The substances which are not found in the periodic table are called ?

undiscovered elements (by their atomic number).

(I don't know if this is the correct answer)

Explanation:

The letters “J” and “Q” are the only two letters not found on the periodic table. These letters do not occur in either element symbols or element names.

one negative thing it that it can kill water animals. another negative thing is it can cause the destruction of ecosystem. one way water pollution can be reduced is to conserve energy.