Chemical Contaminants

1. Chemical Contaminants D.E. Armstrong University of Wisconsin-Madison Water Resources Management Seminar February 5, 2007

2. What chemical contaminants are important in the wetland? • Nutrients • Metals • Organic Chemicals • How do biogeochemical processes influence their distribution and fate? • Partitioning between water and solids (sediments) • Partitioning between water and air. • Transformations – degradation, removal. • What is the nature and composition of the waste water effluent to be discharged into the wetland? • Salinity, suspended solids, DOC, BOD, major elememts • Concentrations and forms of N and P • Metals in water and suspended solids • Organic chemicals in effluent and/or sludge

3. What are the Characteristics of the Waste Water Treatment Plant Effluent? Thibodaux Sewage Treatment Plant: “Experimental sewage treatment plant, using natural microbial rock filter, outdoor oxidation ponds, UV light disinfection, composting of sewage sludge, and discharge of final effluent into a formerly dying wetland area” Are these same processes used at the plant that would discharge into Bayou Bienvenue wetland? Suspended solids may be enriched in chemical contaminants “Wetland discharge permits allow discharge of higher levels of solids to increase accretion rates” “--- the benefits of wetland wastewater treatment is the additions of solids. The added solids increase accretion rates and therefore counter subsidence” (From proposal to the Coastal Impact Assistance Program)

4. Thibodaux, LA Waste Water Effluent (Approximate concentrations) WW discharged to Ponte-au-Chene Swamp; hydraulic detention time = 120 days Compared treatment and control cypress-tupelo forest sites Concentrations of metals were low; Cu~ 6, Zn ~50 g/L Organic contaminants not reported Zhang et al. 2000. A water chemistry assessment of wastewater remediation in a natural swamp. J Environ Qual 29:1960-1968

5. Mercury Mercury exists in several forms: Hg(II) or inorganic Hg, e.g., HgCl2, Hg(OH)2, Hg(OH)+, HgDOM Hg(0) or elemental Hg – a volatile form CH3Hg+ - methyl mercury (MeHg) – the most toxic form May be in water or solids (sediments, suspended particulate matter) • MeHg • Formed in anoxic environments such as water logged sediments in wetlands • Formed from Hg(II) by sulfate reducing bacteria (SRB) • Bioaccumulates in aquatic foodwebs • Is found in effluents from waste water treatment plants

6. Methylation - Schematic Higher organisms (SRB) (ingestion) Hg(II) MeHg plankton Fish Microbial Sulfate Reduction CH2O Stoichiometry (SRB) SO42- H2S CO2 • Sulfate is required • Use of sulfate as a terminal electron acceptor is required • Organic matter is required – used as carbon source • Other bacteria may also be involved in methylation • Total Hg about 500 ng/L in influents and 25 ng/L in effluents at midwest WWTPs

7. Metal Speciation The bioavailability, toxicity, and treatability of metals is related to their chemical forms (speciation). • Distribution between aqueous and solid phase forms • Controlled mainly by adsorption reactions • Often represented by the distribution coefficient, Kd • Distribution among aqueous (“dissolved”) forms • Controlled mainly by complexation reactions • Association of metals with anions an molecules • Influences the fate and effects of metals • Bioavailability and toxicity • Transport by water • Removal during water and waste water treatment

8. Metal Complexation • Metals in water associate with anions and molecules termed “ligands” • The equilibrium constant or “stability constant” is: A high KMLcorresponds to a strong complex • Example Complexation Reactions: • The strength of the complex depends on the metal and the ligand “Weak” Ligands: Cl-, HCO3-, SO42- “Strong” Ligands: S2-, R-NH2, R-SH, NOM (natural organic matter)

9. Metal SorptionBinding to Solids • Sorption Mechanisms • Ion Exchange • Surface Complexation • Important Solids • Suspended Particulate Matter (SPM) • Soil, Sediment, Biosolids • Important Solids Components • Metal Oxides; FeOOH(s), AlOOH(s) • Clay Minerals • Natural Organic matter (NOM)

10. Metal Adsorption on Fe(OH)3(S) • Adsorption is dependent on pH (surface charge) • Adsorption is varies among metals (binding strength) • Other influences: • Other ions • Surface coatings such as organic matter (From Stumm, 1992)

11. Sorption of Metals to Particles (Solids) Partitioning of the metal between Solid and Aqueous Phases The Distribution Coefficient, Kd : Represents extent of sorption The Kd is usually obtained from data, i.e., measurements of suspended particulate matter (solids) concentration and the concentrations of filterable (“dissolved”) and particulate metal. Depends on many factors: Properties of the metal: tendency to adsorb Properties of the solid: sediment particle, FeOOH(s), etc Aqueous species of the metal: Formation of metal-ligand complexes may “compete” with metal adsorption.

12. Fraction sorbed: depends on both Kd and [SPM] [SPM] is the suspended particulate matter concentration, g/mL when Kd units are mL/g In systems with low particle abundance, chemicals with large Kd values may be found mainly in the “dissolved” or aqueous phase (From Elzerman and Coates, 1987)

13. Speciation Calculations The metal is distributed among many forms, e.g. Concentrations of individual species are related to the “free metal ion”concentration [Men+], the equilibrium constant ()for binding the “free metal ion” to the ligand (L), and the concentration of the organic, inorganic or organic ligand. For example for an organic ligand; The total metal speciation can thus be expressed as: The equilibrium calculation requires information total metal concentration, ligand concentration, and stability constants ( values). Dominance of a species is favored by a high ligand concentration and/or a high stability constant. Computer codes are available for making speciation calculations

14. Sorption to Particles in Rivers: Comparison of Metals The tendency of metals to bind to particles influences distribution between particulate and filterable (“dissolved”) forms ,i.e., Kd (Wisconsin Rivers) General Pattern Al>Pb>Zn>Cd>Cu (From Shafer et al., 1999)

15. Pb Zn (Shafer et al., 1999) Dissolved organic carbon influences Kd “competition” between SPM and DOC for the metal

16. Speciation Application: Waste Water TreatmentSorption of Metals • Removal by Sorption to SPM/Biosolids • Efficiency Varies Among Metals • Metal Complexation Impedes Sorption • Dissolved Organic Matter • Synthetic Ligands: EDTA

17. Removal Efficiency Varies with Metal (Shafer et al., 1998)

18. Removal is related to sorption (Kd) Kd values are for metal partitioning in the WWTP effluent (Shafer et al., 1998)

19. Binding to DOC • Impedes sorption • Reduces Kd • Impedes removal (Shafer et al., 1998)

20. Metal (Zn, Cu) Removal During WWT Influence of Complexation (Schematic) Removal during WWT occurs through sorption to suspended particulate matter and subsequent settling Zn also forms complexes with ligands such as natural dissolved organic matter (DOM) or EDTA: These complexes reduce sorption and removal of Zn Addition of iron might free Zn from complexes and enhance removal However, this approach appears to have limited success

21. Metal Bioavailability and Toxicity The binding of metals to particles and aqueous ligands generally reduces bioavailability and toxicity, although there are exceptions MeLWeak (Bioavailable) LWeak Me2+ (Bioavailable) MeLStrong (Unavailable) LStrong Me-Sorbed (Unavailable) Examples: Lstrong = DOM or HS-; Lweak = HCO3- Metal speciation is important to understanding and modeling metal bioavailability and toxicity for a given site (river, lake)

22. Water Quality Criteria for Metals • Toxicity testing shows the total metal concentration in the water is not predictive of toxicity. • Toxicity is more closely related to the dissolved metal concentration. • Toxicity is most closely related to the “free metal ion” concentration, e.g., Cu2+: strong complexes are less available This leads to two approaches for Water Quality Criteria • The “dissolved metal concentration” calculated from the total metal concentration and the Kd • DMT – the Dissolved Trace Metal Translator • The Biotic Ligand Model which calculates metal uptake by the organism based on equilibrium partitioning

23. (Adapted from DiToro et al., 2001) BIOTIC LIGAND MODEL Ca2+Na+ H+ The biotic ligand competes with other ligands for the metal ion Competing Cations Free Metal Ion M-DOC M2+ M-Biotic Ligand Complexation By Organic Matter Site of Action Strong-binding ligands reduce the bioavailability of the metal MOH+ MHCO3+ MCl+ Complexation by Inorganic Ligands

24. Metals In Sediment • Toxicity is related to concentrations in sediment pore waters • Total metal concentrations in dry sediments are not predictive of toxicity • Sulfide plays an important role in controlling toxicity: cadmium, copper, nickel, lead, zinc Schematic: When FeS(s) > Σ(Cd +Ni + Cu + Zn + Pb), metal toxicity is reduced. This is the basis for one approach to assessing metal toxicity in sediments to benthic organisms (Ankley et al. 1996. Technical basis and proposal for deriving sediment quality criteria for metals. Environ Toxicol Chem 15:2056-2066.)

25. Sediment Quality Criteria for Metals • Based on the concept that the metal in the pore water is the bioavailable form • The concentration in the pore water is controlled by equilibrium partitioning between the dissolved and solid phase • The species in solution is also important AVS Criteria Minimum Partition Criteria (also used for organic cpds) SED = simultaneously extracted metals: Cd, Cu, Ni, Zn, Pb AVS = acid volatile sulfide FCV = Final Chronic Values from Water Quality Criteria

26. Nutrients (N and P) Typical concentrations in WWTP Effluents Total P: 2-5 mg/L PO4-P: 2 mg/L NO3- N: 5 – 12 mg/L TKN: 3 mg/L • Removal in Wetlands • Denitrification and nitrate removal • Uptake by phytoplankton (plants) • Partial recycling to NH4+, NO3-, and PO43- during organic matter decomposition • Partial incorporation into sediment organic matter (peat) • Adsorption/precipitation reactions and P retention

28. Denitrification denitrifiers NO3- N2 Microbial respiration using nitrate as the terminal electron acceptor CO2 CH2O • Anoxic conditions required • Respiration creates anoxic conditions in bottom sediments • Requires interchange between surface water and sediments • Requires moderately long hydraulic residence time in wetland Some bacteria reduce nitrate to ammonium-N

29. Removal by other biogeochemical processes: • Formation of organic matter (peat) • Stoichiometry of nutrient incorporation during photosynthesis • Remineralization by microbial respiration • Incorporation of residual organic matter into sediment organic matter • Stoichiometry of residual organic matter • Retention in sediments by adsorption/precipitation • Important for P • Fe (III) hydrous oxides are important for phosphate adsorption • Reduction of Fe(III) to Fe(II) in anoxic sediments reduces P adsorption • Formation of Fe sulfides reduces P adsorption by Fe

30. Biological Cycling of Nutrients by Phytoplankton (algae) Photosynthesis Inorganic Nutrients Biomass Nutrients Respiration 106 CO2 + 16 NO3- + HPO42- + 122 H2O + 18 H+ + Trace Elements P R “Redfield ratios: actual stoichiometry varies somewhat with conditions C106H263O110N16P1 + 138 O2 (CH2O)106(NH3)16(H3PO4)1 “Biomass” Redox Reactions P limitation occurs when N:P > 16 CH2O + O2 CO2 + H2O NO3- + H2O + H+ NH3 + 2 O2

31. Organic Matter Diagenesis (Schematic) (CH2O)106(NH3)16(H3PO4)1 (plant organic matter) bacteria CO2 PO4 (CH2O)x(NH3)y(H3PO4)z NH3 (sediment organic matter) Sediment organic matter is likely depleted in N and P relative to plant organic matter

32. Atmospheric Input Urban Runoff Rural Watershed WWTP Effluent Dissolved P Particulate P Surface water Groundwater Algal Available-P Sediment P Phosphorus interchanges between compartments in lakes

33. Water algae controls SRP PO43- Plankton-P O2 Sediment or Water Fe2(OH)3PO4(s) Fe or Ca, Al control SRP precipitation organic P Fe3+ + PO43- FeOOH=PO4(am) adsorption burial oxidation oxic zone diffusion anoxic zone Fe2(OH)3PO4(s) reduction FeOOH=PO4(am) Fe or Ca,Al control SRP Fe2+ + PO43- organic P HS- CaCO3 CO32- FeS(am) FeCO3(s) Fe3(PO4)2(s) Ca3(PO4)2(s) The “ferrous wheel” Biotic Cycle Retention of Phosphorus From Lake Sediments

34. Organic Chemicals • What compounds are present? • What are the processes that influence fate and persistence • What are the properties of chemicals that influence susceptibility to transport, removal, persistence, and bioaccumulation? • What types of chemicals are not removed by wastewater treatment?

35. Sources to the Environment(Water and Air) • Direct release/discharge • Industrial processes (HFOCs; PCBs) • Use in the environment – pesticides • Waste Water Discharge (OWCs) • Pharmaceuticals • Industrial chemicals • Pesticides • Animal Wastes – Land Application • Stormwater • Pesticides • Asphalt Coatings; Polycyclic Aromatic Hydrocarbons (PAHs) • Environmental transformations • Others

36. Uses of Organic Chemicals(Sources) • Pesticides • Petroleum Compounds • Organic Solvents • Industrial Chemicals • Polychlorobiphenyls (PCBs); electric tranformers; hydraulic fluids • Highly fluorinated organic chemicals (HFOCs); coatings on cooking ware; others • Flame Retardants • Polybrominated diphenyl ethers • Pharmaceuticals • Households, hospitals • Animal feeds • Others

37. Classifications of Organic Chemicals According to Chemical Type or Family Chlorinated hydrocarbons Polychlorobiphenyls (PCBs) Polychlorodibenzodioxins (PCDDs) Polycyclic Aromatic Hydrocarbons (PAHs) Halogenated methanes Chlorophenols, Carbamates, Triazines Polybrominated diphenyl ethers (PBDEs) Highly Fluorinated Compounds (HFCs) Macrolide antibiotics According to Volatility Volatile Organic Compounds (VOCs) Semi-Volatile Compounds

38. Properties of Organic ChemicalsInfluence Transport, Fate, Persistence, Treatability • Vapor Pressure • Hydrophobicity • water solubility • octanol-water partition coefficient • Acid-Base Properties • H-Bonding Tendency • Susceptibility to Reactions

39. Organic Acids and Bases: Partitioning Behavior (acid dissociation) (base protonation by water (dissociation of a protonated base (acid) Ionic species behave much differently than neutral chemicals • Very low vapor pressures • Do not partition from water into air • Much higher water solubility • Partition much less in to octanol, lipids, or biota • May bind to specific adsorption sites through ionic bonding or covalent bonding. • Transported mainly by water or suspended particles

40. The Acid Dissociation Constant and pKA (Change in Species Distribution as a Function of pH) Organic Acids (e.g., R-COOH = RCOO- + H+) ( ) denotes activity [ ] denotes concentration The fraction present as the undissociated acid can be calculated from the pH and pKA for the organic acid. When pH > pKA, (A-) > (HA) When pH < pKA, (HA) > (A-)

41. ProcessesInfluence Transport, Fate, Treatability • Air-water partitioning • Sorption • Bioaccumulation • Chemical/Biological Transformations • Photochemical Reactions

42. Air-Water Partitioning • The Air-Water Partition Coefficient •  This partitioning coefficient is often expressed by the Henry’s Law Constant, KH. • where pi is the partial pressure of chemical i in the air phase and Ci w is the concentration in water (e.g., mol/L). • Pressure is usually represented in bars, atmospheres (atm) or Pascals (Pa), where 1 atm = 101.3 kPa. R is the ideal gas constant,  where R = 0.083 L bar mol-1 K-1 or8.314 Pa m3 mol-1 K-1 or 0.082 L atm mol-1 K-1 (When Kaw = 1, KH = 24.4 atm L/mol) • KH increases with increasing VP • KH may also be high when VP is low and water solubility is also low

43. VP and water solubility co-vary • The range of KH is smaller than ranges of vapor pressure and water solubility. • Compounds with low vapor pressure can be relatively “volatile” from water. KH has a strong temperature dependence (From Schwarzenbach et al., 1993)

44. Sorption of Organic Chemicals(Binding to Solids or Particles) • Transport in Urban and Rural Runoff • Removal from Contaminated Groundwaters by Gas Stripping • Removal by Water and Waste Water Treatment • Removal from Lakes and Reservoirs by Natural Particle Scavenging • Transport into Groundwaters by Infiltration Importance

45. The Sorption Coefficient (Kd) • A distribution coefficient • Used to express sorption of organic chemicals to solids such as soil, sediment, or biosolids in waste water treatment • Shows the degree of sorption from water by solids • A high Kd means a high degree of sorption The dimensionless partition coefficient can be calculated as: where ρsolid is the density of the solid, kg/L

46. Factors Influencing Kd • Properties of the compound and the solid • Cwater for polar and ionic compounds • “Speciation” of the compound in the aqueous phase: Binding to colloids, dissolved organic matter, or metals • pH when the compound is a weak acid or base • Kd does not infer a particular sorption mechanism • Obtained experimentally or by prediction from properties of the compound and the solid.

47. Sorption of Neutral Organic Chemicals • Non-polar compounds - sorbed preferentially by organic components • Generally increases with hydrophobicity • Kow predicts sorption of nonpolar compounds to natural organic matter • H-bonding influences sorption of more polar compounds • Kow does not predict sorption of highly polar compounds • e.g., PCBs > pharmaceuticals

48. The organic carbon-water partition coefficient (Koc) • Non-polar Organic compounds are sorbed preferentially by the organic components of particles such as sediments and biosolids • If chemical i partitions only to the organic phase of the sediment, the organic carbon-water partition coefficient Koc is: • Kd can be calculated from Koc Where foc is the weight-fraction concentration of organic carbon in the soil or sediment. Organic matter is about 50% organic carbon. • Koc can be estimated from Kow Hydrophobic Compounds

49. Prediction of Koc But, this “linear free energy relationship” varies with the class of organic compound. Poly-parameter LFERs are often better. (Schwarzenbach et al., 1993) • The Kow can be used to predict the Koc or Kom for a given compound i. • The Kom and the foc for the sediment or soil can then be used to predict the Kd for a given sediment/soil and compound i.

50. Sorption of Polar and Ionic Compounds • Not related to hydrophobicity (Kow) • Not dominated by organic matter • Other mechanisms • H-bonding • Surface Complexation • Ion Exchange • More complex models are required to predict sorption • Kd often measured rather than predicted