Yeah, that's right.
One of my players brought this up thinking I had some master plan in giving them a random find of some anti-plant grenades (roll on a random table on my part, actually) when they are fighting primarily Orks.
Then I started to think about it... they are largely fungal based lifeforms and anti-plant grenades are manufactured to annihilate any flora they are exposed to, including fungus.
While I am not going to make them Ork Serin gas, I am thinking of having Orks that are exposed to the gases lose their unnatural toughness trait.
What do you all think? For the sake of argument, let's say this idea has merit. I am asking for thoughts on how to negatively affect Orks exposed to the gas.