For persistence in the environment, an important property is the readiness of the bonds to be broken down under ambient conditions, whether it be from radical reactions or through metabolic processes. For instance, the C-F bonds in PFAS (bond dissociation energy of 513.8 ± 10.0 kJ/mol), and aromatic-Cl bonds in PCBs or dioxins (394.9 ± 13.4 kJ/mol), are difficult to break down in the environment, making groups rich in such bonds likely to be persistent .