A cotton t-shitt doesn't contain 'chemicals', but a synthetic one is obviously made of microplastic, and it's manufacturing process might produce them and release them .
that statement is false for the majority of cotton clothing. from dyes to preservation or even agents that prevent wrinkles, a new cotton shirt can be blessed with a nice array of potentially carcinogenic substances. and since you mention the manufacturing process: look up some studies on the deaths and environmental havoc caused by pesticides used in cotton production. chemicals are everywhere.
Dyes are meant to be non-toxic, pesticides are super dangerous, but they are meant to decay in a few weeks, I dont know anything aboit wrincle agents.