Fate and Effects of Sediment-Associated Pyrethroid Insecticides in Central Valley, CaliforniaEPA Grant Number: F6D90525
Title: Fate and Effects of Sediment-Associated Pyrethroid Insecticides in Central Valley, California
Investigators: Trimble, Andrew John
Institution: Southern Illinois University - Carbondale
EPA Project Officer: Zambrana, Jose
Project Period: September 1, 2006 through September 1, 2008
Project Amount: $104,184
RFA: GRO Fellowships for Graduate Environmental Study (2006) RFA Text | Recipients Lists
Research Category: Health Effects , Academic Fellowships , Fellowship - Environmental Toxicology , Hazardous Waste/Remediation
Specific objectives of this research are to: 1) use a rapid toxicity-based censoring approach to estimate the hazard posed by individual and pesticide mixtures in sediments using a database of monitored values from California’s Central Valley; 2) measure sediment toxicity of pyrethroids and legacy effects of organochlorines identified as important from objective 1 as single compounds and in mixtures using Hyalella azteca as the test organism; 3) examine environmental exposure and partitioning of a selected pyrethroid insecticide (i.e., identified from objective 1) in various matrices common in the aqueous environment including sediment, fine particulate organic matter (FPOM), and coarse particulate organic matter (CPOM); and 4) develop a rapid approach for estimating uptake and bioaccumulation potential of a selected pyrethroid insecticide in sediment using chemical-based media (TENAX beads and Solid-Phase Micro Extraction) as an alternative to biological testing.
The first goal of this research is to use a toxicity-based censoring approach to estimate the environmental hazard posed by individual and mixtures of pesticides in order to determine which of the compounds are relevant for further study. The database selected for use has been compiled by researchers at U.C. Berkeley and from our laboratory at Southern Illinois University. Sediment samples were obtained from a number of contaminated agricultural sites and three separate rural sites in California’s Central Valley. The second goal of this research is to examine the toxic effects of mixtures of legacy organochlorine and pyrethroid insecticides. Juvenile (~28-d old) amphipods (H. azteca) will be used for all toxicity tests. Organisms will be pre-exposed to sub-lethal sediment concentrations of an organochlorine (DDE) for two weeks, after which toxicity tests with select pyrethroids will be conducted on organisms cultured with and without DDE in order to determine any effects from DDE to the toxicity of the pyrethroids. The third goal of this research will examine how pyrethroid insecticides partition between different organic matter fractions within sediment. The studies will examine three size-based fractions: Coarse Particulate Organic Matter (CPOM, 1 cm leaf disks), large fine particulate organic matter (LFPOM, 225 μm – 1.0 mm), and small fine particulate organic matter (SFPOM, 5 – 225 μm). Test tubes containing the separate fractions will be spiked with a known concentration of pyrethroid solution and placed on a rotator. At the completion of pre-determined time points and analyses, the results will be modeled by plotting % initial pyrethroid concentration versus time in hours. This will allow for quantitative modeling of the pyrethroid over time as it partitions into each fraction. The final goal of this research will examine uptake and bioaccumulation of select pyrethroid insecticides. Uptake studies will be conducted using disposable Solid-Phase Micro Extraction (SPME) fibers coated with polydimethylsiloxane (PDMS). Fibers will be placed in vials, spiked with pyrethroid solution, and allowed to equilibrate for pre-determined amounts of time. They will then be extracted and analyzed to determine uptake potential of the compound. The bioaccumulation portion of the study will utilize TENAX porous polymer beads composed of 2,6-diphenyl-p-phenylene oxide. Past experiments in our laboratory have successfully utilized this polymer as an infinite sink for organic molecules to determine the rapidly desorbing fraction in sediment. Using methods similar to those described for the SPME fibers, bioaccumulation values for the pyrethroids can be determined by examining amounts of chemical that desorb from the sediment into the beads.
The censoring study should provide a means to identify not only the types and components of mixtures, but also which compounds are the most relevant in terms of presence in the environment and mixture toxicity dominance. This initial portion of the study will define the key compounds of interest to be used for the remainder of the research. The pyrethroids and DDE mixtures are expected to show significant toxicity in H. azteca relative to controls. It should be noted, however, that the DDE concentrations chosen for the mixture experiments are sub-lethal, since it is DDE’s potential effects to pyrethroid toxicity that is of concern and not the toxicity of DDE itself. There are subtle differences in the modes of action of these compounds, so the expected result is a deviation from what is predicted by the additive model, whether synergistic or antagonistic. The partitioning, bioaccumulation, and bioavailability portions of the study are expected to provide accurate determinations of the selected pyrethroid’s affinity for various environmental matrices. Pyrethroids in general are substantially hydrophobic compounds, and fate and transport of these chemicals are expected to show significant correlations with organic carbon, sediment particle size, and pore water concentrations.