On a prior page, Mr. Mik or was it nuts and volts asks: does synthetic oil decompose harmlessly in the ground?
I don't know. I think it does: it is made from entirely natural products.
Silicones don't decompose. Additives, harmless, probably don't decompose,
But I won't hesitate to dispose of used motor oil, small quantities, by flinging it into the weeds of the back yard.
All the oil that was lost by crankcase leakage of ancient cars (right up to the near present day): onto the pavements, then washed by rains into the green swale. Food for grasses after being food for bacteria.
Reading Dykes Automotive Encyclopedia of, say ca. 1916 (it was re-editioned for decades, a problem is brought up. I must paraphrase from memory:
In concrete floored auto garages, a great vexation is caused by the leaks of oil, saturating the concrete,
which, in short order, turns to a species of chalk and gunk and dusts away. There is no cure for this ill.
I was perplexed! I've known thousands (figuratively, of mechanics, and their shops, and of greasy, oiled, concrete floors. Yet, there it was in unimpeachable, authority-print of the distant past.
I figured this out for myself, so quote me:
An idiot I know
says that.....
At that time it was not realized that most all petroleum products contained a high percentage of sulfur,
and that the the seemingly-harmless sulfur, with water produced by the IC process, contaminated so,
simply ate the lime of concrete. It also ate the machinery that it lubricated.
The answer, the fix of the ill, was development of low-sulfur oil products.
To have lived in Birmingham in 1880, as a housekeeper, was to live in a sooty hell, grey on sunny days,
curtains going brown in one week, a film of filth on every surface. No, the extinction of the mills and end of those smoking chimneys was, by the housekeeper, welcomed. We can't appreciate how clean, relatively,
that even coal plants are today.
My windows are open. I live in fresh air. My oil-soaked garage floor (from the Model T days) is not softening at all.
I should just paint it to cover all the old time spills of black gilsonite paint I left: the stuff defies any sort of paint remover, period.
It is a petroleum product, too ancient for even bacteria to have an interest in eating it.
BTW, pulverized gilsonite looks like cocoa powder, is tasteless, edible, non toxic, with no food value.
Similarly, most oils, highly processed (clarified mineral oil) are perfectly edible and help to move bowels.
EITHA+SDG)WQR, OTOH,

only moves vowels.
joking as always,
StinkWeed