In all counties in the State of Mississippi in which there is located a harbor or port of entry where commodities are exported to foreign nations, and where there is maintained a channel and/or harbor or port to a depth of not less than twenty feet, the tax collector of said county shall pay into the county depository, the amount of two mills of all ad valorem taxes due by said county to the State of Mississippi which is collected by the tax collector of said county or which may be collected by any other lawful taxing agency of such county and state for such county.