Hazardous materials in a hard drive

No problem.

There could be a small amount of lead in the solder (if the soldering dates from before ROHS compliancy), but it's locked up in the material. It won't escape unless you take a Dremel or drill to the printed circuit board, or heat it in any way.
And even then the amount is so tiny... You will catch far more lead from air-pollution by car-exhausts if you live near a highway or in a city.

Same goes for chemicals in the PCB and/or electrical components. As long as you don't cut or drill into them it's no problem at all.

People who assemble these things don't take any special precautions either. And they handle far more of them than you will ever do.

The only "danger" I've ever encountered is the voice-coil permanent magnets. If you were to pinch some flesh between them you could end up with a minor but painful hematoma or laceration. When separated by a small distance (3-4mm) they can exert several kilograms of force, which increases quadratically as they get closer together. If you let them stick together it will require significant force and a wedge of some kind to separate them.

I have a couple of dozen pairs in a desk drawer :-)

I recently opened a deceased Seagate laptop drive. ( I have had trouble with this brand in the past but that is another story) The platters in it were indeed glass but looked and felt like metal. I took it to work to show my coworkers and flexed one thinking it was maybe aluminium or magnesium. It shattered into many small pieces all of which were very sharp. This drive was manufactured in 2011 so yours may be different. Just be careful!