in british english usage, "nauseous" has more of a literal meaning, as in "i felt nauseous in the boat", whereas "nauseated" has more of a figurative meaning, something stronger than "disgusted", as in, "i was nauseated by his racist comments" (although "his racist comments were nauseating" would probably be more common.)

This comes from an American dictionary: USAGE A distinction has traditionally been drawn between nauseated, meaning ‘affected with nausea,’ and nauseous, meaning ‘causing nausea.’ Today, however, the use of nauseous to mean ‘affected with nausea’ is so common that it is generally considered to be standard.