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Pesticides

Distribution and toxicity of sediment-associated pesticides in the Sacramento River Watershed

Prepared by:
Donald P. Weston and Erin L. Amweg
Univ. of California, Berkeley

On behalf of:
Sacramento River Watershed Program
Kathy Russick, Executive Director/Watershed Coordinator

With research collaboration by:
Michael Lydy, Southern Illinois University
Scott Ogle, Pacific EcoRisk
David Crane and Abdou Mekebri, California Dept. of Fish and Game
Minghua Zhang, University of California, Davis

Prepared under PRISM Grant 04-110-555-0 for the State Water Resources Control Board
Robert Holmes, Central Valley Regional Water Quality Control Board, Project Manager

March 29, 2007

Introduction

Project purpose, scope and methods

Pyrethroid pesticides have become the dominant insecticide used in urban environments. They also have, for many years, had significant use as agricultural insecticides, and are attracting renewed attention as alternatives for organophosphate insecticides. Yet despite this widespread use, with over a million pounds of pyrethroids used in California annually, there has historically been little study of the environmental fate and effects of these compounds particularly with regard to sediment-bound residues. The PRISM grant to the Sacramento River Watershed Program was intended to fund research that would address several key data gaps related to pyrethroids and their potential environmental effects. There were three general objectives of the studies, listed below along with the approaches used in meeting these objectives:

Monitoring of pyrethroid distribution and toxicity in sediments of the Sacramento River watershed. The primary focus of this effort was on urban water bodies since some monitoring for pyrethroids in agricultural areas had been done, but there were virtually no data on pyrethroids in the sediments of urban creeks. To accomplish this objective, sampling was conducted in Sacramento-area urban creeks on four occasions in 2004 and2005. Sediments were analyzed for pyrethroid pesticides, as well as chlorpyrifos and many organochlorine pesticides. Sediment toxicity testing, using the amphipod Hyalella azteca, was concurrently done on these samples. These data on Sacramento creeks also proved helpful in assessing the effects of aerial mosquito spraying done over the city. Though monitoring of the spray effects was not specifically supported by PRISM, theP RISM data were invaluable baseline information for the assessment. In addition, PRISM funding was used to supplement another urban creek project supported by the Surface Water Ambient Monitoring Program (SWAMP) involving monitoring sediment quality of Pleasant Grove Creek and its tributaries in Roseville, California. This study examined pyrethroid concentrations in sediments, sediment toxicity, and distribution of resident H.azteca within the creeks, and interpreted results in light of pyrethroid use practices in residential neighborhoods.

Determination of thresholds for toxicity of pyrethroids to H. azteca. Interpretation of chemical monitoring data on pyrethroids has been limited by the lack of information on concentrations toxic to aquatic life. In particular, the amphipod H. azteca is a standard species for sediment toxicity testing, but aside from the pyrethroid cypermethrin, there were no published data on the toxicity of the other pyrethroids to the species. In addition, without knowing levels of toxicological concern, analytical laboratories lacked guidance on the detection limits that were necessary to achieve. Under the PRISM-funded project, three Central Valley sediments were spiked with six pyrethroids and used in toxicity tests with H. azteca. For each of the six compounds of interest, 10-day LC50 values for survival and lowest observed effects concentrations for growth were determined.

Determining the persistence of pyrethroids in soils. Mitigation of pyrethroid loss from agricultural fields will require knowledge of the fate of the compounds in the soil. In particular, a key question is whether control of irrigation runoff would be adequate mitigation, or if pyrethroids would remain in the soils through the winter months when stormwater runoff provides another mechanism for off-site transport. Two farms, one producing tomatoes and the other rice, were studied through the PRISM project to follow the persistence and toxicity of the insecticides for several months after application. A third farm, producing pears, was included in the data analysis, though sampling at the third farm was supported through EPA funding to the Sacramento River Watershed Program. At all three sites, soils were tested for toxicity and pyrethroid content immediately prior to insecticide application, and then resampled at intervals after that application for up to six months.

Accomplishments

The findings from this research have been written up in the form of papers publishable in the peer-reviewed literature, most of which have already been published. In some cases, these publications include not only data collected under this PRISM grant, but also data collected under other projects undertaken by the authors. These multiple data sets have been merged in to single papers when doing so increased the value of the resulting product (e.g., broadening geographic coverage or allowing more definitive conclusions to be made). The papers that have been supported in whole or in part by the PRISM project are provided later in this report.

Monitoring pyrethroid distribution and toxicity. Our studies have shown pyrethroids to be widespread in sediments of Sacramento-area creeks, and often present at concentrations acutely toxic to H. azteca, a standard species for sediment toxicity testing. The compound bifenthrin was often present at toxic concentrations, followed to a lesser extent by cypermethrin and cyfluthrin. It was also found that the pyrethroids played a role in determining the aquatic effect of aerial mosquito spraying over the city of Sacramento, for while pyrethroids were not used in that effort, an ingredient in the spray (piperonyl butoxide) may have been in sufficient concentration in creek waters to slightly increase the toxicity of the pyrethroids previously there.

PRISM-supported monitoring in urban creeks provided data incorporated in to three peer-reviewed publications listed below and was also described in Waterways, the newsletter of the Sacramento River Watershed Program. A small number of PRISM samples were also taken in agricultural water bodies. These results are being integrated with much more extensive agricultural data collected through the Region 5 Irrigated Lands Program, and will be later released with results from that program.

Determine thresholds of pyrethroid toxicity. Concentrations of pyrethroids in sediment that cause mortality to H. azteca vary by about a factor of 20 depending on the compound. The most widely used agricultural pyrethroid, permethrin, was the least toxic of the six studied. The most toxic compounds include pyrethroids used in both agricultural and urban settings such as bifenthrin, cypermethrin, and lambda-cyhalothrin. Compounds such as these can have 10-d LC50 values of about 5 ng/g in many Central Valley sediments; a concentration that is only slightly above analytical reporting limits (typically ranging from 0.5-5 ng/g depending on the analyte and laboratory), and less than some reporting limits that had previously been used in some laboratories. One peer-reviewed publication resulted from these PRISM-funded studies, and findings were also described in the Waterways article listed above.

Determine persistence of pyrethroids in soil. In our work at the three farms, environmental half-lives for esfenvalerate and lambda-cyhalothrin in soil were typically in the range of 1-2 months, an estimate comparable to previous reports. Therefore, for summer agricultural applications of pyrethroids, irrigation runoff is likely to be the principal route for transport to surface waters, as most of the compound will have degraded prior to winter rain. Of course, for those applications that are made in the winter, such as dormant sprays of permethrin or esfenvalerate, storm-related runoff remains a significant consideration.

One manuscript has been prepared from these findings.

Material previously submitted under grant agreement 04-110-555-0

  • Monitoring Plan
  • Quality Assurance Project Plan
  • Grant Summary Form
  • Maps of pyrethroid use in the Central Valley
  • Landowner agreements
  • Technical Memorandum for the monitoring component (served by manuscript from ES&T 40:1700-1706)
  • Technical Memorandum for the toxicity threshold component (served by manuscript from ET&C 24:966-972)
  • Technical Memorandum for the persistence component (served by draft manuscript reproduced in this final report)