People are overdoing Captain Planet's weakness a bit here.
You can't just smack him with common litter. Not even a bag of week old sh*t should hurt him.
It has to be something that is detrimental to nature. A bag of sh*t can be fertilizer. A plastic cup is not really detrimental itself. And a majority of raw sewage is what; sh*t, urine, probably sanitary products like ass wipes, the occasional blood soaked underwear and used condoms, and a metric f*ck ton of rain and tap water. Not just any bucket of sewage would do the trick. It'd have be a prime choice selection from an industrial area or the like.
And a big question, what would Captain Planet be doing while Superman is grabbing a toxic water filled Super Soaker™ ? Giving the high hard one to Gaia? He could chase Superman down and drag his ass into the ocean. All that natural ocean water would work wonders. Suppose Captain Planet takes the fight to the Antarctic? The cleanest water in the world. Or if Captain Planet takes the fight to ultra high altitude. The hazardous material Superman has becomes frozen and useless, while Captain Planet remains completely charged by the Sun. Everyone's been busy talking about Superman and the bucket of sh*t play, they forgot that the entire f*cking planet can revitalize Captain Planet instantly. Hell, Captain Planet could just make it rain like Hell - like f*cking 'Nam - before the fight, and then he's covered.
We have a guy who is the physical manifestation of Earth who is empowered BY the Earth AND the Sun and is completely invulnerable and immortal when in good condition, versus a mortal who is merely powered by the Sun alone and was actually beaten to death by brute force.
Captain Planet's power source : Earth and the Sun
Superman's power source : Just the Sun
Now I don't know if Superman necessarily loses, but it'd be far from easy. I guaranty you, win or lose, the prick will know he's been in a fight. And that's IF he wins.