Grantee Research Project Results
Final Report: Ecological Assessment of the Phototoxic Polycyclic Aromatic Hydrocarbon Fluoranthene in Freshwater Systems
EPA Grant Number: R823873Title: Ecological Assessment of the Phototoxic Polycyclic Aromatic Hydrocarbon Fluoranthene in Freshwater Systems
Investigators: Oris, James T. , Guttman, Sheldon I. , Burton, Jr., G. Allen
Institution: Miami University - Oxford , Wright State University - Main Campus
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1995 through October 1, 1998
Project Amount: $505,274
RFA: Exploratory Research - Environmental Biology (1995) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Human Health , Aquatic Ecosystems
Objective:
The overall objective of the project was to determine the environmental hazard of phototoxic polycyclic aromatic hydrocarbons (PAH) to freshwater fish and invertebrates. Previous investigations and research had defined several important aspects of the photo-induced toxicity of PAH. However, there were many environmental factors that still required examination as predictions of photo-induced toxicity had not been rigorously validated in the field. In addition, the importance of differential genetic sensitivity within a population of PAH exposed organisms had not been thoroughly evaluated. If the photo-induced toxicity of PAH to freshwater organisms was determined to be a potential hazard under natural conditions, then the assessment of PAH must include considerations of factors regulating this phenomenon. Because hazard was determined by levels of toxicity, exposure, and genetic variability, the factors involved in the expression of toxicity and the various routes of exposure and bioaccumulation were examined. Effects due to dissolved organic carbon, particulate inorganic matter and primary reproduction were examined in lab, microcosm and in situ field experiments.
Some of the weaknesses of only using the surrogate toxicity assay in stream assessments are avoided by conducting in situ community surveys such as used by the Ohio Environmental Protection Agency or recommended by the U.S. EPA (Rapid Bioassessment Protocols I-III). Various fish and macroinvertebrate community metrics exist which have effectively quantified stream degradation. It is sometimes difficult, however, to separate natural stress causation factors (such as habitat) from anthropogenic stress. In addition, when community degradation is detected, it is "after the fact"; therefore, the stream ecosystem is not protected from initial degradation by biomonitoring.
Given the different attributes of the surrogate toxicity assay and the in situ community survey approaches, it is apparent that combining them into an integrative assessment, which includes key physical and chemical concentration data should provide a more valid product. This approach was effectively used in marine sediment quality assessments, and was recommended by the U.S. EPA as an effective tool for evaluating sediment quality. A weakness, however, in the previously used integrative approaches was that toxicity was only measured directly in the laboratory and not in situ.
A limited number of in situ exposures have been conducted to assess water column toxicity (Burton, et al., 1996). These assays utilized adult fish, phytoplankton, adult amphipods, and protozoans. Some in situ evaluations were based on ecosystems dosing of experimental ponds or streams, followed by monitoring of community structure. This approach has many advantages, however, these systems were difficult to replicate and required extensive resources. The portion of this U.S. EPA project conducted by Wright State University addressed photo-induced toxicity in the laboratory, mesocosms, and in situ and provided important information on controlling factors, effects, and field assessment techniques.
Summary/Accomplishments (Outputs/Outcomes):
Environmental Factors. Environmental factors, such as organic carbon content, clay content, humic acid concentration, light condition, primary production activity and etc. have strong effects on photo-induced toxicity of PAHs in aquatic environments. In order to understand the levels of effects of these environmental factors on photo-induced toxicity of PAHs, microcosm testing was conducted in the laboratory. Environmental factors, organic carbon content in sediment, clay content (turbidity), humic acid concentration and primary production activity were examined individually and combined for effect on PAH toxicity. The results showed that when organic carbon content of sediment, turbidity of water and humic acid concentration in water increased, toxicity decreased accordingly. For example, the mortality of 4-d old fathead minnow at 200 mg/kg of sediment was 100 percent, 70 percent and 30 percent for 0 percent, 3.5 percent and 7.0 percent of organic carbon of sediments, respectively. While, when humic acid was added at 2.5 mg/L, the mortality was decreased dramatically to 30 percent, 20 percent and 10 percent, respectively. Fish (Pimephales promelas) are particularly sensitive to the effect of these factors. For the benthic organisms (Hyalella azteca), the effects of these factors are less obvious. Therefore, it was assumed that these factors could either prevent releasing PAHs from the sediment to water or reduce concentration of PAHs in water. Clay content significantly reduced fluoranthene concentration in water. This could reduce the exposure and consequently reduce toxicity. However, if organisms live in and feed on contaminated sediment, these factors will not prevent them from exposure of contaminants. For example, PAH toxicity towards Hyalella azteca was not reduced very significantly, 100 percent to 90 percent mortality, when the organic carbon content was increased from 0 percent to 7 percent. It also was found that the effects of these factors on reducing toxicity of PAHs were additive. Focusing a reciprocity model that incorporates the product of UV intensity and PAH body residue, good predictions of time to death can be estimated for in situ toxicity. The relationship estimated for this model was based on the following factors:
UVA = intensity of radiation in range 320-400nm (µW/cm^2)
Body Residue = concentration of PAH in organism tissue (µM/g)
Relative Photodynamic Action (RPA) = Quantum yield of phototoxicity reactions
relative to anthracene
These factors were multiplied (unweighted) to form an index of phototoxic dose received by the organism. For multiple PAHs, the concentration of each PAH multiplied by its RPA was summed for a total phototoxic dose measurement. The figure below includes data from minnows, amphipods, zooplankton, and oligochaete exposures in the presence of humic materials, montmorillonite, kaolinite, algae, and MTBE. The top, right-most data point in the graph is from an in situ toxicity test conducted at Lake Tahoe, CA. This model provides reasonable predictions of time to death for a broad range of organisms under numerous environmental conditions and mixed PAH exposures.
Pure chemical and mixture studies were conducted with the amphipod, Hyalella azteca, and the fathead minnow, Pimephales promelas. Anthracene and fluoranthene were tested at multiple concentrations both singly and in combination. Results showed additive interaction effects in acute exposures in the presence of UV. Exposures of H. azteca and the oligochaete, Lumbriculus variegatus were conducted in situ, at a site contaminated with PAHs. The organisms showed slight effects in 4 week exposures. Amphibian effects were studied by collecting field samples of the leopard frog, Rana pipiens and exposing eggs and larvae to multiple concentrations of fluoranthene. No hatching effects were observed, however, effects on larvae were noted as low as 5 µg/L in the presence of sunlight. Effects were dependent on UV intensity, with no effects observed under simulated natural light.
Seven sediments were spiked with 300 mg/kg fluoranthene and weathered outdoors for either 0, 3, 16, 28, 32, 64 or 90 days. For the 90-day weathering treatments, each sediment was weathered both in a refrigerator at 4?C (90-d F) and outside or not in a refrigerator (90-d). The sediment treatments included a reference sediment, kaolin, sand, Acton Lake sediment at 0 percent, 3.5 percent and 7 percent TOC, Little Scioto River sediment at 8 percent TOC, and West Bearskin sediment at 11.7 percent TOC. After weathering, toxicity tests ranging from 3-168 hours were initiated with 4-d Pimephales promelas. Fish exposed to reference sediments from 3-168 hours yielded ~93 percent survival. There seems to be a possible trend between toxicity and TOC levels or particle size. Sediments with little to no TOC (e.g., Sand, Acton Lake at 0 percent and 3.5 percent TOC) yielded the lowest survival. Exposure to sand resulted in 0 percent survival for all weathering treatments by 48 days of exposure, except following 90-d F weathering (~67 percent survival).
The partitioning and effects of fluoranthene also were studied in the laboratory using radioactive fluoranthene (FLU). The concentrations of FLU in three types of media where measured using C14 activity. The media included sediments, water and tissue (e.g., the oligocheate worm, Lumbriculus variegatus and the fish, Pimephales promelas). For sediments, FLU levels remained near 1.0 µg/g for both Acton Lake 3.5 and 7 percent TOC (i.e., > 0.98 µg/g) after 168 hours. However, sand, kaolin and Acton Lake at 0 percent TOC (clay) did not retain FLU as readily as the sediment treatments with higher TOC and the concentrations decreased for all three low TOC sediments over time. The opposite was the case for FLU measures in overlying water. FLU concentration was lowest for water overlying sediments with the highest TOC (e.g., Acton Lake at 3.5 and 7 percent TOC) (< 0.05 ng/mL). For sand, kaolin and Acton Lake at 0 percent TOC, FLU concentrations peaked at about 3 hours, and decreased steadily by 144 hours. The lowest FLU concentrations were 0.191, 0.109 and 0.172 ng/mL for sand, kaolin and Acton Lake at 0 percent TOC, respectively. FLU concentrations in both fish and worm tissues were highest when exposure was to sediments with low TOC. Tissue concentrations were very low for fish (< 0.075 µg/g) and worm (< 0.29 µg/g) tissue exposed to Acton Lake at 3.5 and 7 percent TOC, following 96 hours of exposure. For fish tissue, concentrations from Acton Lake at 0 percent TOC rose steadily over an exposure duration of 48 hours, peaking at 1.235 µg/g. The highest concentrations in fish tissues exposed to sand and kaolin were 1.215 and 1.133 µg/g respectively, both peaking at 24 hours. There was no fish survival after 48 hours of exposure for sand, kaolin and Acton Lake at 0 percent TOC. Worm tissue concentrations increased steadily over time until 24 hours for kaolin (3.12 µg/g), and until 48 hours for sand (3.29 µg/g) and Acton Lake 0 percent TOC (3.45 µg/g). Worm survival was 0 percent for Kaolin after 24 hours, and for sand and Acton Lake 0 percent TOC after 48 hours.
The effect of weathering and fluoranthene toxicity was studied using different sediment types. Test treatments were: water only, water, sand, Acton lake sediment (0, 3.5, and 7 percent TOC), kaolin, montmorillonite, Little Scioto River sediment (8 percent TOC), and West Bearskin sediment (11.7 percent TOC). All treatments except the PAH contaminated Little Scioto River sediments were spiked with fluoranthene (300 mg/kg) and weathered outdoors during the summer for 0, 3, 16, 28, 32, 64, and 90 days. For the 90 day treatments, sediments were compared to split samples maintained at 4?C for 90 days. After weathering, toxicity tests were conducted for 3 to 168 hours of exposure with P. promelas (4 days old). Survival in reference sediments was good (> 90 percent). Survival increased with increased time of weathering. Survival also was higher in sediments containing higher levels of TOC. Longer exposure times increased mortality.
Hyalella azteca and Pimephales promelas were exposed to three types of sediments, at three in situ exposure treatments within mesocosms. The field mesocosm exposures were compared with laboratory microcosm exposure of PAH contaminated sediment (Little Scioto River) and the sediments (ACTON) spiked with fluoranthene. The amphipod and fathead minnow where exposed in the mesocosms in in situ chambers in three locations: near surface, near sediment, and on the sediment surface. Survival was determined after 4 and 7 days of exposure. Survival was relatively good in the reference sediments. The turbidity treatment showed a slight increase in amphipod mortality after 7 days, primarily in the spiked and Little Scioto?near sediment treatments. The fathead minnow, conversely showed greater mortality in the near surface treatments containing PAHs. However, a second experiment showed slightly different trends. The amphipods and fish were adversely affected in only the spike, near surface treatment. No significant differences were observed in the humic acid treatments, with all surviving relatively well. A population of 200 fathead minnows was placed unconfined in each of the treatments, throughout the baseline, turbidity, and humic acid treatments. So, unlike the in situ chamber exposures, these fish were exposed to all treatments which provided a combined exposure period of 37 days. Dry weight measures of these fish showed an average wet weight of 0.6 g vs. spiked and Little Scioto mesocosm weights of 0.29 and 0.30, respectively. These results suggest that exposure periods of > 7 days would have detected greater effects from PAHs and perhaps more treatment interactions with turbidity and humic acids. This is supported by the results of the weathering experiment and in-lab experiments.
in situ test exposures were conducted in the Little Scioto River, which is heavily contaminated with polycyclic aromatic hydrocarbons, including high concentrations of fluoranthene. Experiments were conducted at seven locations on the river from upstream reference sites to the mouth of the river, 9.5 miles downstream. Sediment chemistry analysis was conducted on these samples and showed a gradient of PAH contamination existed from river mile 6.5 to the mouth. Based on chemical data, five locations were selected as in situ testing sites. The upstream reference site was at Pleasant Hill Road (level of PAHs is <0.02 ng/L and not detectable), which is 2.5 miles upstream from the input of contaminants. The highest contamination site was at St. Hwy 95, 2 miles downstream from the input source. The intermediate contaminant site was at Keener Pike, 4 miles from the input. The less contaminated sites were at St. Hwy 203 an Green Camp Road, 6 and 8 miles from the source, respectively. The concentrations of total PAHs (16 priority) in the sediment at these sites are 3,631.1, 583.6, 110.1 and 33.9 mg/mg for St. Hwy 95, Keener Pike, HW203 and Green Camp Rd., respectively. During base flow these testing locations had a thick layer of fine sediment (rich in organics and clay), a shallow stream (25-40 cm), clear water (1.8-5.2 NTU), and slow flow (0.01-0.15 m/sec).
in situ exposures were conducted for 2, 4, and 7 days using 4-day old Pimephales promelas and 2-week old Hyalella azteca. The in situ chamber design in which organisms were exposed to sediment through mesh often underestimated toxicity, particularly for benthic organisms that could not be fully exposed to the contaminated sediments. A new chamber design was used to allow the organisms inside to be exposed directly to sediments and also allowed 50 percent of ultraviolet wavelengths of sunlight to penetrate the chambers. This partially improved the correlation between mortality and contaminant concentration. In order to compare the toxicity evaluation conducted in situ an in the laboratory, acute toxicity tests were conducted at WSU for 2, 4, and 7 days. Results showed that toxicity responses differed between laboratory and field exposures. For severely contaminated sites, toxicity in the laboratory was higher than that in situ. However, at less contaminated sites, toxicity in the laboratory was lower than in situ.
At these less contaminated sites, follow-up experiments were conducted to better understand the toxicity contribution from different environmental compartments. A chamber was designed which allowed organism exposures to only water or only sediment. It was found that the major contribution of toxicity was from sediments, with a minor component from overlying waters. According to chemistry analysis, the concentration of PAHs in soluble phase was not detectable (<0.02 ng/L), therefore, the toxicity contribution could be from the suspended solids in water column. Light was shown to be a major inducer of acute toxicity in Little Scioto River. Non-photo-induced toxicity in Little Scioto River only comprises a small portion of the total toxicity.
Toxicity responses differed between laboratory and field exposures. For traditional laboratory testing, the sediment toxicity was correlated with the concentration of contaminants, however, the toxicity assessed in situ exposure were not concentration dependent. Several different in situ exposures also were tested. The toxicity of the contaminants in the real environment was strongly influenced by all the aspects of environmental factors and stressors.
Conclusions from Environmental Factors Studies. The combination of laboratory, field mesocosm, and field confined chamber exposures provided unique information documenting the effects of PAHs on freshwater organisms. Differences observed between the three types of experiments appear to be related to exposure differences, such as: (1) length of exposure; (2) turbidity, humic acid, and organic carbon levels; (3) location of the organism (near surface vs. sediment); and (4) weathering/PAH fate issues. Therefore, caution should be used in reaching broad- based conclusions on PAH threshold levels since the toxicity and fate of compounds are linked closely to so many physicochemical factors and spatial-temporal exposure issues. It is apparent that organic carbon, turbidity, weathering, and sediment contact have dominant roles in determining whether PAHs will adversely affect aquatic biota. Focusing a reciprocity model that incorporates the product of UV intensity and PAH body residue, relatively good predictions of in situ toxicity can be made. However, the complex dynamics and unknowns associated with these factors at most sites will make extremely accurate predictions (modeling) of effects difficult a priori, but these predictions will help risk assessors determine the relative likelihood that adverse conditions exist.
Genetics. The ability of a species to survive and adapt to changing environmental conditions may be increased by it possessing a greater pool of genetic variability that can respond to varying selection forces. Under natural conditions (e.g., absence of anthropogenic influence), the allelic frequencies of a population should fluctuate with time according to stochastic and environmental selection pressures while maintaining a certain level of genetic variability. However, severe perturbations, such as pollution, may reduce genetic variability of populations and thereby increase their susceptibility to the effects of further environmental changes. The plasticity of enzyme formation, maintained by genetic diversity, may increase the chance of survival for a species by allowing for adaptation to natural and human-induced environmental changes. The loss of genetic diversity may, therefore, weaken the stability of the species. The technique most commonly used to quantify genetic structure in populations employs electrophoretic analysis of selected enzymes to determine allele and genotype frequencies for specific gene loci. These data are used to describe the genetic structure of populations and to compare the genetic diversity among populations.
Our published data suggest that individuals with certain allozymes are more sensitive than others to the toxic effects of environmental contaminants. Electrophoretic assessment of genetic structure (allozyme diversity) in fishes thus appears to be sensitive to changes in water quality. It is a potentially useful tool both to monitor the health of existing aquatic populations and, by using laboratory bioassays, to predict the potential impact of byproducts on natural populations.
The purpose of the genetic study described here was to examine the effect of genotype at variable enzyme loci on the photo-induced toxicity of fluoranthene contaminated sediment to Hyalella azteca and Pimephales promelas. In addition, we wanted to determine the effect of genotype at variable enzyme loci on the photo-induced toxicity of sediment from a field site with known PAH contamination to juvenile Hyalella azteca and Pimephales promelas.
Genetically-based tolerance of contaminant exposure has been found in populations in contaminated areas, and has been developed in laboratory cultures. Such tolerance can develop only when appropriate genetic variability exists in the stressed population. Enzyme electrophoresis has been used to elucidate relationships between variation at enzyme loci and differential survivorship in laboratory exposures. To test for the presence of genotype-survivorship relationships one-month-old fathead minnows (Pimephales promelas) were exposed to fluoranthene-contaminated sediment (1.24 mg/gm organic carbon) during a 96 h exposure. Of the 909 minnows exposed to fluoranthene, 684 (75 percent) minnows died during the exposure. Horizontal starch-gel electrophoresis was used to determine genotypes at six variable enzyme loci (?-GAL*, GPI-1*, GPI-2*, IDHP-1*, MDH-2*, and PGM*). Statistical analyses were used to evaluate the relationships between the genetic data and weight, length and time-to-death (TTD) of fish using an accelerated failure time regression model (LIFEREG). The GPI-1*, MDH-2*, and PGM* loci were found to be significantly related to TTD. Multi-locus heterozygosity also was related to TTD. Lower heterozygosity was related to a longer TTD and a greater chance of survival. Fish weight was strongly related to TTD and survival. Larger fish had a longer TTD and a greater chance of survival. Mean fish weight differed significantly among genotypes at each locus. This resulted in large differences between LIFEREG regression models that factored weight out and those models that did not separate weight from the genotypes or multi-locus heterozygosity. The results of the study indicated that differential survival to fluoranthene was genetically related. The frequencies of several genotypes were significantly different in the survivors of the fluoranthene exposure compared with those in the initial population.
A second study examined genotypic responses of Hyalella azteca to the toxicity of sediment contaminated by the PAH fluoranthene (310 µg/goc). We monitored time to death of 696 Hyalella azteca, which were exposed to UV and sediment spiked with fluoranthene. The survival distribution functions (SDFs) within genotypes at each of three variable allozyme loci [acid phosphatase (ACP*), glucose-6-phosphate isomerase (GPI*) and phosphoglucomutase (PGM*)] were compared using a log-rank test. Results showed significant differences among SDFs at all three loci. No association of heterozygosity with time to death was observed. The homozygote ACP*-CC was associated with decreased survivorship when compared with ACP*-AA, ACP*-BB and ACP*-AB. However, GPI*-AA was associated with increased survivorship when compared with GPI*-BB, GPI*-CC and GPI*-BC. Significant differences in resistance also were observed for PGM*-BB vs either PGM*-AC or PGM*-BC. These results indicate that differential resistance to PAH phototoxicity was genetically related resulting in the significant alteration in frequencies of several genotypes in the population.
During July 1999 populations of both H. azteca and P. promelas were caged in the Little Scioto River for 4 days in clear plastic cages developed by WSU. One control site (replicates exposed to sunlight and under bridge) and one contaminated site (replicates exposed to sunlight and under bridge) were utilized. A total of 2000 Hyalella and 600 Pimephales were used. None died! It was subsequently determined that the plastic cages did not allow penetration of sufficient UV light. Nw cages were designed in September 1999; these were tested utilizing a smaller number of H. azteca and P. promelas in unshaded exposures for a 7d period. hile few deaths occurred in the control exposures, most of the Hyalella and Pimephales at the contaminated site died. ample size of Pimephales was too small to provide useful experimental data and,therefore, the exposure will be repeated in summer 2000. The data for Hyalella could be valuable; we will analyze genetic data on Hyalella during spring 2000.
Conclusions from Genetics Studies. Acute exposures of H. azteca and P. promelas to fluoranthene-contaminated sediment and UV light results in differential resistance to PAH phototoxicity. Differential resistance was genetically related resulting in the significant alteration in frequencies of several genotypes in the population of each species.
Since multi-locus heterozygosity was significantly associated with survivorship in P. promelas but not in H. azteca, it appears that selection acts at the level of the individual locus.
Journal Articles on this Report : 12 Displayed | Download in RIS Format
Other project views: | All 43 publications | 13 publications in selected types | All 12 journal articles |
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Burton Jr GA. Realistic assessments of ecotoxicity using traditional and novel approaches. Aquatic Ecosystem Health and Management 1999;2(1):1-8. |
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Cho E-A, Bailer AJ, Oris JT. Effect of methyl tert-butyl ether on the bioconcentration and photoinduced toxicity of fluoranthene in fathead minnow larvae (Pimephales promelas). Environmental Science & Technology 2003;37(7):1306-1310. |
R823873 (Final) |
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Choi J, Oris JT. Anthracene photoinduced toxicity to PLHC-1 cell line (Poeciliopsis lucida) and the role of lipid peroxidation in toxicity. Environmental Toxicology and Chemistry 2000;19(11):2699-2706. |
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Choi J, Oris JT. Evidence of oxidative stress in bluegill sunfish (Lepomis macrochirus) liver microsomes simultaneously exposed to solar ultraviolet radiation and anthracene. Environmental Toxicology and Chemistry 2000;19(7):1795-1799. |
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Duan Y, Guttman SI, Oris JT, Bailer AJ. Genotype and toxicity relationships among Hyalella azteca: I. Acute exposed to heavy metals or low pH. Environmental Toxicology and Chemistry 2000;19(5):1414-1421. |
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Duan Y, Guttman SI, Oris JT, Huang X, Burton GA. Genotype and toxicity relationships among Hyalella azteca: II. Acute exposure to fluoranthene-contaminated sediment. Environmental Toxicology and Chemistry 2000;19(5):1422-1426. |
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Hatch AC, Burton Jr GA. Effects of photoinduced toxicity of fluoranthene on amphibian embryos and larvae. Environmental Toxicology and Chemistry 1998;17(9):1777-1785. |
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Hatch AC, Burton GA. Photo-induced toxicity of PAHs to Hyalella azteca and Chironomus tentans: effects of mixtures and behavior. Environmental Pollution 1999;106(2):157-167. |
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Hatch AC, Burton Jr GA. Phototoxicity of fluoranthene to two freshwater crustaceans, Hyalella azteca and Daphnia magna: measures of feeding inhibition as a toxicological endpoint. Hydrobiologia 1999;400:243-248. |
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Hatch AC, Burton Jr GA. Sediment toxicity and stormwater runoff in a contaminated receiving system: consideration of different bioassays in the laboratory and field. Chemosphere 1999;39(6):1001-1017. |
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Schlueter MA, Guttman SI, Duan Y, Oris JT, Huang X, Burton GA. Effects of acute exposure to fluoranthene-contaminated sediment on the survival and genetic variability of fathead minnows (Pimephales promelas). Environmental Toxicology and Chemistry 2000;19(4):1011-1018. |
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Weinstein JE, Oris JT. Humic acids reduce the bioaccumulation and photoinduced toxicity of fluoranthene to fish. Environmental Toxicology and Chemistry 1999;18(9):2087-2094. |
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Supplemental Keywords:
ecology, ecological assessment, PAH, polycyclic aromatic hydrocarbons, fluoranthene, toxicity, fish, freshwater, Lake Tahoe, CA, California, Acton Lake, invertebrates., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Contaminated Sediments, exploratory research environmental biology, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, ecological exposure, ecological effects, flouranthene, photoreactivation, contaminated sediment, bioavailability, microcosm studies, PAH, ecological assessment, photo-induced toxicity, fish , genetic differentiation, exposure assessmentProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.