Influence of Dissolved Organic Matter on Aquatic in -Rich Environments

Kathleen S. Smith, James F. Ranville, Daniel J. Diedrich,,g, Diane M. McKnight, and Ruth M. Sofield

U.S. Department of the Interior Colorado School of Mines U.S. Geological Survey Golden, Colorado Mineralized areas commonl y generate acidic water with elevated dissolved concentrations, Low-pH water Higher-pH esppyecially iron and (pH <5) water (pH >7) aluminum

At confluences with higher pH water, Mixing Zone dissolved iron and aluminum precipitate Iron Coating Aluminum (pH > 3.5) Coating (pH >5) Fundamentals

¾ Chemical speciation of influences their potential toxicity to aquatic biota

¾ Dissolved free metals constitute the main bioavailable fraction of metals

¾ Presence of dissolved or ganic matter (DOM) decreases metal toxicity to aquatic biota by binding with dissolved metals Dissolved Organic Matter Fractionation

McKnight et al. (1992) demonstrated that DOM fractionates in the presence of precipitating iron and aluminum oxides 9 Some DOM is removed from solution byyp sorption onto precipitating iron and aluminum oxides 9 DOM sorption results in chemical fractionation – Molecules with greater metal-binding affinities are preferentially sorbed 9 Remaining DOM is depleted in constituents having greatest metal-binding affinity Dissolved Organic Matter Isolation McKnight et al., 1992

High er-pH ¾ Filtered stream water (pH >7) Low-pH water Deer Creek Dissolved water (pH <5) ¾ XAD-8 columns DOM

¾ H+ sattituration

¾ Freeze dried Snake River Dissolved DOM

Aluminum Suspended SnakeCoating River Fe & Al O xides (with sorbed Sediment organic matter) Dissolved Organic Matter Collection Sites

1. Stream water from a pristine Colorado stream (Deer Creek Dissolved)

2. Stream water below the confluence of an acidic, metal-enriched stream with Deer Creek (Snake River Dissolved)

3. Suspended sediment (with sorbed organic matter) below the confluence of an acidic, metal-enriched stream with Deer Creek (()Snake River Sediment)

4. Suwannee River Fulvic Acid (standard reference material) Question

How does DOM fractionation in mineralized areas affect copper bioavailabilityyq to aquatic biota? (Water Flea) A sensitive fresh-water invertebrate commonly used in toxicity testing of contaminants mm

Ceriodaphnia dubia 1mm 1 Four replicate test cups containing five organisms in each cup

Toxicity Decreasing copper Testing concentration

Controls Laboratory Toxicity Tests

¾ One set with no DOM added (just EPA moderatelyy) ) ¾ Freeze-dried DOM (6 mg/L = 3 mg/L DOC) from the different sources was added to solutions containing different copper concentrations and allowed to equilibrate ¾ 48-hour static tests at 20ºC were conducted with CidhiCeriodaphnia dubia dbi

¾ Determine mortalityyg( of test organisms (LC50) LC50 is a measurement of aquatic 100 toxicity, and is the metal concentration that is lethal to 50% of a group of test organisms ) %% ity ( ll 50 orta MM

0 Lower concentration Higher concentration More toxic Less toxic

LC50 (µg/L Copper) Toxicity Results

6 mg/L DOM Ceriodaphnia dubia 1 0.8 Suwannee River Fulvic Acid tality rr 060.6 LC50 n Mo 0.4 No Dissolved Organic Matter oo 0.2 Shift shows the protective effect racti of DOM on copper toxicity FF 0 0 50 100 150 Total Copper Concentration (μg/L) Toxicity Results 6 mg/L DOM Ceriodaphnia dubia 1 0.8 Deer Creek DOM tality rr 060.6 LC50 0.4 n Mo oo Deer Cr. DOM (unf rac tiona te d) 0.2 is similar to Suwannee R. FA racti

FF 0 0 50 100 150 Total Copper Concentration (μg/L) Toxicity Results 6 mg/L DOM Ceriodaphnia dubia

yy 1 080.8 Snake R. Sediment

tality 0.6 rr LC50 0.4

n Mo Snake R. DOM oo 0.2 Shift shows the effect of DOM fractionation on racti

FF 0 copper toxicity 0 50 100 150 Total Copper Concentration (μg/L) Toxicity Results 6 mg/L DOM Ceriodaphnia dubia 1 No DOM

Snake R. Deer Cr. DOM 080.8 DOM (unfractionated) Snake R. tality 0.6 Sediment rr LC50

0.4 Suwannee R. FA n Mo oo 0.2 Less Toxic racti

FF 0 0 50 100 150 Total Copper Concentration (μg/L) Free Copper Measured with a Cu ISE 130 6 mg/L DOM

Cu2+ 120 No DOM

110

V Deer Cr. mm 100 DOM Suwannee R. Snake R. DOM FA 90

80 Snake R. Sediment Bound Cu 70 -7.000 -6.800 -6.600 -6.400 -6.200 -6.000 -5.800 -5.600 -5.400 log Copper Concentration (M) What does this mean for the Biotic Ligand Model?

(BLM…not th e agency) The Biotic Ligand Model is incorporated into the U.S. Environmental Protection Agency 2007 Uppqdated Aquatic Life Copp er Criteria Biotic Ligand Model (BLM)

¾ Computational approach to estimate acute metal toxicity ¾ Considered to be an alternative to expensive and extensive toxicological testing to determine site-specific water-quality criteria ¾ Quantifies the “ bioavailable” fraction Biotic Ligand Model (BLM) The BLM is an interf ace betw een the f ields o f a queous , physiology, and

(Pagenkopf, 1983)

WHAM v.5 (Ti i 1994)pping, 1994) CHESS (Santore and Driscoll, 1995)

After Paquin et al., 2002 Use of the Biotic Ligand Model in Mineralized Areas

It is likely that a modified version of the BLM that incorporates the effects of iron and aluminum will need to be used to compute site- specific water-quality criteria and potential metal toxicity in many mineralized areas Overall Summary

¾ DOM with greater affinity for metal binding tends to be ppyreferentially sorbed to sediment p hases in iron- and aluminum-rich streams

¾ DOM isolated from an iron- and aluminum-rich stream was 3 times less effective at reducing copper toxicity

¾ Fracti ona tion of organ ic ma tter bbtetween disso lve d an d sediment phases in iron- and aluminum-rich streams can result in more bioavailable dissolved copper and greater potential for copper toxicity to aquatic biota Overall Summary, cont.

¾ Stream ecosystems downstream of iron- and aluminum-rich streams may be more vulnerable to adverse effects from metal toxicity

¾ Modifications to the Biotic Ligand Model may be necessary for applilitication to iron- and aluminum-rich environments Acknowledgments

This work was funded by the U.S . Geological Survey Resources Program R 82951501-0 R 82950001

Visit our websites at http://crustal.usgs.gov/projects/minewaste/ http://crustal.usgs.gov/projects/integrated_methods/ References Di Toro, D.M., H.E. Allen, H.L. Bergman, J.S. Meyer, P.R. Paquin, and R.C. Santore. 2001. Biotic ligand model of the acute toxicity of metals. I. Technical basis. Environ. Toxicology and Chemistry, v. 20, p. 2383–2396. McKnight, D.M., K.E. Bencala, G.W. Zellweger, G.R. Aiken, G.L. Feder, and K.A. Thorn. 1992. Sorption of by hydrous aluminum and iron oxides occurring at the confluence of Deer Creek with the Snake River, Summit County, Colorado. Environ. Sci. Technol., v. 26, p. 1388-1396. Pagenkopf, G.K. 1983. Gill surface interaction model for trace-metal toxicity to fishes: role of complexation, pH, and water hardness. Environ. Sci. Technol., v17p342v. 17, p. 342-347. Paquin, P.R. and others. 2002. The biotic ligand model: a historical overview: Comparative Biochemistry and Physiology, v. 133C, p. 3-35. Playle, R.C., D.G. Dixon, and K. Burnison. 1993a. Copper and binding to fish gills: modification by dissolved organic carbon and synthetic ligands. Canadian Journal of Fisheries and Aquatic Sciences, v. 50, p. 2667-2677. Playle, R.C., D.G. Dixon, and K. Burnison. 1993b. Copper and cadmium binding to fish gills: estimates of metal-gill stability constants and modeling of metal accumulation. Canadian Journal of Fisheries and Aquatic Sciences, v. 50, p. 2678-2687. Santore, R.C. and C.T. Driscoll. 1995. The CHESS model for calculating chemical equilibria in soils and solutions. In: Loeppert, R ., Schwab , A .P ., Goldberg , S . (eds .) , Chemical Equilibrium and Reaction Models, SSSA Special Publication 42. The Soil Science Society of America, American Society of Agronomy, Madison, WI. Smith, K.S., J.F. Ranville, D.J. Diedrich, D.M. McKnight, and R.M. Sofield. 2009. Consideration of iron-organic matter interactions when predicting aquatic toxicity of copper in mineralized areas. Proceedings of Securing the Future and 8th International Conference on Acid Rock Drainage (ICARD), Skellefteå, Sweden, June 22-26, 2009, 9 p. (Available online at http://www. proceedings-stfandicard-2009.com/ ) Tipping, E. 1994. WHAM--A chemical equilibrium model and computer code for waters, sediments, and soils incorporating a discrete site/electrostatic model of -binding by humic substances. Computers & Geosciences, v. 20, p. 973-1023. U.S. Environmental Protection Agency. 2007. Aquatic life ambient freshwater quality criteria – copper: 2007 revision. U.S. Environmental Protection Agency. EPA-822-R-07-001 (CAS Reg. No. 7440-50-8), February, 2007. (Available online at http://www.epa.gov/waterscience/criteria/copper/2007/index.htm)