inscrutable means mysterious, difficult to penetrate, difficult to solve, impenetrable, inscrutable, incomprehensible.
It can be used as an adjective showing a characteristic of what can not be scrutinized; which can not be investigated or understood; incomprehensible, can not be penetrated because it is impenetrable.
E-cigarettes, like JUUL, can leak heavy metals and residual nicotine into the environment. Because of heavy metals and residual nicotine, e-cigarettes may qualify as both e-waste and biohazard waste.
