A relative of mine listed in the 1900 Philadelphia Census was listed clearly as "D & D" which I always viewed as Deaf & Dumb.
His father worked as an Iron Moulder for someone. Could it be an issue?? Not sure unless he carried it home on his clothes.
However, in the 1910 Census the same relative was not mentioned as D & D.
I agree with Joel in one sense as I worked worked for a company in the late 1990's that remediated "leather tanning sites".
The "tanning" sites were horrible. The acrid smell of acids used in the process permeated the neighborhood and could cause according to OSHA, tertogentic problems in children that have speech, vision and hearing issues.