If you need to run the start command from cron, and the start command requires the environment variable, then yes the variable would be stored in your crontab. Crontabs are stored in a secure directory that can't be accessed by non-root users, but your shell user can still see the variable when running crontab -l.
Also, when running the start command in your shell user you probably want to turn off your shell history to prevent the variable from being stored there, eg by running unset HISTFILE or by running set +o history prior to running the start command.
