55 (FAR-1117-856769) Evaluation of critical metal loads using the Unit World Model for lakes.
Start time: 8:00 AM
Farley, K^{1, 2}, Carbonaro, R¹, Di Toro, D^{2, 3}, ¹ Manhattan College, Riverdale, NY, USA² HydroQual, Inc., Mahwah, NJ, USA³ University of Delaware, Newark, DE, USA
The overall goal of this work is to develop a quantitative method or model for assessing the risks posed by metal inputs to lakes. For initial lake applications, we have considered a vertically well-mixed water column overlying a sediment layer. Processes specifically considered in the model include dissolved and particulate phase transport, a simplified description of the biogeochemical cycling of organic carbon and sulfur, metal complexation to organic carbon and inorganic ligands (as described by WHAM), and competitive interactions of metals and major cations to the biological site of action for water column and sediment-dwelling organisms (as described by the Biotic Ligand Model). The model calculations are used to evaluate the relative ranking for the critical loading of metals (Cd, Cu, Ni, Pb, Zn) in an idealized lake. In addition, the cycling of metals is examined and is shown to be a function of metal binding affinity to organic carbon, pH, hardness, organic carbon production rates, and organic carbon diagenesis and net sulfide production in sediments.

56 (MOR-1117-574367) pH and Zn profiles in photosynthetic biofilm using ion-selective electrodes: An explanation for diel metal cycling?
Start time: 8:20 AM
Morris, J¹, Farag, A², Meyer, J¹, ¹ University of Wyoming, Laramie, Wyoming, USA² U.S. Geological Survey, Jackson, Wyoming, USA
We investigated the driving mechanism(s) behind diel Zn uptake and release in photosynthetic biofilm by using miniaturized, ion-selective electrodes (300 m tip diameter) to measure pH and Zn activity in the overlying water and within the matrix of a mixed community of photosynthetic biofilm. In darkness, the pH in a 1- to 2-mm thick layer of biofilm decreased from 9.7 to 7.3 in 51 min; and then, under relatively weak lighting (100 mol/m²/s PAR), the pH increased from 7.3 to 9.5 in 14 min. Concurrently, Zn activity in the biofilm layer increased from 0 to 2.6 x 10^-5 M in darkness and subsequently decreased from 2.6 x 10^-5 to 0 M in light. Additionally, a steep gradient existed between the relatively neutral pH in the water column (∼7.1) and the elevated pH in the diffusive boundary layer and within the biofilm matrix (∼9.7). These high and low pH values generally are only separated by 1 to 2 mm, and this gradient does not occur in darkness. Gradients of Zn activity are also steep, wherein Zn activity decreases from 7.6 x 10^-6 to 0 M within 1 mm near photosynthesizing biofilm and increases from 1.2 x 10^-5 to 1.9 x 10^-5 M within 1 mm near non-photosynthesizing biofilm. Therefore, photosynthetic biofilm can decrease Zn activity very quickly in light that is 10 to 20x less intense than full sunlight, and a steep gradient of pH and Zn activity exists near the water-biofilm interface of photosynthesizing biofilm. This suggests that Zn adsorption or precipitation of Zn-hydroxides and/or Zn-carbonates within the photosynthesizing biofilm matrix could be driving diel metal cycling in mining-impacted streams.

57 (BUT-1117-763669) Comparing equilibrium and transport modeling predictions to observed particulate metal transport in a mining-impacted stream (North Fork Clear Creek, CO).
Start time: 8:40 AM
Butler, B¹, Ranville, J¹, Ross, P¹, ¹ Colorado School of Mines, Golden, Colorado, USA
Acid-mine drainage (AMD) is an important source of metals to aquatic ecosystems. Once AMD is mixed with oxygenated stream water of neutral pH, there are changes associated with the metals present. These changes include the oxidation of metal ions, precipitation of metal oxyhydroxides, and co-precipitation and/or sorption of metals. Models exist for the prediction of metal speciation in aqueous systems with various processes occurring, such as sorption, precipitation, and physical transport mechanisms. One model that is used to predict the equilibrium speciation of a metal is Visual-MINTEQ. Another model, WASP4/META4, combines equilibrium speciation with physical transport mechanisms. This paper discusses the predicted particulate copper and zinc using both Visual-MINTEQ and WASP4/META4, as compared to observed particulate copper and zinc during both high- and low-flow spatial sampling events in North Fork Clear Creek. It was found that the dominant processes controlling the fate and transport of metals in the stream include precipitation of iron oxyhydroxides (HFO) and subsequent sorption of the metals to the HFO, and flow conditions. Dissolved organic carbon also appeared to contribute to the fate and transport of copper. Inclusion of HMO for modeling of the zinc improved the prediction of percentage particulate zinc, however results indicate that there may be another process controlling particulate zinc in the creek.

58 (WOO-1117-675119) How hard is that diet? Implications for metal accumulation and toxicity.
Start time: 9:00 AM
Wood, C¹, Franklin, N¹, Alves, L.¹, Ojo, A.¹, Niyogi, S.¹, Kamunde, C.¹, Pyle, G.¹, Chowdhury, J.¹, Kjoss, V.¹, Nadella, S.¹, ¹ McMaster University, Hamilton, Ontario, Canada
The importance of the hardness of the exposure water in reducing the uptake and toxicity of waterborne metals is well-established. However, the importance of dietary hardness has been largely overlooked. This presentation will synthesize recent evidence indicating that relatively small elevations (2- 3 fold) in the calcium content of the diet (added as CaCO3) can offer a major protective impact against the uptake and toxicity of both waterborne and dietary metals to freshwater rainbow trout. To date, protective effects have been documented against cadmium, zinc, and lead, all of which can behave as calcium analogues. Analogous protective effects of elevated dietary sodium (added as NaCl) may occur for metals such as copper which are sodium analogues. The mechanistic nature of this protection will be explored, with an emphasis on the sites and mechanisms of action in the digestive tract and gills.(Supported by NSERC, MITE-RN, ICA, CDA, NiPERA, ILZRO, Teck-Cominco, Noranda-Falconbridge, & Inco).

(59326) break.
Start time: 9:20 AM

59 (BHA-1117-863731) Estimating Critical Loads of metals to surface aquatic systems using a coupled metal TRANsport-SPECiation-TOXicity (TRANSPEC-TOX) model.
Start time: 10:00 AM
Bhavsar, S¹, Gandhi, N^{1, 2}, Diamond, M¹, ¹ University of Toronto, Toronto, ON, Canada² Current address: Gartner Lee Ltd, Markham, ON, Canada
Environmental regulators and water resources managers seek science-based critical loads (CL) for compounds discharged into aquatic ecosystems. Estimating CL for metals is challenging because metal bioavailability and toxicity depend on water chemistry and fate and transport processes. To address this need, we developed a generic model termed as TRANSPEC-TOX by integrating the coupled metal fate/TRANsport and SPECiation/complexation (TRANSPEC) model of Bhavsar et al. (2004a,b) with a TOXicity module. The TRANSPEC-TOX uses (1) the multi-species fugacity/aquivalence concept (Diamond et al. 1992) for the fate calculations, (2) incorporates the effects of chemistry parameters (e.g., pH, metal and ligand concentrations) on metal partitioning/distribution and speciation by means of a chemical equilibrium speciation module (e.g., WHAM, MINEQL+), and (3) assesses toxicity to aquatic receptors (e.g., fish) using the toxicity module. TRANSPEC-TOX calculates critical loads of the metals using a toxicity reference value such as an LC50. We illustrate utility of the model through application to several lakes with characteristics varying in trophic status and we use use the Biotic Ligand Model (BLM) as the toxicity module. We focus on Zn in Rainbow trout. Results suggest that for the systems where sediments are acting as a source of the metal in water column, critical load may not be linearly related to LC50 water concentrations. However, effects of chemistry parameters (e.g., pH) with constant fate/transport parameters (e.g., particle movement rates) on LC50 and CL can be possibly explained by linear relations between LC50 and CL.

60 (CAR-1117-853756) Investigation of metal-ligand interactions of model ligands for modeling metal-organic carbon binding.
Start time: 10:20 AM
Di Toro, D¹, Carbonaro, R², ¹ University of Delaware, Newark, DE, USA² Manhattan College, Riverdale, NY, USA
The Windermere Humic Aqueous Model version V (WHAM V) formulated by Tipping and coworkers is central to the prediction of toxicity of metals in sediments. It is used to compute the concentration of metal on organic carbon that is in equilibrium with the biotic ligand concentration. The WHAM formulation is based on the idea that there is a universal constant, K_MHA, that relates the strength of metal binding to the strength of proton binding. K_MHA represents the equilibrium constant for the following reaction: HL + M²⁺ = ML⁺ + H⁺ where L represents a metal binding site on humic or fulvic acid. We have been investigating QSARs which will allow for the calculation of K_MHA values for which a constant is not currently available. Correlation of K_MHA to the proton-metal exchange constant for lactic acid as suggested by Tipping (1992) and to acetic acid yields reasonable relationships with the exception of the most strongly bound cation (Th⁴⁺). An alternate approach involves correlating the log K_ML (metal-ligand formation constant) versus ligand pKa for a series of monodentate ligands containing oxygen donor atoms. Slopes from linear regression are metal specific, and a correlation of this slope with the log K_MHA for a series of metals is highly linear. This approach is especially appealing because it avoids the use of a single ligand, e.g. lactate or acetate, but rather relies on the global behavior of the metal-proton replacement for a variety of ligands.

61 (BRO-1117-832713) Photochemical control of copper speciation by dissolved organic matter in Rocky Mountain Streams, Colorado USA.
Start time: 10:40 AM
Brooks, M¹, Clements, W¹, McKnight, D², ¹ Colorado State University, Fort Collins, CO, USA² University of Colorado, Boulder, CO, USA
We investigated photochemical, source, and seasonal effects on copper (Cu) complexation by dissolved organic matter (DOM). Cu-DOM complexation regulates Cu toxicity by decreasing the activity of the cupric ion ({Cu²⁺}), the most bioavailable Cu species. Because DOM is photochemically unstable, we analyzed Cu-DOM complexation before and after photooxidation of DOM collected from 3 wetlands and 3 rivers during spring run off and late summer (n = 12 DOM solutions). After irradiation of DOM solutions for 24 h in a solar simulator, (∼4 d of sunlight), we analyzed Cu-DOM complexation during potentiometric titrations of Cu into dissolved organic carbon (DOC) concentrations of 5 mg L^-1. Across the range of titrations (7.8×10^-8 to 8.7×10^-6 mol Cu L^-1), photooxidation of DOM decreased Cu complexation, increasing {Cu²⁺} by 154% in 10 DOM types. However, in another DOM solution irradiation enhanced Cu complexation and decreased {Cu²⁺} by 30% but had no net effect on a final DOM solution (8 + 7%, mean + SD). Cu-DOM complexation did not vary between wetland versus riverine sources of DOM before or after irradiation. Similar Cu complexation before irradiation decreased significantly more during photooxidation of spring DOM (-184%) than summer DOM (-144%). Although fluorescence of DOM did not covary with Cu-DOM complexation, the specific ultraviolet absorbance (SUVA; absorbance₂₅₄ nm per mg DOC) explained 52 to 70% of the variation in Cu complexation regardless of DOM source, season, or extent of photooxidation.

62 (SCH-1117-771592) Metal speciation and mobility in mine waste piles and surface waters in a mine-impacted area.
Start time: 11:00 AM
Schaider, L.¹, Senn, D.¹, Brabander, D.², Holton, M.¹, Shine, J.¹, ¹ Harvard School of Public Health, Boston, MA, USA² Wellesley College, Wellesley, MA, USA
The Tar Creek Superfund Site in northeastern Oklahoma is heavily impacted by decades of lead and zinc mining in the Tri-State Mining area. A notable feature of this area is the presence of mine waste piles that contain elevated concentrations of Zn, Pb and Cd. Runoff from these piles, together with acid mine drainage originating from abandoned mine shafts, contribute to metal loading into Tar Creek. As part of a larger project to identify routes of exposure to children and health impacts of exposure to metals in mining materials, we characterized variations in metal concentration and speciation as a function of particle size using XRF, XRD and sequential extraction techniques. Total concentrations of Zn, Pb and Cd were found to increase with decreasing particle size (up to 10% Zn and 2% Pb by mass and 200 ppm Cd in the <37 m size fraction). The speciation of the metals also changed as a function of particle size. While the parent ore material contained metals in sulfide forms (galena and sphalerite), particles in the smallest size fraction contained metals in secondary mineral phases. We also explored the sources and mobility of Zn, Pb, Cd, Cu, Mn and Ni within Tar Creek, which drains part of the Superfund site. Using sulfate as a conservative tracer and PCA analysis, we estimated relative contributions of waste pile runoff, groundwater seepage and acid mine drainage to metal loading into the creek. Once in the creek, metal mobility was related to affinity for ferric hydroxides, which are abundant in the creek. An improved understanding of the speciation of metals in exposure media and variations in concentration and bioavailability as a function of distance from their sources will lead to a more complete assessment of the health impacts of mining activities on human and ecological health.

63 (WAL-1117-828122) Interaction between Chlorella vulgaris and dissolved inorganic selenium species.
Start time: 11:20 AM
Harrison, G, Simmons, D, Wallschlager, D,
In this study, we investigated the uptake of the three inorganic Se species selenite [Se(IV)], selenate [Se(VI)] and selenocyanate [SeCN-] by the green algae Chlorella vulgaris. Uptake experiments were conducted at typical ambient Se concentrations (1 and 10 g/L) for four weeks. In all experiments, Se addition had a positive effect on algal growth, confirming previous reports that algae require Se as a micronutrient. Despite high algal densities (typical of eutrophic conditions), we observed no statistically-significant loss of Se from solution in any experiment. In some experiments, we observed evidence of algae-mediated Se species transformations in the aqueous phase. These results suggest that although Se uptake into algae may lead to large increases of Se concentration in algae (and thereby induce ecotoxicological effects), it is not a significant pathway for Se removal from ambient waters, but may indirectly affect Se cycling and fate by causing Se speciation changes.