State of California

M e m o r a n d u m

To: Don Weaver Date: June 6, 1997
Senior Environmental Research Scientist
Environmental Hazards Assessment Program

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



The purpose of this memorandum is to provide results from surface water monitoring conducted by the Department of Pesticide Regulation (DPR) in the San Joaquin River (SJR) watershed. Information included here is from the monitoring period of December 2, 1996 to March 7, 1997 and includes results from chemical analyses conducted by the California Department of Food and Agriculture (CDFA) and bioassays conducted by the California Department of Fish and Game (DFG). This memorandum does not include in-depth interpretation of the data which will be provided in the final report.


The SJR flows from the Sierra Nevada Mountain Range through the San Joaquin Valley to its terminus in the Sacramento-San Joaquin Bay Estuary. The river extends approximately 134 miles from Friant Dam to Stevinson where flows are intermittent, and from Stevinson to Vernalis (about 60 miles) where flows are perennial (Figure 1). Runoff from rain events occurring in the San Joaquin Valley provides short term increases in river discharge. Seasonal rains occur from October to March with little significant rain from June to September. River discharge during the summer is composed of dam releases of snow-melt water for agricultural, urban, recreational, and wildlife purposes.

From 1988 to 1990, the Central Valley Regional Water Quality Control Board (CVRWQCB) conducted an aquatic toxicity survey in the San Joaquin Valley. Surface water samples collected from certain reaches of the SJR watershed during this survey were acutely toxic to the water flea, Ceriodaphnia dubia (Foe and Connor, 1991). The cause of toxicity was not determined but was attributed to pesticides in general. A further study was conducted in the Valley during the winter of 1991-92, and the resultant toxicity was attributed to the presence of chlorpyrifos and diazinon (Foe and Sheipline, 1993; Foe, 1995; Kuivila and Foe, 1995). These two organophosphorus insecticides are commonly used as dormant sprays to control peach twig borer, San Jose scale, European red mite, and brown mite pests on nut and stone fruit trees. The toxicity found in these studies was in violation of the CVRWQCB's narrative water quality objective (Foe, 1995) which states that, "All waters shall be maintained free of toxic substances in concentrations that produce detrimental physiological responses in human, plant, animal, or aquatic life" (CVRWQCB, 1994).

DPR staff monitored the SJR watershed during the winters of 1991-92 and 1992-93 and reported the detection of chlorpyrifos, diazinon, and methidathion in 10, 72, and 18 percent of the 108 water samples collected, respectively (Ross et al., 1996). In addition, a study conducted in 1993 by Kuivila and Foe (1995) found diazinon detections in the SJR near Vernalis ranged from 0.148 to 1.07 ug/L(1), on 12 consecutive days. They concluded that chronic toxicity due to diazinon might be problematic at this site. Dormant spray insecticides, at levels acutely toxic to test organisms, also have been reported in Orestimba Creek, a tributary to the SJR, during the 1992-93 dormant spray period (Domagalski, 1995).

This study was conducted to monitor the concentrations of dormant spray insecticides and the occurrence of aquatic toxicity, both acute and chronic, in portions of the SJR watershed. Additional organophosphate and carbamate insecticides were monitored as these chemicals are historically used in the region during the dormant spray season (Table 1). Acute toxicity to C. dubia was examined in a relatively small watershed which does not contain major inputs from municipal or industrial sources. Chronic toxicity was examined in the SJR at a point where major agricultural sources contributed to the total flow of the river. A memorandum reporting the results of a similar study, conducted concurrently in the Sacramento River watershed, is also available (Nordmark, 1997). Long-term monitoring of aquatic toxicity in these watersheds will help DPR scientists evaluate the effectiveness of programs designed to decrease the runoff of dormant spray insecticides.


Site Description

One site each was selected for acute and chronic toxicity monitoring. Acute toxicity monitoring was conducted at Orestimba Creek, a western tributary to the SJR, where runoff was predominantly agricultural (Figure 1). Monitoring for chronic toxicity was conducted on the SJR near Vernalis, where discharges from all of the River's major agricultural tributaries, including the Merced, Tuolumne, and Stanislaus Rivers, are received. Discharge records for both monitoring sites were available from collocated gaging stations.

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 in the region in early January, sampling did not resume until January 20, 1997. Sampling continued until March 7, 1997, 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, established analytical methods, and to standardize analyses between the San Joaquin and Sacramento 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 commence chronic toxicity tests. Water collected on Wednesday and Friday was used to renew chronic test water (see "Chemical Analysis and Toxicity Tests" section below).

From December 2, 1996 to February 12, 1997, a depth-integrated sampler (D-77), with a 3-liter Teflon® bottle and nozzle, was used to collect water samples from Orestimba Creek at River Road and the SJR near Vernalis. A center channel water sample was collected at the Orestimba Creek site. Three locations, spaced evenly across the SJR, were used to collect samples from the SJR near Vernalis site. This sampling technique has historically been used at this site by U.S. Geological Survey (USGS) personnel. Due to the unusually high flows at the SJR near Vernalis site, key components of the D-77 sampling equipment were lost on February 14. Subsequent samples were collected with a 10-liter stainless steel bucket from center channel for the remainder of the monitoring period. For both methods, sub-samples were composited in a larger 38-liter stainless steel container until 11 to 12 liters were collected. This composited sample was then stored on wet ice until it was delivered to the DPR processing facility in West Sacramento later that day.

Immediately upon arrival at West Sacramento, the samples were split into ten 1-liter glass bottles using a Geotech® 10-port water splitter and sealed with Teflon®-lined lids. For the Orestimba site, 1 liter each was analyzed for organophosphate, diazinon, and carbamate pesticides, 2 liters each were tested for acute toxicity and its corresponding quality control (see QC section below), and 3 liters were stored as backups (10 liters, total). For the SJR near Vernalis site, 1 liter each was analyzed for organophosphate, diazinon, and carbamate pesticides, 2 liters were tested for chronic toxicity, and 4 liters were stored as backups (9 liters, total). Additionally, split samples that would have normally been stored as backups, were provided to the CVRWQCB, for acute aquatic toxicity testing on February 3, and 26, 1997, and chronic testing on February 24, 26, and 28, 1997 to augment their continued research in the region. The results of those analyses will be provided in the final report.

Samples to be analyzed for organophosphate and carbamate pesticides were first acidified with 3N hydrochloric acid to a pH between 3.0 and 3.5 to preserve them during storage and transport. Diazinon readily degrades under acidic conditions (Ross et al., 1996), therefore, it was analyzed for in a separate unacidified sample. All samples were delivered to the appropriate laboratory within 24 hours of collection and kept at 4oC until tested or analyzed.

Environmental Measurements

Dissolved oxygen (DO), electrical conductivity (EC), pH, and water temperature were measured in situ for each collection event. Additionally, alkalinity, hardness, and ammonia were measured by the DFG's Aquatic Toxicology Laboratory (ATL) upon delivery of the toxicity samples.

In addition to the above parameters, daily rainfall measurements were obtained from the Burns Creek Dam weather station located approximately 40 miles east of the Orestimba Creek site. Discharge data from two USGS gaging stations were collected. Orestimba Creek discharge was obtained from Orestimba Creek at River Road (station indentification # 11274538), and discharge for the SJR site was obtained from "San Joaquin River near Vernalis" (station identification # 11303500). This information will be used to follow annual changes in pesticide concentrations with respect to fluctuations in flow and will also be useful for modeling efforts, should they be undertaken.

Chemical Analysis and Toxicity Tests

Chemical Analysis

Pesticide analyses were performed by the CDFA Center for Analytical Chemistry and consisted of organophosphate and carbamate screens and diazinon analysis (Table 1). Comprehensive chemical analytical methods will be provided in the final report.

Quality control was conducted in accordance with Standard Operating

Procedure QAQC001.00 (DPR, 1996). In addition to a continuing quality control program, approximately 10 percent of the total number of primary analyses were submitted with field samples as blind spikes and equipment rinse blanks. There were no detections in any of the rinse blanks. Detailed quality control data including method development, establishment of control limits, and spike recoveries will be provided in the final report.

Toxicity Tests

Two sample splits (1 primary/1 quality control) per collection event from Orestimba Creek were delivered to DFG's ATL for acute toxicity testing. Acute tests were performed in undiluted sample water using 96-hour, static-renewal bioassays with the cladoceran Ceriodaphnia dubia in accordance with current U.S. Environmental Protection Agency procedures (U.S. EPA, 1993). One sample per week from the SJR was delivered to DFG's ATL for chronic toxicity testing. Chronic tests were performed using a 7-day bioassay with C. dubia in accordance with current U.S. Environmental Protection Agency (1994) procedures. Test organisms used in chronic testing were placed in sample water on day one of the testing, with test water replenished on days three and five. All bioassays were commenced and renewal water used within 36 hours of sample collection. Data were reported as the percent survival for both acute and chronic tests and the average number of offspring per surviving female adult (fecundity) for the chronic tests.

Quality control for acute toxicity tests consisted of submission of a split sample to DFG's ATL for each sample collected from Orestimba Creek. Samples were labeled only with a sample number and were submitted along with samples from the companion Sacramento River study. The resultant data will help DPR scientists better understand and characterize intralaboratory 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 winter followed by a dry second half. Any interpretation of the results by the reader should take into account the fact that conditions during this monitoring period were not necessarily characteristic of a typical winter season.

Environmental Measurements

Orestimba Creek

Dissolved oxygen measurements at the Orestimba Creek site ranged from 9.0 to 11.3 ug/L and water temperature there ranged between 8.6 and 12.8 oC (Figure 2). EC measurements ranged from 348 to 784 uS/cm and pH ranged between 7.7 and 8.6. Alkalinity ranged from 84 to 178 ug/L and hardness ranged from 121 to 296 ug/L. Ammonia concentrations ranged from below a detection limit of 50 ug/L to 237 ug/L. 

During the weekly monitoring period from January 20, 1997 to March 7, 1997, rainfall reported at Burns Dam totaled 1.06 inches (Figure 3). Discharge in Orestimba Creek ranged from no flow to 2,240 cfs. Flooding of the San Joaquin River resulted in periods of backwater moving upstream into Orestimba Creek, interrupting discharge measurements (Figure 3). Records outside those dates were considered reliable. Rainfall and discharge data were collected from the California Department of Water Resources and USGS, respectively. These data are provisional and subject to change.

San Joaquin River near Vernalis

Dissolved oxygen measurements at the SJR site ranged from 8.9 to 11.1 ug/L and water temperature ranged between 8.8 and 12.1 oC (Figure 4). EC measurements ranged from 142 to 556 uS/cm and pH ranged between 6.7 and 8.2. Alkalinity ranged from 25 to 86 ug/L and hardness ranged from 37 to 133 ug/L. Ammonia concentrations ranged from below the detection limit of 50 ug/L to 189 ug/L.

During the weekly monitoring period from January 20, 1997 to March 7, 1997, discharge at the SJR site ranged from 23,000 to 37,500 cfs (Figure 3).

Chemical Concentrations and Toxicity Data

Chemical Concentrations

No detectable pesticide residues were found in background samples. Water samples from Orestimba Creek were found to have residues of diazinon, carbofuran, and dimethoate in 20, 13, and 7 percent of the samples collected, respectively (Table 2). The maximum diazinon, carbofuran, and dimethoate concentrations detected were 0.092, 0.238, and 0.082 ug/L, respectively.

Water samples from the SJR near Vernalis were found to have diazinon residues in 12 percent of the samples collected. The maximum concentration was 0.070 ug/L. No other pesticides were detected at either site throughout the monitoring period.

Toxicity Tests

Ceriodaphnia dubia survival ranged from 45 to 100 percent for acute toxicity samples from Orestimba Creek (Table 2). Diazinon was present at 0.04 ug/L in the samples collected on February 17, with 80 and 60 percent survival of C. dubia in the two split samples. However, the samples collected on January 27, and January 29 showed the lowest survival rates, 65 and 45 percent, respectively, and had no detectable pesticide residues. Relationships between the occurrences of pesticides and aquatic toxicity will be investigated in the final report.

Ceriodaphnia dubia displayed either 90 or 100 percent survival in chronic toxicity tests with water samples collected at the SJR near Vernalis (Table 2). Fecundity ranged from an average of 22.5 to 42.5 offspring per adult and 15.4 to 27.2 offspring per adult in field samples and control, respectively. 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.

Kevin P. Bennett
Environmental Research Scientist
Environmental Hazards Assessment Program
(916) 324-4200



CVRWQCB, 1994. (Central Valley Regional Water Quality Control Board) Water quality control plan (Basin Plan): Central Valley Region, Sacramento River and San Joaquin River Basins. December 9, 1994.

Domagalski, J.L. 1995. Nonpoint sources of pesticides in the San Joaquin River, California: Input from winter storms, 1992-93. U.S. Geological Survey Open-File Report 95-165. National Water-Quality Assessment Program. 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.

Foe, C. 1995. Insecticide concentrations and invertebrate bioassay mortality in agricultural return water from the San Joaquin Basin. Central Valley Regional Water Quality Control Board. December 1995.

Foe, C. and V. Connor. 1991. San Joaquin Watershed bioassay results, 1988-90. Central Valley Regional Water Quality Control Board. July 1991.

Foe, C. and R. Sheipline. 1993. Pesticides in surface water from applications on orchards and alfalfa during the winter and spring of 1991-92. Central Valley Regional Water Quality Control Board. February 1993.

Kuivila, K. and C. Foe. 1995. Concentrations, transport and biological effects of dormant spray pesticides in the San Francisco estuary, California. Environ. Toxicol. Chem. 14(7):1141-1150.

Nordmark, C. 1997. Preliminary results of acute and chronic toxicity monitoring in the Sacramento River watershed, Winter 1996-97. Memorandum to

Don Weaver, Environmental Hazards Assessment Program, California Environmental Protection Agency -- Department of Pesticide Regulation.

May 1997.

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, Report EH 96-02, California EPA--Department of Pesticide Regulation. November.

U.S. Environmental Protection Agency. 1993. Methods for measuring the acute toxicity of effluents and receiving waters to freshwater and marine organisms.

Fourth edition. 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.

Third edition. 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 San Joaquin 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 analyzed from a separate, unpreserved, split sample. Other chemical samples preserved with 3N HCl to a pH of 3-3.5 to retard analyte degradation. See text.

Table 2. Results of the San Joaquin River Watershed toxicity study, winter 1996-97. Only results for diazinon, carbofuran, and dimethoate are shown since no other pesticides in the organophosphate or carbamate screens were detected.
Sampling Date Diazinon 






Acute Toxicity A 

(percent survival1)

Acute Toxicity B 

(percent survival1)



Chronic Toxicity 

(percent survival1)

Chronic Toxicity 

(offspringper female1)

12/2/96 nd2 nd nd 100/100 100/100 nd
12/4/96 nd nd nd 100/100 100/100 nd
12/6/96 nd 100/90  22.5/16.8
1/20/97 nd nd nd 90/100 100/100 nd
1/22/97 nd nd nd 95/100 100/100 nd
1/24/97 0.070 90/100 24.1/20.6
1/27/97 nd nd nd 65/95 65/95 0.051
1/29/97 nd nd nd 45/100 45/100 0.050
1/31/97 nd 100/100 42.5/27.2
2/3/97 nd nd  nd ---/---3 ---/--- nd
2/5/97 nd nd nd 100/90 100/90 nd
2/7/97 nd 100/90 24.1/15.4
2/10/97 nd nd nd 100/100 100/100 nd
2/12/97 0.092 nd 0.082 85/100 100/100 nd
2/14/97 nd 90/90 26.1/16.4
2/17/97 0.040 nd nd 80/100 60/100 nd
2/19/97 0.076 nd nd 100/90 100/90 nd
2/21/97 nd 100/100 31.9/24.5
2/24/97 ns4 ns ns ns ns nd
2/26/97 nd nd nd 95/95 95/95 nd
2/28/97 nd 100/100 26.1/21.8
3/3/97 nd 0.238 nd 95/100 95/100 nd
3/5/97 nd 0.095 nd 95/100 95/100 nd
3/7/97 nd 100/100 30.0/25.1

1) Two numbers are reported for all toxicity tests. The first number is the result from the sample and the second is the result from the corresponding control.

2) nd = none detected.

3) The February 3 acute toxicity tests were inadvertently terminated after 48 hours with 100 percent 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 specified by U.S. EPA.

4) ns = not sampled. No observable flow at the time of sample collection.

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