Recently I came across someone talking about Carefresh and similar pulp-based products (Boxo, Clean and Cozy, etc) being dangerous due to high levels of dioxins within the substrate from where they are made. The exact phrase being that Carefresh is "repackaged sludge from the sewer stream of pulp mills". This phrase is inaccurate as this is not quite what wood pulp is. These beddings are made form wood pulp, which is the product of the tree that cannot be used to make paper products. It was often put into landfills and other let to go to waste before. It is not "sludge from the sewer", it is taken before that point is reached. It is also not recycled paper and contains no ink.
The main concern brought up was that during this process dioxins (Wiki: Dioxins) were put into the wood pulp. Thus our small animals would be exposed to these deadly compounds.
This concern is not a new one it seems, searching for more information many forums came up with similar posts about "sewer sludge" though all from different times, the oldest one I found dating back to 2003. Finally I found a page that was put up by a pine mill company that promoted pine over wood pulp based substrates. (Please see: Toxicity of Pine and Cedar Shavings). This page seems to be the source of this rumour. Yet the question still needed to be considered: Are wood-pulp based substrates really safe?
Looking at the Carefresh Website they say that "Carefresh is non-toxic, sanitised and it has been tested for dioxins. As a result Carefresh is guaranteed to be clean, safe and natural."