Toxic Waste is a perk that's available from the start to all heroes. Toxic Waste improves the damage and area of effect for both your Nukes and the Irradiate aura, while also reducing the Irradiate structure penalty. Since you most likely won't start with the Irradiate Aura Talent as an option, you will gain increased life regeneration and shield armor as a bonus until you do. Once you gain Irradiate Aura, you will lose the bonus life regen and shield armor gained from this perk.
This perk is rather special, as it's only really good for one class, the Predator - However, its also the predators strongest perk, because it increases his AOE by an insane amount, as well as helping with nukes in the endgame. The reason its not really good for other heroes, is because it's based around a talent that can either be gained early on, or never at all, making it a very big "hit or miss". The increased shield armor and life regen isn't worth it compared to other perks, so this perk should only be taken by the predator.