Am I ever glad our environmental policies are so strict we can rule out human behaviour as a cause of all of this. I'm particularly fond of MSN's hypothesis:
No one knows what the substance was, but the official explanation says it was a material used to soften soil for a nearby subway construction, and was as harmless as soap bubbles. Many people are skeptical, preferring to blame China's corner-cutting efforts to save money. Whatever it was, it soon seeped back into the cracks, raising two even more important questions: Where did it go, and what is it planning?