im getting this error to my email:

S.M.A.R.T Errors on /dev/sda
From Command: /usr/sbin/smartctl -q errorsonly -H -l selftest -l error /dev/sda
Please note the following marginal Attributes:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
190 Airflow_Temperature_Cel 0x0022 048 040 045 Old_age Always In_the_past 52 (0 47 60 32)
----END /dev/sda--


sda was a USB stick i mount and then remove it, or unmount, there is nothing on the /etc/fstab

how to unmount?? or what to fix??

thanks