Here's a correction for you. Chewing gum is such a normal phenomenon in daily life, but with the increase of spitting the used gum out, it causes the serious problem of dealing with the litter (or waste). Your sentence is ok, a few grammatical errors, but makes sense. It does, however, feel a bit unnatural. You could say this instead. Chewing gum is an everyday phenomenon, but it causes a serious litter problem when people spit it on the ground.

我会说 it causes a serious problem of cleaning up chewing gum litter

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