The following are descriptions of the Elemental Effects:
When you use fire on an enemy they will take gradual damage until they die or it goes out. Fire damages enemies more if they don't have a shield. Enemies will become less accurate when being attacked with fire.
Shock damage deals an large amount of damage to an enemy's shield, but loses effectiveness once they're down to their health meter.
Acid damage eats through armored opponents and can spread to multiple enemies if they touch each other while panicking. However, some Acid-type enemies are mostly immune to it.
Sometimes when you shoot an enemy from an explosion-type gun, the bullet will explode and deal extra damage. This is useful when attacking groups of enemies.
If you find an Eridian weapon, try shooting an enemy. Extra effects may occur. The 10101 Cannon is a good example of a Shock/Explosion combination element.