Soil-to-Invertebrate Concentration
Modeling ingestion exposures for insectivorous wildlife receptors requires information on chemical concentrations in invertebrate tissues. Chemical concentrations in invertebrate tissues are calculated from soil concentrations using point estimates of soil-to-invertebrate bioaccumulation factors (BAF), estimated bioaccumulation factors based on octanol-water partitioning coefficients (for nonionic organic analytes), or soil-to-invertebrate tissue regression relationships. Regression relationships are the preferred means of calculating invertebrate concentrations.
Default point estimates appear as Custom BAFs. Default are largely based on data for earthworms. Earthworms live in direct contact with soil, process large amounts of soil through their bodies, and are assumed to be on the high end of bioaccumulation by invertebrates. Users can modify these values if they have site-specific values or prefer values from a source other than that used to derive default values for SADA.
Kow-based soil-to-invertebrate BAFs were generated using the following equation from EPA (2000):
where BAFworm = soil to earthworm bioaccumulation factor (
)
foc = fraction organic carbon in soil. Default is set to 1%.
Kow = octanol-water partitioning coefficient.
Soil-to-invertebrate tissue regression relationships are of the form:
where Ctissue = Chemical concentration in invertebrate tissue (mg/kg, dry weight)
C soil = Chemical concentration in dry soil (mg/kg)
Slope = coefficient for slope of the regression model
Intercept = value for the y-intercept of the regression model.