Chemical Mixtures and Environmental Effects: 

A Pilot Study to Assess Ecological Exposure and 

Effects in Streams

By Herbert T. Buxton,1 Timothy J. Reilly,1 Kathryn M. Kuivila,1 Dana W. Kolpin,1 Paul M. Bradley,1

Daniel L. Villeneuve,2 and Marc A. Mills2

1

U.S. Geological Survey.

2

U.S. Environmental Protection Agency.

Contaminant Mixtures in 

Surface Waters 

Streams and lakes accumulate chemicals from many 

different human activities across the landscape (fig. 1). 

Watersheds collect water from precipitation that runs off 

the land surface, carrying with it chemicals from urban and 

residential areas (streets, sidewalks, parking lots, lawns, and 

gardens); crop lands treated with pesticides, manures, and 

other organic and inorganic fertilizers; pastures and animalproduction facilities; and lands where energy and mineral 

resources are extracted. Municipal, commercial and domestic wastewater-treatment systems, industries, and landfills can 

discharge their wastewaters directly to streams, and although the 

wastewater typically is treated, current treatment technologies 

are not designed to remove all chemicals. Groundwater, which 

discharges to streams and accounts for much of streamflow 

during dry seasons, also can carry contaminants from spills, 

leaks, septic systems, and land-applied chemicals that infiltrate 

to the water table as well 

as naturally occurring 

chemicals that leach from 

aquifer material. Even 

chemicals from smokestacks, automobiles, and 

other emissions to the 

atmosphere can make their 

way into streams. As a 

result, surface waters can 

have complex mixtures of 

natural and anthropogenic 

chemicals that include pesticides, pharmaceuticals, 

household chemicals, and 

a wide range of chemicals 

produced as waste byproducts of commercial and 

industrial activities.

What chemicals occur together in our streams and at what concentrations? How do land-use and chemical-use patterns influence 

the complex chemical mixtures in streams across the Nation? How do these chemicals enter streams and do they persist? Can 

exposure to chemical mixtures result in unanticipated, adverse health effects in fish and other aquatic organisms? Could people 

be exposed to these chemical mixtures? This document presents some of the challenges associated with chemical mixtures in 

streams and describes an interagency (U.S. Geological Survey and U.S. Environmental Protection Agency), field-based investigation 

designed to help answer these and other questions and to provide information to guide future research.

Figure 1. Contaminant sources and principal pathways to the environment. From Bright and 

others (2013).

Stack

emissions Waste water

treatment plant

discharge

Cropland with 

applied pesticides, 

manure, biosolids 

and fertilizer

Residential 

leach and

septic

Industrial

discharges and

urban runoff

Mine and 

mineralized

rock drainage

Animal feeding 

operations

SEEPAGE SEEPAGE SEEPAGE

WATER TABLE WATER TABLE

WIND

WIND

RUNOFF

RUNOFF

RUNOFF

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2015–1113

June 2015

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151113
2

The Challenge of Chemical Mixtures

Assessment and management of the risks of exposure to 

complex chemical mixtures in streams are priorities for human 

and environmental health organizations around the world, 

including the U.S. Environmental Protection Agency (Doyle 

and others, 2014), the U.S. National Institute of Environmental 

Health Sciences (Carlin and others, 2013), the U.S. Geological 

Survey (Bright and others, 2013), the European Commission 

(European Commission, 2015), and the World Health Organization (World Health Organization, 2015). The current lack 

of information on the composition and variability of environmental mixtures and a limited understanding of the combined 

effects are fundamental obstacles to timely identification and 

prevention of adverse human and ecological effects of exposure

to chemical mixtures. 

The number of chemicals registered for use in the United 

States is immense and increasing rapidly. In comparison, 

assessment of health risks and subsequent development of 

environmental regulations have progressed slowly, been conducted largely on a chemical-by-chemical basis, and focused 

primarily on mortality, acute toxicity, and carcinogenicity. As 

a result, the vast majority of these chemicals remain untested 

for their biological mode(s) of action and toxicity, and very 

few mixtures have been assessed for potential chemical interactions and their combined effect. To address this knowledge 

gap, high throughput testing and other automated methods are 

being developed for more efficient evaluation of the biological 

activity and toxicity of chemicals (National Research Council, 

2007; Collins and others, 2008). However, even robust chemical characterization of environmental chemical mixtures has 

been found to explain only a small fraction of the observed 

biological response to exposure (Tang and others, 2014). 

Environmental Health Effects of 

Chemical Mixtures

Predicting the Combined Effects of Chemical 

Mixtures

Testing for the health effects of all potential chemical 

mixtures is not feasible. Therefore, multiple approaches have 

been developed for using the results of chemical-specific 

testing to assess the combined effects of chemical mixtures. 

Chemicals often are assumed to act additively in terms of their 

concentration, dose, potency, or biological response to exposure. These approaches are challenged by changes in response 

with exposure time, the biological interaction of chemicals 

within an organism, and complex dose-response relations 

including the effects thresholds below which individual chemicals do not demonstrate effects. Adverse health effects have 

been demonstrated from exposure to multiple chemicals at 

low concentrations, which individually would not cause harm 

(Brian and others, 2007; Smith and others, 2013; Kortenkamp, 

2014). Chemical interactions can result in impacts that are 

greater than (synergistic) or less than (antagonistic) those 

predicted by additive approaches. An everyday example of 

an unanticipated chemical interaction is the need to avoid 

consuming grapefruit when taking specific medications due 

to its potential to amplify pharmacological effects in some 

patients (Kane and Lipsky, 2000). Examples of environmental 

contaminants known to interact synergistically or antagonistically include polycyclic aromatic hydrocarbons (Schneider 

and others, 2002), pesticides (Belden and Lydy, 2006; Laetz 

and others, 2009; Christen and others, 2014; Chen and others, 

2015), metals (Norwood and others, 2003), pesticides and 

metals (Chen and others, 2015), antibiotics (Gonzalez-Pleiter 

and others, 2013), pharmaceuticals with similar (Cleuvers, 

2004) and different modes of action (Pomati and others, 

2008), pharmaceuticals and metals (Aslop and Wood, 2013), 

pharmaceuticals and synthetic musks (Schnell and others, 

2009), polycyclic aromatic hydrocarbons and metals (Wang 

and others, 2013), and more diverse chemical mixtures (Boltes 

and others, 2012; Orton and others, 2014). 

Health Outcomes

Adverse human and environmental health outcomes other 

than acute toxicity and mortality may occur in streams even 

at low contaminant concentrations due to the complexity of 

chemical mixtures and associated chemical modes of action. 

Modes of action may include carcinogenicity, genotoxicity, 

mutagenicity, toxicity modulation, endocrine disruption, and 

selection of microbial antibiotic resistance.

As an example, many of the chemicals that enter our 

streams can disrupt the endocrine systems of aquatic organisms. Hormones, secreted by an organism’s endocrine system, play a major role in biological function and metabolic 

stability. Endocrine disrupting chemicals can interfere with 

natural hormone signaling in exposed organisms, resulting in 

altered growth, sexual development and function, neurological development, metabolism, and stress response (DiamantiKandarakis and others, 2009). Estrogenically active contaminants can interfere with natural estrogen binding, affecting 

sexual differentiation and development, among other things. 

Estrogenic contaminants in streams may include estrogens 

produced naturally in animals and subsequently excreted 

(biogenic estrogens), estrogenic chemicals produced in plants 

(phytoestrogens), synthetic pharmaceutical estrogens (ovulation inhibitors or estrogen supplements), and estrogen mimics 

(a wide range of chemicals with industrial and commercial 

uses including some pesticides, flame retardants, surfactants, 

and products in plastics). In one study, severe population 

declines were documented in fish in a Canadian lake dosed 

with a single compound, 17-α ethinyl estradiol, an active 

ingredient in human birth control pills (Kidd and others, 

2007). Fish and other aquatic organisms that inhabit contaminated streams are often exposed to many endocrine-active 

chemicals, not just one. Because endocrine disruption effects 
3

often do not conform to established, dose-response relations, 

these chemicals pose a serious challenge to traditional toxicological risk assessment practices (Fuhrman and others, 2015).

The adverse effects of antimicrobial resistance on human 

health and the potential significance of both clinical and 

natural environments in resistance selection are also widely 

acknowledged (Wellington and others, 2013; Martinez, 2014). 

The ability of microorganisms to resist antibiotic and antimicrobial agents can be affected by multiple chemical exposures 

and can be transferred between organisms (Kummerer, 2009). 

Chemicals with the potential to select resistance genes and 

resistant microbial populations include metals (Baker-Austin 

and others, 2006), quaternary ammonium compounds (Gaze 

and others, 2005), biocides (Sanchez and others, 2005), and 

herbicides (Kurenbach and others, 2015). Resistance to an 

individual antibiotic can be further affected by other antibiotics and metals acting on the same genetic target or on different 

targets on the same genetic element (Baker-Austin and others, 2006). Common antibiotic pathways to the environment 

include chemical use and disposal in animal agriculture, in 

healthcare facilities, and in the home.

The combined adverse health effects of 

exposure to multiple chemicals and of physical 

insults from other stressors that affect different 

organs or biological functions, as well as indirect 

effects on complex ecological relations such as 

host-pathogen interactions, are critical challenges 

(Sexton and Hattis, 2007; Lokke and others, 2013; 

Hadrup, 2014). 

A Pilot Study

The U.S. Geological Survey (USGS) and 

the U.S. Environmental Protection Agency (EPA) 

are collaborating to provide new information on 

environmental chemical mixtures in United States 

streams. The objective of the study is to characterize chemical mixtures and biological activity in 

surface waters that are affected by diverse chemical sources. The study is intended to provide fieldbased information for the prioritization and design 

of future research on environmental chemical 

mixtures. The study represents the most comprehensive assessment of the chemical composition 

and biological activity of contaminant mixtures in 

surface waters ever performed in the United States.

Pilot Study Approach

Site Selection

Data from more than a thousand stream sites from previous USGS studies of contaminants of emerging environmental 

concern were used to select 38 stream sites spanning 24 States 

and Puerto Rico (fig. 2; table 1). Thirty-four stream sites were 

selected because they have highly developed watersheds with 

a wide range of contaminant sources; the remaining four 

stream sites were selected as undeveloped reference sites. 

Sites vary widely in upstream drainage area, ranging 

from 4.6 square miles (mi2) for a small reference site on Penn 

Swamp Branch in the Pinelands of New Jersey to 6,265 mi2 

for the Trinity River, an arid southwestern stream in Texas 

(table 1). Most of the study watersheds cover areas less than 

100 mi2 (fig. 3A). Population density also varies widely 

(fig. 3B), ranging from zero (Swiftcurrent Creek, a reference 

site near Many Glacier, Montana) to almost 3,000 people 

per mi2

 (Rush Creek near Arlington, Texas). 

EXPLANATION

Site type

Mixed sources (34)

Reference (4)

0 250 500 Miles

0 250 500 Kilometers

PUERTO RICO

Figure 2. Stream sampling locations. Thirty-four of 38 stream sites (red 

markers) have a wide range of contaminant sources within their watersheds; 

the remaining four stream sites (blue markers) were selected as reference 

sites because their watersheds are minimally affected by contaminant 

sources and their biological communities are considered to be unaffected or 

minimally affected by development.
4

Table 1. Stream sampling sites, location, watershed drainage area, and date sampled.—Continued

[Latitude and longitude in decimal units, referenced to the North American Datum of 1983 (NAD 83); drainage area in square miles]

Stream name Location Station number Latitude Longitude Drainage 

area Sample date

Developed watersheds

Abrams Creek near Oakfield, Georgia 2350524 31.7187847 –83.98851469 79.58 July 23, 2013

Blue River at Kansas City, Missouri 06893500 38.957 –94.5588889 184.19 February 11, 2014

C-111 Canal near Homestead, Florida 252414080333200 25.40428063 –80.5586705 51.04 April 9, 2013

Chicago Sanitary and Ship 

Canal

at Lockport, Illinois 05537000 41.57027778 –88.0794444 749.34 February 11, 2014

Chisholm Creek at Edmond, Oklahoma 07159735 35.72560669 –97.5272639 38.78 November 28, 2012

Deep Creek at Highway 224, Oregon 452340122251000 45.39429 –122.42064 48.98 January 13, 2014

East Branch Perkiomen 

Creek

near Derstines, 

Pennsylvania

01472705 40.35402778 –75.31327778 29.35 January 14, 2014

Enoree River at Pelham, South Carolina 02160326 34.85650727 –82.22622468 84.80 May 19, 2014

Fall Creek near Ithaca, New York 423400 42.4533333 –76.47277778 126.35 June 9, 2014

Fishtrap Creek near Lynden, Washington 12211900 49.00261838 –122.4073816 16.45 December 10, 2013

Fourmile Creek downstream of the 

Ankeny WWTP outfall, 

Iowa

05485605 41.7173771 –93.5701332 60.94 November 19, 2012

Hawksbill Creek at Route 648, Springfield, 

Virginia

01630540 38.70817319 –78.4563966 68.52 April 15, 2014

Hillsboro Canal at S-6, near Shawano, 

Florida 

02281200 26.4720184 –80.4458857 311.34 March 12, 2013

Hite Creek at Sleepy Hollow Road 

near Prospect, 

Kentucky

382054085332600 38.34833 –85.55722 5.54 May 20, 2014

Hohokus Brook at Ho-Ho-Kus, New 

Jersey

01391100 40.95527778 –74.1005556 20.47 November 28, 2012

Jordan Creek at the mouth, at Allentown, Pennsylvania01452040 40.6018 –75.46208889 82.32 June 17, 2013

Mill Creek near Bellepoint, Ohio 03220000 40.24839457 –83.1738026 177.93 June 4, 2013

New River near Westmorland, California10255550 33.10476565 –115.6644382 1,471.12 March 5, 2013

North Dry Creek South of Kearney, 

Nebraska

06770195 40.6411236 –99.1159223 78.74 June 10, 2013

Rio Bairoa at the mouth, Puerto Rico 50055410 18.26106496 –66.0187762 7.68 March 19, 2013

Rio Fajardo downstream of the Fajardo WWTP outfall, 

Puerto Rico

181932065383501 18.31297222 –65.6536111 20.38 March 25, 2013

Rush Ck at Hwy 303 near Arlington, Texas324305097101900 32.71794 –97.17201 28.89 May 13, 2013
5

Table 1. Stream sampling sites, location, watershed drainage area, and date sampled.—Continued

[Latitude and longitude in decimal units, referenced to the North American Datum of 1983 (NAD 83); drainage area in square miles]

Stream name Location Station number Latitude Longitude Drainage 

area Sample date

Developed watersheds

Sand Run Gulch at Highway 95 crossing 

near Parma, Idaho

13210360 43.7640501 –116.9120956 79.49 June 18, 2013

Santa Ana River downstream of Prado 

Dam, California

11074000 33.88334875 –117.6453296 2,261.44 March 25, 2014

Sope Creek near Marietta, Georgia 02335870 33.95388889 –84.4433333 30.81 April 16, 2013

South Fork Iowa River near New Providence, 

Iowa

05451210 42.31498375 –93.1524252 266.39 May 20, 2013

South Fork Zumbro River downstream of WWTP 

near Rochester, 

Minnesota

05373005 44.0738534 –92.46767819 312.00 December 5, 2012

South Platte River near Commerce, Colorado 39484710457700 39.8130418 –104.9524794 4,082.21 December 11, 2012

Sunrise River Tributary near Lindstrom, 

Minnesota

 05340041 45.4076111 –92.8805889 6.59 December 4, 2012

Sycamore Slough at County Line Road near 

Dunnigan, California

385531121532001 38.92527778 –121.8888889 64.30 June 18, 2013

Tembladero Slough at Castroville, California 364554121453401 36.765 –121.7594444 153.97 March 3, 2014

Trinity River downstream of Dallas, 

Texas

08057410 32.70763139 –96.7358319 6,264.63 December 4, 2012

West Branch Delaware 

River

at Hobart, New York 01421640 42.3436111 –74.72 48.22 November 19, 2012

Zollner Creek near Mount Angel, 

Oregon

14201300 45.10039816 –122.8217596 15.90 May 19, 2014

Reference Sites

North Sylamore Creek near Fifty Six, Arkansas 07060710 35.99166667 –92.2138889 58.7 January 7, 2014

Penn Swamp Branch near Batsto, New Jersey 01409480 39.68416667 –74.65027778 4.6 December 10, 2012

Swiftcurrent Creek upstream of Swiftcurrent 

Lake at Many Glacier, 

Montana

05014300 48.7954444 –113.6805833 15.4 August 28, 2013

West Clear Creek near Camp Verde, 

Arizona

09505800 34.53863606 –111.6940356 241 January 15, 2014
6

Some watersheds are characterized almost entirely by 

agricultural land (fig. 4A). Mixed urban/agricultural land use 

is common, with urban land (fig. 4B) generally covering less 

area than agricultural land. The Hite Creek site in Kentucky 

(fig. 5) is an example of a developed watershed affected by 

highly varied contaminant sources. The 5.5 mi2

 watershed is 

approximately 52 percent urban land and 10 percent agricultural land. It has a population density of about 2,323 people 

per mi2

 and includes a National Pollutant Discharge Elimination System (NPDES) major discharger. 

The watersheds of the four stream reference sites are 

largely undeveloped, minimally affected by contaminant 

sources, and considered to have minimally disturbed fish and 

aquatic macro-invertebrate communities. For example, the 

15.4 mi2

 Swiftcurrent Creek watershed in Montana (fig. 6) 

has no urban land, 0.1 percent agricultural land, and no major 

NPDES dischargers. The population density of the watershed 

is less than 1 person per mi2

. 

0

5

10

15

20

25

A

Drainage area (mi2)

0

2

4

6

8

10

12

14

0–10 10–100 100–1,000 1,000–10,000

0–10 10–100 100–1,000 1,000–10,000

Number of sites

B

Population density (people per mi2)

Figure 3. Watershed characteristics of sampled stream 

sites. A, Distribution of drainage areas in square miles. 

B, Distribution of watershed population densities in 

people per square mile.

A

Percent urban land use

Number of sites

B

Percent agricultural land use

0

5

10

15

20

25

30

0

2

4

6

8

10

12

14

16

18

0–20 20–40 40–60 60–80 80–100

0–20 20–40 40–60 60–80 80–100

Figure 4. Distribution of A, Agricultural and B, Urban land 

use as a percentage of total drainage area for streamsite watersheds. (2011 National Land Cover Database 

[conterminous United States, http://www.mrlc.gov/nlcd2011.php]; 

Puerto Rico 2001 National Land Cover Database [Puerto 

Rico, http://www.mrlc.gov/nlcd01_data.php])

Figure 5. Hite Creek Kentucky, looking upstream at the 

sampling location. Photograph by Angela Crain, USGS.
7

Sample Collection and Analysis

Water samples were collected once from each stream 

from December 2012 to June 2014. Samples taken from the 

center of flow at each stream were collected by USGS staff 

using established trace-level protocols (Shelton, 1994; Wilde, 

2004a; Wilde and others, 2004b; Hladik and others, 2009). 

Composite water samples were homogenized and decanted 

into the specified container or collected within the specified 

container as appropriate. Water samples were kept at 3 degrees 

Celsius (°C) while in the field and more than 60 sample bottles 

were shipped overnight to USGS and EPA national laboratories for analysis (fig. 7).

Stream water samples were tested using (1) sensitive 

and specific direct analysis for more than 700 organic and 

inorganic chemicals and physical properties (table 2), (2) environmental diagnostics for identification of unknown chemical 

contaminants using Gas Chromatography-Mass Spectrometry 

and Liquid Chromatography-Time of Flight Mass Spectrometry, and (3) a variety of bioassays to evaluate biological activity and toxicity, including hormonal activity, carcinogenicity, 

and mutagenicity (table 3). In addition, a subset of 8 ambient 

water extracts from sites selected from a range of environmental settings were screened for approximately 80 different biological activities using the Attagene, Inc., subset of ToxCastTM

assays (U.S. Environmental Protection Agency, 2015). The 

chemical analytes measured include anthropogenic and naturally occurring chemicals as well as associated metabolites and 

environmental transformation byproducts. 

Figure 6. Swiftcurrent Creek, Montana, looking upstream at the 

sampling location. Photograph by Hannah Nilges, USGS.

Figure 7. U.S. Geological Survey scientist collecting water 

samples and measuring water field properties at North Sylamore 

Creek, Arkansas, on January 7, 2014, a study reference site. 

Photograph by J. Tyler Mays, USGS.

Table 2. Chemicals measured by direct analysis of stream 

water samples.

339 Pesticides and transformation byproducts

160 Pharmaceuticals and metabolites

 32 Antibiotics and metabolites

 38 Biogenic and synthetic hormones and conjugates

 40 Volatile organic compounds

 25 Disinfectants and byproducts

 22 Metals

 17 Flame retardants

 17 Perfluorocarbons (PFCs)

 11 Surfactants

 10 Phytoestrogens and plant sterols

 9 Fragrances

 9 Nutrient species, and

Other industrial chemicals

Table 3. Bioassays used to measure biological activity and 

toxicity of stream water samples.

Estrogen agonist and antagonist assays

Androgen assays

Glucocorticoid assays

Steroidogenesis (estrogen and testosterone production) assays

DNA binding transcription factor activity assays

Carcinogenicity and mutagenicity assays

DNA damage assays

Gene expression and metabolite profiling
8

Pilot Study Significance

The results of this pilot study will (1) document the 

mixtures and associated concentrations of chemicals found 

in stream waters, (2) help identify potential ecological and 

human exposures, (3) guide prioritization of toxicological 

studies of chemical mixtures, (4) provide insight into potential 

biological interaction of multiple contaminants, (5) help relate 

bioassay screening approaches to environmental chemical 

characterization in support of new monitoring strategies, and 

(6) provide a base of data for models to predict chemical mixtures in watersheds affected by diverse land-use and chemicaluse patterns. 

This pilot study also provides the basis for evaluating 

the feasibility of future field-based research on environmental 

chemical mixtures. The information about these sites can be 

used to design more detailed studies that address additional 

environmental media (sediment and tissue), multiple concurrent exposure pathways, temporal variations in chemical 

mixtures resulting from the timing of chemical-use practices 

and environmental transformation, acute and chronic effects of 

exposure to mixtures, and adverse health effects from varied 

chemical and physical insults at the organism, population, and 

community levels. 

Integrated Approach to Chemical 

Mixtures Assessment, Source 

Identification, and Mitigation

Understanding and mitigating the human and ecological 

health risks associated with chemical- and land-use practices 

require knowledge of environmental chemical mixtures, 

the pathways different chemicals take to the 

environment, the environmental persistence of 

chemicals and associated transformation products, the way chemicals interact biologically, 

and the associated risk of human and ecological 

exposure. This knowledge must be sufficient to 

prioritize and inform ecological and human risk 

assessments; support regulation and motivate 

voluntary actions to reduce the use of specific 

chemicals; improve chemical and waste handling, use, and disposal practices that mitigate 

environmental releases; and effectively upgrade 

wastewater and drinking-water treatment 

technologies. An integrated approach (fig. 8) 

simultaneously employing field-based biological (Environmental Biology) and chemical 

(Environmental Chemistry) testing along with 

systematic laboratory assessment of the effects 

of environmentally relevant chemicals and 

chemical mixtures (Laboratory Testing) offers 

a promising means of addressing these multiple 

environmental health objectives. 

Environmental bioassays allow for rapid assessment 

of environmental samples and can be used as cost-effective 

screening tools to identify susceptible environmental settings, 

the biological activity exhibited by environmental waters, and 

the associated adverse health outcomes on aquatic organisms. 

Field testing using test organisms (such as caged fish studies) can play an important role in documenting adverse health 

effects. Environmental chemical analyses permit spatial and 

temporal characterization of actual environmental chemical 

mixtures, allow for identification of unknowns (environmental diagnostics) for future chemical and biological methods 

development, and provide information on specific chemicals 

of concern that supports mitigation and management actions. 

Laboratory-based testing is well suited to identifying the range 

of biological activities and adverse health effects of specific 

chemicals and environmental chemical mixtures, defining the 

mechanisms of biological interaction across multiple modes 

of action, identifying exposure criteria for vulnerable species, 

and expanding the available bioassay toolbox. Use of fieldbased laboratories at long-term research sites provides unique 

laboratory control in a field-based setting. Continued use of 

high throughput testing of the biological activity of specific 

chemicals as well as more focused toxicological testing on a 

wide range of organisms are essential elements of the laboratory research component. Improved coordination among the 

three components of this integrated approach enables (1) feedback between field-based biological and chemical testing that 

results in detailed chemical characterization in environmental 

settings with documented biological activity and adverse 

health effects, (2) laboratory testing to identify the causes of 

toxicity in environmental chemical mixtures that are demonstrated to have biological consequences, and (3) improved, 

cost-efficient monitoring approaches that employ complementary use of bioassays and chemical analysis, and include 

high throughput testing of waters from demonstrated high-risk 

Mitigation & Management

 Supporting regulatory actions and 

motivating voluntary actions for prevention 

and mitigation

Science -Based Priority Setting

Integrating scientific knowledge to assess risk of exposure 

and adverse health effects and to provide a basis for 

prioritizing action

Environmental 

Chemistry

Chemical compositional 

analysis of targeted 

environments and 

media

Environmental 

Biology

Bioassay of 

targeted environments 

and species

Laboratory Testing

Testing chemicals and 

chemical mixtures for 

toxicity and mode of 

action 

Figure 8. Diagram describing an approach to assessing environmental 

chemical mixtures that integrates field-based biological testing, field-based 

chemical testing, and systematic laboratory testing.
9

environmental settings across the Nation. Furthermore, such 

an integrated approach enables efficient development of a 

robust scientific basis for prioritization of preventive and mitigating actions, support of regulatory action, and motivation of 

voluntary action by industry and the public. 

Federal Role

The pilot study described herein is a collaborative effort 

that draws on the unique capabilities of the USGS and the EPA 

to

• Address a wide range of environmental settings across 

the Nation,

• Employ uniform field and laboratory protocols with 

extensive quality-assurance programs, and 

• Apply the unprecedented scope of chemical and biological analytical capabilities available at USGS and 

EPA laboratories.

• Implement an integrated approach to assessing environmental chemical mixtures as described above.

Federal agency collaboration and coordination is essential 

for national-scale assessment of the potential adverse health 

effects of chemical mixtures in the environment; examples of 

recent field-based efforts are Glassmeyer and others (2005), 

Glassmeyer and others (2009), Beaver and others (2014), 

Cavallin and others (2014), and Barber and others (2015). The 

study described herein and subsequent national-scale, fieldbased efforts will support development of more cost-effective, 

environmentally representative, and scientifically defensible 

assessment approaches for chemical mixtures in a range of 

surface-water settings. 

Acknowledgments

This interagency project was made possible by the 

cooperation of numerous scientists and technicians within the 

USGS and the EPA, including USGS field crews who collected samples at each stream site, USGS and EPA staff at the 

laboratories who processed and analyzed the samples, and the 

principal investigators who played a major role in designing 

and implementing the study (table 4).

Principal Investigators

U.S . Geological Survey U.S. Environmental Protection Agency

Project Design and Coordination Project Coordination

Herbert T. Buxton Su san T. Glassmeyer

Dana W. Kolpin Marc A. Mills (Chemistry)

Kathryn M. Kuivila Daniel L. Villeneuve (Bioassays)

Timothy J. Reilly

Analytical Chemistry

Analytical Chemistry Angela L. Batt

Larry B. Barber Mitchell Kostich

William T. Foreman Heath Mash

Edward T. Furlong Kathleen M. Schenck

Michele L. Hladik

Keith A. Loftin Bioassays

Michael T. Meyer Gerald T. Ankley

Kelly L. Smalling Adam D. Biales

Timothy W. Collette

Bioassays David M. DeMarini

Luke R. Iwanowicz Drew R. Ekman

Phillip C. Hartig

Watershed and Chemical Data David L. Lattier

Kristin Romanok James M. Lazorchak

James L. Orlando Jane Ellen Simmons

Celeste Journey Mary Jean See

Quincy Teng

Vickie S. Wilson

Table 4. U.S. Geological Survey and U.S. Environmental Protection Agency principal 

investigators on the interagency project team.
10

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For Additional Information 

Online: Contacts:

USGS Environmental Health science Coordinator, Toxic Substances

www.usgs.gov/envirohealth/ Hydrology Program, 

USGS Research on Toxic Substances in the environment Michael Focazio mfocazio@usgs.gov

toxics.usgs.gov Chemical Mixtures Team Leader,

USGS Research on environmental chemical mixtures Paul Bradley pbradley@usgs.gov

toxics.usgs.gov/chemmix