The simplest thing can be a quick wash or rinse with demineralized water.

Bacteria doesn’t feed on plastic (not for nothing bottles take decades to biodegrade).
The high injection blow molding process @chemicalmatt mentioned, degrades any bacteria there.

As for contaminants you’d need to define what do you want to avoid. Some plastic manufacturing uses nasty solvents and raw materials.
But testing is expensive, you’d need to hire a chromatography lab for that.