What you are noticing ties in with the following information:
"The reduction of the clearance of toxic metals due to GSH is easily observed in the population as it plays a direct role in why hair turns gray. Grey hair is caused principally by rising levels of Hg or mercury in the body being incorporated into the hair follicles causing the loss of pigment from the higher cellular ROS problems. Grey hair has higher levels of mercury in it than pigmented hair strands and the effect helps to pull some mercury from tissues. Grey hair for many people begins in areas of the chin and face, where the highest concentrations of mercury tend to accumulate in tissues from mercury dental fillings. With increasing age the gray hair can affect most of the head's hair. This is a common example of the effects of reduced GSH and SOD enzymes that happens with age and rise of internal retention of PCB, pesticides, HF, and Hg that act to damage GSH and SOD production."