Petrochemicals are naturally occurring. In soil they are digested by soil bacteria and used as a food source. A few drops of straight oil will return to nature very quickly. Of course you could lube your bike with veg oil, that's very green indeed but not the best lubricant out there. That said, a lot of food machinery does just that - all potential food contact areas of butter packers are lubricated with - guess what - butter.
But am I concerned about the half-dozen drips of mineral oil I drip on the ground or hose off every week? No, no more than I worry that the salt I use in cooking and tip down the sink or a smear of handwash soap are going to poison the water treatment works. I probably burned more petrochemicals this evening cooking my pasta than I use on my bike in a month.
