Activated carbon (AC) is one of the most widely used media for water filtration. It's effective at removing chlorine taste and odor, and it's recognized as being safe.

However, most activated carbon filters have an indicated lifespan of about 4-6 months, after which they need to be replaced. But is there any risk to using an AC filter past its lifespan other than the fact that it won't effectively filter contaminants anymore? 

I've read in passing that an AC filter past its lifespan can actually release contaminants in water, because some contaminants in the influent water may be preferentially adsorbed by the AC, replacing existing contaminants previously trapped in the AC and causing them to be released in the effluent water. Is this something that has been explored in research?

**In particular, has it been shown that using a saturated AC filter can cause the levels of certain contaminants — e.g. a trihalomethane such as bromoform, or perhaps fluoride or lead — to rise to a level that is well above the EPA maximum contaminant level?**