There are several scientific field dealing with pollution. Some of them are:
an ecologist
An ecologist studies pollution
The name for this type of scientist is a teuthologist
A geological scientist studies rock and stones.
a type of scientist who studies about metal is called metallururgist
A scientist who studies animal life is a zoologist. There is no particular name for a scientist that specialises in platypuses.
The type of scientist that studies the environment is an enviromentologist.
what scientist studies hydrogen and oxygen
chromotologists
Aeronomist
A botanist.
An Entomologist