Poisoned San Pedro

[nostawk]

I recently purchased my first pachanoi from a reputable vendor and after planting it I covered the soil surface with a nice layer of gravel from the alley behind my house. Well, I later came to find out that they spray the allies every so often with some sort of chemical to stop plants from growing so much. So, I was hoping to eventually get to know my cactus a little better but now I'm not sure how safe it is and I'm also worried that this will slow its growth?

So, I was just wanting you alls opinions on what to do.