• Sediment;
  • Porewater;
  • Bioaccumulation;
  • Toxicity;
  • Landfill leachate


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

Runoff of leachate from East Lake and Dare County Construction and Demolition Debris landfills has the potential to impact wildlife resources at Alligator River National Wildlife Refuge, Dare and Hyde Counties, North Carolina. Sediment quality of samples collected in August 2000 at 14 locations down-gradient from the landfills was assessed by measuring metal and organic contaminants in the sediments, chronic toxicity of solid-phase sediment (28-d static-renewal exposures; survival and growth as test endpoints) and acute toxicity of sediment porewater (96-h static exposures) to Hyalella azteca (Crustacea: Amphipoda). In addition, contaminant bioaccumulation from 4 sediments was determined using 28-d exposures of Lumbriculus variegatus (freshwater oligochaete). Although survival was not impaired, length of H. azteca was significantly reduced in sediments from 5 locations. Pore water from 4 locations was acutely toxic to H. azteca. Metals and a few polycyclic aromatic hydrocarbons (PAHs) were bioaccumulated by L variegatus from the sediments. Several metals and PAHs exceeded sediment quality guidelines, and metals in porewater from several sites exceeded water quality criteria for the protection of aquatic wildlife. Runoff of leachate from the landfills has reduced sediment quality and has the potential to adversely affect wildlife resources at Alligator River National Wildlife Refuge.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

Alligator River National Wildlife Refuge (NWR), located in Dare and Hyde Counties, North Carolina, USA, encompasses 2 municipal landfills that may pose a potential hazard to fish and wildlife resources. Established in 1984, this 152,262 acre refuge contains a variety of wetland habitats with the most exceptional being the “pocosin” or perched wetland. Bordered on the west by the Alligator River and Intracoastal Waterway, on the north by Albemarle Sound and on the south by Croatan and Pamlico Sounds, the refuge abounds with a diversity of wetland habitats that include private agricultural and forested lands, high and low pocosins, bogs, hardwood swamps, and brackish and freshwater marshes. The mission of the refuge is to preserve and protect these habitats and their fish and wildlife species, which include the federally listed endangered red wolf and red-cockaded woodpecker, the black bear, and resident and migratory birds and waterfowl.

The 2 landfills, 1 closed and the other active, have a history of contaminant releases. Located in a palustrine forested wetland at the northern end of the refuge and operated from 1980 to 1993, East Lake Landfill violated National Pollutant Discharge Elimination System permit requirements for discharge into surface waters. Preliminary evaluations of aquatic systems receiving discharge and leachate from this landfill demonstrated elevated concentrations of metals (arsenic [As], chromium [Cr], copper [Cu], nickel [Ni], and zinc [Zn]) in sediments and biota (North Carolina Division of Water Quality, unpublished data). The active Dare County Construction and Demolition Debris Landfill (C/D Landfill) is located on about 800 acres in the central portion of the refuge and has operated since October 1993. Although designated as “converted cropland” for permitting purposes (and, therefore, not required to adhere to wetland restrictions on discharges), this landfill is located over hydric soils and drained by a series of canals that flow into the refuge. A fire at the landfill in 1998 and subsequent suppression activities released surface runoff from the landfill into the down-gradient canals. Potential impacts of drainage from the C/D Landfill to the refuge have not been assessed, but metal concentrations (cadmium [Cd], Cr, Cu, mercury [Hg], Ni, lead [Pb], and Zn) in grab samples of surface water collected after the fire suppression exceeded North Carolina water quality standards or action levels (NC DENR 2000) for the protection of aquatic life (North Carolina Division of Water Quality, unpublished data). Organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), originating from the 1998 fire and other materials currently disposed of in the landfill may also be of concern but have not been investigated previously.

Pollution potential from these landfills presents management concerns for the refuge. The U.S. Department of the Interior's Fish and Wildlife Service manages the refuge in the public trust and is charged with ensuring the biological integrity, diversity, and environmental health of refuge land and waters (National Wildlife Refuge System Improvement Act of 1997; Public Law 105–57; 16 U.S. Code 668dd). Because the landfills are surrounded by refuge property, normal site drainage establishes a connection with refuge lands. Also, the refuge operates a pumping station on the canal network adjacent to the C/D Landfill. Pumping of water through the canals is done to manage some refuge lands for cooperative farming programs, but pumping enhances pathways for any surface or subsurface contamination leaving the landfill to enter refuge property.

The objective of this study was to ascertain the potential impact of discharges from the East Lake and C/D landfills to the resources of the Alligator River NWR. This was accomplished by determining habitat quality through a sediment quality assessment of the canals located down-gradient from the landfills. The sediment quality assessment included chemical analyses of contaminants (metals and organics) in sediments and sediment porewaters, chronic toxicity testing of solid-phase sediments, acute toxicity testing of sediment porewaters, and contaminant bioaccumulation studies on a selected set of sediment samples.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

Study sites

Sediment samples were collected from 14 locations in the canal systems associated with the 2 landfills (East Lake Landfill and C/D Landfill) within the Alligator River NWR during August 2000 (Figure 1). Six sampling locations were established in the ditches and streams associated with the East Lake Landfill and 8 sampling locations around the C/D Landfill. Two of the 14 stations were selected as reference sites and were considered to be outside the potential area of impact by the landfills. Sampling areas were located at varying distances down-gradient from each of the landfills.

Sample collection and handling

Sediment samples were collected between 22–24 August 2000 from the canals associated with the landfills using a stainless-steel, petite Ponar grab sampler. The top 10 to 15 cm of sediment were collected and individual grab samples composited and homogenized by stirring with a stainless-steel spoon. Debris (e.g., sticks and leaves) was removed during homogenization. Collection equipment was thoroughly cleaned using detergent, nitric acid, and acetone and rinsed with distilled/demineralized water between sampling events. From each site, 2 (1 for metals and 1 for organic chemical contaminants) 500-ml aliquots of sediment were placed into glass jars and sealed with Teflon-lined lids. Sediment samples for analyses of organic chemicals were shipped to Mississippi State Chemical Laboratory (Mississippi State, MS, USA). Sediment samples for elemental analyses were shipped to Midwest Research Institute (Kansas City, MO, USA). In addition, approximately 8 L of sediment from each site were shipped to the U.S. Geological Survey Patuxent Wildlife Research Center Field Station (University of Georgia, Athens, GA, USA) for toxicity testing and sediment characterization. Samples were kept in the dark at 4°C and held less than 2 weeks before testing and sediment characterization.

Toxicity testing

Sediment toxicity was assessed following procedures described by Ingersoll et al. (1994), with the exception that exposure time was increased from the 10-d period typically used for acute testing to 28 d for the assessment of chronic effects. Testing included laboratory control sediment (prepared using sand that was conditioned for 2 weeks in moderately-hard test water and a suspension of Selenastrum sp.) and a field-collected reference sediment (representing depositional sediment collected from the Ogeechee River, GA, USA, located 300 m upstream from Interstate 95). Five replicate samples from each sediment were prepared following rehomogenization. Each consisted of 100 ml of sediment and 175 ml of laboratory-prepared (reconstituted) overlying water in a 300-ml high-form beaker with a notch in the lip covered with stainless-steel mesh (250 μm). The individual replicates were randomly positioned within a static-renewal system that replaced the overlying water twice daily (Zumwalt et al. 1994). Ten 7-d-old Hyalella azteca (Amphipoda: Crustacea) were placed into each test chamber. Test exposures were maintained at 23 ± 1°C under wide-spectrum fluorescent lights with a 16-h light to 8-h dark regime. Animals were fed 1.5 ml (1.8 g solids/L) of yeast, Cerophyl, and trout chow (YCT) daily. The reconstituted water used as overlying and renewal water was prepared according to Ingersoll et al. (1994) and consisted of deionized water, calcium sulfate (CaSO4), calcium chloride (CaCl2), magnesium sulfate (MgSO4), sodium hydrogen carbonate (NaHCO3), and potassium chloride (KCl) mixed to achieve a hardness of 100 mg/L, alkalinity of 70 mg/L, 350 μS/cm conductivity, and a pH of 8. Test endpoints were survival and growth. Growth of H. azteca was determined by measuring the length of a projected image using a microscope slide projector and a device calibrated with a stage micrometer. Basic chemistry (dissolved oxygen, temperature, pH, alkalinity, hardness, conductivity, and ammonia) of the overlying water was monitored during the test. Temperature, dissolved oxygen, pH, conductivity, and ammonia were measured periodically using appropriate meters and electrodes. Hardness and alkalinity were determined by titration.

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Figure Figure 1.. Sediment sampling locations in drainage areas associated with the 2 landfills at the Alligator River National Wildlife Refuge, North Carolina, USA.

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Porewater for toxicity testing and chemical analyses was isolated from the sediments by inserting 10 porewater extractors into each sediment sample and applying a vacuum (Winger and Lasier 1995). Porewater extractors consisted of fused-glass air stones attached with airline tubing to 60 cc syringes (Winger and Lasier 1991). Approximately 300 ml of pore water were isolated from each sediment sample, aerated for 15 min, and 20 ml was transferred to each of 5 replicate 30 ml glass beakers. Each replicate contained 10 H. azteca and 1 cm2 Nitex netting (275 μm). The animals were not fed during the 96-h exposures, and survival was the test endpoint. Basic chemistry (the same as that for overlying water in the sediment test) of porewater was measured after aeration.

After exposures to solid-phase sediment and pore water, surviving H. azteca were exposed to ultraviolet light for 4 h to evaluate potential phototoxicity resulting from the exposure to certain PAHs (Ankley et al. 1994).

Bioaccumulation study

Bioaccumulation of contaminants from 4 selected sediments was determined following procedures described by Ingersoll et al. (1994). Sediments demonstrating the greatest toxicity (based on reduced survival and/or length) were selected for further study. For each sediment, 4 replicate samples were tested, and each consisted of a 4-L glass chamber that contained 1 L of sediment and 3 L of overlying water. One thousand freshwater oligochaetes, Lumbriculus variegatus, were introduced into each replicate. An equal number of oligochaetes was retained for use as the control for comparison of contaminant uptake. The chambers were randomly placed within a water-renewal system similar to that used in the solid-phase tests, and overlying water was renewed twice daily. Bioaccumulation exposures lasted for 28 d, and animals were not fed during the test. At the end of the test, the animals were separated from the sediments and placed in freshwater for 24 h to purge their guts before being frozen and submitted for chemical analyses. Concentrations of organic contaminants and trace elements in oligochaete tissues were reported on a dry-weight basis. Percent moisture of oligochaetes (91.5 ± 1.5% w/w) was based on the difference between a blotted wet weight and the constant weight after drying at 90°C

Chemical analyses

As sediments were prepared for testing, aliquots were taken for determination of the percentage of organic content, particle-size analysis, and acid-volatile sulfides (AVS) and simultaneously extracted metal (SEM) concentrations. Sediment particle sizes were measured following procedures described by Miller and Miller (1987) except that coarse organic material was measured by loss on ignition and subtracted from the total. The percentage of organic content was estimated by loss on ignition at 430°C for 4 h (Davies 1974). Acid-volatile sulfides were determined following the method outlined by Brouwer and Murphy (1994). The AVS digestates were filtered through a 0.2 μm nylon filter and analyzed for Cd, Cu, Hg, Ni, Pb, and Zn. Twenty ml of each porewater sample were collected before aeration, filtered (0.2 μm nylon filter) and acidified with ultrapure nitric acid in preparation for metal analyses (As, barium [Ba], calcium [Ca], Cd, Cr, Cu, iron [Fe], Hg, potassium [K], magnesium [Mg], manganese [Mn], sodium [Na], Ni, Pb, selenium [Se], and Zn). Metals in porewater were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Total organic carbon in porewater was determined after acidification with a Leco CR-412 carbon analyzer (St. Joseph, MI, USA) calibrated with calcium carbonate (CaCO3). Chloride and sulfate were measured using an ion chromatograph.

Samples for measuring the elemental contaminants (metals) in sediments and oligochaetes were digested with nitric acid and hydrochloric acid. Metal analyses were performed by ICP-MS. For Hg analyses of sediments and tissues, samples were digested with aqua regia and potassium permanganate, reduced with stannous chloride, and measured by cold-vapor AAS using a PerkinElmer FIMS mercury analyzer (Wellesley, MA, USA). Oligochaetes (animal tissue) analyzed for aliphatic and polynuclear aromatic hydrocarbons were digested in 6 N aqueous potassium hydroxide, extracted with methylene chloride, dried, and reconstituted with petroleum ether (Mississippi State Chemical Laboratory Method Code 003). Aliphatic and polycyclic aromatic hydrocarbons in sediments were extracted with petroleum ether and methylene chloride using gel-permeation chromatography (Mississippi State Chemical Laboratory Methods Code 040). Aliphatics were separated from aromatic hydrocarbons by eluting with petroleum ether. Aromatics were eluted with methylene chloride and petroleum ether. Aliphatic compounds were quantified by capillary column, flame-ionization gas chromatography. Cleanup of the eluates containing the aromatic fraction was performed by gel permeation chromatography and quantified by capillary flame-ionization gas chromatography and fluorescence using high-performance liquid chromatography. For semivolatile organic compounds, samples were Soxhlet-extracted with methylene chloride and quantified with a Finnigan Incos 50 mass spectrophotometer (Thermo Electron, Karlsruhe, Germany; Mississippi State Chemical Laboratory Methods Code 021). Samples for organochlorine pesticides and polychlorinated biphenyls (PCBs) were Soxhlet-extracted with hexane and separated by high-pressure gel-permeation chromatography. Additional cleanup with silicic acid was used for PCBs. Following cleanup with Florisil (US Silica, Berkeley Springs, WV, USA), compounds were quantified by electron-capture gas chromatography (Mississippi State Chemical Laboratory Methods Code 050).

Quality assurance data, including blanks, duplicates, spikes, and standard samples, indicated that analyses were within acceptable limits for precision and accuracy. Instrument detection limits were corrected according to dilution factors, sample weights, and interferences. The limit of quantitation was established as 3 times the lower limit of detection. Detection limits for sediments and tissues were 0.05 μg/g dry weight for Pb; < 0.16 μg/g dry weight for As, Ba, beryllium (Be), Cd, Cr, Cu, Hg, Mn, molybdenum (Mo), Ni, and strontium (Sr); 0.26 μg/g dry weight for Se and vanadium (V); 0.51 μg/g dry weight for boron (B); 1.70 μg/g dry weight for aluminum (Al); 2.30 μg/g dry weight for Mn; 3.60 μg/g for Zn; 18 μg/g for Fe; and 64 μg/g for Mg. Sediment blanks were less than detection levels for all analytes except for Al (6.7 μg/g dry weight), Cr (0.28 μg/g dry weight), Cu (0.66 μg/g dry weight), Mn (2.36 μg/g dry weight), and Pb (0.25 μg/g dry weight). Differences between duplicate samples for sediments averaged 2.6 ± 1.7%. Recoveries from spiked sediment samples averaged 97.2 ± 6.3% (w/w). The instrument detection limits for porewater and SEM samples were 0.01 μg/L for Hg; 0.03 μg/L for Cd, Na, and Pb; <0.25 μg/L for As, Ba, Cu, Mg, Mn, and Ni; 0.50 μg/L for Zn; 0.61 μg/L for Se; 0.92 μg/L for Cr; 2.89 μg/L for Fe; and <13.00 μg/L for Ca and K. Relative standard deviation between duplicates averaged 13% for the ICP-MS analyses of metals and 11 % for Hg analyses. Blanks for porewater analyses were below detection levels for all metals except K (7.8 μg/L) and Fe (6.9 μg/L). Differences between samples of porewater split in the laboratory averaged 1 ± 1.1% for all metals except Cr (25%), As (28%), and Cd (16%). Recovery from spiked samples of porewater averaged 95.0 ± 5.3% (w/v).

Blank samples for organic analyses were below detection levels, which were less than 1 μg/g dry weight. Spiked tissue and sediment samples were within normal limits except for 1,2,4-trichlorobenzene, 1,4-dichlorobenzene, and 4-nitrophenol in sediment from sampling location EL5; 1-methylnaph-thalene, 2,6-dimethylnaphthalene, 2-methylnaphthalene, c1-naphthalenes, and c2-naphthalenes in sediment from location CD1; and dibenz[a,h]anthracene in animal tissue; these anomalies were slightly outside the laboratory quality assurance/quality control specifications but were not expected to affect the interpretation of the data. Laboratory splits were within acceptable limits (<10% relative difference) except for bis(2-ethylhexyl) phthalate at sampling location EL5 where laboratory contamination was suspected.

Statistical analyses

Following tests for normality (Shapiro-Wilks), ANOVA was performed, and then Dunnett's pair-wise tests were performed to evaluate differences (p < 0.05) with the controls. The controls for these tests included sediments from 3 reference sites, a laboratory reference (Ogeechee River sediment [OGRef]) and 2 field references (C/D Landfill [CDRef] and East Lake Landfill [ELRef]). Spearman rank correlations among variables and the test metrics were then determined. Statistical analyses were performed using Statistical Analysis Systems (SAS 1990).

Sediment elemental and organic contaminant data were compared with freshwater sediment quality guidelines (SQGs) (MacDonald et al. 2000). The SQGs used in this study were consensus-based, effects guidelines, which establish the lower-bound concentrations below which adverse effects to sensitive aquatic organisms should not occur (referred to as threshold effects concentrations [TECs]) and an upper range of concentrations above which adverse effects to sediment dwelling organism may be expected (referred to as probable effects concentrations [PECs]). The relevance of the concentrations of contaminants (metals and PAHs) in sediments and porewaters were further summarized by calculating the sum of the associated sediment quality quotients (SQQ). Sediment quality quotients was based on the ratio of the concentrations of contaminants in the sediments and pore-waters and established sediment and water quality criteria. For each contaminant with an SQG value, an SQQ was calculated by dividing the concentration in the sediment by the SQG value (MacDonald et al. 2000). The SQQs for all contaminants were summed at each sampling location. The SQQs for metals in the pore water were similarly determined using water quality criteria (USEPA 2002). The statistical significance of the relationship between the total SQQs and toxicity endpoints was evaluated using simple linear regression.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

Toxicity of sediments and porewaters

Survival of H. azteca exposed for 28 d to sediments collected from canals associated with the 2 landfills was similar, although survival from EL1 was significantly (p < 0.05) less than that shown for CDRef, the reference site located closest to the C/D Landfill (Table 1). Length (an indicator of growth) of H. azteca, however, was significantly reduced at sampling locations CD3, CD5, and CDRef when compared with the laboratory reference (OGRef). Contrasted with the reference site closest to the East Lake Landfill (ELRef), length was also significantly (p < 0.05) less in animals exposed to sediments from locations CD1, CD3, CD5, CDRef, and EL1. The length of H. azteca exposed to sediments from CD3 was significantly reduced when compared with CDRef.

Considerable variation often exists among reference sites, and the sites are not necessarily free from contaminants or other stressors (Ingersoll et al. 1994; Hughes 1995). To at least account for some of this variability, multiple references sites (3 in this case, 1 laboratory reference and 2 field references) were used for statistical comparisons between metrics. Each comparison was considered a different line of evidence. Concordance among test endpoints was good, with 3 of the 5 sites showing impaired growth from the solid-phase exposures and reduced survival in porewater (Table 1). Acute toxicity in the 96-h porewater tests occurred at sampling locations CD1, CD2, EL1, and CDRef. Based on tests with solid-phase sediment and porewater, sediment quality was reduced relative to at least 1 of the 3 reference sediments at 5 locations associated with the C/D Landfill (CD1, CD2, CD3, CD5, and CDRef) and the sampling location closest to the East Lake Landfill (EL1). Survival and growth of H. azteca exposed to sediment and pore water from these 6 sites ranked the lowest, demonstrating impaired conditions when compared with the other sites.

Toxicity (survival) was not influenced by exposure of the test animals to ultraviolet light subsequent to the sediment and porewater tests (therefore, data are not shown). Animals exposed to some PAHs have been shown to elicit a marked increase in mortality following a short exposure to ultraviolet light (Ankley et al. 1994). The absence of increased toxicity to animals from the solid-phase and porewater tests with exposure to ultraviolet light suggests that PAH (at least the compounds that are photoactivated by ultraviolet light) contamination may not be contributing to the toxicity shown by these sediments.

Table Table 1.. Survival and length (with standard deviations) of Hyalella azteca in 28 d, solid-phase sediment and 96 h, porewater tests using sediments collected in canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USAa
 Solid-phase sediment test resultsPorewater test results
Sampling location% SurvivalSDLength (mm)SD% SurvivalSD
  1. a Significant differences between test endpoints from the study locations compared with the 3 reference sediments are indicated by: A = significantly < Ogeechee River sediment (OGRef); B = significantly < East Lake Landfill (ELRef); C = significantly < reference site located closest to the Construction and Demolition Landfill (CDRef) (Dunnett's 1-tailed test, α = 0.05).

Table Table 2.. Physical characteristics of sediments and chemistry of overlying water in solid-phase sediment tests with Hyalella azteca exposed to sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USA
 Sampling location
  1. a AVS = acid volatile sulfides; SEM = simultaneously extracted metals.

Moisture (%)39.853.469.744.060.234.579.352.360.871.076.884.580.374.766.4
Total organic (%)
Sand (%)373332805387365910564251566966
Silt-clay (%)636868214713644190445749443134
AVS (μmol/g)44.0241.49124.820.8268.441.442.4919.11221.83.192.370.630.300.831.28
SEM (μmol/g)0.210.340.400.
Dissolved oxygen (mg/L)
Conductivity (μS/cm)418393361415351359423353516455457530448467354
Alkalinity (mg/L CaCO3)927870767072727282767670707678
Hardness (mg/L CaCO3)12811210811611210410010811211611211210410492
Total ammonia (mg/L)

Factors influencing toxicity

The significance of specific contaminants that may be responsible for the impaired growth and toxicity shown by H. azteca exposed to sediments associated with the landfills depends not only upon the concentration but also on the matrix and route of exposure (sediment or porewater) and the physical and chemical factors that influence the availability of the toxicant to the organism. Primary factors that could influence the availability include the basic chemistry (e.g., pH, alkalinity, hardness, and redox potential) and physical composition of the sediment (e.g., percentage of organic matter and sediment particle-size distribution). Characteristics (total organic material, particle size, and percent moisture) of the sediments evaluated during this study showed some variability among stations but were within ranges that would be expected from these types of systems (Table 2). The percentage of fines (silt and clay) at the sampling locations that elicited toxicity tended to be higher than that at other locations with lower toxicity. Acid-volatile sulfides varied from low (1.4 μmol/g) to high (221.8 μmol/g) in the sediments, but concentrations of the SEM were uniformly low, and the SEM to AVS ratios were less than 1. SEM to AVS ratios greater than 1 are generally predictive of metal toxicity, and ratios less than 1 indicate that metal-sulfide forming metals (Cd, Cu, Hg, Pb, Ni, and Zn) would not be expected to elicit toxicity (Di Toro et al. 1992; Ankley et al. 1993). Chemistry of the overlying water from the solid-phase exposures showed no anomalies corresponding to locations considered to have impaired sediment quality. Concentrations of ammonia in the overlying water from the solid-phase exposures were low (< 2 mg/L). Basic characteristics (e.g., pH, hardness, and conductivity) of porewater were within normal ranges, although alkalinity and ammonia were elevated at several sampling locations (Table 3).

Exceedences of screening values

Factors responsible for the toxicity shown by H. azteca exposed to sediments and porewater are not clearly identified, although concentrations and correlative associations suggest that metal concentrations in the sediments and porewaters may be implicated (Table 4). Metal concentrations in sediments from several sampling locations were elevated above those from reference locations, and some exceeded specific guidelines or criteria and may have contributed to the reduced growth and survival of H. azteca shown in the chronic tests and acute tests (Table 5).

Concentrations of As, Cu, and Zn in sediments at several locations, for example, exceeded published TECs (MacDonald 2000). Arsenic concentrations at CD1 (38.7 μg/g) and CD2 (37.1 μg/g) exceeded both the TEC (9.79 μg/g) and PEC (33.0 μg/g) screening values. No other sediment samples exceeded PECs for any contaminant. Sediments with metal concentrations that exceeded consensus-based TECs would be expected to have adverse effects on sensitive sediment-dwelling organisms. Concentrations of Cr, Cu, and As were elevated (Table 5) at the 3 locations down-gradient from the C/D Landfill (CD1, CD2, and CD3). Average concentrations of Cr (30.0 μg/g), Cu (35.4 μg/g), and As (31.5 μg/g) at these 3 locations exceeded levels measured during baseline monitoring in 1988 before development of this area as a landfill: average (n = 3) Cr = 14.8 μg/g, Cu = 8.7 μg/g, and As = 4.2 μg/g (North Carolina Division of Water Quality, unpublished data). A possible source for these contaminants may be from lumber treated with chrome-copper-arsenic (Weis and Weis 1996) disposed of at the landfill.

Porewater is generally considered a major route of contaminant exposure to sediment-dwelling organisms (Adams et al. 1985), and the elevated concentrations of metals in this matrix, particularly at several of the sampling locations showing toxicity, may have contributed to the impaired conditions (Table 6). In this study, SEM to AVS ratios were <1 at all locations, suggesting that metal concentrations in the porewater would be low and not expected to elicit toxicity (Di Toro et al. 1992; Ankley et al. 1993). The lack of correlation between survival of H. azteca in porewater and concentrations of metals in the porewater is consistent with this observation (Table 4). However, porewater concentrations at several locations exceeded water quality criteria for As, Cr, Cu, Pb, Se, and Zn (USEPA 2002) for the protection of aquatic life. The lack of correlation does not preclude the possibility that elevated concentrations of these metals could adversely affect survival. Survival in porewater was, however, significantly (p < 0.05), negatively correlated with concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the sediments, as well as with total metal concentrations. Concentrations of several of these metals in porewater exceeded those that have been shown to be harmful to aquatic organisms. For example, concentrations of As ranging from 19 to 48 μg/L have been found to adversely impact aquatic species (Eisler 1994), and Miller and Hendricks (1996) reported that aqueous Zn concentrations of 62 μg/L reduced the growth of Chironomus riparius. Porewater from 10 of the 14 sampling locations had Zn concentrations that exceeded 62 μg/L (Table 6). Similarly, Cr concentrations exceeded levels that have been shown to cause toxicity (Eisler 1986), and concentrations >20 μg/g in the sediments have been shown to cause toxicity to fish in the overlying water (Gendusa et al. 1993). Copper at concentrations of 5 to 10 μg/L are toxic to sensitive species (Eisler 1997).

Table Table 3.. Chemistry of porewater used in 96-h exposures with Hyalella azteca. Porewater was extracted from sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USA
 Sampling location
Dissolved oxygen (mg/L)
Conductivity (μS/cm)1,6151,1325611,4764805211,6094542,9202,1601,9403,3101,9482,290419
Alkalinity (mg/L CaCO3)45836820020817616212824431025220017898162240
Hardness (mg/L CaCO3)57828014523213072141176272164170297161213312
Total ammonia (mg/L)5.310.
Total organic carbon (mg/L)108.7122.438.926.637.747.860.925.555.340.5455.126.344.361.649.9
Chloride (mg/L)237147624484968541291,0226806171,337690854242
Sulfate (mg/L)
Table Table 4.. Spearman rank correlation between sediment and porewater toxicity with Hyalella azteca, sediment, and porewater characteristics; metal concentrations in porewater and sediments (normalized to organic content); and total PAH concentrationa
  1. a Significant correlations between variables and toxicity-test end-points are shown as A = p < 0.001, B = p < 0.01, and C = p < 0.05.

  2. b PAH = polycyclic aromatic hydrocarbons; AVS = acid volatile sulfides; SEM = simultaneously extracted metals; SQQ = sediment quality quotient.

Moisture (%)−-0.180−-0.2450.354
Organic (%)−-0.021−-0.4080.500
Sand (%)0.721B−-0.0810.520C
Fines (%)−-0.718B0.096−-0.528C
Porewater conductivity−-0.1120.0340.070
Porewater alkalinity−-0.2450.615C−-0.577C
Porewater hardness0.0520.510−-0.634C
Porewater ammonia−-0.676B0.410−-0.064
Arsenic in sediment−-0.3520.516C−-0.756B
Cadmium in sediment−-0.4530.616C−-0.557C
Chromium in sediment−-0.2730.614C−-0.798A
Copper in sediment−-0.2660.495−-0.717B
Mercury in sediment−-0.0250.459−-0.513
Nickel in sediment−-0.3510.662B−-0.619C
Lead in sediment−-0.2330.649B−-0.565C
Zinc in sediment−-0.3730.608C−-0.625C
SQQ in sediment−-0.522C0.406−-0.439
Total metals in sediment−-0.2730.608C−-0.708B
Total PAHs in sediment0.1140.179−-0.374
Arsenic in porewater−-0.4430.176−-0.238
Cadmium in porewater0.022−-0.571C0.385
Chromium in porewater−-0.592C0.137−0.415
Copper in porewater−-0.272−-0.311−-0.061
Mercury in porewater−-0.022−-0.169−-0.311
Nickel in porewater−-0.2960.308−-0.261
Lead in porewater−-0.097−-0.3050.466
Zinc in porewater−-0.2600.0440.174
Total metal in porewater−-0.316−-0.1790.045
SQQ in porewater−-0.367−-0.105−-0.158
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Figure Figure 2.. Relationship between porewater toxicity to Hyalella azteca and the sum of the sediment quality quotients for metals in sediments collected from areas draining 2 landfills at the Alligator River National Wildlife Refuge, North Carolina, USA.

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Other factors or contaminants not tested in this study could have contributed to or influenced the toxicities observed in the acute and chronic tests. In addition, chemical conditions associated with the basic water chemistry of the test waters could also have influenced the toxicity shown in the porewater (Table 3). Alkalinity, which has been shown to be a confounding factor associated with porewater testing (Lasier et al. 1997), was elevated at several of the sampling locations that showed the highest toxicities. Ammonia, which was elevated at some locations where toxicity was high (>10 mg/L at CD2 and EL1), has also been identified as a confounding factor in porewater testing. Ammonia concentrations, however, were below levels that are generally considered toxic to H. azteca (Ankley et al. 1990).

Table Table 5.. Metal concentrations (μg/g dry wt) in sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USA and used for 28-d chronic-toxicity tests with Hyalella azteca and 28-d bioaccumulation studies with Lumbriculus variegatus (locations in bold were used in the bioaccumulation study)a
 Sampling location
  1. aValues underlined exceed threshold effects concentrations from consensus-based sediment-quality guidelines (MacDonald et al. 2000).

Boron6.645.293.872.371.85< 0.499.571.
Mercury<< 0.17< 0.170.27< 0.17<< 0.17
Table Table 6.. Concentrations of metals in porewater from sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USAa
 Sampling location
  1. a Concentrations that are underlined exceeded water quality criteria (USEPA 2000).

  2. b ND = concentrations were less than the detection level.

Arsenic (μg/L)271.6133.919.
Barium (μg/L)97.8161.9106.1150.2118.063.1150.9136.6162.1101.1133.2142.260.1187.034.0
Cadmium (μg/L)NDbND0.04NDND0.110.04NDNDND0.020.060.05ND0.07
Calcium (mg/L)166.067.427.766.925.727.218.244.830.418.715.621.514.116.56.6
Chromium (μg/L)54.814.
Copper (μg/L)69.615.311.12.64.431.859.
Iron (mg/L)7.360.824.32.418.540.20.20.414.
Lead (μg/L)0.160.850.86NDND1.371.90NDND1.833.330.671.322.721.44
Magnesium (mg/L)40.027.418.715.916.111.223.310.347.839.032.059.430.742.16.3
Manganese (mg/L)
Mercury (μg/L)
Nickel (μg/L),
Potassium (mg/L)
Selenium (μg/L)
Sodium (mg/L)159.6113.352.9169.444.844.0274.742.4477.8361.3313.6561.6349.2395.731.6
Zinc (μg/L)120.8121.0109.267.2101.0154.056.065.960.3128.4169.714.5111.334.285.5
Table Table 7.. Concentrations of organic (phthalates, polynuclear aromatic hydrocarbons, and aliphatic hydrocarbons) contaminants (μg/g dry wt) in sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USA. Sediments from locations that are in bold were included in the bioaccumulation studya
 Sampling location
  1. a Concentrations that are underlined exceeded the threshold effects level of the consensus-based sediment quality guidelines (MacDonald et al. 2000).

  2. b ND = concentrations were less than the detection level; NA = no analysis was performed.

Table Table 8.. Concentrations of metals (μg/g dry wt) and bioaccumulation factors (in parentheses) for Lumbriculus variegatus exposed for 28 d to selected sediments from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USA
 Sampling location 
MetalCD1CD3CD5EL1ELRefCulture reference
Aluminum467.0 (0.04)245.0 (0.01)184.0 (0.01)729.0 (0.03)97.8 (0.01)22.6
Arsenic107.0 (2.76)25.4 (1.35)16.1 (1.85)10.2 (0.73)2.43 (0.71)1.57
Boron1.95 (0.29)0.65 (0.16)<0.51 (0.27)0.59 (0.11)0.65 (0.04)2.52
Barium106.0 (2.24)101.0 (1.56)100.0 (1.98)87.5 (0.92)77.0 (2.51)37.8
Beryllium<0.09< 0.09<0.10<0.09<0.09<0.18
Cadmium0.29 (1.03)0.31 (0.81)0.23 (0.88)0.25 (0.58)0.28 (1.55)<0.22
Chromium2.29 (0.07)1.14 (0.04)1.01 (0.06)1.29 (0.03)0.73 (0.04)0.90
Copper48.4 (1.37)51.2 (1.70)46.5 (3.14)33.7 (1.80)35.4 (3.40)12.3
Iron2,408 (0.01)2,224 (0.07)1,890 (0.09)1,869 (0.05)965 (0.07)713
Magnesium993 (0.20)889 (0.40)896 (0.60)957 (0.20)2,541 (0.50)763
Manganese16.6 (0.07)8.26 (0.09)8.81 (0.01)9.08 (0.06)9.25 (0.15)5.81
Molybdenum0.53 (0.92)0.36 (0.78)0.39 (0.95)0.42 (0.34)0.49 (0.24)0.58
Nickel1.99 (0.13)1.01 (0.10)1.03 (0.12)1.20 (0.05)1.07 (0.12)0.68
Lead3.25 (0.17)2.37 (0.11)1.56 (0.13)2.12 (0.10)4.50 (0.02)0.89
Selenium5.63 (8.15)4.38 (4.42)4.45 (6.26)4.71 (5.11)3.38 (2.33)2.02
Strontium86.4 (2.74)80.6 (2.76)81.6 (3.90)88.7 (1.63)88.2 (1.35)46.6
Vanadium3.93 (0.15)2.81 (0.12)2.91 (0.15)3.28 (0.05)2.68 (0.13)4.00
Zinc448.0 (3.58)476.0 (4.32)429.0 (5.64)355.0 (3.28)245.0 (7.65)278.0
Table Table 9.. Uptake of organic contaminants (μg/g dry wt) by Lumbriculus variegatus exposed during a 28-d bioaccumulation study to sediments collected from canals associated with 2 landfills at Alligator River National Wildlife Refuge, North Carolina, USAa
 Sampling location 
  1. a ND = concentrations were less than the detection limits; NA = no analysis was performed; DDE = dichlorodiphenyldichloroethylene.

1 -MethylphenanthreneNDNDNDND0.17ND
Butyl benzylphtha lateNDNDNDNDNDND

The toxicities shown in the solid-phase sediment and porewater tests may be in response to the combination of metals (As, Cr, Cu, Pb, Se, and Zn) present. Metal mixtures have been shown to be important in eliciting toxicity (de March 1988; Kraak et al. 1994). Eisler (1997) also reported that Cu has been shown to have more than additive toxicity in the presence of Al, Cr, Fe, Mn, Mo, and Zn. A significant relationship was shown between survival of H. azteca in porewater and the total SQQ calculated for metal concentrations in the sediments (Figure 2). However, there was not a statistically significant relationship between the total SQQ for metals in porewater with survival in porewater or between survival/length from solid-phase tests and the corresponding SQQ for either matrix. Filtering of the porewater samples in preparation for submission for analytical testing may have contributed to the lack of correlation between survival in porewater and concentrations of metals. The test animals were exposed to porewater that had not been filtered, and filtering has been shown to remove metals from porewater samples (Winger et al. 1998). Ankley and Schubauer-Berigan (1994) found that unfiltered porewater was more toxic to test species than filtered porewater.

Table Table 10.. Quality criteria for protection of fish and wildlife resources from contaminants of concern addressed in this study
ContaminantSediment threshold effects criteriaaWater quality criteriab (100 mg/L hardness)North Carolina water quality criteriacProtection levelsdDietary limitse
  1. a Concentrations below which harmful effects on sediment-dwelling organisms are not expected.

  2. b Concentrations (criteria continuous concentration) below the water quality criteria are protective of freshwater organisms.

  3. c Concentrations established by North Carolina to be protective of freshwater organisms.

  4. d Concentrations considered protective of freshwater organisms.

  5. e Consumption of food material with concentrations less that the dietary limit would be protective of fish and wildlife species.

  6. f Superscript numbers represent references as follows: 1 MacDonald et al. 2000; 2 USEPA 2000; 3 NC DENR 2000; 4 Eisler 1988a; 5 Eisler 1985; 6 Eisler 1986; 7 Eisler 1997; 8 Eisler 1988b; 9 Wolfe and Norman 1998; 10 Bouton et al. 1999; 11 Eisler 1998; 12 Lemly 1997; 13 Lemly 1996; 14 Eisler 1993; 15 Nagpal 2001; 16 Eisler 1987a.

  7. g NA = not available; PAH = polycyclic aromatic hydrocarbons.

Arsenic9.79 mg/kg dry wt1f150 μg/L250 μg/L3190 μg/L450 μg/g4
Cadmium0.99 mg/kg dry wt12.2 μg/L22 μg/L31 μg/L5200 μg/g5
Chromium43.4 mg/kg dry wt111 μg/L250 μg/L310 μg/L610 μg/g6
Copper31.6 mg/kg dry wt19 μg/L27 μg/L312 μg/L7200 μg/g7
Lead35.8 mg/kg dry wt12.5 μg/L225 μg/L31.3 μg/L82.8 μg/g8
Mercury0.18 mg/kg dry wt10.77 μg/L20.012 μg/L30.001 μg/L90.5 μg/g10
Nickel22.7 mg/kg dry wt152 μg/L288 μg/L325 μg/L11200 μg/g11
Selenium1–4 mg/kg dry wt125 μg/L25 μg/L32 μg/L133 μg/g13
Zinc121 mg/kg dry wt1120 μg/L250 μg/L35 μg/L14178 μg/g14
Anthracene57.2 μg/kg dry wt10.01 μg/L15NAg4 μg/L15NA
Fluoranthene423 μg/kg dry wt10.01 μg/L15NA4 μg/L15NA
Phenanthene204 μg/kg dry wt10.01 μg/L15NA0.03 μg/L15NA
Pyrene195 μg/kg dry wt10.01 μg/L15NA0.02 μg/L15NA
Total PAHsg1,610 μg/kg dry wt10.01 μg/L15NA0.1 μg/L161.6 μg/g16

Organic contaminants could also have contributed to the toxicities shown at several of the sampling locations (Table 7). The presence of phthalates (plasticizers in plastic material) at all locations may be characteristic of landfill leachates, but these chemicals are generally considered relatively nontoxic and would be expected to have minimal impact to resident biota, especially at the concentrations measured in this study. The more toxic PAHs (aromatics) were measured at several locations, particularly CD1 and CD3. Interestingly, the highest total concentration of PAHs occurred at ELRef, the reference for the East Lake Landfill, but toxicity was not shown at this location. The reference site is adjacent to US Highway 64 where road runoff, a significant source of PAHs (Eisler 1987a), may occur. This location also had high concentrations of Pb in the sediments and porewater, which is consistent with proximity to a highway (Harrison et al. 2003). Total PAHs in the sediments did not exceed the SQG (1.61 μg/g dry weight) (MacDonald et al. 2000) at any location, although total concentrations surpassed 1 μg/g dry weight at CD1, CD3, and ELRef. Individual PAHs (anthracene, fluoranthene, phenanthrene, and pyrene) exceeded SQGs at several locations. Alkanes (aliphatic hydrocarbons) were ubiquitous in the sediment samples collected around the landfills. Paraffins (straight-chain hydrocarbons common in the environment and also present in petroleum products) have relatively low toxicities and would not be expected to adversely impact aquatic systems at the concentrations measured in this study. Individual or total PAHs were not significantly correlated with survival or length of H. azteca exposed to the sediments or porewater (Table 4). Other chemicals, such as volatile compounds (benzene, toluene, ethylbenzene, and xylene), priority pollutants, and industrial chemicals may have been present in the landfill leachate but were not included in the chemical analyses.

Bioaccumulation study

Four of the sediments that demonstrated acute and/or chronic toxicity, plus a reference sediment (CD1, CD3, CD5, EL1, and ELRef), were further assessed through an evaluation of biological uptake of contaminants by L. variegatus during a 28-d bioaccumulation study (Table 8). Residue concentrations of contaminants in oligochaetes from the laboratory cultures were used as the baseline reference. For field comparisons, the sediment from the reference site located at ELRef was used. With the exception of B, Mo, and V, metal residues in the oligochaetes increased during the 28-d exposure to the sediments when compared with metal levels measured in the culture animals. Increases in concentration varied with each metal, but most ranged between 2 and 4 times higher, and some increased over 20 times (Al and As). Concentrations of metals were also generally lower in oligochaetes exposed to the ELRef sediment than in animals exposed in sediments from other locations, with the exceptions of Mg, Pb, and Sr. Metal residues were generally highest in the oligochaetes exposed to sediments from sampling location CD1. Sediment from CD1 also had the highest concentrations of metals (Table 5). Bioaccumulation factors, calculated as the ratios of concentration of metals (w/w) in the oligochaetes and concentrations in the sediments, were highest for As (0.7:2.7), Ba (0.9:2.5), Cu (1.4:3.4), Se (2.3:8.2), Sr (1.3:2.7), and Zn (3.3:7.6). Mercury, a heavy metal that bioaccumulates and biomagnifies (Eisler 1987b) was present in the sediments and at levels exceeding SQGs at several of the locations (Table 5), but uptake by the oligochaetes was insignificant (i.e., residues were at or below analytical detection levels).

Uptake of organic contaminants from the sediments by L. variegatus was limited to a few PAHs; however, aliphatic hydrocarbons were not included in analytical testing of oligochaete tissues (Table 9). Concentrations were low and the bioaccumulation factors for the various PAHs ranged from 0 to 6. Perylene bioaccumulated in oligochaetes at all locations except ELRef; bioaccumulation factors ranged from 2.28 to 5.25. Total PAHs in oligochaetes were highest at CD1 (1.2 μg/g), with residues at the other locations reaching only about half of this total level. The significance of PAH residues and bioaccumulation factors for aquatic organisms or wildlife are not known (Eisler 1987a). The limited bioaccumulation of organic contaminants by the oligochaetes probably reflects the relatively low concentrations present in the sediments, but their presence in the sediments and bioaccumulation does raise concern that the potential exists for transport of contaminants from both landfills that could result in further impairment of sediment and habitat quality.

The accumulation of some metals may be influenced by the organism's ability to regulate them (Rainbow 1996). Essential elements (e.g., As, Cu, Cr, Ni, Se, and Zn) are often regulated in tissues and organs (Miller and Hendricks 1996; Borgmann and Norwood 1997). Low doses are beneficial and are often needed physiologically, but at higher concentrations, essential elements can be detrimental or toxic to the organisms. Just as importantly, some organisms may bioaccumulate these contaminants to relatively high levels without significant adverse effects, but the levels that accumulate in tissue may exceed biological-effects levels for animals that feed upon them. Interpretation of the significance of body residues and the level of bioaccumulation shown in these tests is not clear cut, but the fact that there was accumulation above baseline levels suggests the availability of these contaminants and the potential for adverse biological impacts.

Environmental significance of tests

The routes of exposure may also be important in understanding the potential impact of contaminants to the organisms. Potential sources of contaminants to the aquatic organisms are ingestion of the sediments directly, the overlying water, and the sediment porewater (Power and Chapman 1992). Ingestion of the sediments and sediment organic matter is the most likely route of contaminant exposure to organisms such as L. variegatus that burrow and feed in the sediment. However, some organisms can also be adversely affected through direct exposure to the sediment and sediment porewater whereas others, especially those that reside in the water column, may take up the contaminants from the overlying water. During this study, the sediments did not appear to elicit an adverse response by L. variegatus, but a number of metals bioaccumulated through exposure to the sediments (Table 8). Growth of H. azteca (an epibenthic organism that occasionally burrows into the sediments but also spends time in the water column) was reduced in sediments from several locations. One or more of the metals, as well as PAHs, in the solid-phase sediment or porewater tests could have contributed to the toxicity elicited (Tables 1, 5, and 6). Direct exposure of H. azteca to porewater isolated from sediment from several locations also elicited a toxic response. Elevated concentrations of metals could have contributed to the observed toxicity, although alkalinity and ammonia may also have been confounding factors.

Concentrations of metals and PAHs that exceeded specific guidelines or criteria have a high probability of being responsible for the toxic responses shown by H. azteca exposed to sediment and porewater. The environmental impact or significance of these contaminants in the sediments from the canals located down-gradient from the landfills can only be inferred from the multiple lines of evidence shown by the laboratory evaluations. The demonstration that the sediments elicited toxic reactions in test organisms and that contaminants were bioaccumulated from these sediments provides strong support for these inferences. The comparison of contaminant concentrations in the sediments and pore-waters, in addition to the residues taken up by the oligochaetes during the bioaccumulation study, with SQGs and protection levels is further evidence that habitat quality at several locations receiving drainage from the landfills has been impaired (Table 10). Of particular significance is the number of metals (As, Cu, Hg, Ni, and Zn) and PAHs (anthracene, fluoranthene, phenanthene, and pyrene) that exceed SQGs (Tables 5 and 7). Water quality criteria and aquatic-life protection levels were also exceeded by As, Cr, Cu, Pb, Se, and Zn in the porewater (Table 6). An assessment conducted in October 2000 of the benthic macroinvertebrate communities in canals associated with the landfills also revealed evidence of biological impairment immediately down-gradient from the C/D Landfill near location CD-2 (North Carolina Division of Water Quality 2000). This information provides additional evidence of contaminant effects on aquatic resources situated down-gradient from the landfills.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

Habitat quality, as demonstrated by multiple lines of information developed as part of a sediment quality assessment, has been reduced at several locations down-gradient from the 2 landfills adjoining Alligator River NWR. Elevated concentrations of contaminants, primarily metals, in the sediments appear to be implicated in the acute and chronic toxicity measured in solid-phase sediment and porewater testing. PAHs were also present in the sediments and concentrations from several individual PAHs exceeded SQGs and bioaccumulated in test organisms, demonstrating the bioavailability of several metals and PAHs in the sediments. Metals, mainly As, Cr, Cu, Pb, Se, and Zn, were elevated, and levels exceeded sediment and water quality guidelines at several locations. The bioavailability of these metals in the sediments was demonstrated by their uptake during the bioaccumulation study. Although habitat impairment is not currently extreme and appears to be limited to down-gradient areas located closest to the landfills, these evaluations have shown that runoff of leachate from the 2 landfills has reduced habitat quality in canals and has the potential, especially if surface runoff is allowed to continue, to impact biota inhabiting down-gradient aquatic environments. These impacts could include acute and chronic toxicity as well as food-chain impacts. Impacts at the East Lake Landfill appear limited in scope and the facility is now closed. Changes in existing management are not recommended at this facility. Contamination of canals draining the active C/D Landfill, however, is a concern and efforts to reduce, eliminate, or isolate surface discharge from this landfill are recommended for the future protection of wildlife resources associated with Alligator River NWR.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References

This work was supported by the U.S. Fish and Wildlife Service under Intra-Agency Agreement Number 41630–0-N082 and Division of Environmental Quality Study Identifier 200040002.1. The authors wish to acknowledge Charles Mathis who assisted with sample collection.


  1. Top of page
  2. Abstract
  7. Acknowledgements
  8. References
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