I may be the only one who thinks that the toxic trait doesn't really add a lot a to games of this level. Certainly a DW:SM his little chance of being effected. I think the following rule might be interesting and not particularly more complicated.

The Toxic trait stays the same, effectively becoming Toxic 0. For weapons with Toxic 1 and higher the Toxic number is the number of stages of increased difficulty on the toughness roll to resist the effects. In additional it is the number of turns after the after the original attack. That the user has to re-make the same resistance test with the same penalties, each failure inflicts a 1d10 points of damage that bypass armour and toughness as normal.

Example: Acolyte Sebastian is bitten by a visciously poisonous creature while investigating a feral world. The creature manages to penetrate the acolytes feeble armour and toughness with an attack and has the Toxic 1 trait. The Sabastians Toughness is 55 for resisting poison, he must pass a test by rolling 45 or below or take 1d10 damage that ignores armour and toughness. In addition next turn, regardless of whether he is attacked again or if he passes the initial test, he must make another test at 45 or below or take an additional 1d10 damage ignoring armour and toughness.

If someone can reach the an effected person they can use a full action to make a Challenging medicae test to stop that dose of poison affecting them any further. (optional, mediacae tests are affected by the Toxins modifier).