If an employee works consistently over 9-10 hours per day, is there a low stating the employee should be compensated?

I think it's down to the individual, if they don't want to work, then don't.

If you do work those hours then obviously you are paid for them, which doesn't require a compensation payment, however you would be entitled to a break during that time.

It's usually left to the managements disgression whether or not it is a paid break.
If you choose not to take your break then that's your choice.

I can only speak from a UK point of view, which over here after 5 hours you would be entitled to 10-15 minutes, if you take a lunch break, having worked 9-10 hours you would be entitled to 30 minutes unpaid.

If you are 16 years of age, you are not given the choice by law you have to have a break, but again you would not be paid.