The six forbidden cargoes were cargoes that Leviathans like Moya could not carry, primarily because they were harmful to Leviathans. Known examples of the forbidden cargoes were:
- Clorium: An atmospherically induced isotope of twinium. This element numbed Leviathans and could be used as an anesthetic.
- Novatrin gas: A weaponized gas used by the Plokavians. When inhaled, it ate organic tissue from the inside out. As Leviathans are organic, Novatrin gas would consume them as well.