Grantee Research Project Results
Final Report: Meiofaunal Validation of EqP-Based Sediment Quality Criteria for Metal Mixtures in Estuarine Sediments Population to Community-Level Culturing Studies of Biogeochemical Controls on Bioavailability and Toxicity
EPA Grant Number: R825279Title: Meiofaunal Validation of EqP-Based Sediment Quality Criteria for Metal Mixtures in Estuarine Sediments Population to Community-Level Culturing Studies of Biogeochemical Controls on Bioavailability and Toxicity
Investigators: Chandler, G. Thomas , Shaw, Timothy J.
Institution: University of South Carolina at Aiken
EPA Project Officer: Aja, Hayley
Project Period: January 1, 1997 through December 31, 1999 (Extended to December 31, 2000)
Project Amount: $484,376
RFA: Risk-Based Decisions for Contaminated Sediments (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
Frequent and widespread contamination of estuarine sediments with metals have necessitated development of sediment quality guidelines (SQG) for effective risk management. Guidelines typically are directed toward single metals, but metals almost always occur as mixtures in field sediments. Essential in the development of robust SQG's is the determination of interrelationships between metal mixtures and sediment geochemical binding phases and their subsequent influences on bioavailability and toxicity.The objectives of this study were to:
1. Determine the additive effects of an EPA priority five-metal mixture on the survival and reproductive success of a metals-sensitive laboratory-cultured copepod Amphiascus tenuiremis.
2. Determine the effects of a five-metal mixture on the survival and reproductive output of naturally occurring copepod populations cultured in whole-sediment meiobenthic microcosms.
3. Determine those sediment geochemical phases that are important in controlling metal bioavailability to meiobenthic copepods, and evaluate the usefulness of EqPT (AVS:SEM) in prediction of metal toxicity to meiobenthos.
4. Assess the utility of copepod reproductive and genetic bioassays for evaluation of field sediments contaminated with complex mixtures of metals and toxic organics (e.g, PAHs).
5. Develop technologies for body-burden measurements of mixed toxicants in meiobenthic sized animals via high resolution ICP-MS and GC-MS.
Summary/Accomplishments (Outputs/Outcomes):
The results of this project are summarized below.Laboratory Mixture Bioassay Studies. The acute effects of many individual, seawater-solubilized metals on meiobenthic copepods and nematodes are well known. In sediments, however, metals most often occur as mixtures, and it is not known whether such mixtures exhibit simple additive toxicity to meiobenthos. The estuarine meiobenthic copepod Amphiascus tenuiremis was tested in four acute (96-hour) sediment bioassays to determine sediment and pore-water LC50's for single-metal exposures to copper, lead, nickel, and zinc. Laboratory-cultured copepods were exposed to clean 98 percent silt:clay sediments spiked with metal chloride solutions to yield five exposure concentrations plus a control. Trimmed Spearman-Karber analysis gave sediment 96-hour LC50 values of 4.4 µmole Cu/g, 5.7 µmole Ni/g, 11.9 µmole Pb/g, 10.3 µmole Zn/g, and pore-water 96-hour LC50 values of 2 µmole/L, 11.7 µmole/L, and 5.7 µmole/L for Cu, Ni, and Zn, respectively. Male survival after exposure to Cu, Pb, and Ni was significantly less than female survival ( = 0.05). Toxicity of a combined USEPA priority metal mixture to A. tenuiremis was assessed using sediment spiked equitoxically with Cd, Cu, Ni, Pb, and Zn. The sum toxic unit that produced a median lethal dose was 0.72. The mixture had a significantly greater than additive effect on A. tenuiremis survival, with the mixture being 1.4 x more toxic than that expected by simple additivity. In the next phase of this project, these respective metal toxicity relationships for A. tenuiremis were used to design a more holistic meiofaunal sediment microcosm test of metal mixture toxicity with a focus on geochemical phases as controls on metal bioavailability.
Microcosm Metal Mixture Studies. In order to determine the geochemical phases important in controlling metal bioavailability to meiofauna in estuarine sediments, a novel microcosm culturing method was employed. Sixty microcosm sediment cores containing live, intact meiofaunal communities were collected from a pristine salt marsh at North Inlet Estuary, Georgetown, SC, and cultured under flowing seawater in the laboratory. Two dialysis tubes (Cutoff = 500MW) were installed onto stopcock ports at two depths in each microcosm. Sediments spiked with increasing concentrations of Cd, Cu, Ni, Pb, and Zn (Nominal Toxic Units = 0, 0.5, 1.0, 5.0) were added to the surface layer of each microcosm. The addition of sediments buried the dialysis tubes; one poised just below the sed:water interface and the second at approximately the redox boundary. Laboratory-cultured, Amphiascus tenuiremis, were added to each microcosm as a model reference control, and were then cultured for 14 days on a single-pass flow-through seawater system. The microcosm study was repeated over three seasons (Summer, Fall, and Spring) to account for seasonal variability in natural copepod abundances and sediment geochemistry (e.g., redox boundary).
Results and Conclusions. The naturally-occurring deep infaunal copepod,
Enhydrosoma propinquum, exhibited a strong dose response to the increasing
toxicity of metals in the summer and fall replicates. The epibenthic to shallow
infaunal copepods, Halicyclops coulli and Microarthridion littorale, also
naturally-occurring copepods, exhibited a less strong overall decrease in
survival in the summer and fall. Natural differences in species-specific
burrowing depth preferences likely influence porewater metal exposure risk in
field sediments. In the spring experiments, all three field species (E.
propinquum, H. coulli, and M. littorale) exhibited a decrease in survival from
TU=0 to TU=1.0, with an apparent "metals preservation effect" at TU=5.0; i.e.,
death of many individuals but depressed bacterial breakdown of their bodies. The
introduced copepod, A. tenuiremis, exhibited an overall decrease in survival
during the fall replicate, and a variable increase in survival in the summer. A.
tenuiremis exhibited the same pattern in the spring as seen with the field
species?a general dose-response decrease in survival.
The reproductive
success (number of offspring surviving at 14-d per surviving female) of A.
tenuiremis was depressed in all three seasons with increasing toxicity of the
metal mixture. The reproductive success of M. littorale exhibited an average
increase at the highest dose in the fall, but response was variable. M.
littorale reproductive success was consistently depressed in the spring at all
concentrations.
Surprisingly, pore-water measured toxic units of ~2 and 7 in the two highest doses of the spring experiment would suggest that there should have been complete mortality in these treatments. Complete mortality was not observed, however, but a significant reproductive depression was seen in the field copepod, M. littorale, and the introduced copepod, A. tenuiremis.
The current paradigm of metal bioavailability to benthic fauna stresses that pore-water concentrations and sediment ingestion dictate toxic response. However, estuarine clay sediments'ability to bind trace metals, in oxic and suboxic regimes, through iron/manganese oxides, organic carbon, and sulfide precipitation decreases metal bioavailabilities to infauna. These meiofaunal microcosms with metal-mixture spiked sediments showed poor correlation between measured sediment-bound and pore-water metal concentrations, and toxic response by the meiobenthic copepod Amphiascus tenuiremis. Despite mixed metal treatments of five sediment toxic units (TU on an SEM basis), and measured pore water metal concentrations of greater than five aqueous TU, complete copepod lethality was not achieved. This is in direct contradiction to toxic response in 96-hour spiked clean-sediment bioassays (above Laboratory Bioassay section). The sediment binding phases acid-volatile sulfides (AVS), iron- and manganese-oxides, and dissolved organic carbon (DOC) were measured in the oxic sediment horizons of control and treatment microcosms (where >98 percent of meiofaunal copepods reside). Sediment AVS values were consistently low and below detection (0.60 µmol/g dry sediment) indicating that AVS was not an important nor useful factor in controlling and predicting metal bioavailability/toxicity to copepods. Copepods did not (do not) burrow into anoxic horizons of sediments, thus their immediate metal exposure is not strongly influenced by AVS. Total sediment iron and manganese ranged from 142-258 µmol/g dry sediment and 0.4-2.0 µmol/g dry sediment, respectively. Pore-water DOC ranged from 22-60 mg/L.
These results suggest that the geochemical factors likely controlling metal bioavailability to copepods were iron- and manganese-oxides and organic carbon. One very important finding was that pore-water dialysate metal concentrations in the <500 molecular weight fraction were not predictive of metal toxicity to meiobenthic copepods. This fraction may have contained low molecular weight DOC (e.g., small peptides, carbohydrates, etc.) that associate with free metals and reduce their bioavailability and transport across cell membranes.
To further explore the role of sediment geochemical phases and mixed metal bioavailability, an additional replicate microcosm study was conducted detailing DOC molecular weight (MW) distribution (<500 MW or >500 MW) in pore waters between oxic/suboxic regimes. This study found higher concentrations of <500 MW DOC in unspiked control treatments (405 ? 17.1 µg/mL), but a reduction in <500 MW DOC concentration in priority-metal spiked sediment (303 ? 175 µg/mL). This finding, though not statistically significant, does suggest that high MW natural organic matter (NOM) may degrade less in spiked sediments; or that NOM binding with high MW metals limits transport across a 500 MW cut-off dialysis membrane by increasing DOC MW. Metal fractionation among control microcosms indicated that sediments sequestered Ni, Zn, and Pb, while Cu and Cd were detected in pore waters only. Mixed-metal microcosms had all measured divalent metals except Cu associated with sediments and pore waters, while Cu was found only within the sediment particulate fraction. It appears from these data that organic carbon, and especially DOC, and oxic sediment processes may have an important but overlooked influence on meiobenthic metal bioavailability in field sediments that is difficult to duplicate in low DOC laboratory spiked-sediment bioassays (porewater DOC typically 40-60 µg/mL).
Field Mixed-Contaminant Studies. As a field population-level assessment of copepod adaptation to a complex sediment-associated mixture, meiobenthic copepod populations (Microarthridion littorale) were collected from three South Carolina, U.S.A., estuaries having different pollution stress histories (i.e., pristine sediments, high PAH-sediments, high metals/moderate PAH-sediments) and assayed for survival and reproductive output in 14-day exposures to pristine and heavily PAH/metals-contaminated sediments. Whole-sediment reproduction bioassays were used to determine: (1) whether copepods exposed to a highly-contaminated sediment mixture exhibit differential survival and reproductive output as a function of prior environmental histories, and (2) whether genetic relatedness among populations measured as DNA sequences of the mitochondrial gene, cytochrome apoenzyme b, are linked to copepod contaminant tolerance. Overall, adult survival and reproductive success in contaminated sediments were significantly reduced relative to controls for all three populations irrespective of environmental histories. However, differential resistance to sediment contaminant mixtures by the two copepod populations inhabiting the contaminated sites was not found despite their prior exposures to mixed contaminants at PAH and Metal concentrations of 7286.7 to 2466.9 ng/g dry weight and 460.5 to 3497 µg/g, respectively. There was, however, significant genetic differentiation between copepod populations from the control and the two contaminated sites. Generally, cross-population survival and reproductive outputs were not significantly different from one another and could not be linked to genetic differentiation at the population level using cytochrome apoenzyme b.
Technology Development for Micro-Mass Body Burden Analyses of Meiobenthos. We have determined the first trace metal partitioning coefficients obtained from reproducing cultures of shallow and deep water meiobenthic foraminifera. We have cultured and analyzed cadmium trace metal uptake by one of the most common and ecologically important shallow-water benthic foraminifers, Ammonia beccarii, using ICP-MS techniques developed specifically for this project. Metal partitioning coefficients in the shells of benthic foraminifera provide a record of dissolved trace metals in the growth habitat of the organism (i.e., porewater and bottom water normalized to Ca). Juvenile foraminifera were cultured, cleaned and dissolved under trace-element clean conditions for ICP-MS determination of trace metal partition coefficients on recently deposited (1-3 months old) foraminiferal calcite. We measured a D-Cd for Ammonia of 1.0 ?0.5 which fell within the ranges reported for typical core-top calibrations from field oceanographic studies. Partition coefficients for Cd present the most difficult analyses at the low control concentrations (<1nM) used for this study, but provide a valid proof of concept. This project partially funded acquisition of a "Laser Ablation" ICP-MS which has the potential of providing single animal metal uptake measurements in shells and soft tissues of meiobenthos. To date, we have had some success measuring metal isotope ratios of abundant metals in meiobenthos such as Ca and Sr; but our results suggest that better limits of detection are needed before this method is applicable to specimens from very low metal environments. We have a Ph.D. candidate in the process of developing these techniques for additional metals (e.g., Pb, Ni, and Co) as part of his dissertation research.
A micro-mass, lipid-normalized body burden measurement approach was developed for this project to allow assessment of PAH (and metals) uptake by meiobenthic copepods inhabiting a mixed contaminant, salt-marsh EPA Superfund site?Diesel & Kopper's Creeks, Charleston, SC. Microtechniques for polycyclic aromatic hydrocarbon (PAH) body burden and total lipid analysis were developed to determine the first lipid normalized bioaccumulation factors for a hydrophobic organic contaminant in a meiobenthic organism (0.063-0.500 mm) living in naturally contaminated sediments. Fluoranthene, benz[a]anthracene, and benzo[a]pyrene biota-sediment accumulation factors (BSAFs) were determined in situ for field-collected meiobenthic copepods (Microarthridion littorale). This allowed comparisons of sex- and reproductive stage-specific BSAFs in order to assess the role of lipid content in M. littorale PAH bioaccumulation. Gravid female, non-gravid female, and male BSAFs varied by sex and reproductive state at 0.82 (0.58-1.13), 0.54 (0.39-0.72), and 0.36 (0.23-0.53) for fluoranthene, 0.50 (0.37-0.66), 0.44 (0.33-0.56), and 0.40 (0.25-0.68) for benzanthracene, and 0.09 (0.06-0.15), 0.12 (0.08-0.18), and 0.0.15 (0.07-0.32) for benzo[a]pyrene. M. littorale bioaccumulated PAHs on a gram lipid basis as predicted by equilibrium partitioning theory. BSAFs were below the predicted equilibrium partitioning maximum, indicating that M. littorale is not in an equilibrium state with PAH's in its surrounding sediments. BSAFs declined with increasing PAH log Kow for all copepods. Tissue sample sizes needed with this approach ranged from only 55-80 µg-dry weight for body burden analysis (10 pg PAH/sample) and 80-400 µg-dry weight for total lipid analysis (MDL 1 µg lipid). This work has been submitted to Environmental Science and Technology.
Journal Articles on this Report : 7 Displayed | Download in RIS Format
Other project views: | All 23 publications | 7 publications in selected types | All 7 journal articles |
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Chandler GT, Green AS. Developmental stage-specific life-cycle bioassay for assessment of sediment-associated toxicant effects on benthic copepod production. Environmental Toxicology and Chemistry 2001;20(1):171-178. |
R825279 (Final) R826399E02 (Final) R827397 (2000) R827397 (2002) R827397 (Final) |
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Ferguson PL, Chandler GT. A laboratory and field comparison of sediment polycyclic aromatic hydrocarbon bioaccumulation by the cosmopolitan estuarine polychaete Streblospio benedicti (Webster). Marine Environmental Research 1998;45(4-5):387-401. |
R825279 (Final) |
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Hagopian-Schlekat T, Chandler GT, Shaw TJ. Acute toxicity of five sediment-associated metals, individually and in a mixture, to the estuarine meiobenthic harpacticoid copepod Amphiascus tenuiremis. Marine Environmental Research 2001;51(3):247-264. |
R825279 (Final) R826399E02 (Final) |
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Kovatch CE, Chandler GT, Coull BC. Utility of a full life-cycle copepod bioassay approach for assessment of sediment-associated contaminant mixtures. Marine Pollution Bulletin 1999;38(8):692-701. |
R825279 (Final) R826399E02 (Final) |
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Schizas NV, Chandler GT, Coull BC, Klosterhaus SL, Quattro JM. Differential survival of three mitochondrial lineages of a marine benthic copepod exposed to a pesticide mixture. Environmental Science & Technology 2001;35(3):535-538. |
R825279 (Final) R825439 (1999) R825439 (Final) R826399E02 (Final) R827397 (2002) R827397 (Final) |
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Schlekat CE, Decho AW, Chandler GT. Dietary assimilation of cadmium associated with bacterial exopolymer sediment coatings by the estuarine amphipod Leptocheirus plumulosus: effects of Cd concentration and salinity. Marine Ecology Progress Series 1999;183:205-216. |
R825279 (Final) R826399E02 (Final) |
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Schlekat CE, Decho AW, Chandler GT. Bioavailability of particle-associated silver, cadmium, and zinc to the estuarine amphipod Leptocheirus plumulosus through dietary ingestion. Limnology and Oceanography 2000;45(1):11-21. |
R825279 (Final) R826399E02 (Final) |
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Supplemental Keywords:
ocean, environmental health, marine biology., RFA, Scientific Discipline, Water, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Geochemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Chemical Mixtures - Environmental Exposure & Risk, Environmental Microbiology, Ecological Effects - Environmental Exposure & Risk, chemical mixtures, Biochemistry, Ecological Effects - Human Health, Ecology and Ecosystems, Ecological Risk Assessment, Ecological Indicators, aquatic ecosystem, biogeochemical partitioning, chronic exposure, sediment bioassay, ecological exposure, culturing studies, estuarine sediment, contaminated sediment, marine biology, metal release, metal mixtures in estuarine sediments, sediment quality survey, copepod life-cycle bioassays, sediment quality criteria, ocean, benthos-associated organisms, water quality, meiobenthos, equilibrium partitioning based criteria, meiofaunal validationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.