No previous trials have been conducted because it is unethical to deliberately expose humans to chemicals suspected of being harmful. That ethical prohibition remains true of chemicals which commonly leach from plastics such as Bisphenol A and phthalates, and which are allowed by the FDA in food, beverages and other daily exposure. (And which, according to the Centers for Disease Control are carried in the bodies of nearly all Americans)

See Why Have Regulators Failed To Regulate? for more on that FDA issue.

This prohibition against human research is why rats and mice (known as a murine model) are commonly used.

However, research conducted on a murine model is no guarantee that the same effects will be seen in humans. This disconnect is often cited as one of the main reasons why the majority of new pharmaceuticals which have shown promise in the lab (murine) fail in trials with humans.