Pesticides in Stream Sediment and Aquatic Biota

Current Understanding of Distribution and Major Influences

REGIONAL TRANSPORT

DRY

DEPOSITION

EVAPORATION

SPRAY DRIFT

WIND EROSION

RUNOFF

WASTE

WATER

RUNOFF

PRECIPITATION

GROUND-WATER

DISCHARGE

TO STREAMS

DIFFUSION

(DURING TISSUE

DECOMPOSITION) BURIAL

RESUSPENSION

INGESTION

ELIMINATION

OF WASTES

REPRODUCTION

SORPTION TO BIOTA 

DIFFUSION

DESORPTION

DIFFUSION

DIFFUSION

SORPTION TO 

BED SEDIMENT

DESORPTION

DESORPTION

MIXING

SETTLING

REMOVAL BY

PEOPLE AND

WILDLIFE

SORPTION TO 

SUSPENDED PARTICLES

SEEPAGE SEEPAGE

DOWNSTREAM TRANSPORT

Highlights

Organochlorine pesticides such as DDT are still 

detected in many streams today, more than 20 years 

after their use in agriculture was prohibited.

DDT, dieldrin, and chlordane are the pesticides most 

frequently present in sediment and biota at levels that 

may be toxic to aquatic life, wildlife, or people. 

Nationally, levels of most organochlorine pesticides in 

whole freshwater fish have declined since the 1960s.

Organochlorine pesticides continue to enter United 

States streams from atmospheric deposition and 

erosion of soils contaminated from past use.

Pesticides with moderate-to-low water solubility, and 

moderate-to-high environmental persistence, have the 

potential to accumulate in sediment and aquatic biota. 

More research is needed on pesticides in urban areas, 

accumulation of currently used pesticides in sediment 

and aquatic biota, and the toxic and long-term effects of 

pesticide mixtures on people and wildlife.

This report summarizes a comprehensive analysis of existing

information on pesticides in bed sediment and aquatic biota of

United States rivers and streams: their geographic distribution,

sources, trends, environmental fate, and biological significance. It

is one of a four-part series that synthesizes current knowledge

and understanding of pesticides in the nation’s water resources

as part of the National Water-Quality Assessment Program.

Pesticides in the Hydrologic System

About 1 billion pounds of pesticides are used each year in

the United States to control weeds, insects, and other organisms.

About 80 percent of this quantity is used in agriculture. Although

the use of pesticides has resulted in increased crop production and

other benefits, it has raised concerns about potential adverse

effects on the environment and human health. 

In many respects, the greatest potential for unintended

adverse effects of pesticides is through contamination of the

hydrologic system, which supports aquatic life and related food

chains and is used for recreation, drinking water, irrigation, and

many other purposes. Water is one of the primary pathways by

which pesticides are transported from their application areas to

other parts of the environment (see Figure 1).

Importance of Stream Sediment and Biota

Sediment serves as a habitat for benthic biota (such as

insects and clams, which are commonly consumed by fish), as

both a source and a removal mechanism for some contaminants to

and from the stream, and as a vehicle for contaminant transport

downstream. Aquatic biota also are important in the food web of

terrestrial organisms, with some aquatic biota, such as fish, being

consumed by people and wildlife. Analyzing contaminants in

sediment and aquatic biota provides an efficient way to test

whether hydrophobic contaminants are present in the stream.

Hydrophobic chemicals have little or no affinity for water; such

chemicals have a low solubility in water, a high solubility in

lipids (fats), and a strong tendency to sorb to organic material in

soil and sediment. Many hydrophobic chemicals also are resistant

to degradation, so they persist for a long time in the environment.

Persistent hydrophobic contaminants in a stream may accumulate

in sediment and aquatic biota (Figure 1), even when

concentrations in the water are too low to be detected using

conventional sampling and analytical methods. Historically, the

pesticides of primary concern in sediment and aquatic biota have

been the organochlorine insecticides, such as DDT, which were

heavily used in agriculture, termite control, and malaria control

programs from the mid-1940s to the 1960s or later.

Historical Study Efforts

During the past 30 years, over 400 scientific studies have

looked for pesticides in stream sediment or aquatic biota in the

Figure 1. Pesticide movement in the hydrologic cycle including pesticide 

movement to and from sediment and aquatic biota within the stream. Modified

from Majewski and Capel (1995).
j

j j

j j jjj

Rarely detected (at <5 percent of sites in sediment and biota)

Intermediate (detected at 5–20 percent of sites in sediment and 

 5–60 percent in biota)

Commonly detected (at >20 percent of sites in sediment and biota)

Water solubility, in micrograms per liter

104

103

102

10

103 105 10 0.1 10 -3 10-5

Soil half-life, in days

EXPLANATION

i

i

i

i

i

i

i i

ii

iiii

ii

j

Increasing hydrophobicity

Increasing persistence

total DDT

p,p9-DDE total nonachlor

trans-nonachlor

p,p9-DDD total chlordane

p,p9-DDT a-chlordane

dieldrin g-chlordane pentachloroanisole dacthal

a-HCH

cis-nonachlor

endosulfan I

HCB

lindane

total heptachlor oxychlordane endosulfan II

o,p9-DDT toxaphene photomirex mirex

pentachlorophenol

o,p9-DDD

o,p9-DDE DDMU

heptachlor epoxide chlorpyrifos total HCH

endrin aldehyde endrin

oxadiazon

kepone trifluralin

total endosulfan

dicofol

endosulfan sulfate

diuron

zytron

ametryn 2,4-DB

dicamba

isodrin

100

100

80

80

60

60

40

40

20

20

0

Percent of total sites with detectable levels

Organochlorine insecticides

Other insecticides

Herbicides

Fungicides

Aquatic Biota

Bed Sediment

United States. These include five major national programs that

sampled in rivers or estuaries. Most monitoring studies (97

percent) focused on organochlorine insecticides. These studies

differed widely in their design features, such as site selection

strategy, sample collection methods, and species and tissue type

of biota sampled. The study durations ranged from less than one

month to 24 years. Fish was the most common type of aquatic

biota sampled, followed by mollusks and other invertebrates.

Because of differences among studies in study design and

sampling dates, it is difficult to combine data from different

studies into an overall national assessment. However, data from

individual national programs can be used to assess the

occurrence, geographic distribution, and trends of pesticides in

fish and, to a lesser extent, sediment from United States rivers.

Pesticides Found in Sediment and Biota

A large number of pesticides have been detected in stream

sediment and aquatic biota in various studies over the last 30

years. Forty-four percent of the pesticides targeted (41 of 93)

were detected in sediment, and 64 percent (68 of 106) were

detected in aquatic biota (whole fish, edible fish, or mollusks).

Most of the compounds detected were organochlorine

insecticides or their degradation products. This reflects the

hydrophobicity and persistence of these compounds, plus the fact

that more monitoring studies looked for organochlorine

insecticides (97 percent of studies) than for any other types of

pesticides (27 percent). Figure 2 shows the detection frequencies

for pesticides most commonly found in sediment and biota (fish

and mollusks) by all the monitoring studies reviewed. Because

these detection frequencies reflect the study designs and sampling

dates of the studies that looked for specific compounds, they are

not necessarily representative of all streams in the United States.

The organochlorine insecticides DDT, chlordane, and

dieldrin were commonly detected in sediment and aquatic biota

(Figure 2), even though their agricultural uses in the United States

were discontinued during the 1970s. A few currently used

pesticides also were detected in sediment or biota at more than 10

percent of total sites. These include dacthal, 2,4-DB, dicamba,

diuron, and trifluralin (herbicides), and chlorpyrifos, dicofol,

endosulfan, and lindane (insecticides). These pesticides tend to be

intermediate in hydrophobicity and persistence, compared with

other pesticides used now or in the past. For most organochlorine

pesticides, detection frequencies generally were higher in aquatic

biota than in sediment.

Pesticide Physical and Chemical Properties

Two key properties of pesticides that control their

accumulation in sediment and aquatic biota are hydrophobicity

and persistence. Historical data were used to develop structure–

activity relations between these properties and pesticide

occurrence in sediment or aquatic biota (see Figure 3). Generally,

pesticides were found to have the potential to accumulate in

sediment and aquatic biota if they had (1) a water solubility less

than 1 milligram per liter (mg/L) or an octanol-water partition

coefficient (Kow) greater than 1,000, and (2) a soil half-life greater

than 30 days. Kow is an indirect measure of lipid solubility, so that

hydrophobic compounds tend to have a high Kow and low water

solubility. Soil half-life is the best measure of relative persistence

that is available for a large number of pesticides. Each point in

Figure 3 represents a different pesticide, color coded according to

the frequency with which it was detected in sediment and biota

when data were aggregated from past monitoring studies. Figure

3 shows only the effect of hydrophobicity and persistence on

pesticide occurrence and does not show the influence of pesticide

use. The most commonly detected compounds (red squares) tend

to have low water solubility and high persistence. Conversely,

most pesticides that are rarely detected in sediment and biota

(blue circles) have higher water solubilities and shorter soil halflives. Several pesticides with intermediate detection frequencies

(green–white squares) are moderate in hydrophobicity and

persistence. Two pesticides—mirex and endrin (the two

uppermost green–white squares)—have lower detection

frequencies than predicted from their low water solubilities and

long soil half-lives, probably because their use was relatively low.

These structure-activity relations were used to evaluate

which currently used pesticides have the potential to accumulate

in sediment and aquatic biota. Because most currently used

pesticides have relatively high water solubility and short soil halflives, they are not as likely to accumulate in these media.

Figure 2. Detection frequencies for pesticides in aquatic biota (top) and in bed 

sediment (bottom) that were targeted at 15 or more sites by the monitoring studies 

reviewed and that were detected at 10 percent (or more) of total sites.

Figure 3. The relation between pesticide occurrence in sediment and aquatic 

biota in past monitoring studies (color symbols) and pesticide properties (water 

solubility—a measure of hydrophobicity, and soil half-life—a measure of 

environmental persistence). Only those pesticides targeted at 50 sites or more were 

included.
0 500 MILES

0 500 KILOMETERS

EXPLANATION

Boundaries of farm production regions used for estimating pesticide use

# 45.1

45.2–103.8

103.9–193.9

> 193.9

no reported use 

< 3.9

3.9–11

12–21

> 21

Median concentration of total 

DDT in whole freshwater fish, 

1986 (in micrograms per 

kilogram, wet weight)

Use of DDT plus DDD (pounds 

active ingredient) per square 

mile of agricultural land, 1966

However, some currently used pesticides that are intermediate in

both hydrophobicity and persistence (see Table 1) are likely to be

detected if analyzed in sediment and aquatic biota, although at

lower detection frequencies than the very hydrophobic, persistent

pesticides such as DDT. It also would be important to consider

where, and in what amounts, these pesticides are applied. Studies

of the herbicide oxadiazon in California suggest that currently

used pesticides that are intermediate in water solubility and

persistence may reach fairly high concentrations in sediment and

aquatic biota in areas of high pesticide use.

Geographic Distribution in Relation to Use

The occurrence of a pesticide in a stream depends on the

sources of that pesticide in the drainage basin (such as pesticide

use), the characteristics of the stream (such as water flow), and

the physical and chemical properties of the pesticide (such as

water solubility). Organochlorine insecticides are still detected in

sediment and biota in many streams because of their

environmental persistence and their extensive use in the past. 

The occurrence of organochlorine pesticides during the

1980s still showed some association with its use in agriculture 20

years earlier. For example, Figure 4 shows the geographic

distribution of total DDT (DDT plus its metabolites DDD and

DDE) in freshwater fish from the U.S. Fish and Wildlife Service’s

National Contaminant Biomonitoring Program (NCBP) in 1986

in relation to regional estimates of agricultural use of DDT plus

DDD in 1966, the decade of highest use. In Figure 4, each site is

represented by a circle, color coded to represent the quartile in

which its median total DDT concentration falls. For example, the

red circles correspond to the 75th–100th percentile group.

Agricultural land within each region is shaded according to the

appropriate quartile of agricultural use of DDT plus DDD.

In 1986, the highest total DDT concentrations in fish were

observed in the south, near the Great Lakes, along the northeast

Atlantic coast, and at scattered Pacific sites. The southeastern

sites correspond to the regions of highest agricultural use in 1966.

Higher-than-expected levels of DDT in the Great Lakes and

northeast Atlantic areas may be due to nonfarm use, incidental

release from chemical manufacturing plants, or atmospheric

deposition. High residues at scattered Pacific sites may reflect use

on orchards, or proximity to agricultural cropland within the

region. Other organochlorine pesticides in fish showed similar

associations with land use. Dieldrin concentrations were strongly

associated with corn production acreage. High dieldrin levels also

occurred at sites in the northeast and Pacific regions, possibly

because of urban use and proximity to farmland, respectively.

Some currently used pesticides (such as chlorpyrifos,

dacthal, and trifluralin) showed an association with recent

agricultural use in some studies. Some pesticides were associated

with nonagricultural sources in some studies. For example, mirex

was found in fish from areas treated for control of red fire ants

(the southeast) or near manufacturing sources. Preliminary data

from the U.S. Geological Survey’s National Water-Quality

Assessment Program (1991 to the present) indicate that urban

streams have high concentrations and detection frequencies of

DDT, chlordane, and dieldrin in sediment and whole fish (see

http://water.wr.usgs.gov/pnsp/rep/bst).

 Long-Term Trends

The existing data for pesticides in stream sediment are not

sufficient to assess national long-term trends, but trends in

pesticide concentrations in whole freshwater fish can be assessed

using NCBP data from 1969 to 1986. Nationally, levels of

chlordane, total DDT, dieldrin, endrin, and toxaphene have

declined since their agricultural uses were discontinued. An

example (DDT trends) is shown in Figure 5. For DDT and

dieldrin, data for the 1980s suggest that concentrations may be

leveling off, which is consistent with the slow degradation of

these pesticides in the environment. For DDT, this trend is

supported by changes in the proportional composition of total

DDT residues in fish, with the degradation product DDE

constituting an increasing percentage of total DDT over time.

Organochlorine detection frequencies in the NCBP remain high,

with total DDT detected at more than 97 percent of sites, and

dieldrin at more than 70 percent of sites, each year.

Table 1. Currently used (1990s) pesticides predicted to have potential to 

accumulate in sediment and aquatic biota

[Abbreviations: Kow, n-octanol-water partition coefficient; mg/L, milligram per liter; <, less 

than; >, greater than]

Currently used (1990s) pesticides that meet the selection criteria 1

Insecticides Herbicides Fungicides or wood

preservatives

Chlorpyrifos2 Benfluralin Dichlone

Dicofol2,3 Bensulide PCNB2

Endosulfan2,3 Dacthal2 Pentachlorophenol2

Esfenvalerate Ethalfluralin

Fenthion Oxadiazon2

Fenvalerate2 Pendimethalin

Lindane2,3 Triallate

Methoxychlor2,3 Trifluralin2

Permethrin2

Phorate4

Propargite

1

 Selection criteria: (1) water solubility < 1.0 mg/L or log Kow > 3, and (2) soil half-life > 

30 days. 2

 Detected in one or more past studies of stream sediment or biota.

3

 Organochlorine insecticide.

4

 Analyzed in >1,000 total samples by past studies, but not detected.

Figure 4. Total DDT in whole fish sampled by the National Contaminant 

Biomonitoring Program in 1986, shown in relation to 1966 agricultural use of DDT 

plus DDD by farm production region. Data are from U.S. Geological Survey, 1992 

(DDT concentrations) and Eichers and others, 1970 (DDT use). 
1,000

500

0

1,500

2,000

2,500

3,000

3,500

1969 1973 1977 1981 1985

Total DDT concentration, in

micrograms per kilogram, in whole fish

90th percentile

Average

50th percentile

Agricultural use of 

 DDT cancelled

DDT and other persistent organochlorine pesticides

continue to enter surface waters from sources such as

atmospheric deposition and erosion of soils that have been

contaminated from past use. Field studies indicate that DDT halflives in soil are on the order of 15 years or longer.

 Significance to Water Quality

Pesticide concentrations measured by the monitoring studies

that were reviewed can be used to gauge potential adverse effects

at the time the samples were taken. The maximum concentrations

measured in each study were compared with guidelines for the

protection of aquatic life, fish-eating wildlife, and human health.

Because the maximum concentrations from each study were

used, these comparisons indicate what percentage of studies may

have adverse effects at the most contaminated site in each study,

but not what proportion of sites may be affected. Such guidelines

generally were based on the results of single-species, singlechemical toxicity tests conducted in the laboratory—therefore,

they do not consider more complex issues such as the toxicity of

chemical mixtures or the potential for endocrine-disrupting

effects on development and reproduction. Also, the monitoring

studies reviewed may not be representative of sediment and biota

from streams throughout the United States.

The potential effects on aquatic life, fish-eating wildlife, and

human health were assessed by comparing the maximum

concentrations of pesticides measured by each study in sediment,

whole fish, and fish fillets (respectively) with applicable

guidelines. Sediment-quality guidelines were selected using

procedures developed by the U.S. Environmental Protection

Agency (1997). Wildlife guidelines are from the State of New

York (Newell and others, 1987), and consider chronic and

reproductive toxicity, but not cancer effects. Human-health

guidelines are recommended screening values from U.S.

Environmental Protection Agency (1995), which consider both

chronic toxicity and carcinogenicity. 

Even when studies published prior to 1984 were excluded,

sediment guidelines were frequently exceeded by maximum

concentrations of total DDT (in 52 percent of studies), chlordane

(42 percent), and dieldrin (29 percent), indicating a high

probability of adverse effects on aquatic life at the most

contaminated sites in these studies. New York wildlife guidelines

were exceeded for total DDT (77 percent of studies) and dieldrin

(25 percent), which indicates potential adverse effects on fisheating wildlife at the most contaminated sites in these studies.

EPA-recommended screening values were exceeded for

chlordane, total DDT, dieldrin, and heptachlor epoxide in at least

50 percent of studies. This suggests possible adverse human

health effects at the most contaminated sites in these studies, if

fish from these sites were consumed at average rates by the

general adult population. Adverse health risks may be higher for

sport and subsistence fishers, who consume more local fish than

the average population.

Human exposure to organochlorine pesticides has been

documented by studies detecting these compounds in various

human tissues, including breast milk. Consumption of

contaminated food (including fish and shellfish) is a major route

of human exposure to organochlorine pesticides. Organochlorine

concentrations in human blood have been shown to increase after

fish consumption and to be correlated with long-term fish

consumption rates. Organochlorine compounds tend to be stored

in high-fat tissues within the body, but can be mobilized during

lactation or starvation. Levels of some organochlorine

compounds in human tissues in the United States do not appear to

have declined, at least through the early 1980s. Examples include

DDT in breast milk and dieldrin in adipose tissue (fat).

The wealth of information on pesticides in bed sediment and

aquatic biota in the scientific literature has provided a national

perspective on organochlorine pesticides in United States rivers.

Nonetheless, significant gaps remain in our understanding of the

extent and significance of pesticides in stream sediment and

aquatic biota. This analysis suggests a need for additional studies

of pesticide occurrence in urban settings, together with more

information on urban pesticide use. Also, researchers should look

for currently used pesticides with the potential to accumulate in

sediment and aquatic biota in areas of high use. Finally, questions

remain about the effects of remaining pesticide levels on human

and ecosystem health.

Additional Reading

This Fact Sheet is based on the book by L.H. Nowell, P.D. Capel, and P.D. 

Dileanis, 1999, Pesticides in Stream Sediment and Aquatic Biota—Distribution, 

Trends, and Governing Factors: Boca Raton, Fla., CRC Press, Pesticides in the 

Hydrologic System series, v. 4, 1040 p. (Tel: 1-800-272-7737)

References

 Eichers, T., Andrilenas, P., Blake, H., Jenkins, R., and Fox, A., 1970, Quantities 

of pesticides used by farmers in 1966: U.S. Department of Agriculture, Economic Research Service, Agricultural Economic Report No. 179, 61 p.

Majewski, M.S., and Capel, P.D., 1995, Pesticides in the atmosphere—distribution, trends, and governing factors, Ann Arbor Press, Inc., Chelsea, Mich., 

228 p.

Newell, A.J., Johnson, D.W., and Allen, L.K., 1987, Niagara River Biota Contamination Project: Fish flesh criteria for piscivorous wildlife: New York State 

Department of Environmental Conservation, Division of Fish and Wildlife, 

Bureau of Environmental Protection, Technical Report 87-3.

U.S. Environmental Protection Agency, 1995, Guidance for assessing chemical 

contaminant data for use in fish advisories, v. 1, Fish sampling and analysis, 

2nd ed.: U.S. Environmental Protection Agency, EPA 823-R-95-007.

_______, 1997, The incidence and severity of sediment contamination in surface 

waters of the United States, v. 1, National Sediment Quality Survey: U.S. 

Environmental Protection Agency, EPA 823-R-97-006.

U.S. Geological Survey, 1992, U.S. Fish and Wildlife Service National Contaminant Biomonitoring Program Fish Data File, 1969–1986: Columbia Environmental Research Center, Columbia, Mo., Lotus and ASCII files.

For more information:

Information on technical reports and hydrologic data related to National 

Water-Quality Assessment (NAWQA) pesticide studies can be obtained from:

Chief, Pesticide National Synthesis

U.S. Geological Survey

6000 J Street, Placer Hall

Sacramento, CA 95819-6129

Additional information on NAWQA and other U.S. Geological Survey programs can be found by accessing the NAWQA home page on the World Wide Web 

at <http://water.usgs.gov/nawqa>.

Figure 5. Trends in total DDT concentrations in whole fish sampled by the 

National Contaminant Biomonitoring Program from 1969 to 1986. Data are from 

U.S. Geological Survey, 1992. For the 90th (or 50th) percentile concentration, 90 

(or 50) percent of samples were below the concentration shown. 

USGS Fact Sheet 092-00