if you take an area over and have a nest, but don't pick up a mate, you can sleep in it. I believe if you go to sleep it brings toxicity down to 0%. I'm also ok with one of my creatures dying if I'm in a pack. You switch to the next one with 50% tox. Not great, but removes some of the stress. Also, if you do have a mate and use them your next gen is back at 0%.
Or, I will just gorge if I find some food and it will bring you down fairly quickly. Plus I carry food around (in my mouth) for hunger/reduce tox (if you are a predator)
Wear the Gas Mask in smog... if you have it. Stock up on water, pet food and magazine. Keep hunting animals and eating them... if they're not purple. Use a faster animal. Speed is your best friend in this jungle.