EPA 903-R-99-009
                              CBP/TRS 222-103
                              May 1999
    A Probabilistic Ecological
    Risk Assessment of Zinc
        in Surface Waters
of the Chesapeake Bay Watershed
     Chesapeake Bay Program

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A Probabilistic Ecological Risk Assessment
           of Zinc in Surface Waters
      of the Chesapeake Bay Watershed
                       May 1999
                   Chesapeake Bay Program
                  410 Severn Avenue, Suite 109
                  Annapolis, Maryland 21403
                     1-800-YOUR-BAY
                  http://www.chesapeakebay.net
      Printed by the U.S. Environmental Protection Agency for the Chesapeake Bay Program

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                                    May 1999
                                   Final Report

A Probabilistic Ecological Risk Assessment of Zinc in Surface Waters of the Chesapeake Bay
                                    Watershed
                               Lenwood W. Hall, Jr.
                                  Mark C. Scott
                                 William D. Killen

                              University of Maryland
                           Agricultural Experiment Station
                         Wye Research and Education Center
                                  P.O. Box 169
                            Queenstown, Maryland 21658

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                                       ABSTRACT




       The goal of this study was to conduct a screening level probabilistic ecological risk assessment




for zinc  in the  Chesapeake  Bay watershed  by using the following distinct  phases:  problem




formulation,  analysis and  risk characterization.   This  probabilistic ecological risk assessment




characterized  risk  by  comparing  the probability distributions  of environmental  exposure




concentrations with the probability distributions of species response data determined from laboratory




toxicity studies. The overlap of these distributions was a measure of risk to aquatic life. Cpmparative




risk from zinc exposure was determined for various basins in the Chesapeake Bay watershed.




        Zinc exposure data were available from  116 stations in 19 basins in the Chesapeake Bay




watershed from 1985 through 1996. Highest environmental concentrations of zinc (based on 90th




percentiles) were reported in selected locations in the Middle River, Potomac River, Choptank River




and Nanticoke River.  Sources of zinc responsible for these exposures can not be identified with




certainty but human activities associated with urban runoff, industrial/municipal effluents, antifouling




paints and non-point source  runoff (fertilizers) are likely candidates. As expected, the lowest




concentrations of zinc were reported in areas with the least amount of direct human activity such as




the lower mainstem Chesapeake Bay, Sassafras River and York River.




       The ecological effects data used for this  risk assessment  were derived  from zinc acute




laboratory toxicity tests conducted in both fresh and salt water.  Freshwater acute toxicity data for




zinc were standardized to a hardness of 50 mg/L to allow for accurate rankings of species sensitivity.




The 10th percentile (concentration protecting 90% of the species) for all species derived from  the




freshwater acute zinc toxicity data base was 142 ug/L. Within the acute freshwater zinc data base,




a 10th percentile of 212 ug/L was reported for the most sensitive trophic group (benthos) containing

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data from at least eight species. For acute saltwater zinc toxicity data, the acute 10th percentile for




all species v/as 79 ug/L. The lowest 10th percentile for the most sensitive trophic group within the




saltwater acute zinc data base was 10 ug/L for plants. The acute toxicity benchmarks described




above, with at least 8 data points by trophic group,  were used to characterize ecological risks for




zinc in the 19 basins where exposure data were available.




       Highest potential ecological risk from zinc water column exposures based on saltwater acute




effects for all species and the most sensitive trophic group (plants) was reported in the Middle River




area of the northern Chesapeake Bay watershed. Potential ecological risk from zinc exposure in the




Wye River was reported to be low when all species were considered but somewhat higher risk was




suggested when using the plant 10th percentile of 10 ug/L. However, based on the documented




recovery potential of plant  populations to episodic stressors this risk is still judged to be low.




Potential ecological risk from zinc water column exposure in the other 17 basins was either low or




data were lacking to assess ecological risk.

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                              ACKNOWLEDGMENTS
      We would like to acknowledge the U. S. Environmental Protection Agency's Chesapeake Bay




Program Office for funding this studythrough grant number CB993589010.  The "Toxics of Concern




Workgroup" of EPA's Toxics Subcommittee is also acknowledged for their support. The following




individuals are acknowledged for providing data: G. F. Reidel, J. R. Scudlark and B. Gruessner.
                                          111

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                              TABLE OF CONTENTS


                                                                            Bags
ABSTRACT	i

ACKNOWLEDGMENTS	 Hi

TABLE OF CONTENTS  	 iv

LIST OF TABLES 	vi

LIST OF FIGURES	,	vii

1.  INTRODUCTION	1
       1.1 Problem Formulation	2
             1.1.1 Stressor Characteristics	3
             1.1.2 Analysis of Exposure Data	3
             1.1.3 Analysis of Ecological Effects Data	4
             1.1.4 Risk Characterization	5
             1.1.5 Endpoints  	5
             1.1.6 Stressors Potentially Impacting Aquatic Communities 	6
             1.1.7 Conceptual Model	7

2. EXPOSURE CHARACTERIZATION 	8
       2.1 Introduction	8
       2.2 Zinc Loading in the Chesapeake Bay Watershed	8
       2.3 Chemical Properties of Zinc 	9
       2.4 Measured Concentrations of Zinc in the Chesapeake
         Bay Watershed	10
             2.4.1 Data Sources and Sampling Regimes	10
             2.4.2 Methods of Zinc Analysis	12
             2.4.3 Methods of Data Analysis  	13
       2.5 Measured Concentrations by Basin	15
       2.6 Temporal Trends	15
             2.6.1 Patuxent River	15
             2.6.2 James and Susquehanna Rivers 	16
       2.7 Summary of Exposure Data	16

3.  ECOLOGICAL EFFECTS	18
       3.1 Mode of Toxicity	18
       3.2 Methods of Toxicity Data Analysis	18
                                       iv

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      3.3 Effects of Zinc from Laboratory Toxicity Tests  	20
             3.3.1 Acute Toxicity of Zinc	,	21
             3.3.2 Chronic Toxicity of Zinc	22
      3.4 Mesocosm/Microcosm Studies	22
      3.5 Summary of Effects Data	23

4. RISK CHARACTERIZATION	24
      4.1 Characterizating Risks	24
      4.2 Risk Characterization of Zinc in the Chesapeake Bay Watershed  	25
      4.3 Uncertainty in Ecological Risk Assessment	26
             4.3.1 Uncertainty Associated with Exposure Characterization	27
             4.3.2 Uncertainty Associated with Ecological Effects Data	.,	29
             4.3.3 Uncertainty Associated with Risk Characterization 	31

5. CONCLUSIONS AND RESEARCH NEEDS	32

6. REFERENCES	35

  TABLES	51

  FIGURES	79

 APPENDICES

      Appendix A - Zinc risk characterization by basin

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                                    LIST OF TABLES




                                                                                      Bags



Table 1. Summary of 19 zinc data sources used for this risk assessment  	51




Table 2. Summary of zinc exposure data for all basins and stations.




        Maximum concentrations and 90th percentile values (minimum




        of four detected concentrations) are presented by station and basin	52




Table 3. Freshwater acute zinc toxicity data presented in order from most




        to least sensitive species 	56




Table 4. The 10th percentile intercepts for freshwater and saltwater zinc




       toxicity data by test duration and trophic group. These values represent




       protection of 90% of the test species  	66




Table 5. Saltwater acute zinc toxicity data presented in order from most to least




       sensitive species	67




Table 6. Freshwater chronic zinc toxicity data presented in order from most to




       least sensitive species	75




Table 7. Saltwater chronic zinc toxicity data presented in order from most to




       least sensitive species	77




Table S.The percent probability of exceeding the acute zinc




       freshwater or saltwater 10th percentile for all species and the percent




       probability of exceeding the acute 10th percentile for the most




       sensitive trophic group with n > 8 	78
                                            VI

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                                  LIST OF FIGURES




                                                                                   Rage




Figure 1. Ewlogical risk assessment approach	79




Figure 2. Location of the 116 stations where zinc was measured from 1985 to 1996.




        See key to map where stations are described	80




Figure 3. The zinc 90th percentile determined for basins with at least 4 detected




       concentrations	v	84




Figure 4. Seasonal pooled mean zinc concentrations and ranges (ug/L) from 15 stations




       during Patuxent River sampling (May 1995 to February 1996)  	85




Figure 5. Zinc measurements from the James River (1990 to 1993) 	86




Figure 6. 2inc measurements from the Susquehanna River (1990 to 1993) 	87




Figure 7. Distribution of acute zinc toxicity data (LC/EC 50s) for freshwater species	88




Figure 8. Distribution of acute zinc toxicity data (LC/EC 50s) for saltwater species	89




Figure 9. Distribution of chronic zinc toxicity data for freshwater species	90




Figure 10. Distribution of chronic zinc toxicity data for saltwater species	91
                                          Vll

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                                       SECTION 1
                                    INTRODUCTION

       The Chesapeake Bay Basinwide Toxics Reduction Strategy is a critical component of the

 1987 Chesapeake Bay Agreement that contains various commitments in areas such as research,

monitoring and toxic substance management that are directed to overall chemical reduction in the

Chesapeake Bay watershed (Chesapeake Bay Executive Council, 19S8). A specific commitment in

the Toxic Reduction Strategy is the creation of a Toxics of Concern List (TOC) for the Chesapeake

Bay. This TOC list was designed to: (1) prioritize over 1000  chemicals that may be impacting

aquatic life or human health in Chesapeake Bay by using a risk based ranking system and (2) direct

future research efforts and management.

       The first TOC list was completed in 1990 and was recently revised in 1996 (U. S. EPA,  1991;

U. S. EPA, 1996a). The proposed revised list is currently under review. The proposed revised TOC

list was developed  using a chemical ranking system that incorporates sources, fate, exposure and

effects of chemicals on Chesapeake Bay living resources and human health (Battelle, 1989).  The

TOC list contains both a list of primary toxics of concern as well as a secondary list (chemicals of

potential concern). For both the 1990 and 1996 TOC lists, zinc was identified  as a toxic of potential

concern.  Zinc is found naturally in the aquatic environment at low concentrations and is an essential

micronutrient for all living organisms. This metal enters the aquatic environment from both point and

non-point sources. Possible anthropogenic sources of zinc in the Chesapeake Bay watershed include

electroplaters, smelting and ore processors, mine drainage, domestic sewage, industrial effluents,

combustion of solid wastes, fossils fuels (e. g. coal fired power plants), road surface runoff, corrosion

of zinc alloys and galvanized  surfaces, antifouling paints, pesticides,  fertilizers and erosion of

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agricultural soils (Eisler, 1997).




       AlUhaugh zinc has been identified as a Toxics of Concern in the Chesapeake Bay watershed,




a quantitative probabilistic ecological risk assessment has not been conducted for this metal. The




objectives cf this study were to (1) quantify the probability and significance of potential ecological




effects from zinc water column exposure in the Chesapeake Bay watershed and (2) rank basins in




the Chesapeake Bay watershed from high to low probability of ecological risks based on zinc




exposures. Procedures described in the following documents were used for this risk assessment:




Report of the Aquatic Risk Assessment and Mitigation Dialogue Group (SET AC, 1994), the EPA




Framework for Ecological Risk Assessment (U. S. EPA, 1992),  a  paper entitled "An Ecological




Risk Assessment ofAtrazine in North American Surface Waters" (Solomon et al., 1996) and a recent




report entitled  "A  Screening  Level Probabilistic Ecological Risk Assessment of Copper and




Cadmium in the Chespeake Bay Watershed' (Hall et al., 1997b).




1.1 Probfiein Formulation




       The following distinct phases are included in this ecological risk assessment: Problem




Formulation, Analysis and Risk Characterization (Figure 1).  The problem formulation phase identifies




major issues to be addressed in the risk assessment and describes how analysis will be conducted. The




analysis phase reviews existing zinc data on exposure (environmental monitoring) and ecological



effects (laboratory toxicity studies). The risk characterization phase involves estimation of the




probability of adverse effects on aquatic populations and communities in potentially impacted areas




of the Chesapeake Bay watershed.




       The problem formulation phase of this risk assessment identified the following  major issues




to be addressed: stressor characteristics, exposure data, ecological effects data, risk characterization,

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endpoints, stressors impacting aquatic communities, and a conceptual model for risk assessment.




       1.1.1 Stressor Characteristics




       The chemical and physical properties of zinc are described in detail in the Exposure section




(Section 2) of this report. In the problem formulation phase of this risk assessment, the  solubility,




persistence in water and sediment and bioconcentration potential were considered critical.




       Zinc is a bluish-white metal that dissolves readily in strong acids and occurs in nature as a




sulfide, oxide or carbonate. Zinc and its salts are soluble  in water,  persistent and may bind to




particulates. Zinc mobility in aquatic systems is a function of the following factors: composition of




suspended and bed sediments, dissolved and  paniculate iron and manganese concentrations, pH,




salinity,  concentrations of complexing ligands and the concentration of zinc (U. S, EPA, 1987).




Aquatic biota bioconcentrate zinc in their tissues. Bioconcentration factors  (BCFs) as high as 1,130




for freshwater insects and 4,000,000 for saltwater scallops have been reported (Eisler, 1997).




       1.1.2 Analysis of Exposure Data




       Determining estimation of exposures  to aquatic biota is an  important part of the risk




assessment process for ecosystems. Environmental exposures (ECs) may be determined by using




actual measured concentrations from monitoring studies, derivations from highest exposure scenarios




and reasonable-high-exposure computer simulations (SETAC, 1994).   For deterministic ecological




risk assessments, the EC is expressed as a single value but the quantitative likelihood is unknown




because  a probabilistic approach has not been used to determine the  variability of  measured




environmental  concentrations. In recent years, an  approach has been endorsed that  estimates




exposures by taking natural variation into account by using distributions of ECs rather that single




point values (SETAC,  1994, Giddings et al., 1997). These probabilistic EC distributions can be used

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to estimate how frequently concentrations of a contaminant (e. g. zinc) exceed a given toxicity




benchmark (threshold) in the environment.




       The zinc exposure data used in this risk assessment were obtained from surface water




monitoring studies from 19 different data sources in the Chesapeake Bay watershed from 1985 to




1996 (116 stations). Most of the exposure data were collected from Maryland waters of the




Chesapeake Bay watershed (Figure 2).




       1.1.3 Analysis of Ecological Effects Data




       An analysis of toxicity data for risk assessment should cover the range of sensitivity of species




to the contaminant being evaluted. This is particularly true for contaminants that have receptor-




mediated modes of toxicity. Receptor-mediated modes of toxicity usually result in high toxicity to




organisms that possess the receptor system and lower toxicity in non-receptor organisms (e. g. plants




- receptor species - are more sensitive to herbicides than non-receptor species such as animals).




Toxicity data from sensitive  and non-sensitive species  should be used in  the characterization.




However,  calculation of  10th  percentiles for  the  most sensitive trophic group  is useful for




conservative determinations of risk and this conservative determination  assumes that protecting the




most sensitive species (taxonomic group) will also protect non-sensitive species (Giddings et al.,




1997).




       A comprehensive review and synthesis of the zinc aquatic toxicity literature was conducted




by using literature searches (AQUIRE etc.through 1997) and various review documents such as the




U. S. EP A water quality criteria reports (U. S.  EPA,  1987) and a recent review of zinc by Eisler




(1997).  These data were used to determine the distribution of sensitivity of aquatic species to zinc.




Limited mesocosm data were also reviewed to address issues of ecological interaction and population

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recovery.




       1.1.4 Risk Characterization




       This probabilistic risk assessment characterizes risk by comparing probability distributions of




environmental exposure concentrations with the probability distributions of species toxicity data  from




laboratory studies (SET AC, 1994).  The overlap of these distributions is a measure of potential risk




to aquatic life in the Chesapeake Bay watershed. The probabilistic approach for characterizing effects




and exposure has been suggested as a way to account for the range of species sensitivities to many




contaminants (SET AC, 1994). This approach has a number of advantages over a quotient method




(comparing the most sensitive species with the highest environmental concentrations) because it




allows, if not exact quantification, a least a strong sense for the magnitude and likelihood of potential




ecosystem effects of zinc in Chesapeake Bay.  An implied assumption of this approach is that




protecting a large percentage of species will also preserve ecosystem structure and function. The final




result of the risk characterization is expressed  as the probability that exposure concentrations of zinc




(within a defined spatial and temporal range) will exceed concentrations protective of aquatic life in




the Chesapeake Bay watershed.




       1.1.5 Endpoints




       Endpoints are critical measures used in ecological risk assessment. Two types of endpoints




defined in the Framework for Ecological Risk Assessment are assessment endpoints and measurement




endpoints (U. S. EPA, 1992). Assessment endpoints have  recognized  societial  value and are the




actual environmental values that are to be protected (e. g. fish populations). Measurement endpoints




are the measured responses to a stressor that can be correlated with or used to protect assessment




endpoints (Suter, 1990).  With each higher level of testing, measurement endpoints differ while

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assessment jndpoints remain the same.




       The assessment endpoints for this risk assessment are the long term viability of aquatic




communities in the Chesapeake Bay (fish, benthos etc.). Specifically, the protection of at least 90%




of the species 90% of the time (10th percentile from species susceptibility distributions) from acute




zinc exposure is the defined assessment endpoint. Measurement endpoints include all acute toxicity




data (survrral, growth and reproduction) generated from freshwater and saltwater laboratory toxicity




studies.




       LL6 Stressors Potentially Impacting Aquatic Communities




       When assessing the potential impact of zinc on aquatic communities in the Chesapeake Bay




watershed it is important to remember that both biotic (food quality and quantity) and abiotic factors




(water quality,  other contaminants, physical habitat alteration)  influence the status of biological




commun ties. Zinc is an example of a metal often  measured in the Chesapeake Bay environment




concurrently with  other  metals  such as  cadmium and  copper  (Hall,  1985;  Hall et  al.,




1986,19?!7,1989,1991b,1992b). Co-occurance of zinc with cadmium and copper may therefore induce




additive or antagonistic toxicity (Eisler, 1997).




       In ecological risk assessment, it is important to remember that individuals are part of the food




web and somewhat expendable - either consumed or being consumed.  Individuals within the various




biological communities are more sensitive to contaminant stress than the community as a whole.




Therefore, individual losses due to a stressors such as zinc may or  may not impact the viability




(persistence, abundance, distribution) of the population depending on all the factors influencing the




population.

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       1.1.7 Conceptual Model




       Problem formulation is completed with the development of a conceptual model where a




preliminary analysis of the ecosystem  at risk, stressor characteristics,  exposure pathways and




ecological effects are used to define the possible exposure and effects scenarios.  The goal is to




develop a working hypothesis to determine how the stressor might affect exposed ecosystems. The




conceptual model is based on information about the ecosystem at risk and the relationship between




the measurement and assessment endpoints. Professional judgement is used in the selection of a risk




hypothesis.  The conceptual model describes the approach that will be used for the analysis phase and




the types of data and analytical tools that will be needed. Specific data gaps and areas of uncertainty




will be described later in this report.




       The hypothesis considered in this risk assessment was:




       Zinc may cause permanent reductions at the species and community level for fish,  benthos,




       zooplankton or plants in the Chesapeake Bay watershed and these reductions may adversely




       impact community structure and function.

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                                       SECTION 2
                           EXPOSURE CHARACTERIZATION

2.1 Introduction

       Ar. important component of a probabilistic ecological risk assessment for zinc is the potential

exposure of aquatic organisms. Exposure data are used in conjunction with effects data (see next

section) to conduct a risk characterization.  The exposure analysis for zinc  considers use rates,

sources, loadings, chemical properties and spatial/temporal scale of measured concentrations (data

sources, sampling regimes, analytical methods and data analysis).

2.2 Zinc Loading in the Chesapeake Bay Watershed

       Unlike various pesticides, the sources for trace metals such as zinc are often difficult to

identify because zinc is found naturally in the aquatic environment and numerous point and non-point

sources exist. Anthropogenic activities that contribute to zinc loading in Chesapeake Bay watershed

are electroplaters, smelting and ore processors, mine drainage, domestic sewage, industrial effluents,

combustion of solid wastes, fossils fuels (e. g. coal fired power plants), road surface runoff, corrosion

of zinc iilloys and galvanized surfaces, pesticides, fertilizer, erosion of agricultural soils,  industrial

effluents and atmospheric deposition (Eisler, 1997). Zinc is employed in the following major types

of  industries  that are  located  in  the  Chesapeake  Bay  watershed, paper mills,  organic

chemical/petroleum, alkalis-chlorine-inorganic chemicals, fertilizers, petroleum refining, basic steel

works foundries, basic non-ferrous metal works foundries and steam generating power plants (Dean

et al., 1972).

       The estimated total basinwide annual loading of zinc and zinc compounds to the Chesapeake

Bay was 482,500 pounds based on data collected from 1987 to 1992 (U. S. EPA, 1994). The annual


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load of zinc from February 1994 through January 1995 for the Susquehanna River, Maryland (the




major source of freshwater in the Chesapeake Bay) was 438 metric tons (U. S. EPA, 1996b).




2.3 Chemical Properties of Zinc




       Zinc always has an oxidation state of +2 in aqueous solution and therefore has a strong




tendency to react with acidic, alkaline  and inorganic compounds (Merian, 1991). Due to its




amphoteric properties, zinc forms a variety of salts. Zinc chlorate, zinc chloride, the sulfates, and the




nitrates are readily soluble in water whereas the oxide, carbonate, phosphates, silicates, sulfides and




organic complexes have limited solubility in water (Merian, 1991). Zinc is one of the most mobile of




the heavy metals. Complexes of zinc with common ligands of surface waters are soluble in neutral




and acidic solutions, so that zinc is readily transported in most natural waters.




       In natural waters and sediments zinc occurs in many forms. For example,  at a pH = 6 in




freshwater,  the dominant forms of dissolved zinc are the  free ion (98%) and zinc sulfate (2%),




whereas at pH = 9, the dominant forms are the mon-hydroxide ion (78%), zinc carbonate (16%) and




the free ion (6%) (Turner et al., 1981). In seawater at pH = 8.1, the dominant species of soluble zinc




are zinc hydroxide (62%), the free ion (17%), the mono-chloride (6.4%) and zinc carbonate (5.8%)




(Zirino and Yamamoto, 1972). The percentage of dissolved zinc present in sea water as the free ion




increases to 50% at a pH of 7.0. The major fraction of dissolved zinc  is in the form of zinc-organic




complexes in the presence of dissolved organic material such as humic acids (Lu and Chen, 1977).




       Most of the zinc  introduced into aquatic environments is sorbed onto hydrous iron and




manganese oxides, clay materials, and organic materials where it is  eventually partitioned into




sediments   (U.  S. EPA,  1987). Zinc can be present in  sediments is several  forms,  including




precipitated Zn(OH)2,  precipitates with ferric and manganic  oxyhydroxides, insoluble organic

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complexes, insoluble sulfides, and residual forms (Patrick et al., 1977). Zinc is mobilized and released




in a soluble form as sediments change from a reduced to an oxidized state (Lu and Chen, 1977).




Benthic organisms play an important role in partitioning zinc between the water column and sediment




(U. S. EPA, 1987). Aquatic biota have a moderate to high  potential to bioconcentrate zinc depending




on the species. Bioconcentration factors (BCFs) as high as 4,000,000 have been reported in scallops




(Eisler, 1997).




       The potential for sediment-bound zinc to cause risk to sediment dwelling aquatic biota exists;




however, the focus of this risk assessment was an evaluation of risk to aquatic biota from exposures




to surface water concentrations. Probabilistic risk assessment techniques for assessing risk of aquatic




species to sediment exposures is still developmental and contains a higher degree of uncertainty than




water column exposures. By using surface water concentrations in this risk assessment, the results




can be more closely related to regulatory issues such as the U. S. Environmental Protection Agency's




water quality criteria (U. S. EPA,  1987).




2.4 Measured Concentrations of Zinc in the Chesapeake Bay Watershed




       2.4.1 Data Sources and Sampling Regimes




       Dissolved zinc exposure data from 19 data sources  were available from  1985 to 1996 at 116




stations (19 basins) in freshwater and saltwater tributaries and mainstem areas of the Chesapeake Bay




watershed ( Figure 2, Tables 1 and 2).   The zinc data sources are described below.




Ambient Toxicity Testing Program (Hall et al.r 1991a, 1992a. 1994ar 1996f 1997fl)




       These  data were collected over a period of five years (1990 -1995) on a limited temporal




scale (August through October and April 1993) at the following locations: Elizabeth River, Potomac




River, Wye River and Patapsco River in 1990; Patapsco River, Potomac River, Wye River in 1991;





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Middle River, Nanticoke River and Wye River in 1992-3; Patapsco River (Baltimore Harbor),




Magothy River, Sassafras River and Severn River in 1994 and James and York Rivers in 1995.




Fall Line Monitoring Data (MDE. 1993r 1995^




       These data were collected at one station each in the Susquehanna and James Rivers monthly




from 1990 to 1993.




NOAA Data (Riedel et al.. in press!




       These data were collected quarterly (May, August, November and February) at >15 stations




during 1995 and 1996 in the Patuxent River.




Striped Bass Data fHallr 1985; Hall  etal.. 1986r 1987. 1989r 1991b and 1992K1




       Zinc was measured from 1985 through 1990 in following tributaries or mainstem areas during




April and May as part of an in-situ striped bass contaminant study: Chesapeake and Delaware (C and




D) Canal in 1985; Potomac River in 1986; Choptank River and C and D Canal in 1987; Potomac




River in 1988; Potomac River and Upper Chesapeake Bay in 1989 and Potomac River and Upper




Chesapeake Bay in 1990.




Maryland Coastal Plain Stream Data (Hall et al. 1994b. 1995^




       Data were collected at 24 Maryland coastal plains stream stations at five different sampling




periods over a two year  period (1992-93).  Streams from the following basins were  sampled:




Nanticoke, Choptank,  Chester, West Chesapeake, Patuxent and Potomac.




Interstate Commission on  the Potomac River Basin (Velinisky et'al., 1994)




       Zinc data were collected from four sites (one or two samples per site) in the Anacostia River




during September of 1992).




District of Columbia Environmental Regulation Commission (Gruessner et al.r 1997)






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       A total of 36 zinc measurements were reported from two sites in the Anacostia River from




September 1995 to September 1996.




University of Delaware Data (Culberson and Church, 1988)




       Date, were collected at 20 stations in mainstem Chesapeake Bay from the mouth of the Bay




in Virginia lo the northern section in Maryland during August of 1985.




       2.4.2 Methods of Zinc Analysis




       Zinc data reported during the Ambient Toxicity Testing Program were  collected from




subsurface depth integrated grab samples (a composite of bottom, mid-depth and surface samples).




All samples were filtered using a 0.40 urn polycarbonate membrane and preserved in ultrex grade




nitric acid. Zinc was analyzed using an atomic absorption-furnace (AA-F) method as outlined in U.




S. EPA (1S79). The limit of detection ranged from 2 to 10 ug/L.




       Zinc from the Fall Line Monitoring Program was measured from grab samples at the James




River  and  Susquehanna River  stations using ultra clean sampling  procedures. Dissolved




concentrations of zinc were measured using an Inductively coupled plasma mass spectrometer (ICP-




MS) method as described in Fishman and Friedman (1989). The detection limit was 0.14 ug/L.




       In the NOAA/COASTES study, zinc was measured from surface water grab samples using




an ultra-clean technique. All samples were filtered using 0.45 urn polypropylene capsule filters and



preserved using 0.2% ultrex grade hydrochloric acid. Zinc analysis was conducted by using an AA-F




method as described in Bruland et al. (1979). The detection limit was <0.3  ug/L.




       The zinc data from the Striped Bass Study were collected from both subsurface grab samples




and composite samples  (usually  24  h in duration). All samples were filtered  using 0.40 urn




polycarbonate membranes and preserved using ultrex grade nitric acid. Zinc was analysed using an





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atomic absorption furnace (AA-F) method as outlined in U. S. EPA (1979). Detection limits for zinc




ranged from 3 to 20 ug/L (for five of the six studies detection limits were < 10 ug/L).




       For the Maryland Coastal Plain Stream Data Base, zinc was measured from grab samples




taken seasonally.  All samples were filtered using 0.40 um polycarbonate membranes  and preserved




in ultrex grade nitric acid.  Zinc was analysed using an AA-F method  (U. S. EPA, 1979). The




detection limit was 3 ug/L.




       Zinc data from the Interstate Commission on the Potomac River Basin were collected




from grab samples. All samples were filtered through pre-cleaned and tared 0.4 um Nuclepore filters.




Filtered water samples were acidified with double-distilled quartz HCL (0.04% volume/volume) and




kept frozen until analysis. Zinc was analysed by an Atomic Absorption Spectrometer with an HGA




graphite furnace. The detection limit was 0.14 ug/L.




       Zinc  measurements  from  the District  of Columbia  Environmental Regulation




Administration  were from grab samples.  These samples were filtered through 0.4 um Nuclepore




membranes. All  samples were acidified with Ultrex grade nitric acid and kept refrigerated until




analysis. Zinc was analysed by dictation ion chromatography using the method described by Long and




Martin (1992). The detection limit was <0.8 ug/L.




       Zinc measurements from the University of Delaware Data Base were taken from discrete




water column depths in the mainstem Chesapeake Bay. All samples were  filtered with 0.4 um acid




cleaned nuclepore membranes, acidified to pH<2 and frozen until analysis. Zinc was analysed using




an AA-F method as described in Danielsson et al.(1978). The detection limit was <0.7 ug/L.




       2.4.3 Methods of Data Analysis




       Approaches for handling values below the detection limits include assigning these values as





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zero, one-half the detection limit or the detection limit (MacBean and Rovers, 1984; Giddings et al.




1997 ). For this risk assessment, zinc values below the detection limit were assumed to be log-




normally distributed. The distribution of exposure data was calculated based on the measured values




and the concentrations of the non-detects were assumed to be distributed along a lower extension of




this  distribution. For example, if 80 out of 100 samples were reported as non-detects, the 20




measured viilues were assigned ranks from 81 to 100 and the frequency distribution was calculated




from these 20 values. In some cases in these data sets, actual concentrations were repprted even




though they were below the detection limits. When this occurred, the concentrations were used in




the analysis   For cases where more than one value was available at the same time and station, the




highest value was used in the frequency distribution.




       For data sets arranged by basin or station with four or more values above the detection limit,




log-normal distributions of exposure concentration were determined as follows. The observations in




each data set were ranked by  concentration and for each observation the percentile ranking was




calculated as n/(N+l) where n is the  rank  sum of the observation and N is the total number of




observations including the non-detects. Percentile rankings were converted to probabilities and a




linear regression was performed using the logarithm of concentration as the independent variable and




normalized rank percentile as the dependent variable. Although non-detects observations were not




included in the regression analysis, they were included in the calculation of the observation ranks.




The  90th percentile concentrations (exceedence of a given value  only 10% of the time)  were




calculated for  sampling stations (or basins) based  on the calculated log-normal concentration




distributions.
                                            14

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2.5 Measured Concentrations by Basin




       The 90th percentile values for zinc in 19 basins presented in Table 2 showed that values




ranged from a high of 140 ug/L in the Middle River to 5.2 ug/L for the lower Bay (Table 2, Figure




3). Due to concentrations below the detection limit, 90th percentile values could not be calculated




for Baltimore Harbor, Magothy River, Sassafras River, Severn River  and the York River .  The high




90th percentile value in the Middle River was likely related to anthropogenic activities near marina




areas and/or urban runoff as copper and cadmium concentrations above background have also been




reported in this basin (Hall et al., 1997b). The second highest zinc 90th percentile of 70 ug/L was




reported in the Potomac River was likely related to the proximity of these sampling stations near




point source discharges from facilities such as Quantico Marine Base, the Possum Point Power Plant




or the Indian Head Military Facility. Elevated cadmium concentrations were also reported at these




stations (Hall et al.,  1997b). The lower 90th percentiles in Lower Chesapeake Bay, Magothy River,




Sassafras River, Severn River and York River were likely related to less anthropogenic activity.




2.6 Temporal Trends




       The NOAA data from the Patuxent River (quarterly sampling in 1995 and 1996) and the Fall




Line Monitoring Data from the James and Susquehanna River (monthly sampling in 1990 to 1993)




were used to examine temporal trends in zinc over single or multiple years (Riedel et al. in press,




MDE,  1993,1995). These were the only data sets that were appropriate for temporal analysis.




       2.6.1 Patuxent River




       The quarterly mean  zinc concentrations (May, August, November - 1995 and February -




1996) from the 15 pooled stations in the Patuxent River showed  that concentrations were elevated




during February (Figure 4).  The mean zinc concentration for the February time period (2.57 ug/L)





                                           15

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was approximately twice as high the other three sampling periods ( 0.99 to 1.34 ug/L). The highest




zinc concentrations (10.8 ug/L) in this data set was also reported in February.  The elevated




concentrations of zinc during the winter were likely related to the increased flow during this time




period.




       2.6.1 James and Susquehanna Rivers




       Monthly measurements of zinc in the James River over 4 years (1990 to 1993) ranged from




below the detection limit to 30  ug/L (Figure 5). The highest value of 30 ug/L occurred in October




of 1990. Other peak values of 15 and 13 ug/L were reported May of 1992 and December of 1992,




respectively. There appears to be no consistent temporal trends of zinc concentrations in the James




River.




       Monthly measurements of zinc in the Susquehanna River during 1990 through 1993 ranged




from belov/ the detection limit  to 22 ug/L (Figure 6). The four peak concentrations of zinc (~ 20




ug/L) were reported in June of 1990, January of 1991, April of 1992 and September of 1993. There




is no apparent temporal trend with zinc exposure data from the Susquehanna River.




2.7 Summary of Exposure Data




       Highest environmental concentrations of zinc (based on 90th perceniiles) in the Chesapeake




Bay watershed were reported in the Middle River, Potomac River, Choptank River and Nanticoke




River. Sources of zinc responsible for these exposures can not be identified with certainty but human




activities  associated with urban  runoff and marina facilities (Middle  River), industrial effluents




(Potomac IXiver), fertilizers (Choptank and Nanticoke Rivers) and a power plant (Nanticoke River)




are likely candidates.  Natural  sources of zinc in some of these areas may also be a source. As




expected tie lowest concentrations of zinc were generally reported in areas with the least amount of





                                          16

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direct human activity such lower mainstem Chesapeake Bay, Sassafras River and York River.




It is noteworthy that Baltimore Harbor, a highly industralized area, had low concentrations of zinc




in the water column. However, sediment concentrations of zinc for the various stations sampled for




water column measurement were relatively high and in some cases exceeded the Long et al. (1995)




Effects Range Median values (Hall et al., 1996). Quarterly measurements of zinc in the Patuxent




River showed somewhat elevated concentrations of zinc during the winter months that were related




to increased flow. There were no apparent temporal trends in zinc concentrations from monthly




measurements (1990-1993) in the James and Susquehanna Rivers.
                                          17

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                                       SECTION 3
                                ECOLOGICAL EFFECTS

3.1 Mode ofToxkity

       Zinc is an essential micronutrient for all living organisms and is ubiquitous in the tissues of

plants and animals (U. S. EPA, 1987). Zinc is particularly critical for normal growth and reproduction

in aquatic biota. Numerous different enzymes require zinc for maximum catalytic activity, including

carbonic  imhydrase,   alkaline  phosphate,  alcohol dehydrogenase,  acid  phosphatase,  lactic
                                                                               >
dehydrogenase,  carboxypeptidase and  superoxide dismutase  (Eisler, 1997). Zinc is critical in

controlling; zinc-dependent enzymes that regulate the biosynthesis and catabolic rate of RNA and

DNA  (Pn.sad,  1979). Zinc deficiency effects  have  been  reported  in  aquatic organisms at

concentrations between 0.65 and 6.5 ug/L (Eisler, 1997).

       Bic availability of zinc is important to consider when assessing the toxicity to aquatic biota.

Zinc toxicily to aquatic biota is influenced by the chemical and physical forms of zinc, the toxicity of

each form, and the degree of interconversion for each form. In most cases aquatic fish and plants are

unaffected by suspended zinc; however,  many invertebrates and some fish may be impacted if zinc-

containing, particulates are ingested (U. S. EPA,  1987). Zinc adversely impacts fish by causing

mortality, growth retardation, tissue alteration (destroys gill epithelium), respiratory and cardiac

changes and inhibition of spawning (Sorenson, 1991). Inhibition of photosynthesis and disruption

of plant growth resulting from impairment of enzyme systems are suspected to be the major adverse

effects from excessive zinc exposure in plants.

3.2 Methods of Toxicity Data Analysis

       Hardness (concentrations of calcium and magnesium) is one water quality variable that
                                           18

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significantly influences the toxicity of zinc in freshwater. As hardness increases, the toxicity of zinc




to biota generally decreases  due to reduced bioavailability of the  metal  or  alteration of the




osmoregulatory capacity of the organism. The U. S. Environmental Protection Agency addresses the




influence of hardness on zinc toxicity in their development of freshwater water quality criteria (U. S.




EPA, 1987). For the zinc toxicity data used in this risk assessment, hardness was also considered in




the ranking of sensitivities of various freshwater species. In order to realistically compare freshwater




toxicity data among species, all data were standardized to a hardness of 50 mg/L CaC03. Fifty mg/L




was  selected because it is the mean hardness value of 24 coastal plains streams sampled five times




over a two year period in 1992-93 (Hall et al., 1994b; 1995). The following equation was used to




hardness adjust the freshwater acute and chronic toxicity data:




In LCjo^.brtto, = In LCJOotaeived - (b[l]ln hardness,*^^ - In




         fized = 50 mg/L as CaCO3
Slope = b[l] = 0.8473 for zinc acute and chronic toxicity data (U. S. EPA, 1987)




       It is also important to note that other water quality parameters such as pH and dissolved




organic carbon also influence zinc toxicity. These and other parameters have been the basis for the




Biotic Ligand model the U. S Environmental Protection Agency is considering for use in revising




water quality criteria for metals (Andrew Green, personal communication, International Lead and




Zinc Research Organization).




       The 10th percentile of species sensitivity (protection of 90% of the species) from acute




exposures was the primary benchmark used for this risk assessment. The implied assumption when




using this benchmark is that protecting a large percentage of the species assemblage will preserve




ecosystem structure and function. This level of species protection is not  universally accepted,





                                           19

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especially if the unprotected  10%  are keystone species and have commercial or recreational




significance.  However, protection of 90% of the species 90% of the time (10th percentile) has been




recommend 3d by the Society of Environmental Toxicology and Chemistry (SET AC, 1994) and others




(Solomon et al., 1996).  Recent mesocosm studies have reported that this level of protection is




conservative (Solomon et al.,1996; Giddings, 1992).




       Zinc toxicity data were analyzed as a distribution on the assumption that the data represented




all species h the Chesapeake Bay ecosystem.  An approximation was made since it is not possible to




test all species in the Chesapeake Bay.  This approximation assumes that the number of species tested




(N) is one less than the number in the Chesapeake Bay.  To obtain graphical distributions for smaller




data sets that are symmetrical (normal distributions) percentages were calculated from the formula




(100 x n/(N + 1)) where n is the rank number of the datum point and N is the total number of data




points in the set (Parkhurst et al., 1994). This formula compensates for the size of the data sets as




small (uncertain) data sets will give  a flatter distribution with more chance of overlap than larger




(more certain) data sets.  In cases where there were multiple data points for  a given species, the




lowest value was used in the regression analysis of the distribution. When  data were available for




multiple life stages of a species, the lowest values were generally reported for early life stage. Using




the lowest value therefore provides a conservative approach for protecting the most sensitive life




stage of a species. Data were plotted using Sigma Plot (Jandel Corporation, 1992).




3.3 Effects of Zinc from Laboratory Toxicity Tests




       Acute and chronic zinc toxicity data used in this risk assessment were obtained from the




AQUIRE database through 1998, U.  S. EPA water quality criteria document (U.  S. EPA, 1987), a




recent review of zinc (Eisler, 1997) and manual  searches of grey literature from academia, industry





                                           20

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and government sources. Zinc acute and chronic toxicity data by water type (freshwater and saltwater




) are discussed below.




       3.3.1 Acute Toxicity of Zinc




       Acute freshwater zinc toxicity data were available for 101 species, primarily fish and benthos,




as shown in Table 3 and Figure 7. Hardness data were available for approximately half of these




species (n=55) and these data were used for the analysis of species sensitivity distribution and




calculation of 10th percentiles. The range of acute toxicity values was 32 ug/L for Ceriodaphnia to




260,000 ug/L for the climbing perch (Table 3). The acute 10th percentile for all freshwater  species




was 142 ug/L (Table 4). This value is approximately twice as high as the U. S. EPA freshwater water




quality criteria (5th percentile) of 65 ug/L at 50 mg/L  hardness (U. S. EPA, 1987). The order of




sensitivity from most to least sensitive trophic group using   10th percentiles was as follows:




zooplankton (4.3 ug/L), benthos (212 ug/L), fish (216 ug/L), amphibians (629 ug/L) and plants (789




ug/L). Data for amphibians (n=2) zooplankton (n=5),  and plants (n=2) were limited and were




therefore not used for assessing risk to the most sensitive trophic. The 10th percentiles for fish (216




ug/L) and benthos were similar (212 ug/L).




       Acute zinc saltwater toxicity data were available for 82 species as shown in Table 5  and




Figure 8. As reported above for freshwater acute data, most of the saltwater acute toxicity data were




with fish and benthos. Zinc toxicity ranged from 19 ug/L for a diatom to  119,300 ug/L for a  fish




species (Table 5). The acute 10th percentile for all species was 79 ug/L (Table 4). This value is similar




to the U. S. EPA water quality criteria (5th percentile) of 95 ug/L (U. S. EPA, 1987). The order of




sensitivity from most to least sensitive trophic group using 10th percentiles was plants (10 ug/L),




zooplankton (46 ug/L), fish (69 ug/L) and benthos (102 ug/L). The plant 10th percentile of 10 ug/L





                                            21

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was substantially lower than the 10th percentiles for other trophic groups.




       3.3.2 Chronic Toxicity of Zinc




       Chronic zinc toxicity data were available for 14 freshwater species (Table 6 and Figure 9).




Hardness was reported for 12 of the 14 species tested (data used for calculation of 10th percentiles).




Chronic values ranged from 25 ug/L for a cladoceran to > 5,243 ug/L for a caddisfly for non-hardness




adjusted data. A hardness adjusted value of 5.5 ug/L was reported for a cladoceran. The chronic 10th




percentile for all freshwater species was 11 ug/L. This value is substantially lower than the U. S. EPA




chronic freshwater criteria (5th percentile) of 59 ug/L at a hardness of 50 mg/L (U. S. EPA, 1987).




The order of sensitivity from most to least sensitive trophic groups based on 10th percentiles was




zooplankton (0.8 ug/L), fish (56 ug/L) and benthos (74 ug/L).




       Saltwater chronic toxicity data were limited to six species  and actual chronic values were only




reported for the Pacific oyster (30 ug/L) and two mysid species (152 ug/L) (Table 7 and Figure 10).




The 10th percentile for the  saltwater chronic toxicity data was 8.7 ug/L (Table 4).  This 10th




percentile is much lower that the U. S. EPA saltwater chronic criteria (5th percentile) of 86 ug/L (U.




S. EPA, 1987). However, value is similar to the freshwater chronic value of 11 ug/L reported above.




 3.4 Mesoc osm/Microcosm Studies




       Zinc mesocosm studies with reported MATC (maximum acceptable toxicant concentrations),




LOEC (lowest observed effect concentrations) or NOEC (no observed effect concentrations) values




were   very limited. Genter et al. (1987) exposed algal communities to zinc concentrations of 0




(control),  50,  500 and 1,000 ug/L  for 30 days in outdoor flow-through stream mesocosms.




Treatmentu as low as 50 ug/L were reported to significantly change community composition from




diatoms to green or blue green-algae. However, this species shift does not necessarily imply that the





                                           22

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functions of aquatic communities have been impaired. In another study, Center et al. (1989) exposed




algal and protozoa communities  to zinc concentration ranging from 0 to 10,000 ug/L for 7 days.




Results from this study showed that none of the algal or protozoan species had reduced biovolume




density in high zinc concentrations (10,000 ug/L) even though the total number of protozoan species




decreased.




3.5 Summary of Effects Data




       The 10th percentile for all species derived from the freshwater acute zinc toxicity data base




was 142 ug/L. Most of the data used for the calculation of this  10th percentile were from toxicity




studies with fish and benthos. Cladocerns were reported to be the most sensitive freshwater species




to zinc exposure (LCSOs of 35 and 21 (hardness adjusted) ug/L).  A ranking of sensitivity among




trophic groups from most to least sensitive showed the following order: zooplankton, benthos, fish,




amphibians and plants. The 10th percentiles for zooplankton, amphibians and plants were not used




for risk characterization for the most sensitive trophic group because these data were very limited.




The freshwater chronic 10th percentile for all species was 11 ug/L.  As reported above for acute




freshwater data, zooplankton were the most sensitive trophic group subjected to chronic zinc




exposures.




       The saltwater acute zinc 10th percentile for all species was 79 ug/L. Diatoms (phytoplankton)




were reported to be the most sensitive species (ECSOs of 19 to 26 ug/L). The ranking of sensitivity




among trophic groups from most to least sensitive was as follows based on acute 10th percentiles:




plants, zooplankton, fish and benthos. The acute saltwater 10th percentile for plants (10 ug/L) was




lower than for other trophic groups. The chronic 10th percentile for all saltwater species (8.7 ug/L)




was based on a limited set of toxicity data from six benthic species.





                                           23

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                                        SECTION 4
                               RISK CHARACTERIZATION

4.1 Chara< terizating Risks

       Risk quotients are one simple and commonly used method for characterizing risks to aquatic

biota. Risk quotients are simple ratios of exposure and effects concentrations where the susceptibility

of the most sensitive species is compared with the median, mean or  highest environmental exposure

concentration. Safety factors such as the division of the effect concentration by a number ranging

from one 1:o 100 are often applied to allow for unquantified uncertainty in effect and exposure

concentrations. If the exposure concentration equals or exceeds the effects concentration in the risk

quotient approach then an ecological risk is suspected. The quotient method is a valuable first tier

assessment that allows a determination of a worst case effects and exposure scenario for a particular

contaminant.  However, some of the major limitations of  the quotient method for ecological risk

assessment are that it fails to consider variability of exposures among individuals in a population,

ranges of sensitivity among species in the aquatic ecosystem and the ecological function of these

individual species. The probabilistic approach addresses these various concerns as it expresses the

results of an exposure or effects characterization as a distribution of values rather than a single point

estimate. (Quantitative expressions of risks to aquatic communities are therefore determined by using

all relevant single species toxicity data in conjunction with exposure distributions.   A detailed

presentation of the principles used in a probabilistic ecological risk assessment are presented by

Solomon <;t al. (1996).

       The following sections will summarize the results of the risk characterization phase of this

probabilistic  ecological risk assessment of zinc in the Chesapeake Bay watershed.  The toxicity
                                            24

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benchmark used for the risk characterization will be either the freshwater or saltwater acute 10th




percentile, depending on whether freshwater or saltwater is present within the basin. The acute 10th




percentile was selected for the following reasons: (1) based  on laboratory  experimental data,




dissolved and bioavailable zinc are only in the water column of the aquatic environment for short




periods of  time (due to complexation with natural organic particulates) which are more closely




related to acute exposures that chronic exposures; (2) the low acute to chronic ratio (~2) reported




for zinc by the U. S. EPA (1987) suggests that exposure duration does not significantly increase




toxicity  and (3) toxicity data are much more numerous and represent a wider range of trophic




groups for acute studies than chronic studies. In addition to using the acute 10th percentile for all




species in freshwater or saltwater, the trophic group with the lowest acute 10th percentile with at




least  8 data points (8  species) was also used as an additional benchmark (more conservative




approach) to  assess possible ecological risk. The U.S. Environmental Protection Agency uses a




minimum value of 8 species for development of acute numeric water quality criteria (Stephan et al.,




1985).




4.2 Risk Characterization of Zinc in the Chesapeake Bay Watershed




       Potential ecological risk from zinc exposure was characterized by using freshwater acute




effects data for freshwater areas and saltwater effects data for saltwater areas (Table 8, Appendix A).




There were five saltwater and nine freshwater basins where data were sufficient for characterizing




risk. The highest potential ecological risk area for zinc exposures in the Chesapeake Bay watershed




was reported in the Middle River (Table 8).  The percent probability of exceeding the acute saltwater




10th percentile  for all species was  21%. For the most sensitive trophic group (based on acute




saltwater exposures), the probability of exceeding the 10th percentile for plants was even higher






                                            25

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(79%). The 1 Middle River was the only basin where the potential ecological risk from zinc exposure




was judged to be significant.  The second highest risk area for zinc exposures in the Bay watershed




was the Wyt: River (Table 8). The probability of exceeding the 10th percentile for all species and the




probability of exceeding the  10th percentile of the most sensitive trophic group with at least eight




species (baasd on acute saltwater exposures) was 2.7 and 42%, respectively. The 2.7% exceedence




for all species in the Wye River basin is relatively low risk. The 42% exceedence for plant species




does suggest a  somewhat higher potential risk to this trophic group although 90% of the plants




species would not be at risk based on the probabilistic risk analysis used. The third highest risk area




for zinc exposures was the Potomac River. The percent probability of exceeding the 10th percentile




for all specie and most sensitive trophic group with at least eight species (benthos = 212 ug/L) was




3.3 and 1.6 %, respectively. The  percent exceedence for  both of these benchmarks or overall




ecological risk in the Potomac River is low.  For all other 11  basins in Table 8, ecological risk from




zinc exposure was generally low using either the acute saltwater or freshwater 10th percentiles.




4.3 Uncertainty in Ecological Risk Assessment




       All scientific endeavors have uncertainty and ecological risk assessment is no exception.




Development of exposure benchmarks, such as the 90th percentile for environmental concentrations,




or toxicity benchmarks, such as the  10th percentile for species susceptibility, may seem to be exact.




However, iiese values involve uncertainty when extrapolating risks from laboratory data to aquatic




ecosystem?. Uncertainty plays a particularly important role in ecological risk assessment as it impacts




problem formulation, analysis of exposure and effects data and risk characterization.  Evaluation of




uncertainty in this risk assessment was critical in determining data gaps (research needs) as described




in the final section of the report. Addressing these various research needs in future efforts will reduce





                                            26

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uncertainty.




       Uncertainty associated with metals risk assessment  such as zinc have some fundamental




differences when compared to pesticides (European Commission, 1996). The following differences




exist:




(1) Unlike most organics, metals such as zinc (micronutrients) and some organometallic compounds




(e. g. methylmercury) are a class of chemicals that occur naturally in the environment. Therefore,




natural background concentrations and exposure to these concentrations should be factored in risk




characterization.




(2) The availability of zinc for uptake by organisms under field conditions is limited, will vary from




site to site and is highly dependent on the speciation of the metal. Exposure and effects data should




therefore be based on similar levels of availability (in this case disssolved concentrations).




(3) The same toxic form of zinc can originate from a variety of different substances (e. g. Zn+2 from




ZnS04, ZnCl2 etc.). Therefore, it is necessary to take into account all metal species that are emitted




to the environment which may result in concentrations of the toxic form.




       Uncertainty in ecological risk assessment has three basic sources: (1) lack of knowledge in




areas that should be known; (2) systematic errors resulting from human or analytical error and (3)




non-systematic errors resulting from the random  nature of the ecosystem  ( e.g. Chesapeake Bay




watershed). The following sections will address specific uncertainty from the above three sources




as associated with exposure data, effects data and risk characterization.




       4.3.1 Uncertainty Associated with Exposure Characterization




       Zinc exposure data used for this risk assessment were obtained from 19 different data sources




from  1985 to 1996 as described in Section 2.  The spatial scale of these data (116 stations in 19





                                            27

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basins/mainstem areas) was somewhat limited considering that there are at least 50 major rivers and




numerous smaller tributaries that discharge into the Chesapeake Bay. Exposure data from basins in




Virginia waters of Chesapeake Bay were particularly limited as only the James River, York River and




the lower mainstem Bay were represented.  The temporal scale (sampling frequency) of the available




data for the Bay watershed was  even more  limited. In many  cases there were only a few




measurements made for these metals at various stations. Rain event sampling for these metals in




tributaries and streams was generally not considered in the sampling designs of the various monitoring




studies. Although rain event sampling is more relevant for pesticides that are applied on agricultural




crops  and  enter aquatic systems during runoff, such events may be important  for zinc loading




resulting from fertilizer (chicken manure based fertilizer) used on  crops or zinc loading from urban




stormwater discharges or  municipal/ industrial  overflow.  Roman-Mas  et  al.  (1994)  have




recommenced a sampling interval of 5% of the duration of the storm flow as adequate to characterize




pesticide concentration distributions in runoff with an error of less than 5% (for example during an




event with  storm flow lasting 100 h sampling should be every 5 h).  The sampling frequency of the




present exposure data for zinc is clearly inadequate for rain event sampling.




       The zinc analysis associated with the various laboratories introduces uncertainty because




analytical procedures differed among the laboratories (see Section 2). For example, samples were




collected for analysis using either grab, depth integrated or composite  techniques. In all cases




samples were filtered with either 0.4 or 0.45 urn  membranes but the membranes were made of




different material  ( polycarbonate, polypropylene or nucleopore ). The method of metal analysis was




somewhat consistent among laboratories as an Atomic Absorption - Furnace method (AA-F or HGA)




was  used for  all data sets except for  the  Fall Line Data (Inductively Coupled  Plasma Mass






                                          28

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Spectrometer - ICP-MS) and the District of Columbia Environmental Regulation Administration data




(chelation ion  chromatography). The detection limits varied among the different laboratories (




generally 0.14 to 10 ug/L; for one study 20 ug/L was used).




       4.3.2 Uncertainty Associated with Ecological Effects Data




        There is uncertainty when extrapolating laboratory toxicity data to responses of natural taxa




found in the Chesapeake Bay watershed due to the relatively small number of species that can be




cultured and tested in laboratory toxicity studies. In the case of zinc  in the Chesapeake Bay




watershed, freshwater and saltwater acute toxicity were available for 55 (hardness adjusted data) and




82 species, respectively, for use in the calculation of the 10th percentile.  Although these data seem




adequate for all species, the distribution among the various trophic groups was weighted more with




fish and benthos. Acute  zinc toxicity data were particularly limited for plants (phytoplankton and




macrophytes),  zooplankton and amphibians in freshwater. Chronic data, although not used in this




risk assessment, were limited for both types of water but particularly for saltwater species (n = 6).




In addition to more data with an expanded list of species, more ecologically relevant zinc toxicity data




are needed to reduce uncertainty and address comparisons  of laboratory and field data. Metal




speciation, dissolved organic carbon, suspended  particulates and  bedded sediments  should  be




considered with laboratory to field extrapolations.




       Variability in the results of toxicity tests for a given species tested  in different experiments  or




by different authors is a potential source of random and systematic errors. In this assessment, the




most conservative (lowest) effect value was used when multiple data points were available for a given




species. The range of toxicity data among trophic groups differed for each water type. For example,




the acute  zinc freshwater  10th percentile values  among  trophic groups ranged from 4.3 ug/L





                                            29

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(zooplantkton) to 789 ug/L (plants) - a factor of 183x. Acute saltwater 10th percentiles by trophic




group ranged from 10 ug/L (plants) to 102 ug/L (benthos). This 10 fold difference for saltwater




species is much less than the factor of 183x reported above for freshwater 10th percentiles. Using the




distribution of species susceptibility accounts for  this range of data points. Distributions will be




flatter, with greater chance of overlap with exposure distributions, when the range is large.




       Acute freshwater  and saltwater zinc toxicity   data were primarily used  in  the  risk




characterization as previously discussed.  The use of acute data for predicting ecosystem effects is




often questioned and assumed to be an area of significant uncertainty. However, Slooffet al. (1986)




in their rewew of single species and ecosystem toxicity for various chemical compounds, have




reported that there is no solid evidence that predictions of ecosystem level effects from acute tests




are unreliable.  The result of  Slooffet al. (1986) coupled with the use of a distribution of acute




toxicity data reduces some of the uncertainty associated with using acute data.




       Although single species laboratory toxicity tests are valuable in risk assessment, microcosm




and mesocosm data provide the following useful information for assessing the impact of a stressor




on aquatic communities in an ecosystem: (1) aggregate responses of multiple species; (2) observation




of population and community recovery after exposure and (3) indirect effects resulting from changes




in food supply.  Unfortunately, microcosm and mesocosm studies that determined No Observed




Effect Concentrations (NOEC) were limited. The lack of these type data, where the interaction of




biotic communities have been assessed under zinc exposure, was a source of uncertainty in this risk




assessment  since microcosm/mesocosm  toxicity benchmarks  were  not  available for  risk




characterization.
                                            30

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       4.3.3 Uncertainty Associated with Risk Characterization




       The Society of Environmental Toxicology and Chemistry (SET AC, 1994) reported that many




of the uncertainties associated with the variability in the exposure and effects characterizations




discussed above are incorporated in the probabilistic approach used in this risk assessment.  A




distribution of exposure and effects  data are used for quantitative analysis of risks.




       Ecological  uncertainty includes   the effects of confounding stressors  such as other




contaminants (e. g. zinc often occurs concurrently with other metals such as copper and cadmium)




and the ecological redundancy of the functions of affected species. In the Chesapeake Bay watershed,




numerous contaminants may be present simultaneously in the same aquatic habitats; therefore, "joint




toxicity"may occur. For zinc, additive toxicity is likely if other metals such as copper and cadmium




are present. The concurrent presence of various contaminants along with zinc makes it difficult to




determine the risk of zinc in isolation.




       Ecological redundancy is known to occur in aquatic systems. Field studies have shown that




resistant taxa tend to replace more sensitive species under stressful environmental conditions




(Solomon et al., 1996; Giddings, 1992)  The resistant  species may replace the sensitive species if it




is functionally equivalent in the aquatic ecosystem and the impact on overall ecosystem function is




reduced by these species shifts. For this risk assessment, information on the ecological interactions




among species would help to reduce this area of uncertainty.
                                            31

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                                      SECTION 5
                        CONCLUSIONS AND RESEARCH NEEDS
       Potential ecological risk from zinc water column exposure was higher in the Middle River than

any of the other basins in the Chesapeake Bay watershed. Ecological risk from zinc exposure in the

Wye River was insignificant when all acute species data were used but the most sensitive trophic

group (plants) suggested that some risk may occur with the most sensitive 10% of plant species.

Based on tie documented recovery of plant populations to episodic stressors, however, the zinc

exposure to plant populations is still judged to be low in the Wye River since 90% of the plant species

would not be affected. Ecological risk from zinc water column exposure was judged to be low or data

were lacking for assessing risks in the other 17 basins.

       The following research is recommended to supplement existing data for assessing the

ecological lisks of zinc in the Chesapeake Bay watershed:



(1) A probabilistic ecological risk assessment for zinc exposure in sediment is recommended to

complement  this water column risk assessment. Most of the  zinc introduced into the aquatic

environment is sorbed onto hydrous iron, manganese oxides, clay materials and organic materials

where it u, eventually partitioned into sediments. Therefore, assessing risk of sediment  dwelling

organisms exposed to zinc would expand our knowledge on the potential ecological risk of this metal

in the environment.



(2) Exposure assessments for zinc using randomly selected stations are needed on a broad spatial and

temporal ucale in the Chesapeake Bay watershed.  On a spatial scale, zinc data are needed for the


                                          32

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major rivers (tributaries) and representative  freshwater streams where these data are lacking,




particularly in Virginia waters of the Chesapeake Bay watershed ( e.g. Rappahannock River and




lower eastern shore). Exposure assessments with increased sampling frequency covering all seasons




of the year at representative locations in the Bay watershed (including some of the basins in this




report where data are lacking) are also needed to improve our ability to determine risk of aquatic




biota to zinc. Specifically, rain event sampling (e.g. samples every 2 to 4 h during the duration of the




event) and subsequent measurement of metals  in streams or tributaries near known sources of zinc




are needed (agricultural fields using chicken manure based fertilizer). These data may provide insight




on why zinc concentration were higher than ambient concentrations in agricultural areas such as the




Choptank, Nanticoke and Wye Rivers. All exposure assessments of zinc should be conducted by




laboratories using the most updated analytical methods (with documented and approved Quality




Assurance/Quality Control procedures) with detection limits  below the toxicity thresholds for the




most sensitive species.








(3) An extensive spatial and temporal exposure assessment of zinc (including rain event sampling) is




recommended in the Middle River area over multiple years. Since the Middle River was the highest




risk area for zinc based on limited data collected in 1993, the obvious question is whether this area




still has concentrations that may pose a risk to aquatic biota. Biological communities should also be




sampled in the Middle River  area to  see if they are impaired when compared to communities  in




similar habitats.








(4) Acute zinc toxicity data for various trophic groups in freshwater and saltwater are needed for





                                           33

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improving the present toxicity data base. Specifically, acute freshwater and saltwater toxicity data for




zinc (with measured concentrations) are needed with plants such  as phytoplankton and aquatic




macrophytes. Acute freshwater data are also needed for amphibians and zooplankton. Chronic data




for all trophic groups would also be useful.








(5) Microcosm/mesocosm toxicity data that include the calculation  of NOEC, LOEC and chronic




values for zinc in freshwater and saltwater environments are needed to provide insight on the




interaction of aggregate species assemblages during zinc exposure,  recovery potential of exposed




species and possible indirect effects on higher trophic groups. These studies should be designed to




simulate environmentally realistic pulsed exposures of these zinc concentrations documented to occur




in the environment.








(6) Assessments of biological communities (Index of Biotic Integrity for fish, invertebrates etc.) in




aquatic systems that receive the highest exposures of zinc are recommended to determine if the




predicted ecological risk (impaired biological communities) from this metal in the water column can




be confirmed with actual field data.








(7) Investigations are needed to determine how to incorporate the essentiality of relevant metals (such




as zinc) for aquatic organisms into the risk assessment process.
                                           34

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                                      SECTION 6
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                                          50

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TABLES

-------
  Table 1. Summary of the 19 zinc exposure data sources used for this risk assessment.
Reference
Data ID
Total #    Sample Period
samples	'
Detection Limit
Halletal., 199 la
Halletal., 1992a
Halletal, 1994a
Halletal., 1996
Halletal., 1997a
MDE, 1993,1995
Hall, 1985
Halletal., 1986
Halletal., 1987
Halletal., 1989
Halletal., 1991 b
Halletal., 1992b
AMBTOX90
AMBTOX91
AMBTOX93
AMBTOX94
AMBTOX95
Fall Line Monitoring
Reidel et al. in press        NOAA/COASTES
Striped Bass Study'85
Striped Bass Study '86
Striped Bass Study'87
Striped Bass Study '88
Striped Bass Study'89
Striped Bass Study '90
Velinsky et al., 1994        ICPRB
Gruessner et al., 1997       DC ERA
Culberson & Church, 1988   UDE
     12   Aug-Sep 1990


     13   Aug-Sep 1991


     14   Octl992&Aprl993


     12   Oct 1994


      8   Oct 1995


    164   monthly 1990-93


     60   quarterly 1995-96


     51   Apr 1985


     39   Apr 1986


     40   Apr 1987


     49   Apr-May 1988


     71   Apr-May 1989


     36   Apr-May 1990
Hall et al., 1994b, 1995      MD Coastal Plain (CPS)        120  Apr, Jun, Oct 1992-93
                            7   September 1992


                           36   Sept 1995-Sep 1996


                           20   Aug 1985
           10
           10
         0.14
                                                                  <0.3
          10
          20
          10
          10
          10
                                           <0.8
                                           <0.7
                                              51

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Table 2. Summary of zinc exposure data for all basins and stations. Maximum and 90th percoitile concentrations
(minimum of 4 detected concentrations) are presented by station and basin.
Basin
Data ID
Baltimore Harbor
AMBTOX90,?!
AMBTOX94
AMBTOX94
AMBTOX94
AMBTOX94
AMBTOX94
AMBTOX94
Baltimore Hart tor
C&D Canal
Striped Bass S tudies
Striped Bass Studies
Striped Bass Studies
C&D Canal
Chester
CPS
CPS
Chester
Choptank
Striped Bass Studies
CPS
CPS
Choptank
James
AMBTOX90
AMBTOX9S
AMBTOX95
AMBTOX95
AMBTOX95
Fall Line Monitoring
James
Lower Bav Mainstem
UDE
UDE
UDE
UDE
UDE
UDE
UDE
Lower Bay Mai astern
Middle Bav Mainstem
UDE
UDE
UDE
UDE
Concentration (ug/L)
Station

PatapscoR.
Bear Creek
Curtis Bay
Middle Branch
Northwest Harbor
Outer Harbor
Sparrows Point
Stations combined

Chesapeake City
Delaware City
Courthouse Pt.
Stations combined

URL
USE
Stations combined

Martinak
KGC
UTK
Stations combined

Elizabeth River
JRANN
JRBNN
Willoughby Bay
Lynnhaven River
02035000
Stations combined

CB1
CB2
CB3
CBS
CB6
CB7
CB8
Stations combined

CB9
CB10
CB11
CB12
# Samples

5





1
11

37
16
II
71

2
1
4

20
2
1
24

2
1
1
1
1
11
77







1
7

1
I
1
1
# Detections

0
0
0
0
0
0
Q
0

19
16
IS
53

2
2
4

20
2
2
24

2
0
0
0
0
21
26







1
7

1
1
1
1
Maximum

BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD

80
55
2S
80

23
22
30

80
10
2
80

15
BLD
BLD
BLD
BLD
20.
30

1.7
2.8
0.8
3.6
0.7
2.8
12
3.6

3.7
6.4
2.2
3.6
90* pereentile

-
-
-
-
.
-
-
-
\
49
78
&
53

.
;
35

70
.
-
66

.
.
.
-
-
8
8

.
.
.
.
.
.
-
5.2

.
.
-
.
                                                      52

-------
Basin
Data ID
UDE
UDE
UDE
Middle Bay Mainstem
Upper Bay Mainstem
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
UDE
UDE
UDE
UDE
UDE
UDE
Upper Bay Mainstem
Magothv
AMBTOX94
AMBTOX94
Magothy
Middle
AMBTOX93
AMBTOX93
Middle
Nanticoke
AMBTOX93
AMBTOX93
CPS
CPS
CPS
CPS
CPS
CPS
CPS
Nanticoke
Patuxent
CPS
CPS
CPS
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
Concentration (ng/L)
Station
CB13
CB14
CRIP
Stations combined

Grove
Howell
Spesutie
Elkton
Kentmore
Havre de Grace
CB15
CB16
CB17
CB18
CB19
CB20
Stations combined

Gibson Island
South Ferry
Stations combined

Frog Mortar
Wilson Point
Stations combined

Bivalve
Sandy Hill Beach
DMP
FBB
FBI
NDB
TLB
TWM
UMH
Stations combined

CAB
LYC
SEW
LPXT0173
PTXCF8747
PTXCF9575
PTXDE2792
PTXDE5339
PTXDE9401
it Samples
1
1
1
7

19
18
19
6
5
6





1
79

1
1
2

3
2
6

2
2
2
2
2
2
2
2
2
18

2
2
2
4
4
4
4
4
4
# Detections
1
1
1
7

18
18
17
6
5
5





1
75

1
1
2

3
a
6

2
2
2
2
2
2
2
2
2
18

2
2
2
3
4
4
2
2
3
Maximum
9.2
2.8
2£
9.6

31
16
69
24
28
13
5.6
1.0
29
3.4
1.5
26
69

BLD
BLD
BLD

38
1H
134

23
48
49
21
19
29
23
36
41
49

24
13
9.9
0.79
1.1
1.1
0.98
0.46
0.98
90* percentile
-
-
;
12

19
16
32
26
34
16
\
-
-
-
.
;
23~

-
;
-

-
-
140

.
-
-
.
.
.
.
.
-
56

.
.
.
.
1.6
1.3
.
.
.
53

-------
Basin
Data ID
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
NOAA/COASTES
Patuxent Basin
Potomac
AMBTOX90
AMBTOX90
AMBTOX90
AMBTOX90
AMBTOX90
CPS
CPS
CPS
CPS
CPS
CPS
DC ERA
DC ERA
ICPRB
ICPRB
ICPRB
ICPRB
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Striped Bass Studies
Potomac
Sassafras
AMBTOX94
AMBTOX94
CPS
Sassafras
Susquehanna
Fall Line Monitoring
Severn
AMBTOX94
AMBTOX94
Severn
Concentration (u,g/L)
Station
PTXDF0407
PTXED4892
PTXED9490
PXT0402
PXT0494
PXT0603
PXT0809
PXT0972
WBPXT0045
Stations combined

Freestone Point
Indian Head
Morgantown
Possum Point
Dahlgren
BTM
CHP
COF
DYN
FOR
MTW
Anacostia 01 649500
Anacostia01651000
Anacostia T 120
Anacostia T800
Anacostia T500
Anacostia T 1100
Cherry Hill
Maryland
Mid
Virginia
Quantico
Widewater
Stations combined

Betterton
Turners Creek
MLC
Stations combined

01578310

Junction Rt. 50
Annapolis
Stations combined
# Samples
4
4
4
4
4
4
4
4
4
66

1
1
5
1
5
2
2
2
2
2
2
18
18
2
2
2
1
13
25
26
32
13
n
190

1
1
2
7

93

1
1
2
n Detections
3
4
4
4
4
4
3
3
4
57

1
1
0
1
1
2
2
2
2
2
2
18
18
2
2
2
1
13
25
26
32
13
12
180

0
0
2
2

59

1
1
2
Maximum
1.1
2.4
1.8
2.0
6.6
7.7
1.6
2.1
11
24

27
22
BLD
20
7.4
26
8.9
6.9
29
16
23
21
16
3.5
4.8
2.3
2.1
110
310
220
184
90
12Q
310

BLD
BLD
11
15

22

BLD
BLD
BLD
90* percentile
-
3.4
2.5
2.9
11
8.5
.
.
21
7.1

\ .
.
.
.
.
.
.
.
.
.
.
26
14
_
.
.
.
73
86
73
96
75
142
70

_
.
.
-

9.3

.
-
.
54

-------
Basin
Data ID
West Chesapeake
CPS
CPS
CPS
West Chesapeake
Wve
AMBTOX90.91.93
AMBTOX93
Wye
York
AMBTOX95
AMBTOX95
AMBTOX95
AMBTOX95
York
Concentration (ng/L)
Station

BEB
BRB
NRV
Stations combined

Manor House
Quarter Creek
Stations combined

YRACA
YRBCA
PRAWP
PRBWP
Stations combined
# Samples

2
2
2
6

7
2
9

1
1
1
1
4
# Detections

2
2
2
6

2
2
4

0
0
0
Q
0
Maximum

29
29
22
29

28
22
29

BLD
BID
BLD
BID
BLD
90* percentile

.
.
;
35

-
-
36
%
-
.
.
.
-
55

-------
Table 3.  Freshwater acute zinc toxicity data presented in order from most to least sensitive species. Symbols used include:
*NR=not reported, S=static test. N=nominal concentration, F=flow-thru test, M=measured concentration,  R= renewal test
Species
Cladoceran,
Ceriodaphnia
reticulata
Green algae,
Selenastrum
capricornutum
Cladoceran,
Daphnia magna
u, Chinook salmon,
* Onchorhynchus
tshawytscha
Cutthroat trout,
Salmo clarki
Rainbow trout,
Oncorhynchus mykiss
Cladoceran,
Ceriodaphnia dubia
Cladoceran,
Daphnia pulex
Arctic grayling,
Thymallus arcticus
Method
S,N
S,N
S,N
F,M
S,M
F,M
S,M
S,N
S
Chemical
zinc
chloride
zinc
sulfate
zinc
zinc
sulfate
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
zinc
chloride
Hardness
(mg/L as
CaCO3)
45
*NR
45
21
*NR
23
289.8
280-300
45
soft*
LC50
(ug/L)
32
50
68
84
90
93
95
107
112
Hard adj. Duration
LC50 & Effect
(ug/L)
34.99 48 hr
LC50
72 hr
EC50,
GRO
74.35 48 hr
LC50
175.2 96 hr
LC50
96 hr
TLm
179.6 96 hr
LC50
21.4 48 hr
LC50
117.0 48 hr
LC50
96 hr
LC50
Reference
Carlson & Roush
1985
Vasseuretal. 1988
Mount & Norberg
1984
Finlayson & Verrue
1982
Rabe & Sappington
1970
Chapman 1975
Schubsuer°Bsrigan
et al. 1993
Mount & Norberg
1984
Buhl & Hamilton
1990

-------
Fathead minnow,
Pimephales promelas
Loach,
Noemacheilus
montanus
Cladoceran,
Daphnia similis
Ciliate,
Chilodonella
uncinata
Big claw river
shrimp,
Macrobrachium
carcinus
Mussel,
Anodonta imbecillis
Snail,
Bellamya bengalensis
Scud,
Hyalella azteca
Cyprinid fish,
Barilius bendelisis
Striped Bass,
Morone saxatilis
R
S

S
S

S

S
R
S, M
S
S,N
zinc
sulfate



zinc
chloride

zinc
sulfate

zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc
zinc
chloride
46.5
*NR

*NR
*NR

*NR

39
*NR
290
*NR
285
204
140

165
<170

200

268
280
290
400
430
216.9 96 hr
LC50
96 hr
LC50

96 hr
LC50
24 hr
LC50

96 hr
LC50

330.8 96 hr
LC50
96 hr
LC50
65.4 96 hr
LC50
*NR
98.4 96 hr
LC50
Norberg-King 1989


Joshi & Chamoli
1987
Soundrapandian &
Venkataraman 1990

Madoni et al. 1996
Correa 1987
Keller &Zam 1991
Rao & Jayasree
1987

Schubauer-Berigan
et al. 1993

Deoray & Wagh
1987

Palawski et al. 1985

-------
      Snail,                 S,N
      Physa heterostropha
zinc         100        434
sulfate      (10.6 C)
241.2      96 hr      Wurtz 1962
           LC50
in
00
Cladoceran,
Daphnia lumholzi
Shrimp,
Paratya compressa
Atlantic salmon,
Salmo solar
Sockeye salmon,
Onchorhynchus
nerka
Longfin dace,
Agosia chrysogaster
Coho salmon,
Oncorhynchus
kisutch
Nematode,
Caenorhabditis
elegans
Snail,
Helisoma
campanulatum
Snail,
Physa gyrina
R
S
F,M
F,M
R,M
F,M
S
S,N
F,M
zinc
zinc
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
chloride
*NR
*NR
14
22
217
25
*NR
100
(22.8 C)
36
437.5
722
740
749
790
905
1000
1,270
1,274
96 hr
LC50
48 hr
LC50
2,176
1,502 96 hr
LC50
227.8 96 hr
LC50
1,628 96 hr
LC50
96 hr
LC50
705.9 96 hr
LC50
1,683 96 hr
LC50
Vardia et al. 1988
Hatakeyama&
Sugaya 1989
Carson & Carson
1972
Chapman
1975,1978a
Lewis 1978
Chapman & Stevens
1978
Williams &
Dusenbery 1990
Wurtz 1962
Nebekeretal. 1986

-------
Ln
Diatom,
Navicula semimtlum
Rotifer,
Brachionus
calyciflorus
Water flea,
Moina macrocopa
Flagfish,
Jordanella floridae
Brook trout,
Salvelinus fontinalis
Mozambique tilapia,
Tilapia mossambica
Pond snail,
Lymnaea luteola
Colorado squawfish,
Ptychocheilus Indus
Guppy,
Poecilia reticulata
Ciliate,
Colpidium campylum
Leech,
Erpobdella
octoculata

S

S,N
F,M
F,M
S,N
R
S
S,M
S
R

zinc
chloride

zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
sulfate
58
36.2

*NR
44
46.8
115
200.6
175-230
191.2
182-201
30
*NR
*NR
1,320
1,320

1,320
1,500
1,550
1,600
1,680
1,700
1,740
1,850
2,050
1,164 120 hr
EC50
1,735 24 hr
LC50

48 hr
LC50
1,672 96 hr
LC50
1,639 96 hr
LC50
790 96 hr
LC50
518 96 hr
LC50
546 96 hr
LC50
2,682
24 hr
EC50,
IMM
96 hr
LC50
Academy of Natura
Sciences 1960
Couillard et al. 198<

Hatakeyama &
Sugaya 1989
Spehar 1976a,b
Holcombe &
Andrew
1978
Qureshi & Saksena
1980
Khangarot & Ray
1987b
Hamilton 1995
Pierson 1981
Madoni et al. 1992
Willis 1989

-------
     White Sucker,
     Catostomus
     commersoni
F,M     zinc       18
        chloride
ON
O
Scud, F
Gammarus lacustrts
Tubificid worm, S,N
Limnodrilus
hoffmeisteri
Ciliate, S
Evplotes sp.
Protozoa, S
Aspidisca cicada
Green algae,
Chlorella vulgaris
Ciliate, S
Paramecium
caudatum
Protozoa, S
Uronema nigricans
Razorback sucker, S
Xyrauchen texanus
Protozoa, S
Euplotes affinis
zinc
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
*NR
100
*NR
*NR
*NR
*NR
*NR
199.4
196-203
*NR
2,240
>2,274
2,390
2,400
2,400
2,500
2,900
2,920
3,100
96 hr
LC50
> 1,264 11 day,
LC50
24 hr
LC50
24 hr
EC50
96 hr
EC50
24 hr
EC50,
IMM
24 hr
EC50,
IMM
904 96 hr
LC50
24 hr
EC50
IMM
2,200     5,228     96 hr      Duncan &
                    LC50      Klaverkamp 1983
                                                            De March 1988


                                                            Wurtz and Bridges
                                                            1961


                                                            Madonietal. 1996


                                                            Madonietal. 1992


                                                            Rachlin and Farran
                                                            1974

                                                            Madoni et al. 1992



                                                            Madoni et al. 1992
                                                                                     Buhl & Hamilton
                                                                                     1996

                                                                                     Madoni et al. 1992

-------
Common Carp,
Cyprinus carpio
River Limpet,
Ancylus fluviatilis
Cyclopoid copepod,
Cyclops sp.
Bluegill,
Lepomis macrochirus
Northern squawfish,
Ptychochellus
Oregonensis
Clawed toad,
Xenopus laevis
Ciliate,
Vorticella
convallaria
Diatom,
Nitzschia linearis
Bryozoan,
Pectinatella
magnified
Fish,
Lepidocephalichthyes
guntea
R,N
S
S
F,M
F,M
R
S
S
S,N
S
zinc
sulfate
zinc
sulfate
zinc
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
zinc
sulfate
19
*NR
*NR
45
24.4
20-30
100
*NR
294.6
204.4
190-220
*NR
3,120
3,200
3,310
3,314
3,498
3,600
3,790
4,300
4,310
4400
7,083 96 hr
LC50
96 hr
LC50
48 hr
LC50
3,623 96 hr
TLm
6,423 96 hr
LC50
2,001 96 hr
EC50,
ABN
24 hr
LC50
957 120 hr
LC50
1,307 96 hr
LC50
96 hr
LC50
          Khangarot et al.
          1983

          Willis 1988


          Abbasictal. 1988


          Cairns & Scheier
          1959

          Andros & Carton
          1980


          Dawsonetal. 1988



          Madoni et al. 1996



          Patrick et al. 1968
          Pardue & Wood
          1980
96 hr      Bengeri & Patil
          1987

-------
Bonytail,
Gila elegans
Bryozoan.
Plumatella
emarginata
Bryozoan,
Lophopodella carteri
Golden shiner,
Notemigonus
crysoleucas
Asiatic clam,
Corbicula fluminea
Worm, oligochaete
Lwnbriculus
variegatus
Green alga,
Chlorella
saccharophila
Goldfish,
Carassius auratus
Amphipod,
Gammarus sp.
Ostracod,
Cypris subglobosa
Isopod,
Lircetts alabamae
S
S..N


S,N
S.N
S,M
S,N

S,M

S,N
S,M
R
F.M
zinc
chloride
zinc


zinc
zinc
sulfate
zinc
sulfate
zinc
chloride

zinc
sulfate

zinc
sulfate
zinc
zinc
zinc
sulfate
191.2
182-201
204.4
190-220

204.4
190-220
50
64
30

*NR

50
50
*NR
152
4,800
5.300


5,630
6,000
6,040
6,300

7,100

7,500
8,100
8,352
8,375
1,540
1.607


1,707
6,000
4,900
9,712



7,500
8,100

3,265
96 hr
LC50
96 hr
LC50

96 hr
LC50
96 hr
TLm
96 hr
LC50
9 day,
LC50

96 hr
EC50

96 hr
TLm
96 hr
TLm
96 hr
LC50

Hamilton, S.J. 1995


Pardue & Wood
1980
Pardue & Wood
1980

Cairns et al. 1969
Cherry et al. 1980
Rodgers et al. 1980

Bailey & Liu 1980
Rachlin et al. 1982
Cairns et al. 1969
Rehwoldt et al. 1973
Vardiaetal. 1988
Bosnak & Morgan
1981

-------
CO
Isopod,
Asellus communis
Diatom,
Navicula incerta
Duckweed,
Lemna minor
Zebra danio,
zebrafish
Brachydanio rerio
Southern platyfish,
Xiphophorus
maculatus
Tilapia,
Tilapia zillii
Snail,
Amnicola sp.
White perch,
Morone americana
American eel,
Anguilla rostrata
Tubificid worm,
Tubifex tubifex
Worm,
Nais sp.
S,N
S,M

R

S,N
S
S,M
S,M
S,N
R
S,M
zinc
sulfate
zinc
chloride

zinc
chloride

zinc
sulfate
zinc
sulfate
zinc
zinc
nitrate
zinc
nitrate
zinc
sulfate
zinc
100
*NR
*NR
*NR

166
*NR
50
55
55
*NR
50
8,755
10,000
10,000
10,000

12,000
13,000
14,000
14,400
14,500
17,780
18,400
4,866 96 hr
LC50
96 hr
EC50
96 hr
EC50
168 hr
LC50

4,341
96 hr
LC50
14,000 96 hr
TLm
13,280 96 hr
TLm
13,380 96 hr
TLm
96 hr
EC50,
IMM
18,400 96 hr
TLm
Wurtz & Bridges
1961

Rachlin et al. 1983


Wang 1986


Van Leeuwen et al.
1990


Rachlin &
Perlmutter 1968


Hilmy et al. 1987


Rehwoldt et al. 1973


Rehwoldt et al. 1972


Rehwoldt et al. 1972


Khangarot 1991



Rehwoldt et al. 1973

-------
Banded killifish,
Fundulus diaphanus
Amphipod,
Crangonyx
psuedogracilis
Common indian toad,
Bufo melanosticlus
Pumpkinseed,
Lepomis gibbosus
Isopod,
Asellus bicrenata
Frog,
Microhyla ornata
Catfish,
Clarias lazera
Damselfly,
Argia sp
Harlequinfish, red
rasbora, Rasbora
heteromorpha
Ciliate,
Aspidisca lynceus
Protozoa,
Euplotes patella
S,M
R,N
S
SSM
F,M
R
S
S,N
S
S
S
zinc
nitrate
zinc
sulfate
zinc
sulfate
zinc
nitrate
zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc salt
zinc
chloride
zinc
chloride
55
50
188.3
165-215
55
220
*NR
*NR
20
*NR
*NR
*NR
19,200
19,800
19,860
20,100
20,110
22,410
26,000
40,930
46,400
50,000
50,000
17,710 96 hr
TLm
19,800 96 hr
EC50,
IMM
6,457 96 hr
LC50
18,540 96 hr
TLm
5,731
96 hr
LC50
NR 96 hr
LC50
88,960 120hr
LC50
48 hr
LC50
24 hr
LC50
24 hr
EC50,
IMM
Rehwoidt et al. 1972
Martin & Koldich
1986
Khangarot & Ray
1987a
Rehwoidt et al. 1972
Bosnak & Morgan
1981
Rao & Madhyastha
1987
Hilmyetal. 1987
Wurtz & Bridges
1961
Svobodova &
Vykusova 1988
Madoni et al. 1996
Madoni et al. 1992

-------
Bullfrog,
Rana catesbeiana
Indian catfish, R
Heteropneustes
fossilis
Jaguar guapote,
Cichlasoma
managuense
Snake-head catfish, R
Channa punctatus
Green alga,
Chlorella
pyrenoidosa
Green alga,
Chlorella salina
Green alga,
Scenedesmus
quadricauda
Climbing perch, S
Anabas testudineus
zinc
zinc
chloride
zinc

zinc
chloride
zinc
sulfate

zinc
sulfate
zinc
sulfaste

zinc
chloride
*NR
*NR
*NR

*NR
*NR

*NR
*NR

*NR
70,000
75,000
77,980

80,000
>200,000

>200,000
>200,000

260,000
96 hr
LC50
96 hr
LC50
96 hr
LC50

96 hr
LC50
96 hr
LC50

96 hr
LC50
96 hr
LC50

24 hr
LC50
Zhang et al. 1992
Hemalatha&
Banerjee 1993
Zhang et al. 1992

Dalai &
Bhattacharya 1994
Wong et al. 1979

Wongetal. 1979
Wong et al. 1979

Banerjee & Kumari
1988

-------
Table 4. The 10* percentile intercepts for freshwater and saltwater zinc toxicity data by test
duration and trophic group. These values represent protection of 90% of the test species.
Water typo
Freshwater*





Freshwater*



Saltwater




Saltwater
Acute or Chronic Trophic Group
acute All species
amphibians
zooplankton
benthos
fish
plants
chronic All species
zooplankton
benthos
fish
acute All species
zooplankton
benthos
fish
plants
chronic All species
n
55
2
5
20
26
2
12
3
2
7
82
10
51
12
9
6
10* Percentile (ug/L)
142
629
4.3
212
216
789
11
0.8
\
74
56
79
46
102
69
10
8.7
* Hardness adjusted values are used (50 mg/L).
                                            66

-------
Table 5. Saltwater acute zinc toxicity data presented in order from most to least sensitive species.  Symbols used include: *NR=not
reported, S=static test, N=nominal concentration, F=flow-thru test, M=measured concentration. R=renewal test
Species
Diatom,
Schroederetta schroederi
Purple sea urchin,
Strongylocentrotus
purpurat
Diatom,
Thalassiosira rotula
Sand dollar,
Dendrasler excentricus
Inland silverside,
Menidia beryllina
Red abalone,
Haliotis rufescens
Calanoid copepod,
Temora stylifera
Mysid,
Acanthomysis costata
Brine shrimp,
Artetniafranchiscana
Method Chemical
zinc
sulfate
S zinc
chloride
zinc
sulfate
S zinc
chloride
R zinc
chloride
F,U zinc
sulfate
S,N zinc
sulfate
R, M zinc
sulfate
S zinc
sulfate
LC50
(ug/L)
19.01
23
25.8
28
30
37
40
46
65
Duration
& Effect
96 hr
EC50
GRO
120 hr
EC50,
DVP
120 hr
EC50
GRO
1.3 hr
EC50,
REP
96 hr
LC50
48 hr
EC50
48 hr
LC50
168 hr
LC50
72 hr
LC50
Reference
Kayser 1977
Dinnel et al. 1989
Kayser 1977
Dinnel et al. 1989
Lewis 1993
Conroyetal. 1996
Nipper etal. 1993
Martin et al. 1989
MacRae & Pandey
1991

-------
ON
00
Coccolithophorid,
Cricosphaera carterae
Mediterranean mussel, S
Mytilus galloprovincialis
Lobster, S,N
Homanis americanus
Cabezon, S
Scorpaenichthys
marmoratus
Quahog clam, S,N
Mercenaria mercenaria
Eastern oyster, S,N
Crassostrea virginica
Pacific oyster, S,M
Crassostrea gigas
Diatom,
Nitzschia closterium
Copepod, S,N
Acartia tonsa
Fleshy prawn, S
Penaeus chinensis
zinc 76.69
sulfate
zinc 145
sulfate
zinc 175
chloride
zinc 191
chloride
zinc 195
chloride
zinc 205.7
chloride
zinc 206.5
chloride
zinc 271
sulfate
zinc 294.2
chloride
zinc 300
sulfate
96 hr
EC50
GRO
48 hr
EC50,
DVP
96 hr
LC50
96h
EC50,
IMM
48 hr
LC50,
MOR
48 hr
EC50,
DVP

96 hr
EC50
GRO
96 hr
LC50
96 hr
LC50
                                                                        Stillwell  1977



                                                                        Pavicic et al. 1994



                                                                        Johnson 1985


                                                                        Dinnel et al. 1989
                                                                        Calabrese & Nelson
                                                                        1974
                                                                        Maclnnes & Calabrese
                                                                         1978
                                                                        Dinnel et al. 1983


                                                                        Rosko and Rachlin
                                                                        1975


                                                                        Lussier & Cardin 1985


                                                                        Wu & Chen 1988

-------
Opossum shrimp,
Mysidopsis bahia

Rea sea urchin,
Strongylocentrotus
francisc

Dinoflagellate,
Procentrwn micans
 Calanoid copepod,
 Acartia lilljeborgi

 Shrimp,
 Mysidopsis juniae

 Green sea urchin,
 Strongylocentrotus
 droebach

 Hermit Crab,
 Pagurus longicarpus

 Harpacticoid copepod,
 Tisbe holothuriae
 Striped bass,
 Morone saxatilis

 Mysid,
 Mysidopsis bahia

 Red tongue sole,
 Cynoglossusjoyneri
s
s

S,N
S,N
S
S,N
S
S,N
F.M
S
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
sulfate
303
313
319.1
320
340
383
400
421
430
499
500
96 hr
LC50
1.3 hr
EC50,
REP
96 hr
EC50
GRO
48 hr
LC50
96 hr
LC50
1.3 hr
EC50,
REP
96 hr
LC50
48 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
Cripe 1994


Dinnel et al. 1989



Kayser  1977



Nipper etal. 1993


Nipper etal. 1993


Dinnel et al. 1989
Eisler & Hennekey
1977

Verriopoulos &
Moraitou-
Apostolopoulou 1989

Palawski et al. 1985
Lussier et al. 1985


Cui et al. 1987

-------
Scud,
Allorchestes compressa

Dungeness crab,
Cancer magister


Mysid,
Mysidopsis bigelawi

Diatom,
Thalassiosira pseudonana


Harpacticoid copepod,
Nitocra spinipes

Polychaete worm,
Neanthes arenaceodentata

Amphipod,
Corophium volutator

Green crab,
Carcims maenas

Pink shrimp,
Penaeus duorarum

Sheepshead minnow,
Cyprinodon variegatus

Polychaete worm,
Ophryotrocha diadema
R,M
S
S,M
S
F
S,N
S,N
S,N
S
R
S,N
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
zinc
sulfate
zinc
sulfate
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
sulfate
580
586
591.3
823.1
850
900
1,000
1,000
1,050
1,000=
10,000
1,400
96 hr
LC50
96 hr
EC50,
IMM
96 hr
LC50
72 hr
EC50
GRO
96 hr
LC50
96 hr
LC50
96 hr
LC50
48 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
Ahsanullah 1976


Dinnel ci al. 1989



Lussier & Gentile 198S


Fisher etal. 1984



Bengtsson &
Bergstrom 1987

Reish et al. 1976


Bryant etal. 1985


Connor 1972


Cripe 1994


Lewis 1993


Reish & Carr 1978

-------
Polychaete worm,
Nereis diversicolor

Copepod,
Acartia clausi

Brine shrimp,
Artemia salina

Polychaete worm,
Capitella capitata

Polychaete worm,
Neanthes grubei

Polychaete worm,
Ophryotrocha labronica

Scud,
Corophium insidiosum

Squid,
Loligo opalescens
Indian prawn,
Penaeus indicus

Bay scallop,
Argopecten irradians

Blue mussel,
Mytilus edulis planulatus

Atlantic silverside,
Menidia menidia
R,N
S,N
*NR
S,N
S
s
*NR
S
*NR
R
R,M
S,N
zinc
sulfate
zinc
chloride
zinc
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
zinc
zinc
chloride
zinc
chloride
zinc
chloride
1,500
1,507
1,700
1,700
1,800
1,800
1,900
> 1,920
1,990
2,250
2,500
2,728
96 hr
LC50
72 hr
LC50
48 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
EC50,
IMM
48 hr
LC50
96 hr
LC50
96 hr
LC50

Bryan & Hummerstone
1973

Lussier & Cardin 1985
Govindarajan et al.
1993

Reish et al. 1976
Reish&LeMayl991


Reish &LeMay 1991


Reish 1993


Dinnel et al. 1989



Govindarajan et al.
1993

Nelson etal. 1988


Ahsanullah 1976


Cardin 1985

-------
IS)
Cone worm,
Pectinaria californiensis

Surf clam,
Spisula solidissima

Green mussel,
Perna viridis

Dinoflagellate,
Gymnodinium splendens


Copepod,
Eurytemora qffinis

Rotifer,
Brachiomts plicatilis

Winter flounder,
Pseudopleuronectes
americanus

Mollusk,
Neotrigonia margaritacea

Soft-shell clam,
Mya arenaria

Polychaete worm,
Neanthes vaali

Tidewater silverside,
Menidia peninsulae
s
R
*NR

S,N
*NR
S,N
R,M
S,N
R.M
S,N
zinc
chloride
zinc
chloride
zinc
zinc
sulfate
zinc
chloride
zinc
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
zinc
sulfate
2,800
2,950
3,100
3,716
4,074
>4,800
4,922
>5,000
5,200
5,500
5,600
96 hr
LC50
96 hr
LC50
24 hr
LC50
96 hr
EC50
GRO

24 hr
LC50

96 hr
LC50
96 hr
LC50
96 hr
LC50

                                                                         Reish&LeMay 1991
                                                                         Nelson et al. 1988
                                                                         Govindarajan et al.
                                                                         1993

                                                                         Kayser 1977
Lussier & Cardin 1985


Snelletal. 1991b


Cardin 1985



Ahsanullah 1976


Eisler 1977a


Ahsanullah 1976


Hansen 1983

-------
UJ
Nematode,
Monhystera disjuncta


Hirarne flounder,
Paralichthys olivaceus

Polychaete worm,
Ctenodrilus serratus

Polychaete worm,
Nereis virens

Santa Domingo
falsemussel,
Mytilopsis sallei

Starfish,
Patiriella exigua

Diatom,
Navicula incerta
      Crab,
      Paragrapsus
      quadridentatus

      Daggerblade grass shrimp,
      Palaemonetes pugio

      Green alga,
      Dunaliella tertiolecta
s
*NR
S,N
S,N
R
R,M

F,M
S
S
zinc
zinc
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
zinc
chloride
5,700
6,700
7,100
8,100
8,360
> 10,000
10,100
10,500
11,300
13,000
96 hr
EC50,
DVP
48 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
EC50
GRO
120 hr
LC50
48 hr
LC50
72 hr
EC50
GRO
                                                                         Vranken et al. 1988



                                                                         Wuetal. 1990


                                                                         Reish & Carr 1978
                                                                         Eisler & Hennekey
                                                                         1977

                                                                         UmaDevi 1995
Ahsanullah 1976


Rachlin et al. 1983



Ahsanullah 1976



Burton & Fisher 1990


Fisher etal.  1984

-------
Mummichog,
Fundulus heteroclitus
Fiddler crab.
Uca annulipes
Spot,
Leiostomus xanthurus
Starfish,
Asteriasforbesil
Fiddler crab,
Uca triangularis
Mud snail,
Nassarius obsoletus
Clam,
Macoma balthica
Rivulus,
Rivulus marmoratvs
S,N
R
' S,N
S,N
R
S,N
S,N
F
zinc
chloride
zinc
sulfate
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
chloride
zinc
sulfate
zinc
sulfate
17,500
31.930
38,000
39,000
39,050
50,000
60,000
119,300
96 hr
TLm
96 hr
LC50

96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
96 hr
LC50
Dorfinan 1977
Devi 1987
Hansen 1983
Eisler & Hennekey
1977
Devi 1987
Eisler & Hennekey
1977
Bryant et al. 1985
Lin&Dunson 1993

-------
•xl
in
    Table 6.  Freshwater chronic zinc toxicity data presented in order from most to least sensitive species.  Symbols used include:
    LC=life cycle test, ELS= early life stage test, R=renewal test, S=static test, F=flow-thru test, M=measured concentration,
    N=nominal concentration, REP=reproduction endpoint, GRO=growth endpoint, MOR=mortality endpoint, HAT=hatching
    endpoint, DVP=development endpoint
Species
Cladoceran,
Moina irrasa
Flagfish,
Jordanellafloridae
Cladoceran,
Daphnia magna
Snail,
Potamopyrgus
jenkinsi
Fathead minnow,
Pimephales promelas
Guppy,
Poecilia reticulata
Sockeye salmon,
Onchorhynchus nerka
Rainbow trout,
Salmo gairdneri
Method Chemical
R Zinc
chloride
LC zinc
sulfate
LC zinc
chloride
R zinc
chloride
LC zinc
sulfate
LC zinc
sulfate
ELS zinc
chloride
ELS, F zinc
sulfate
Hardness
(mg/Las
CaCO3)
<5
44
211
*NR
46
30
32-37
25
Chronic
Value*
(ug/L)
NOEC
25
LOEC
51
46.73
59.7
106.3
<173
>242
191
Hardness
adjusted
Chronic
value
(ug/L)
176
57
14

114
267
332
344
Duration
& Effect
3 week,
REP
30 day,
GRO

77-112
day,
GRO
8wk,
MOR
134 day
GRO
21 month
MOR
21 month
.MOR
Reference
Zou 1997.
Spehar 1976a,b
Chapman et al.
manuscript
Dorgelo, J. et al.
1995
Benoit & Holcombe
1978
Pierson 1981
Chapman 1978
Sinleyctal. 1974

-------
Cladoceran,
Ceriodaphnia
reticulata
Chinook salmon,
Oncorhynchus
tshawytscha
Snail,
Physa gyrina
Brook trout,
Salvelinus fontinalis
Zebra danio zebrafish,
Brachydanio rerio
Caddisfly,
Clistoronia magnified
R.M
ELS.F
F,M
LC,F
R
LC
zinc
zinc
chloride
zinc
chloride
zinc
sulfate

zinc
chloride
372.5
25
36
45.9
*NR
31
221.4 5.5
371.1 668
NOEC 753
570
854.7 919
1,102
>5,243 >7,860
7 day,
MOR
4 month,
MOR
30 day
MOR
4-27
month,
MOR
< 16 day,
HAT
76 day
DVP
Carlson & Roush
1985
Chapman 1975
Nebekeretal. 1986
Holcombe et al. 1979
Dave et al. 1987
Nebecker et al. 1984
* If chronic value was not reported a NOEC or LOEC was used.

-------
Table 7. Saltwater chronic zinc toxicity data presented in order from most to least sensitive species . Symbols used include:
LC=life cycle test, ELS= early life stage test, R=renewal test, S=static test, F=flow-thru test, M=measured concentration,
N=nominal concentration, REP=reproduction endpoint, GRO=growth endpoint, MOR=mortality endpoint, HAT=hatching
endpoint, DVP=development endpoint
Species
Mysid,
Acanlhomysis costata
Red abalone,
Haliotis rufescens
Pacific oyster,
Crassostrea gigas
Scud,
Allorchestes
compressa
Mysid,
Mysidopsis bahia
Mysid,
Mysidopsis intii
Method
R,M
F
S,N
F

R.M
R,M
Chemical
zinc sulfate
zinc sulfate
zinc
zinc sulfate

zinc sulfate
zinc sulfate
Chronic Value*
(ug/L)
NOEC
18
NOEC
19
30
LOEC
99

152 MATC
152 MATC
Duration
& Effect
7 day, MOR
9 day,
DVP
6dayEC50,
DVP
28 day, MOR

7 day, MOR
7 day, MOR
Reference
Martin et al. 1989
Hunt & Anderson
1989
Waiting 1983
Ahsanullah &
Williams 1991

Harmon and
Langdon 1996
Harmon and
Langdon 1996
* If chronic value was not reported a NOEC or LOEC was used.

-------
Table 8.  The percent probability of exceeding the zinc acute freshwater (FW) or saltwater
          (J!W)10th percentile for all species and the percent probability of exceeding the acute
          10th percentile for the most sensitive trophic group with n>8.
Location
Middle .Wver (SW)
PotomasRiver(FW)
Wye River (SW)
Choptaiik River (FW)
Nanticoke River (FW)
C and E) Canal (FW)
James EJver (FW)
Patuxer t River (SW)
Upper mainstem Bay (FW)
Chester River (FW)
Susquehanna River (FW)
Lower mainstem Bay (SW)
West Chesapeake (FW)
Middle mainstem Bay (SW)
Acute 10* Percentile (^g/L)
( ) - most sensitive trophic group 10th
percentile
79
142
79
142
142
142
142
79
142
142
142
79
142
79
(10 -plants)
(2 12 -benthos)
(10 - plants)
(212 - benthos)
(212 -benthos)
(212 -benthos)
(212 -benthos)
(10 - plants)
(212 -benthos)
(212 - benthos)
(212 -benthos)
(10 - plants)
(212 -benthos)
(10 - plants)
% Probability >
10th percentile
21
3.3
2.7
1.2
0.8
0.6
0.3
0.3
<0.1

-------
FIGURES

-------
Figure 1. Ecological risk assessment approach.

      PROBLEM FORMULATION
  • Stressor Characteristics
  • Exposure Data
  • Ecological Effects Data
  • Risk Characterization
  • Endpoints
  • Stressors Potentially Impacting Aquatic Communities
  • Conceptual Model
               ANALYSIS
Characterization of Exposure: Water column monitoring data
on zinc in the Chesapeake Bay watershed.
Characterization of Ecological Effects: Laboratory toxicity
 studies.
    RISK CHARACTERIZATION
 Probabilistic comparison of species sensitivity and surface
 water exposure distributions.
                      79

-------
Figure 2. Location of the 116 stations where zinc concentrations were measured from 1985 to

1996. See key to map where stations are described.
                                                                        95
       w
       25
                                 80—
                       111-11
                                                  3   L  104
                                                               103
 0           25  Miles
—'TJgg-^gaarwKS'ai
                                            80

-------
Key to map for Figure 2    Stations where zinc was measured from 1985 to 1996. Latitude and longitude
coordinates are given in decimal degrees. Station number corresponds to station location on Figure 2.
Abbreviated station names are in parentheses.
Station niimh«- Station
1 Susquehanna River Fall Line (15783 10)
2 James River Fall Line (2035000)
3 Elizabeth River
4 Freestone Point
5 Indian Head
6 Morgantown
7 Patapsco River
8 Possum Point
9 Wye River (Manor House)
10 Bell Branch (BEB)
1 1 Bacon Ridge Branch (BRB)
12 Burnt Mill Creek (BTM)
13 Bear Creek
14 Curtis Bay
15 Middle Branch
16 North West Harbor
17 Outer Harbor
18 Sparrows Point
19 Cabin Branch (CAB)
20 CB1
21 CB10
22 CB11
23 CB12
24 CB13
25 CB14
26 CB15
27 CB16
28 CB17
29 CB18
30 CB19
31 CB2
32 CB20
33 CB3
34 CBS
35 CB6
36 CB7
37 CBS
38 CB9
39 Martinak
40 Chaptico Creek (CHP)
41 Coffee Hill (COF)
42 CR1D
43 Davis Millpond (DMP)
44 Dynards Run (DYN)
45 Dahlgren
46 Faulkners Branch - Bradley Rd. (FBB)
T ntitiiHp
39.6586
37.6708
36.8081
38.5833
38.6000
38.3337
39.2167
38.5362
38.9028
38.9917
38.9992
38.3322
39.2358
39.2064
39.2528
39.2767
39.2089
39.2081
38.7694
36.9950
38.2467
38.3717
38.5633
38.7517
38.9183
38.0717
39.1883
39.2567
39.3683
39.5500
37.0833
39.4300
37.1883
37.3650
37.5267
37.6200
37.8217
38.1000
38.8750
38.3817
38.3614
38.5700
38.6708
38.3164
38.3012
38.6989
T rmpitiufo
7671744
78.0861
76.2933
77.2667
77.2167
77.0157
76.5000
77.2920
76.1298
76.6333
76.6136
76.6369
76.4% 1
76.5803
76.5883
76.5742
76.5247
76.5075
76.6528
75.9467
76.2617
76.3233
76.4317
76.4350
76.3883
76.3233
76.2883
76.2400
76.1433
76.0800
76.0950
76.0333
76.1633
76.0750
76.0433
76.1200
76.1750
76.2200
75.8417
76.7822
76.7578
76.3833
75.7639
76.7344
77.0660
75.7853
                                                 81

-------
Station tmmkpr RtAtirin
47 Faulkners Branch -IscherRd. (FBI)
48 Forest Hall (FOR)
49 Kings Creek (KGC)
50 LPXT0173
51 Lyons Creek (LYC)
52 Mill Creek (MLC)
53 Mattawoman Creek (MTW)
54 Gibson Island
55 South Ferry
56 Frog Mortar
57 Wilson Point
58 North Davis Branch (NDB)
59 North River (NRV)
60 Bivalve
61 Sandy Hill Beach
62 Cherry Hill
63 Maryland
64 Mid
65 Virginia
66 Quantico
67 Widewater
68 PTXCF8747
69 PTXCF9575
70 PTXDE2792
71 PTXDE5339
72 PTXDE9401
73 PTXDF0407
74 PTXED4892
75 PTXED9490
76 PXT0402
77 PXT0494
78 PXT0603
79 PXT0809
80 PXT0972
81 Sewell Branch (SEW)
82 Betterton
83 Turners Creek
84 Junction RL 50
85 Annapolis
86 Tull Branch (TLB)
87 Twiford Meadow (TWM)
88 Trib. to Marshyhope Creek (UMH)
89 Grove
90 Howell
91 Spesutie
92 Delaware City
93 Chesapeake City
94 Courthouse Point
95 Elkton
96 Kentmore

38.7214
38.3989
38.7897
39.1333
38.7689
39.2825
38.6161
39.0600
39.0767
39.3083
39.3083
38.6783
38.9878
38.3214
38.3567
38.5667
38.5167
38.5222
38.4917
38.5278
38.4333
38.3133
38.3265
38.3800
38.4243
38.4940
38.3413
38.5828
38.6582
38.7118
38.8062
38.9500
39.1083
39.2350
38.6083
39.3742
39.3631
39.0056
38.9669
38.7194
38.7236
38.7631
39.4000
39.3583
39.3917
39.5417
39.5167
39.5000
39.5667
39.3750

75.8261
76.7492
76.0094
76.8183
76.6239
76.1436
77.0486
76.4350
76.5014
76.4028
76.4125
75.7478
76.6233
75.8894 l
75.8558
77.2583
77.2583
77.2667
77.3083
77.2750
77.3250
76.4222
76.3713
76.5150
76.6008
76.6645
76.4858
76.6783
76.6845
76.6858
76.7075
76.6950
76.8617
77.0583
76.5867
76.0503
75.9842
76.5067
76.4717
75.7719
75.7625
75.7431
76.0500
76.0833
76.1250
75.7250
75.8000
75.8750
75.8500
75.9583
82

-------
Stntinn nnmhw Station
97 Havre de Grace
98 Trib. to Red Lion Branch (URL)
99 Trib. to Southeast Creek (USE)
100 Trib. to Tuckahoe Creek (UTK)
101 WBPXT0045
102 Quarter Creek
103 Lynnhaven River
104 WilloughbyBay
1 05 James River above Newport News (JRANN)
1 06 James R. below Newport News (JRBNN)
107 York River above Cheatham Annex (YRACA)
108 York R. below Cheatham Annex (YRBCA)
1 09 Pamunkey River below West Point (PRB WP)
1 1 0 Pamunkey R. above West Point (PRAWP)
111 Anacostia River (T800)
112 Anacostia River (T500)
113 Anacostia River (Tl 100)
114 Anacostia River (T 120)
115 Anacostia River (01 649500)
116 Anacostia River (01 65 1000)
T Jititiirte
39.5417
39.1767
39.1308
38.8831
38.8085
38.9167
36.8972
36.9528
37.0103
36.9758
37.3050
37.2833
37.5319
37.5464
38.9322
38.9378
38.9453
38.9350
38.9603
38.9525
T immtnAf.
7670667
,75.8992
75.9794
75.9269
76.7507
76.1667
76.0886
76.2819
76.5883
76.4389
76.6104
76.5767
76.8036
76.8122
76.9394
76.9419
76.9406
76.9397
76.9261
76.9667
83

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   Figure 3. The zinc 90th percentiles determined for basins with at least 4 detected concentrations.
            150

            140

            130

            120
00
0)100

^  90

-------
  Figure 4. Seasonal pooled mean zinc concentrations and ranges (fJg/L) from 15 stations during Patuxent River

        sampling (May 1995-February 1996).
00
      2.5


        2
     c
    N
        1


      0.5


        0
                       Patuxent River Zn Concentrations

                          NOAA/COASTES Sampling
               (.39-5.04)
                MAY 95
   (<.33-5.82)
                    (<.33-5.04)
                                                                (<33-10.8)
    AUG 95         NOV 95
Pooled Station Means By Season

 -----'--	J..-.-.J- ...


FEB96

-------
    Figure 5. Zinc concentrations from the James River (1990 - 1993).
                        Zinc Concentrations in James River
        35
00
        30 -
     O)
      zi.
        25 -
     •^ 20 -
     03
 C
 0
 o
 c
 o
O
 o
 c
Kl
        15 -I
        10 -
         5 -
         0 -
           o
           o>
           —i—

            o
                  O
                  0>
                                              CD
—i—

CM
—i—



 CD


 ^
CM
O)
                  CM
                  CD
CO
CD
CO
0>
                                           Date

-------
Figure 6. Zinc concentrations from the Susquehanna River (1990 -1993).
                Zinc Concentrations in Susquehanna River
    35


    30


>-x  25


:§  20


*C  15
CD
O
f~

O
O
0   5
C

"   o
 O)
o

r-
^
           o
           o
                                  T
               o
               o
                     CO   05
CM
O)
                                  O)    ^

                                  V~    T—

                                  O    ^
CM
O)
-I—I—1—I-


  co
  O)
CO
CD
CO
O)
CO
O)
                                                                            O)
                                                     O    T-
                                                                        O   T-
                                      Date

-------
Figure 7.  Distribution of acute zinc toxicity data (LC / ECSOs) for freshwater species.
                   Zinc Effects - Freshwater Acute Tests
                     100              1000              10000

                            Zinc Concentration (pg/L)
100000
                               •  amphibians
                               O  benthos
                               v  fish
                               v  zooplankton
                               •  plant
                               — regression line
                                       88

-------
    Figure 8. Distribution of acute zinc toxicity data (LC / ECSOs) for saltwater species.
                       Zinc Effects - Saltwater Acute Tests
   99
   90 -
£ 70 -
05

I 50 J
= 30 -I

I
Q- 10 -j
      10
100           1000          10000

           Zinc Concentration (M9/L)
100000
1000000
                                   •  benthos
                                   O  fish
                                   T  zooplankton
                                   v  plant
                                  	regression line
                                          89

-------
       Figure 9. Distribution of chronic zinc toxicity data for freshwater species.
                    Zinc Effects - Freshwater Chronic Tests
   99 -r-
   90 -
CO

I 50
I
0)
0-  10
     1 --
                    10           100           1000

                             Zinc Concentration (M9/L)
10000        100000
                                •  benthos
                                O  fish
                                y  zooplankton
                               	 regression line
                                        90

-------
        Figure 10.  Distribution of chronic zinc toxicity data for saltwater species.
                      Zinc Effects - Saltwater Chronic Tests
   99
   90 -
eo
§ 70
   50
cc
| 30
I
0>
0- 10 -\
                               10                      100
                               Zinc Concentration (pg/L)
1000
                                         benthos
                                         regression line
                                          91

-------
        APPENDIX A




Zinc risk characterization by basin

-------
                     Middle River Basin  Exposures
   99 T-

'•J3

0
O 10-]
0)
Q_
    1 --
                                                      Probability of
                                                      exceedence =
            Probability of
            exceedence = 79%
                           10                   100

                         Zinc Concentration (M9/L)
                                                                     1000
                               A-l

-------
                     Potomac Basin Exposures
   99.9
O
CL
X
0)

•D
(D

C
OJ

-------
            Wye River Basin Exposures
Probability of
exceedence = 42%
Probability of
exceedence = 2.7%
                                     100
                1000
               Zinc Concentration (M9/L)
                       A-3

-------
                     Choptank River Basin Exposures
   99.9
V)
(0
o
CL
X
0

TJ
0

C
CO
0
2
0
Q.
     99 -|
90 -
70 -


50 -
     30 -
     10 -
      1 -
    0.1
                                   Probability of
                                   exceedence = 0.3%
                                                     I    I
                        Probability of
                        exceedence = 1.2%
                            10                   100

                           Zinc Concentration (pg/L)
                                                                1000
                                    A-4

-------
                     Nanticoke River Basin Exposures
   99.9
0)

13
(/>
o
Q.
X
0)

T3
0)
-^
c
 0)
 s
 0)
Q_
99 -





90 -



70


50


30



10 -





 1 -
    0.1
                                  Probability of
                                  exceedence = 0.8%
Probability of
exceedence
= 0.2%
                             10                   100

                           Zinc Concentration (M9/L)
                                                                 1000
                                    A-5

-------
                           C&D Canal Exposures
   99.9
(0
o
CL
X
0
•o
0

c
(0
•=
"c
0
l_
0
CL
     99 -
90 -
70 -


50 -
     30 -
10 -
      1  -
    0.1
                                  Probability of
                                  exceedence = 0.6
                                                            Probability of
                                                            exceedence = 0.1
                             10                   100

                           Zinc Concentration (|jg/L)
                                                                 1000
                                    A-6

-------
                    James River Basin Exposures
99.9
CO
o
CL
X
0)

"O
0)
J£
c

5
»4—
o
JD
'-?


I

 'o
 a
 M

 15

 £
 .*
 •.=


 I

 s.

£o
                                                              Probability of
                                                              exceedence
                                                              = 0.2%
                                                             (0





                                                             0)
                                                             ^3
                                                             JU
                                                             '•?

                                                             0>

                                                             y
                                                             0)
                                                             Q.


                                                            £o
                     1               10              100

                         Zinc Concentration (pg/L)
               1000
                                 A-7

-------
                       Patuxent River Basin Exposures
o
Q.
X

-------
            Upper Chesapeake Bay Mainstem Exposures
   99.9
13
CO
o
Q.
X
0)

O
CD
.*:
c
03

-------
                    Chester River Basin Exposures
CO
o
GL
X

-------
               Susquehanna Fall Line Exposures
99.9
D
CO
O
Q.
X
Q)



                                                 O

                                                 Q>
                                                 Q.
                                   3
                                   |

                                   I
                                   0)
                                   Q.
1              10             100

   Zinc Concentration (|jg/L)
                                                               1000
                              A-ll

-------
            Lower Chesapeake Bay Mainstem Exposures
   99.9
8>
3
(0
O
Q.
X
0)
c
0)
2
0)
CL
99 -




90 -



70 -


50


30



10 -I
                      Probability of
                      exceedence = 1.4%
                         1                  10

                        Zinc Concentration (pg/L)
                                                          100
                                A-12

-------
                 West Chesapeake Basin Exposures
   99.9
o
0.
X
0)




I

I
<+-
o

0)
(D
Q_
99 -







90 -





70



50



30





10 -







 1 -
    0.1
                                               ID

                                               g>

                                               'Q

                                               O


                                               M



                                               15
                                               OJ
                         10                 100


                        Zinc Concentration (|jg/L)
o
£

£
.0

o
0)
                                                    (D
                                                    Q.



                                                    O
          1000
                                A-13

-------
            Middle Chesapeake Bay Mainstem Exposures
   99.9
    99 -I
(0
s>
13
<0
O   90

X
0)
•o

-------