The inclusion of two additional chlorine substituents on the non-phenol ring (with

respect to 4'-OH-PCB79) resulted in both 4'-OH-PCBl59 and 4'-OH-PCBl65 being

very poor substrates. Ineffieient sulfonation may be one reason why the related

compound 4'-OH-PCBl72 accumulates in polar bears. Some degree of substrate

inhibition may also be expected to contribute to this accumulation, as was observed with

4'-OH-PCBl165.

 Sulfonation was not an efficient pathway of OHMXC detoxification. The rate of

OHMXC-sulfonate formation was around 7 times lower than for 4'-OH-PCB79. Since

resonance delocalization of negative charge on the phenolic oxygen by the flanking

chlorines in chlorophenols may decrease Vmax by increasing the energy of the transition

state of the reaction (Duffel and Jakoby, 1981), it is possible that in the case of OHMXC

(with no chlorines flanking the phenolic group), product release, rather than sulfonate

transfer, may have been the rate-limiting step.

 TCPM was a poor substrate for sulfonation, and this may be one reason why it has

been measured in such high amounts in polar bear liver. To our knowledge, sulfonation

of acyclic tertiary alcohols has not been reported in the literature. Despite the

considerable steric hindrance of three phenyl groups, the alcohol group could be

sulfonated. Although the alcohol in TCPM is not of the benzylic type, the presence of

three proximal phenyl groups may give this group some benzylic character, rendering

sulfonation of the alcohol possible. Both SULT 1El and SULT 2Al have been shown to

sulfonate benzylic alcohol groups attached to large molecules (Glatt, 2000). Sulfation of

the benzylic hydroxyl group leads to an unstable sulfate conjugate that readily degrades

to the reactive carbocation or spontaneously hydrolyzes back to the alcohol. Attempts to