Qualifications
Ah, yes—toxicology, the traditional profession of middle-school dropouts.
Whoa, whoa, whoa. Hold on...
You'll actually need to stay in school to become a toxicologist—and not just for a couple of years, but for a while.
Toxicology is a profession and career wholly defined by your type of degree, the number of years of school you've had, and of course, the thousands upon thousands of dollars you dumped into your education.
First of all, toxicologists need a bachelor's degree in, ideally, toxicology. Unfortunately, there are only a few undergrad programs in the subject, so most people get their bachelor's in a related field, like biochemistry, ecology, or even physics. The important thing is that future toxicologists have a strong background in the hard sciences and plenty of experience with investigating chemical makeups in labs.
Aspiring professors and dedicated researchers should invest in a PhD. That's generally four more years of graduate school and a dissertation. Not in it to become a doctor? That's fine—but you'll still need to get a master's of science (MS) in pharmacology or toxicology. Typically, a toxicologist at this point specializes in an area of the subject, be it clinical, environmental, or forensic.
If, after three degrees and like ten years in higher education, you're still feeling unqualified, you can get certified through the American Board of Toxicology (ABT) by passing a three-part exam. You'll need to recertify every five years (source), but won't it be worth it for the peace of mind?