Melamine (like all particle board) off gasses formaldehyde (toxic, known carcinogen), whether wet or dry. PVC relases pthalates (some types cause breast cancer, all are endocrine disruptors) and Persistent Organic Pollutants. Basically both have very nasty chemicals in them that are known to be bad for people, and are probably bad for snakes too. But we also get continuously exposed to repetitive low doses of these chemicals everywhere we go, for example BPA is used to lubricate receipt paper, and manufacturers are legally required to put flame retardants in couches and matresses. Offgassing from a snake rack is a tiny drop in a very large, scary bucket, so get whichever one works best for you.