U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3071

November 2016 Printed on recycled paper

Compounds of Emerging Concern in the San Antonio

River Basin, Texas, 2011–12

Introduction

The City of San Antonio and the 

surrounding municipalities in Bexar County, 

Texas, are among the fastest growing cities 

in the Nation (U.S. Census Bureau, 2013). 

Increases in residential and commercial 

development are changing runoff patterns 

and likely will increase chemical loads 

into streams (Ockerman and McNamara, 

2003). The U.S. Geological Survey (USGS), 

in cooperation with the San Antonio 

River Authority (SARA), evaluated the 

concentrations and distributional patterns of 

selected “compounds of emerging concern” 

(CECs) by collecting and analyzing waterquality samples from 20 sites in the San 

Antonio River Basin, Tex., during 2011–12. 

On the basis of their chemical composition 

or similar uses, the CECs discussed in 

this fact sheet are wastewater compounds, 

pharmaceutical compounds (hereinafter 

referred to as “pharmaceuticals”), and 

steroidal hormone and sterol compounds 

(hereinafter referred to as “steroidal 

hormones and sterols”). The locations of the 

sampling sites (map identifiers EC01–EC20) 

are depicted in figure 1, along with graphs 

showing the analytical results during the 

first of three synoptic sampling events for a 

subclass of the wastewater compounds. 

What Is a Compound of Emerging 

Concern (CEC)?

Broadly defined, a CEC is “any 

synthetic or naturally occurring chemical or 

any microorganism that is not commonly 

monitored in the environment but has the 

potential to enter the environment and cause 

known or suspected adverse ecological and 

(or) human health effects” (U.S. Geological 

Survey, 2016). Many CECs are known 

endocrine disrupters or potential human 

carcinogens (White and others, 1994), but 

the potential for individual CECs or some 

combination of CECs to affect human health 

and aquatic life remains poorly understood, 

and most CECs remain unregulated (U.S. 

Environmental Protection Agency, 2016). 

Data on the detection and concentration of 

CECs are becoming more widely available, 

however, thereby providing managers and 

policy makers with more information that 

may be used for water treatment and water 

resource management. 

Broadly defined, a 

compound of emerging 

concern (CEC) is “any 

synthetic or naturally 

occurring chemical or any 

microorganism that is 

not commonly monitored 

in the environment but 

has the potential to enter 

the environment and 

cause known or suspected 

adverse ecological and (or) 

human health effects” (U.S. 

Geological Survey, 2016).
BLANCO

COUNTY

HAYS COUNTY

KERR COUNTY

KENDALL

COUNTY

CALDWELL COUNTY

REAL COUNTY

COMAL COUNTY

BANDERA COUNTY

GUADALUPE COUNTY

GONZALES COUNTY

BEXAR 

COUNTY MEDINA COUNTY

LAVACA COUNTY

UVALDE COUNTY

WILSON COUNTY

DEWITT COUNTY 

ATASCOSA COUNTY

KARNES

COUNTY

VICTORIA COUNTY

FRIO COUNTY

GOLIAD 

COUNTY

LIVE OAK

COUNTY

BEE COUNTY

MCMULLEN COUNTY

REFUGIO 

ARANSAS 

Martinez

Creek

San Antonio River

San Antonio

San 

Antonio

0 10 20 30 40 MILES0 10 20 30 40 KILOMETERS

Medina River Subbasin

Lower San Antonio 

River Subbasin

Cibolo Creek

Subbasin

Upper San Antonio 

River Subbasin

WW03

EC17

EXPLA

Subclass of w Value belo concentra Size of pie  Detergent m Personal-u Pesticides Industrial c Disinfectio Polycyclic  Flame retaSan Antonio Subbasin boWastewater 

identifier

Water-qualit

identifier

Canyon

Lake

MedinaLake

Calaveras Lake

Victor Braunig Lake

River

West Prong

Medina River

Alazan Creek

ApacheCreek

San Pedro

Creek

Medio

Creek

Salitrillo

Creek

North Prong

Medina River

Medina River

Guadalupe River

Medina River

San Antoni o River

Salado Creek

Ecleto Creek

Cibolo Creek

Escondido Creek

Guadalupe River

Cibolo Creek

Mitchell 

Lake

Leon Creek

97°00'

98°00'

99°00'

30°00'

29°30'

29°00'

28°30'

0.62

2.53 1.39

1.98

5.86

2.46

2.30

0.22

1.36

0.81

1.61

2.34

EC01

EC02

EC03

EC04

EC05

EC06

EC07

EC08 EC09 EC10

EC11

EC12

EC13

EC14

EC15

EC16

EC17

EC18

EC19

EC20

W

W01 W

W02

W

W03

W

W04

W

W05

W

W06

W

W07

W

W08

W

W09

W

W10

W

W11

W

W13 W

W12 W

W14

W

W15

W

W16

W

W17

Base map modified from U.S. Geological Survey 1:100,000-scale digital dataUniversal Transverse Mercator projection, zone 14North American Datum of 1983

EC01EC02EC03EC04EC05EC06EC07EC08EC09EC10EC11EC12EC13EC14EC15EC16EC17EC18EC19EC20

North ProngMacdonaMedioLeon 35MedinaDos RiosSAR WitteAlazanSAR MitchellSan PedroSAR 410Salado 13SAR ElmendorfSAR Falls CitySalitrilloMartinez St. HedwigCibolo St. HedwigCibolo Falls CityEcletoSAR Goliad

Map 

identifier

Short name

WW01WW02WW03WW04WW05WW06WW07WW08WW09WW10WW11WW12WW13WW14WW15WW16WW17

Boerne WWTPBoerne WWTP and WRCCibolo WWTPSalitrillo WWTPUpper Martinez WWTPMartinez II WWTPDos Rios WRCDos Rios TuletaDos Rios Flood TunnelDos Rios RittimanDos Rios Convention CenterDos Rios Blue WingLeon Creek WRCLeon Creek Mitchell LakeMedio Creek WRCFloresville WWTPKenedy WWTP

Map 

identifier

Short name

TEXAS

San Antonio 

River Basin

Figure 1. Locations of wastewater discharge and water-quality sampling sites (2011–12) and relative concentrations and proportions of wastewater cocollected during the first synoptic sampling event, San Antonio River Basin, Texas, March–May 2011 (modified from fig. 13, Opsahl and Lambert, 2013).
Detections and Concentrations of CECs 

Three synoptic sampling events were completed during 

2011–12 to analyze for CECs in the San Antonio River Basin. 

During a synoptic sampling event, samples are collected from 

a number of sites at the same time to get a “snapshot” of how 

concentrations vary throughout the basin. The first and second 

synoptic sampling events included samples collected at the same 

12 sampling sites. The third sampling event included samples 

collected at seven sites that were added to the study after the 

first two synoptic sampling events were completed. When the 

synoptic sampling events took place, there was no flow at the 

Ecleto site (EC19, fig. 1), so the samples at this rural site were 

collected at a separate date and time. Samples were analyzed 

for 54 wastewater compounds, 13 pharmaceuticals, 17 steroidal 

hormones, and 4 sterols. Overall, the concentrations of all CECs 

analyzed for during this study were low, generally close to or 

less than the laboratory reporting level. 

Wastewater Compounds

Wastewater compounds typically found in treated domestic 

and industrial wastewater effluent are introduced to the 

environment primarily through point-source discharges from 

wastewater treatment plants (WWTPs) and water recycling 

centers (WRCs) and to a lesser degree through nonpoint sources 

such as seepage from septic systems, leakage from sewer 

lines, and urban runoff (Kolpin and others, 2004; Katz and 

others, 2010). During this study, wastewater compounds were 

aggregated into seven subclasses of compounds on the basis of 

similar uses or sources (fig. 2). 

Wastewater compounds were detected more often than 

were pharmaceuticals or steroidal hormones and sterols. 

The subclasses of wastewater compounds that were most 

commonly detected were personal-use compounds, industrial 

compounds, and flame retardants and plasticizers. Thirty-two 

of the 54 compounds analyzed for were detected in at least 

one of the samples collected (fig. 2). The flame retardants tris 

(2-chloroethyl) phosphate and tris (dichloroisopropyl) phosphate 

were the most frequently detected wastewater compounds 

with measureable concentrations detected in 28 of 33 samples. 

Tris (2-chloroethyl) phosphate and tris (dichloroisopropyl) 

phosphate are possible endocrine disruptors commonly used 

in clothing garments, mattresses, and sofa cushions (Stapleton 

and others, 2009). The highest measured concentration of a 

wastewater compound (1.90 micrograms per liter [μg/L]) was 

for the fragrance hexahydrohexamethyl-cyclopentabenzopyran 

(HHCB); for all samples, concentrations of this compound 

ranged from an estimated concentration of 0.006 μg/L to 

1.90 μg/L. The second highest concentration of a wastewater 

compound measured in the study was 1.4 μg/L for the compound 

5-methyl-1H-benzotriazole, a corrosion inhibiter used in 

numerous products including dishwater detergents, de-icing 

fluids, automotive antifreeze formulations, brake fluids, fluids 

for industrial cooling systems, and metal-cutting fluids (Kiss 

and Fries, 2009). Sample concentrations for this compound 

ranged from an estimated 0.1 to 1.4 μg/L. All of the remaining 

wastewater compounds were measured at concentrations less 

than 1.0 μg/L or were not detected. 

Pharmaceuticals

Pharmaceuticals are manufactured chemical substances 

administered to humans or animals to treat or prevent illness 

or disease or to promote the growth of food animals (Landers 

and others, 2012). Polar (2007, p. 7) explained that the 

active ingredients in pharmaceuticals “are of special concern 

because of the volumes introduced to the environment, their 

endocrine disrupting activity, and a potential increase of 

bacterial resistance.” Pharmaceuticals and their metabolites 

are introduced into the environment as a component of 

treated wastewater effluent (Polar, 2007), direct excretion, 

or discharge of effluent from pharmaceutical manufacturing 

facilities (Phillips and others, 2010). Samples were analyzed 

for 13 pharmaceuticals, and 4 were detected: 1 nonprescription 

pharmaceutical (diphenhydramine) and 3 commonly used 

prescription pharmaceuticals or pharmaceutical metabolites 

(carbamazepine, dehydronifedipine, and sulfamethoxazole) 

(fig. 3). Diphenhydramine, primarily used as an antihistamine 

(O’Neil, 2001), was detected in 6 of 34 samples. Carbamazepine, 

an anticonvulsant, was the most frequently detected 

pharmaceutical (24 of 34 samples). Carbamazepine degrades 

slowly in the environment and is resistant to breakdown 

during water treatment (Polar, 2007; Walker and others, 2012). 

Dehydronifedipine is the main metabolite of nifedipine, a drug 

used to treat cardiac disorders (Polar, 2007); dehydronifedipine 

was detected in 13 of 34 samples. The antibiotic 

sulfamethoxazole was detected in 15 of 34 samples.

Steroidal Hormones and Sterols

Steroidal hormones and sterols are natural, biologically 

produced chemicals that serve a variety of functions in animal 

and plant metabolism. Synthetic hormone derivatives such as 

anabolic steroids and birth-control compounds are widely used 

by humans (Reif and others, 2012). Both natural and synthetic 

hormones can be introduced into the environment through 

direct excretion or disposal into wastewater treatment systems 

and have been detected in aquatic systems, promoting concerns 

about negative effects on freshwater biota (National Academy of 

Sciences, 1999). Eight of 17 steroidal hormones and sterols were 

detected in at least one of the samples collected (fig. 4). Estrone, 

a metabolite of 17-beta-estradiol, was the most commonly 

detected compound related to estrogen and was detected in 9 of 

34 samples. Four plant and animal sterols were analyzed (plant 

sterols beta-sitosterol and beta-stigmastanol; animal sterols 

3-beta-coprostanol and cholesterol), resulting in a total of 41 

detections in 34 samples. Cholesterol was detected in 19 of 34 

samples, making it the most frequently detected sterol.

Distribution of CECs in the San Antonio River Basin

Results from the synoptic sampling events during 

2011 indicated that the number of detections and the total 

concentrations of CECs were higher in samples collected at 

sites downstream from WWTP and WRC outfalls compared 

to the number of detections and total concentrations measured 

in samples collected at other sampling sites in the study 

area. Among all of the sampling sites, the highest number of 

detections and concentrations of CECs were measured in the 

sample collected at the SAR Elmendorf site (EC13, fig. 1) 
laf16-0775_fig 02

0

5

10

15

20

25

30

Number of detections

Wastewater compound

4-n-Octylphenol

4-Nonylphenol diethoxylate

Camphor

3-Methyl-1H-indole

Acetophenone

Acetyl hexamethyl tetrahydro naphthalene (AHTN)

Caffeine

N, N-diethyl-meta-toluamide (DEET)

Hexahydrohexamethyl-cyclopentabenzopyran (HHCB)

Indole

Triclosan

1, 4-Dichlorobenzene

Bromacil

Prometon

p-Cresol

5-Methyl-1H-benzotriazole

9, 10-Anthraquinone

Benzophenone

Methyl salicylate

Triethyl citrate

Phenol

Tribromomethane

1-Methylnaphthalene

Fluoranthene

Naphthalene

Phenanthrene

Pyrene

Tributyl phosphate

Triphenyl phosphate

Tris (2-butoxyethyl) phosphate

Tris (2-chloroethyl) phosphate

Tris (dichloroisopropyl) phosphate

Detergent metabolites

(9) 

Pesticides

(19) 

Personal-use compounds 

(88)

Industrial compounds

(62) 

Disinfection compounds

(13) 

Polycyclic aromatic hydrocarbons

(11) 

Flame retardants and plasticizers

(100) 

Detection of wastewater

 compound, by subclass

 Detergent metabolites

 Personal-use compounds

 Pesticides

 Industrial compounds

 Disinfection compounds

 Polycyclic aromatic

 hydrocarbons

 Flame retardants and

 plasticizers

Number of detections per

 subclass of compound

EXPLANATION

(9)

Figure 2. Wastewater compounds detected in 33 water-quality samples collected from the San Antonio River Basin, Texas, 2011–12 

(modified from fig. 2, Opsahl and Lambert, 2013).

0

2

4

6

8

10

12

14

16

18

20

Number of detections

4-Androstene-3,17-dione

17-alpha-Estradiol

17-beta-Estradiol

Estrone

3-beta-Coprostanol

Cholesterol

beta-Sitosterol

beta-Stigmastanol

Steroidal hormone or sterol compound

Steroidal hormones - natural androgens

(2)

Steroidal hormones - natural estrogens

(14) 

Sterols - animal

(21)

Sterols - plant

(20)

(21)

Pharmaceutical compound

0

5

10

15

20

25

30

Number of detections

Diphenhydramine

Carbamazepine

Dehydronifedipine

Sulfamethoxazole

Nonprescription

(6) 

Prescription

(52) 

EXPLANATION

Detection of 

pharmaceutical

compound

(52) Number of detections

per subclass of

compound

EXPLANATION

Detection of steroidal

 hormone or sterol

 compound

Number of detections

per subclass of

compound

Figure 3. Pharmaceutical compounds detected in 34 water-quality 

samples collected from the San Antonio River Basin, Texas, 2011–12 

(modified from fig. 3, Opsahl and Lambert, 2013). 

Figure 4. Steroidal hormones and sterols detected in 34 waterquality samples collected from the San Antonio River Basin, Texas, 

2011–12 (modified from fig. 4, Opsahl and Lambert, 2013).
downstream from San Antonio. There also were detections 

of CECs in samples collected from urban sites with no large 

upstream source of treated wastewater; these detected CECs 

included 1,4-dicholorobenzene, p-cresol, phenol, acetyl 

hexamethyl tetrahydro naphthalene (AHTN), HHCB, tributyl 

phosphate, triethyl citrate, and triphenyl phosphate. Detections 

of these compounds indicate that many CECs can be present 

in streams flowing through urbanized areas without a large 

upstream source of treated wastewater. The presence of 

wastewater compounds at the Ecleto site (EC19, fig. 1) indicates 

that at least some wastewater compounds can be introduced 

into surface waters in rural parts of the San Antonio River 

Basin during runoff or by seepage from onsite wastewater 

treatment systems.

Few pharmaceuticals were detected in samples from 

streams without upstream outfalls of treated wastewater. 

The lower concentrations of these compounds at the furthest 

downstream sampling sites in the basin also indicate that some 

dilution or natural attenuation of pharmaceuticals may occur 

during transport. Because the Ecleto site (EC19, fig. 1) is in 

a rural rangeland area that does not receive runoff from San 

Antonio, the steroidal hormones and sterols detected in the sample 

collected at this site likely were derived from cattle waste rather 

than from wastewater effluent.

References Cited

Katz, B.G., Griffin, D.W., McMahon, P.B., Harden, H., Wade, 

E., Hicks, R.W., and Chanton, J.P., 2010, Fate of effluentborne contaminants beneath septic tank drainfields overlying 

a karst aquifer: Journal of Environmental Quality, v. 39, p. 

1181–1195. 

Kiss, A., and Fries, E., 2009, Occurrence of benzotriazoles 

in the rivers Main, Hengstbach, and Hegbach (Germany): 

Environmental Science and Pollution Research, v. 16, no. 6, p. 

702–710.

Kolpin, D.W., Skopec, M., Meyer, M.T., Furlong, E.T., and 

Zaugg, S.D., 2004, Urban contribution of pharmaceuticals 

and other organic wastewater contaminants to streams during 

differing flow conditions: Science of the Total Environment, v. 

328, p. 119–130. 

Landers, T.F., Cohen, Bevin, Wittum, T.E., and Larson, E.L., 

2012, A review of antibiotic use in food animals—Perspective, 

policy, and potential: Public Health Reports, v. 127, p. 4–22, 

accessed July 27, 2016, at http://www.ncbi.nlm.nih.gov/pmc/

articles/PMC3234384/pdf/phr12700004.pdf. 

National Academy of Sciences, 1999, Hormonally active agents 

in the environment: Washington, D.C., National Academy 

Press, 430 p.

Ockerman, D.J., and McNamara, K.C., 2003, Simulation of 

streamflow and estimation of streamflow compound loads in 

the San Antonio River watershed, Bexar County, Texas, 1997–

2001: U.S. Geological Survey Water Resources Investigations 

Report 2003–4030, 44 p.

O’Neil, M.J., ed., 2001, The Merck index—An encyclopedia 

of chemicals, drugs, and biologicals (13th ed.): Whitehouse 

Station, N.J., Merck and Company, Inc., 1,735 p. 

Opsahl, S.P., and Lambert, R.B., 2013, Detections, 

concentrations, and distributional patterns of compounds of 

emerging concern in the San Antonio River Basin, Texas, 

2011–12: U.S. Geological Survey Scientific Investigations 

Report 2013–5200, 44 p. [Also available at http://dx.doi.

org/10.3133/sir20135200.]

Phillips, P.L., Smith, S.G., Kolpin, D.W., Zaugg, S.D., Buxton, 

H.T., Furlong, E.T., Esposito, K., and Stinson, B., 2010, 

Pharmaceutical formulation facilities as sources of opioids 

and other pharmaceuticals to wastewater treatment plant 

effluents: Environmental Science and Technology, v. 44, no. 

13, p. 4910–4916.

Polar, J.A., 2007, The fate of pharmaceuticals after wastewater 

treatment: Florida Water Resources Journal, p. 26–31. [Also 

available at https://www.fwrj.com/TechArticle07/0607%20

FWRJ_tech1.pdf.]

Reif, A.G., Crawford, J.K., Loper, C.A., Proctor, Arianne, 

Manning, Rhonda, and Titler, Robert, 2012, Occurrence 

of pharmaceuticals, hormones, and organic wastewater 

compounds in Pennsylvania waters, 2006–09: U.S. Geological 

Survey Scientific Investigations Report 2012–5106, 99 p.

Stapleton, H.M., Klosterhaus, Susan, Eagle, Sarah, Fuh, 

Jennifer, Meeker, J.D., Blum, Arlene, and Webster, T.F., 

2009, Detection of organophosphate flame retardants in 

furniture foam and U.S. house dust: Environmental Science 

and Technology, v. 43, no. 19, p. 7490–7495, accessed 

July 29, 2016, at http://pubs.acs.org/doi/full/10.1021/

es9014019?src=recsys.

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population growth, Census Bureau reports: Accessed June 

21, 2016, at https://www.census.gov/newsroom/pressreleases/2013/cb13-94.html.

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disruption: Endocrine Disruptor Screening Program (EDSP), 

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concern in the environment: U.S. Geological Survey Toxic 

Substances Hydrology Program, accessed July 22, 2016, at 

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of carbamazepine in soils under different land uses receiving 

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This fact sheet is based on the following report:

Opsahl, S.P., and Lambert, R.B., 2013, Detections, 

concentrations, and distributional patterns of compounds of 

emerging concern in the San Antonio River Basin, Texas, 

2011–12: U.S. Geological Survey Scientific Investigations 

Report 2013–5200, 44 p., http://dx.doi.org/10.3133/

sir20135200.

By Rebecca B. Lambert and Stephen P. Opsahl

Front page photograph: View of the San Antonio River oriented 

upstream in San Antonio, Texas (photograph taken on November 

14, 2013, by Michael B. Nyman, U.S. Geological Survey; from Opsahl 

and Lambert, 2013).

Back page photograph: U.S. Geological Survey hydrographers 

collecting water sample for analysis of compounds of emerging 

concern (photograph taken on May 31, 2011, by Chiquita S. Lopez, 

U.S. Geological Survey; from Opsahl and Lambert, 2013).

For more information, please contact:

Director, Texas Water Science Center

U.S. Geological Survey

1505 Ferguson Lane

Austin, TX 78754– 4501

http://tx.usgs.gov/

Publishing support provided by 

Lafayette Publishing Service Center

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20163071