U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3090

August 2011

Prepared in cooperation with the San Antonio River Authority and the San Antonio Metropolitan Health District Public Center for 

Environmental Health

Occurrence, Distribution, and Concentrations of Selected 

Contaminants in Streambed- and Suspended-Sediment 

Samples Collected in Bexar County, Texas, 2007–09

Printed on recycled paper

•	 The U.S. Geological Survey collected streambed- and

suspended-sediment samples during 2007–09 from 20 sites

in 8 watersheds in Texas: Medio Creek, Medina River, Elm

Creek, Martinez Creek, Chupaderas Creek, Leon Creek,

Salado Creek, and San Antonio River (fig.1). The samples

were analyzed for major and trace elements, pesticides,

polychlorinated biphenyls (PCBs), and polycyclic aromatic

hydrocarbons (PAHs).

•	 The most frequently detected organic chemicals were the

chlordane pesticides. The samples from Leon Creek and San

Antonio River had more detections of all contaminants than

other watersheds.

•	 Concentrations of cadmium, chromium, and DDE in the

samples collected from the Leon Lackland, Leon Quintana,

and Leon 35 sites were above their probable effect concentrations, indicating harmful effects are likely on organisms

living in the sediments at those sites.

Key Findings

Cadmium

A naturally occuring trace element

used in batteries, pigments, metal coatings, and plastics.

Chromium

A naturally occurring trace element

used as an alloy in metals (predominantly steel) and in chrome plating.

Lead

A naturally occurring trace element

used in gasoline until the 1970s and

currently used in batteries, ammunition,

metal products, and radiation shields.

Zinc

A naturally occurring element used

for coatings, batteries, and metal alloys.

What Are Some of the Chemicals in the Sediments?

Chlordane

A synthetic pesticide used between

1948 and 1983 on corn and citrus crops

and home lawns and gardens; its use

continued until 1988 to control termites.

DDT, DDE, and DDD

Dichlorodiphenyltrichloroethane

(DDT) is a synthetic pesticide used

between 1939 and 1972 to control

insects on crops and disease-carrying

insects such as mosquitoes with malaria. 

Dichlorodiphenyldichloroethylene

(DDE) and dichlorodiphenyldichloroethane (DDD) are breakdown products

of DDT and have similar chemical and

physical properties to DDT.

PCBs

Polychlorinated biphenyls (PCBs)

are mixtures of organic compounds

manufactured between the 1930s and

1977 and used as plasticizers, lubricants,

and coolants. Total PCB is the sum of 18

individual PCB compounds.

PAHs

Polycyclic aromatic hydrocarbons

(PAHs) are a group of organic compounds that form during the burning of

carbon-based substances such as wood,

gasoline, or meat. PAHs also are in tires,

coal tar, crude oil, medicines, plastics,

and pesticides. Total PAH is the sum of

the most commonly reported individual

PAH compounds.

Elm Creek Medio Creek Rosillo Creek
When possible, streambed-sediment 

sampling met the following criteria: sites

were at or near previously sampled sites

and USGS streamflow-gaging stations, in

areas that were accessible by wading, and in

the upper and lower parts of each watershed.

Streambed-sediment samples were

combined from multiple depositional zones

within a single stream reach at each site.

The sediments were scooped into a glass

bowl, mixed, and then sieved to a standard

grain size.

Suspended-sediment sampling sites

were located at the downstream-most sites

in most of the watersheds in the study area.

Suspended-sediment samples were

collected with passive samplers (25-liter

bottle inside a steel cylinder) installed

near the stream channels. The bottle inside

the passive sampler filled when it rained

and streamflow rose. Suspended-sediment

samples were isolated from the stormwater

through filtration.

Figure 1. Locations of streambed-sediment and suspended-sediment sampling sites in Bexar County, Texas, 2007–09.

EXPLANATION

Watershed

 Medio Creek

 Medina River

 Elm Creek

 Martinez Creek

 Chupaderas Creek

 Leon Creek

 Salado Creek

 San Antonio River

Study area boundary

Municipal boundary

Sediment sampling site

 and map identifier

1 !

 6 Martinez 1518

 7 Chupaderas

 8 Leon Rodriguez

 9 Leon 90

10 Leon Morey

11 Leon Lackland

12 Leon Military

13 Leon Quintana

14 Leon 35

15 Salado 13

16 Rosillo

17 Salado Southton

18 San Antonio River Theo

19 San Antonio River 410

20 San Antonio River Elmendorf

Map

identifier Site identifier Mapidentifier Site identifier Mapidentifier Site identifier Map

identifier Site identifier

 1 Medio 90

 2 Medio Pearsall 

 3 Medina

 4 Elm

 5 Martinez St. Hedwig

Figure 1. Locations of streambed-sediment and suspended-sediment sampling sites in Bexar County, Texas, 2007–09.

TEXAS

San Antonio

River Study area

1

2

3 4

5

6

7

8 9

10 11

12 13

14 15

16

17

18

19

20

!

!

!

!

!

!

!

!

!

!

! !

!

!

!

!

!

!

!

!

San Antonio

St. Hedwig

Elmendorf

WILSON COUNTY

BEXAR COUNTY

ATASCOSA COUNTY

COMAL

COUNTY

BANDERA COUNTY

KERR COUNTY

GUADALUPE

COUNTY

KENDALL

COUNTY

MEDINA COUNTY

Leon Creek

Salado

Medio

Creek

San

Rosillo

Medina

Lake

Mitchell

Lake

Medina

River

Cibolo

Creek

Creek

Antonio River

Creek

Martinez

Creek

San

Braunig

Lake

Calaveras

Lake

Chupaderas Creek

Antonio River

Creek Elm

353

£¤1604

£¤16

£¤ £¤181 57

£¤281

£¤ £¤87 90

§ ̈¦35

§ ̈¦37

§ ̈¦10 LOOP 410 LOOP 13

SOUTHWEST MILITARY DRIVE

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

15'

99°30'

99°00'

45' 30'

98°15'

29°30'

29°45'

Base modified from U.S. Geological Survey

digital data, 1:24,000 quadrangles

Texas State Plane Coordinate System, FIPS 4204

North American Datum of 1983 

Leon Creek

Leon Creek

Background

High concentrations of

sediment-associated contaminants

are typically associated with urban

areas such as San Antonio, Texas,

in Bexar County, the seventh most

populous city in the United States

(U.S. Census Bureau, 2009). U.S.

Geological Survey personnel

periodically collected surficial

streambed-sediment samples

during 2007–09 and collected

suspended-sediment samples from

selected streams after storms

during 2008 and 2009. All

sediment samples were analyzed

for major and trace elements,

pesticides, polychlorinated

biphenyls (PCBs), and polycyclic

aromatic hydrocarbons (PAHs).

Two Methods of Sediment Sampling
How Often Were These Chemicals Found?

All of the trace elements discussed in this fact sheet

occur naturally and were found in all of the sediment samples;

however, the pesticides, PCBs, and most PAHs are associated

with human activities and were not found in all of the sediment

samples, particularly those samples collected in the watersheds

with low human populations (Medina River, Elm Creek, and

Chupaderas Creek). The number of times pesticides, PCBs,

and PAHs were found varied widely by watershed (fig. 2).

•	 Chlordane pesticides were found most often, occurring in

94 percent of the samples and in every watershed.

•	 DDT pesticides were found in 22 percent of the samples.

No DDT pesticides were found in the samples collected from

Medina River, Elm Creek, or Chupaderas Creek; they were

found most often in the samples collected from Leon Creek

and San Antonio River.

Table 1. The sediment-quality guidelines of MacDonald and 

others (2000) were used to to evaluate the potential toxicity of 

contaminants to organisms living in the sediment. 

[μg/g, micrograms per gram; μg/kg, micrograms per kilogram; DDE,

dichlorodiphenyldichloroethylene; PCB, polychlorinated biphenyls; PAH,

polycyclic aromatic hydrocarbons]

•	 TEC, threshold effect concentration; concentrations below the TEC 

should not have a harmful effect on organisms living in the sediment. 

•	 PEC, probable effect concentration; concentrations above the PEC are 

likely to have a harmful effect on organisms living in the sediment. 

•	 Samples with concentrations between the TEC and PEC are predicted 

 to be neither toxic nor nontoxic.

Chemical TEC PEC

Cadmium (μg/g) 0.99 4.98

Chromium (μg/g) 43.4 111

Lead (μg/g) 35.8 128

Zinc (μg/g) 121 459

Chlordane (μg/kg) 3.24 17.6

DDE (μg/kg) 3.16 31.3

Total PCB (μg/kg) 59.8 676

Total PAH (μg/kg) 1,610 22,800

Figure 2. Detection frequencies of pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons in streambed- and 

suspended-sediment samples, by watershed, in Bexar County, Texas, 2007–09. 

Figure 2. Detection frequencies of pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons

(PAHs) in streambed and suspended-sediment samples, by watershed, in Bexar County, Texas, 2007–09.

cis-Chlordane trans-Chlordane

cis-Nonachlor trans-Nonachlor

Oxychlordane

p,p’-DDT

p,p’-DDD

p,p’-DDE

PCB 49

PCB 52

PCB 70

PCB 101

PCB 110

PCB 118

PCB 138

PCB 146

PCB 149

PCB 151

PCB 170

PCB 174

PCB 177

PCB 180

PCB 183

PCB 187

PCB 194

PCB 206

Anthracene

Benzo(a)pyrene

Fluoranthene

Naphthalene

Phenanthrene

Pyrene

Fluorene

Chrysene

Indenopyrene

Chemical

Chlordane

pesticides

DDT

pesticides

Polychlorinated biphenyls

(PCBs)

Polycyclic aromatic

hydrocarbons (PAHs)

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

Detections, in percent

Detections, in percent

Medio 

Creek

watershed

Medina 

River

watershed

Elm 

Creek

watershed

Martinez 

Creek

watershed

Chupaderas 

Creek

watershed

Leon 

Creek

watershed

San Antonio 

River

watershed

Salado 

Creek

watershed

Medio 

Creek

watershed

Medina 

River

watershed

Elm 

Creek

watershed

Martinez 

Creek

watershed

Chupaderas 

Creek

watershed

Leon 

Creek

watershed

San Antonio 

River

watershed

Salado 

Creek

watershed

•	 PCBs were found in 90 percent of the samples; they were

found in every watershed and most often in the samples

collected from Leon Creek and San Antonio River.

•	 PAHs were found in 75 percent of the samples;

no PAHs were found in the samples collected from

Medina River or Chupaderas Creek. PAHs were found

most often in the samples collected from Leon Creek

and San Antonio River.

Sediment-Quality Guidelines—Are These 

Concentrations High?

The concentrations of chemicals in sediments can be

compared to sediment-quality guidelines (table 1, fig. 3) to

evaluate the potential toxicity of contaminants to organisms

living in the sediment. The sediment-quality guidelines

used in this fact sheet (MacDonald and others, 2000) are

not regulatory limits and do not necessarily mean harmful

effects are expected on humans or other animals exposed to

the sediments.
For additional information, contact 

Director, USGS Texas Water Science Center

http://tx.usgs.gov/

gs-w-txpublic-info@usgs.gov

•	 Cadmium concentrations were greater than the

probable effect concentration (PEC) in two

samples collected from the Leon Quintana site;

six samples collected from the Leon 35 site had

concentrations greater than the threshold effect

concentration (TEC).

•	 Chromium concentrations were greater than the

PEC in two samples collected from the Leon

Quintana site and in two samples collected from

the Leon 35 site; 69 percent of all samples had

concentrations greater than the TEC.

•	 Lead concentrations were greater than the TEC

in 33 percent of all samples, no samples had

concentrations greater than the PEC.

•	 Zinc concentrations were greater than the TEC

in 35 percent of all samples, no samples had

concentrations greater than the PEC.

•	 Chlordane concentrations were greater than the

TEC in one sample collected from each of the

following sites: Medio Pearsall, Leon Lackland,

and SAR 410.

•	 DDE concentration was greater than the

PEC in one sample collected from the Leon

Lackland site; 19 percent of all samples had

concentrations greater than the TEC.

•	 Total PCB concentration was greater than the

TEC in one sample collected from the Leon

Lackland site.

•	 Total PAH concentrations were greater than the

TEC in 15 percent of all samples.

References Cited

MacDonald, D.D., Ingersoll, C.G., and Berger, T.A.,

2000, Development and evaluation of consensusbased sediment quality guidelines for freshwater

ecosystems: Archives of Environmental

Contamination and Toxicology, v. 39, p. 20–31.

U.S. Census Bureau, 2009, Table 1—Annual

estimates of the resident population for

incorporated places over 100,000, ranked by

July 1, 2008 population (April 1, 2000 to July 1,

2008): U.S. Census Bureau, Population Division,

p. 1.

This fact sheet is based on the following report:

Wilson, J.T., 2011, Assessment of selected

contaminants in streambed- and suspendedsediment samples collected in Bexar County,

Texas, 2007–09: U.S. Geological Survey

Scientific Investigations Report 2011–5097, 57 p.

—Jennifer T. Wilson

Medio 90

Medio Pearsall

Medina

Elm

Martinez St. Hedwig

Martinez 1518

Chupaderas Leon Rodriguez

Leon 90

Leon Morey Leon Lackland

Leon Military Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR Theo

SAR 410

SAR Elmendorf

Medio 90

Medio Pearsall

Medina

Elm

Martinez St. Hedwig

Martinez 1518

Chupaderas

Leon Rodriguez Leon 90

Leon Morey Leon Lackland

Leon Military Leon Quintana

Leon 35

Salado 13

Rosillo

Salado Southton

SAR Theo

SAR 410

SAR Elmendorf

Site identifier Site identifier Concentration, in micrograms per kilogram (μg/kg)

Concentration, in micrograms per gram (μg/g)

0

2

4

6

8

0

5

10

15

20

0

10

20

30

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0

50

100

150

200

0

20

40

60

80

0

40

80

120

160

0

1

2

3

4

5

6

7

41 μg/kg

77 μg/kg

Chlordane

DDE

Total PCB

Zinc Total PAH

Lead

Chromium

Cadmium

EXPLANATION

Streambed-sediment sample concentration

Concentration more than probable

 effect concentration (PEC)

Concentration more than threshold

 effect concentration (TEC)

Concentration less than threshold

 effect concentration (TEC)

Nondetection at interim reporting level; 

 not shown for total PCB or total PAH

Suspended-sediment sample concentration

Concentration more than probable

 effect concentration (PEC)

Concentration more than threshold

 effect concentration (TEC)

Concentration less than threshold

 effect concentration (TEC)

Nondetection at interim reporting level; 

 not shown for total PCB or total PAH

SAR San Antonio River

Figure 3. Comparison of sediment-quality guildelines to concentrations in streambedsediment (circles) and suspended-sediment (triangles) samples collected from sites in 

Bexar County, Texas, 2007–09.

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