Have you considered using natural painting (e.g. clay, lime…) and water-based colours instead of oil paint ?
Or even making your own oil paint by mixing natural earth pigments and walnut or linseed oil ?
The true environmental danger in Oil paint comes from the paint thinners that are highly toxic, and often give off dangerous flammable fumes. These harsh chemicals, when disposed of incorrectly, leak into watersheds and can pollute waterways and groundwater.
If you use white spirit to clean the brushes, do not throw it in the sink as the solvents contain chemicals that are harmful to the environment. Solvents must be collected and disposed of as special waste !
One tip: you can use a small amount of white spirit, pouring it into a reuseable jar ; once the brush has been cleaned, the paint residues and sediments will settle on the bottom and you can use it several times.