A-1 with high 

organic carbon adsorption coefficient [Koc] values), 

some of the pesticide concentrations could have been 

higher than reported here. 

While no pesticides were detected in the 

Clackamas River at Estacada (river mile 23.1), several 

compounds were found downstream in the lower 

main-stem Clackamas River. Nine pesticides, including 

the insecticide diazinon and the herbicides 2,4-D, 

atrazine, dichlobenil, diuron, imazaquin, metolachlor, 

simazine, and trifluralin were detected at relatively low 

concentrations in five water samples collected from 

the lower Clackamas River or water-treatment-plant 

intakes during high, moderate, and low-flow conditions 

(table 2 and table 3). Diazinon and diuron were each 

detected in the Clackamas River twice, whereas the 

other seven pesticides were detected once. 

Despite these detections of pesticides in the 

Clackamas River and in untreated drinking water, no 

pesticides were detected in three samples of treated 

drinking water collected from a conventional-type 

treatment plant in October and January or from a sand 

filtration treatment plant in August (table 3). Although 

this is a positive finding, other studies are now showing 

that certain organophosphate insecticides, including 

some found in this study (malathion, diazinon, and 

chlorpyrifos), may produce toxic breakdown products 

called oxons during water treatment that were not 

tested for in this study. A national survey of pesticides 

in untreated and treated drinking water, for example, 

found malaoxon, the oxon of malathion, in treated 

water only (Blomquist and others, 2001). Of these 

parent compounds, only diazinon was found in the 

main-stem Clackamas River or in untreated drinking 

water, although all three were detected in the tributaries 

that discharge to the Clackamas River upstream from 

the drinking-water intakes. 

Pesticides were detected with greater frequency 

(up to 15 pesticides in 1 sample) and at higher 

concentrations in the 4 lowermost tributaries (Deep, 

Richardson, Rock, and Sieben Creeks) compared 

with the main-stem Clackamas River, Eagle Creek, 

or Clear Creek. The 4 lowermost tributaries contained 

between 12 and 18 pesticides each (table 2). Much of 

the farmland and forestland in this part of the basin 

is being cleared and developed as Portland’s urban 

growth boundary expands. Streams in this area are 

particularly susceptible to pesticide runoff, given the 

wide range of potential applications, moderate to steep 

drainages, and abundant rainfall. 

7 
-- --

-- --

-- -- --

--

-- --

-- --

-- --

-- --

Table 1. Pesticides detected in the Clackamas River Basin, Oregon, 2000–01, and commercial products containing them 

[μg/L, micrograms per liter, or parts per billion; 2,4-D, 2,4-dichlorophenoxyacetic acid; DCPA, dimethyl-2,3,5,6-tetrachloroterephthalate; DDE, 

dichlorodiphenyldichloroethylene; DDT, dichlorodiphenyltrichoroethane; all product names are trademarked] 

(μg/L) 

Atrazine 

uracil 

insecticide 

2,4-D 

p,p'-DDE p,p' 

Diazinon insecticide 

benzonitrile 

Dieldrin 

urea 

Mocap 

Dyfonate insecticide 

Imazaquin 

Linuron urea 

insecticide 

Napropamide amide 

Pronamide amide 

Simazine Aquazine, Princep 

urea 

.04 

i −August 2001 

Laboratory method 

Pesticide or detection limit 

breakdown product Commercial product Chemical class Use 

AAtrex, Atratol, Atred, Gesaprim triazine herbicide 0.004 

Bromacil Krovar, Bromax, Hyvar, Uragon herbicide .04 

Carbaryl Sevin, Savit, Carbamine, Denapon carbamate insecticide .021 

Chlorpyrifos Dursban, Lorsban, Brodan organophosphorus .003 

Crossbow, Aqua-Kleen, Weed-B-Gone chlorophenoxy acid herbicide .06 

DCPA Dacthal, DAC 893, Dachthalor chlorobenzoic acid herbicide .0015 

-DDT breakdown product organochlorine none .0013 

Deethylatrazine Atrazine breakdown product triazine none .003 

Gardentox, Knoxout, pest strips organophosphorus .003 

Dichlobenil Casoron, Diclomec, Norosac herbicide .025 

Dieldrex organochlorine insecticide .0024 

Diuron Krovar, Diurex, Aguron, Karmex herbicide .025 

Ethoprop organophosphorus nematcide .002 

Fonofos organophosphorus .0013 

Image, Scepter, Squadron, Tri-Scept imidazolinone herbicide .008 

Afalon, Lorox, Dulain, Linex herbicide .018 

Malathion Cythion, malathion organophosphorus .014 

Metolachlor Dual, Pennant acetanilide herbicide .006 

Devrinol herbicide .003 

Pendimethalin Prowl, Pendulum, Stomp dinitroaniline herbicide .005 

Prometon Pramitol triazine herbicide .007 

Kerb herbicide .0021 

triazine herbicide .006 

Tebuthiuron Graslan, Spike, Perflan herbicide .008 

Terbacil Sinbar uracil herbicide .017 

Triclopyr Garlon, Curtail, Crossbow, Remedy organochlorine herbicide 

Trifluralin Treflan dinitroaniline herbicide .005 

Table 2. Summary of sampling regime and pestic de detections in the Clackamas River Basin, May 2000 

2000 

of 

Sites samples a 

1 0 0 

4 9 2 6 0 3 

3 0 0 0 0 

2 2 2 0 

Clear Creek 2 4 2 4 

2 

2 9 6 

Rock Creek 2 

3 

a 21 27 20 23 0 3 

Number of pesticides detected 

Number 2001 

Total May October January August 

Main-stem 

Tributaries 

Clackamas River at Estacada 

Clackamas River at Carver or

 untreated water from drinking-water intakes 

Treated drinking water 

Eagle Creek 

Deep Creek 14 12 11 

Richardson Creek 12 

18 14 15 

Sieben Creek 16 12 13 

Total 

a Total number of individual pesticides detected. 

8 
9
 

μ

River at 

Carver 

RM 23.1 RM 7.9 a 

Pesticide or May 

2000 2000 

Prometon 

H 

H 

I 

I 

H 

H 

IBP 

I 

HBP 

H 

I 

H 

N 

I 

H 

H 

I 

H 

H 

H 

H 

H 

H 

H 

H 

H 

H 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

690 na 

0 2 6 0 3 0 0 

Table 3. Pesticide concentrations in the main-stem Clackamas River, untreated, and treated drinking water, and tributaries of the Clackamas River, May 20[All samples collected during storm runoff conditions; pesticide concentrations in micrograms per liter ( g/L), or parts per billion; e, estimated values; nd, not detected; H, 

IBP, insecticide breakdown product; HBP, herbicide breakdown product; N, nematocide; RM, Clackamas River mile; cfs, cubic feet per second; na, not applicable; 2,4-D, 2

dimethyl-2,3,5,6-tetrachloroterephthalate; DDE, dichlorodiphenyldichloroethylene]


 Clackamas Clackamas 

River at Clackamas River— Clackamas River— 

Estacada untreated water treated drinking 

(lower river intake) water 

May October January August October, January, and Au

breakdown product Type 2000 2001 2001 2000-01 

Atrazine Bromacil Carbaryl Chlorpyrifos 2,4-D DCPA p,p’-DDE Diazinon Deethylatrazine 

Dichlobenil Dieldrin 

Diuron Ethoprop 

Fonofos 

Imazaquin 

Linuron 

Malathion 

Metolachlor Napropamide 

Pendimethalin 

Pronamide 

Simazine Tebuthiuron 

Terbacil 

Triclopyr 

Trifluralin 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

0.011 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

e.014 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

e0.003 

.24 

e.016 

e.004 

e.003 

e.002 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

0.052 

nd 

nd 

e.003 

nd 

nd 

e.047 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

Streamflow (cfs) 5,390 7,110 3,640 4,170 na 

Number of detections 
Table 3. Pesticide concentrations in the main-stem Clackamas River, untreated, and treated drinking water, and tributaries of the Clackamas River, May 20

10
 

Clear 

Creek 

RM 8.0 RM 12.1 RM 9.1 

Rock 

Creek 

May May May 

2000 2000 2000 2000 2000 20

Atrazine Carbaryl 2,4-D p,p’-DDE Diazinon Dichlobenil Dieldrin Diuron Prometon Pronamide 

H H 

I I 

H H 

I 

HBP 

H 

I 

H N 

I 

H H 

I 

H H H H H H H H H H 

nd 

nd nd 

nd nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd nd 

nd 

nd nd nd nd nd nd nd nd nd nd 

nd 

nd nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd nd 

nd 

nd nd nd nd nd 

nd 

nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

nd 

n

n

n

n

n

n

n

330 217 36 26 10 

2 4 12 11 9 6 14 15 12 

Deep Richardson 

Creek Creek 

RM 6.4 

Pesticide or October October May October October M

breakdown product Type 2000 2000 2000 

Bromacil Chlorpyrifos DCPA Deethylatrazine Ethoprop Fonofos Imazaquin Linuron Malathion Metolachlor Napropamide Pendimethalin Simazine Tebuthiuron Terbacil Triclopyr Trifluralin 

IBP 

0.017 

e.007 

e0.002 

e.004 

.008 .045 

0.12 

.27 

e.079 

.004 

e.013 

.15 .008 

.060 

.039 

nd 

.024 

e.026 

nd 

.012 

0.007 

nd 

nd 

e.002 

e.004 

e.005 

nd 

.010 

e.008 

.110 

e.004 

e.002 

.017 

nd 

nd 

e.001 

0.012 

nd 

nd 

nd 

e.057 

nd 

.005 

e.006 

e.014 

nd 

e.016 

nd 

nd 

nd 

nd 

e.010 

.080 

e.084 

e0.004 

nd 

nd 

nd 

nd 

e.005 

nd 

nd 

.007 

nd 

e.006 

nd 

nd 

e.006 

nd 

e.007 

nd 

nd 

nd 

nd 

0.30 

nd 

.24 

.020 

nd 

.052 

e.021 

e.031 

nd 

.071 

nd 

nd 

nd 

.012 

nd 

e.011 

.011 

.19 

.026 

nd 

e.087 

e.004 

e0.006 

nd 

nd 

.056 

nd 

.46 

.009 

nd 

e.008 

.086 

nd 

nd 

.59 

.017 

.008 

.011 

e.012 

.17 

.015 

.034 

1.30 

0

n

e

n

e

e

n

e

n

n

n

1

n

e

n

e.0

Streamflow (cfs) 141 7.2 8.6 4

Number of detections 

a Collected from a conventional (settling basin plus filtration) drinking-water treatment plant in October and January, and from a slow-sand filtration drinking-water tr
Figure 4. Pesticide detections in the Clackamas River Basin, Oregon, 2000−01 (includes 119 detections in 13 tributary and 4 main-stem 

Clackamas River samples; no pesticides were detected in untreated or treated water in January). 

Rapid runoff of storm water from impervious 

surfaces (roofs, roads, and driveways) may transport 

pesticides to streams via storm drains in urban areas or 

through tile drainage on farms. Together, these 

transport mechanisms produce high streamflows in 

these lower basin tributaries during storms. Previous 

studies (Clackamas County Soil and Water Conservation District, 2002; Carpenter, 2003) have found 

other indications of degraded water quality in these 

four streams, including elevated concentrations of 

nitrogen and phosphorus, and high pH. 

Pesticide concentrations were generally highest 

in Sieben and Rock Creeks due to the combined effects 

of draining relatively greater amounts of urbanized area 

and farmland, and to their relatively low streamflows, 

which afforded less dilution compared with the other 

tributaries. In contrast, higher streamflow in Deep 

Creek (fig. 3) probably resulted in lowering pesticide 

concentrations through dilution, although the actual 

amounts (loads) were generally higher in Deep Creek. 

Most of the highest pesticide concentrations 

were observed in Sieben Creek, where the herbicides 

dichlobenil, napropamide, and triclopyr were found at 

concentrations ranging from about 1 to 16.8 μg/L 

(micrograms per liter, or parts per billion; fig. 5). All of 

these herbicides are applied in urban areas or along 

roads and other right-of-ways. Napropamide and 

dichlobenil also are used on nursery and greenhouse 

crops, hazelnuts, and cane berries, and triclopyr is one 

of the ingredients (along with 2,4-D) in CrossbowTM, 

a potent herbicide that is widely used to control blackberries and other brush. 

Nearly half of the pesticides applied to agricultural lands in 

Clackamas County are used for nursery and greenhouse crops. 

11 
Figure 5. Maximum concentrations of herbicides and insecticides in the Clackamas River Basin, May and October 2000. (** Indicates 

value equal to or exceeding an aquatic-life criterion. Quality-control data indicate a high bias [323% recovery] for carbaryl, see 

table A-2 in appendix.) 

Spot applications may help reduce the amount of pesticides that 

eventually enter streams. 

Rock Creek contained the greatest number of 

pesticides—18 (table 2 and table 3). The highest 

concentration of atrazine (0.30 μg/L) and triclopyr 

(1.3 μg/L) were found in Rock Creek, and one highly 

turbid sample collected from Rock Creek in October 

contained 15 pesticides. Twelve pesticides were found 

in Richardson Creek, and concentrations were somewhat lower than in Sieben, Rock, and Deep Creeks. 

Fifteen compounds were detected in Deep Creek, 

with the herbicides bromacil, diuron, atrazine, 

napropamide, metolachlor, and 2,4-D occurring at the 

highest concentrations, ranging from 0.06 to 0.27 μg/L 

(table 3). The breakdown product of the banned 

insecticide DDT (p,p’-DDE) was found only at this site 

in October, at a concentration of 0.002 μg/L. Other 

USGS studies have shown high concentrations of 

p,p’-DDT and its breakdown products in nearby 

Johnson Creek, possibly due to erosion of sediments in 

agricultural areas (Edwards, 1994). 

Eagle and Clear Creeks, which drain larger 

watersheds consisting mostly of forestland, Christmas 

tree plantations, and some rural residential land, 

contained fewer pesticides (from 2 to 5 pesticides each) 

at lower concentrations compared with the other lowerbasin tributaries (table 3). Atrazine, an herbicide 

commonly applied to conifer trees, and its breakdown 

product deethylatrazine, were detected in both Eagle 

and Clear Creeks. Another herbicide that is applied to 

Christmas trees, pendimethalin (Oregon State 

University, 2001b), also was detected in Clear Creek. 

Due to their higher streamflows, these two streams had 

pesticide loads that were sometimes high, particularly 

for atrazine in May and metolachlor in October. 

12 
Herbicides are used for weed control in Christmas tree plantations. 

Potential Pesticide Source Areas 

In order to examine the potential sources of 

pesticides detected in the Clackamas River, the relative 

pesticide load from each of the sampled tributaries was 

determined for each of the pesticides detected in the 

main stem. This approach estimates the relative 

amounts, calculated as the instantaneous pesticide 

loads (in grams per day [g/d]) that, in theory, could be 

contributed by each of the tributaries during sampling. 

Several factors, however, contribute uncertainty 

in such analyses, including the dynamic nature of 

streamflow during storms, determined largely by the 

timing and spatial pattern in rainfall and runoff. Heavy 

precipitation may transport pesticides and other 

chemicals to streams initially, but continued runoff may 

actually lower pesticide concentrations in the streams 

through dilution after a period of sustained rainfall. 

Additional uncertainty complicates the relationship 

between pesticide loads in the tributaries with those in 

the main stem, including unknown travel times from 

sampling locations in the tributaries to those in the 

main stem, and in the reporting accuracy of pesticide 

concentrations by the laboratory. 

Of the 20 pesticides detected in the tributaries 

during the May storm, only atrazine and diuron were 

detected in the main-stem Clackamas River (table 3), 

where the high streamflow (more than 7,000 cfs) 

provided a high degree of dilution. Two of the top 

three loads for pesticides detected from all tributaries 

combined were from atrazine and diuron, making up 

34% of the total (table 4). Only bromacil had a higher 

load—143 g/d or about 25% of the total pesticide load, 

all from Deep Creek. Bromacil, which was found only 

in Deep Creek, was not detected in the main-stem 

Clackamas River due to a combination of dilution 

(75% of the flow originated from forestland in the 

upper basin) and a relatively high laboratory detection 

limit for bromacil (0.04 μg/L; table 1). 

More than 80% of the total pesticide load from 

the six tributaries combined during the May storm 

was attributable to inputs from Deep and Rock Creeks, 

and nearly 90% of the total pesticide load during the 

October storm was attributable to Sieben Creek (fig. 6). 

In May, the herbicides atrazine and diuron were 

detected in the Clackamas River at Carver and in each 

of the four lowermost tributaries (table 3). Deep Creek 

accounted for 53% of the atrazine and 94% of the 

diuron load measured in the tributaries in May (fig. 7), 

which by calculation accounted for 33% of the atrazine 

and 33% of the diuron load in the main-stem Clackamas River. Eagle, Clear, and Rock Creeks also were 

important contributors of atrazine. Atrazine is used to 

control broadleaf and grassy weeds in corn, Christmas 

trees, and other crops. It is also used as a nonselective 

herbicide on noncroplands, golf courses, and on urban 

landscaping (Extoxnet, 1996). 

Diuron is used to kill moss and broadleaf and 

grassy weeds in urban areas and is also used on a 

variety of agricultural crops—especially grass seed, 

hay, and hazelnuts (Oregon State University, 2001b). 

Diuron is also applied along roads to control vegetation in a formulation called KrovarTM that also contains 

the herbicide bromacil (Robert Edgar, Oregon Department of Transportation, written commun., 2000). 

Concentrations of diuron and bromacil were both 

high in Deep Creek relative to concentrations in most 

other streams (table 3). The higher concentrations 

13 
c 

May 

of total 

Pesticide or a load (g/d)b 

Main-stem 

load (g/d)c a load (g/d)b load (g/d)c 

Bromacil 143 nd Dichlobenil 799 

Atrazine 117 144 

Diuron Diuron 1.9 54 

nd 1.4 

Napropamide 1.3 

nd 1.1 

.6 

.6 

.4 

nd .4 

Diazinon nd .4 

nd .3 

nd .3 

Ethoprop nd .2 

nd .1 

nd .1 

Prometon .1 

Pronamide nd .1 

.1 .3 nd 

nd 

.2 nd 

.02 

a 

b 

Table 4. Pesticide loads from the main-stem Clackamas River and lower-basin tributaries, May and October 2000 

[Pesticide load in grams per day (g/d) is the product of streamflow (in cubic feet per second) and pesticide concentration (in micrograms per liter, or parts per 

billion); pesticide loads are estimates due to the combined variation in streamflow and pesticide concentrations during storms; nd, not detected in the main 

stem; 2,4-D, 2,4-dichlorophenoxyacetic acid; DCPA, dimethyl-2,3,5,6-tetrachloroterephthalate; DDE, dichlorodiphenyldichloroethylene] 

October 

Percentage Percentage 

of total 

breakdown product 

load from 

tributaries 

Tributary Pesticide or 

breakdown product 

load from 

tributaries 

Tributary Main-stem 

24.6 76.8 792 

20.1 187 Triclopyr 13.8 nd 

 14.9 86.6 239 19.6 

2,4-D 10.7 61.9 Linuron 14.7 nd 

6.3 36.7 nd Napropamide 13.8 nd 

Metolachlor 5.5 32.0 DCPA 11.4 nd 

Simazine 4.5 26.3 nd Trifluralin 6.6 6.0 

Deethylatrazine 3.9 22.9 nd Pendimethalin 5.9 nd 

Terbacil 2.4 13.9 nd Diazinon 4.5 9.1 

Dichlobenil 1.7 9.7 Pronamide 4.3 nd 

1.3 7.8 Metolachlor 4.0 12 

Triclopyr 1.2 7.1 Chlorpyrifos 3.4 nd 

Trifluralin 1.1 6.4 Simazine 2.7 9.6 

 .8 4.5 Atrazine 2.0 nd 

Tebuthiuron .3 1.7 Ethoprop .9 nd 

DCPA .2 1.3 Tebuthiuron .9 nd 

.2 1.0 nd Carbaryl .9 nd 

.1 .7 Prometon .6 nd 

Carbaryl Deethylatrazine .04 .5 nd 

Chlorpyrifos .1 .3 Dieldrin .03 .3 nd 

Malathion .02 

p,p'-DDE .2 nd 

Fonofos .01 .1 nd 

Percentage of the total instantaneous pesticide load (all pesticides) from all measured tributaries for each storm combined. 

Total measured load of each pesticide from all measured tributaries combined for each storm. 

Sample was collected from the Clackamas River at Carver in May, and therefore does not include contributions from downstream tributaries, including 

Rock and Sieben Creeks; October sample was collected from a water-treatment-plant intake in the lower river, but streamflow was measured upstream 

at Carver. 

Figure 6. Relative pesticide loads from the lower-basin tributaries, May and October 2000. (Percentage of total load for all pesticides, for all 

streams sampled). 

14 
of these herbicides in Deep Creek may be related to the 

greater number of road miles in the Deep Creek Basin 

relative to the other basins. Further, both diuron and 

bromacil appear to be relatively persistent; Wood (2001) 

found both herbicides in a roadside drainage ditch that 

received an experimental application of Krovar after more 

than 3 months and 20 inches of rain, indicating a 

long-term residual for these compounds. The aquatic-life 

criterion for bromacil—the concentration of pesticide 

above which aquatic organisms might be adversely 

affected—is 5 μg/L (table 5), or 18 times higher than the 

concentration in Deep Creek. The possible effect of the 

diuron concentration in Deep Creek (0.150 μg/L) is 

difficult to evaluate because no aquatic-life criterion 

exists for diuron. Extoxnet (1996), however, reports that 

diuron is moderately toxic to fish and highly toxic to 

aquatic invertebrates. 

Six pesticides were detected in the lower 

Clackamas River during the October storm (table 3). At 

this time, most of the measured pesticide load from the 

tributaries was from Sieben Creek (fig. 8). The highest 

Herbicides are applied to Clackamas River Basin roadsides for 

vegetation control; shown here is U.S. Highway 26 in the 

Deep Creek Basin. 

15 

Figure 7. Relative pesticide loads in the main-stem Clackamas River 

and lower-basin tributaries, May 2000. (Relative loads from the 

tributaries are the percentage of total load, by mass, of each 

pesticide from all the measured tributaries combined.) 

measured load of metolachlor, however, came from Clear 

Creek, with lesser contributions from each of the other 

four tributaries. Metolachlor is a preemergent herbicide 

used to control broadleaf weeds and annual grasses on 

nursery and field crops, including grass seed, sweet corn, 

beans, and peas. It also is applied to woody ornamentals 

and along right-of-ways (Extoxnet, 1996). 

Most (about 80%) of the measured simazine load 

from the tributaries came from Deep and Sieben Creeks 

during the October storm (fig. 8). Simazine is a selective 

herbicide used to control broadleaf weeds and annual 

grasses on nursery and field crops, including Christmas 

trees, hazelnuts, and cane berries. Simazine also may be 

used to control aquatic plant growth in farm ponds, 

swimming pools, and fish hatcheries (Extoxnet, 1996). 
Figure 8. Relative pesticide loads in the main-stem Clackamas River 

and lower-basin tributaries, October 2000. (Relative loads from 

tributaries are the percentage of total load, by weight, of each 

pesticide from all the measured tributaries combined.) 

Pesticide Concentrations Relative to Water-Quality 

Standards and Suggested Guidelines to Protect Human 

Health and Aquatic Life 

Despite the detection of nine pesticides in the 

Clackamas River and untreated drinking water, no 

pesticides were detected in three samples of treated 

drinking water collected during this study. None of the 

pesticides detected in the Clackamas River exceeded 

U.S. Environmental Protection Agency (USEPA) 

drinking-water standards (table 5), although no 

standards exist for two of the compounds detected 

in the main stem, dichlobenil and imazaquin (U.S. 

Environmental Protection Agency, 2000a). 

Aquatic-life criteria exist for 17 of the 27 

pesticides or breakdown products detected in the 

Clackamas River Basin (table 5). Multiple guidelines 

are presented in table 5 due to the large range of values 

among the different agencies. Concentration criteria 

suggested by the National Academy of Sciences/ 

National Academy of Engineering (NAS/NAE), for 

example, are lower than those of other agencies 

because NAS/NAE criteria incorporate a 100-fold 

safety factor, thereby providing a greater amount of 

protection for aquatic life. Some of the rationale for 

this “safety buffer” includes the fact that criteria are 

typically developed for single pesticides and do not 

account for exposure to multiple compounds or 

repeated exposures. Studies by the USGS in 

agricultural and urban watersheds throughout the 

United States since the early 1990s found that more 

than half of the streams sampled contained pesticides at 

concentrations that exceeded aquatic-life criteria (U.S. 

Geological Survey, 1999). Although biological 

communities in many of these streams were impaired 

or otherwise degraded, it is difficult to isolate the 

effects of pesticides from other impacts, such as 

sedimentation, nutrient enrichment, and habitat 

degradation. 

Six compounds (all insecticides), including 

carbaryl, chlorpyrifos, diazinon, dieldrin, malathion, 

and the breakdown product of DDT (p,p’-DDE), were 

found at concentrations that exceeded an aquatic-life 

criterion (fig. 5 and table 5), sometimes for multiple 

pesticides in one sample. Each of the four lowermost 

tributaries (Deep, Rock, Richardson, and Sieben 

Creeks) contained at least one pesticide at a concentration that equaled or exceeded a criterion. Rock and 

Sieben Creeks each contained three pesticides at concentrations that exceeded aquatic-life criteria (table 3 

16 
and table 5). Concentrations of the organophosphate 

insecticides chlorpyrifos and diazinon exceeded their 

aquatic-life criteria by several-fold in these streams. 

Diazinon was detected in each of the four lowermost 

tributaries, and concentrations exceeded the NAS/NAE 

aquatic-life criterion in all samples collected from 

Sieben and Rock Creeks. The highest diazinon 

concentration (0.160 μg/L, measured in Sieben Creek 

in May) exceeded its aquatic-life criteria by a factor of 

1.5–18, depending on which criterion is applied (table 

5). Diazinon and chlorpyrifos are restricted-use 

insecticides that were commonly found together in 

urban streams during a survey of pesticides in streams 

across the country (U.S. Geological Survey, 1999), 

although both may have agricultural uses (table 7). 

The Koc values of these compounds range from 1,000 

to 6,070 (table A-1 in the appendix), indicating a 

relatively strong tendency to adsorb to soil particles. 

It is likely that soil erosion is an important transport 

process for mobilizing diazinon and chlorpyrifos, 

which is consistent with the high turbidity values in 

Rock and Sieben Creeks, particularly during the 

October sampling. As mentioned previously, because 

water samples were filtered prior to analysis, it is likely 

that concentrations reported here are lower than what 

aquatic organisms are exposed to. 

Potential Effects of Pesticides on Aquatic Life 

Many pesticides have the potential to harm 

aquatic life, especially benthic macroinvertebrates, 

fish, amphibians, and various stream microbes (Nowell 

and others, 1999) that are exposed to high concentrations of pesticides. The Clackamas River and some of 

its tributaries support a variety of anadromous and 

resident fish species, although declines in some 

populations, including winter steelhead trout, spring 

Chinook, and coho salmon, have resulted in their being 

on the Endangered Species List. Potential explanations 

for such declines include overharvesting of fish, dams, 

degraded water quality, and poor stream habitat, but the 

effects of pesticides have not been fully evaluated. 

One of the complicating factors in determining 

safe exposure levels for aquatic life to pesticides is that 

laboratory studies typically involve only a single 

compound and do not consider additive or possibly 

synergistic effects of exposing aquatic life to multiple 

pesticides at once. While it is logical to assert that two 

pesticides with the same mode of action would act in 

an additive fashion (such as the organophosphate 

insecticides chlorpyrifos and diazinon, which both 

inhibit the nervous system enzyme acetylcholine 

esterase), certain pesticides may increase the toxicity of 

others through various physiological mechanisms that 

are just beginning to be understood. For example, the 

toxicity of organophosphate insecticides to chironomid 

midge larvae can increase markedly by simultaneous 

exposure to the herbicide atrazine (Pape-Lindstrom and 

Lydy, 1997). Kao and others (1995) demonstrated that 

this occurs because atrazine stimulates cytochrome 

P450 and general esterase activity in insects, which 

increases the conversion of organophosphates into 

oxon breakdown products, such as diazoxon and 

malaoxon, which are more toxic than the parent 

pesticide compounds (diazinon and malathion). 

In addition, toxicity tests in the past were most 

often designed to detect effects on growth and survival 

rates, not on developmental or reproductive attributes. 

New research suggests that exposure to environmentally relevant pesticide concentrations may cause such 

effects. Laboratory experiments by Hayes and others 

(2002a), for example, showed that exposure to the 

herbicide atrazine produced developmental deformities 

in frog gonads in 20% of male frogs studied at 

concentrations as low as 0.10 μg/L. This concentration is 30 times lower than the USEPA maximum 

contaminant level allowable in drinking water (3 μg/L; 

table 5). However, because the results of Hayes and 

others contradict studies used to develop drinkingwater standards, and also because those results have not 

yet been replicated, more study is needed. This is 

particularly true considering that atrazine is the most 

widely used pesticide in the world and is the most 

frequently detected pesticide in streams nationwide 

(U.S. Geological Survey, 1999). Atrazine was the most 

frequently detected pesticide in the Clackamas River 

Basin, occurring in all of the tributaries sampled, with 

the highest concentrations occurring in Rock and Deep 

Creeks (0.30 and 0.12 μg/L, respectively). 

Sublethal effects on aquatic life from exposure to 

pesticides, such as impaired reproduction and development, have been documented by numerous laboratory 

and field studies. Cope and others (1970) showed 

delayed fish spawning from exposure to 2,4-D. 

17 
Table 5. Pesticide concentrations relative to human health standards and aquatic-life criteria 

[Pesticide concentrations in micrograms per liter (μg/L), or parts per billion; USEPA, U.S. Environmental Protection Agency; CCME, Canadian Council of 

Ministers of the Environment; NAS/NAE, National Academy of Sciences/ National Academy of Engineering; USGS, U.S. Geological Survey; ** concentration exceeds a criterion; ns, no standard available; 2,4-D, 2,4-dichlorophenoxyacetic acid; DCPA, dimethyl-2,3,5,6-tetrachloroterephthalate; DDE, dichlorodiphenyldichloroethylene] 

a 

Lakes 

of 

detections acuteb c d e NAS/NAEf g 

Atrazine 0.30 3 350h 12h 1.8 

.16** .6 HAL .1h .1h ns 0.009 .08 

Simazine 9 4 ns ns 10 ns 10 10 

Diuron 8 10 HAL ns ns ns ns 1.6 ns 

8 100 HAL ns ns 7.8i

 ns ns 7.8 

7 ns ns ns ns ns ns ns ns 

7 1.3 ns ns ns ns ns ns ns ns 

7 5 HAL ns ns .20 ns ns 

Dichlobenil 6 16.8 

Prometon 6 100 HAL ns ns ns ns ns ns 

2,4-D 5 .3 70 MCL ns ns 4.0j

 ns 3 j 

5 1.3 ns ns ns ns ns ns ns ns 

4 20 HAL .041 ns .041 

Pendimethalin 4 ns ns ns ns ns ns ns ns 

3 700 HAL ns ns .20 ns .20 

2 70 HAL ns ns ns ns ns ns 

Dieldrin 2 .02 RSD5 .056 ns ns .005 .056 

Ethoprop 2 ns ns ns ns ns ns ns ns 

Pronamide 2 1 HAL ns ns ns ns ns ns 

2 500 HAL ns ns 1.6i

 ns ns 1.6 

Bromacil 1 90 HAL ns ns 5.0i

 ns ns 5.0 

p,p'-DDE 1 1 RSD5 1.1k .001k ns ns ns .001k 

1 10 HAL ns ns ns ns ns ns 

Imazaquin 1 .047 ns ns ns ns ns ns ns ns 

Linuron 1 ns ns ns ns 7.0i

 ns ns 7.0 

1 .025** 100 HAL ns .1 ns ns .008 .1 

1 90 HAL ns ns ns ns ns ns 

a 

b 

c 

d 

e 

f 

/ 

g 

h 

i 

j 

k 

USEPA 

human health 

Clackamas River Basin standards Aquatic-life criteria/guidelines/recommendations/benchmark 

Great 

WaterPesticide or Number Quality 

breakdown Maximum USEPA USEPA Canada Objecproduct concentration Value Type chronic CCME tives USGS 

13 MCL ns ns 1.8 

Diazinon 10 0.08 

.19 MCL 

.22 

Metolachlor .06 

Deethylatrazine .021 

Napropamide 

Trifluralin .082 .20 

ns ns ns ns ns ns 37 ns 

.012 

4.0 

Triclopyr 

Chlorpyrifos .056** .083 .0035 .001 

.03 

Carbaryl .026** .02 

DCPA .46 

.008** .24 

.01 

.17 

Tebuthiuron .034 

.27 

.002** 

Fonofos .007 

.59 

Malathion 

Terbacil .026 

USEPA maximum contaminant level (MCL), lifetime health advisory 

(HAL), or risk-specific dose at a cancer risk level of 1 in 100,000 

(RSD5) allowable in drinking water (U.S. Environmental Protection 

Agency, 2000a). 

Criterion maximum (acute) concentration—the highest concentration 

that organisms can be exposed to for a short (1-hour) period; protects 

95% of a diverse group of genera; should not occur more than once 

every 3 years (U.S. Environmental Protection Agency, 1999). 

Criterion continuous (chronic) concentration—the highest concentration that organisms can be exposed to for an extended period; protects 

95% of a diverse group of genera; should not occur more than once 

every 3 years (U.S. Environmental Protection Agency, 1999). 

Intended to protect all aquatic life and should not be exceeded at any 

time (Canadian Council of Ministers of the Environment, 2001). 

Represents the maximum allowable concentration in the boundary 

waters between the United States and Canada to protect recognized, 

most sensitive uses (International Joint Commission Canada and the 

United States, 1978). 

Recommended maximum concentrations in all waters at all times (National Academy of Sciences National Academy of Engineering, 

1973). 

“Preferred” ecological benchmark adopted by the USGS National 

Water-Quality Assessment Program to evaluate pesticide concentrations in streams nationwide (U.S. Geological Survey, 1999). 

Draft guideline (U.S. Environmental Protection Agency, 2000; 

2001a; 2001b). 

Interim guidelines (Canadian Council of Ministers of the Environment, 2001). 

Sum of phenoxy herbicides. 

Based on the total concentration of the parent compound p,p’-DDT 

plus metobolites (p,p’-DDE and others). 

18 
Von Westernhagen and others (1989) showed reduced 

fish fertilization from exposure to dieldrin. Choudhury 

and others (1993) and Baatrup and others (2001) 

showed reproductive system disruption in fish from 

exposure to carbaryl and p,p’-DDE, respectively. 

Hayes and others (2002b) showed developmental 

irregularities in frogs from low-level exposure to 

atrazine. Colborn and others (1993) reported endocrine 

system disruption in wildlife and humans. Exposure to 

pesticides also may affect fish behaviors, including 

predator avoidance and homing (Scholz and others, 

2000), swimming (Matton and Laham, 1969), and 

feeding (Bull, 1974). Many pesticides thought to elicit 

such sublethal effects, including 2,4-D, atrazine, 

carbaryl, dieldrin, and p,p’-DDE, were found in the 

Clackamas River or its tributaries during this study, but 

their effects on aquatic life in the Clackamas River 

Basin are not yet known. 

To address the problem of evaluating the effects 

of exposure to multiple pesticide compounds, Munn 

and Gilliom (2001) developed a pesticide toxicity 

index (PTI) that combines pesticide exposure (measured concentrations of pesticides in stream water) with 

toxicity estimates from laboratory studies (typically 

96-hour LC50 values, the lethal concentration for 50 

percent of the test population for a 96-hour chemical 

exposure). The PTI is the sum of toxicity quotients for 

each pesticide compound measured in a stream: 

n ⎛

⎜ ⎟

⎞ Ei PTI =	 ⎜

Σi ⎟--------------------

⎜i = 1⎟ MTCx i , ⎝ ⎠

where: 

Ei = concentration of pesticide i 

MTC x, i = median toxicity concentration for the 

pesticide i for taxonomic group x 

n = number of pesticides, and 

E and MTC are expressed in the same units 

Although the PTI does not determine whether 

water in a sample is toxic, its values can be used to rank 

or compare the toxicity of samples on a relative basis. 

The PTI approach may be useful for comparing the 

significance of pesticides in different streams on a 

common basis, for evaluating relations between 

pesticide exposure and observed biological conditions, 

and for prioritizing future studies. PTI values for 

samples collected in the Clackamas River Basin were 

calculated for both benthic invertebrates and fish (table 

6). 

In all samples, the PTI values were higher for 

benthic invertebrates than for fish, indicating a greater 

risk to invertebrates. Moreover, EPT taxa richness (the 

number of mayfly, stonefly, and caddisfly taxa in a 

sample, an index often used to indicate the health of the 

benthic invertebrate community) declined steadily, 

from 31 EPT taxa in Eagle Creek to 1 in Sieben Creek, 

as the PTI values increased (fig. 9). Dewberry and 

others (1999) found a low diversity of aquatic insects in 

both Rock and Sieben Creeks and attributed the poor 

community condition to habitat impairment. In light of 

this study’s findings, pesticide exposure also may be a 

factor affecting aquatic life in these and other 

tributaries in the Clackamas River Basin. 

One of the potential explanations for the low 

EPT taxa richness in Rock and Sieben Creeks is the 

occurrence of the insecticides diazinon and chlorpyrifos, which were found in both streams at concentrations exceeding their aquatic-life criteria (table 5). 

Both of these organophosphorus insecticides impair 

nervous system function through inhibition of the 

enzyme acetylcholinesterase (AChE) (Nowell and 

others, 1999). Exposure to these compounds may 

inhibit AChE activity in aquatic life such as benthic 

invertebrates. Studies also have found that diazinon 

impairs predator avoidance behavior and homing 

ability in Chinook salmon at concentrations of 1 and 

10 μg/L, respectively (Scholz and others, 2000). 

Although these concentrations are much higher than 

those found in the Clackamas River Basin, diazinon 

was detected in the main-stem Clackamas River twice 

(table 3), the effects of sustained or multiple exposures 

to diazinon are not known. The recent cancellation 

order for all products containing diazinon (U.S. 

Environmental Protection Agency, 2003), however, 

should help reduce the occurrence of this pesticide in 

the environment and subsequent exposure to aquatic 

life. 

19 
Table 6. i i 

−

Date PTI-Fish 

Rock Creek 

Rock Creek 

Clear Creek 

Clear Creek 

20 October 2000 

3.4x10-3 1 

3.4x10-3 2 

2.5x10-3 3 

1.2x10-3 4 

8.5x10-4 5 

2.4x10-4 6 

1.9x10-4 7 

1.5x10-4 8 

8.1x10-5 9 

5.7x10-5 10 

5.7x10-5 11 

4.4x10-5 12 

3.3x10-6 13 

1.1x10-6 14 

8.7x10-7 15 

nd nd 

nd nd 

nd nd 

nd nd 

nd nd 

Rock Creek 

Rock Creek 

Clear Creek 

Clear Creek 

20 October 2000 

1.1x10-1 1 

5.3x10-2 2 

5.2x10-2 3 

3.2x10-2 4 

2.9x10-3 5 

9.8x10-4 6 

9.4x10-4 7 

8.6x10-4 8 

3.5x10-4 9 

3.5x10-4 10 

1.6x10-4 11 

1.3x10-4 12 

1.6x10-5 13 

1.9x10-6 14 

1.4x10-6 15 

nd nd 

nd nd 

nd nd 

nd nd 

nd nd 

Pesticide toxic ty index (PTI) values for f sh and benthic invertebrates for samples collected in the Clackamas River Basin, 

May 2000 August 2001 

[Larger PTI values indicate greater relative toxicity; nd, no pesticides detected] 

Rank, in order of 

Sample descending toxicity 

Sieben Creek 

Sieben Creek 

Sieben Creek 

Richardson Creek 

Deep Creek 

Clackamas River untreated water 

Richardson Creek 

Deep Creek 

Clackamas River untreated water 

Clackamas River at Carver 

Eagle Creek 

Eagle Creek 

Clackamas River at Estacada 

Clackamas River 

Treated drinking water 

Treated drinking water 

Treated drinking water 

October 2000 

9 October 2000 

May 2000 

October 2000 

May 2000 

May 2000 

August 2001 

May 2000 

October 2000 

October 2000 

October 2000 

May 2000 

May 2000 

May 2000 

October 2000 

May 2000 

October 2000 

January 2001 

August 2001 

Rank, in order of 

Sample Date PTI-Benthic invertebrates descending toxicity 

Sieben Creek 

Sieben Creek 

Sieben Creek 

Deep Creek 

Deep Creek 

Richardson Creek 

Richardson Creek 

Clackamas River un treated water 

Clackamas River untreated water 

Clackamas River at Carver 

Eagle Creek 

Eagle Creek 

Clackamas River at Estacada 

Clackamas River 

Treated drinking water 

Treated drinking water 

Treated drinking water 

October 2000 

May 2000 

9 October 2000 

May 2000 

May 2000 

October 2000 

May 2000 

October 2000 

October 2000 

October 2000 

August 2001 

May 2000 

May 2000 

May 2000 

October 2000 

May 2000 

October 2000 

January 2001 

August 2001 

20 
 
Figure 9. Pesticide toxicity index (PTI) values compared with EPT 

taxa richness for samples collected from tributaries in the Clackamas River Basin, Oregon. (Pesticide samples were collected from 

sites in May and October 2000; invertebrate data in September 1999 

[USGS, unpublished data] and August/September 1997 [Dewberry 

and others, 1999]. No pesticides were detected in Eagle Creek in 

October.) 

Potential Uses of Pesticides in the Clackamas River 

Basin 

According to the USEPA, most (77% by volume) 

of the national pesticide use occurs on agricultural 

land, about 11% is used in homes and gardens, and 

12% is used by industries, commercial operations, and 

governments (U.S. Environmental Protection Agency, 

1997). Identifying the sources of pesticides detected in 

the Clackamas River Basin is difficult because most of 

the pesticides detected have multiple uses, and all of 

the sampled streams drain areas of mixed land use. 

Of the 25 parent compounds detected, 22 have agricultural applications, 24 have urban applications, 16 are 

approved for application to golf courses, 11 are approved for application along right-of-ways, and 5 have or 

once had forestry applications (table 7). Thirteen of the 

pesticides were previously banned or have some form 

of restricted use. 

Agricultural uses—Approximately 100,000 

acres of land is used for agriculture in Clackamas 

County. Pastureland, hay fields (mostly alfalfa), 

nurseries, and greenhouses make up about 60% of the 

agricultural land in the basin (fig. 10). In 2000, the top 

agricultural commodity in Oregon was production from 

nurseries and greenhouses. Nursery and greenhouse 

sales have steadily increased in Oregon, from $347 

million in 1993 to $642 million in 2000 (Oregon 

Department of Agriculture, 2001). Clackamas County, 

which was the leading county for nursery sales in 

Oregon, had approximately 21,370 acres in nursery and 

greenhouse production in 1997. Clackamas County 

also is one of the top Christmas tree producing counties 

in the country. According to the National Agricultural 

Statistics Service (2002), 18 herbicides, 12 insecticides, and 4 fungicides are used on Christmas trees in 

Oregon, and several of these were detected in the 

Clackamas River Basin (table 7). 

Figure 10. Top agricultural crops and commodities grown in 

Clackamas County, Oregon, 1997 (by percentage of total acreage). 

(Source: Oregon Department of Agriculture, 1997.) 

Of the estimated agricultural applications in 

Clackamas County, most of which is in the Clackamas 

River Basin, the highest amounts of pesticides (49%) 

are applied to nursery and greenhouse crops, with 

lesser amounts, ranging from 4 to 15%, applied to 

pastureland, Christmas trees, hay fields, hazelnuts, 

and grass seed fields (fig. 11). These estimates were 

calculated using crop acreage obtained from the 

Oregon Department of Agriculture (1997) and average 

pesticide application rates obtained from Oregon State 

University Extension Services (2001a, b) and from the 

National Agricultural Statistics Service (2002). It is 

important to note, however, that the application rates 

used here are approximations and assume a single 

application per year, which may not be the case for 

crops receiving multiple pesticide applications in a 

season, such as strawberries and fruit trees. Therefore, 

these estimates may differ considerably from what is 

actually applied. 

21 
22
 

−01 

Right-	 

a b c d e a	 

BromacilCarbaryl2,4-D

p,p’ g 

DiazinonDichlobenil

Diuron

Imazaquinh 

MalathionNapropamidePrometon 

H X X X 

H X 

I X
 

I X
 

H X
 

H X
 

IBP X 

I X 

H X 

I

H X 

N X 

I X 

H

H X 

I X 

H X 

H X 

H X 

H

H X 

H X 

H X 

H X 

H X 

H X 

X

X X 

X X 

X X 

X X 

X X 

X X 

X

X

X X 

X X 

X

X X 

X X 

X

X X 

X

X X 

X X 

X

X X 

X X 

X 

X	

X X

X 

X

X	 

X 

X

X

X

X

X

X X 

X 

abc defgh

Table 7. Potential uses of pesticides detected in the Clackamas River Basin, Oregon, 2000 [H, herbicide; I, insecticide; IBP, insecticide breakdown product; N, nematocide; X, indicates likely use; DCPA, dimethyl-2,3,5,6-tetrachloroterephthalate; 2,4-D, 2,4-dic

DDE, dichlorodiphenyldichloroethylene; DDT, dichlorodiphenyltrichloroethane] 

Golf 

Compound Type Agriculture Urban courses of-ways Forestry Top agriculture uses 

Atrazine Chlorpyrifos 

DCPA 

-DDE 

Dieldrin Ethoprop Fonofos 

Linuron Metolachlor Pendimethalin Pronamide Simazine Tebuthiuron Terbacil Triclopyr Trifluralin 

Christmas trees, sweet corn 

None reported 

Pastureland, hay, cane berries, wheat, sweet corn 

Nurseries, hazelnuts, sweet corn, Christmas trees, strawberri

Pastureland, hay, grass seed, hazelnuts, wheat 

Nurseries, cucumbers, strawberries, squash, snap beans 

DDT was once used on numerous crops 

Grass seed, cane berries, fescue seed, nurseries, squash 

Nurseries, hazelnuts, cane berries, cauliflower, blueberries 

None reported 

Grass seed, hay, hazelnuts, fescue seed, cane berries 

Sweet corn, snap beans 

Nurseries, sweet corn, snap beans, broccoli, strawberries 

Cottonwood trees grown for pulp and grass turf 

Garden crops such as corn, potatoes, fruit trees, wheat, oats, 

Pastureland, hay, cane berries, hazelnuts, wheat 

Nurseries, grass seed, sweet corn, snap beans, green peas 

Nurseries, hazelnuts, cane berries, strawberries, rhubarb

Nurseries, Christmas trees, grass seed, snap beans, grapes 

None reported 

Nurseries, Christmas trees, cane berries, grass seed, alfalfa 

Nurseries, Christmas trees, hazelnuts, cane berries, blueberri

Pastureland 

Grass seed, cane berries, alfalfa, apples, peaches 

Pastureland, hay, Christmas trees, clearing heavy brush 

Nurseries, wheat, alfalfa, cucumbers, cauliflower 

Agricultural uses estimated from average pesticide application rate for crops in the Pacific Northwest (Oregon State University, 2001a; 2001b) and from estimated cro

Department of Agriculture, 1997). 

Anderson and others (1996); Krastzer, C.R. (1998); Panshin and others (1998); U.S. Geological Survey (1999). 

Pesticides used on and detected in ground water beneath golf courses (Jack Barbash, U.S. Geological Survey, Web page http://ca.water.usgs.gov/pnsp/golf.html, ac

Roadside applications (Rob Edgar, Oregon Department of Transportation, written commun., 2002; Ron Buck, Clackamas County Department of Public Works, wr

Cramer (1974). 

Oregon State University (2001a; 2001b). 

p,p’-DDE is one of several breakdown products of p,p’-DDT, an organochlorine insecticide. Estimated use is for p,p’-DDT, not p,p’-DDE. 

Imazaquin is applied to hybrid cottonwood trees grown for pulp and on grass turf. 
Figure 11. Percentage of total estimated pesticide applications to 

agricultural crops grown in Clackamas County, Oregon, 1997. 

[Source: Pesticide application estimates from Oregon State 

University Extension Services (2001) and from grower surveys 

published by the National Agricultural Statistics Service, 2002. Crop 

acreage for Clackamas County from the Oregon Department of 

Agriculture (1997).] 

Urban uses—Pesticides are used in urban areas 

to control weeds and insect pests on lawns, gardens, 

and ornamental trees and plants, and in homes to 

control pests such as ants and fleas. Nearly all of the 

pesticides detected in the Clackamas River Basin have 

urban uses, and several herbicides also are applied 

along right-of-ways such as roads, utility lines, and 

fences (table 7). The two streams draining the largest 

proportion of urban land in this study—Rock and 

Sieben Creeks—contained the greatest number and 

highest concentrations of pesticides (table 3). Several 

herbicides were found in all four of the lowermost 

tributaries in the Clackamas River Basin, many of 

which, including atrazine, metolachlor, simazine, 

prometon, diuron, and 2,4-D, are the most commonly 

detected herbicides in urban streams nationwide (U.S. 

Geological Survey, 1999). 

Pesticide Management and Future Studies 

Pesticide occurrence in streams is directly related 

to their use in upstream areas (U.S. Geological Survey, 

1999). The transport of pesticides from their target 

areas to streams and ground water depends on several 

factors, some of which are listed in table A-1 in the 

appendix. These include their solubility in water, 

half-lives (rate of breakdown in the environment), and 

physical or hydrologic characteristics of the watershed. 

Reducing pesticide contamination may be achieved 

through educating the public on the use of alternatives 

to pesticides (see Northwest Coalition for Alternatives 

to Pesticides, http://www.pesticide.org); avoiding 

application to areas adjacent to waterbodies; avoiding 

applications during windy periods or prior to rainfall; 

taking care when cleaning pesticide application 

apparatus; and controlling soil erosion from application 

areas. Developing and implementing other best 

management practices also may reduce the transport 

of pesticides to streams and ground water. 

From October 2002–September 2003, the USGS 

collected monthly samples of the lower Clackamas 

River for 234 contaminants, including pesticides, 

pharmaceuticals, fuel oxygenates, and other 

compounds as part of the National Water-Quality 

Assessment Program’s Source Water Assessment. 

These data will help characterize the temporal 

variations in contaminants in the main-stem Clackamas 

River. Additional sampling for pesticides in the 

lower-basin tributaries might be used to identify areas 

where pesticides are already contaminating streams 

and/or ground water. 

Future studies in the basin could also include 

land use or crop studies whereby smaller streams that 

drain areas with more homogeneous land uses are 

sampled for pesticides. Small-scale land use/land cover 

data also would facilitate future study design by 

identifying subbasins with a large percentage of a 

particular crop or land use. Such studies would benefit 

from pesticide use data, which would help determine 

which areas to focus on and which pesticides to test for. 

Follow-up studies could include evaluation of the 

benthic ecosystem (invertebrates and algae) or examination of potential reproductive, developmental, or 

behavioral effects on fish caused by exposure to 

pesticides. 

ACKNOWLEDGMENTS 

The author thanks the Clackamas River Water 

Providers and Clackamas County Department of 

Water Environment Services whose interest in 

protecting water quality in the Clackamas River 

Basin led to the development and funding of this 

23 
study. The author especially wishes to thank Gordon 

McGhee (Clackamas River Water) and Tim Jannsen 

(Clackamas County Water Commission) for helping 

with water-sample collection. Special recognition is 

due to the Portland Field Office and the Environmental 

Quality Section of the USGS Oregon District for their 

efforts during the storm sampling, especially Micelis 

Doyle, who coordinated the sampling in May 2000. 

Thanks also to Chauncey Anderson and Dan Wise 

(USGS) and Clair Klock and Rick Gruen (Clackamas 

County Soil and Water Conservation District) for their 

technical expertise and help with data analysis. Homer 

Rowley (U.S. Department of Agriculture) provided 

data on agricultural crops and pesticides, and Robert 

Edgar (Oregon Department of Transportation) and 

Ronald Buck (Clackamas County Road Maintenance 

Division) provided data on roadside herbicide 

applications. 

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26 
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___________________________________________________________________________________________ 

APPENDIX
 


27
 
28
 
APPENDIX TABLE A-1. Properties of pesticides detected in the Clackamas River Basin, Oregon, 2000−01 

[Pesticide movement rating is derived from empirical data on pesticide half-life and soil Koc from the Oregon State 

University Extension Pesticide Properties Database (P.A. Vogue, written commun., 1994); H, herbicide; I, insecticide; 

] 

Pesticide 

movement solubility half-life Soil 

(mg/L) Koca 

Atrazine H 33.0 60 

Bromacil H 60 32 

Carbaryl I 10 

I 30 

2,4-D H 

H 100 

p,p'-DDE IBP 1,000 

Diazinon I 60.0 

Dichlobenil H 21.0 60 

I 1,000 

Diuron H 42.0 90 

N 

I 17.0 40 

Imazaquin H 60.0 60 20 

H 75.0 

I 1 

H 

Napropamide H 74.0 70 

Pendimethalin H 90 

Prometon H 500 

H 15.0 

H 60 

H 360 80 

H 120 55 

H 46 20 

H 

N, nematocide; HBP, herbicide breakdown product; IBP, insecticide breakdown product; nd, no data 

Water Soil 

Compound Type rating (days) 

high 100 

very high 700.0 

low 120.0 300 

Chlorpyrifos very low 0.4 6,070 

moderate 900.0 10 20 

DCPA very low .5 5,000 

extremely low .1 50,000 

Deethylatrazine HBP nd nd nd nd 

low 40 1,000 

moderate 400 

Dieldrin extremely low .2 12,000 

moderate 480 

Ethoprop high 750.0 25 70 

Fonofos low 870 

very high 

Linuron moderate 60 400 

Malathion extremely low 130.0 1,800 

Metolachlor high 530.0 90 200 

moderate 700 

very low .3 5,000 

very high 720.0 150 

Pronamide low 60 800 

Simazine high 6.2 130 

Tebuthiuron very high 2,300.0 

Terbacil very high 710.0 

Triclopyr very high 430.0 

Trifluralin very low .3 60 8,000 

a

Organic carbon and sorption coefficient. Compounds with higher values have relatively greater affinity to 

adhere to sediment than those with lower values. 

Evaluation of quality-control data—No finding them in only one of the two samples. Differpesticides were detected in the blank samples, and the ences between these replicate samples also may have 

split sample contained similar concentrations of both resulted from real temporal variations in pesticide 

atrazine and diuron (table A-2). Replicate samples concentrations, because replicate samples were collectcollected from the Clackamas River at Carver in May ed about 15 minutes apart near the peak of the storm 

also were similar, with only atrazine and its breakdown hydrograph (fig. 2). No pesticides were detected in 

product deethylatrazine being detected at similar either replicate sample of treated drinking water 

concentrations. The second set of replicate samples collected in January. The spike sample indicated 

collected from Clear Creek in October showed greater that most of the detected pesticides had acceptable 

variation. Metolachlor was detected in both samples at recoveries—the median recovery for all pesticides 

similar concentrations, but three compounds—atrazine, was 111%. A few compounds (carbaryl, terbacil, 

triclopyr, and pendimethalin—were detected in just the and linuron) exhibited a high bias with recoveries of 

first sample. Concentrations of these compounds were between 174 and 330%. A low bias (recovery of 65 and 

less than the detection limit and therefore had a 50% 83%, respectively) was found for the breakdown 

probability of being detected, which is consistent with products p,p’-DDE and deethylatrazine. 

29 
--

--

--

μ

Sample Replicate/split Relative percent 

difference 

Atrazine 0.0109 e0.0106 3 

Diuron e.0133 e.0142 6 

Replicate—October 2000 Metolachlor .004 

Atrazine e.002 <.001 

<.25 

Pendimethalin e.008 <.01 20 

Replicate—January 2001 0 

Pesticide or 

Atrazine 

spike 

0.120 

e.088 

Percent 

107 

83 

Carbaryl .100 e.323 323 

.100 .106 106 

.100 .111 111 

p,p’-DDE .100 .065 65 

Diazinon .100 .106 106 

Dieldrin .100 .108 108 

.100 .111 111 

.100 .106 106 

.174 174 

Malathion .130 130 

Metolachlor .117 117 

Napropamide .100 .117 117 

Pendimethalin .100 .126 126 

.100 .105 105 

.100 .117 117 

.129 129 

.100 e.330 330 

APPENDIX TABLE A-2. Quality-control data 

[Pesticide concentrations in micrograms per liter ( g/L), or parts per billion; e, estimated value; spike data reported for only those compounds that were 

detected] 

Quality–assurance sample Pesticides detected concentration concentration 

Equipment blank—May 2000 None 

Laboratory blank—October 2000 None 

Equipment blank—January 2001 None 

Split—May 2000 

e.005 

Triclopyr e.040 

None None detected None detected 

Quality–assurance sample 

Spike—May 2000 

breakdown product 

Deethylatrazine 

Calculated 

0.113 

.105 

Reported 

concentration recovery 

Chlorpyrifos 

DCPA 

Ethoprop 

Fonofos 

Linuron .100 

.100 

.100 

Prometon 

Simazine 

Tebuthiuron .100 

Terbacil 

30