Science

As a chemist, but without organics specialization (my specialty is rocks), I think that what we're seeing here is a collection of three main things, aside from polyethylene:

1. decomposition byproducts: plastics break down under heat, stress and in light. It's not surprising that some of their breakdown byproducts might be found in plastic that has been melted into a new shape.
2. dyes: plastic is dyed with different additives, and there are a LOT of different colors of plastic being recycled. They usually try to keep the colors generally consistent among batches for recycling, but the dyes that make a sprite bottle green are different from the ones that make a dasani bottle teal.
3. Plasticizers and other additives: the things the corporations add to their plastics just to eke out that 1 cent of savings from thinner, more durable plastic, or to get the texture just right, are insane. These are things like BPA. There are loads of them, and every plastic has different types. Some of them also have different heat tolerances, but it's not like the recyclers are keeping track.

So, yeah, be afraid. There's a metric fuckton of shit in there, and literally no one knows what it all is, let alone how much of it made it through the manufacturing, use, recycling and manufacturing process without becoming prone to leaching. Virtually all plastic recycling is a scam perpetrated by the corporations to get us to blithely ignore how they are destroying the planet to save money, all while convincing us to blame ourselves.