I just have a spray bottle with white vinegar. Simple, dirt cheap and seems effective.

You would have to drink quite a few gallons to actually get cancer.

Weed barrier is a misnomer
 

Landscape mat, or weed barrier, is no insurance that there won't be weeds. Soil and any other stuff that gets between the rocks or pine bark mulch create an environment perfect for seedlings to grow.

You can Stand On Your Head and Spit Chicklets. There is no way you can stop the weeds and grass from growing exactly where you don't want it to be. I tried the Vinegar route with very little success. We even excavated the stones and put down a triple layer of the finest weed barrier and still son of a gun the weed were back. I bought something on the advice of a professional at Lowes in a Black one-gallon container and a sprayer and at long last no weeds. We glow in the dark but at least no weeds. Good Luck.

It was worth it. My wife's happy and that's what counts more than anything else in the world. (I hope she reads this post)

I would also avoid salt (sodium chloride) around any garden area. Salt can affect other plants as well. Vinegar, being the natural result of aerobic fermentation, is biodegradable and is much safer.