Tools for exposure scenarios in REACH evaluations 2.
Parameter evaluation and validation for FATEMOD model.
Seija Sinkkonen and Jaakko Paasivirta,
Department of Chemistry, University of Jyväskylä, Finland University of Jyväskylä
Tools for exposure scenarios in REACH evaluations 2.
Parameter evaluation and validation for FATEMOD model.
Seija Sinkkonen and Jaakko Paasivirta,
Department of Chemistry, University of Jyväskylä, Finland University of Jyväskylä
Application of structural chemistry to environmentally relevant compounds in Jyväskylä started in 1970’s as cooperation of biology and chemistry researchers. Environmental fate modeling was realized to be central for estimation and management of risk from toxic and ecotoxic pollutants. Scientific base for practical models was developed first in 1970’s and 1980’s especially in Canada, USA, Germany and Switzerland. It was adopted to organic chemistry education and studies in Jyväskylä university at 1980’s. Practical modeling was developed first alone, but then by international cooperation since 1989, when ESF project ”Chemical Exposure Prediction” (1989-1995) started in Miland, Italy, J.Paasivirta as partner. S.Sinkkonen joined to this project in second workshop in France 1990. Later, several other environmental chemists from Jyväskylä contributed. Furthermore, to build models for Baltic Sea Area projects were active within Nordic Council in 1991-1993 and as EU project in 1996-1999. Our role in these programs was parametrization and testing of exposure models. We learnt that temperature correction of several compound properties was essential to achieve realistic fate predictions for different climates. Therefore, we worked for fast automatic procedure, to be included in model code. The pioneer paper was: J.Paasivirta, S.Sinkkonen, P.Mikkelson, T.Rantio and F.Wania (1999): Estimation of vapor pressures, solubilities, and Henry’s law constant or selected persistent organic pol...
FATEMOD database: parametrization of the values
for properties of the environments and chemicals Properties of the environments.
Instead using unit world box 1 x 1 x 1 Km as suggested by D.Mackay
Multimedia Environmental Models L-242, Lewis, Chelsea, MI, USA)
suitable for general risk estimation of chemicals, we adopted natural
catchment areas as model environments to achieve more flexibility
for different cases of risk evaluations. Properties of the chemical compounds.
Molecular properties: Name, Group, Subgroup, CAS register
number, Molar mass (WM), Melting point (Tm K), Entropy of Fusion
(ΔSf), Liquid state molar volume (Vb), pKa (for acids or bases) Temperature-dependent properties: Log(pr) = Apr – Bpr. Vapor pressure in liquid state (Pl Pa), Solubility in water (S mol m-3),
Henry’s law function (H Pa m3 mol-1), Hydrophobity LogKow (where Kow is the octanol-water partition coefficient) and….
Degradation half-life times HL(i) (i = 1 air, 2 water, 3
soil/plants and 4 sediment; reference time HLT
(usually 20 or 25 C)
/ Plants
FATEMOD window for editing property values of the environment box Southwest Finland (SWF) = catchment area of the Finnish Rivers
flowing to the Bothnian Sea. Major compartments for mass balance: Air,
surface Water, Soil (including surface plants), and Sediment. Minor compartments
for concentration data: Suspended sediment and Fish (aquatic biota).
FATEMOD editing window for substance parameters
Herbicide DNOC: evaluation of parameters for FATEMOD CAS 534-52-1, WM 198.122, Mp 86.5 C →Tm 359.65 K
Enthalpy of fusion Δ Hf = 20515 J mol-1 (DSC by C.Plato
(1972) Anal. Chem. 44, 1531-1534).
Entropy of fusion Δ Sf = ΔHf / Tm = 57.04 J K-1 mol-1. Liquid state molar volume Vb = 137.4 cm3 mol-1 [from increments
of P.Ruelle et al. (1991) Pharm. Res. 840-850. pKa = 4.31 Solubility parameter DB = Σ Fdi / Vb according to P.Ruelle (2000) Chemosphere 40, 457-512. Σ Fdi is the dispersion component of molar attraction constant calculated from increments of C.W.van Krevelen (1990) in: Properties of Polymers, Elsevier, Amsterdam, pp. 212-213. Value calcd. for DNOC = 18.20. Parameters needed for estimation of water solubility and hydrophobity of the
chemicals are association terms [P.Ruelle (2000) Chemosphere 40, 457-512].
vAcc and vDon are the numbers of active sites. KAccW(i) and KDonW(i) are stability constants for proton acceptor and donor groups of the compound in the water. Similar terms for the compound in n-octanol are KAccO(i) and KDonO(i). The greatest value of these association terms, MAXW or MAXO are also needed in evaluation. Additionally, sum of the hydroxyl groups is NOH, and parameter boh has value of 1, 2 or 2.9 for primary, secondary of tertiary OH group, respectively. Example: association terms for DNOC are (KAccO values are zeros)
vAcc vDon KAccW(i) KDonW(i) MAXW KDonO(i) MAXO
2 1 100,100 50...
Determination of the compound property as function of temperature VPLEST for evaluation the coefficients Apl and Bpl for:
Log Pl = Apl - Bpl / T Method is from Clark F. Grain in Handbook of Chemical Estimation Methods, W.J.Lyman, W.F.Reehl and D.H.Rosenblatt (Eds), ACS, Washington, DC (1990) in Chapter 14. Liquid state vapor pressures are computed in one Celsius intervals at environmental range (e.g. -2 to + 30C) by Grain’s equation 14-25 using one known Vp and temperature as reference. Then, the coefficients are determined by linear regression. (SUBCOOLED) LIQUID STATE VAPOR PRESSURE The reference Vp can be for either solid or liquid state (Ps or Pl). They can be converted to each other by equation: Log Ps = Log Pl + ∆Sf x (1-Tm/T) / (R x Ln10) 0bs. R x Ln10 = 19.1444 Conversions between temterature coefficients for Vp’s are:
Aps = Apl + ∆Sf / (RxLn10) and Bps = Bpl + ∆Sf x Tm / (R*Ln10) VPLEST result for liquid state Vp’s of DNOC is:
Compound Mp C ∆Sf Pl(25) Apl Bpl Aps Bps
DNOC 86.5 57.04 0.243 11.31 3496 14.29 4567
Validation of Pl estimates by two independent methods * Lei YD, Wania F and Shiu WY (1999): J.Chem.Eng.Data 44, 577-582.
Solubility in water S mol m-3 WATSOLU.bas for evaluation the coefficients for: Log S = As - Bs / T WATSOLU is based on mobile order thermodynamics estimation for log S at 25 C (P.Ruelle et al. (1997) Int. J. Pharm. 157, 219-232). We have divided equations to temperature dependent (Bs/T) and non-dependent (As) parts: As = 5.154 + ∆Sf / (RxLn10) - 0.036xVb-0.217xLnVb
+ ΣNOHx(2+boh) / Ln10 + ΣvAcc(i)xLog(1+KaccW(i)/18.1)
+ ΣvDon(i)xLog(1+KDonW(i)/18.1) Bs = ∆Sf x Tm / (RxLn10) + (DB- 20.5)2 x Vb / (RxLn10)
x Log (1+MAXW / 18.1) Example: Output from WATSOLU for DNOC: As = 4.617, Bs = 1071.7 VOLATILITY: Henry’s law fuction
Simple conversions for Log H = Ah – Bh / T
At the narrow temperature range of environments values of Ah and Bh are in fair agreement with the relation H = Pl / S. Therefore, FATEMOD model automatically calculates them by conversions Ah = Apl – As, and Bh = Bpl - Bs . Example: conversion result for DNOC: Ah = 6.693 Bh = 2424.3
WATSOLU HPLC Validation of S estimate by two independent methods: Tam D, Varhanikova D, Shiu WY and
Mackay D (1994) J.Chem.Eng.Data 39, 82-86. pKa = 4.31 pH of the eluent = 5.60
TDLKOW.bas for octanol/water partition: LogKow = Aow – Bow / T
Is based on thermodynamic estimation of LogKow at 25 C of P.Ruelle (2000) Chemosphere 40, 457-512. We have divided Ruelle’s equations in two parts to obtain the temperature coefficients Aow and Bow: Aow = ∆B + ∆F + ∆Acc + ∆Don
∆B = (0.5 x Vb x (1/124.2-1/18.1) + 0.5 x Ln(18.1/124.2) / Ln10
∆F = [(vB x (rw/18.1 – ro/124.2) – ΣNOH x (boh + rw – ro)] / Ln10
ΔAcc = ΣvAcc x Log[(1 + KaccO(i) / 124.2)/(1 + KaccW(i) / 18.1)]
ΔDon = ΣvDon x Log[(1 + KdonO(i) / 124.2) / (1 + KdonW(i) / 18.1)]
Bow = (Vb/(RxLn10)x[(DB-20.5)2/(1+MAXW/18.1)–(DB-16.38)2/(1+MAXO/124.2)]
Where 18.1 is the molar volume of pure water, 124.2 the reduced molar volume of water-
saturated n-octanol, rw structuration factor for water (2.0) and ro structuration factor for
wate-saturated n-octanol. Observe that association coefficients for water are the same
as those in WATSOLU.bas (see above). The temperature coefficient Bow is practically
zero for compounds (often POP’s) having only one kind of substituents, but with several
polar and different substituents in structure Bow can be significant. Example1: TDLKOW output for DNOC:
Aow = 3.826 Bow = - 0.439 Hydrophobity (lipophility) as Log Kow is also temperature-dependent! Example 2: Musk xylene parameters from TDLKOW are
Aow = 5.022 and Bow =361.6 in fair agreement...
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