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The Little Scioto River is located just west of the city of Marion in north-central Ohio, USA (Fig. 1). The Little Scioto River feeds into the Scioto River, a major tributary of the Ohio River. Coal-tar creosote was discharged from the Baker Wood Creosoting site directly to the combined sewers that drain into North Rockswale Ditch and the Little Scioto River 1. Analytical data from sampling events conducted by the Ohio Environmental Protection Agency in 1987 and 1998 indicated that sediments were grossly contaminated with polycyclic aromatic hydrocarbons (PAHs) at concentrations among the highest observed in published literature at the time 2–4.
Based on the results of those studies, the Ohio Department of Health issued fish consumption and no physical contact advisories in 1992 for the four-mile segment of the river below North Rockswale Ditch. These advisories remain in effect to this day.
Between 2002 and 2006, 48,000 cubic yards of contaminated sediment were removed from North Rockswale Ditch and the Little Scioto River by isolation of segments of the river using sheet piling, bypass pumping of river water, and dry excavation of sediment from the isolated river segments 5. In 2007, the Ohio EPA completed an expanded site inspection for a 7.5-river mile section of the lower Little Scioto River, which evaluated biological, sediment, and surface water resources 6. As part of this investigation, fish biomarker methods (DNA damage in blood cells and PAH metabolites in bile of carp and white suckers) were used to determine whether the removal of contaminated sediments reduced exposure of fish and other biota to PAHs in both remediated and nonremediated sections within the project area.
Polycyclic aromatic hydrocarbons are an environmental concern because they are widely distributed in various environmental media, and many are mutagenic and carcinogenic. High levels of PAHs in sediment have been associated with the development of tumors and lesions in fish 7–9. The single-cell gel electrophoresis method (comet assay) 10 can be used to quantify DNA damage and provide an index of exposure to genotoxic, tumor-inducing chemicals in biological populations, including fish. This method can be used with any age class of fish and provides a measure of genetic damage at the time of animal capture. The comet assay has been applied to tissues of laboratory-exposed fish as well as indigenous and caged fish from sites contaminated with a variety of compounds, including PAHs, polychlorinated biphenyls (PCBs), and metals [see 11–13 for reviews]. Previous work by Yang et al. 14 indicated that higher DNA damage, as measured by the comet assay, was associated with higher prevalence of external lesions in brown bullhead catfish (Ameiurus nebulosus). Several studies employing the comet assay have examined the induction of DNA damage as related to the time elapsed after the treatment of fish with genotoxic chemicals in the laboratory 15, 16. These studies show that the comet assay can detect genotoxic responses within 24 h of exposure, thus providing a relatively rapid indicator of recent exposure.
Because gallbladder bile accumulates PAHs to a greater extent than other fish tissues, PAH metabolite levels in fish bile are an excellent biomarker of PAH exposure. Detection of PAH metabolites in bile indicates recent exposure on the order of days, demonstrating the utility of the method for measuring current, ongoing exposure of fish to PAHs 17. Fish bile samples can be analyzed for PAH-type compounds using high-performance liquid chromatrography separation with fluorescence detection 18 or by fixed wavelength fluorescence 19, 20.
The specific objectives of the present study were to: (1) document ongoing exposure of select fish species to sediment contaminants; (2) establish biological conditions in the Little Scioto River by evaluating fish and macroinvertebrate communities; (3) evaluate surficial sediment and surface water chemical quality at stations in the Little Scioto River and at several tributary locations; and (4) determine the aquatic life use attainment status of the Little Scioto River with regard to the modified warmwater habitat (MWH) or warmwater habitat (WWH) aquatic life use designations codified in the Ohio Water Quality Standards 21. The results from the present study were compared with similar sampling efforts conducted in 1992 by the Ohio EPA and the U.S. EPA 3 to determine whether exposure of biota and biological communities have improved. An overall objective of the expanded site inspection described in the present study was to determine whether the site should be included on the National Priority List (i.e., Superfund listing) for possible further clean-up action. The results of the site assessment supported the recommendation by then-Governor Ted Strickland of Ohio to the U.S. EPA Region 5 to include the Little Scioto River study site on the National Priority List. Such a listing subsequently occurred in September 2009 22.
MATERIALS AND METHODS
Site selection and characteristics
Sampling locations were identified by river mile (RM) and chosen based on reference condition, remediation, and areas of historical sediment contamination. The study area covered 7.5 RMs, including the remediated section between RMs 6.0 and 6.8, as well as areas upstream and downstream of that locale. The following five sampling locations were chosen for fish, macroinvertebrate, and sediment samples, based on their position relative to the primary source of historical PAH sediment contamination: upstream (RM 9.2)—background or reference site; adjacent (RM 6.5)—sediment remediation or removal site; and downstream (RMs 5.7, 4.4, and 2.7; Fig. 1). Surface water samples were collected at RM 4.4 and at five additional locations within the study area: RMs 7.9, 7.1, 2.8, 2.0, and 1.4.
Surficial sediment sampling and analysis
Surficial sediment samples were collected at five sampling sites in the Little Scioto River by the Ohio EPA on July 30 and 31, 2007. Sediments were sampled by focusing on depositional areas of fine-grain material (silts and clays) in the upper four inches of bottom material. Surficial sediment samples are typically collected for comparison with biological quality because the upper four inches are the biologically active zone of sediment. Also, these surficial, fine-grain sediment areas typically experience higher contaminant levels compared with areas of coarse sand and gravel. Sediment samples were collected at each sampling site using a stainless steel scoop. At each location, 15 to 20 scoops of fine-grained material were collected over a 200- to 300-m section of river and composited into a single sample for analytical purposes. This technique is designed to give a better overall idea of the average concentration of contaminants throughout the assessment unit (i.e., sampling location). Sediment samples were mixed in stainless steel pans, transferred into glass jars with Teflon-lined lids, placed on ice, and shipped to a U.S. EPA Contract Laboratory Program laboratory for analysis. Surficial sediment samples were analyzed for total analyte list inorganics (metals), volatile organic compounds, semivolatile organic compounds (including PAHs), organochlorinated pesticides, and PCBs 23. Sediment evaluations were conducted using guidelines established in MacDonald et al. 24.
Surface water sampling and analysis
Surface water samples were collected from the upper 30.5 cm (12 inches) of water at each sampling site and preserved using appropriate methods, as outlined in parts II and III of the Ohio EPA Manual of Surveillance Methods and Quality Assurance Practices 25. These samples were analyzed for total analyte list inorganics (metals), PCBs, volatile organic compounds, semivolatile organic compounds, and organochlorinated pesticides. Surface water samples were evaluated by comparisons with Ohio Water Quality Standards criteria, reference conditions, or published literature.
Collection of fish for community assessment and biomarker studies
All animal studies were performed under a protocol approved by the U.S. EPA Animal Facility Institutional Animal Care and Use Committee at the Andrew W. Breidenbach Environmental Research Center in Cincinnati, Ohio (USA). Fish were collected within a 400- to 500-m zone at each sampling site for assessment of fish assemblages and determination of index of biotic integrity (IBI) scores. Fish were sampled using pulsed direct current wading or boat electrofishing methods, and processed in the field (e.g., identifying each individual as to species, counting, weighing, and recording any external abnormalities per established Ohio EPA field and laboratory methods 21, 25). Common carp (Cyprinus carpio) and white suckers (Catostomus commersoni) were the two species of fish selected for evaluation of biomarkers. These species were chosen due to their natural sediment-dwelling habits, which make them ideal test subjects for sediment contamination evaluations. A minimum of 10 fish of each of these species were collected from each sampling site for biomarker analysis; all other species of fish were released back into their collection area.
The carp and white suckers were anesthetized with tricaine methane sulfonate, measured (total length), and weighed. Mixed arteriovenous blood was drawn from the caudal artery and vein of the white suckers using the lateral approach described by Schmitt et al. 26. Approximately 0.5 ml of blood was collected using a heparinized syringe with a needle. The blood was stored and shipped overnight on ice to the U.S. EPA Andrew W. Breidenbach Environmental Research Center facility. The blood was then processed within 48 h of collection through the slide-storage step of the comet assay procedure (see below). After the blood was sampled, the carp and white suckers were euthanized by cervical dislocation under anesthesia and necropsied. The sex of the fish was determined and recorded. Bile was collected from the gallbladder via a hypodermic syringe, transferred to cryogenic vials, quick-frozen in liquid nitrogen, and shipped in liquid nitrogen dry shippers to the Geochemical and Environmental Research Group at Texas A&M College of Geosciences (College Station, TX, USA) for bile metabolite analysis. Approximately 2-cm2 sections of liver were also removed from the white suckers, placed into vials of mincing solution, and transported to the U.S. EPA Andrew W. Breidenbach Environmental Research Center laboratory for analysis of liver cell DNA damage.
The Geochemical and Environmental Research Group at Texas A&M College of Geosciences analyzed the bile collected from the carp and white suckers for naphthalene- and benzo[a]pyrene (BaP)-type metabolites using high-performance liquid chromatrography–fluorescence methodology 18. Total protein analysis was performed on each bile sample as well, using the modified Lowry method, with bovine serum albumin as the calibration standard. The PAH metabolite concentrations are reported on a weight basis (µg/g) assuming a bile density of 1 g/ml and are also normalized to protein content as nanogram metabolites per microgram protein.
The comet assay was performed on blood and liver cells of white suckers using the method described by Tice et al. 27. The blood (3 µl) was first diluted with 1 ml of cold mincing solution. Duplicate 10-µl aliquots of the diluted blood were mixed with 75 µl of 0.5% (w/v) low-melting agarose at 37°C and pipetted onto a microscope slide precoated with a layer of 1.2% (w/v) normal-melting agarose. The slides were cooled on ice until the agarose layer hardened. Another layer of low-melting agarose was added, and the slides were cooled on ice again. The slides were then placed overnight in 4°C lysing solution. Following this, the slides were placed in alkaline electrophoresis buffer (pH >13) for 15 min to allow for unwinding of the DNA. Electrophoresis was run for 10 min (25 V, 265 mA) at room temperature, and then the slides were neutralized, fixed by immersing in cold methanol, air-dried, and stored at room temperature until the time of scoring.
The slides were stained with ethidium bromide and scored on a fluorescent microscope at 400× magnification using comet image-analysis software (Komet 4.0; Kinetic Imaging). The comet parameters that were analyzed for each cell included the length of DNA migration (i.e., tail length, in µm), the percentage of migrated DNA (i.e., percentage of DNA in the tail relative to total DNA in the image), and the tail-extent moment (calculated as the tail length multiplied by the percentage of DNA in tail). Fifty cells per slide and a total of 100 cells per fish were analyzed to evaluate the extent of DNA damage for each fish.
Macroinvertebrate community assessment
The macroinvertebrate communities were sampled using both qualitative (multihabitat composite) and quantitative (artificial substrate) sampling protocols. Macroinvertebrates were collected from artificial substrates and from the natural habitat at all five locations, per established Ohio EPA macroinvertebrate field and laboratory procedures 21, 25. The artificial substrate collection provided quantitative data and consisted of a composite sample of five modified Hester–Dendy multiple-plate samplers colonized for six weeks. At the time of the artificial substrate collection, a qualitative multihabitat composite sample was also collected. This sampling effort consisted of an inventory of all observed macroinvertebrate taxa in the natural habitat at each site, with no attempt to quantify populations other than notations on the predominance of specific taxa or taxa groups within the major macrohabitats present (e.g., riffle, run, pool, margin).
Statistical analyses were performed using SigmaPlot 12 software (Systat Software). To test for differences in bile metabolites for carp and white suckers among collection sites, a two-way analysis of variance was performed. A one-way analysis of variance was used to test for differences in DNA damage in white suckers among sites. Post hoc multiple comparison procedures (Holm–Sidak method) were used to discriminate differences between mean values. Correlation analysis among bile metabolite and DNA damage parameters was performed using the Pearson product moment correlation method. All data are reported as mean ± standard error of the mean. Significant differences were defined as having a p value less than 0.05.
Surficial sediment quality
In the present study, fine-grained depositional areas were uncommon at RM 9.2, but very common in the channel-modified, low-gradient segment from RM 9.0 to the river mouth. Concentrations of PCBs, organochlorinated pesticides, and volatile organic compounds were not detected in the surficial sediment samples analyzed. Table 1 shows the results of analysis for those specific chemical parameters measured above ecological screening values in surficial sediment testing (i.e., inorganics and semivolatile organic compounds); sediment data are reported on a dry weight basis.
Table 1. Chemical parameters measured above screening levels in surficial sediment samples collected from the Little Scioto River in July 2007
Parameter value above the probable effect concentration 24.
Parameter value above the threshold effect concentration 24.
Parameter value above the sediment reference values 33.
RM = river mile; PAH = polycyclic aromatic hydrocarbon.
The consensus-based sediment guidelines define two levels of ecotoxic effects—threshold effect concentration (TEC) and probable effect concentration (PEC) 24. A TEC is a level of sediment chemical quality below which harmful effects are unlikely to be observed, and a PEC indicates a level above which harmful effects are likely to be observed. At the background or reference location (RM 9.2), chemical compounds in the sediment were below the TEC values, while all four sampling locations in the channel-modified section of the Little Scioto River exhibited some degree of elevated sediment chemical levels (Table 1). The area most recently remediated (RM 6.5), where contaminated sediment has been removed, exhibited minimally elevated levels of three metal parameters; however, overall sediment conditions at RM 6.5 were considered good, according to guidelines. Sampling sites further downstream (RMs 5.7–2.7) had sediment levels exceeding the PEC for PAHs or metals, with high PAH levels recorded at RM 5.7. Overall sediment conditions in the Little Scioto River from RM 5.7 to RM 2.7 suggest contamination levels likely to cause harmful effects to river biology.
Surface water quality
Concentrations of PCBs, organochlorinated pesticides, volatile organic compounds, and semivolatile organic compounds (with the exception of bis-2 ethylhexyl phthalate) were not detected in the surface water samples collected. Bis-2 ethylhexyl phthalate was detected, but measurements were below water quality criteria. Metals concentrations were generally very low, with half of the tested parameters less than detection limits. Nearly all parameters with measurable concentrations were below applicable Ohio Water Quality Standards human health criteria and all were below Ohio Water Quality Standards aquatic life criteria; exceptions included elevated mercury in the Little Scioto River samples downstream from the Marion wastewater treatment plant and landfill (i.e., RMs 4.4, 2.8, and 1.4; Fig. 1). Mercury concentrations detected exceeded the human health nondrinking water quality criterion, although none exceeded the aquatic life water quality criterion. With the exception of the wastewater chemical parameters noted, good chemical water quality was evident in all sampling locations.
A total of 1,699 fish representing 35 species were collected from the Little Scioto River study area between July and September 2007. Sampling locations were evaluated using either MWH or WWH biocriteria 21. The most upstream fish sampling site (RM 9.2) was represented by natural channel conditions, but a moderate to heavy layer of silt covering the river bottom probably contributed to the fish community not achieving the WWH biocriterion. The IBI and Modified Index of Well Being (MIwb) scores for RM 9.2 were within the fair range of environmental quality (Table 2). Reduced habitat quality was observed between RMs 6.5 and 2.7—an area designated MWH due to past channel modification activities. From 2002 to 2006, the section of river from RM 6.8 to RM 6.0 was dredged to the hardpan layer to remove highly contaminated sediments. Because habitat diversity was lower in the dredged MWH segment, fish community quality was not expected to compare to the upstream WWH section. The MWH biological criteria are not set as high as WWH biocriteria because of the expected implications of habitat modifications. Sampling results from RMs 6.5 and 5.7 fully achieved the MWH biocriteria; however, the fish community was impaired at RMs 4.4 and 2.7, where both IBI and MIwb scores were in the poor range (below biocriteria values).
Table 2. Index of biotic integrity (IBI) and modified index of well-being (MIwb) scores for fish communities at sampling locations along the Little Scioto River in 2007
Stream river mile (RM)
Relative weight (kg)
Significant departure from ecoregion biocriterion (>4 IBI units or >0.5 MIwb units).
Historical trends in the health of the Little Scioto River fish community—as represented by average IBI and MIwb scores and deformities, fin erosions, lesions, and tumors (i.e., DELT anomalies)—are presented in Table 3. Substantial improvement in fish communities in the (historically-contaminated) channel-modified section of the Little Scioto River occurred from 1987 to 2007. Improvement occurred in both IBI and MIwb scores; IBI values increased 8.3 points and MIwb values increased 3.8 points. In terms of narrative quality, fish communities improved from very poor in 1987 to poor to fair in 2007. In addition, a substantial improvement in DELT anomaly occurrence corresponded with the improved fish communities. Overall, fish communities of the lower Little Scioto River have improved over the last 20 years of monitoring.
Table 3. Average index of biotic integrity (IBI) scores, modified index of well-being (MIwb) scores, and percentage of DELT anomalies for the natural and channel-modified segments of the Little Scioto River for 1987, 1992, and 2007
River mile 9.2 represents the natural section, and river miles 6.5 to 2.7 represent the channel-modified section of the Little Scioto River.
DELT anomalies = deformities, fin erosions, lesions, and tumors; RM = river mile.
Patterns of bile PAH metabolites were very similar for both fish species across the sites (Fig. 2). No significant differences in metabolite levels were found between the carp and white suckers. However, there were highly significant differences across sites for both napthalene-type and BaP-type metabolites (p < 0.001). Metabolite levels for fish collected from the remediated site (RM 6.5) did not differ from the upstream reference site (RM 9.2), but both of these sites were significantly lower in both types of metabolites than the three unremediated downstream sites. Metabolite levels at RM 9.2 were within statewide reference levels established using Ohio EPA biological reference sites 19, 28 and sites sampled in Ohio for the Regional Environmental Monitoring and Assessment Program 24. Although metabolite levels were elevated above reference conditions in the sediment remediation zone (RM 6.5), the fish collected from RM 6.5 may have reflected some exposure to contaminated sediments located within a half-mile of the sampling site. Median levels of naphthalene and BaP metabolites at the three sites with both historical and current sediment PAH contamination (RMs 5.7, 4.4, and 2.7) were highly elevated above reference conditions; these levels confirm heavy exposure to PAH contaminants.
Comparison of sediment BaP levels and bile BaP-type metabolite levels (Fig. 3) showed apparent spatial correlations of the bile and sediment parameters except at the most downstream sampling site (RM 2.7), where bile metabolite levels were discordantly high compared with sediment BaP concentrations. Comparison of sediment BaP levels for 1992 and 2007 at RM 6.5 confirm substantial reduction in BaP concentrations as a result of the removal of contaminated sediment; in fact, BaP could not be detected in sediment collected in 2007 (Fig. 4). Fish bile PAH metabolite levels and BaP sediment concentrations in 2007 appear similar or even higher at the sites downstream (RM 2.7, 4.4 and 5.7) of the remediated area (RM 6.5) compared with 1992 concentrations.
Significant differences in the DNA damage in white suckers were seen based on collection site (p < 0.001) (Fig. 5). Significant increases were found at RMs 5.7 and 4.4 compared with both the upstream reference site (RM 9.2) and the remediated section (RM 6.5) (p < 0.05). The fish collected at RM 6.5, 9.2, and 2.7 (the most downstream site) did not differ significantly from each other. The DNA damage levels in blood cells of white suckers correlated with BaP-type (r = 0.50, p < 0.01) and napthalene-type (r = 0.049, p < 0.01) metabolite levels in bile.
Results of macroinvertebrate sampling efforts are summarized in Table 4 by Invertebrate Community Index (ICI) scores. The macroinvertebrate community at RM 9.2 was evaluated as exceptional (ICI = 46) and met the designated WWH biocriterion (ICI = 36). Good in-stream physical habitat (i.e., pool, riffle, and run habitats) with gravel and cobble substrates contributed to the good condition of the macroinvertebrate community at this location. Downstream from RM 9.2, the designated use for the Little Scioto River is MWH due to past channel modification; however, none of the macroinvertebrate communities sampled in this portion of the Little Scioto River met the MWH designated use (ICI = 22). The macroinvertebrate communities from RMs 6.5 and 2.7 were designated in poor condition (ICI = 10 for both). Poor in-stream habitat (i.e., only pool habitat), an absence of measurable current velocities, and bottom substrates limited to clay and silt all probably contributed to the poor condition of the macroinvertebrate community. The macroinvertebrate communities from RMs 5.7 and 4.4 were evaluated as fair, with scores in the low end of the fair ICI range of 14 to 30. These sites were marginally better than the poor sites (RMs 6.5 and 2.7), primarily due to the presence of glide habitats with measurable current velocities and more in-stream cover. The 2007 macroinvertebrate sampling did indicate some apparent improvement from 1992 and 1987 survey results (Table 5).
Table 4. Summary of macroinvertebrate data collected from artificial substrates (quantitative sampling) and natural substrates (qualitative sampling) along the Little Scioto River in 2007
Stream river mile (RM)
Significant departure from ecoregion biocriterion (>4 ICI units).
Total EPT = ephemeroptera [mayflies], plecoptera [stoneflies], and trichoptera [caddisflies] taxa richness, a measure of pollution-sensitive organisms; ICI = invertebrate community index.
River mile (RM) 9.2 represents the natural section, and RMs 6.5 to 2.7 represent the channel-modified sections of the Little Scioto River.
DISCUSSION AND CONCLUSIONS
Based on the 2007 analysis of biological communities in the Little Scioto River, 4.6 miles of the 7.5-river mile study area were in partial attainment of designated aquatic life uses, and 2.9 miles were not in attainment. The partial attainment at the upstream, background location was associated with extensive siltation of the river bottom. Partial attainment at the remediated section (RM 6.5) of the Little Scioto River was associated with poor river habitat, low flow, and wastewater discharges from the Holland Road combined sewer overflow pipe at RM 6.6. The urbanized condition of the Little Scioto River study area (e.g., municipal wastewater discharge and combined sewer overflows) and elevated sediment contaminants contributed to the impaired biological communities present from RM 5.7 downstream to RM 2.7. Surficial sediment concentrations of total PAHs, naphthalene, and BaP revealed low levels at the reference and remediated sites (RM 9.2 and 6.5, respectively), but highly elevated levels at the historically contaminated sites at RMs 5.6, 4.4, and 2.7. Sediment PAH concentrations from samples collected in 1998 29 at RM 6.5 were comparable or even higher than those seen in 1992, supporting the fact that the 2007 reductions were due to remediation rather than degradation of contaminants or natural recovery of this river segment prior to remediation. Comparisons of 2007 data with 1992 results at the lower river segments (RM 5.6–2.7) show similar or possibly elevated PAH contaminant levels, further indicating that natural recovery is not occurring in this system.
PAH metabolites measured in bile of white sucker and common carp confirmed heavy exposure of fish to PAH contaminants at sites with elevated sediment PAHs. The patterns of DNA damage in fish blood cells visually correlated with the bile metabolite results as related to collection site, providing confirmatory evidence of exposure and response to genotoxic contaminants. It should be noted that the comet assay is recognized as a sensitive, rapid, economical, but nonspecific biomarker for the detection of genetic damage in natural biota 11–13, 30. Thus the assay should not be considered diagnostic of exposure to a particular class of contaminants, such as PAHs. This was evident in a recent study on the effects of urbanization on bluegill sunfish using the comet assay, which found that PAHs may have contributed to the DNA strand breaks in the fish, but they were probably not the only genotoxic compounds present 31. As emphasized in the review by Jha 30, the comet assay continues to play an important role in assessing the induction of genetic damage of natural biota, but further studies are needed to identify sources of variability and factors influencing the outcome of the assay in field or biomonitoring studies.
Overall, the fish biomarker results were consistent with the sediment PAH results, showing a pattern of low levels of PAH metabolites and DNA damage at the upstream reference location and remediated section (RMs 9.2 and 6.5, respectively), but high levels at the two immediate downstream sites (RM 5.7 and 4.4), and lower levels at the furthest downstream site sampled (RM 2.7). These results suggest that additional remedial investigation and potentially further remediation is needed for at least 1.6 miles downstream of the current remediated area (RMs 6.8–6.0). The possibility was considered that the remedial action conducted from 2002 to 2006 may have resuspended contaminated sediments and led to their downstream transport, deposition, contaminant dissolution, and resultant increased exposures of biota, as can occur during environmental dredging of sediment 32. However, resuspension of the contaminated sediments during the Little Scioto remediation appears unlikely because the segments of the river under remediation were completely isolated using sheet piling and bypass pumping operations, and other precautions were taken to prevent resuspension and transport during rain events 5. While there is always a possibility of resuspension during a removal action, the likelihood that this occurred to such an extent as to significantly influence the data miles downstream is minimal. Resuspension impacts farther downstream of the remediated section would be from natural causes such as flood events and sediment erosion from the numerous log jams in the river.
Biological communities have shown improvement in the lower six miles of the Little Scioto River over the last 20 years. Sediment remediation activities at RM 6.5 have resulted in lowering the PAH exposure to benthic fish, although exposure levels have not been reduced to background or reference levels. This could be the result of fish movements into or from nearby contaminated areas. The remediation was effective in reducing sediment contaminant concentrations and exposure of fish to PAHs and in improving fish assemblages, as evidenced by a 60% increase in IBI scores in the remediated river section; however, the downstream benthic fish community is still heavily exposed to PAH contaminants.
The results of the present study documented severe impacts to the aquatic environment in PAH-contaminated stretches of the Little Scioto River and demonstrated that previously remediated areas were recovering. Ohio EPA's Division of Surface Water recently recommended to the Ohio Department of Health that the physical contact advisory be removed for the remediated segments of the Little Scioto River and North Rockswale Ditch, while maintaining the advisory for the remaining areas. Although fish in remediated areas exhibit fewer signs of PAH exposure, the Ohio EPA has recommended that the fish consumption advisory for the remediated sections of the river should remain in place for now, as the fish in this area are suspected to be migrating to or from contaminated segments of the river.
Human health impacts of PAH exposure may be due to direct physical contact with contaminated sediments or through secondary pathways, such as ingestion of impacted fish and other wildlife. A significant potential exists for human health impacts through these pathways, especially given that large stretches of the Little Scioto River study area are used for public hunting and other recreational activities. Investigations of ongoing risks at the study area and a remedial site investigation are under way. The results from these ongoing studies will help determine whether the conditions warrant additional remedial action.
Although this work was reviewed by the U.S. EPA and approved for publication, it may not necessarily reflect Agency policy. The authors thank M. Mills of the U.S. EPA for peer review of the manuscript and J. Rhodus, Dynamac Corporation, for manuscript editing and formatting.