We bought the blending tools about 2 years ago but have not used them much until recently.  I have been making several batches of dough and at times I would find grayish residue on my hands and in the dough after investigating we discovered the dough hook and flat beater both are discoloring and shedding a grayish black film, very concerning.  We are concerned that are food has been contaminated by this residue.  please advise