I think it was less of a concern back then in many ways, in the 40's and 50's, there were far less boats on the water than there are today. I see the difference in only the past 25 or so years, waterways which were pretty quiet during the week are now jam packed with boats and jetskis all summer long, every day of the week. I think the environment could handle the handful of boats back in the day, but now if they were all older 25:1 mix two strokes not much would be alive in the water these days. But we also have cut back on other pollution as well these days, We don't see nearly as much farm runoff, there's far less waste dumping going on, and larger boats can no longer flush to sea to clear their waste tanks. Even during my time I can remember guys still changing oil in larger boats and dumping oil into the bilge to be pumped out while out on the water the next day. It was somewhat common practice. Just the same i remember farmers collecting drain oil to oil down their driveways and roads to keep dust down. Hundreds of gallons of drain oil being dumped just feet away from the food you ate. I remember a few shops i worked at early on who would just sling waste oil out onto the parking area saying it 'rejuvenated' the asphalt. Some just dug a pit and dumped the oil outback.
So in the grand scheme of things these days, we're far easier on the environment than we can ever imagine these days. Now their talking about not letting us wash our cars at home because it washes 'road dirt' and oil from the chassis onto the ground or down the sewer.
Yet we spray roundup like its water on everything and pesticides by the gallon and don't give it much thought. The guy next door to me goes through a gallon of round-up every week, he coats his driveway, walkway, curb, and all around his house with the stuff weekly. he buys Sevin by the case for his flowers, and sprays his food garden with Preen and every sort of pesticide he can find. Yet he complains if my truck leaves a drip of oil in the street or in my driveway. He rushes over to clean it up. His son-in-law has a 30 year old truck that leaks oil, he was there the other day and it left two 2" spots in the driveway, he was going off on how his truck pollutes the earth. 5 minutes after the guy left, the old man is out there with a scrub brush and a gallon of kerosene and gas scrubbing the stain and hosing if off down the street. He likely dumped two gallons of kero and gas on that oil spot.
In comparison, when you think how much or how little older two strokes actually do pollute, and the type of pollution they make, its a pretty minor issue. I would also think that modern two stroke oils also are made with the whole pollution issue in mind. They likely do not linger in the water nearly as long as say a 24:1 mix of 30w motor oil and gas back in 1955.
From what I've been told over the years, the real pollution we need to worry about is heavy metals not the oil itself. I read an article that mainly was talking about chainsaw and power equipment with two stroke motors, they did extensive analysis of the exhaust and found that most of the oils were at least somewhat bio-degradable, but the heavy metals, minerals, and sulfur deposits were not. The main offender was particulates in the air. Much of that issue is solved when an outboard exhausts into the water but I've not read a study showing what is actually in two stroke outboard exhaust. Especially since they use different two stroke oil formulas.
