acid rain...
CFC's
concetration of common ions
if there is anything about water... well then i will be a head shorter and i guess they cant ignore harber... batteries was last year and i guess considering they had also ethanol, biopolymers would be worthwhile looking at or radioisotopes...
well... as far as i have a clue i guess the carbon can make the metal/alloy whatever stronger, as it goes in the little spaces in the metal lattice... however, when there is too much instead of strengthening the alloy it destroys the orderly arrangement of the lattice and hence makes it somehow...