Biodegradable is perhaps the most mis-used term in the cleaning industry. It makes me cringe every time I see it. I remember visiting Ft. Stewart in GA a few years ago and coming across several young enlisted men degreasing an M1 Abrams tank over grass with a mass marketed "Green" degreaser. They told me their commander told them to use the biodegradable soap so they wouldn't have any environmental problems. I asked them what they though was happening to all the grease they were washing off the tank and one of them said that the chemical was "making it go away".
As to everything returning back to the earth, yes and no. There are many chemical concoctions that man makes and are not found in nature. Some of these molecules will stay in that state for millions if not billions of years. Take persistent organic pollutants for example. These man made chemicals used in pesticides have been washed away into the environment and samples can now be found in deep sea squids. The chemical gets into the food chain through filter feeders and goes on up in everything that eats it.
http://www.nefsc.noaa.gov/press_release/2008/SciSpot/ss0810/ Eventually that stuff could end up in you and I.
Having been in this business for two decades and sold more than a thousand wash water recycling systems, I can tell you that is how many violations are reported. I remember an auto salvage yard in LA back in the 1990's that got nailed for dumping wash water. He was mad he had to pay a fine and about $25,000 for a wash water system. He proceeded to take pictures of his competitors doing the same thing and reported all of them. Unfortunately for him, that industry had some unsavory characters and he fell off the face of the earth shortly there after.
The general public has no idea that washing something and allowing the water into the storm drain could be a problem. I doubt 95% of the public even knows the difference between a storm and sanitary sewer.
