MP6 Quantitative Structure Activity Relationships (QSARs)
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(BIR-1117-819074) A New Method for Estimating Beef and Milk Biotransfer Factors.

Birak, P¹, Yurk, J², ¹ RTI International, RTP, NC, USA² USEPA Region 6, Dallas, TX, USA

ABSTRACT- In multi-media risk assessments, ingestion of contaminated animal products is a commonly considered pathway. Such assessments, typically predict chemical transfer into beef and milk using a biotransfer factor (BTF). BTFs relate chemical intake rates to concentrations at the point of exposure. Unfortunately, experimental data for deriving beef and milk BTFs is limited to a handful of chemicals. For most compounds, risk assessors estimate BTFs based on chemical properties. Existing predictive equations, based on linear regressions, over predict BTFs for high log Kow compounds (i.e., >6). The goal of this research was to develop an improved methodology for predicting chemical BTFs for beef and milk. The primary objectives were to (1) ensure that the methodology was transparent and easy to implement, (2) use only chemical properties for which data were readily available , and (3) demonstrate improvements in the accuracy of biotransfer predictions over current methods. Additionally, we developed an extensive database of biotransfer data. Though alternate chemical properties were considered, BTFs are predicted using log Kow. Chemicals capable of undergoing hydrolysis or oxidation reactions were excluded from regression analyses. Remaining data were fit using a polynomial regression to improve BTF predictions for high log Kow compounds.

Key words: biotransfer, uptake, cattle