Table 4 In conclusion, the Ah receptor and Arnt have been very well conserved during evolu- tion, indicating that they may have impor- tant physiological functions, possibly in development (27). This evolutionary con- servation, in combination with the ligand to CYP1A2 leading to hepatic sequestration, and 3) relative rates of metabolism. Lipophilicity controls the rate and extent of absorption, tissue distribution, and passive elimination. In addition, the chlorine substitu- tion pattern determines hepatic sequestration and rate of metabolism. Pharmacokinetic properties have been shown to play a role in the determination of TEF values for a number The pharmacokinetic behavior of dioxinlike compounds and PCBs is largely governed by three major factors: 1) lipophilicity, 2) binding