Elimination of toxicants in the feces occurs from excretion in bile or by direct excretion into the gastrointestinal tract. The biliary route is very important and generally involves active secretion rather than passive diffusion. The most likely substances to be excreted via the bile are comparatively large, ionized molecules (large molecular weight conjugates) and heavy metals. A substance excreted in bile may undergo enterohepatic circulation. The conjugate is hydrolyzed by intestinal flora. This releases the xenobiotic which can be reabsorbed