Really nice idea, might be slightly too vague for the DPC crowd - but I could just be being pessimistic. Could do with sharper focus on the pumps - could be it was slightly too dark to take this shot hand held! J
How does this convey the periodic elements? Ok - so it doesn't really matter too much but the image is just not very good. Out of focus, dark and the pumps looks a little like junk in this particular setting.
I do however like how how you used the tree to frame the picture.
I haven't heard that riddle before, but I would guess the answer is oil, pollution, or something along those lines. I'm not sure what element you are trying to convey here. Carbon?