U.S. Geological Survey Toxic Substance Hydrology Program --
Proceedings of the Technical Meeting, Charleston, South Carolina,
March 8-12, 1999, v.2
Contamination of hydrologic Systems and related Ecosystems
U.S. GEOLOGICAL SURVEY
Excerpts from Water Resources Investigation Report 99-4018B
Download Acrobat Reader
ABSTRACT
Degradation Rates of Six Pesticides in Water from the Sacramento River, California
By Keith Starner, Kathryn M. Kuivila, Bryan Jennings, and G. Edward MoonPDF Version (519K)
ABSTRACT
The degradation rates of six pesticides were measured in water samples collected from the Sacramento River, California, in April and August 1996. Samples were spiked with the pesticides carbaryl, malathion, atrazine, simazine, methidathion, and diazinon, and the concentrations were measured at various intervals. The laboratory experiments were done in the dark in incubators at 10ºC or 25ºC to represent a range of conditions. Carbaryl and malathion degraded rapidly, with half lives of 2-3 weeks at 10ºC and of 1-5 days at 25ºC. In contrast, atrazine and simazine were stable under all conditions. For methidathion and diazinon, the degradation rates were quite variable, with halflives ranging from 9 days to no observed degradation during the 34-37 days of the experiment. Differences between the water collected in April and August were more important than temperature in controlling the degradation rates of methidathion and diazinon. A more complete understanding of the factors that control this variability is necessary for accurate modeling of environmental fate.
Herbicide Concentrations in the Sacramento-San Joaquin Delta, California
By Kathryn M. Kuivila, Holly D. Barnett, and Jody L. EdmundsPDF Version (199K)
ABSTRACT
The Sacramento-San Joaquin Delta watershed in California encompasses agricultural areas that receive intense applications of various herbicides, including some designed to inhibit photosynthesis. This study is to determine whether herbicides impair phytoplankton primary productivity in the Sacramento-San Joaquin Delta. The sampling strategy contrasted conditions in May-June, a time of expected high herbicide concentrations, with conditions in October-November, a time of expected low herbicide concentrations. Water samples from May through November 1997 were analyzed for herbicide concentrations and phytoplankton primary production rates. Thirteen herbicides were detected in one or more water samples. Herbicide concentrations varied considerably spatially and temporally. Diuron, metolachlor, and diethatyl-ethyl had the highest concentrations in the study. Two sites, Paradise Cut at Paradise Road and French Camp Slough at McKinley Road, had the most frequent detections and highest concentrations of herbicides. The highest concentrations of molinate and thiobencarb were detected at the site receiving input from the Sacramento River watershed, following application of these herbicides on rice in May.
The highest use of EPTC is in the San Joaquin River watershed and the highest concentrations were detected at the site representing this watershed. In contrast, the source of the other herbicides could not be attributed to a single watershed. Diuron and metolachlor had widespread detections that can be explained by their relatively high use in all the watersheds, whereas diethatyl-ethyl primarily was detected at the one site near the highest application in the Delta. The distributions of 2,4-D and hexazinone were more complex, and the amounts and timing of application do not readily explain the pattern of occurrence.
The results of this part of the study illustrate the complexity of herbicide concentrations in the Sacramento-San Joaquin Delta. In particular, the occurrence of diuron and hexazinone needs to be studied in more detail to determine their influence on primary production and phytoplankton species composition.
Pesticides Associated with Suspended Sediments in the San Francisco Bay During the First Flush, December 1995
By Brian A. Bergamaschi, Kathryn M. Kuivila, and Miranda S. FramPDF Version (232K)
ABSTRACT
The majority of suspended sediments are transported into estuaries by the "first flush" - runoff from the first major storm of the water year. Pesticides associated with these sediments may represent a significant fraction of pesticides transported to estuaries, where they have different environmental effects than dissolved pesticides.
Water and suspended sediment samples were collected at the head of the San Francisco Bay during a peak in suspended sediment concentration, following the first major storm. These samples were analyzed for a variety of pesticides that span a wide range of hydrophobicity. For the 19 compounds analyzed, an average of 10 was found on the samples. Few pesticides were found dissolved in concurrent water samples and at concentrations much lower than would be expected from equilibrium partitioning between the aqueous and sedimentary phases.
DDT and its metabolites were observed in all suspended sediment samples in concentrations ranging from 5.1 to 11.1 nanograms per gram dry sediment weight. Other compounds were sporadic in occurrence, but did occur at higher concentrations. For example, oxyflurofen and endosulfan each exceeded 20 nanograms per gram in a single sample. However, there were no significant trends in the total or individual pesticide concentrations, or in the number of compounds observed as the peak in suspended sediment concentration passed the sampling site. Also, there were no significant relations between sediment-associated pesticide concentration and parameters such as KOC of the pesticide, organic carbon content of the sediment, or amount of pesticide applied in the drainage basin, suggesting that observed sediment-associated pesticide concentrations may reflect disequibrium between sedimentary and aqueous phases resulting from long equilibration times at locations where pesticides were applied, and relatively short transit times for reequilibration to occur.
Studies Relating Pesticide Concentrations to Potential Effects on Aquatic Organisms in the San Francisco Bay-Estuary, California
By Kathryn M. KuivilaPDF Version (39K)
ABSTRACT
A variety of pesticides are applied in large quantities to agricultural and urban areas in the Central Valley of California and are transported into the San Francisco Bay-Estuary dissolved in water and associated with suspended sediments. These pesticides can have deleterious effects on aquatic organisms. Three studies that relate pesticide concentrations to potential effects on aquatic organisms are currently underway by the U.S. Geological Survey's San Francisco Bay-Estuary Toxic Substances Hydrology Project. These studies are (1) measuring the impacts of herbicides on phytoplankton primary production, (2) determining the exposure of Delta smelt to dissolved pesticides, and (3) assessing the effects of pesticides on the Asian clam, Potamocorbula amurensis .
Do Herbicides Impair Phytoplankton Primary Production in the Sacramento-San Joaquin River Delta?
By Jody L. Edmunds, Kathy M. Kuivila, Brian E. Cole, and James E. CloernPDF Version (47K)
ABSTRACT
The effect of herbicide concentration on the maximum rate of phytoplankton primary production (Pmax) was examined for 53 water samples collected at 9 sites in the Sacramento-San Joaquin River Delta between May and November, 1997. Samples were analyzed for Pmax and the concentrations of diuron, atrazine, cyanazine, simazine, thiobencarb, and hexazinone. The herbicide concentrations ranged between 0 µg/L and 2.1 µg/L, with 50%of the values (n=318) between 0 and 0.018 µg/L. Herbicide concentrations in 52 of the water samples were well below the lowest observable effect concentrations (LOECs) that have been reported in laboratory experiments to inhibit primary production. Pmax ranged between 2 and 11 milligrams of carbon per milligrams of chlorophyll a per hour (mg C (mg chla-h)) -1 for the 52 samples where the herbicide concentrations were less than any reported LOEC. However, for the one sample where the diuron concentration (2.1 µg/L) exceeded the reported LOEC of 2.0 µg/L, Pmax was the lowest observed during the study, 0.9 mg C (mg chla-h) -1. Herbicide concentrations we observed throughout the system do not appear to limit production; however, localized occurrences of elevated herbicide concentrations exist and may affect primary production.
For additional information Copies of this report can be write to: purcahsed from: District Chief U.S. Geological Survey U.S. Geological Survey Information Service Placer Hall, Suite 2012 Box 25286 6000 J Street Federal Center Sacramento, CA 95819 Denver, CO 80225-0286
