Re: why are the chemicals : dioxins, organic mercaptans and hydrogen sulfides f

T answer your question "back to front": hydrogen sulfide is emitted from 
kraft paper-pulp mills because it is a by product of the kraft paper 
process, a process by which lignin is removed from wood pulp by a 
chemically reducing method (kraft paper is high wet-strength paper: e.g., 
paper bags, copy paper).  Similarly, sulfite-process pulp mills, that 
produce low wet-strength papers like paper towels and egg carton cardboard, 
emit sulfur dioxide as a by product. the sulfite process removes the lignin 
by a chemically oxidizing process. In high enough concentrations, both 
hydrogen sulfide and sulfur dioxide are very hazardous to health; hydrogen 
sulfide can kill you.   However, both have threshold concentrations in air 
below which there is no noticeable effect.  the health effects of both are 
concentration-dependent.  Neither one accumulates in the body.  EPA has set 
emission standards designed to protect health for both these air 
pollutants, and pulp mills in the United States are generally well 
controlled.  Kraft mills have a distinctive unpleasant odor when hydrogen 
sulfide is emitted in excess or violation of the EPA standard.

Mercaptans are produced by kraft mills and in other industrial processes.  
they are also the class of compounds that give excrement its foul odor.  
All mercaptans have a strong, highly unpleasant odor that actually prevents 
their being inhaled in significant amounts.  They will nauseate you before 
they cause permanent health damage.  Mercaptan emissions are controlled by 
a variety of oxidation processes.  Few industries in the U. S. emit 
mercaptans in significant quantities because of the complaints they get 
about the odor.

Dioxins are produced by a wide variety of processes, including ordinary 
barbecuing.  There has been considerable controversy over whether or not 
they have any adverse health effects, and how severe those effects might 
be.  After the accidental emission of a large quantity of a dioxin (TCDD) 
from a plant in Seveso, Italy, the community was evacuated, but eventually 
allowed back because of pressure from people who wanted to return to their 
homes.  The feared health effects did not materialize.  Dioxins are 
ubiquitous in the U. S.  It is unlikely that the small concentrations found 
in U. S. air have averse health effects.  However, the jury is still out.