I found this article with a great list and some tips for selecting non-toxic backpacks for back to school. My daughter is just 2, so I have not looked into this, but lucky for those who do have school-aged children, someone has already done the research for safe back pack options.
“While Congress has recently voted to ban toxic lead and phthalates from toys, the legislation does not cover children’s backpacks, many of which are made of vinyl containing both toxic substances. Lead, high exposures of which cause learning problems (not so cool for back to school) and phthalates, linked to obesity and lower sperm counts, readily migrate out of vinyl and onto children’s fingers, and thence into their mouths. Phthalates also evaporate into the air and get inhaled; studies have shown they contribute to asthma and other respiratory problems in children.
When shopping for backpacks, make sure they’re PVC-free at a minimum, and made of recycled materials to get an E (for eco and excellence) plus. Here are some recommendations.”
PVC and Lead-free lunch boxes