It is highly unlikely that person could develop mercury poisoning from eating tuna, simply because there is so little of it in this particular type of fish. One of the best things about tuna is that it is so nutritionally beneficial while containing a very minimal amount of mercury.
You will find that unlike other types of fish, tuna does not have a very significant amount of mercury at all, especially the white albacore variety. There are certain types of tuna that do contain more mercury than others, though you will find that in general this type of fish does not have a lot in it. It would take an outrageous quantity of tuna to be consumed on a daily basis for someone to succumb to mercury poisoning so you shouldn’t worry about this at all, even if you eat it on a regular basis.