They occur in such trace amounts in natural, or «whole,» coal that they aren't a problem. (scientificamerican.com)
By - products are defined as» non - rendered clean parts of carcasses such as heads and viscera (organs), free from fecal content and foreign material except in such trace amounts as might occur unavoidably in good factory practice.» (suffieldvet.com)
By all the rules of paleontology, such traces of life should have long since drained from the bones. (discovermagazine.com)