RP6 Chiral Chemistry: Toxicology of Environmental Contaminants and Phase Transfer|
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall
RP040 (LAO-1117-844033) Enantioselective Degradation and Algal Phytotoxicity of Imidazolinone Herbicides.
Start time: 8:00 AM
Lao, Wenjian1, Gan, Jay1, 1 University of California, Riverside, CA
Imidazolinones are a class of low-use-rate herbicides. They have excellent activity against annual and perennial grasses and broad-leaved weeds when applied either pre- or post-emergence. Acetohydroxy acid synthase (AHAS) is an essential enzyme for many organisms, but not in animals. It catalyzes the first step in the biosynthesis of the branched-chain amino acids valine, isoleucine, and leucine. Imidazolinones act by inhibiting AHAS. The two enantiomers of Imidazolinone herbicides result from a chiral center contained in the imidazolinone ring that is a common feature of all members of its class. The imidazolinone enantiomers have been shown to have different herbicidal activities, with the R isomer eight-times more inhibitory to AHAS than the S isomer. Imidazolinone herbicides are currently used as a racemic mixture. Additionally, it was reported to persist in soil. Presently, little is known about the differences in the enantioselective degradation and acute phytotoxicity of imidazoline herbicides. In this study, a method for the chromatographic chiral separation of imidazolinone isomers was developed. Enantiomer resolution and separation were carried out on HPLC using derivatized cellulose stationary phase OD-R and OJ column. Various soil samples were spiked with racemic imazapyr, imazethapyr and imazaquin, and incubated under sterile and nonsterile conditions at room temperature. Degradation curves were fitted on a first-order decay model. Degradation in the tested soil samples was found to be enantioselective. Differences in algal growth inhibition between enantiomers were also observed in standard toxicity tests with Selenastrum capricornutum.
RP041 (KON-1117-830343) Assessing bioaccumulation and biotransformation of current-use pesticides in rainbow trout.
Start time: 8:00 AM
Konwick, B1, Garrison, W2, Kenneke, J2, Avants, J2, Ekman, D2, Fisk, A1, 1 University of Georgia, Athens, GA, USA2 U.S. Environmental Protection Agency, Athens, GA, USA
Quantifying exposure of aquatic species to current-use pesticides is important for assessing risks and establishing safe regulatory criteria for their use. Unfortunately, it is difficult to assess exposure and accumulation in aquatic species because current-use pesticides are usually broken down rapidly by abiotic and biotic reactions. Therefore, there is a need for toxicokinetic data, particularly biotransformation data, for current-use pesticides so that estimates of exposure, and any associated effects, can be made. This study examined bioaccumulation and biotransformation for a series of current use pesticides, including the insecticide fipronil and selected conazole fungicides. The conazole fungicides represent a large group of compounds widely used for the protection of crops and in the treatment of topical and systemic infections. Fipronil is a commercially used pesticide for rice culture protection and in turf grass management of golf courses. Fipronil and almost all conazoles possess at least one chiral center and thus exist as a pair of enantiomers with differing biological properties. In this research, rainbow trout (Oncorhynchus mykiss) were fed spiked food (uptake) containing either fipronil or a series of conazole fungicides followed by clean food (depuration) to measure their bioaccumulation parameters and biotransformation. Results from the fipronil exposure indicate rapid biotransformation of this compound in the fish based on the formation of a metabolite, a change in the enantiomeric fraction, and a high biotransformation rate which accounted for the majority (88%) of its elimination. Bioaccumulation parameters for the conazoles and fipronil will be compared to those generated for organochlorines from a previous study to examine structure activity relationships for bioaccumulation and biotransformation. This abstract has been reviewed and approved for presentation and publication by the U.S. EPA, but does not necessarily reflect U.S. EPA policy.
RP042 (BRO-1117-835254) Effects of bioaugmentation on the extent and enantioselectivity of PCB132 anaerobic dechlorination.
Start time: 8:00 AM
Brothersen, T1, Lee, C1, Freedman, D1, 1 Environmental Engineering and Science, Clemson University, Clemson, SC, USA
Microcosms were prepared using polychlorinated biphenyl (PCB) contaminated sediments from Lake Hartwell, SC, USA, as inoculum and a commercially available chloroethene dechlorinating culture, to determine 1) if bioaugmentation would increase the extent of PCB dechlorination; and 2) the effect on enantioselectivity. The microcosms were spiked with 234-236-hexachlorobiphenyl (PCB132), providing an initial concentration of 1385 mol/kg dry sediment (500 ppm). After 114 days of incubation, 56% of the PCB132 was dechlorinated in the treatment with sediment, while 66% of the PCB132 was removed in the bioaugmented treatment. The pattern of dechlorination in both treatments was the same, with the initial removal of a doubly flanked meta chlorine to form 236-24-pentachlorobiphenyl (PCB91), followed by removal of the singly flanked meta chlorine, leaving 24-26-tetrachlorbiphenyl (PCB51) and then removal of the para chlorine, leaving 26-2-trichlorobiphenyl (PCB19) as the end product of dechlorination. This pattern is the same as that seen by other researchers using Lake Hartwell sediments (Pakdeesusuk et al., 2003). The enantiomeric fraction (EF) of PCB132 remained constant (0.46 ± 0.046) throughout the incubation period. The daughter product of PCB132 dechlorination, PCB91, is also chiral and was dechlorinated enantioselectively with the EF decreasing from 0.34 ± 0.059 to 0.21 ± 0.039 in the native microbe treatment and from 0.32 ± 0.10 to 0.21 ± 0.026 in the bioaugmented treatment. There was no difference in the enantioselectivity between the two treatments. Studies are underway to determine whether the lack of differences in the treatments is due to inactivity of the chloroethene bioaugmentation culture against these PCBs or whether the chloroethene culture demonstrates similar kinetics and enantioselectivity to the native microorganisms.
RP043 (LAO-1117-840170) Warfarin Enantioselective Degradation in Soils and Interaction with Humic Acid.
Start time: 8:00 AM
Lao, Wenjian1, Gan, Jay1, 1 University of California, Riverside, CA, USA
Anticoagulant warfarin is widely used as rodenticide applied to control rodent populations in urban, farmland and forest, and an active ingredient in drugs used for the treatment of certain types of irregular heartbeat, and after a heart attack or heart valve replacement surgery, as well as in thromboembolic disease in humans. In the environment, warfarin is highly toxic to mammals and other non-target species. It is prepared and used as racemates, although the S (-) enantiomer is more active than R (+) enantiomer. Knowledge on the enantioselectivity of warfarin in environment is currently limited. The information of persistence of racemic warfarin in soil is essential for use and management this chemical. This study investigated the enantioselective degradation of warfarin in soils and interaction of warfarin with humic acid. Chiral separation of warfarin in HPLC was conducted in a new chiral stationary phase based on three L-prolines. The mobile phase is a mixture of hexane containing 0.1% trifloroacetic acid and isopropanol. Racemic warfarin was degraded in soil samples under sterile and nonsterile conditions at room temperature. The model of enantioselective dissipation of single enantiomer of warfarin was then obtained. The humic substances are the most important soil components affecting warfarin behavior and fate in the environment. We further investigated the enantioselective interaction of warfarin with humic acid. Adsorption and desorption isotherms of individual enantiomers with humic acid were determined at two pH levels below and above the pKa of warfarin. The Kd values were also calculated. The data on warfarin enantioselectivity of adsorption and desorption behaviours with humic acid are effective to understand the enantiomeric leaching potential.
RP044 (OVE-1117-805571) Acute Toxicity of Fipronil Enantiomers to Marine and Freshwater Non-Targets.
Start time: 8:00 AM
Overmyer, J1, Garrison, A2, Avants, J2, DeLorenzo, M3, Key, P3, Chung, K3, Konwick, B1, Wilson, W1, Black, M1, 1 University of Georgia, Athens, GA, USA2 US Environmental Protection Agency, Athens, GA, USA3 NOAA/National Ocean Service, Charleston, SC, USA
Fipronil is a phenylpyrazole insecticide used in agriculture and domestic settings for controlling various insect pests in crops, lawns and residential structures. Fipronil is chiral; however, it is released into the environment as a racemic mixture of the two enantiomers. A recent study has shown that aquatic non-target organisms can be more susceptible to one enantiomer than the other. However, current work has demonstrated that susceptibility to the separate enantiomers might be organism specific. In this study, the acute toxicity of the (+) and (-) enantiomers and the racemic mixture of fipronil will be assessed using Ceriodaphnia dubia (water flea), Simulium vittatum IS-7 (black fly), Xenopus laevis (African clawed frog), Palaemonetes pugio (grass shrimp), Mercenaria mercenaria (hardshell clam), and Dunaliella tertiolecta (phytoplankton). Results will provide a better understanding of the toxicity of the individual enantiomers in diverse organisms and might aid in identifying a form of fipronil with reduced environmental impacts.
RP045 (LEH-1117-807124) Disposition of Chiral PCBs in the Laboratory Rat.
Start time: 8:00 AM
Lehmler, H.1, Kania-Korwel, I.1, 2, Avants, J.3, Hornbuckle, K.4, Robertson, L.1, Sulkowski, W.2, Garrison, A.3, 1 Department of Occupational and Environmental Health, University of Iowa, Iowa City, Iowa, USA2 Department of Environmental Chemistry and Technology, University of Silesia, Katowice, Poland3 U.S. Environmental Protection Agency, National Exposure Research Laboratory, Athens, Georgia, USA4 Department of Civil and Environmental Engineering, University of Iowa, Iowa City, Iowa, USA
In order to investigate the tissue distribution and enantiomeric fractions (EFs) of Polychlorinated Biphenyl (PCB) atropisomers, immature male Sprague-Dawley rats were administered environmentally relevant doses of (a) Aroclor 1254 or (b) an environmental mixture extracted from soil contaminated with Chlorofen, a Polish PCB mixture. Tissue PCB extracts were separated by chiral capillary gas chromatography with electron capture detection using a Chirasil-Dex column. The comparison of the EFs of PCBs 84, 91, 95, 132, 135, 136, 149, 174 and 176 reveals drastic differences between the two treatment groups. The EFs of PCB 95 (adipose tissue, liver and skin), PCB 149 (adipose tissue, liver, skin and blood), PCB 135 (liver) and PCB 174 (kidney) in tissues from Aroclor 1254-treated animals differed significantly from EFs measured in the Aroclor standard, while only EFs of PCB 95 (blood), PCB 135 (adipose tissue and skin) and PCB 174 (adipose tissue) in tissues from soil extract-treated animals were different from the Chlorofen soil extract standard. No statistically significant enantiomeric enrichment was observed for PCB 149 in tissues from soil extract-treated animals. In this study cytochrome P-450 1A activity was 28.7 times higher in the Aroclor group whereas cytochrome P-450 2B activity was 4.7 times higher in soil extract treated animals. The differences in the induction of PCB metabolizing enzymes may be responsible for the differences in the enantiomeric enrichment between both groups. If further studies confirm this hypothesis, EFs may be useful chemical markers to assess the disposition of complex mixtures in laboratory animals and to evaluate past exposures in human populations (Supported by ES 012475 and ES 07380 from NIH; this abstract does not necessarily reflect USEPA policy).
RP046 (WIL-1117-818200) Enantioselective chronic toxicity of fipronil in Ceriodaphnia dubia.
Start time: 8:00 AM
Wilson, W1, Konwick, B1, Garrison, A2, Black, M1, 1 University of Georgia, Athens, GA, US2 US Environmental Protection Agency, Athens, GA, US
The pesticide fipronil is widely used in commercial applications that range from rice culture protection and the turf management of golf courses, to small-scale residential pest elimination. Fipronil is released into the environment in a racemic (1:1) mixture of two mirror image isomers, called enantiomers. Although enantiomers undergo the same abiotic reactions and have identical physical properties, they may exhibit differing biological activity. Fipronil exhibited enantioselective toxicity in acute (48 h) toxicity tests with the aquatic crustacean Ceriodaphnia dubia, with the (+) enantiomer being up to three times more toxic. The racemic mixture was shown to have an intermediate toxicity. The only endpoint measured in these previous trials was mortality. Our initial chronic (8 day) experiments looked at the toxicity of these compounds with respect to both mortality and reproductive fitness in Ceriodaphnia dubia. Organisms exposed to the (+) enantiomer of fipronil exhibited an LC50 of 45.2 g/L, and at the highest concentration tested (64 g/L) a reduction in the average number of neonates was observed. C. dubia exposed to the (-) enantiomer suffered negligible mortality in the same range of concentrations (0.5-64 g/L) and no significant reduction in the number of offspring. However, decreased neonate fitness was observed for both enantiomers in a dose dependent manner. Based on these initial studies, the (+) enantiomer appears to be much more toxic than the (-). We plan to continue this research with a series of definitive chronic studies testing both enantiomers and the racemate. These tests will include observations on neonate fitness for 48 h following their birth in addition to the chronic endpoints of mortality and brood size. This abstract has been reviewed and approved for presentation and publication by the U.S. EPA, but does not necessarily reflect U.S. EPA policy.
RP047 (NIL-1117-822313) Acetylcholinesterase Inhibition of Chiral Organophosphorus Insecticides.
Start time: 8:00 AM
Nillos, M1, Schlenk, D1, Gan, J1, 1 University of California - Riverside, Riverside, CA, USA
A number of organophosphorus pesticides (OPs), although mainly marketed and used in racemic form, have chiral centers. OPs are among the most commonly used pesticides because they inhibit acetylcholinesterase (AChE) in insects, by phosphorylation and phosphonylation of the enzyme. Studies on the differences in bioactivity between enantiomers of a chiral pesticide are still limited. Enantioselective biological recognition of enantiomers is often observed in and is determined by the stereochemistry of the biological system (e.g. macromolecules such as enzymes, cellular receptors or molecules involved in membrane transport). The specific stereochemistry in these systems can result in the preferential interaction with one of the enantiomers over the other. Prior acute toxicity studies with D.magna suggest that the (-) enantiomer of trichloronate, crotoxyphos, fonofos and profenofos was consistently more active than the (+) enantiomer. This study measured AChE inhibition by individual enantiomers of each chiral OP. Resolution and isolation of OP enantiomers were carried out on HPLC using a chiral column. Preliminary results from in vitro AChE inhibition tests with D. magna suggest a 32% reduction in activity of AChE exposed to 100 ppb profenofos racemate, while exposure to 300 ppb (-) enantiomer of profenofos resulted in approximately 74% reduction in activity but no significant reduction with the (+) enantiomer of the same concentration. These results indicate significant differences in toxicity between the (-) and (+) enantiomers that is consistent with acute toxicity results.
RP048 (ASH-1117-044641) Source apportionment of chiral PCBs in the Hudson River Estuary.
Start time: 8:00 AM
Asher, B1, Wong, C1, Totten, L2, 1 University of Alberta, Edmonton, Alberta, Canada2 Rutgers University, New Brunswick, New Jersey, USA
Previously collected air, water, soil, and sediment samples from urban areas of the North-eastern U.S., particularly the Hudson River Estuary (HRE), were analyzed for chiral polychlorinated biphenyls (PCBs) to determine the major sources of PCBs to the atmosphere. Previous studies have used various models to link PCB concentrations in phytoplankton to those in the atmosphere – suggesting that air-water exchange of PCBs is the major source of the pollutant to phytoplankton. However, these studies have failed to provide definitive evidence of the relative contributions of PCBs in the ecosystem. Using chiral analysis, the enantiomeric fraction (EF) of a PCB signal can be used to distinguish whether the atmospheric concentrations of the pollutant are due to fresh sources yielding a racemic signal (EF=0.5), or due to biologically weathered sources, such as volatilization from soil or sediment, yielding a non-racemic signal. Air samples in this study gave racemic signals, while our previous work has shown a non-racemic signal for various PCB congeners in sediments in the HRE. This data suggests that the atmospheric load of PCBs in these urban areas are primarily due to fresh racemic sources rather than volatilization from the river and its sediment. The EFs of PCB signals in other compartments provide additional insights into the distribution of PCBs in the HRE.