risk assessment of water quality in three north carolina, usa, streams supporting federally...

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Environmental Toxicology and Chemistry, Vol. 26, No. 10, pp. 2075–2085, 2007� 2007 SETAC

Printed in the USA0730-7268/07 $12.00 � .00

Contaminant Sensitivity of Freshwater Mussels

RISK ASSESSMENT OF WATER QUALITY IN THREE NORTH CAROLINA, USA,STREAMS SUPPORTING FEDERALLY ENDANGERED FRESHWATER MUSSELS

(UNIONIDAE)

SARA WARD,*† TOM AUGSPURGER,† F. JAMES DWYER,‡ CINDY KANE,§ and CHRISTOPHER G. INGERSOLL�†U.S. Fish and Wildlife Service, P.O. Box 33726, Raleigh, North Carolina 27636

‡U.S. Fish and Wildlife Service, 101 Park DeVille Drive, Suite A, Columbia, Missouri 65203§U.S. Fish and Wildlife Service, 6669 Short Lane, Gloucester, Virginia 23061

�U.S. Geological Survey, Columbia Environmental Research Center, 4200 New Haven Road, Columbia, Missouri 65201

(Received 7 November 2006; Accepted 9 April 2007)

Abstract—Water quality data were collected from three drainages supporting the endangered Carolina heelsplitter (Lasmigonadecorata) and dwarf wedgemussel (Alasmidonta heterodon) to determine the potential for impaired water quality to limit therecovery of these freshwater mussels in North Carolina, USA. Total recoverable copper, total residual chlorine, and total ammonianitrogen were measured every two months for approximately a year at sites bracketing wastewater sources and mussel habitat.These data and state monitoring datasets were compared with ecological screening values, including estimates of chemical con-centrations likely to be protective of mussels, and federal ambient water quality criteria to assess site risks following a hazardquotient approach. In one drainage, the site-specific ammonia ecological screening value for acute exposures was exceeded in 6%of the samples, and 15% of samples exceeded the chronic ecological screening value; however, ammonia concentrations weregenerally below levels of concern in other drainages. In all drainages, copper concentrations were higher than ecological screeningvalues most frequently (exceeding the ecological screening values for acute exposures in 65–94% of the samples). Chlorineconcentrations exceeding the acute water quality criterion were observed in 14 and 35% of samples in two of three drainages. Theecological screening values were exceeded most frequently in Goose Creek and the Upper Tar River drainages; concentrationsrarely exceeded ecological screening values in the Swift Creek drainage except for copper. The site-specific risk assessment approachprovides valuable information (including site-specific risk estimates and ecological screening values for protection) that can beapplied through regulatory and nonregulatory means to improve water quality for mussels where risks are indicated and pollutantthreats persist.

Keywords—Freshwater mussels Stream monitoring Site-specific standards Ecological risk assessment Wastewatertreatment plant

INTRODUCTION

The decline of freshwater mussels (family Unionidae) inNorth America has been well documented [1,2]. Habitat al-teration, competition from exotic species, overuse, disease,predation, and pollution are considered causal or contributingfactors in many areas of the United States [3,4], particularlyin the eastern states [5,6]. In North Carolina, resource agenciesare working to recover six species of freshwater mussels fed-erally listed as endangered. Impaired water quality is a poten-tial limiting factor in the recovery of imperiled mussel species.Toxic substances were one of the top five stressors cited aslimiting freshwater mussels in a recent survey of experts forthese taxa [7]. A separate review identified water quality deg-radation and habitat alteration as the most likely causes offreshwater mussel declines [8].

Several studies indicate that early life stages of freshwatermussels are among the most sensitive aquatic organisms testedfor the effects of inorganic chemicals, including copper [9–11] and ammonia [12–14]. Results of recent toxicity tests re-

* To whom correspondence may be addressed(sara�[email protected]).

This paper has been reviewed in accordance with U.S. Fish andWildlife Service and USGS policies; the publication does not implyofficial Departmental endorsement of the findings presented here.

ported in this series [15–17] confirm the sensitivity of musselglochidia and juveniles to acute and chronic copper and am-monia exposures. Genus mean acute values (GMAVs) forfreshwater mussels are frequently lower than values for themost commonly tested species of fish or other aquatic inver-tebrates included in the acute databases for derivation of U.S.Environmental Protection Agency (U.S. EPA) ambient waterquality criteria (WQC) for ammonia and copper [14,18].

In-stream exposure of freshwater mussels to copper andammonia can be substantial, and in some cases, concentrationsexceed harmful concentrations. Although mussels do not ap-pear to be uniquely sensitive to chlorine [16,19], exposure tochlorine in excess of WQC [20] and North Carolina state waterquality standards could occur downstream of outfalls.

Because little or no water quality monitoring data are avail-able for many important mussel habitats, the extent to whichwater quality is a limiting factor to mussel recovery efforts isuncertain. The focus of this study was to collect water chem-istry data in three drainage basins in North Carolina supportingmussel species of concern to determine potential risks. Eco-logical screening values (ESVs) included criteria maximumconcentrations (CMCs) and criteria continuous concentrations(CCCs) for each contaminant of concern to develop hazardquotients (HQs) for quantifying the risks associated with mus-

2076 Environ. Toxicol. Chem. 26, 2007 S. Ward et al.

sel exposure to these chemicals. For ammonia and copper,recent mussel toxicity data were added to U.S. EPA criteriadatabases to derive estimates of chemical concentrations pre-dicted not to be toxic to mussels (adjusted to local pH con-ditions for ammonia and to local hardness conditions for cop-per) for acute (CMCFM) and chronic (CCCFM) exposures[14,18]. Because mussel species appear to be of intermediatetolerance to chlorine [16,19], derivation of special ESVs formussel protection was not needed and federal WQC were usedas ESVs.

METHODS

Site description

Study streams were selected on the basis of the presenceof occupied habitat for two federally listed mussel species andpermitted wastewater discharges. Water quality conditions inthree drainage basins were evaluated. Goose Creek (Mecklen-burg and Union Counties, NC, USA) in the Pee Dee Riverbasin is one of only two small streams in North Carolinaoccupied by the endangered Carolina heelsplitter (Lasmigonadecorata). Existing ambient chemistry data for this watershedwere largely limited to a single station located near the head-waters and upstream of several small wastewater treatmentplants and nonpoint pollutant sources. Data from that stationand altered benthic macroinvertebrate community structure ledto Clean Water Act section 303(d) listing of this creek asimpaired on the basis of nonattainment of the designated aquat-ic life use [21,22]. One of the two best remaining habitats forthe dwarf wedgemussel (Alasmidonta heterodon) in NorthCarolina occurs in the upper Tar River drainage basin (Gran-ville, Vance, and Franklin Counties, NC, USA). Although wa-ter quality in the vicinity is rated as good by the North CarolinaDivision of Water Quality (NCDWQ), a 3.5 million gallon perday permitted discharge from a municipal wastewater treat-ment plant has been a concern. Also, Swift Creek (Wake andJohnston Counties, NC, USA) in the Neuse River basin is animportant stream for the dwarf wedgemussel. Four minor dis-charges are located in this drainage. Ammonia, copper, andchlorine are primary constituents of concern for freshwatermussels that are associated with these wastewater discharges.

Goose Creek in the Yadkin–Pee Dee River basin is ap-proximately 20 km southeast of Charlotte, North Carolina,whereas the Tar River drainage is approximately 40 km northof Raleigh, North Carolina, and the Swift Creek sites are ap-proximately 25 km southeast of Raleigh. Sample sites on eachstream reach were selected on the basis of accessibility andproximity to known sources of contamination (e.g., wastewatertreatment plants). Goose Creek is characterized by a substrateof bedrock and rubble and is susceptible to low flow duringdry periods. Sampling was conducted at five sites bracketingdischarges from six small municipal wastewater facilities. Thedrainage area above the Goose Creek sampling station locatedfarthest downstream is 62 km2. The five sample sites alsoprovide additional resolution to the NCDWQ long-term mon-itoring site in the basin (station Q8360000 at State Road 1524near Mint Hill) with our sampling points in this stream locatedapproximately 0.16 and 2.5 km upstream and 1.1, 3.8, and14.1 km downstream. Sites in the upper Tar River were selectedto examine the influence of a 3.5 million gallon per day mu-nicipal discharge to Fishing Creek, a tributary to the Tar Riverwith a drainage area of 123 km2. The five sample sites in thisarea included three sites in Fishing Creek (one located 75 mupstream and two located 75 m and 8.5 km downstream of

the discharge) and two sites in the Tar River (located 2 kmupstream and 1.2 km downstream of the Fishing Creek con-fluence). Although located in a separate river basin, the upperTar River watershed, like Goose Creek, is susceptible to sea-sonal low flow because of limited groundwater recharge. Thedrainage area above the sampling site farthest downstream inthe Tar River is approximately 430 km2. These five samplingsites provide additional spatial resolution to NCDWQ long-term monitoring stations O0100000 (at Highway 96 near TarRiver, colocated with our upstream Tar River sampling point)and O0600000 (Fishing Creek at State Road 1463 near Clay,colocated with our Fishing Creek sampling point just abovethe confluence with the Tar River). The Swift Creek study areaencompassing our sampling sites drains a watershed area ofapproximately 300 km2. Five monitoring locations in the SwiftCreek drainage included two sites in White Oak Creek (onefour km upstream and one km downstream of a small dis-charge) and three sites on Swift Creek (one �1.5 km abovethree small discharges and two located 7 and 28 km down-stream of the discharges). The long-term monitoring site (sta-tion J4510000) at Highway 42 near Clayton was colocatedwith our Swift Creek sampling point downstream of three smalldischarges.

Environmental exposure concentrations

Samples were collected every two months for one year fromJune 2002 to July 2003. Physiochemical parameters (dissolvedoxygen, temperature, and pH) were determined at each site byuse of an in situ dissolved oxygen probe (model 51B, YSI,Yellow Springs, OH, USA) and a pH meter (model 955, FisherScientific, Hampton, NH, USA). For all parameters, grab sam-ples were collected at least 3 m away from the bank towardmidchannel. No attempt was made to avoid storm flows, butthe majority of the samples were collected during base flowconditions.

Grab samples for total ammonia were collected in chemi-cally cleaned 125-ml polyethylene bottles and acidified withconcentrated H2SO4 to pH �2. Samples were stored on ice (at�4�C) in the field and shipped overnight to the U.S. GeologicalSurvey’s Columbia Environmental Research Center (USGS-CERC, Columbia, MO, USA) for analysis. Total ammonia wasmeasured by an ion electrode method following protocols de-scribed in method 4500-D [23]. Quality control for ammoniameasurements included analyses of reagent blanks, duplicateanalyses, and independent calibration verification standards(ICVSs) with each group of samples. The method detectionlimit (MDL) was 0.04 mg/L, and the method quantitation limitwas 0.13 mg/L ammonia (computed as 3.3 times the MDL).All ammonia results presented are for total ammonia as nitro-gen unless otherwise noted. Reagent blanks for ammonia anal-yses were �0.04 mg/L. Percent recovery of 1.0 and 10 mg/Lammonia ICVSs run with each batch of samples ranged from93 to 105%. The relative percent difference for analyses ofduplicate samples averaged 8% (range 0–48%, n � 12).

Grab samples for copper analyses were collected unfilteredin chemically cleaned 125-ml polyethylene bottles and storedon ice for overnight delivery to USGS-CERC. Copper sampleswere acidified upon receipt with Ultrex HNO3 (1%, v/v; J.T.Baker, Phillipsburg, NJ, USA). The samples were digested withnitric acid, and digestates were analyzed for total recoverablecopper by inductively coupled plasma mass spectrometry. Acalibration blank and an ICVS were analyzed every 10 samplesto confirm the calibration status. Calibration curves included

Assessment of water quality risks to freshwater mussels Environ. Toxicol. Chem. 26, 2007 2077

5-, 10-, and 20-�g/L standards and any sample or digestateover the upper calibration standard was automatically diluted10 times via a Cetac ASD-500 autodiluter (CETAC Technol-ogies, Omaha, NE, USA) in a serial fashion until concentra-tions were within the confines of the standard line. Massesmonitored included Cu63 and Cu65 and were selected for re-porting on the basis of least interferences, which varied fromone sample batch to another. For digestion, quality controlincluded digestion blanks, a reference solution, sample rep-licates, and sample spikes. For inductively coupled plasmamass spectrometry analysis, quality control included repeatedanalysis of calibration blanks and standards throughout therun, laboratory control samples, analytical duplicates, andspiked samples. The MDL ranged from 0.38 to 1.70 �g/L, andthe method quantitation limit ranged from 1.25 to 5.61�g/L. All copper results are reported as total recoverable unlessotherwise noted. Reagent blanks for copper were �1.7 �g/Lin 18 of 19 blanks (2.28 �g/L in one blank). Percent recoveryof 15 �g/L ICVSs (n � 33) run with each batch of samplesranged from 96 to 103%. Recoveries from a reference solutiondigested and analyzed for copper ranged from 98 to 105% (n� 5). Analytical precision for inductively coupled plasma massspectrometry was determined by analyzing samples in tripli-cate during the instrumental run and determining the relativepercent differences, which averaged 11% (range 3.4–26%, n� 6).

Samples for chlorine analyses were collected in amber glassbottles and were analyzed immediately on site. The high re-activity and volatility of chlorine make accurate measurementa challenge, particularly in field applications in which a 15-min holding time is limiting [24]. Chlorine was measured astotal residual chlorine and was determined with a HACH DR/2010 spectrophotometer (Loveland, CO, USA) according toU.S. EPA method 4500-Cl E G (N,N-diethyl-p-phenylenedi-amine) and HACH method 10014 (total chlorine, ultra-lowrange for treated wastewater). A MDL of 5.7 �g/L chlorinewas determined from repeated measures of 10 �g/L chlorinestandards (prepared with deionized water) according to U.S.EPA protocol [25]. Quality assurance/quality control includedanalyses of blanks, a series of chlorine standards, and duplicateanalyses for all field applications. Reagent blanks for chlorineanalyses were �5.7 �g/L. Accurate (coefficient of determi-nation from calibration curves averaging 0.996) and precise(relative percent differences for duplicates ranging from 1.9to 29% and averaging 14%) measurements of chlorine over arange of 6 to 300 �g/L were achieved in the field.

Additional site-specific ammonia (n � 136) and copper (n� 512) data were obtained from the NCDWQ ambient mon-itoring stations in the upper Tar River (stations O0100000 andO0600000), Goose Creek (Q8360000), and Swift Creek(J4510000) (http://www.epa.gov/storet/). Chlorine is not rou-tinely monitored at these sites. Monthly results were obtainedfor the period of record for each station. The MDLs forNCDWQ datasets were 0.02 mg/L for ammonia and 2 �g/Lfor copper. Ambient ammonia data were culled to excluderesults before July 2001 when nutrient analytical optimizationby NCDWQ occurred to address uncertainties associated withearlier results (C. Brower, NCDWQ, Raleigh, NC, personalcommunication). Copper results for the period of record ateach station were used in the assessment (ranging from 1985to present).

Statistical Analyses

All ammonia, copper, and chlorine concentrations for eachsite were analyzed for goodness of fit to a normal distributionby the Shapiro–Wilk test (JMP 5.1.2, SAS Institute, Cary, NC,USA). Only copper data for Swift Creek fit a normal distri-bution. Log transformations produced data fitting a normaldistribution for less than half of the other datasets (whichtended to be positively skewed as a result of a few high con-centrations). Consequently, nonparametric summary statisticsare reported for ammonia, copper, and chlorine, including themedian, 10th, and 90th percentiles, range of concentrations,and frequency of detection. The use of percentiles negated theneed for any manipulation of results below detection limits inreporting summary statistics and in deriving the HQs.

Ecological risk assessment

An HQ approach was used to assess risks to freshwatermussels associated with surface water exposure to contami-nants of concern. Water quality data from this assessment andthe NCDWQ database were screened against ESVs includingpreviously recommended guidance for the protection of fresh-water mussels [14,18] for ammonia and copper and WQC [26]for chlorine. Augspurger et al. [14] and March et al. [18] usedrecent freshwater mussel toxicity data to expand databases inthe U.S. EPA criteria documents [27,28] for these parameters,allowing recalculation of acute water quality guidance (or acriteria maximum concentration for freshwater mussels[CMCFM]) and calculation of chronic water quality guidance(or freshwater mussel criteria continuous concentration[CCCFM]) by applying acute to chronic ratios to the acute da-tasets. Although a state action level for copper (7 �g/L) anda standard for chlorine (17 �g/L) are available [29], we didnot use these values for risk screening because they do notaddress acute and chronic exposures and, for copper, mightnot be protective of mussels. Throughout this paper, ESVs referto site-specific CMCFM and CCCFM values for ammonia andcopper and CMC and CCC values presented in the WQC forchlorine [26].

The toxicity of ammonia varies strongly with pH; therefore,the equations in the 1999 U.S. EPA criteria document [27]were used to adjust the acute and chronic estimates of con-centrations that should not harm mussels for site-specific pHconditions. The 90th percentile pH value from each drainagebasin for the period of record was selected to recalculate site-specific acute mussel protection guidelines. Because ammoniatoxicity increases with increasing pH, concentrations of am-monia established to be protective at the upper end of the pHrange will be protective at any lower pH. When paired am-monia and pH values at a given station were available, pH-specific screening values were also determined for each sam-pling event. The toxicity of copper varies strongly with hard-ness; therefore, the equations in the 1996 U.S. EPA criteriadocument [28] were used to adjust the acute and chronic es-timates of concentrations that should not be toxic to musselsfor hardness previously observed in each stream on the basisof NCDWQ datasets. In the recently published 2007 U.S. EPAupdated aquatic life criteria for copper [30], the hardness-dependent criteria (serving as the basis for development of thesite-specific CMCFM and CCCFM values developed in thisstudy) have been updated with a biotic ligand model (BLM)approach. Water quality information for several parametersrequired to run the BLM (e.g., dissolved organic carbon, dis-solved metal concentrations, hardness) are not available for


Table 1. Concentrations of contaminants measured in three North Carolina, USA stream segments supporting federally-listed freshwater mussels:Tar River (Granville, Vance, and Franklin Counties), Goose Creek (Union County), and Swift Creek (Wake and Johnston Counties)a

Drainage basin

This study

Ammonia(mg/L)

Copper(�g/L)

Chlorine(�g/L)

State ambient monitoring datasetb

Ammonia(mg/L)

Copper(�g/L) pH (SU)c

Hardness(mg/L asCaCO3)

Tar Rivern 30 30 20 55 299 524 242FOD (%)d 83 90 40 67 65 100 99Median 0.06 2.8 �5.7 0.02 3.1 6.9 36Min �0.04 �0.82 �5.7 �0.02 �2.0 5.7 5Max 2.5 7.9 290 0.25 70 8.0 18010th percentile �0.04 1.1 �5.7 �0.02 �2.0 6.4 2390th percentile 0.14 6.0 58 0.05 8 7.4 57

Goose Creekn 34 34 29 52 87 137 65FOD (%) 100 100 31 92 83 100 100Median 0.13 4.5 �5.7 0.12 3.7 7.2 44Min 0.05 1.9 �5.7 �0.02 �2.0 5.9 22Max 3.8 84 210 15 26 9.8 8210th percentile 0.06 2.3 �5.7 0.02 �2.0 6.6 3490th percentile 0.87 13 35 1.3 8.4 8.0 65

Swift Creekn 31 31 25 29 126 248 108FOD (%) 84 77 28 97 51 100 99Median 0.07 1.4 �5.7 0.05 2.7 6.9 24Min �0.04 �0.82 �5.7 �0.02 �2.0 4.4 12Max 0.45 4.4 14 0.99 36 8.3 14010th percentile �0.04 �0.82 �5.7 0.02 �2.0 6.4 1890th percentile 0.18 2.8 6.8 0.07 8.2 7.2 39

a Concentrations were measured as total ammonia nitrogen, total recoverable copper, and total residual chlorine.b Summarized North Carolina Division of Water Quality ambient monitoring data (http://www.epa.gov/storet/).c SU � standard units.d FOD � frequency of detection (percent).

streams evaluated in this study, so we used the hardness-de-pendent equations from the 1996 copper criteria document [28]to derive site-specific guidelines for mussel protection. The10th percentile hardness value from each drainage basin forthe period of record was selected to recalculate site-specificacute guidelines for mussels. Concentrations of copper estab-lished to be protective at the lower end of the hardness rangeshould be protective at any higher hardness.

An assessment of ecological risk was performed by cal-culating HQs from the ratio of measured exposure concentra-tions to our ESVs for copper, ammonia, and chlorine. The HQsexceeding unity were used to indicate elevated risk. The max-imum exposure concentration from our dataset was used in theHQ derivation; this conservative approach was used given thesmall dataset (resulting from bimonthly sampling) and the ap-parent sensitivity of the species for which risks are being as-sessed.

RESULTS

Environmental exposure concentrations

Water chemistry data generated in this study are summa-rized in Table 1. Ammonia and copper were detected at allthree sites (detection frequency between 77 and 100%). Of the95 ammonia samples for all sites, only six of these sampleswere above 0.5 mg/L. Most of the elevated ammonia concen-trations were detected in Goose Creek (all stations), and themaximum concentration (3.8 mg/L) was found at a samplingstation located upstream of all point source discharges (butdowngradient of a livestock grazing area). Copper was �10

�g/L in all but seven samples from all sites, all of whichoccurred in Goose Creek where samples from all stations (in-cluding a site upstream of point sources) ranged from 11 to84 �g Cu/L during a January 30, 2003 collection. Field notesindicate that recent heavy rainfall contributed to a significantin-stream sediment load on that date; therefore, elevated cop-per levels were likely associated with suspended sediment.Chlorine was detected less frequently (28–40% of samples).Chlorine concentrations at one site on Fishing Creek and onesite on Goose Creek were exceedingly high (e.g., 2–15 timesthe acute WQC of 19 �g/L) relative to other results. Both sitesare located downstream of wastewater treatment plants, wheredischarge monitoring reports have indicated concerns regard-ing release of chlorine [31].

State ambient monitoring data for ammonia and copper arealso summarized in Table 1. Even though most monitoringsites used in this study are geographically distinct from stateambient monitoring stations (in each drainage, one or twosample sites are colocated with an ambient station and themaximum distance between sample sites and ambient stationsis 25 km), median ammonia and copper concentrations fromthe two datasets are similar. In particular, the state ambientmonitoring results and data generated in this study indicatethat concentrations of ammonia and copper in the Goose Creekdrainage are consistently greater than concentrations in theother streams.

Table 2 lists the site-specific ESVs for ammonia and copperlikely to be protective of freshwater mussels as adjusted withstream-specific pH and hardness. The pH-adjusted site-specific


Table 2. Site-specific estimates of pollutant concentrations likely tobe protective of freshwater mussels in the Tar River (Granville, Vance,and Franklin Counties), Goose Creek (Union County), and SwiftCreek (Wake and Johnston Counties) drainages in North Carolina,USA. The criteria maximum concentration for freshwater mussels(CMCFM) and criteria continuous concentration for freshwater mussels(CCCFM) for ammonia (mg/L total ammonia nitrogen) and copper (�g/L total recoverable copper) based on stream-specific pH and hardness

conditions, respectively

Drainage areaSitepHa

Sitehardnessa

Ammonia

CMCFMb CCCFM

c

Copper

CMCFMb CCCFM

c

Tar River 7.4 23 4.78 0.97 1.34 0.90Goose Creek 8.0 34 1.75 0.50 1.94 1.25Swift Creek 7.2 18 6.15 1.11 1.07 0.73

a Hardness data are mg/L as CaCO3. pH and hardness values are basedon the state ambient dataset 90th and 10th percentile values for periodof record, respectively (Table 1).

b A stream- and parameter-specific CMC obtained by substituting theCMCFM at pH 8 (for ammonia) [14] and hardness of 50 mg/L (forcopper) [18] into equations in criteria documents of the U.S. EPA[27, p 34, eqn. 11] and [28, p E-2] for ammonia and copper, re-spectively.

c Obtained by substituting the mean of estimated CCCFM values from0.3 to 0.7 mg/L total ammonia nitrogen at pH 8 and 25�C (0.5 mg/L as N) (for ammonia) into equation 12 [27] to determine a site-specific CCC for the 90th percentile pH value. For copper, hardness-specific CCC for the 10th percentile hardness value for each drainagearea obtained by substituting CCCFM at hardness of 50 mg/L intoequations in original criteria document [28, p E-2].

Table 3. Hazard quotients (HQ) derived for exposure concentrations of ammonia (mg/L total ammonia as nitrogen), copper (�g/L total recoverablecopper) and chlorine (�g/L total residual chlorine) using site-specific ecological screening values (ESVs)a in North Carolina, USA streams

supporting listed freshwater mussels

Ammonia

Tar River Goose Creek Swift Creek

Copper


Chlorineb


Current study resultsn 30 34 31 30 34 31 20 29 25Acute HQ 0.52 2.2 0.07 5.9 43 4.1 15 11 0.74Chronic HQ 2.6 7.6 0.41 8.8 67 6.0 26 19 1.3

State ambient dataset resultsn 55 52 29 299 87 126 N/A N/A N/AAcute HQ 0.05 8.6 0.16 52 13 34 N/A N/A N/AChronic HQ 0.26 30 0.89 78 21 49 N/A N/A N/A

a Hazard quotient calculated using maximum exposure concentration as numerator and appropriate site-specific criteria maximum concentrationfor freshwater mussels (CMCFM) and freshwater mussel criteria continuous concentration (CCCFM) values (ammonia and copper, Table 2) oraquatic life criteria of 19 (CMC) and 11 (CCC) �g/L (chlorine [26]) as denominator.

b No chlorine data were included in the state ambient monitoring dataset.

ammonia CMCFM and CCCFM values for freshwater musselprotection in these drainages ranged from 1.75 to 6.15 mg/Land 0.50 to 1.11 mg/L. Site-specific CMCFM and CCCFM valuesfor copper ranged from 1.07 to 1.94 �g/L and 0.73 to 1.25�g/L as a function of the 10th percentile hardness value ineach stream. Site-specific chlorine criteria for mussels werenot developed because the WQC of 19 �g/L [CMC] and 11�g/L [CCC] were considered protective of mussels.


Ammonia HQs exceeded 0 unity in Goose Creek (acuteexposure) and Goose Creek and Upper Tar River (chronicexposure) (Table 3). Elevated risks (as indicated by HQs �1.0)associated with in-stream ammonia concentrations were rel-atively infrequent with the exception of Goose Creek, where

the site-specific ESV for chronic exposures predicted to beprotective of mussels was exceeded in 15% of samples. Max-imum concentrations of ammonia in Goose Creek are approx-imately two to eight times higher than site-specific acute andchronic ESVs. Figure 1 illustrates the frequency that ESVswere exceeded in each drainage basin. On the basis of acuteammonia exposure risks in Goose Creek, event-specific am-monia CMCFM and CCCFM values were determined from bi-monthly sampling results (this study) and ambient monitoringdata (state dataset) and are presented in Figures 2 and 3, re-spectively. Because ammonia concentrations were generallybelow the ESVs in the Tar River and Swift Creek drainages,event-specific CMCFM and CCCFM values were not determinedfor these areas.

Copper risk to freshwater mussels in these areas is alsoindicated on the basis of acute and chronic HQs above unityat each site. In all drainages, copper concentrations exceededsite-specific ESVs for mussel protection (by up to 43 timesthe CMCFM and 67 times the CCCFM) for acute (65–94% ofsamples) and chronic (87–100% of samples) exposures. Themedian copper concentrations exceed the site-specific acuteand chronic ESVs at all three sites.

All chlorine results were below ESVs with the exceptionof multiple measurements at one site each in the Tar Riverand Goose Creek drainages. Chlorine concentrations above theESV for acute exposures were observed in 14% of the GooseCreek samples and 35% of the Tar River samples. Swift Creekchlorine concentrations exceeded the chronic ESV in 4% ofsamples. The chlorine levels measured on three separate oc-casions immediately downstream of a package wastewatertreatment plant outfall on Goose Creek exceeded the ESV foracute exposures by approximately three to 15 times (concen-trations were between 50 and 290 �g/L). Therefore, althoughchlorine concentrations were often low (as evidenced by me-dian concentrations below the MDL in all three drainages),maximum chlorine concentrations present potential risks tomussels locally in both acute and chronic exposures (on thebasis of HQs �10 at Tar River and Goose Creek sites).

Monthly ammonia concentrations reported in the state’s am-bient monitoring dataset exceeded site-specific acute andchronic ESVs in 10 and 17% of samples collected from GooseCreek, resulting in an acute HQ of 8.6 and a chronic HQ of30 (Table 3). Protective acute ammonia exposure concentra-


Fig. 1. Frequency that ecological screening values (ESVs) were exceeded in Tar River (TR, Granville, Vance, and Franklin Counties, NC, USA),Goose Creek (GC, Union County, NC, USA), and Swift Creek (SC, Wake and Johnston Counties, NC, USA) drainages supporting the endangeredCarolina heelsplitter (Lasmigona decorata) and dwarf wedgemussel (Alasmidonta heterodon). Ecological screening values included chemicalconcentrations predicted not to be toxic to mussels (adjusted to local pH conditions for ammonia and to local hardness conditions for copper,derived by adding recent toxicity data to U.S. Environmental Protection Agency criteria databases) for acute (CMCFM) and chronic (CCCFM)exposures (ammonia and copper, Table 2) and federal ambient water quality criteria of 19 (CMC) and 11 (CCC) �g/L for chorine. Percent ofsamples exceeding CMC (□) and CCC (�) values shown.

tions for mussels were not exceeded in the Tar River and SwiftCreek drainages. Ambient copper data reported by the stateindicate that site-specific copper ESVs for mussel protectionwere exceeded at all sites for both acute and chronic exposures(51–83% of samples). Accordingly, risk to mussels in theseareas is indicated on the basis of HQs for acute (ranging from�13 to 52) and chronic (ranging from �21 to 78) ESVs.

DISCUSSION

Derivation of site-specific water quality guidance forfreshwater mussel habitats

Review of chlorine toxicity data for freshwater musselsindicates unionids tested to date are not uniquely sensitive tothis common pollutant. The databases used by the U.S. EPAfor calculating current 1999 WQC for ammonia and 1996WQC for copper do not include data for unionids, a taxa sen-sitive to these pollutants; therefore, we derived local CMCFM

and CCCFM values using previously published data for mussels[14,18] and the U.S. EPA’s equations for parameter-specificcriterion adjustment [27,28] to assess risks to mussels asso-ciated with water quality conditions that occur in the streamswe evaluated.

Recently, additional data on the effects of ammonia onfreshwater mussels have become available [16,17], and a stan-dard method with recommendations for test acceptability [32]has been developed that can be used to re-evaluate the esti-mated ammonia concentrations that would not likely be toxicto freshwater mussels in acute and chronic exposures presentedin Augspurger et al. [14]. Although a thorough reexaminationof the data is beyond the scope of this study, we conductedthat analysis separately and determined that the acute andchronic ammonia recommendations from 2003 are still ac-ceptable.

Specifically, adding acute toxicity data for tests conductedsince 2003 [16] and applying the American Society for Testingand Materials standard guide (for test duration and test ac-ceptability) results in a dataset with 50 (vs 30 in 2003) 24- to96-h acute median lethal concentrations to calculate nine (vseight in 2003) unionid GMAVs. The estimated safe concen-tration in acute exposures derived from the revised dataset isslightly higher (2.98 vs 1.75–2.5 mg/L at pH 8) than the es-timate from 2003. Wang et al. [17] have also conducted three28-d exposures with three species of freshwater mussels andammonia (rainbow mussel [Villosa iris], fatmucket [Lampsilis


Fig. 2. Trends in ammonia concentrations in Goose Creek (Union County, NC, USA) based on a bimonthly sampling effort at five monitoringstations. Ecological screening values include chemical concentrations predicted not to be toxic to mussels (adjusted to local pH conditions derivedby adding recent toxicity data to U.S. Environmental Protection Agency criteria databases) for acute (CMCFM, �) and chronic (CCCFM, �)exposures. The CMCFM and CCCFM for ammonia are pH-dependent and vary based on station- and event-specific pH conditions.

siliquoidea], and oyster mussel [Epioblasma capsaeformis]).Endpoints included survival (foot movement) and growth(shell length). The chronic values (geometric mean of the low-est-observed-effect concentration and no-observed-effect con-centration) of �0.4, 0.4, and 0.7 mg/L ammonia for the threetests are within the range of safe concentrations estimated withacute data and acute:chronic ratios reported in Augspurger etal. [14] (0.3–1.0 mg/L ammonia at pH 8 and 25�C). Conse-quently, the 2003 estimates of safe concentrations for acuteand chronic exposures still appear useful for screening pur-poses (although estimates could be further improved throughchronic toxicity tests with additional mussel species).

In addition to the availability of recent toxicity data formussels, the 2007 revision for the WQC for copper was re-cently finalized [30] and replaces the hardness-dependentequations with a BLM approach for determining WQC. It wasnot possible for us to use the BLM for determining site-specificWQC because of insufficient data available for the drainagebasins evaluated; however, an analysis of the implication ofthe use of BLM-based criteria (vs the hardness-dependent ap-proach used here) was possible with data obtained from theUSGS National Water Information System database. Sufficientdata were available for water chemistry parameters needed torun the BLM (e.g., dissolved organic carbon, pH, temperature,major cations and anions) for one sampling event for SwiftCreek (site 02087580, July 2000) and one event for the TarRiver drainage (site 0208123850, July 2000); no relevant datafrom the Goose Creek drainage were available (http://waterdata.usgs.gov). For the July 2000 samples from eachdrainage basin, the BLM-based acute WQC for the Swift Creeksample was approximately six times higher than a CMCFM

calculated on the basis of estimated hardness conditions forthat site while the BLM-based acute WQC was seven timeshigher than the event-specific CMCFM. In this comparison, theBLM-based criteria are based on the 2007 revision database,which uses a much more limited mussel dataset than the oneused to derive local ESVs for mussel protection; however,recalculation of BLM-based WQC with the expanded musseldatabase is beyond the scope of this study. Because the BLMapproach for copper criteria derivation was recently finalized,use of the hardness-dependent approach for deriving site-spe-cific WQC is still appropriate because current methods forcopper WQC development have not yet been widely replacedby the new BLM approach.

Following the Augspurger et al. [14] guidelines, the esti-mated range of CMCFM (1.75–2.5 mg/L total ammonia nitrogenat pH 8) and CCCFM (0.3–1.0 mg/L total ammonia nitrogen atpH 8 and 25�C) was refined by identifying ammonia concen-trations within these ranges likely to be protective (minimumacute and mean chronic value). Copper guideline refinementincluded reassessment of the mussel taxa included in the tox-icity database used to derive CMCFM and CCCFM estimates(CMCFM values of 2.79 �g/L and CCCFM of 1.74 �g/L totalcopper at hardness 50 mg/L as CaCO3 [18]). A case could bemade for culling toxicity data for highly sensitive genera thatare not found locally; however, we included all mussel toxicitydata that met data quality objectives because other untestedmussel species occur in these areas and are of unknown sen-sitivity [18]. Identified CMCFM and CCCFM values for ammoniaand copper were used as the basis for parameter-specific re-calculation of guidelines to reflect local water quality condi-


Fig. 3. Trends in ammonia concentrations in Goose Creek (Union County, NC, USA) based on the state ambient monitoring dataset results(http://www.epa.gov/storet/). Ecological screening values include chemical concentrations predicted not to be toxic to mussels (adjusted to localpH conditions derived by adding recent toxicity data to U.S. Environmental Protection Agency criteria databases) for acute (CMCFM, ···)and chronic (CCCFM,- - - - - - - - -) exposures. The ammonia CMCFM and CCCFM values are pH-dependent and vary based on paired pH and ammoniaresults for each sampling date.

tions (pH and hardness) present in mussel habitats most of thetime.


The ESVs were exceeded relatively infrequently for am-monia and chlorine with a few exceptions; however, copperconcentrations routinely exceeded estimated site-specificguidelines for mussel protection. The HQs used in this as-sessment were derived with the use of maximum exposureconcentrations of ammonia, copper, and chlorine for screeningacute and chronic risks to mussels. A separate analysis wasperformed with HQs derived from less conservative medianexposure concentrations and resulted in maximum HQs forammonia and copper (across all drainages) that were 97 and95% lower, respectively, than the highest HQs calculated onthe basis of maximum exposure concentrations. The medianchlorine concentration was below the MDL in all drainages.With this less conservative approach for HQ calculation,chronic HQ values for copper remain above unity in all drain-ages whereas HQs for ammonia never exceed 1.0.

The ESVs for all three contaminants were exceeded mostfrequently in Goose Creek and the Upper Tar River drainages.Data collected for this study (which captured a drought summerin 2002) generally did not indicate seasonal trends except inGoose Creek, where the highest concentrations of ammoniaand chlorine occurred in summer months. Lack of rainfallduring the summer sampling periods likely concentrated con-taminants, particularly in the vicinity of point sources locatedin headwater streams where limited, if any, dilution capacity

was available. While the potential influence of nonpoint sourcepollution on receiving streams is uncertain and beyond thescope of this project, it is possible that nonpoint pollution loadswere reduced during the drought period because of limitedprecipitation and associated runoff. Some spatial trends werealso evident. In Goose Creek, copper concentrations were high-est on all but one occasion at sites downstream of the sametwo discharges, one of which was consistently associated withspikes in chlorine concentrations. In the Upper Tar River drain-age, copper and chlorine concentrations were frequently ele-vated downstream of a major wastewater treatment plant rel-ative to other sites and Fishing Creek (the receiving streamfor the discharge) copper concentrations exceeded those in theTar River on all but one occasion. In Swift Creek, a generaldecreasing trend in concentrations of ammonia and copper wasobserved moving downstream.

Although frequently detected in all three drainages (83–100% detection frequency), ammonia samples pooled from allsites exceeded their site-specific acute ESVs in only 2% of thesamples and exceeded their chronic ESVs in only approxi-mately 6% of samples. Even in Goose Creek, where ammoniaconcentrations were highest (median value of 0.13 mg/L am-monia—approximately double that of the other sites), the me-dian value was nearly four times lower than the chronic ESVfor mussel protection. Risks to mussels associated with themaximum measured concentrations were clear (HQ for chronicexposure of 7.6 on the basis of data from this study and 30on the basis of the state dataset). Risks were still indicatedwhen the less conservative 90th percentile ammonia value


(0.87 mg/L) was used for calculation of a chronic HQ of 1.7.It appears that the site-specific mussel ESVs derived in thisstudy for ecological risk screening purposes would be achiev-able most of the time if adopted as a site-specific water qualitystandard, with 15% (this study) to 17% (state dataset) of sam-ples exceeding safe chronic exposure concentrations in GooseCreek, and rarely exceeded in the other streams. When event-specific CMCFM and CCCFM values (calculated on the basis ofpaired pH and ammonia results for individual stations on eachsampling date) were used to screen risks associated with am-monia concentrations found in this study, acute ESVs werenever exceeded and chronic ESVs were exceeded twice (6%of samples) (Fig. 2). Ammonia concentrations at state ambientmonitoring stations exceeded acute (2%) and chronic (12%)event-specific ESVs (Fig. 3). Although ESVs derived with the90th percentile pH are protective most of the time, the use ofevent-specific CMCFM and CCCFM values provides a more spe-cific determination of risk as pH conditions fluctuate. In thiscase, ammonia exposure concentrations exceeded screeningvalues based on event-specific pH conditions less frequentlythan ESVs based on the 90th percentile pH value for chronicexposures. These concentrations exceeding site-specific ESVsindicate a need to reduce ammonia loads in Goose Creek. Risksto freshwater mussels associated with ammonia exposure inother streams evaluated were low; consequently, efforts tomaintain existing conditions should be adequate for protectionof mussels against excessive ammonia concentrations in TarRiver and Swift Creek drainages.

Site-specific hardness-adjusted copper ESVs for acute(1.07–1.94 �g/L) and chronic (0.73–1.25 �g/L) mussel pro-tection were frequently exceeded in all streams (Fig. 1), andstate monitoring datasets confirmed that copper concentrationsin these streams were frequently above concentrations of con-cern. The frequency that ESVs reported here were exceeded(65–100% in this study and 51–83% in the state dataset) is ofconcern and suggests that risks to mussels could be excessive;however, it is possible that concentrations exceeding ESVswere associated with suspended copper (i.e., that attached tosuspended sediment). No data for dissolved copper, the mosttoxic form to aquatic life, were available. It would be prudentto obtain these data in the future; they were not collected aspart of this effort because the state regulatory framework forcopper is based on unfiltered (total) copper [29].

The bioavailability and toxicity of particulate-bound copperto freshwater mussels is uncertain. Because mussels are filterfeeders, suspended copper could be a secondary pathway ofexposure and, therefore, could be an appropriate parameterwhen considering risk. Although the state regulatory frame-work for copper is based on total copper, estimating the con-tribution of dissolved versus suspended copper loads has meritgiven uncertainties about the bioavailability of particulate-bound copper. In the absence of dissolved copper data, esti-mating the dissolved fraction of copper on the basis of thetotal copper data presented here is a useful approach, albeitwith some uncertainty. Site-specific total suspended solids da-tasets for each drainage were obtained (http://www.epa.gov/storet/). With the use of U.S. EPA protocols [33,34], the geo-metric mean total suspended solids value for each drainagewas applied to a default partitioning relationship to develop asite-specific translator for estimating dissolved copper fromtotal copper. The dissolved copper fraction ranged from 0.36to 0.38. Estimated dissolved copper (based on paired totalcopper and total suspended solids results for the period of

record from state ambient datasets) exceed ESVs for acute(31–34% of results) and chronic (48–57% of results) expo-sures. Metal partitioning between the dissolved and particulatephases is highly variable and determined by many site-specificfactors (not accounted for in the partitioning equation used fordevelopment of translators here). A comparison of the 90thpercentile total copper value for each drainage to site-specificchronic ESVs indicates that the dissolved fraction would haveto compose just 9 to 15% of the total copper load for copperconcentrations to meet or stay below the ESVs 90% of thetime (e.g., greater than 85% of total copper would have to bebound to suspended solids to stay below the ESVs). The re-lationship between total copper and total suspended solids in-dicated that total copper concentrations could only partiallybe explained by total suspended solids (particularly in the Swiftand Tar drainages) as might be anticipated if copper sorptionto suspended solids was driving total copper loads. Therefore,the estimated frequency with which dissolved copper concen-trations exceed protective thresholds is uncertain, but on thebasis of in-stream total suspended solids loads it is likely thatdissolved copper concentrations alone present a risk to fresh-water mussels in these streams.

At two stations (one each on Goose Creek and FishingCreek), chlorine concentrations exceeded the acute ESV of 19�g/L (14% of the samples in Goose Creek and 35% of thesamples in Fishing Creek). At all sites, the median chlorinevalue was below the MDL of 5.7 �g/L indicating chlorinelevels are typically quite low. The magnitude of chlorine con-centrations above criteria and standards is of concern; maxi-mum chlorine concentrations in Goose Creek on multiple dateswere three to 12 times above the state standard (of 17 �g/L)[29]. Field observations during sampling events indicated thatthe flow above a Goose Creek station below a minor dischargewith a maximum detected chlorine concentration of 210 �g/L was essentially nonexistent during the drought conditionsexperienced in the summer of 2002 [35]. The limited dilutioncoupled with the elevated chlorine concentrations in thisstream lend credibility to concerns about the potential toxicityof chlorinated discharges on Goose Creek fauna, includingmussels.

To determine the extent of the receiving stream affected byelevated chlorine concentrations on one occasion (August 1,2002), several additional samples were collected along a down-stream gradient between this wastewater treatment plant (atapproximately 100, 300, and 400 m downstream of the facilitydischarge point) and the closest downstream discharger locatedapproximately 800 m downstream. Concentrations were belowthe MDL at all sample locations downstream of the outfallpool, with the exception of the site located approximately 300m downstream (where chlorine concentration was 43 �g/L).Elevated chlorine concentrations were also recorded on twooccasions (December 19, 2002, and July 23, 2003) in the upperTar River drainage area (at a station located �75 m down-stream of the wastewater treatment plant on Fishing Creekwith chlorine disinfection followed by dechlorination). Con-centrations approximately 10 m upstream of the dischargepoint were below the MDL at that time. During the December19, 2002, sampling event, an additional chlorine sample wasmeasured about 1 mile downstream of the discharge point, andno chlorine was detected.

Chlorine is highly volatile and its environmental persistencecan be influenced by several stream conditions, including tem-perature, turbulence, turbidity, and light penetration. With


chlorine concentrations exceeding the state chlorine standardup to 17-fold upgradient of stream segments supporting fed-erally listed mussels, further study is needed to evaluate theeffects of stream conditions on the persistence of this pollutantdownstream of known chlorine sources. The limited down-stream sampling effort reported here indicates that in-streamchlorine concentrations rapidly decrease with increasing dis-tance from a source; however, pooled areas with little turbu-lence or flow can continue to exhibit elevated chlorine con-centrations up to 300 m below an outfall. More rigorous datacollection will be necessary to assess the extent of potentialtoxic effects of chlorinated discharges in receiving streams. Itwould also be prudent to assess chlorine levels associated withvarious types of facilities (e.g., package wastewater treatmentplants, municipal wastewater facilities, water treatment plants)releasing chlorinated effluent in important freshwater musselhabitats.

Water quality conditions as a potential limiting factor inunionid survival and recovery

A site-specific risk assessment is a valuable tool in deter-mining to what extent recovery of listed mussels could belimited by water quality conditions. Water quality data col-lection in three North Carolina streams indicates that risksassociated with exposure to ammonia, copper, and chlorine aremost pronounced in the Goose Creek drainage. Copper con-centrations were above levels of concern for mussels in alldrainages; however, collection of dissolved copper samples isrecommended to further refine a risk estimate for these areas.Also, the toxicity of suspended copper to mussels should bedetermined to address existing uncertainty regarding the bio-availability of particulate-bound copper to mussels. Chlorineconcentrations were infrequently above levels of concern, andfurther study is needed to determine the extent of impacts onstreams when and where the magnitude with which ESVs areexceeded is periodically significant.

In areas such as Goose Creek, where pollutant risks areindicated and threats remain, the site-specific risk assessmentis intended as a tool to inform managers responsible for musselrecovery and water quality management. In areas where pol-lution risks are indicated, information from the site-specificrisk assessment (including local guidelines for protection andsite-specific risk estimates) can be applied through regulatoryand nonregulatory mechanisms (e.g., modified discharge per-mit conditions, local water quality management plans, or adop-tion of site-specific water quality standards) to promote pro-tective water quality conditions for mussels.

Acknowledgement—Funding for this project was provided in part bythe U.S. Fish and Wildlife Service Division of Environmental Quality(ID 200230003). Analytical support was provided by Tom May andDoug Hardesty at the USGS Columbia Environmental Research Cen-ter. Chris Mebane of the USGS Idaho Water Science Center providedassistance with biotic ligand modeling. Field assistance from DaleSuiter, Patty Matteson, Garland Pardue, and Mark Fowlkes is alsoappreciated. Two anonymous reviewers provided comments that im-proved the paper.

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