>QUESTION:  Almost all of the twine we get is light green in color,
>>suggesting that there is some type of preservative on/in it.
>  Much jute twine has been
>replaced by a black polypropylene twine...
 
Baler twine (natural, not plastic) is not jute but sisal.  The fibers come
from the agave cactus.  Jute is used for bags, such as potato bags.  I do
not know if it is treated.
 
Sisal twine usually IS treated even if it is not coloured.  The light green
colour is likely copper napthenate.  But if zinc napthenate is used for
treatment there would be no colour.  Almost all sisal twine is treated to be
insect and rodent resistant.  I used it for smoker fuel for years since I
always seemed to have some in my pocket, and found it burnt great.  But I no
longer use it because several people remarked that I was poisoning myself.
It is not really necessary since there are so many other things that are
just as good.  I now grab a bit of sawdust from under the table saw and mix
it with a bit of dried manure that I scrape from the stable wall where it
splashes and dries to a crisp flake.  The smoke from the manure is not at
all unpleasant surprisingly.
 
Even though it is not wholesome smoker fuel, sisal twine is a much nicer
product than the plastic.  It provides an export product for developing
nations.  It is less likely to cause bowel impaction if animals eat it
accidentally.  If some goes out the manure spreader accidentally it
decomposes in the soil  more quickly.  And the treatment actually makes
rodents less likely to chew it than the plastic twine.  Unfortunately this
year the price difference between the two is the highest it has ever been,
with the sisal costing 50 percent more than plastic.
 
An addition to the thread (strand?) on twine
stan