State of California

M e m o r a n d u m

To : Don Weaver Date : June 6, 1997
Senior Environmental Research
Scientist Supervisor
Environmental Monitoring and Pest Management

From: Department of Pesticide Regulation - 1020 N Street, Room 161
Sacramento, California 95814-5624



The purpose of this memorandum is to provide results of water sampling conducted on the Sacramento River by the Department of Pesticide Regulation (DPR). Data included here are from the period December 2, 1996 to March 7, 1997 and encompass results from both chemical analyses conducted by the California Department of Food and Agriculture (CDFA) and bioassays conducted by the California Department of Fish and Game (DFG). An in-depth interpretation of the data is not included here but will be provided in the final report.


The Sacramento River is the largest river in California both in volume of water and in drainage area (Friebel et al., 1995) (Figure 1). From Mount Shasta in the north to the Sacramento-San Joaquin Delta in the south, the river flows for 327 miles and drains approximately 27,000 square miles including agricultural, urban and undeveloped land areas (Domagalski and Brown, 1994). The primary source of water entering the system is surface runoff from the Sierra Nevada Mountains to the east and Cascade Range to the north (CSLC, 1993). Runoff from rain events occurring in the Sacramento Valley and Coastal Range Mountains provide short term increases in river flow. Seasonal rains occur from October to March with little significant rain from June to September. River flow during the summer is composed of dam releases of snow-melt water for agricultural, urban, recreational and wildlife purposes.

In the Sacramento Valley, the organophosphorus insecticides diazinon and methidathion are the primary dormant season insecticides used on stone fruit and nut crops (DPR 1993; DPR 1994; DPR 1995). This dormant spray application period coincides with the bulk of the seasonal rainfall, providing the potential for these pesticides to wash off target areas and migrate with surface runoff to the Sacramento River. Runoff from orchard areas west of the Sacramento River chiefly flows into the Colusa Basin Drain which enters the Sacramento River at Knights Landing (Figure 2). Runoff from dormant spray areas east of the Sacramento River principally flows into Butte Creek, which has been engineered to drain into the Sutter Bypass via the Butte Slough. Runoff from the west side of the Feather River also drains into the Sutter Bypass. During periods of normal flow, the Sutter Bypass enters the Sacramento River via the Sacramento Slough at Karnak. During periods of high flow, the Sutter Bypass channel fills completely with runoff from this area plus water diverted from the Sacramento River. This flow merges with the Feather River eight miles prior to entering the Sacramento River, forming a two mile wide channel which inundates the Sacramento Slough. During floods, a large portion of the flows of the Sacramento River and the Sutter Bypass/Feather River will be diverted into the Yolo Bypass. Runoff from areas east of the Feather River drains into the Feather River above Nicolaus.

Previous studies by U.S. Geological Survey (USGS) and DPR of the Sacramento River have shown that most diazinon detections were observed during the dormant spray season (MacCoy et al., 1995; Nordmark, 1995). The USGS study also detected low levels of methidathion during this season. In a monitoring study by the Central Valley Regional Water Quality Control Board (CVRWQCB), diazinon concentrations were detected as high as 5 ug/L(1) in the Sacramento Slough in January 1996 (personal communication, Chris Foe, CVRWQCB, 1996). In a separate study (Foe and Sheipline, 1993), acute toxicity to Ceriodaphnia dubia in conjunction with high diazinon and methidathion concentrations, was found at Gilsizer Slough, which drains some of the area west of the Feather River and flows into the Sutter Bypass (Figure 2).

The objective of this study was to monitor the concentrations of dormant spray insecticides and the occurrence of aquatic toxicity, both acute and chronic, in portions of the Sacramento River watershed. Additional organophosphate and carbamate insecticides that have historically been applied during the winter months were also monitored (Table 1). Acute toxicity to C. dubia was tested in a relatively small tributary which does not contain major inputs from municipal or industrial sources. The potential for chronic toxicity was investigated in a section of the Sacramento River downstream from dormant spray insecticide inputs into the watershed, yet above input from the American River. A companion study was also conducted to monitor pesticide levels and toxicity in the San Joaquin River (Bennett, 1997) watershed and these results will be presented in a separate memorandum. Long-term monitoring of acute and chronic toxicity in these watersheds will help scientists at DPR evaluate the effectiveness of programs designed to decrease the runoff of dormant spray insecticides.


Study Site Description

Sutter Bypass

A small bridge across the western channel of the Sutter Bypass at the Karnak Pumping Station, just prior to the Sacramento Slough, was selected as the acute toxicity monitoring site. This site receives runoff water from most of the agricultural areas between the Sacramento and Feather Rivers. Previous studies have indicated the potential for high concentrations of pesticides in this area (personal communication, Chris Foe, CVRWQCB, 1996, Wofford and Lee, 1995).

Extensive flooding occurred in late December and early January which inundated the Sutter Bypass at Karnak. Therefore, this site was moved to an alternate site along the western edge of the Sutter Bypass at Sacramento Avenue, approximately 9 miles upstream. Sampling continued at this alternate site until February 17, when water levels had receded enough to allow sampling at the original site.

Sacramento River

The chronic toxicity monitoring site was located on the right bank of the Sacramento River at the water intake to the West Sacramento Water Treatment Plant at Bryte. This site receives discharge from all major agricultural tributaries but is above the confluence of the largely non-agricultural American River and the discharge of urban runoff from the cities of Sacramento and West Sacramento (Figure 2).

Sample Collection

Background sampling was conducted the week of December 2, 1996, prior to the onset of the dormant spray season. Sampling was originally scheduled to resume January 6, 1997 and continue through early March, 1997. However, due to flooding throughout the region in January, sampling did not resume until January 20. Sampling continued until March 7 when no more dormant sprays were reported to be applied.

Chemical analyses were performed on each water sample collected for both acute and chronic tests. Selected organophosphate and carbamate insecticides were analyzed in two separate analyses with diazinon being analyzed in a third analysis (Table 1). Pesticides included in our analyses were chosen based on pesticide use reports indicating historical use during the dormant spray season in the Central Valley, previous detections in the watershed, the availability of analytical methods in the organophosphate or carbamate screens and to standardize analyses between the Sacramento and San Joaquin River studies.

Acute toxicity tests were performed twice per week, with samples collected on Monday and Wednesday. One chronic toxicity test was conducted weekly using water samples collected on Monday, Wednesday, and Friday. Water collected on Monday was used to begin the chronic toxicity tests. Water collected on Wednesday and Friday was used to renew chronic test water (see below).

Originally, water samples were to be collected at both sites, from as close to center channel as possible, using a depth-integrated sampler (D-77) with a 3-liter Teflon® bottle and nozzle. The initial background samples were collected using this method but it was unsuitable for use in the Sutter Bypass at Sacramento Avenue. At this site, samples were collected using a subsurface grab method utilizing a 1-liter bottle on the end of a 4-meter pole. Sample collection using the subsurface grab method continued when sampling resumed in the Sutter Bypass at Karnak on February 17.

During the course of the study, the nozzles for the D-77 sampler were lost due to exceptionally high flows and snagging on underwater debris. Therefore, changes were made in the sampling methods used in the Sacramento River at Bryte. The February 14 sample was started using the full D-77 assembly, but due to the loss of equipment during sampling, completed using a grab sample. All subsequent samples from this site were subsurface grab samples.

Normally eight to ten 1-liter splits were required for each sampling event. At least 12 liters of water were collected and composited in a stainless steel 10-gallon (38-liter) milk can. The composited sample was placed on wet ice for transportation back to the West Sacramento warehouse for splitting. All samples were split on the day of collection into 1-liter amber glass bottles, with Teflon® lined caps, using a (USGS designed) Geotech® 10-port splitter. Two pairs of 1-liter samples were submitted for acute toxicity testing and one pair of 1-liter samples was submitted for chronic toxicity testing. Three 1-liter samples were submitted for chemical analyses: one each for the organophosphate, carbamate and diazinon analyses. Two 1-liter backups were stored at West Sacramento and 1-liter was used for acidification purposes. Additional sample splits from sampling events on February 3 and 24 were provided to the CVRWQCB for acute toxicity and chemical analysis.

Samples designated for organophosphate and carbamate chemical analysis were preserved by acidification with 3N hydrochloric acid to a pH of between 3.0 to 3.5. Most organophosphate and carbamate pesticides are sufficiently preserved at this pH (Ross et al. 1996). Diazinon, however, rapidly degrades under acidic conditions and therefore was analyzed from a separate, unacidified, sample. Samples were stored in a 4o C refrigerator until transported to the appropriate laboratory (on wet ice) for analysis. All samples were delivered to the testing laboratory within 24 hours of collection.

Environmental Measurements

Water quality parameters measured in situ included temperature, pH, electrical conductivity (EC), and dissolved oxygen (DO). Additionally, ammonia, alkalinity and hardness were measured by the DFG Aquatic Toxicity Laboratory upon delivery of the toxicity samples. Water pH was measured using a Sentron (model 1001) pH meter. EC was measured using a Yellow Springs Instruments (YSI) salinity-conductivity-temperature (SCT) meter (model 33). Water temperature and DO were measured using a YSI dissolved oxygen meter (model 57).

Precipitation and discharge information were also gathered for the study area. Precipitation data was averaged from two sites: a Department of Forestry station located near Chico and the National Weather Service station located at the Sacramento Post Office (stations CHI and SPO, respectively) to approximate rainfall in the Sacramento Valley. Discharge records for the Karnak/Sacramento Slough site were unavailable due to flooding from January until the February 17 sample. Discharge for the Butte-Slough-near-Meridian gage was used instead to provide flow estimates for the Sutter Bypass sites. The Department of Water Resources (DWR) gaging station at Bryte was decommissioned after this study began, requiring the use of data from the Verona USGS gaging station, 18 miles up river from the Bryte sampling location. The Verona site captures all major input to the Sacramento River above the sampling site but it does not account for the outflow through the Sacramento Weir, approximately 1 mile above the Bryte sampling site. There was water flowing through this weir from the Sacramento River into the Yolo Bypass during most of this study. All precipitation and discharge data were taken from provisional, DWR, National Weather Service and Department of Forestry information and is subject to revision. Further refinements of flow data at each site will be investigated for the final report as more information becomes available. This information will be used to follow annual changes in chemical concentrations with respect to fluctuations in flow and will also be useful for modeling efforts, should they be undertaken.

Chemical Analysis and Toxicity Testing

Chemical Analyses

Pesticide analyses of water samples were performed by the CDFA Center for Analytical Chemistry. The organophosphate pesticides were analyzed using gas chromatography and a flame photometric detector. The carbamate pesticides were analyzed using high performance liquid chromatography, post column-derivation and a fluorescence detector. The pesticides and reporting limits are listed in Table 1. Details of chemical analytical methods will be provided in the final report.

Quality control (QC) for the chemistry portion of this study was in accordance with Standard Operating Procedure QAQC001.00 (DPR, 1996) and consisted of a continuing QC program, plus the submission of six rinse blanks of the splitting equipment and six blind spikes. There were no detections of any pesticides in any of the six rinse blank samples. Six blind spikes were submitted along with the field samples for analysis as organophosphate, carbamate, or diazinon samples. More detailed quality control data, including method development, the establishment of control limits and spike recoveries, will be included in the final report.

Toxicity Tests

Acute toxicity testing was conducted by the DFG Aquatic Toxicity Laboratory following current U.S. Environmental Protection Agency (U.S.EPA) procedures using the cladoceran Ceriodaphnia dubia (U.S.EPA, 1993). Acute toxicity was determined using a 96-hour, static-renewal bioassay in undiluted sample water. Chronic toxicity was determined using a static renewal 7-day bioassay of undiluted sample water with C. dubia and followed current U.S.EPA guidelines (U.S.EPA, 1994). Test organisms used in chronic testing were placed in sample water on day one of testing, with test water replenished on days three and five. All acute and chronic tests commenced and renewal water was used within 36 hours of sample collection. Data were reported as percent survival for both acute and chronic tests and the average number of offspring per surviving adult for the chronic tests. More complete information on chemical analytical and bioassay methods will be provided in the final report.

Quality control for the acute toxicity monitoring portion of this study consisted of submission of a split sample for each sample collected from the Sutter Bypass site to the DFG Aquatic Toxicity Laboratory for acute toxicity testing. Acute toxicity samples were labeled only with a sample number and were submitted along with samples from the companion San Joaquin River study. The resultant data will help DPR scientists better understand and characterize intra-laboratory precision of acute toxicity tests performed on ambient water samples and will be discussed in the final report.


The following results include data collected during an unusually wet season which included extensive flooding during the first half of the winter followed by an abnormally dry second half. Any interpretation of the results by the reader should take into account that conditions during the monitoring period were not necessarily characteristic of a typical winter spray season.

Environmental Measurements

Sutter Bypass

Figure 3presents the data for pH, DO, temperature, EC, alkalinity and hardness for the Sutter Bypass sites. Ammonia levels remained below the detection limit of 50 ug/L for all samples. pH values ranged from 7.0 to 8.5. Water temperature ranged from 9.6 to 12.1o C, DO ranged from 8.2 to 10.6 ug/L and EC ranged from 95 to 359 uS/cm with the highest readings occurring in the December background samples at Karnak.

Sacramento River

Figure 4 presents the data for pH, DO, temperature, EC, alkalinity and hardness for the Sacramento River at Bryte site. Ammonia levels remained below the detection limit of 50 ug/L for all samples. pH values ranged from 6.9 to 8.5. Water temperature ranged from 8.8 to 10.9o C, DO ranged from 8.6 to 11 ug/L and EC ranged from 60 to 176 uS/cm.

Figure 5 presents precipitation averaged for two stations in the Sacramento Valley and discharge for the Sacramento River and the Sutter Bypass. Due to flooding, all flow data presented in Figure 5 are approximate as all inputs and diversions were not gaged and many gages were not accurately calibrated for such extreme flows (personal communication: Steven Graham, DWR Surface Water Unit). The discharge at Butte-Slough-near-Meridian peaked at 136,000 cfs which exceeded the discharge through the Sacramento River at Verona. This is possible due to the diversion of a large portion of the Sacramento River, Sutter Bypass and Feather River flows into the Yolo Bypass. Discharge for all inputs and outflows are not available. For example, Tisdale Weir was in operation starting December 11 through mid February and would transfer additional water from the Sacramento River to the Sutter Bypass below the Butte-Slough-near-Meridian gage. Daily flows at this weir were not recorded, however a spot flow taken by DWR on January 7 measured 16,687 cfs. Another unknown factor was caused by a large levee break in late January, along the Sutter Bypass near Wadsworth Canal, diverting some of the flow from the bypass back to the town of Meridian, seven miles upstream.

Chemical Concentrations and Toxicity Data

Sutter Bypass

Diazinon was detected in seven of the 16 samples collected in the Sutter Bypass (Table 2). Diazinon was detected in the Sutter Bypass at Sacramento Avenue on January 27 and 29 at 0.086 and 0.063 ug/L, respectively. Diazinon was again detected in the Sutter Bypass at Karnak in five consecutive samples collected between February 17 and March 4 at levels ranging from 0.040 to 0.056 ug/L. Methidathion was also detected in the Sutter Bypass at Sacramento Avenue on January 27 at 0.057 ug/L. The percent survival of the C. dubia test animals ranged from 85% to 100% in the acute toxicity samples while the corresponding controls ranged from 90% to 100% survival. Relationships between the occurrence of pesticides and aquatic toxicity will be investigated in the final report.

Sacramento River

Diazinon was detected in four of 24 samples collected from the Sacramento River at Bryte. These detections occurred from January 24 through February 1 and ranged in concentration from 0.061 to 0.065 ug/L (Table 2). In addition, methidathion was detected in the January 27 sample collected at Bryte at 0.056 ug/L.

No chronic toxicity test or control had less than 90% survival. All chronic toxicity samples had between 17.1 and 35 offspring and controls had between 15.4 and 25.1 offspring average per surviving adult at the end of the seven day test. Statistical analysis of reproduction data will be included in the final report as it may be used, in conjunction with chemical data, to identify potential sub-lethal effects in the test organisms.

If you have any questions, please feel free to contact me.

Craig Nordmark
Environmental Research Scientist
Environmental Hazards Assessment Program
(916) 324-4138



Bennett, K., 1997. Preliminary Results of Acute and Chronic Toxicity Testing of Surface Water Monitored in the in the San Joaquin River Watershed: Winter 1996-97. Memorandum to Don Weaver, Environmental Hazards Assessment Program, Department of Pesticide Regulation. Sacramento, California. May 1997

Central Valley Regional Water Quality Control Board. 1994. Water Quality Control Plan (Basin Plan), Central Valley Region, Sacramento River and San Joaquin River Basins. Sacramento, California.

California State Lands Commission (CSLC), 1993. California's rivers-A public trust report. Second Edition. CSLC, Sacramento, California.

Domagalski, J., and L.R. Brown. 1994. The Sacramento Basin Fact Sheet, U.S. Geological Survey. National Water Quality Assessment (NAWQA) Program. Sacramento, California.

Department of Pesticide Regulation. 1993. Pesticide Use Report. Sacramento, California.

Department of Pesticide Regulation. 1994. Pesticide Use Report. Sacramento, California.

Department of Pesticide Regulation. 1995. Pesticide Use Report. Sacramento, California.

Department of Pesticide Regulation. 1996. Standard Operating Procedure Number QAQC001.00: Chemistry Laboratory Quality Control. Environmental Hazards Assessment Program, California Environmental Protection Agency. Sacramento, California.

Foe, C. and R. Sheipline, 1993. Pesticides in Surface Water From Applications on Orchards and Alfalfa During the Winter and Spring of 1991-92. California Regional Water Quality Control Board, Central Valley Region, Sacramento, California. February 1993.

Friebel M.F., K.L. Markham, S.W. Anderson and G.L. Rockwell, 1995. Water Resources Data, California, Water Year 1994. Volume 4. U.S. Geological Survey Water-Data Report CA-94-4. Sacramento, California

MacCoy, D., K.L. Crepeau, and K.M. Kuivila. 1995. Dissolved pesticide data for the San Joaquin River at Vernalis and the Sacramento River at Sacramento, California, 1991-94. U.S. Geological Survey Rep. 95-110. U.S. Gov. Print. Office, Washington DC.

Nordmark, C., 1995. Preliminary Results of the Four River Monitoring Study, Sacramento River, November 1993-November 1994. Memorandum to Roger Sava, Environmental Hazards Assessment Program. Department of Pesticide Regulation, Sacramento, California. June 22, 1995.

Ross, L.J., R. Stein, J. Hsu, J. White, and K. Hefner, 1996. Distribution and Mass Loading of Insecticides in the San Joaquin River, California. Winter 1991-92 and 1992-93. Environmental Hazards Assessment Program. Department of Pesticide Regulation, Sacramento, California.

Wofford, P.L. and P. Lee, 1995. Results for Monitoring for the Herbicide MCPA in Surface Water of the Sacramento River Basin. Environmental Hazards Assessment Program. Department of Pesticide Regulation, Sacramento, California.

U.S. Environmental Protection Agency. 1993. Methods for measuring the acute toxicity of effluents and receiving waters to freshwater and marine organisms. 4th ed. EPA/600/4-90/027F. August 1993.

U.S. Environmental Protection Agency. 1994. Short-term methods for estimating the chronic toxicity of effluents and receiving waters to freshwater organisms. 3rd ed. EPA-600-4-91-002. July 1994.

Table 1.California Department of Food and Agriculture, Center for Analytical Chemistry organophosphate and carbamate pesticide screens for the Sacramento River toxicity monitoring study.
Organophosphate Pesticides in Surface Water by GC 

Method: GC/FPD

N-Methyl Carbamate in Surface Water by HPLC 

Method: HPLC/Post Column-fluorescence


Reporting Limit 



Reporting Limit 


Chlorpyrifos 0.04 Carbaryl 0.05
Diazinon1 0.04 Carbofuran 0.05
Dimethoate (Cygon) 0.05
Fonofos 0.05
Malathion 0.05
Methidathion 0.05
Methyl parathion 0.05
Phosmet 0.05

1 Diazinon was analyzed from a separate, unpreserved, split sample. Other chemical samples were preserved with 3N HCl to a pH of 3-3.5 to retard analyte degradation. See text.

Table 2. Results of Sacramento River Watershed Toxicity Study, Winter 1996-97. Only results for diazinon and methidathion are shown since no other pesticides in the organophosphate and carbamate pesticide screens were detected.
Sampling Date Methidathion 




Chronic Toxicity Percent Survival1 Chronic Toxicity Offspring /animal1 Site Methida-thion 




Acute Toxicity A Percent Survival1 Acute Toxicity B Percent Survival1
12/2/96 nd2 nd - Karnak nd nd 95/100 100/100
12/4/96 nd nd - Karnak nd nd 100/100 100/100
12/6/96 nd nd 90/90 17.1/16.8
1/20/97 nd nd - Sac. Ave. nd nd 100/100 85/100
1/22/97 nd nd - Sac. Ave. nd nd 100/100 100/100
1/24/97 nd 0.061 90/100 22.5/20.6
1/27/97 0.056 0.061 - Sac. Ave 0.071 0.086 100/95 95/95
1/29/97 nd 0.065 - Sac. Ave nd 0.063 90/100 90/100
1/31/97 nd 0.064 90/100 35.1/27.2
2/3/97 nd nd - Sac. Ave nd nd --/--3 --/--3
2/5/97 nd nd - Sac. Ave nd nd 100/90 100/90
2/7/97 nd nd 100/90 25.2/15.4
2/10/97 nd nd - Sac. Ave nd nd 100/100 100/100
2/12/97 nd nd - Sac. Ave nd nd 100/100 100/100
2/14/97 nd nd 100/90 25.5/25.1
2/17/97 nd nd - Karnak nd 0.056 100/100 100/100
2/19/97 nd nd - Karnak nd 0.052 100/90 100/90
2/21/97 nd nd 90/100 27.9/24.5
2/24/97 nd nd - Karnak nd 0.047 100/95 100/95
2/26/97 nd nd - Karnak nd 0.041 95/95 100/95
2/28/97 nd nd 90/100 24.9/21.8
3/3/97 nd nd - Karnak nd 0.040 100/100 90/100
3/5/97 nd nd - Karnak nd nd 100/100 95/100
3/7/97 nd nd 100/100 25.5/25.1


1 Two numbers are reported for all Toxicity tests. The first number is the result from the sample, the second is the result from the corresponding control. Chronic toxicity water was replaced twice each week using new sample water . The numbers reported for percent survival refers to the survival at the end of the test.

2 nd = none detected at the reporting limit for that chemical.

3 The February 3 acute toxicity tests were accidentally terminated after 48 hours with 100% survival in all samples and controls. New 96-hour tests could not be run on the sample within the 72-hour maximum time limit from collection to test initiation, as required by U.S. EPA.

1. One ug/L is equivalent to one part per billion (ppb).