Lately, postal cardboard packages have been arriving with an increasing level of exterior contamination with generic black dirt. Although the composition of this dirt is unknown, this can be a concern in manufacturing certain recycled products, such as food packaging. Since it is generally infeasible to separate the contaminated portions, this has also become an issue for me in maintaining a recycling stream of the highest possible quality.
My question is then twofold. From the perspective of the recycler, in particular in the US, to what extent can such contamination be tolerated or mitigated? From the perspective of the consumer, what should be the threshold for sending such cardboard instead to the landfill stream?