By Lawrence A. LeBlanc, James L. Orlando and
Kathryn M. Kuivila
U.S. GEOLOGICAL SURVEY
Data Series 104
Sacramento, California 2004
ONLINE ONLY
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This report contains pesticide concentration data for water, and suspended and
bed sediment samples collected in April 2003 from twelve sites along the New and Alamo Rivers in the Salton
Sea watershed, in southeastern California. The study was done in collaboration with the California State
Regional Water Quality Control Board, Colorado River Region, to assess inputs of current-use pesticides
associated with water and sediment into the New and Alamo Rivers. Five sites along the New River and seven
sites along the Alamo River, downstream of major agricultural drains, were selected and covered the lengths
of the rivers from the international boundary to approximately 1.5 km from the river mouths. Sampling from
bridges occurred at seven of the twelve sites. At these sites, streamflow measurements were taken. These
same sites were also characterized for cross-stream homogeneity by measuring dissolved oxygen, pH, specific
conductance, temperature, and suspended solids concentration at several vertical (depths) and horizontal
(cross-stream) points across the river.
Large volume water samples (200–300 L) were collected for isolation of suspended
sediments by flow-through centrifugation. Water from the outflow of the flow-through centrifuge was sampled
for the determination of aqueous pesticide concentrations. In addition, bottom sediments were sampled at
each site. Current-use pesticides and legacy organochlorine compounds (p,p´-DDT, p,p´-DDE and p,p´-DDD)
were extracted from sediments and measured via gas chromatography/mass spectrometry (GC/MS). Organic carbon
and percentage of fines were also determined for suspended and bottom sediments.
Cross-stream transects of dissolved constituents and suspended sediments showed that
the rivers were fairly homogeneous at the sites sampled. Streamflow was higher at the outlet sites, with the
Alamo River having higher flow (1,240 cfs) than the New River (798 cfs).
Twelve current-use pesticides, one legacy organochlorine compound (p,p´-DDE), and
the additive piperonyl butoxide were detected in water samples. Trifluralin was found in the highest
concentration of all detected compounds (68.5–599 ng/L) at all sites in both rivers, except for the
international boundary sites. Atrazine was also detected in high concentration (51.0–285 ng/L) at several
sites. The outlet sites had among the highest numbers of pesticides detected and the international boundary
sites had the lowest numbers of pesticides detected for both rivers. The numbers of pesticides detected were
greater for the Alamo River than for the New River.
Six current-use pesticides and two legacy organochlorines (p,p´-DDE and p,p´-DDD)
were found associated with suspended and bed sediments. The DDT metabolite p,p´-DDE was detected in all
suspended and bed sediments from the Alamo River, but only at two sites in the New River. Dacthal,
chlorpyrifos, pendimethalin, and trifluralin were the most commonly detected current-use pesticides.
Trifluralin was the compound found in the highest concentrations in suspended (14.5–120 ng/g) and bed
(1.9–9.0 ng/g) sediments. The sites along the Alamo River had more frequent detections of pesticides in
suspended and bed sediments when compared with the New River sites. The greatest number of pesticides that
were detected in suspended sediments (seven) were in the samples from the Sinclair Road and Harris Road
sites. For bottom sediments, the Alamo River outlet site had the greatest number of pesticide detections
(eight).
Abstract
Introduction
Hydrographic Setting
Purpose and Scope
Sample Collection Methods
Large Volume Water Samples
Isolation of Sespended Sediments
Water Samples for Aqueous Pesticide Analysis
Bed Sediment
Laboratory Methods
Water Analysis
Quality Assurance and Quality Control for Water Samples
Sediment Analysis
Quality Assurance and Quality Control for Sediment Samples
Instrument Analysis
Sediment Organic Carbon Analysis
Grain-Size Analysis
Results
Station Characteristics
Aqueous Pesticide Concentrations
Percentage of Organic Carbon and Percentage of Fines in Suspended and Bed Sediments
Pesticide Concentrations Associated with Suspended and Bed Sediments
References
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