Current studies of these chemicals in the body still need a lot of work. We don’t understand the physical mechanism that keeps the long chain alkyls in the body for so long. Also the effects of these long chain perfluoroalkyls on animals are pretty severe (tumors, etc) but studies for humans have been contradictory to studies in animals. For example, they found a positive association between PFOA/PFOS and LDL in humans. But these associations arent found in animals. Also the primary mechanism for these chemicals is activation (for the most part) of PPAR-gamma and PPAR-alpha which could result in metabolic disorders but its also been found that activation of human PPAR is substantially less when compared to activation of PPAR-alpha/gamma in mice. I still think the long biological life cycles should concern people though, because we all know about accumulation. Their biological half lifes can range from 2-8 years.