M4: Is it possible to access bash env vars from within m4 script?

Suppose I define:

$: export my_setting="whatever"

Next, I open up my foo.m4 and write (pseudocode, for illustrative purposes):

define(__SETTING__,${my_setting})

This would be pretty useful, because now I can hide away my m4. But how would one go about accessing environment vars from the .m4 script?

$> cat my.m4
qux

$> ( export foo=bar; m4 "-Dqux=${foo}" my.m4 )