some chemicals have been shown to disperse oil spills into droplets, which microbes can then destroy.
= some chemicals /have been shown /to disperse oil spill into droplets + microbes/ can then destroy/ oil.
공통인 대상은 oil이고 oil이 사물이니까 목적어인 oil을 which로 받고 그 뒤에 주어(microbes) 동사(can then destroy)가 되는거 맞나요?