> my car uses full synthetic. No clue what that shit's made of. Hydrocarbons, stabilizers, detergents. There's just more control over which long-chain hydrocarbons make it in, and ideally it's the ones least-prone to oxidation. Stabilizers and detergents take the form of magnesium, boron, and calcium salts (usually with some charged hydrocarbon chain). Zinc organic phosphates as anti-wear additive... organic silicon compounds for anti-foam... lubricating metals like molybdenum are present in trace amounts... essentially that's probably the worst thing you'd be dumping since it's a heavy metal. The rest of the stuff (when I say "organic" I'm talking "carbon chemistry" not "pesticide-free" or whatever) is either readily broken down (lots of stuff eats basic hydrocarbons) or is present in trace amounts in the soil already. Honestly synthetic means they can just get the cream of the hydrocarbon crop; all of those additives are likely in your "dino" oil, but they're less effective since dino oil has conjugated carbons and alkenes that are more prone to heat degradation and oxidation (among other things). Easier to just make oil without those things than to try to filter them out of crude. In that regard you have likely fewer other contaminants; pretty hard to control the heavy metal content of what comes out of the ground - much easier if you just make it yourself. Idk I'd wager synthetic is actually more environmentally friendly. I might lose, but it's a bet I'd be willing to take. End-product wise anyway; not talking like cradle-to-grave byproducts and all that.