First we'll look at oils.
While some of the pigments in this medium may be poisonous or toxic, depending on their color, the biggest drawback with it is experienced during clean-up.
Oil paints enjoy a bad reputation when it comes to the cleaning of brushes, pallet, and work area.
One must rely on paint thinners such as turpentine or mineral spirits, which can be toxic if used improperly, and the fumes are unpleasant and potentially harmful if not used in a well-ventilated area.
Also, paint thinners are highly flammable.
Now, to be sure, oil paints are not all bad.
Artists prefer them because of the beautiful colors and the easy blending.
Plus, many of the colors are made from food-grade linseed oils, which are not harmful to the environment at all.
And then we have acrylic paints.
They are a petroleum-derived polymer; in other words, plastic.
On the good side, they are easy to clean up with just good old tap water.
But on the bad side, do we really want to be washing plastic down our drains? How good can that be on the surrounding ecosystem? What's the solution? Well a couple of major oil paint manufacturers have reworked their formulas so that it can be cleaned with just water! And the appearance and workability of the medium remain basically the same.
Of course they still offer the original formula for the non-green artist.
So if you're interested in going green with your oils, just use "water-soluble oil paints".