First of all, a tim Burton
Alice in Wonderland would be awesome - that's exactly the kind of movie where his dark and moody style would fit perfectly.
Second, mercury poisoning is a topic of that ought to be of interest to me, since my job is to analyze environmental and industrial samples for mercury content. The following link seemed to be a good summary of mercury poisoning symptoms, and did not mention gray or white hair specifically.
http://curezone.com/dental/mercury_symptoms.asp(I was particularly amused by the mention of skin creams, since I have analyzed samples of skin cream at work that showed a possible mercury content of near 10%, though organic interference was also a possibility I couldn't rule out since some organic molecules absorb the same wavelength as mercury. Atomic absorption is the techniques I use to quantify mercury concentration in analyzed samples.)
Another link, describing hair color and its loss however, does mention toxins and pollutants as possible causes of graying hair, though mercury is not specifically mentioned. If mercury in the body interfered with the manufacture or deposit of pigments into the hair's keratin, then the hair would grow out gray or white.
http://www.loc.gov/rr/scitech/mysteries/grayhair.html