Chemical Properties & Fate (L02 Fate PL 2024 PDF)

CHEMICAL PROPERTIES & FATE PIM LEONARDS air water natural agricult. industr. soil soil soil...

CHEMICAL PROPERTIES & FATE PIM LEONARDS air water natural agricult. industr. soil soil soil sediment A-LIFE: Amsterdam Institute for Life and Environment 1 Content ▪ Processes involved in chemical fate ▪ Partitioning coefficients, sorption, organic carbon, Koc ▪ QSPRs & QSARs ▪ Transport processes in aquatic environment 2 Fate of chemicals in the environment air emission to air water Benzene natural agricult. industr. soil soil soil sediment PCBs 3 Example of chemical fate (1): emission to air Fate chemical depends: compound and environment-properties emission path (e.g. to air or water) emission air Benzene 98 % to air PCBs 1% Benzene 0 % Benzene water PCBs 35 % Benzene 2 % PCBs 1% natural agricult. industr. soil soil soil sediment Benzene 0 % PCBs PCBs 63 % 4 Example of chemical fate (2): emission to water air Benzene 5 % PCBs 0% emission Benzene 0 % to water water PCBs 0% Benzene 93 % PCBs 1% natural agricult. industr. soil soil soil sediment Benzene 2 % PCBs 99 % Van Leeuwen e.a (2007) 5 Regional distribution air water natural agricult. industr. soil soil soil sediment emission advection diffusion degradation 6 Physico-chemical properties and partitioning coefficients Henry-constant (water – air) – volatility Octanol-water-partitioning coefficient (water – lipid) – Lipophilicity, hydrophobicity Acid dissociation constant pKa (acid – H+) – Release of H+ or OH– (polarity, ionisation) Sorption coefficient (water – solid phase) – Binding to soil or sediment (or food) 7 Evaporation of chemical X from water to air 8 Henry-constant (KH): a measure for volatility In equilibrated water- Vp gas system KH = 𝑆𝑤 Vp vapour pressure (Pa) 𝑆𝑤 water solubility (mol/m3) KH in Pa m3/mol benzene 4.84 naphthalene 1.08 anthracene 0.0587 → Benzene will readily volatilize from water, anthracene not 9 Examples KH and air-water partition coefficients (Kair-water) calculated for five chemicals Vapor pressure Solubility KH Kair-water Chemical (Pa) (mol/m3) (Pa.m3/mol) (L/L, or m3/m3) Ethanol 7.50⋅103 1.20⋅104 6.25⋅10-1 2.53⋅10-4 Phenol 5.50⋅101 8.83⋅102 6.23⋅10-2 2.52⋅10-5 Pyrene 6.00⋅10-4 6.53⋅10-4 9.18⋅101 3.71⋅10-4 DDT 2.00⋅10-5 2.82⋅10-6 7.08 2.86⋅10-3 10  Octanol-water-partition coefficient Kow or P or logP ▪ n-octanol is a good surrogate for lipids in organisms: Prediction of bioaccumulation potential ▪ Partitioning of chemical between n-octanol and water phases represents distribution between lipid and water Coctanol Kow = Cwater Coct = 540,000 Cw Coct = 0.58 Cw 11  Determination of Kow - Shake flask method (reliable up to log Kow 5) Octanol Coct Kow = Cwater Coct Water Cwater - Chromatographic parameters: retention time indicative of lipophilicity (reliable upto log Kow 6-7) - Prediction from chemical structure: using computer models (for higher log Kow chemicals) → e.g. EPISUITE 12 Kow calculation Fragment constants (K ) for a few fragments, ow from the EPISUITE program Fragment Fragment constant (f)a -CH3 aliphatic carbon 0.5473 Aromatic Carbon 0.2940 -OH hydroxy, aromatic attach -0.4802 -N aliphatic N, one aromatic -0.9170 attach 13 Hydrophobicity and octanol-water partition coefficient Kow Hydrophobicity is tendency of a chemical to “escape” from water, and it depends on: - size - presence of polar groups Also called lipophilicity Hydrophilic hydrophobic phase: phase lipid phase (biota) H2O organic carbon (sediment) Kow chemical X Cl CCl 3 Cl methanol 0.17 O OH acetone 0.58 benzene 134 Cl Cl Cl DDT 1.0 107 Hydrophilic Hydrophobic 14 Sorption and desorption to soil and sediment adsorption Soil or sediment (pore)water desorption Cs Kp = Pore water Ca Grain Kp = sorption coefficient Cs: Concentration in soil or sediment Ca : Concentration in water Kp depends on: - chemical properties of chemical - physico-chemical properties of soil or sediment (organic matter, clay) 15 Carbon Normalized Sorption Coefficient: ▪ But Kp values varies greatly because of large differences in carbon contents of soils ▪ Therefore preferred value is Koc (corrected for organic carbon) ▪ Koc considers the organic carbon content of the soil or sediment Sorption Coefficient, Kp Koc = ------------------------------------ Fraction Organic Carbon foc: fration organic carbon Karickhoff et al. (1979) 16 Equilibrium partitioning theory (EqP or EP) Pore water is main route of exposure for soil or sediment living organisms Pore water Grain Pore water concentrations can be predicted from total concentrations using sorption Koc In laboratory setting equilibrium partitioning between Kp compartments Soil or sediment (pore)water BCF But in field situation: organism often no equilibrium between compartments presence of dissolved organic carbon (DOC) in pore water stronger sorption than predicted from Kp due to ageing or presence of black carbon (bound residues) 17 Log Koc as a function of log Kow Kp = foc * Kow 18  Acid dissociation constant (pKa) 120 100 % ionized 80 60 40 Pentachlorophenol 20 pKa=4.74 0 0 2 4 6 8 10 12 14 pH OH O- + H + Cl Cl Cl Cl Only non-dissociated forms of acids or base will be taken up in Cl Cl Cl Cl organisms Cl Cl Log Kow = 5.0 Log Kow = 2.5 19 General rules on biodegradation resistance in relation to chemical structure 1. Aromatic structures more persistent than aliphatic structures H3C-CH2-CH2-CH2-CH2-CH3 Persistency 2. Saturated aliphatics more persistent than non-saturated ones H3C-CH2-CH2-CH2-CH3 H2C=CH-CH=CH2 Persistency 20 3. Branched long-chain aliphatics more persistent than non-branched ones CH3 H3C-CH-CH2-CH2-CH2 H3C-CH2-(CH2)n-CH2-CH3 CH2 Persistency CH3 4. Highly chlorinated congeners more persistent (persistency increases with degree of chlorination) Cl Cl Cl Cl Cl Cl Cl Cl Cl Persistency Degradation (first order kinetics) conc. DT50 = half life ~ C/C0 = 1/2 50% 0.693 DT50 = --------- k time DT50 -k*t C = Co * e With: C = concentration at time t (in mg/kg) Co = concentration at t = 0 (in mg/kg) k = degradation rate constant (day-1) t = time in days 22  Waste water treatment plant (WWTP) Primary Secondary settling Aeration settling tank tank tank Equilization Raw sewage Effluent water (influent) water River Sewage sludge Dewatered for disposal 23 Removal of chemicals in WWTP Removal efficiency 24 Martinez Bueno et al., 2012  Speciation of trace metals Water M y+ M - anorg. M - partic. M x+ matter M - org. (e.g. DOC, humic acid) M - detrital Porewater M -adsorbed M - bound Sediment 25 Copper speciation in saltwater as a function of pH (from Blust et al., 1991) 26 Quantitative structure-property relationships (QSPR) and quantitative structure-activity relationships (QSAR) Quantitative Structure-Activity Relationship Principle Y = B0 + B1·X1 + B2·X2 + B3·X3 + … Mathematical relationship between a compound property, y (to be predicted or explained) and one or more (chemical/physical/structural/…) parameters, x1, x2…. The coefficients B have to be derived from a training set of (n experimental) data 27 Structural/Physico- chemical properties X variable(s) Prediction model Environmental Training set Properties Validation set Y variable Y = B0 + B1·X1 + B2·X2 + B3·X3 + … Quantitative Structure-Activity Relationship y PC2 Log Kow = 0.9·S + 2.1·V + 3.1 x PC1 28 QSAR: Parameters to be predicted Y Physicochemical properties log Kow Aqueous solubility Vapour pressure Henry’s law constant pKa …… Environmental fate properties Bioconcentration/accumulation Chemical degradation Biodegradation Sorption ……… Effects Mortality Reproduction Growth Enzyme induction ……… 29 QSAR Parameters to be used X Atomic/molecular properties number of electrons connectivity electron densities (on atoms) molecular volume molecular shape molecular fragments …… Molar /macroscopic properties dipole moment polarizability molar volume solubility partition coefficients chromatographic retention ……… Thermodynamic properties (Free) Energy difference between reactants and transition state or end products 30 QSAR: Example substituted vs chlorinated benzene 6 5 y = 0.0636x - 0.8379 R2 = 0.9919 4 log Kow 3 y = 0.0581x - 1.0217 2 R2 = 0.7167 substituted benzenes chlorinated benzenes 1 Linear (substituted benzenes) Linear (chlorinated benzenes) 0 40 50 60 70 80 90 100 110 Molecular volume (cm3/molecule) 31 Prediction software: EPISUITE 4.1 http://www.epa.gov/tsca-screening-tools/download-epi-suitetm- estimation-program-interface-v411 US-EPA / Syracuse Research Corporation QSAR/SAR tools: Database measured values: AOPWIN - atmospheric oxidation rates > 40 000 compounds BCFWIN - bioconcentration factor (BCF) BIOHCWIN - biodegradation of hydrocarbons BIOWIN - biodegradation probability ECOSAR - aquatic toxicity (LD50, LC50) HENRYWIN - Henry’s law constant HYDROWIN - aqueous hydrolysis rates (acid-, base-catalyzed) KOAWIN - octanol-air partition coefficient KOWWIN - octanol-water partition coefficient (Kow) MPBPWIN - melting pt, boiling pt, and vapor pressure PCKOCWIN - soil sorption coefficient (Koc) WSKOWWIN - water solubility (from log Kow) WATERNT - water solubility (using atom-fragments) 32 Transport processes in air and aquatic environment 33 Hydrologic Cycle 34 Global Ocean Conveyor System ▪ Temperature, salinity, wind 35 Cold condensation – arctic and high mountain ranges Grasshopper effect Chemicals travel in multiple cycles of evaporation, transport by air and condensation Source: http://sliwkanich.weebly.com/science-30.html 36  Circulation Patterns – global transport of pollutants http://earth.nullschool.net/#current/wind/surface/level/orthographic=-31.39,32.36,278 37 POPs long range transport to arctic regions POP = persistent organic pollutant PBT = persistent, bioaccumulative, and toxic compound http://www.amap.no/ 38 Example - POPs in polar bears Arctic Monitoring and Assessment Programme AMAP http://www.amap.no/ PCBs CHL= Chlordane 39 Key issues/Questions ▪ What processes are involved in chemical fate? Mention 5 processes ▪ What is speciation? ▪ What is DT50 ▪ How is biodegradation related to chemical structure, give a few examples of some general rules ▪ What are KH, Kow, Koc, Kp ? ▪ Explain how Kow can be used to predict sorption ▪ Describe grasshopper efffect ▪ What is the Global Ocean Conveyor System 40 https://kahoot.it/ Game pin: 2327270 41