Acrylamide

Acrylamide is a known chemical in coal slurry. Although sludgesaftey.org says that they are all "not necessarily toxic," many experts have questioned its health effects--including the possibility that it may be a carcinogen. The most interesting thing about Acrylamide and, really, any investigation into the chemicals used for a process is that it can be found in a wide array of things:  "Most acrylamide is used to synthesize polyacrylamides, which find many uses as water-soluble thickeners. These include use in wastewater treatment, gel electrophoresis (SDS-PAGE), papermaking, ore processing, and the manufacture of permanent press fabrics. Some acrylamide is used in the manufacture of dyes and the manufacture of other monomers" (wikipedia.org). 

The connection between coal washing and press fabrics and dyes reminds me of Thomas Pynchon's connections of dyes to the government's development of bombs, which relates to game theory. Acrylamide can even be found in French Fries:

hammietree.blogspot.com

So looking at the chemical aspects of the cleaning of coal, we see that there are things that are edible with acrylamide in it. But the chemicals all mixed together create a mass of something that is unpredictable and unknowable (at least to the general public).