For a complete list of the 209 PCB congeners, see PCB congener list. Unlike its lighter congener iodine, evidence for diatomic astatine is sparse and inconclusive. As an amphetamine congener, its structure incorporates the backbone of methamphetamine, a potent CNS stimulant. The term pentaBDE alone refers to isomers of pentabromodiphenyl ether (PBDE congener numbers 82-127). Its physical and chemical properties most closely resemble its lighter congener barium. The human body absorbs strontium as if it were its lighter congener calcium. It is especially effective when used in combination with its congener, hypochlorous acid. Each congener has been given a toxicity equivalence factor (TEF). Dihydrovaltrate was also identified as a Rev-export inhibitory congener. The only congener, the white-tufted grebe, does not look very similar. The EPA responded by ordering the facility to conduct a PCB Congener study. It is the only congener to inhabit the Atlantic Ocean. Congener descriptors give a shorthand notation for geometry and substituent positions.