Anthracite is a form of coal and activated carbon is a processed charcoal made from various sources. What hazards you would consider would depend on what you are using it to filter, if there is a kill step later in the processing, and what grade/type of the filtration materials you are using. Look at it from a logical point of view. What risk could anything that contacts your filtrate (the stuff you are filtering) present to your final product? Then apply those risks to the charcoal or anthracite filtering material.
From http://unifilt.com/faqs.php#faq-1:
What’s the difference between granular activated carbon and anthracite?
Anthracite filter media is employed in the filtration process to remove particulate matter that has already been precipitated out of solution and is sometimes chemically treated to improve its filterability. It doesn’t function very well at the molecular level because its pores are very small, much smaller than most of the molecules that must normally be removed.
GAC (granular activated carbon) is made from agglomerations of PAC (powdered activated carbon) particles. PAC is produced by driving out volatiles and burning away carbon in order to increase the size of the pores in the carbon particles until they resemble a molecular sponge. Depending upon the pore size, activated carbon can even be processed to be selective, removing certain molecules and leaving others behind. This pore structure causes the removal of molecules by the process of adsorption onto the surface of the carbon particle, followed by diffusion into and absorption in the pores. Precipitation is not necessary in this case. However, backwashing alone won’t remove the matter that’s been absorbed into the pores. It can only be removed by a re-generation process.
Anthracite filter media also removes particulate matter from the flow by adsorption. However, this is only a surface phenomenon. Generally, there’s no diffusion into the pores, and the adsorbed matter (adsorbate) is easily removed by agitation during backwashing.
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