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User's Guide and Technical Documentation
KABAM Version 1.0
(Kow (based) Aquatic BioAccumulation Model)

Appendix A
Description of Bioaccumulation Model

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Appendix A. Description of Bioaccumulation Model

The bioaccumulation portion of KABAM is based on the model published by Arnot and Gobas (2004). The purpose of this model is to estimate chemical concentrations (CB) and BCF and BAF values for aquatic ecosystems. Conceptually, each aquatic organism is assumed to be a single compartment. Chemicals enter the organism through respiration and diet and leave the organism through respiration and fecal egestion. The chemical concentration in the organism can also be influenced by the growth of the organism as well as metabolism of the chemical within the organism. These processes that define uptake and loss of the chemical from aquatic organisms are described by rate constants and are incorporated into one equation that is used to define the concentration of the chemical in organism tissues (Equation A1, see Table A1). As uptake constants (i.e., k1 and kD) increase, so does the estimated pesticide concentration in an organism. As elimination constants increase (i.e., k2, kE, kG and kM), estimated pesticide concentrations in an organism decrease. However, for respiration and diet, processes of uptake and elimination are linked. Therefore, factors that would influence uptake constants would also influence elimination constants, so these cannot be considered independently. In addition, as the freely dissolved fraction of pesticide in the water (φ) decreases, so do estimated pesticide concentrations in organisms. Rate constants defining the uptake of a chemical through respiration (k1) and diet (kD) and the elimination of a chemical through respiration (k2) and fecal excretion (kE) as well as growth dilution of a chemical (kG) are estimated separately using equations A5-A9, which are described below. Parameter definitions and abbreviations are consistent with those published by Arnot and Gobas (2004) in order to ensure consistency with the publication and transparent methodology used in KABAM.

Use of Equation A1 involves several assumptions. The first assumption is that the organism is at steady state. The second assumption is that the pesticide is distributed homogenously throughout organisms. The third assumption is that the effects of chemical partitioning into egg and sperm cells on chemical mass in parents is not considered as a loss pathway. The fourth assumption is that when data are lacking to define the metabolism rate constant for a chemical, it is assumed that metabolism does not occur and that the elimination rate constant for metabolism (kM) is 0.

Uptake and elimination of a chemical from an organism is influenced by the body composition of the model organism. Body composition includes lipid, non-lipid organic matter (NLOM; e.g., carbohydrates and protein), and water. Chemicals are expected to partition differently to these components of an organism. Partitioning of a chemical into these components is related to the octanol-water partition coefficient (KOW). It is assumed that octanol is a surrogate for the lipid fraction of an organism. It is also assumed that the partitioning of a chemical to NLOM is less than to octanol, but that there is a relationship between the partitioning of the chemical to NLOM and to octanol and that octanol serves as a reasonable surrogate for estimating this parameter.

Arnot and Gobas (2004) recommend that equation A1 be applied to an aquatic food web with seven trophic levels. In increasing order of hierarchy, these trophic levels include:

  1. phytoplankton
  2. zooplankton
  3. benthic invertebrates
  4. filter feeders
  5. small (juvenile) fish
  6. medium sized fish, and
  7. large fish.

Concentrations in organisms are first calculated at the lowest level of the aquatic food chain (phytoplankton). Pesticide concentrations are then calculated for zooplankton, including consideration that the diet of zooplankton includes phytoplankton, which contain pesticide residues. Tissue residues are calculated for the next five trophic levels based on their diets of organisms from lower trophic levels.

Equation A1

CB = [k1 * (m0 * Φ * CWTO + mP * CWDP) + kD *Σ (Pi * CDi)] / (k2 + kE + kG + kM)

Table A1
Equation A1: Calculation of Pesticide Tissue Residue (CB) for Single Trophic Levels and Its Associated Parameters
(Arnot and Gobas 2004)
Parameter SymbolDefinition ValueUnits
CB pesticide concentration in the organism calculatedg/kg
(wet weight)
CBD pesticide concentration in the organism originating from uptake through diet
CBD = CB when k1 = 0
calculated g/kg
(wet weight)
CBR pesticide concentration in the organism originating from uptake through respiration
CBR= CB when kD = 0
(wet weight)
CDi concentration of pesticide in i (prey item) calculatedg/kg
(wet weight)
CS concentration of the chemical in sediment (dry weight of sediment) Equation A4g/(kg (dry) sediment)
CWDP freely dissolved pesticide concentration in pore water of sediment input parameter
CWTO total pesticide concentration in water column above the sediment input parameter
k1 pesticide uptake rate constant through respiratory area
(i.e., gills, skin)
Equation A5L/kg*d
k2 rate constant for elimination of the pesticide through the respiratory area
(i.e., gills, skin)
Equation A6d-1
kD pesticide uptake rate constant for uptake through ingestion of food
  • Animals: Equation A8
  • Phytoplankton: 0
kg food/(kg org*day)
kE rate constant for elimination of the pesticide through excretion of contaminated feces
  • Animals: Equation A9
  • Phytoplankton: 0
kG organism growth rate constant
  • Animals: Equation A7
  • Phytoplankton: 0.1
kM rate constant for pesticide metabolic transformation 0d-1
mo fraction of respiratory ventilation involving overlying water 1 - mpnone
mp fraction of respiratory ventilation that involves pore-water of sediment ≤ 5%; 0 for organisms with no contact with pore waternone
Pi fraction of diet containing i (prey item) user defined none
Φ fraction of the overlying water concentration of the pesticide that is freely dissolved and can be absorbed via membrane diffusion Equation A2none

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