Soil-to-Plant Concentration
Modeling ingestion exposures for herbivorous wildlife receptors requires information on chemical concentrations in plant tissues. Chemical concentrations in plant tissues are calculated from soil concentrations using point estimates of soil-to-plant bioaccumulation factors (BAF), estimated bioaccumulation factors based on octanol-water partitioning coefficients (for nonionic organic analytes), or soil-to-plant tissue regression relationships. Regression relationships are the preferred means of calculating plant concentrations. SADA Version 3 separates plant tissues into two types: foliage and seeds. In many cases, current default settings assume seed and foliage uptake are similar since soil-to-foliage values are more generally available.
Default point estimates appear as Custom BAFs. 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-plant BAFs were generated using the following equation from EPA (2000):
where BAFplant = soil to plant foliage bioaccumulation factor (
)
Kow = octanol-water partitioning coefficient.
Soil-to-plant tissue regression relationships are of the form:
where Ctissue = Chemical concentration in plant 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.